阅读说明：本技术 对二甲苯生产的集成方法 (Integrated process for para-xylene production ) 是由 丁忠义 萨钦·乔什 W·金 于 2019-07-19 设计创作，主要内容包括：公开了对二甲苯生产方法,其中此类方法与提取蒸馏或其它分离集成以有效分离,例如去除和回收,乙苯和其它与二甲苯异构体共沸的组分。这使得能够在对二甲苯与其其它异构体分离的下游在更温和的条件(例如液相,不存在外加氢气)下进行二甲苯异构化,而不需要乙苯转化。相关的降低的副产物(如轻质气体和非芳族烃)的收率以及对苯乙烯单体生产有价值的提纯乙苯的生成可以显著改善整体方法经济性。(Disclosed are para-xylene production processes wherein such processes are integrated with extractive distillation or other separations to effectively separate, e.g., remove and recover, ethylbenzene and other components that are azeotropic with xylene isomers. This enables xylene isomerization to be carried out under milder conditions (e.g., liquid phase, in the absence of added hydrogen) downstream of the separation of paraxylene from its other isomers, without the need for ethylbenzene conversion. The associated reduced yields of by-products (e.g., light gases and non-aromatic hydrocarbons) and the production of valuable purified ethylbenzene from styrene monomer can significantly improve overall process economics.)

1. A process for producing para-xylene, the process comprising:

separation of C from impure ethylbenzene-containing feed in a xylene column₈Aromatic hydrocarbon stream and C₉ ⁺A hydrocarbon stream;

in a xylene separation zone, the para-xylene-rich product is contacted with at least a portion of C₈Separating the aromatic hydrocarbon stream to provide an effluent depleted in para-xylene;

isomerizing at least a portion of the para-xylene depleted effluent in an isomerization zone to provide a xylene-balanced isomerate;

recycling at least a portion of the xylene-equilibrated isomerate to the xylene column, and

separating the ethylbenzene-rich product from (i) all or part of the impure ethylbenzene-containing feed in an Ethylbenzene (EB) separation unit to provide an ethylbenzene-depleted feed from (ii) a portion C₈Separation of ethylbenzene-rich product from aromatic hydrocarbon stream to provide ethylbenzene-depleted productC of (A)₈An aromatic hydrocarbon stream, separating the ethylbenzene-rich product from (iii) a portion of the para-xylene depleted effluent to provide an ethylbenzene-depleted, para-xylene depleted effluent, separating the ethylbenzene-rich product from (iv) a portion of the xylene-equilibrated isomerate to provide an ethylbenzene-depleted, xylene-equilibrated isomerate, or separating the ethylbenzene-rich product from any combination of (v) (i), (ii), (iii), and/or (iv).

2. The process of claim 1, further comprising (i) reacting at least a portion of the ethylbenzene-depleted feed with all or part of C₈Combining the aromatic hydrocarbon streams, (ii) passing at least a portion of the ethylbenzene-depleted C₈Aromatic hydrocarbon stream with a portion C bypassing the EB separation unit₈Combining the aromatic hydrocarbon streams, (iii) combining at least a portion of the ethylbenzene-depleted, para-xylene-depleted effluent with a portion of the para-xylene-depleted effluent that bypasses the EB separation unit, (iv) combining at least a portion of the ethylbenzene-depleted, xylene-equilibrated isomerate with a portion of the xylene-equilibrated isomerate that bypasses the EB separation unit, or (v) combining any combination of (i), (ii), (iii), and/or (iv).

3. The process according to claim 1 or claim 2, wherein the ethylbenzene-rich product is separated from a portion of the para-xylene-depleted effluent to provide an ethylbenzene-depleted, para-xylene-depleted effluent.

4. The process of any one of claims 1 to 3, wherein the impure ethylbenzene-containing feed comprises products of naphtha reforming, naphtha cracking or transalkylation.

5. The process of claim 4 wherein the product of naphtha cracking is pyrolysis gasoline.

6. The process of any one of claims 1 to 5, wherein the xylene separation zone comprises adsorptive separation or crystallization for separating para-xylene-rich products.

7. The process of any one of claims 1 to 6, wherein the isomerization zone comprises an isomerization reactor through which at least a portion of the para-xylene depleted effluent passes in the liquid phase.

8. The process of claim 7, wherein the isomerization reactor is operated at isomerization conditions comprising a temperature of about 200 ℃ (392 ° F) to about 300 ℃ (572 ° F) and an absolute pressure of about 2.5 MPa (363 psi) to about 4.5 MPa (653 psi).

9. The process of any one of claims 1 to 8, wherein a paraxylene process loop is completed by recycling the at least a portion of the xylene-equilibrated isomerate to a xylene column.

10. The process according to any one of claims 1 to 9, wherein the ethylbenzene-rich product separated from between about 1% to about 95% by weight of the para-xylene-depleted effluent or xylene-equilibrated isomerate: (i) an impure ethylbenzene-containing feed or a fraction thereof, (ii) C₈(ii) a portion of an aromatic hydrocarbon stream, (iii) a portion of a para-xylene depleted effluent, or (iv) a portion of a xylene-equilibrated isomerate.

11. The process according to any one of claims 1 to 10, wherein the ethylbenzene-rich product separated from between about 3 wt.% and about 50 wt.% ethylbenzene comprises: (i) an impure ethylbenzene-containing feed or a fraction thereof, (ii) C₈(ii) a portion of an aromatic hydrocarbon stream, (iii) a portion of a para-xylene depleted effluent, or (iv) a portion of a xylene-equilibrated isomerate.

12. The process of any one of claims 1 to 11, wherein the ethylbenzene-rich product comprises greater than about 95 wt.% ethylbenzene.

13. The method of claim 12, wherein the ethylbenzene-rich product comprises greater than about 99.5 wt.% ethylbenzene.

14. The method of any one of claims 1-13, wherein the EB separation unit comprises extractive distillation.

15. A method of making paraxylene, the method comprising forming a paraxylene process flow loop comprising: (i) c separated as low-boiling fraction in xylene column₈An aromatic hydrocarbon stream, (ii) from at least a portion of C in a xylene separation zone₈(ii) a para-xylene depleted effluent separated in the aromatic hydrocarbon stream, and (iii) a xylene-balanced isomerate provided by isomerization of at least a portion of the para-xylene depleted effluent,

wherein the process loop is completed by recycling at least a portion of the xylene-equilibrated isomerate to the xylene column, an

Wherein the conversion of ethylbenzene introduced into said para-xylene process loop is less than about 20%.

16. The process of claim 15, wherein substantially all of the ethylbenzene introduced into the paraxylene process loop is present in the impure ethylbenzene-containing feed to the xylene column and/or Ethylbenzene (EB) separation unit.

17. The process of claim 15 or claim 16, wherein isomerization of at least a portion of the para-xylene depleted effluent is carried out with less than about 2% per pass aromatic ring loss.

18. The process of any one of claims 15 to 17, wherein each of (i), (ii), and (iii) of the process loop comprises less than about 25 wt.% ethylbenzene.

19. The process of any one of claims 15 to 18, further comprising separating the ethylbenzene-rich product from the paraxylene process loop.

20. The process of claim 19, wherein separating the ethylbenzene-rich product is performed by extractive distillation.

21. The method of claim 19 or claim 20, wherein the ethylbenzene-rich product comprises greater than about 95 wt.% ethylbenzene.

22. The method of claim 21, wherein the ethylbenzene-rich product comprises greater than about 99.5 wt.% ethylbenzene.

23. A method of making paraxylene, the method comprising forming a paraxylene process flow loop comprising: (i) c separated as low-boiling fraction in xylene column₈An aromatic hydrocarbon stream, (ii) from at least a portion of C in a xylene separation zone₈(ii) a para-xylene depleted effluent separated in the aromatic hydrocarbon stream, and (iii) a xylene-balanced isomerate provided by isomerization of at least a portion of the para-xylene depleted effluent,

wherein the process loop is completed by recycling at least a portion of the xylene-equilibrated isomerate to the xylene column, an

Wherein the loss of aromatic rings introduced into said para-xylene process loop is less than about 5%.

24. The method of claim 23, further comprising separating an ethylbenzene-rich product from the process loop.

25. The process of claim 24, wherein the ethylbenzene-rich product is separated from a portion of the xylene-equilibrated isomerate.

26. The process of claim 24 or claim 25, wherein separating the ethylbenzene-rich product is performed by extractive distillation.

27. The method of claim 24, wherein the ethylbenzene-rich product comprises greater than about 95 wt.% ethylbenzene.

28. The method of claim 27, wherein the ethylbenzene-rich product comprises greater than about 99.5 wt.% ethylbenzene.

29. A process for producing para-xylene, the process comprising:

separating the ethylbenzene-rich product from the impure ethylbenzene-containing feed to provide an ethylbenzene-depleted feed, and

at least a portion of the ethylbenzene-depleted feed is separated from C as a low boiling fraction from the xylene column₈Aromatic hydrocarbon streams are combined to provide a combined ethylbenzene-depleted feed/C₈An aromatic hydrocarbon stream from the xylene column to separate C₉ ⁺A hydrocarbon stream as a high boiling fraction;

in a xylene separation zone, the para-xylene-rich product is combined with at least a portion of the ethylbenzene-depleted feed/C₈Separating the aromatic hydrocarbon stream to provide an effluent depleted in para-xylene;

isomerizing at least a portion of the para-xylene depleted effluent in an isomerization zone to provide a xylene-balanced isomerate; and are

At least a portion of the xylene-equilibrated isomerate is recycled to the xylene column.

30. The process of claim 29, wherein separating the ethylbenzene-rich product is performed by extractive distillation.

31. The method of claim 30, wherein the extractive distillation further provides a C-rich₉ ⁺Of hydrocarbonsHeavy fraction, said process further comprising enriching C₉ ⁺Heavy fraction of hydrocarbons and C separated from xylene column₉ ⁺The hydrocarbon streams are combined.

Technical Field

The present invention relates to a process for producing para-xylene from an impure ethylbenzene-containing feed comprising mixed xylene isomers, such as reformate obtained from naphtha reforming or pyrolysis gasoline obtained from naphtha cracking. Para-xylene production is integrated with ethylbenzene separation (e.g., via extractive distillation) to recover ethylbenzene.

Background

The isomers of xylene (dimethylbenzene), i.e., ortho-xylene, meta-xylene, and para-xylene, are important chemical intermediates, with para-xylene currently having the greatest commercial significance. The main application of para-xylene includes its oxidation to produce terephthalic acid. Terephthalic acid is in turn used to make polymers such as polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT) and polyethylene terephthalate (PET). PET, one of the largest polymers in the world, is produced via the polycondensation of terephthalic acid and ethylene glycol. Given the large market for PET plastics and fibers, there is a great need for such high purity intermediates, in addition to other end products made from paraxylene.

As a source of these xylene isomers, a refining process known as reforming generally refers to the use of naphtha hydrocarbon feed as a crude oil fraction in addition to benzene and toluene as other important productsConversion (or "aromatization") to these C' s₈An aromatic hydrocarbon. The effluent of a reforming reaction zone or reformer (e.g., a catalytic reformer with continuous or semi-regenerated catalyst regeneration) is separated by distillation, and in particular, using a reformate separator. C₆And C₇The aromatic hydrocarbons, i.e. benzene and toluene, are generally recovered in the separator overhead, while C₈The aromatic hydrocarbons, i.e., xylene isomers other than ethylbenzene, are recovered substantially all at their approximate equilibrium concentration in the bottom fraction of the separator. Containing higher boiling point C in the bottom fraction of the reformate splitter₉And C₁₀The aromatic hydrocarbons are conventionally separated from the C in this stream by downstream distillation (e.g. using a xylene separator or xylene column)₈Aromatic hydrocarbons and ethylbenzene are separated. Involving removal of low boiling point C₆/C₇Aromatic hydrocarbons and/or high boiling C₉/C₁₀Similar separation of aromatic hydrocarbons may be carried out on other known commercial products, such as pyrolysis gasoline obtained from naphtha cracking, to increase the concentration of mixed xylenes and ethylbenzene in the fractions recovered from such products.

High value paraxylene can be separated using a paraxylene separation process from a mixed xylene and ethylbenzene stream obtained, for example, as a low boiling fraction (e.g., overhead) of a xylene column as described above. Due to the similar boiling points of the xylene isomers, the xylene separation process cannot be economically carried out using distillation. Alternatively, such processes typically rely on adsorptive separation using a Simulated Moving Bed (SMB) having an adsorbent with micropores of appropriate size and geometry for selective adsorption of para-xylene over other xylene isomers. Representative adsorbents and methods for selectively separating para-xylene in this manner are described, for example, in US 5,495,061 and US 5,948,950. Alternatively, para-xylene can be separated by selective crystallization because of its higher melting temperature relative to other xylene isomers, for example according to the process described in US 5,329,061.

The resulting lean is obtained regardless of the particular process used for para-xylene separation and recoveryA para-xylene effluent stream or a para-xylene depleted effluent stream. In the case of SMB (adsorbent-based separation), this effluent may be referred to as "raffinate", whereas in the case of crystallization it is usually referred to as "reject filtrate". Downstream of the xylene separation zone, the para-xylene depleted effluent, comprising primarily ortho-xylene and meta-xylene, is further treated, typically in an isomerization reaction zone, to substantially restore the equilibrium concentration of xylene isomers, comprising from about 20 to 25 weight percent para-xylene. Para-xylene produced by such isomerization can advantageously be recycled to the xylene separation zone for its separation and recovery, thereby improving the overall yield of para-xylene recovery while other xylene isomers are substantially recycled to extinction. Otherwise, the product or "isomerate" obtained from the isomerization zone may be recycled to the xylene column so that C as a reaction by-product may be continuously removed₉、C₁₀And/or higher molecular weight hydrocarbons (particularly aromatic hydrocarbons). In either case, successive zones of para-xylene separation (by selective adsorption or selective crystallization) and isomerization (operating in combination with recycle of the less desirable xylene isomers) are commercially practiced to separate from C₈Recovery of para-xylene from aromatic hydrocarbon product, C₈Aromatic hydrocarbon products include those obtained from catalytic reforming, naphtha cracking, and other processes.

To maximize overall product recovery, it is generally desirable to have a substantially closed loop operation, which is formed by continuously recycling the isomerate back to the para-xylene separation zone and/or the upstream xylene column. However, this is known to result in the accumulation of certain components continuously fed into the process flow loop due to their boiling points close to that of the xylene isomers, and accordingly their removal by conventional upstream fractionation (e.g., in a reformate splitter or xylene column, as described above) is difficult. One such component is ethylbenzene (depending on the catalyst used in the isomerization reaction zone), which is isomerized in the isomerization zone only to a limited extent to produce mixed xylenes from which additional para-xylene can ultimately be produced and separated. Processes for separating ethylbenzene by enhanced distillation (e.g., using multiple columns) have proven uneconomical.

Thus, an alternative approach to limiting the accumulation of excess ethylbenzene is to convert this component, for example by increasing its degree of isomerization to xylenes and/or dealkylation (or cracking) to benzene and ethylene, which is more easily separated from the process loop. Benzene formation is not particularly problematic because, nonetheless, benzene is an aromatic hydrocarbon that can be converted to xylenes by disproportionation and/or transalkylation reactions, which are typically incorporated into an aromatics processing complex (complex). However, an increase in the catalytic functionality for ethylbenzene conversion in the isomerization zone (either by dealkylation or enhanced isomerization) always results in a corresponding increase in non-selective side reactions, resulting in the formation of other by-products that are less valuable and/or less readily converted to the desired components.

Specific examples of such byproducts are non-aromatic hydrocarbons (e.g., paraffins, cycloparaffinic hydrocarbons, and/or naphthenic hydrocarbons), which may similarly accumulate in the process loop as ethylbenzene, which is desired to be eliminated. Non-aromatic hydrocarbons and other by-products further lead to an overall loss of product yield and thus to less favorable process economics. The same detrimental effects are encountered when conditions in the isomerization zone are adjusted to increase ethylbenzene conversion, rather than merely changing the catalyst formulation, such as increasing the acidity of the catalyst support to promote cracking. That is, an increase in operating severity (as required to react the components) results in the formation of non-aromatic hydrocarbons and other by-products, again with the overall effect of reducing the yield of paraxylene. It has recently been proposed to add a dehydrogenation reactor downstream of the isomerization reactor to compensate for at least a portion of the by-product formation by converting the alicyclic hydrocarbon back to a more desirable aromatic hydrocarbon.

However, any catalyst formulation and/or process conditions designed to promote reactions other than xylene isomerization, such as the isomerization or dealkylation of ethylbenzene, or the dehydrogenation of naphthenes as described above, invariably add to the cost and complexity associated with para-xylene production according to conventional techniques. The increased severity of the isomerization operation to convert ethylbenzene may involve the introduction and recycle of hydrogen, resulting in significant capital and operating costs. Furthermore, the proposals provided so far have not completely solved the problem of loss of aromatic rings or formation of non-aromatic hydrocarbons by side reactions due to the conversion of ethylbenzene.

Typically, para-xylene production is commercially practiced in large scale facilities, with costs being highly competitive between the various manufacturers in the industry. Therefore, refinery and petrochemical operators must continually strive to achieve the highest possible performance characteristics (e.g., conversion, separation, and recovery) in the integrated process units in the most economically attractive manner (e.g., in terms of capital and operating costs). To this end, conventional aromatics complex plants are described in Meyers et al, Handbook of Petroleum refining Process, 4 th edition (2016). There remains a need in the art for a composition made from C₈The production of aromatic hydrocarbons produces para-xylene, which provides an efficient solution for managing the accumulation of ethylbenzene and other components in the process loop.

Summary of The Invention

The present invention is related to the discovery of a para-xylene production process that is integrated with the efficient removal and recovery of ethylbenzene and other components that are azeotropic with xylene isomers. These components, commonly referred to as non-xylene hydrocarbons, are produced and/or introduced into the process and have boiling points such that the costs associated with conventional distillation are not commensurate with the value obtained in separating and recovering such components from xylene-containing process streams, including those forming para-xylene process flow loops (justify). Such components may typically have boiling points within 15 ℃ (+/-15 ℃ or +/-27 ° F), 10 ℃ (+/-10 ℃ or +/-18 ° F), or 5 ℃ (+/-5 ℃ or +/-9 ° F) of the boiling point of paraxylene (138 ℃ or 280 ° F), and thus include C in addition to ethylbenzene₈Alkanes (e.g. isomers of n-octane and iso-octane), C₇-C₈Cycloalkanes (e.g. ethylcyclohexane and cyclooctane), C₉Cycloalkanes (e.g., isomers of trimethylcyclohexane) and other non-aromatic compounds.

In the absence of their separation and recovery, such as using extractive distillation as described herein, these components must be converted to products (such as benzene and ethylene in the case of ethylbenzene cracking) that can ultimately form para-xylene (e.g., by transalkylation), or otherwise form products that can be removed elsewhere in the para-xylene production process. For example, C formed as a by-product of various reactions (e.g., ethylbenzene cracking)₁₂The hydrocarbon may be in C₉ ⁺The hydrocarbon stream is removed as a high boiling fraction (obtained from the separation in the xylene column). As noted above, conventional para-xylene production processes rely on the conversion of azeotropic components to avoid excessive build-up thereof in the para-xylene process loop. Improvements in isomerization catalysts and/or isomerization operating conditions targeted at such conversions (e.g., ethylbenzene isomerization, ethylbenzene cracking, and/or dehydrogenation of alicyclic hydrocarbons) have resulted in non-selective side reactions that ultimately reduce para-xylene production efficiency.

In contrast, the present invention relates to the discovery of a process for the production of para-xylene in which ethylbenzene and other components that are azeotropic with xylene isomers can be recovered as products without significant conversion. Advantageously, the isomerization zone (e.g., conditions in the isomerization reactor and/or isomerization catalyst used in the reactor) may be substantially or entirely dedicated to the isomerization of ortho-xylene and meta-xylene to para-xylene. According to some embodiments, this may require less stringent and/or less complex operating parameters, such as liquid phase (as opposed to vapor phase) operation in the isomerization zone (or isomerization reactor in that zone), without the need for hydrogen introduction and its associated recycle, consumption (e.g., in an ethylbenzene cracking reaction), and inevitable losses (e.g., gaseous purge stream loss and/or liquid stream solution loss).

In addition to reduced hydrogen consumption relative to conventional para-xylene production processes, the recovery of ethylbenzene according to the processes described herein may provide further economic benefits in terms of reduced byproduct yields, and in particular the byproducts produced in conventional isomerization, where the ethylbenzene conversion functionality is characteristic of the isomerization catalyst and/or process conditions used. Such by-products include non-aromatic hydrocarbons associated with aromatic ring loss reactions, as well as light hydrocarbon gases (e.g., ethylene) associated with cracking reactions. Thus, the processes described herein can be incorporated into an Ethylbenzene (EB) separation unit (e.g., comprising extractive distillation) for recovery of ethylbenzene, thereby improving the yield of liquid products, including, for example, ethylbenzene-rich products of economic value to downstream styrene monomer production. In addition, the yield of low value gaseous products (e.g., a hydrogen-containing purge stream containing by-product ethylene) can be significantly reduced by relaxing or eliminating the requirement for ethylbenzene conversion in the isomerization zone, including avoiding the introduction of hydrogen for ethylbenzene cracking. Overall utility (e.g., hydrogen recycle compressor) costs may also be reduced.

Those skilled in the art will appreciate that even modest improvements in any of the above parameters, such as reduced hydrogen consumption, by-product yield, and/or utility requirements, as well as increased paraxylene yield and/or overall product value (e.g., due to the formation of an ethylbenzene-rich product), can provide significant economic advantages.

These and other embodiments and aspects of the invention will be apparent from the detailed description below.

Brief description of the drawings

Fig. 1-4 depict a representative process for recovering para-xylene, for example, from an impure ethylbenzene-containing feed, wherein an Ethylbenzene (EB) separation unit is employed at various alternate points in the process to prevent excessive accumulation of ethylbenzene in the process stream.

Fig. 5 depicts a representative extractive distillation process, such as may be used as a particular type of EB separation unit integrated in the process depicted in fig. 1-4.

The components referred to in fig. 1-5 are not necessarily drawn to scale and should be understood to represent representative embodiments of the invention and/or to be schematic illustrations of principles involved. To aid understanding, equipment such as reactors and other vessels, valves, pumps, compressors, heat exchangers, instrumentation, and ancillary process streams are not shown, all of which will be apparent to those skilled in the art having the benefit of this description. Methods according to other embodiments of the invention will have configurations, components, and operating parameters determined in part by their intended application and their environment of use.

Detailed Description

General terms

Embodiments described herein utilize the separation of ethylbenzene to improve the overall economics of para-xylene production. For this separation, certain embodiments utilize unit operations for separating and/or recovering ethylbenzene and/or other products that improve the value of the total product stream obtained from the para-xylene production process, such unit operations being referred to as "EB separation units," which may be used at various points in the para-xylene production process. Ethylbenzene separation (e.g., using an EB removal unit) can be performed, for example, by extraction, distillation, or a combination of extraction and distillation, which is a preferred separation technique, referred to as extractive distillation and described in more detail below. Distillation, whether used alone or in combination with extraction, may refer to pressurized or vacuum distillation, and may include the introduction of an upflowing gas (stripping agent) or a downflowing liquid (solvent) to assist in the desired separation. According to preferred embodiments, the EB removal unit described herein may comprise extractive distillation such that the preferred EB removal unit is an extractive distillation zone.

As described herein, steps such as "separating," "isomerizing," "recycling," "removing" (e.g., by extractive distillation) may be described as specifying a process stream (e.g., an impure ethylbenzene-containing feed, C)₈An aromatic hydrocarbon stream, a para-xylene depleted effluent, or a xylene-balanced isomerate). The step may thus be performed on the entire stream, substantially the entire (e.g., at least about 95%) stream, or some other fraction (e.g., at least about 50%) of the stream. The phrase "at least a portion" is therefore intended to emphasize the possibility of intermediate separation (e.g., distillation) that may be used to remove some fraction of a given process stream (e.g., enriched in impurities such as C)₇ ^-Hydrocarbons). Further, the phrase describes that it can be used where it is appropriate to reduce equipment load, prevent byproduct buildup, sample, etcExcept for the possibility of a certain amount of a given process stream.

Although methods of producing paraxylene, for example, utilize the foregoing steps and/or other steps described herein in forming a paraxylene process flow loop, such methods do not preclude the possibility of one or more additional steps or operations occurring upstream and/or downstream of the steps, such as mixing (e.g., with an auxiliary feed stream into a given step), separation (e.g., separation of an intermediate product stream), bypassing the steps (e.g., as part of a process stream), recycling back to the steps (e.g., as part of a process stream), and/or reacting (e.g., reacting undesired components and/or increasing the yield of desired components). In the case of separation, representative additional steps or operations include the removal of dealkylated products (e.g., benzene) occurring downstream of the para-xylene separation zone or the removal of C-rich products occurring downstream of the isomerization zone₇ ^-A fraction of hydrocarbons. In the case of recycle, a representative additional step or operation is to recycle a portion of the xylene equilibrium isomerate back to the xylene separation zone downstream of the isomerization zone. In the case of the reaction, a representative additional step or operation is C which occurs downstream of the isomerization zone₇Aromatic hydrocarbons (e.g. toluene) with C₉Transalkylation or disproportionation between aromatic hydrocarbons, such as trimethylbenzene, to produce xylenes.

However, in some cases, the method may be practiced without any one or any combination of such mixing, separating, bypassing, recycling, and reacting occurring upstream and/or downstream of any of the steps or any two or more of the steps. According to particular embodiments, separation of C-rich isomers from xylene-equilibrated isomerates may be used₇ ^-The process is carried out with a fraction of hydrocarbons and/or an additional step of reacting at least a portion of the xylene-equilibrated isomerate in the transalkylation zone. In these embodiments, at least a portion of the resulting C-lean fraction₇The xylene-balanced isomerate of the hydrocarbons and/or at least a portion of the resulting transalkylation zone effluent (having an increased xylene concentration relative to the xylene-balanced isomerate) may beRecycled to the xylene column, whereby these resulting streams still comprise at least a portion of the xylene-balanced isomerate.

The distillation steps described herein provide what are referred to as distillation steps providing "overhead" and "bottoms" fractions that can be removed from the top or bottom of the respective distillation column. However, "overhead fraction" may be otherwise referred to as "low boiling fraction" and is intended to more broadly include any fraction having a higher volatility (lower boiling range) and/or a lower distillation end temperature relative to the feed to and/or relative to the "bottoms fraction" from each distillation column. Likewise, "bottom fraction" may be otherwise referred to as "high boiling fraction," which is intended to more broadly include any fraction having a lower volatility (higher boiling range) and/or higher initial boiling temperature relative to the feed to and/or relative to the overhead fraction from each distillation column, where the overhead fraction is as defined above. The initial boiling point and the end point temperature may be determined according to ASTM D86.

Process parameters based on "once through" the isomerization zone (e.g., the isomerization reactor in that zone) and based on overall conversion (i.e., conversion of ethylbenzene introduced into the para-xylene process loop and aromatic ring loss introduced into the para-xylene process loop) are as defined herein. The yield of para-xylene can likewise be determined on a "per pass" (one pass) or "total" basis. Yield per pass or recovery refers to the total para-xylene input (e.g., C) to the xylene separation zone₈Para-xylene or a portion thereof in an aromatic hydrocarbon stream, or C depleted in ethylbenzene₈Aromatic hydrocarbon stream with a portion of C bypassing extractive distillation₈Combined para-xylene in the aromatic hydrocarbon stream) present in the para-xylene-rich product, the output from the xylene separation zone. Overall yield refers to the total xylene input to the process, such as the input into the paraxylene process loop described herein (e.g., the total xylenes in an impure ethylbenzene-containing feed) that is present as paraxylene in the paraxylene-rich product. Thus, the yield per pass is based on 100%The yield, which is the overall recovery of para-xylene from the para-xylene-rich product entering the xylene separation zone, is based on 100% yield, is the overall conversion of ortho-xylene and meta-xylene entering the process to para-xylene (i.e., in the para-xylene process loop, these isomers are recycled to extinction), and thus is the overall recovery of all xylene entering the process as para-xylene.

In a para-xylene separation zone, including adsorptive separation or crystallization, the per pass yield and/or overall yield of para-xylene can be greater than about 60%, greater than about 90%, greater than about 95%, or greater than about 98%. The purity of the para-xylene-rich product is typically such that it contains greater than about 93 weight percent (wt-%), greater than about 97 weight percent, greater than about 99 weight percent, or even greater than about 99.7 weight percent para-xylene. Those skilled in the art will appreciate that there is typically a tradeoff between para-xylene recovery or yield per pass and para-xylene purity, according to the "purity/recovery curve" associated with a given process.

The impure ethylbenzene-containing feed to the processes described herein comprises any mixture of ethylbenzene and xylenes from which paraxylene can be recovered in an economically advantageous manner using a combination of paraxylene separation and isomerization of the resulting paraxylene-depleted effluent (e.g., raffinate or reject filtrate). A representative impure ethylbenzene-containing feed comprises C₈An aromatic hydrocarbon in a combined amount greater than about 50 wt%, greater than about 75 wt%, or greater than about 95 wt%. At least a portion of the balance of such feeds can be C₉ ⁺Hydrocarbons, including C₉An aromatic hydrocarbon. For example, the impure ethylbenzene-containing feed may contain C₉ ⁺Hydrocarbons in an amount less than about 20 wt.%, less than about 10 wt.%, or less than about 5 wt.%. Typically, all or substantially all (e.g., greater than about 95 weight percent) of such C₉ ⁺Hydrocarbons may be conveniently removed in a xylene column as described herein and/or in an EB separation unit. In carrying out such removal, the resulting C, which may be obtained, for example, as a top fraction or low boiler fraction from the xylene column₈The aromatic hydrocarbon stream may be greater than about 85 weightAn amount%, a combined amount greater than about 95 wt%, or greater than about 98 wt% comprises C₈An aromatic hydrocarbon.

In impure ethylbenzene-containing feeds or C₈Aromatic Hydrocarbon stream (e.g. C of the feed)₈Aromatic hydrocarbon fraction) ethylbenzene may be present in an amount generally ranging from about 3 wt.% to about 75 wt.%, depending on the source of the impure ethylbenzene-containing feed. For example, the impure ethylbenzene-containing feed may comprise naphtha reformed products (e.g., reformate), naphtha cracked products (e.g., pyrolysis gasoline), transalkylated products (e.g., from toluene and C)₉Reaction of aromatic hydrocarbons to produce C₈An effluent of aromatic hydrocarbons), or any combination of one or more such products. Where the impure ethylbenzene-containing feed comprises, consists of, or consists essentially of (e.g., comprises greater than 95 wt.%) naphtha reformate, ethylbenzene may be present in the feed in an amount of from about 5 wt.% to about 45 wt.%, or from about 10 wt.% to about 35 wt.%. Where the impure ethylbenzene-containing feed comprises, consists of, or consists essentially of (e.g., comprises greater than 95 wt.%) naphtha cracking products (e.g., pyrolysis gasoline), ethylbenzene may be present in the feed in an amount of from about 25 wt.% to about 75 wt.% or from about 35 wt.% to about 65 wt.%. Where the impure ethylbenzene-containing feed comprises, consists of, or consists essentially of (e.g., comprises greater than 95 wt%) transalkylation products, ethylbenzene may be present in the feed in an amount of from about 1 wt% to about 25 wt%, or from about 2 wt% to about 15 wt%. Representative products of naphtha reforming, naphtha cracking, and/or transalkylation include those from which benzene and toluene have been separated upstream in an overhead fraction (e.g., using a reformate splitter as described herein).

Embodiments of the invention

Embodiments of the present invention relate to a process for producing para-xylene, the process comprising: separation of C from impure ethylbenzene-containing feed in a xylene column₈Aromatic hydrocarbon stream and C₉ ⁺A hydrocarbon stream. The C is₈The aromatic hydrocarbon stream may represent a C rich relative to the impure ethylbenzene-containing feed₈Aromatic hydrocarbons and depleted in C₉ ⁺Low boiling fraction of hydrocarbons, and C₉ ⁺The hydrocarbon stream may represent a C-rich stream relative to the impure ethylbenzene stream₉ ⁺Hydrocarbons and lean in C₈A high boiling fraction of aromatic hydrocarbons. Representative impure ethylbenzene-containing feeds include mixtures of ethylbenzene and xylenes, such as products obtained from naphtha reforming (e.g., reformate), naphtha cracking products (e.g., pyrolysis gasoline), and/or transalkylation products (e.g., toluene and C)₉Conversion of aromatic hydrocarbons to C₈Products of aromatic hydrocarbons). For example, such mixtures may be useful in removing C from such products₇ ^-After the hydrocarbons, are obtained in the low-boiling fraction separated in the upstream separator.

The method may further comprise: in a xylene separation zone, the para-xylene-rich product is contacted with at least a portion of C₈The aromatic hydrocarbon stream is separated to provide an effluent depleted in para-xylene. As noted above, in the case of the xylene separation zone using a Simulated Moving Bed (SMB) adsorption process, the para-xylene depleted effluent may be the raffinate obtained from the process. As noted above, where a crystalline xylene separation zone is used, the para-xylene depleted effluent may be a reject filtrate.

The method may further comprise: in the isomerization zone, at least a portion of the para-xylene depleted effluent is isomerized to provide a xylene-balanced isomerate. The product may have a xylene isomer (ortho-, meta-, and para-xylene) concentration that approaches its equilibrium concentration to a greater extent than the para-xylene depleted effluent. The xylene-equilibrated isomerate may also be enriched in (or have a higher concentration of) para-xylene relative to the para-xylene-depleted effluent. The process may additionally comprise recycling at least a portion, and preferably all, of the xylene-equilibrated isomerate to the xylene column. As described in more detail herein, such recycle can result in a paraxylene process loop.

The isomerization zone, or the isomerization reactor in the zone, can be operated as described herein with relatively low levels of ethylbenzene conversion and/or aromatic ring loss, where either parameter can be measured on a "once-through" basis from the isomerization zone (or isomerization reactor) inlet (e.g., para-xylene depleted effluent) to the isomerization zone (or isomerization reactor) outlet (e.g., xylene-balanced isomerate).

For example, the ethylbenzene conversion per pass may be determined on a percentage basis according to the following:

[1-(EB_{go out RX}/EB_{Into RX})]×100，

Wherein EB_{Go out RX}Represents the ethylbenzene output weight from the isomerization reactor (e.g., as present in xylene-balanced isomerate), and EB_{Into RX}Representing the ethylbenzene input weight entering the isomerization reactor (e.g., as present in the para-xylene depleted effluent or portion thereof fed to the reactor). The weight of ethylbenzene input to or output from the isomerization reactor can be calculated (e.g., during steady state operation) from the weight percent of ethylbenzene in the associated input and output process stream(s) multiplied by the weight or mass flow of each of these stream(s). In representative embodiments, the isomerization zone (or isomerization reactor in the zone) is operated at a conversion per pass of ethylbenzene of less than about 5%, less than about 2%, or even less than about 1%.

Aromatic ring loss per pass can be determined on a percentage basis according to the following:

NONAROM_RXδ/AROM_{into RX}×100，

Wherein NONAROM_RXδRepresents moles of non-aromatic hydrocarbons produced in the isomerization reactor (e.g., moles present in xylene-equilibrated isomerate minus moles present in the para-xylene effluent or portion thereof fed to the reactor), and AROM_{Into RX}Representing the moles of aromatic hydrocarbon fed to the isomerization reactor (e.g., the moles present in the para-xylene effluent or portion thereof fed to the reactor). These moles of non-aromatic hydrocarbons produced in the isomerization reactor, as well as the moles of aromatic hydrocarbons fed to the reactor, may be (e.g., during steady state operation) divided by the weight percent of non-aromatic hydrocarbons and aromatic hydrocarbons divided by their relative one or moreThe molecular weight of each of the plurality of input and output streams is calculated by multiplying by the weight or mass flow of each of the one or more streams. In representative embodiments, the operation of the isomerization zone (or isomerization reactor in the zone) is conducted with a loss of aromatic rings per pass of less than about 5%, less than about 2%, or even less than about 1%.

Parameters for ethylbenzene conversion and aromatic ring loss can additionally be based on "global" measurements from a total input to the process (e.g., an impure ethylbenzene-containing feed) to a total output of the process (e.g., para-xylene-rich product, ethylbenzene-rich product, non-aromatic-rich stream, and C₉ ⁺A hydrocarbon stream). The total inputs and outputs may thus be those of a paraxylene process flow loop as described herein, or may additionally include additional inputs and outputs added to or removed from the loop (e.g., C-rich inputs and outputs removed as an overhead from a deheptanizer column)₇ ^-Output of effluent). Thus, the overall ethylbenzene conversion and overall aromatic ring losses may be determined in a manner similar to that described above with respect to these parameters determined on a per pass basis, according to the following:

1-(EB_{discharging method}/EB_{Method of making}) X 100 and

NONAROM_{method delta}/AROM_{Method of making}×100。

Thus, EB_{Discharging method}And EB_{Method of making}Represents the weight of ethylbenzene exiting and entering the process from and into the process, respectively (e.g., exiting and entering the paraxylene process flow loop from and into the paraxylene process flow loop, as described herein), and NONAROM_{Method delta}And AROM_{Method of making}Respectively representing the moles of non-aromatic hydrocarbons produced in the process and the moles of aromatic hydrocarbons fed to the process. In representative embodiments, the process is operated at an overall ethylbenzene conversion of less than about 50%, less than about 20%, less than about 10%, or even less than about 2%. These ranges can thus represent the percent conversion of ethylbenzene introduced into the paraxylene process loop (e.g., under steady state conditions). In a further exemplary embodiment of the present invention,the operation of the process is conducted with an overall aromatic ring loss of less than about 10%, less than about 5%, or even less than about 2%. These ranges can thus represent the percent loss of aromatic rings (e.g., under steady state conditions) introduced into the para-xylene process flow loop.

Whether determined on a per pass or overall basis, relatively lower ethylbenzene conversion and aromatic ring loss levels compared to conventional processes may be present in the isomerization zone with reduced requirements in ethylbenzene conversion (e.g., by isomerization or cracking as described above), and correspondingly in milder operating conditions and/or simplified isomerization catalyst formulations. These effects, combined, can promote increased yields of para-xylene; reduced utility requirements, hydrogen consumption, and byproduct yields; and to produce a high value ethylbenzene-rich product.

According to representative embodiments, extractive distillation or other separation methods (e.g., performed in an EB separation unit) are used to separate one or more streams (e.g., impure ethylbenzene-containing feed, C) identified above₈Aromatic hydrocarbon stream, para-xylene depleted effluent, and/or xylene-balanced isomerate). According to other exemplary embodiments, after the ethylbenzene separation (e.g., to produce an ethylbenzene-rich product), at least a portion of the resulting ethylbenzene-depleted stream (e.g., ethylbenzene-depleted C) is subjected to₈An aromatic hydrocarbon stream, an ethylbenzene-depleted, para-xylene-depleted effluent and/or an ethylbenzene-depleted, xylene-equilibrated isomerate) is combined with a portion of the stream that bypasses the extractive distillation. That is, at least a portion of one or more of the streams identified above is used as a feed to an EB separation unit (e.g., extractive distillation zone), and the resulting ethylbenzene-depleted stream is returned to the process (e.g., to the paraxylene process flow loop) in the same stream (e.g., without subjecting the stream bypassing the EB separation unit to any intermediate separation or conversion prior to being combined with the resulting ethylbenzene-depleted stream).

Thus, the portion of a given process stream that bypasses the EB separation unit can refer to the portion diverted from use as feed to that unit, and this bypassed portion forms the para-xyleneAll or part of a stream of a benzene process flow loop, such as all or part of (i) C₈An aromatic hydrocarbon stream, (ii) a para-xylene depleted effluent, or (iii) a xylene-balanced isomerate. Preferably, the stream bypassing part of the paraxylene process flow loop is formed, corresponding to the part used as feed to the EB separation unit, for example in the following cases: (i) part C₈The aromatic hydrocarbon stream is fed to the EB separation unit and bypasses a portion of C forming a paraxylene process flow loop₈An aromatic hydrocarbon stream; (ii) (ii) feeding a portion of the para-xylene depleted effluent to the EB separation unit and bypassing a portion of the para-xylene depleted effluent forming the para-xylene process flow loop, or (iii) feeding a portion of the xylene-balanced isomerate to the EB separation unit and bypassing a portion of the xylene-balanced isomerate forming the para-xylene process flow loop. In the case of separating the ethylbenzene-rich product from all or part of the impure ethylbenzene-containing feed, it is also possible to combine the ethylbenzene-depleted feed obtained with all or part of the C₈The aromatic hydrocarbon streams are combined. In such a case, a portion of the impure ethylbenzene-containing feed (the bypass portion) bypassing the EB separation unit may form all or part of the fresh feed to the xylene column, such that a fraction of the fresh feed (i.e., C removed from the xylene column as an overhead fraction) may form part of the fresh feed₈A fraction contained in the aromatic hydrocarbon stream) can be introduced into the paraxylene process flow loop. In this regard, certain aspects of the present invention are associated with improved processing flexibility in the operation of para-xylene production processes. Advantageously, a smaller or larger amount of the feed portion of a given process stream may be fed to the EB separation unit regardless of its location along the paraxylene process flow loop and the loop may be formed using a larger or smaller amount of the bypassed portion of the stream, respectively. This is in turn adjusted to accommodate changing characteristics (e.g., ethylbenzene content) in view of the economic tradeoff between handling more throughput in the EB separation unit versus the potential to achieve greater ethylbenzene recovery, and additionally between handling more throughput in the paraxylene process flow loop versus the potential to reduce process requirements (e.g., utilities) of the EB separation unitProvides significant benefits in terms of impure ethylbenzene-containing feeds.

Advantageously, representative processes may further comprise removing all or substantially all (e.g., greater than about 80%, greater than about 90%, or greater than about 95%) of the ethylbenzene introduced into the process (e.g., the paraxylene process flow loop as described herein) without converting it. The degree of ethylbenzene conversion, which can be measured on a per pass or overall basis as described herein, depends on the operating conditions and the catalyst used in the isomerization reaction zone (e.g., isomerization reactor conditions and catalyst), which, as described above, can reduce side reactions relative to conventional processes that do not use extractive distillation for ethylbenzene separation. For this process loop, all or substantially all (e.g., greater than about 80%, greater than about 90%, or greater than about 95%) of the ethylbenzene introduced may be present in the impure ethylbenzene-containing feed to the xylene column. The extent to which ethylbenzene is introduced into the process loop will depend on the operation of the xylene column and its separation into C₈Efficiency in aromatic hydrocarbon streams.

Process for producing paraxylene and process loop

According to the representative process depicted in fig. 1, impure ethylbenzene-containing feed 2 is fed to a xylene column 100 as described above to separate C as a low boiling fraction (or overhead fraction)₈Aromatic hydrocarbon stream 4 and C as a high boiling fraction (or bottom fraction)₉ ⁺A hydrocarbon stream 12. C is to be₈A portion 4A of the aromatic hydrocarbon stream 4 is fed to an EB separation unit (e.g., extractive distillation zone) 400 to separate an ethylbenzene-rich product 402 and optionally a non-aromatic-rich stream 401 and provide ethylbenzene-depleted C₈Aromatic hydrocarbon stream 4B. Non-aromatic-rich stream 401 (if produced) is relative to C₈The aromatic hydrocarbon stream 4 is rich in (or has a higher concentration of) non-aromatic compounds. The non-aromatic hydrocarbons present in non-aromatic rich stream 401 may include C₈Alkanes (e.g. isomers of n-octane and iso-octane), C₇-C₈Cycloalkanes (e.g. ethylcyclohexane and cyclooctane) and/or C₉Alicyclic hydrocarbons (e.g. isomers of trimethylcyclohexane), the non-aromatic hydrocarbonBoiling point of hydrocarbon close to C₈The boiling point of the aromatic hydrocarbon. The non-aromatic-rich stream 401 may comprise greater than about 75 wt.%, greater than about 85 wt.%, or greater than about 95 wt.% non-aromatic hydrocarbons.

The ethylbenzene-rich product 402 may comprise primarily ethylbenzene and preferably comprises a high concentration of ethylbenzene suitable for direct use in styrene monomer production. For example, the ethylbenzene-rich product 402 may comprise ethylbenzene in an amount greater than about 90 wt.%, greater than about 95 wt.%, greater than about 98 wt.%, greater than about 99 wt.%, or greater than about 99.5 wt.%. The ethylbenzene-rich product 402 from the EB separation unit 400 (e.g., obtained from extractive distillation) thus represents a high value product that can be recovered from the para-xylene production process as described herein. Thus, such processes may alternatively be referred to as paraxylene and ethylbenzene production processes. Relative to C₈Aromatic Hydrocarbon stream 4, ethylbenzene depleted C₈Aromatic hydrocarbon stream 4B is depleted (or has a lower concentration) of ethylbenzene. According to the embodiment depicted in fig. 1, ethylbenzene-depleted C from EB separation unit 400 is separated₈Aromatic hydrocarbon stream 4B with C bypassing the unit₈Portions 40 of aromatic hydrocarbon stream 4 are combined to provide a combined feed 45 to xylene separation zone 200.

In the para-xylene separation zone 200, the para-xylene-rich product 10 as described above is separated, for example using adsorption separation or crystallization, to provide a para-xylene-depleted effluent 6 (e.g., as a para-xylene-depleted raffinate of an SMB adsorption separation process, or as a para-xylene-depleted reject filtrate of a crystallization process). Generally, with respect to combined feed 45, or otherwise with respect to C₈The aromatic hydrocarbon stream 4, the para-xylene depleted effluent 6 is depleted (or has a lower concentration) of para-xylene. For example, the para-xylene depleted effluent 6 can comprise para-xylene in an amount less than about 10 wt.%, less than about 5 wt.%, or less than about 2 wt.%.

The para-xylene depleted effluent 6 is fed to an isomerization zone 300 to isomerize the effluent to provide a xylene-equilibrated isomerate 8 having a concentration of xylene isomers (ortho-xylene, meta-xylene, and para-xylene) that approaches its equilibrium concentration to a greater extent relative to the para-xylene depleted effluent 6. Typically, the xylene-equilibrated isomerate 8 is also enriched in (or has a higher concentration of) para-xylene relative to the para-xylene-depleted effluent 6. For example, xylene-equilibrated isomerate 8 can comprise para-xylene in an amount greater than about 10 wt.%, greater than about 20 wt.%, or greater than about 30 wt.%. All or a portion of xylene-equilibrated isomerate 8 can then be recycled to xylene column 100.

According to an alternative embodiment depicted in fig. 2 and 3, it is understood that EB separation unit 400 can be used to remove ethylbenzene from the various streams of the process. Although these figures show that the ethylbenzene-depleted streams are each returned or recombined into the same stream (from which a portion is subjected to EB separation, for example by extractive distillation), typically such ethylbenzene-depleted streams may be returned elsewhere in the process or used for alternative purposes. As shown in fig. 2, a portion 6A of the para-xylene depleted effluent 6 is fed to an EB separation unit 400 to separate a non-aromatic rich stream 401 and an ethylbenzene rich product 402, for example by extractive distillation, as described above. The EB separation unit 400 provides ethylbenzene, a para-xylene depleted effluent 6B that is depleted (or has a lower concentration) of ethylbenzene relative to the para-xylene depleted effluent 6. As further shown in fig. 2, ethylbenzene, para-xylene depleted effluent 6B from EB separation unit 400 is combined with a portion 60 of para-xylene depleted effluent 6 bypassing the unit to provide a combined feed 65 to isomerization zone 300.

As shown in fig. 3, a portion 8A of the xylene-equilibrated isomerate 8 is fed to an EB separation unit 400 to separate a non-aromatic-rich stream 401 and an ethylbenzene-rich product 402, as described above, such as by extractive distillation. EB separation unit 400 provides xylene-balanced isomerate 8B depleted in ethylbenzene, which is depleted in (or has a lower concentration of) ethylbenzene relative to xylene-balanced isomerate 8. As further shown in fig. 3, the ethylbenzene-depleted xylene-balanced isomerate 8B from the EB separation unit 400 is combined with a portion 80 of the xylene-balanced isomerate 8 that bypasses the unit to provide a combined recycle 85 to the xylene column 100.

In some cases, the embodiment depicted in fig. 3, in which the ethylbenzene-rich product 402 is separated from the portion 8A of the xylene-equilibrated isomerate 8, may provide additional advantages. These may be associated with an extractant used in EB separation unit (e.g., extractive distillation zone) 400 that provides residual amounts directly to xylene column 100 and not to para-xylene separation zone 200 or isomerization zone 300, where such extractants may interfere with operations occurring in these zones. As mentioned above, a small loss of extractant from extractive distillation zone 400 may, for example, result in its presence in ethylbenzene-depleted streams 4B, 6B, 8B, and a suitable solution may therefore be C to separate it in xylene column 100₉ ⁺The hydrocarbon stream is immediately removed.

According to various embodiments depicted in fig. 1-3, it can be appreciated that such methods include forming a paraxylene process flow loop comprising: (i) c separated as a lower boiling fraction (or overhead fraction) in xylene column 100₈Aromatic hydrocarbon stream 4 (or portion 40 thereof), (ii) from C in xylene separation zone 200₈(ii) a para-xylene depleted effluent 6 (or portion 60 thereof) separated in the aromatic hydrocarbon stream 4 (or portion 40 thereof), and (iii) a xylene-balanced isomerized product 8 (or portion 80 thereof) provided by isomerization of the para-xylene depleted effluent 6 (or portion 60 thereof) in the isomerization zone 300. The process can be accomplished by recycling the xylene-equilibrated isomerate 8 (or portion 80 thereof) to the xylene column 100. Advantageously, the EB separation unit 400 can be used to remove the ethylbenzene-rich product 402 from the loop to simultaneously take advantage of the reduced ethylbenzene concentration in the loop and its recovery as a high value product. According to a representative embodiment, C₈The aromatic hydrocarbon stream 4, the para-xylene depleted effluent 6, and the xylene-equilibrated isomerization product 8 each contain less than about 25 wt.% ethylbenzene. As more particularly shown in FIGS. 1-3, an impure ethylbenzene-containing feed 2 may be continuously fed into the loop, from which ethylbenzene-rich product 402, para-xylene-rich product 10, and optionally non-aromatic-rich stream 401 may be fedThe output is continuous, with the accumulation of ethylbenzene and optional non-aromatics in the loop being controlled by integration with the EB separation unit 400. Specific types of non-aromatic compounds that may be present in non-aromatic-rich stream 401 and thus may be separated from the paraxylene process flow loop include non-aromatic hydrocarbons such as those described above, i.e., C₈Alkanes (e.g. isomers of n-octane and iso-octane), C₇-C₈Cycloalkanes (e.g. ethylcyclohexane and cyclooctane) and/or C₉Alicyclic hydrocarbons (e.g., isomers of trimethylcyclohexane).

Figure 4 shows a further embodiment in which ethylbenzene and optional non-aromatics are also separated from the process. However, in this embodiment, the ethylbenzene-rich product 402 and the optional non-aromatic-rich stream 401 are separated using an EB separation unit 400 fed with all or part of the impure ethylbenzene-containing feed 2. That is, the process according to this embodiment may include separating the ethylbenzene-rich product 402 from the total impure ethylbenzene-containing feed 2 or portion 2A of the feed, in which case portion 20 bypassing the EB separation unit is fed to the xylene column 100. In either case, at least a portion of the ethylbenzene-depleted feed 2B may be separated from C as a lower boiling fraction (e.g., overhead) from the xylene column 100₈Aromatic hydrocarbon streams 4 are combined to provide a combined ethylbenzene-depleted feed/C₈Aromatic hydrocarbon stream 43. At least a portion of the stream 43 may then be fed to a xylene separation zone 200 to separate the stream 43 from C₈The aromatic hydrocarbon stream 4, the para-xylene depleted effluent 6, and the xylene-equilibrated isomerate 8 are combined to form a para-xylene process flow loop as described above for the embodiments depicted in fig. 1-3. However, the embodiment depicted in FIG. 4 differs in that ethylbenzene is separated upstream (prior) to the loop. Thus, while parameters such as overall yield of para-xylene, overall conversion of ethylbenzene, and overall aromatic ring loss may be within the above-noted ranges, these parameters may be based on the input side in the impure ethylbenzene-containing feed upstream of the para-xylene process loop (e.g., in section 2A sent to EB separation unit 400 and section 20 bypassing that unit)All xylenes, ethylbenzene and aromatic hydrocarbons of the process. In addition, other parameters associated with the circuit, such as ethylbenzene concentration, may be as described above, for example, with respect to the embodiments depicted in FIGS. 1-3.

According to the embodiment depicted in FIG. 4, in addition to the ethylbenzene-rich product 402, an EB separation unit 400, for example, comprising extractive distillation, may further provide a C-rich product₉ ⁺A heavy fraction 47 of hydrocarbons. This fraction 47 may be separated from C from xylene column 100₉ ⁺The hydrocarbon streams 12 are combined.

In controlling the extent of ethylbenzene accumulation in a paraxylene process loop, the degree of C transferred from the loop for ethylbenzene separation can be varied₈An aromatic hydrocarbon stream 4, a para-xylene depleted effluent 6 and/or a portion 4A, 6A, 8A of a xylene-equilibrated isomerate 8 or a portion 2A of an impure ethylbenzene-containing feed (embodiment of fig. 4). By increasing the fractions 2A, 4A, 6A, 8A, the concentration of ethylbenzene in the loop is directionally reduced, and the process requirements (e.g., equipment and utilities) associated with the streams making up the loop, such as the para-xylene separation zone 200 and the isomerization zone 300, are also reduced. However, the processing requirements of the EB separation unit 400 increase. Conversely, by reducing the 2A, 4A, 6A, 8A fractions, the orientation increases the concentration of ethylbenzene in the loop and also increases the process requirements (e.g., equipment and utilities) associated with the streams making up the loop, such as the para-xylene separation zone 200 and the isomerization zone 300. However, the processing requirements of the EB separation unit 400 are reduced. One skilled in the art, with the knowledge of this specification, will understand that a given integrated para-xylene production/extractive distillation process can be operated with these tradeoffs in mind.

To characterize the tradeoff between the fraction 4A, 6A, 8A withdrawn from the para-xylene process flow loop or the fraction 2A of the impure ethylbenzene-containing feed (embodiment of fig. 4) and the ethylbenzene concentration in the loop, the para-xylene depleted effluent 6 and the xylene-balanced isomerate 8 can serve as convenient references. These streams are both downstream of the para-xylene separation zone 200 and may generally have the same or about the same mass flow rate. According to a representative embodiment, (i) isPure ethylbenzene-containing feed 2 or a fraction thereof 2A, (ii) C₈Part 4A of the aromatic hydrocarbon stream 4, (iii) part 6A of the para-xylene depleted effluent 6, or (iv) part 8A of the xylene-equilibrated isomerate 8 is fed to (or from which is separated the ethylbenzene-rich product 402), which can typically comprise from about 1 wt% to about 95 wt% of the para-xylene depleted effluent 6 or the xylene-equilibrated isomerate 8. More typically, however, such portion 2A, 4A, 6A, 8A or total impure ethylbenzene-containing feed 2 comprises from about 3 wt.% to about 50 wt.% of the para-xylene depleted effluent 6 or xylene-equilibrated isomerate 8, and typically comprises from about 5 wt.% to about 15 wt.%, each typically at comparable flow rates. According to further representative embodiments, (i) the impure ethylbenzene-containing feed 2 or a fraction thereof 2A, (ii) C₈Part 4A of the aromatic hydrocarbon stream 4, (iii) part 6A of the para-xylene depleted effluent 6, or (iv) part 8A of the xylene-equilibrated isomerate 8 is fed to (or from which is separated an ethylbenzene-rich product 402), which may typically comprise from about 3 wt% to about 50 wt% ethylbenzene. More typically, however, such a portion 2A, 4A, 6A, 8A or total impure ethylbenzene-containing feed 2 comprises from about 10 wt% to about 40 wt% ethylbenzene, and typically from about 15 wt% to about 25 wt% ethylbenzene.

According to more specific embodiments, it relates to a desirable compromise between the fraction 4A, 6A, 8A withdrawn from the para-xylene process loop or the fraction 2A of the impure ethylbenzene-containing feed (the embodiment of FIG. 4) and the ethylbenzene concentration in the loop, and preferably between (i) the fraction 2A, 4A, 6A, 8A determined based on the para-xylene depleted effluent 6 or the xylene-balanced isomerate 8 (e.g., based on the flow of the para-xylene depleted effluent 6 or the xylene-balanced isomerate 8, the flow percentage of the fraction 2A; based on the flow of the para-xylene depleted effluent 6 or the xylene-balanced isomerate 8, the flow percentage of the fraction 4A; based on the flow of the para-xylene depleted effluent 6, the flow percentage of the fraction 6A; or based on the flow of the xylene-balanced isomerate 8, the percent flow of portion 8A) and (ii) the ethylbenzene concentration in the para-xylene depleted effluent 6 or the xylene-equilibrated isomerate 8, the value of (i) can be from about 5 wt.% to about 15 wt.%, and the value of (ii) can be from about 15 wt.% to about 25 wt.%. For example, the value of (i) may be about 7 wt% to about 11 wt%, and the value of (ii) may be about 16 wt% to about 20 wt%. Additionally, for the smaller portion withdrawn from the paraxylene process flow loop, or the smaller portion 2A fed to the EB separation unit 400 (the embodiment of fig. 4), and the higher concentration of ethylbenzene in the loop, (i) can have a value of from about 4 wt% to about 8 wt%, and (ii) can have a value of from about 23 wt% to about 27 wt%.

Isomerization zone conditions

As noted above, in the operation of such a para-xylene process loop, integration with an EB separation unit such as an extractive distillation zone to prevent excess ethylbenzene from building up in the loop is advantageous in terms of reduced severity of the isomerization zone 300 operation, such as associated with reduced ethylbenzene conversion requirements and correspondingly reduced aromatic ring losses. Thus, in a representative process, the conversion of ethylbenzene introduced into the paraxylene process loop (e.g., during steady state operation) is less than about 20%. In other representative processes, the aromatic ring loss introduced into the paraxylene process flow loop (e.g., during steady state operation) is less than about 5%.

The isomerization zone may comprise one or more separate isomerization reactors containing a suitable isomerization catalyst in various catalyst bed configurations (e.g., fixed or moving bed) and flow configurations (e.g., axial flow or radial flow). One reactor is generally used. In the isomerization reactor, typical isomerization conditions include a temperature of about 150 ℃ (302 ° f) to about 500 ℃ (932 ° f), and preferably a temperature of about 200 ℃ (392 ° f) to about 300 ℃ (572 ° f), and an absolute pressure of about 1.5 MPa (218 psi) to about 5 MPa (725 psi), and preferably an absolute pressure of about 2.5 MPa (363 psi) to about 4.5 MPa (653 psi). Based on the effluent depleted in para-xylene and/or any other input to the isomerization reactorThe isomerization conditions may further comprise a gravimetric flow rate of the hydrocarbon-containing stream (e.g., ethylbenzene-depleted, para-xylene-depleted effluent 6B as described above) of about 0.5 hr^-1To about 20 hr^-1And preferably about 1 hr^-1To about 10 hr^-1Weight Hourly Space Velocity (WHSV). As understood in the art, WHSV is the weight flow rate fed to the reactor divided by the weight of catalyst in the reactor and represents the equivalent catalyst bed weight of the feed stream processed per hour. WHSV is related to the inverse of the reactor residence time.

Hydrogen, which is typically introduced as a gaseous mixture (e.g., containing recycled hydrogen) at different purity levels, can be introduced into the isomerization reactor. The molar ratio of hydrogen to hydrocarbons may generally range from about 0.5:1 to about 15:1, and typically from about 0.5:1 to about 10:1, based on the molar flow rate of the para-xylene depleted effluent and/or any other hydrocarbon-containing stream (e.g., ethylbenzene-depleted, para-xylene depleted effluent 6B, as described above) fed to the isomerization reactor. Advantageously, however, the isomerization reactor of isomerization zone 300 can be operated under liquid phase conditions and in the absence of added hydrogen, taking into account the reduced severity isomerization conditions possible with the processes described herein. That is, the isomerization zone 300 can include an isomerization reactor through which the para-xylene depleted effluent 6, or at least a portion 60 thereof, passes in the liquid phase.

The reactor in the isomerization reaction zone 300 typically contains a catalyst that functions to perform the desired isomerization of ortho-xylene and meta-xylene to para-xylene, but does not function to convert ethylbenzene, such as by isomerization or dealkylation (cracking). In this manner, the formulation of the catalyst used in the isomerization reactor can be advantageously simplified relative to those catalysts formulated with the conventional requirements for ethylbenzene conversion due to the integration with the extractive distillation zone 400 for ethylbenzene separation. For example, the acidity of the isomerization catalyst support may be reduced and thereby promote a lower degree of ethylbenzene dealkylation and thus may produce less light hydrocarbons and other by-products resulting in a loss of desired para-xylene yield.

A representative isomerization catalyst for use in the isomerization reaction zone comprises a metal component and a molecular sieve component which may be zeolitic or non-zeolitic, and optionally an inorganic oxide component. Representative zeolite aluminosilicate molecular sieves include pentasil zeolites such as those having the structure type of MFI, MEL, MTW, MFS, MTF and FER (IUPAC zeolite nomenclature committee), MWW, beta zeolites or mordenite. Representative non-zeolitic molecular sieves include those having one or more of the AEL framework Types, such as SAPO-11, or those having one or more of the ATO framework Types, such as MAPSO-31 (see "Atlas of Zeolite Structure Types", Butterworth-Heineman, Boston, MA, 3 rd edition, 1992). Representative metal components of the isomerization catalyst include at least one precious metal and optionally at least one base metal modifier in combination with or in place of the at least one precious metal. The noble metal comprises a platinum group metal selected from the group consisting of platinum, palladium, rhodium, ruthenium, osmium, iridium, and mixtures thereof. The base metal may be selected from rhenium, tin, germanium, lead, iron, cobalt, nickel, indium, gallium, zinc, uranium, dysprosium, thallium, and mixtures thereof. The metal component may also comprise a combination of one or more base metals and/or one or more precious metals. The total content of the one or more metals in the isomerization catalyst is typically from about 0.01 wt.% to about 10 wt.%, and typically from about 0.01 wt.% to about 3 wt.%. The total content of molecular sieve in the isomerization catalyst is typically from about 1 wt% to about 99 wt%, typically from about 10 wt% to about 90 wt%, and often from about 25 wt% to about 75 wt%. Additional components of the isomerization catalyst may include inorganic oxide components, such as binder materials (e.g., alumina). A representative isomerization catalyst for use in an isomerization reactor comprises platinum on a zeolite aluminosilicate molecular sieve in the amounts described above relative to total metal content.

Extractive distillation zone

As described herein, in EB separation unit 400, (i) impure ethylbenzene-containing feed 2 or portion 2A thereof, (ii) C, fed to the unit₈Part 4A of aromatic hydrocarbon stream 4, (iii) part 6A of para-xylene depleted effluent 6, or (iv) of xylene-equilibrated isomerate 8Portion 8A is subjected to extractive distillation or other separation of ethylbenzene. For the sake of brevity, this stream may be referred to generally as the portion 2A/4A/6A/8A fed to the EB separation unit (where portion 2A may represent all of the impure ethylbenzene-containing feed 2), all or a portion of which may be combined with one or more extractant compounds described herein to provide a liquid mixture. By increasing ethylbenzene to other C₈Relative volatility of aromatic compounds (e.g., ortho-, meta-, and/or para-xylene), the extractant compound effectively facilitates the desired separation of the ethylbenzene-rich product 402. In addition, the extractant compound itself is readily enriched in the other C or C's relative to the portion 2A/4A/6A/8A or a portion of these individual streams fed to the EB separation unit₈The aromatic compounds are separated from the distillate of the extractant compound (e.g., recovered as the bottoms fraction of the extractive distillation). This allows the extractant compound to be conveniently reused (recycled), for example in a continuous extractive distillation process.

A representative extractive distillation process involves distilling a liquid mixture comprising a portion 2A/4A/6A/8A (portion 2A of which may represent the total impure ethylbenzene-containing feed 2) or a portion thereof fed to an EB separation unit, and an extractant compound as described herein. A portion 2A/4A/6A/8A or a portion thereof can be considered to comprise ethylbenzene and one or more other C' s₈Hydrocarbon component of aromatic compounds. Thus, a particular process involves distillation of a feedstock comprising ethylbenzene, other C₈A liquid mixture of an aromatic compound (e.g., ortho-xylene, meta-xylene, and/or para-xylene) and an extractant compound.

The extractant properties may be based on its ability to increase ethylbenzene and at least one other C to be separated₈The relative volatility between aromatic compounds (e.g., at least one, at least two, or all of ortho-xylene, meta-xylene, and para-xylene) to thereby increase the separation efficiency of each stage of the vapor-liquid equilibrium. According to representative embodiments, the one or more extractant compounds may be present in the liquid mixture in an amount such that ethylbenzene is at a given pressure (e.g., 200 millibar absolute) to at least one otherC₈The relative volatility (α) of the aromatic compound is at least about 1.14, preferably at least about 1.16, more preferably at least about 1.20 and even more preferably at least about 1.22.

The performance of the extractive agent in the extractive distillation process described herein can alternatively be enhanced by its ability to separate with respect to ethylbenzene and other C or C's to be separated from ethylbenzene₈The competitive factor of the aromatic compound (e.g., ortho-xylene, meta-xylene, and/or para-xylene). The competition factor (D) can be quantified by the following expression

。

The molecule of D is ethylbenzene and the given one of the other C at 80 deg.C (176 DEG F) and atmospheric pressure₈Gas phase weight ratio of aromatic compounds to (i) 1 part by weight of 60% by weight of ethylbenzene and 40% by weight of other C₈An aromatic compound and (ii) 5 parts by weight of an extractant compound (or a mixture of two or more extractant compounds). The denominator of D is the reference gas phase weight ratio of the same compound at 80 ℃ (176 ° F) and atmospheric pressure, in equilibrium with the liquid composition of (i) only. Thus, a D value in excess of one indicates an improved ease of separation of ethylbenzene into the vapor phase due to the presence of the extractant compound. Thus, the competition factor can be measured according to standard protocols, such as those described herein. Advantageously, the competition factor can generally be at least about 1.10, typically at least about 1.18, and often at least about 1.20, depending on the representative extractive distillation method. In addition, the extractant may provide a competition factor (D) of less than one, for example generally up to about 0.95, usually up to about 0.90, and often up to about 0.85, meaning that the extractant indicates a less volatile additional C₈Improved ease of separation of aromatic compounds (e.g., meta-xylene or para-xylene) into the liquid phase.

In the presence of (for ethylbenzene and other C(s) as described above)₈Aromatic) or combinations thereofAn exemplary extractant compound or mixture of extractant compounds may have a competition factor for one or more non-aromatic hydrocarbons and ethylbenzene that is greater than or less than one. Advantageously, the one or more extractive agents may thereby promote such non-aromatic hydrocarbons with ethylbenzene and other one or more C₈Separation of aromatics, for example, by enriching such non-aromatic hydrocarbons in a low boiling fraction or overhead removal fraction upstream of extractive distillation column 455 (fig. 5), as discussed in more detail below in the context of non-aromatic removal column 445 (fig. 5). According to some embodiments, one or more representative extractant compounds may have a competition factor D of more than one, determined in a similar manner as described above, but with the relevant weight ratio in the numerator and denominator being the weight ratio of a given non-aromatic compound to ethylbenzene. According to particular embodiments, one or more of the extractant compounds may have the following competition factor D: which is (i) generally at least about 2.0, usually at least about 2.3, and often at least about 2.6 for n-octane and ethylbenzene, (ii) generally at least about 1.7, usually at least about 1.9, and often at least about 2.1 for ethylcyclohexane and ethylbenzene, and/or (iii) generally at least about 1.6, usually at least about 1.7, and often at least about 1.8 for cyclooctane and ethylbenzene.

In representative embodiments, the desired relative volatility (α), competition factor (D), and/or other favorable extractive distillation operating characteristics are obtained after distilling the liquid mixture at sub-atmospheric pressures, such as at absolute pressures generally less than about 800 millibar, typically less than about 400 millibar, and often less than about 300 millibar, with exemplary pressures ranging from about 50 millibar to about 800 millibar, about 100 millibar to about 400 millibar, and about 150 millibar to about 300 millibar.

A flow scheme corresponding to a representative extractive distillation zone 400 (as EB separation unit 400) is shown in fig. 5. According to this embodiment, the feed to extractive distillation zone 400 comprises ethylbenzene and other C(s) in addition to one or more non-aromatic compounds (e.g., non-aromatic hydrocarbons, such as isomers of trimethylcyclohexane and/or n-octane)₈Aromatic compounds (e.g. ortho-bis)Toluene, meta-xylene and/or para-xylene) fraction 2A/4A/6A/8A (of which fraction 2A may represent the total impure ethylbenzene-containing feed 2) is subjected to upstream distillation in a non-aromatics removal column 445. Non-aromatic extractant (selective for extractive distillation of non-aromatics, such as non-aromatic hydrocarbons) stream 410 can be combined with portion 2A/4A/6A/8A prior to or in non-aromatic removal column 445 to facilitate the desired removal of at least one non-aromatic compound (e.g., non-aromatic hydrocarbons). As shown, optional non-aromatic extractant compound make-up stream 412A may also be introduced continuously or intermittently to non-aromatic compound removal column 445 to replace any minor amounts of non-aromatic extractant compounds not recovered in recycle stream 422. An overhead removal fraction is withdrawn from non-aromatic removal column 445 as enriched in at least one non-aromatic compound and depleted in at least one C relative to fraction 2A/4A/6A/8A₈A non-aromatic rich stream 401 of aromatic compounds. This results in the removal of at least one non-aromatic compound, which may have a C which is identical to the other C or C's present in the moiety 2A/4A/6A/8A₈The boiling points of aromatic compounds (e.g., ortho-xylene, meta-xylene, and/or para-xylene) are comparable, such as boiling points within 15 ℃ (+/-15 ℃ or +/-27 ° f), within 10 ℃ (+/-10 ℃ or +/-18 ° f), or possibly within 5 ℃ (+/-5 ℃ or +/-9 ° f) thereof. Non-aromatic removal column 445 may also be used to remove water from portion 2A/4A/6A/8A, for example to achieve a desired low water content in pretreated bottoms fraction 414 and/or Liquid Mixture (LM). Alternatively, section 2A/4A/6A/8A may be subjected to a separate, optional water removal step upstream of non-aromatic removal column 445. Removal of water may be economically advantageous, the economically advantageous range lying in: the total material subjected to extractive distillation is reduced and therefore the associated energy requirements are also reduced. Other advantages in terms of separation performance may also result.

The pretreated bottoms fraction 414 is recovered from non-aromatic removal column 445 (i.e., from the upstream distillation) as a purification feed stream to the extractive distillation. The purified feed stream is enriched in ethylbenzene and other C or C's relative to fraction 2A/4A/6A/8A₈Aromatic compounds, and optionally non-aromatic-rich extractant compounds, are introduced to non-aromatic removal column 445 along with non-aromatic extractant stream 410. The pretreated bottom fraction 414 is also depleted in one or more non-aromatic compounds present in the stream relative to the fraction 2A/4A/6A/8A. The pretreated bottoms fraction 414 is then introduced into extractive distillation column 455 along with a recycle portion 422B of recycle stream (or second bottoms fraction) 422 comprising ethylbenzene extractant (or extractant compound as described herein). The pretreated bottoms fraction 414 and recycle portion 422B can be combined before or within extractive distillation column 455. Recycle portion 422B can thus provide a portion or all (at least a portion) of the extractant compound fed to extractive distillation column 455. As shown, optional extractant compound make-up stream 412B may also be introduced continuously or intermittently to extractive distillation column 455 to replace any minor amounts of extractant compound not recovered in recycle stream 422.

Thus, a Liquid Mixture (LM) comprising pretreated bottoms fraction 414 and the extractant compound present in recycle portion 422B and optional make-up stream 412B is distilled in extractive distillation column 455. The extractive distillation provides an ethylbenzene-rich product 402 that is enriched in ethylbenzene relative to the pretreated bottoms fraction 414 and also relative to the Liquid Mixture (LM), and depleted in extractant compounds and at least one other C present in the pretreated bottoms fraction 414₈Both aromatic compounds (e.g., one or more isomers of xylene). Extractive distillation column 455 also provides a bottoms fraction 418 that is enriched in at least one other C relative to pretreated bottoms fraction 414 and also relative to Liquid Mixture (LM)₈Both aromatic compounds and extractant compounds, and is depleted in ethylbenzene. To purify and recover the extractant compounds, bottom fraction 418 is then introduced to extractant recovery column 465 and distilled therein to provide a second bottom fraction 422, which second bottom fraction 422 is enriched in extractant compounds and optionally also non-aromatic extractant compounds relative to bottom fraction 418. Second bottom fraction 422 is also depleted in at least one other C relative to bottom fraction 418₈An aromatic compound. In this manner, at least a portion of second bottoms fraction 422 can then be recovered and recycled to extractive distillation column 455 as recycle portion 422B to advantageously conserve material resources by providing at least a portion of the extractant compound in the Liquid Mixture (LM). Optionally, at least a second portion of the second bottoms fraction 422 can also be recycled to the non-aromatic removal column 445 as non-aromatic extractant stream 422C. According to some embodiments, the second bottoms fraction 422, the recycled portion 422B, and/or the non-aromatic extractant stream 422C may be further purified (e.g., using further distillation, adsorbent separation, extraction, etc.) to remove contaminants from these extractant-containing streams prior to introduction to their respective columns. Optionally, second bottom fraction vent stream 422A can be used to prevent excessive accumulation of undesirable impurities in the recycle of extractant. According to the embodiment depicted in fig. 4, all or a portion of second bottom fraction effluent stream 422A (fig. 5) may correspond to a C-rich stream₉ ⁺Heavy fraction 47 of hydrocarbons, all or part of which may be associated with C₉ ⁺The hydrocarbon streams are combined and exit xylene column 100 as a lower boiling fraction (e.g., bottoms).

Distilling the bottoms fraction 418 in extractant recovery column 465 further provides: (i) feed 2B depleted of ethylbenzene, (ii) C depleted of ethylbenzene₈An aromatic hydrocarbon stream 4B, (iii) an ethylbenzene-depleted, para-xylene-depleted effluent 6B, or (iv) an ethylbenzene-depleted, xylene-equilibrated isomerate 8B, which is fed to the para-xylene process flow loop in the case of (i) and returned to the para-xylene process flow loop in the case of (ii), (iii), and (iv) (e.g., combined with portions bypassing the extractive distillation, as described above). For simplicity, this stream may be generally referred to as ethylbenzene depleted stream 2B/4B/6B/8B, which is fed or returned to the paraxylene process loop after extractive distillation. This stream 2B/4B/6B/8B is enriched with respect to the bottom fraction 418 with at least one other C₈Aromatic compounds (e.g., ortho-, meta-, and/or para-xylene) and are depleted in extractant compounds, and optionally also depleted in non-aromaticsAn extractant compound. The entire extractive distillation zone 400 thus advantageously provides an ethylbenzene-rich product 402 (which purifies ethylbenzene), a non-aromatic-rich stream 401 (which purifies non-aromatics), and an ethylbenzene-depleted stream 2B/4B/6B/8B (which is rich in at least one other C) as a further overhead fraction₈Aromatic compounds). Extractive distillation zone 400 thus advantageously breaks down (resolve) these purified products while also providing for recycle of the extractant compounds. If desired, one or both of these purified products may be further purified (e.g., using further distillation, adsorbent separation, extraction, etc.) to achieve higher purity levels.

According to the embodiment shown in fig. 5, the extractant compounds used in upstream non-aromatic removal column 445 as well as in extractive distillation column 455 (and in each case separated from second bottom fraction 422) may be the same compounds. Alternatively, different extractant compounds may be used for these different purposes, in which case optional separation (e.g., distillation) may be used to obtain non-aromatic extractant stream 422C and recycle portion 422B introduced into these various columns. An exemplary non-aromatic extractant is acetonitrile. Preferably, however, the same compound can be used for both extractive distillations, resulting in further advantages in terms of process simplification (e.g., less separation requirements) and associated cost reduction. As further shown in fig. 5, the total non-aromatic extractant input 410 to the non-aromatic compound removal column 445 may be a combined amount of non-aromatic extractant compound make-up stream 412A and non-aromatic extractant stream 422C. In addition, the entire ethylbenzene extractant input 416 to the extractive distillation column 455 may be a combined amount of make-up stream 412B and recycle portion 422B.

Extractant compounds

For the extractant compounds used in the processes described herein, and in particular the extractive distillation zone 400 (e.g., EB separation unit 400), the binding energy between such extractant compounds and ethylbenzene is advantageously different than between the extractant compounds and at least one other (e.g., non-ethylbenzene) C₈Between aromatic compounds, e.g. o-, m-or p-xyleneThe binding energy of (1). Binding energy is determined by a combination of several factors related to the respective interacting compounds, including their polarity and steric effects. It has now surprisingly been found that the following extractant compounds are effective extractants for extractive distillation, for example for the extraction from at least one other C₈Ethylbenzene is separated from an aromatic compound (e.g., ortho-, meta-, and/or para-xylene) having a carbocyclic (e.g., as well as aromatic) or heterocyclic ring structure substituted at a substitutable ring position with (i) at least one NR substituted^aR^bGroup (i.e., -NR)^aR^bSubstituent) wherein R is^aAnd R^bIndependently selected from the group consisting of oxy, hydrogen, and hydrocarbyl groups having from about 1 to about 20 carbon atoms, and (ii) at least two halogen groups (i.e., halogen substituents derived from their respective halogen atoms). While not being bound by theory, it is believed that the presence of both the nitrogen and halogen atoms together with the cyclic (e.g., aromatic) ring structure provides the appropriate polarity, while the cyclic (e.g., aromatic) base structure itself provides an important steric hindrance effect. Thus, an extractant compound comprising a combination of these features can be attracted to non-ethylbenzene C₈Aromatics interact with but can exclusively interact with ethylbenzene to facilitate distillative separation of non-ethylbenzene C in the bottoms fraction₈Aromatic compounds are in particular xylene and one or more extractant compounds and ethylbenzene in the overhead fraction.

According to representative embodiments, the extractant compound is a compound according to formula (I):

wherein R is^aAnd R^bEach bonded to a nitrogen atom illustrated in the formula and independently selected from the group consisting of oxy, hydrogen, and hydrocarbyl groups having from about 1 to about 20 carbon atoms. R^aAnd R^bEach bonded to the nitrogen atom represented by formula (I) above through a single covalent bond, a double covalent bond, or a resonance-stable covalent bond.

At R^aAnd R^bIn the case where both are oxy, the group-NR^aR^bRepresents a nitro group (-NO)₂) As substituents of the benzene ring illustrated by formula (I), wherein the nitro group has a structure that can be represented as:or stabilized by resonanceIs expressed in terms of the form.

At R^aAnd R^bIn the case where both are hydrogen, the group-NR^aR^bRepresents a primary amino group (-NH)₂）。

In addition, R^aAnd R^bTogether with the nitrogen atom of formula (I) above to which they are jointly bound, may form a 5-to 8-membered ring, wherein one or more ring members (e.g. carbon atom ring members) may be substituted. Suitable substituents for the ring members are those defined below as substituents (1) or (2) for one or more carbon atoms of the hydrocarbyl group. According to exemplary embodiments, NR^aR^bA 5-membered ring substituent such as pyrrolyl, dihydropyrrolyl, tetrahydropyrrolyl or pyrrolidinyl may be formed, or a 6-membered ring substituent such as pyridyl, dihydropyridinyl, tetrahydropyridinyl or piperidinyl may be formed.

In the above formula (I), R²-R⁶Is a substituent (substituent NR) in which a benzene ring is illustrated^aR^bOther) and is independently selected from the group consisting of halogens, hydrogen radicals, and hydrocarbon radicals having from about 1 to about 20 carbon atoms. Preferably, R²-R⁶At least two of which are halogen, e.g. in R²-R⁶In the case of at least two of which are chlorine. For example, R³And R⁴May both be halogen, for example chlorine. Or, R²And R³May be halogen, such as chlorine.

At R^a、R^b、R²、R³、R⁴、R⁵Or R⁶One or more ofIn the case where a plurality is a hydrocarbon group having from about 1 to about 20 carbon atoms, such a hydrocarbon group means a saturated or partially unsaturated, linear, branched or cyclic hydrocarbon group in which one or more carbon atoms in such a hydrocarbon group are optionally substituted and/or substituted, for example, according to the following (1) and/or (2), or according to the following (3). In particular, among the representative hydrocarbon groups having from about 1 to about 20 carbon atoms,

(1) one or more carbon atoms having one or more bonded hydrogen atoms (i.e., a hydrogen radical) are optionally substituted with a monovalent group independently selected from: alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, -OH, -SH, -SOH, -SO₂H、-SO₃H、-NH₂、-NO₂、-CO₂H、-CONH₂-CN, -F, -Cl, -Br and-I, wherein the monovalent heteroatom groups-OH, -SH, -SOH, -SO₂H、-SO₃H、-NH₂、-CO₂H、-CONH₂Optionally having one or more bound hydrogen atoms independently replaced by: alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, -OH, -SH, -SOH, -SO₂H、-SO₃H、-NH₂、-NO₂、-CO₂H、-CONH₂-CN, -F, -Cl, -Br or-I;

(2) one or more carbon atoms having two or more bound hydrogen atoms are optionally substituted with a divalent group independently selected from = O, = S, = NH, = NOH, and = NNH₂Wherein divalent heteroatom group = NH, = NOH, and = NNH₂Optionally having one or more bound hydrogen atoms (i.e., hydrogen groups) independently replaced by: alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, -OH, -SH, -SOH, -SO₂H、-SO₃H、-NH₂、-NO₂、-CO₂H、-CONH₂-CN, -F, -Cl, -Br or-I; and

(3) one or more methylene carbon atoms (-CH)₂-) may optionally be replaced by a divalent group independently selected from alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl、-O-、-S-、-NH-、-OCO-、-CO₂-, -CONH-, -OCONH-and-CO₂NH-, wherein the divalent heteroatom group-NH-, -CONH-, -OCONH-, and-CO₂NH-optionally having one or more hydrogen groups independently replaced by: alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, -OH, -SH, -SOH, -SO₂H、-SO₃H、-NH₂、-NO₂、-CO₂H、-CONH₂-CN, -F, -Cl, -Br, or-I.

According to other examples, R^aAnd R^bOne or both of, and/or R²、R³、R⁴、R⁵Or R⁶(e.g., those substituents R which are not halogen)²、R³、R⁴、R⁵Or R⁶) May additionally be independently selected (in addition to a hydride or hydrocarbyl group having from about 1 to about 20 carbon atoms as defined above) from a monovalent heteroatom group such as-OH, -SH, -SOH, -SO₂H、-SO₃H、-NH₂、-NO₂、-CO₂H、-CONH₂and-CN, wherein the monovalent heteroatom groups-OH, -SH, -SOH, -SO₂H、-SO₃H、-NH₂、-CO₂H and-CONH₂Optionally having one or more hydrogen radicals independently replaced by: alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, -OH, -SH, -SOH, -SO₂H、-SO₃H、-NH₂、-NO₂、-CO₂H、-CONH₂-CN, -F, -Cl, -Br, or-I.

Representative hydrocarbyl groups having from about 1 to about 20 carbon atoms can be saturated or partially unsaturated, straight chain, branched chain, or cyclic hydrocarbyl groups, optionally wherein no carbon atoms are substituted according to (1) above, or wherein no carbon atoms are substituted according to (2) above, or wherein no carbon atoms are substituted according to (3) above. In the case of saturated cyclic hydrocarbon groups, a representative hydrocarbon group may be a cycloalkyl group (e.g., cyclopentyl or cyclohexyl). In the case of partially unsaturated cyclic hydrocarbyl groups, representative hydrocarbyl groups can be aryl groups (e.g., cyclopentadienyl or phenyl).

Representative hydrocarbon groups having from about 1 to about 20 carbon atoms can be saturated straight, branched, or cyclic groups of aliphatic hydrocarbons, optionally wherein no carbon atoms are substituted according to (1) above, or wherein no carbon atoms are substituted according to (2) above, or wherein no carbon atoms are substituted according to (3) above.

Representative hydrocarbyl groups having from about 1 to about 20 carbon atoms can be selected from alkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, (cycloalkyl) alkyl, (heterocycloalkyl) alkyl, aralkyl, heteroaralkyl, hydroxy, alkoxy, cycloalkoxy, aryloxy, hydroxycarbonyl, hydroxycarbonylalkyl, alkanoyl, alkanoyloxy, alkoxycarbonyl, thiol, alkylthiol, amino, halogen, haloalkyl, acylamino, alkylamido, (cycloalkyl) acylamino, (heterocycloalkyl) acylamino, arylacylamino, and (heteroaryl) acylamino.

Representative hydrocarbyl groups having from about 1 to about 20 carbon atoms can be alkyl, e.g., C₁-C₄Alkyl groups (e.g., methyl, ethyl, propyl, and butyl).

According to other embodiments, R^aAnd R^bOne or both of, and/or R²、R³、R⁴、R⁵Or R⁶Of (e.g. those substituents R which are not halogen)²、R³、R⁴、R⁵Or R⁶) E.g. R^aAnd R^bBoth, and/or R (not being halogen)²、R³、R⁴、R⁵Or R⁶All are hydrogen radicals.

According to a particular embodiment, the aromatic compound of the extractant may be an isomer of dichloronitrobenzene, such as the compound: wherein NR is^aR^bRepresents a nitro group (-NO)₂) A substituent R²、R³、R⁴、R⁵And R⁶Two of which represent chlorine and the remaining substituents R²、R³、R⁴、R⁵And R⁶Represents hydrogen. In a specific case, where NR^aR^bRepresents Nitro (NO)₂）；R³And R⁴Represents chlorine and R²、R⁵And R⁶Representing hydrogen, the aromatic compound of the extractant is 1, 2-dichloro-4-nitrobenzene. In a specific case, where NR^aR^bRepresents a nitro group (-NO)₂）；R²And R³Represents chlorine; and R is³、R⁵And R⁶Representing hydrogen, the aromatic compound of the extractant is 1, 2-dichloro-3-nitrobenzene. The compounds 1, 2-dichloro-4-nitrobenzene and 1, 2-dichloro-3-nitrobenzene have the following structures:

。

according to other specific embodiments, the aromatic compound of the extractant may be an isomer of dichloroaniline, such as the compound: wherein NR is^aR^bRepresents amino (NH)₂) Substituent R²、R³、R⁴、R⁵And R⁶Two of which represent chlorine, and the remaining substituents R²、R³、R⁴、R⁵And R⁶Represents hydrogen. In a specific case, where NR^aR^bRepresents amino (NH)₂）；R³And R⁴Represents chlorine; and R is²、R⁵And R is⁶The aromatic compound representing hydrogen and the extractant is 3, 4-dichloroaniline. The compounds have the following structure:

。

mixtures of any two or more extractant compounds, for example two or more compounds according to formula (I) above, may also be used, for example, in the Liquid Mixture (LM) of the extractive distillation process described above. According to particular embodiments, mixtures of dichloroaniline isomers and dichloronitrobenzene isomers may be used, for example, mixtures of (i) 3, 4-dichloroaniline and (ii) 1, 2-dichloro-4-nitrobenzene or 1, 2-dichloro-3-nitrobenzene in any mixing ratio (e.g., 5/95 weight/weight of (i): (ii), 25/75 weight/weight of (i): (ii), 50/50 weight/weight of (i): (ii), 75/25 weight/weight of (i): (ii), or 95/5 weight/weight of (i): (ii)).

For the purposes of the present invention, and consistent with accepted chemical nomenclature for groups such as substituents,

"halogen", alone or in combination, represents a halogen radical selected from fluorine, chlorine, bromine, and iodine (i.e., -F, -Cl, -Br, and-I, respectively). According to a preferred embodiment, "halogen" represents fluorine or chlorine, and more preferably represents chlorine.

"alkyl", as used alone or in combination with other groups (i.e., alone or in combination), means a straight or branched chain saturated hydrocarbon group that may be bonded at one end of the chain (e.g., as in a methyl group, -CH)₃In) or at both ends of the chain (e.g. as in the methylene group, -CH₂-in). Unless otherwise specified, alkyl groups contain 1 to 10 carbon atoms. "alkenyl", alone or in combination, means an alkyl group containing one or more carbon-carbon double bonds. "alkynyl", alone or in combination, refers to an alkyl group containing one or more carbon-carbon triple bonds.

"cycloalkyl", alone or in combination, represents a monocyclic, bridged monocyclic, bicyclic, tricyclic, or spirocyclic saturated hydrocarbon group that can be bonded to the parent molecule at one or more (e.g., one or two) bonding sites, wherein each ring contains 3 to 8 carbon atoms. "heterocycloalkyl", alone or in combination, represents a cycloalkyl group having one or more carbon atoms replaced by oxygen, nitrogen or sulfur (including sulfoxides and sulfones), or otherwise by a divalent group having such a heteroatom (e.g., = NH, = NOH, = NNH)₂And = SO₂) And (4) replacing. "aryl", alone or in combination, means an unsaturated or partially unsaturated monocyclic, bridged monocyclic, bicyclic, tricyclic, or spirocyclic hydrocarbon group that can be bonded to the parent molecule at one or more (e.g., one or two) bonding sites, wherein each ring contains 3 to 8 carbon atoms. "heteroaryl", alone or in combination, represents an aryl group having one or more carbon atoms replaced by an oxygen, nitrogen or sulfur heteroatom, or otherwise by a divalent group having such a heteroatom (e.g., = g =)NH、= NOH、= NNH₂And = SO₂) And (4) replacing. Unless otherwise indicated or apparent from the name of a particular cycloalkyl, heterocycloalkyl, aryl, or heteroaryl, these cyclic groups may be bonded to any on-ring position (i.e., at any substitutable on-ring position) available for bonding in the molecules described herein.

"aralkyl", alone or in combination, denotes an alkyl group in which a hydrogen atom is replaced by an aryl group. "aralkenyl", alone or in combination, denotes an alkenyl group wherein a hydrogen atom is replaced by an aryl group. "arylalkynyl", alone or in combination, denotes an alkynyl group in which a hydrogen atom is replaced by an aryl group. "heteroarylalkyl", "heteroarylalkenyl" and "heteroarylalkynyl", alone or in combination, represent alkyl, alkenyl and alkynyl groups, respectively, wherein a hydrogen atom is replaced by a heteroaryl group.

"hydroxy", alone or in combination, represents the group-OH. "alkoxy", "alkenyloxy" and "alkynyloxy", alone or in combination, represent alkyl, alkenyl and alkynyl groups, respectively, bonded to the molecule through an-O-bond. For example, alkoxy, alone or in combination, represents the group alkyl-O-. "cycloalkoxy", "heterocycloalkoxy", "aryloxy" and "heteroaryloxy", alone or in combination, respectively, represent cycloalkyl, heterocycloalkyl, aryl and heteroaryl, respectively, bonded to the molecule via an-O-bond.

"carbonyl", alone or in combination, represents a group- (C = O) -. "thiocarbonyl", alone or in combination, denotes a radical- (C = S) -. "hydroxycarbonyl", alone or in combination, means a carboxylic acid group- (C = O) -OH. "alkanoyl", "alkenoyl", "alkynoyl" individually or in combination denote alkyl, alkenyl and alkynyl groups, respectively, bonded to the molecule via a carbonyl bond. For example, alkanoyl represents the group alkyl- (C = O) -, either alone or in combination. "cycloalkanoyl", "heterocycloalkanoyl", "aroyl" and "heteroaroyl", alone or in combination, respectively, represent cycloalkyl, heterocycloalkyl, aryl and heteroaryl, respectively, bonded to a molecule through a carbonyl bond.

"carbonyloxy", alone or in combination, means a carbonyl group bonded to a molecule through an-O-bond. "alkanoyloxy", "alkenoyloxy", "alkynyloxy", "cycloalkanoyloxy", "heterocycloalkanoyloxy", "aroyloxy" and "heteroaroyloxy", individually or in combination, denote alkanoyl, alkenoyl, alkynoyl, cycloalkanoyl, heterocycloalkanoyl, aroyl and heteroaroyl, respectively, which are bonded to a molecule via an-O-bond. For example, alkanoyloxy represents the group alkyl-C (= O) -O-.

"thio/mercapto" ("thio") represents either an-S-or-SH bond, alone or in combination. "alkylthio", "alkenylthio" and "alkynylthio", alone or in combination, represent alkyl, alkenyl and alkynyl groups, respectively, bonded to the molecule through an-S-bond. For example, alkylthio represents the group alkyl-S-. "mercaptoalkyl", "mercaptoalkenyl" and "mercaptoalkynyl", alone or in combination, respectively, represent groups of the formula: HS-alkyl-, HS-alkenyl-, and HS-alkynyl-.

"amino", alone or in combination, comprises a primary amine (-NH)₂) And secondary amines (-NH-) as well. Unless otherwise specified, both primary and secondary amino groups may be substituted on a hydrogen, or in the case of a primary amino group, on both hydrogens by one or two groups independently selected from alkyl, alkenyl, alkynyl, cycloalkyl, aryl and heteroaryl. "alkylamino", "alkenylamino" and "alkynylamino" individually or in combination represent alkyl, alkenyl and alkynyl groups, respectively, bonded to the molecule via a secondary amino (-NH-) linkage. "amido", alone or in combination, represents carbonylamino- (C = O) -NH-. "alkylamido", "alkenylamido" and "alkynylamido", individually or in combination, represent alkyl, alkenyl and alkynyl groups, respectively, bonded to a molecule through an amido linkage. For example, alkylamido refers to the group alkyl- (C = O) -NH-. "imino", alone or in combination, means a group- (C = NH) -, wherein imino, unless otherwise specified, may be substituted at hydrogen by a group as defined above for amino.

"heteroatom(s)", "heteroatom group(s)", and "heteroatom group(s)", mean the atoms of oxygen, nitrogen and sulfur, and the groups and radicals having these heteroatoms (groups and radials),for example = O, = S, = NH, = NOH and = NNH₂。

The following examples are set forth as illustrative of the invention. These examples should not be construed as limiting the scope of the invention, as other equivalent embodiments will be apparent in light of the disclosure and the appended claims.

Example 1

Using process simulations, the economics of para-xylene production in a conventional aromatics complex were compared to those utilizing integration with extractive distillation (and particularly distillation with an extractant compound as described above) used to separate ethylbenzene from the process loop. The comparison is based on this separation occurring between the para-xylene separation zone and the xylene isomerization zone, as shown in figure 2. In addition to illustrating the upstream reformate splitter operation, the above-described xylene column distillation, para-xylene separation and isomerization steps were also simulated. To improve the applicability of the simulation to industrial processes, C is also included in the model₇(toluene)/C₉Operation of the transalkylation (disproportionation) unit. The paraxylene separation is based in each case on crystallization.

Three separate cases were identified and analyzed. The first case, identified as "conventional", was modeled not using extractive distillation but rather on the basis of using a conventional isomerization catalyst with ethylbenzene dealkylation activity to limit the accumulation of ethylbenzene in the process loop. The second case, identified as "EB-X18%", was modeled on the basis that the para-xylene depleted effluent from the para-xylene separation zone and thus the feed to the extractive distillation column contained 18 wt.% ethylbenzene. In the third case, identified as "EB-X25%", the modeling was performed on the basis of these streams containing 25 wt% ethylbenzene. Due to the higher concentration of ethylbenzene in the process loop, only 6 wt% of the para-xylene depleted effluent was required for extractive distillation in the third case compared to 9 wt% in the second case. The simulations thus show that the desired compromise is achieved between the ethylbenzene concentration recycled and the proportion of the recycle loop fed to the extractive distillation. In both the EB-X18% and EB-X25% cases, the requirement for ethylbenzene conversion over the isomerization catalyst was eliminated, and correspondingly milder operating conditions were used in the isomerization reactor simulation, including liquid phase operation without hydrogen addition.

The estimated investment costs for the "conventional", "EB-X18%" and "EB-X25%" cases are comparable based on the method simulation study. Although the latter two cases require additional capital associated with carrying out extractive distillation, it has been found that this can be compensated by a cost reduction due to a reduction in capacity of other process operations, most notably an approximately 50% reduction in isomerization costs.

When considering the total operating costs (including utilities), for the case of the model based extractive distillation step, the calculated hydrogen consumption is only about 40% of the "conventional" case, resulting in a significant saving, since there is no hydrogen added to the isomerization zone. Furthermore, simulating the isomerization reactions that occur in the liquid phase according to the second and third cases results in significantly lower estimated aromatic ring losses in terms of product yield and associated product stream value, compared to the gas phase isomerization in the "conventional" case. Other advantages of using extractive distillation operations according to the process model, in the case of EB-X18% and EB-X25%, include an increase of > 2% in total liquid product and a reduction of > 15% in tail gas production for the aromatics complex. In addition, in the case of EB-X18% and EB-X25%, approximately 6.5% by weight of the total liquid product was recovered as high purity ethylbenzene suitable for styrene monomer production. Consistent with current commercial paraxylene production facilities, there is no such revenue-generating steam (steam) associated with the "traditional" case.

For the case of the model complex producing about 309,000 kg/hr (2.6 million metric tons/year) of para-xylene, the operating benefit of the extractive distillation with ethylbenzene addition (increased product credit minus increased operating costs) was measured as 70-80 million dollars/year based on the EB-X18% and EB-X25% conditions, assuming a crude oil price of about $ 50/barrel relative to the "traditional" case.

An overall aspect of the invention relates to a process for producing para-xyleneProcess for separating C by means of a distillation step₈An aromatic hydrocarbon stream, and subsequently separating a para-xylene-rich product from the vapor and isomerizing the residual para-xylene-depleted effluent to produce an additional amount of para-xylene. Such additional amounts may also be recovered by forming a recycle loop, returning to distillation, and/or downstream separation of the paraxylene-rich product. Advantageously, extractive distillation or other separation is used to remove ethylbenzene and optionally other azeotropic compounds (e.g. C)₉Non-aromatic hydrocarbons) may improve process economics, which are within the following ranges: the conventional requirement for ethylbenzene conversion in the isomerization zone can be reduced and a purified ethylbenzene product can be produced.

Those skilled in the art, having the benefit of this disclosure, will appreciate that various changes can be made in the methods without departing from the scope of the invention. Mechanisms for interpreting theoretical or observed phenomena or results are to be construed as merely illustrative and not limiting the scope of the appended claims in any way.