阅读说明：本技术 一种用于甲醇高选择性制备二甲苯和二甲苯异构体定向转化的系统和方法 (System and method for high-selectivity preparation of xylene from methanol and directional conversion of xylene isomers ) 是由 李建伟 陈杰 张艳君 张佳瑾 于 2021-02-03 设计创作，主要内容包括：本发明提供了一种以甲醇为原料高选择性制备二甲苯和二甲苯异构体定向转化的系统和方法。所述系统包括以下装置：甲醇芳构化反应单元(R-1)；三相分离单元(D-1)；脱苯塔单元(T-1)、脱甲苯塔单元(T-2)和脱二甲苯塔单元(T-3)；苯-甲苯烷基化反应单元(R-2)；甲苯-三甲苯烷基转移反应单元(R-3)和二甲苯异构化反应单元(R-4)。通过所述系统和方法,能够灵活、有效地控制二甲苯产品类型,获得单一结构(对位、邻位或间位)或根据需要预设比例的二甲苯异构体产物,具有工艺完整、成本低、二甲苯收率高和产品方案灵活的特点。(The invention provides a system and a method for preparing xylene with high selectivity and directionally converting xylene isomers by taking methanol as a raw material. The system comprises the following devices: a methanol aromatization reaction unit (R-1); a three-phase separation unit (D-1); a debenzolization tower unit (T-1), a debenzolization tower unit (T-2) and a debenzolization tower unit (T-3); a benzene-toluene alkylation reaction unit (R-2); a toluene-trimethylbenzene transalkylation reaction unit (R-3) and a xylene isomerization reaction unit (R-4). The system and the method can flexibly and effectively control the type of the xylene product, obtain the xylene isomer product with a single structure (para position, ortho position or meta position) or preset proportion according to requirements, and have the characteristics of complete process, low cost, high xylene yield and flexible product scheme.)

1. A system for the high selectivity production of xylene from methanol and the directional conversion of xylene isomers, characterized in that it comprises the following units and devices:

a methanol aromatization reaction unit (R-1) for subjecting a raw material methanol to aromatization reaction to generate an aromatization product, wherein the aromatization product comprises an aromatic hydrocarbon mixture of benzene, toluene, xylene and/or trimethylbenzene;

a three-phase separation unit (D-1) for separating the aromatization product produced by the methanol aromatization reaction unit into an aromatization gas phase product, an aromatization oil phase product and an aromatization water phase product;

the device comprises a debenzolization tower unit (T-1), a debenzolization tower unit (T-2) and a debenzolization tower unit (T-3), wherein the debenzolization tower unit (T-1), the debenzolization tower unit (T-2) and the debenzolization tower unit (T-3) are sequentially connected in series and used for enabling the aromatized oil phase product separated by the three-phase separation unit (D-1) to be sequentially sent to the debenzolization tower unit (T-1), the debenzolization tower unit (T-2) and the debenzolization tower unit (T-3) for fractional separation so as to separate benzene, toluene, xylene and trimethylbenzene;

a benzene-toluene alkylation reaction unit (R-2) for carrying out a co-alkylation reaction of benzene, toluene and methanol to generate xylene;

a toluene-trimethylbenzene transalkylation reaction unit (R-3) for carrying out transalkylation reaction on toluene and trimethylbenzene to generate a xylene mixed isomer;

a xylene isomerization reaction unit (R-4) for the directed conversion of xylene isomers to xylene isomer products in single structures or mixed proportions.

2. The system according to claim 1, further comprising a two-phase separation unit (D-2) for feeding the alkylation product from the benzene-toluene alkylation reaction unit (R-2) to the two-phase separation unit (D-2) for oil-water separation, and returning the separated oil-phase product to the debenzolization column unit (T-1) for benzene separation.

3. The system according to claim 2, further comprising an alcohol-water separation column unit (T-4) for feeding the aromatized gas phase product separated in the three-phase separation unit (D-1) to the alcohol-water separation column unit (T-4) for separation of methanol and water, the methanol as an overhead product being subsequently recycled to the methanol main.

4. The system as claimed in claim 1, further comprising a xylene separation column unit (T-5) and a xylene isomer product tank (P) for feeding the xylene isomer mixture product produced by the xylene isomerization reaction unit (R-4) to the xylene separation column unit (T-5) for xylene separation, feeding a bottom product to the xylene separation column unit (T-5), and returning an overhead product to the xylene separation column unit (T-5).

5. A method for preparing xylene with high selectivity and directionally converting xylene isomers by using methanol, which is implemented by using the system for preparing xylene with high selectivity and directionally converting xylene isomers according to any one of claims 1 to 4, and comprises the following steps:

(1) methanol aromatization reaction:

sending the aromatization product generated by the methanol aromatization reaction unit (R-1) into the three-phase separation unit (D-1) for gas-oil-water separation. Carrying out light hydrocarbon treatment on the aromatization gas-phase product separated from the tower top, using the aromatization water-phase product separated from the tower bottom as industrial water, and carrying out the operation of the step (2) on the aromatization oil-phase product separated from the tower;

(2) fractionation of the aromatized oil phase product:

the aromatized oil phase product separated from the three-phase separation unit (D-1) is subjected to fractional separation sequentially through the debenzolization tower unit (T-1), the debenzolization tower unit (T-2) and the debenzolization tower unit (T-3), so that benzene, toluene, xylene and trimethylbenzene are separated sequentially;

(3) benzene-toluene alkylation reaction:

mixing benzene extracted from the top of the debenzolization tower unit (T-1) and partial toluene extracted from the top of the debenzolization tower unit (T-2), mixing the mixture with methanol from a methanol main pipe, and sending the mixture to the benzene-toluene alkylation reaction unit (R-2) for carrying out a co-alkylation reaction to generate an alkylation product containing toluene, xylene and water;

(4) toluene-Trimethylbenzene transalkylation reaction:

mixing part of toluene extracted from the top of the demethanizer unit (T-2) and trimethylbenzene extracted from the bottom of the demethanizer unit (T-3), and then sending the mixture into the toluene-trimethylbenzene transalkylation reaction unit (R-3) for toluene-trimethylbenzene transalkylation reaction to generate a product containing xylene, toluene and trimethylbenzene;

(5) xylene isomerization reaction:

sending the mixed xylene isomer extracted from the top of the xylene removal tower unit (T-3) to the xylene isomerization reaction unit (R-4), and directionally converting the mixed xylene isomer into a xylene isomer product with a single structure or a mixed proportion.

6. The method of claim 5, wherein step (1) further comprises feeding a liquid methanol feedstock to said methanol aromatization after vaporizing said liquid methanol feedstockA step of a reaction unit (R-1), wherein the methanol aromatization reaction unit (R-1) adopts a fixed bed, a fluidized bed, a moving bed or a simulated moving bed, the reaction temperature is 435-500 ℃, the reaction pressure is 0.1-5.0 MPa, and the mass space velocity of the fed methanol is 0.1-5 h^-1。

7. The method according to claim 5, wherein in the step (3), the benzene-toluene alkylation reaction adopts a fixed bed, a fluidized bed, a moving bed or a simulated moving bed, the reaction temperature is 350-520 ℃, the reaction pressure is 0.1-5.0 MPa, and the mass space velocity of the feeding material is 0.1-5 h^-1The molar ratio of the benzene alcohol fed is 0.1-10.

8. The method according to claim 5, wherein in the step (4), the toluene-trimethylbenzene transalkylation reaction adopts a fixed bed, a fluidized bed, a moving bed or a simulated moving bed, the reaction temperature is 280-550 ℃, the reaction pressure is 2.0-4.0 MPa, and the mass space velocity of the feeding material is 0.3-3 h^-1The molar ratio of the toluene to the trimethylbenzene in the raw materials is 0.1-10.

9. The process according to claim 5, wherein in the step (4), the product withdrawn from the bottom of the toluene-trimethylbenzene transalkylation reaction unit (R-3) is returned to the three-phase separation unit (D-1) to be separated.

10. The method according to claim 5, wherein the catalyst for the methanol aromatization reaction adopts a ZSM-5 molecular sieve modified by any one or more than two metals of Zn, Ga, Ni and Cd, and the silica-alumina ratio is 8-100; the catalyst for benzene-toluene alkylation reaction adopts a ZSM-5 molecular sieve modified by Ni, P, Mg or La, and the silica-alumina ratio is 30-200;

the catalyst for toluene-trimethyl benzene alkyl transfer reaction adopts SiO₂-Al₂O₃Or Al₂O₃-B₂O₃The solid acid catalyst of (2) or ZSM-5 molecular sieve, beta molecular sieve, mordenite and Y-type molecular sieve,the silicon-aluminum ratio is 25-130; the catalyst for the xylene isomerization reaction is an HZSM-5 molecular sieve or an HZSM-5 molecular sieve modified by any one or more than two metals of Ga, Pt, Fe and Co, and the silica-alumina ratio is 40-240.

Technical Field

The invention relates to the field of chemical processes for preparing dimethylbenzene from methanol, in particular to a system and a method for preparing dimethylbenzene and a xylene isomer by high-selectivity directional conversion by using methanol as a raw material.

Background

Aromatic hydrocarbons, which account for about 30% of the 800 thousands of known organic compounds, are important basic materials for the petrochemical industry. Among them, BTX aromatic hydrocarbons (benzene, toluene and xylene) are called primary organic basic raw materials, the yield is second to ethylene and propylene, and the derivatives thereof can be used for producing various chemical products such as rubber, chemical fibers and plastics, and occupy a very important position in national economy in China. Among BTX aromatic hydrocarbons, PX (paraxylene) is the most demanded and is mainly used as a raw material for producing polyester resin, polyester fiber and the like; OX (o-xylene) is a chemical raw material for producing phthalic anhydride, dyes, insecticides and the like; MX (meta-xylene) is used in much lower amounts industrially than the former two, and is currently used mostly for the production of PX (para-xylene) and OX (ortho-xylene) by means of isomerization or as an organic solvent.

Currently, BTX comes primarily from the petroleum-based feedstock route, obtained by catalytic reforming and pyrolysis gasoline hydrogenation. China is the largest country consuming BTX aromatic hydrocarbons in the world, so the dependence degree on petroleum is high, but China is a country relatively rich in coal and less in oil, and the shortage of petroleum resources causes the production of BTX aromatic hydrocarbons to face larger economic pressure, so that the problems of high cost and low self-sufficient rate exist. Taking PX (p-xylene) as an example, the import quantity is only 353 ten thousand tons and the external dependence is only 35.19% in 2010, the import quantity reaches 1200 ten thousand tons and the external dependence is 57.6% in 2016, and the import quantity is increased to 1590.3 ten thousand tons and the external dependence is increased to 61.2% in 2018. Meanwhile, the technology for synthesizing methanol by taking coal as a raw material is mature, and if a new path for preparing BTX aromatic hydrocarbon, especially PX (paraxylene) by taking methanol as a raw material can be developed, a feasible path can be developed for deep processing of methanol products in China, the dependence of aromatic hydrocarbon demand on petroleum resources can be greatly reduced, and the method has important economic and strategic significance.

Patent CN1880288A discloses a process for preparing aromatic hydrocarbons from methanol. The process takes methanol as a raw material, takes a modified ZSM-5 molecular sieve as a catalyst, and has the operating temperature of 300-500 ℃, the operating pressure of 0.1-5.0 MPa and the mass space velocity of the raw material liquid of 0.1-10 h^-1Under the condition of (1), a two-step catalytic conversion process is completed. Methanol is firstly converted into mixed hydrocarbons in a first reactor, and the liquefied products enter a second reactor for aromatization reaction to finally generate aromatic hydrocarbon mixture. The process has the disadvantages of high energy consumption and C₆、C₇And C₉The aromatics are not further converted to xylenes and, therefore, the overall xylene yield is low.

Patent CN104098418A discloses a methanol aromatization process, which comprises the steps of: 1) the methanol enters a tube pass of the reactor to contact with a tube pass catalyst, the operating temperature is 400-450 ℃, the operating pressure is 0.1-5 Mpa, and the liquid airspeed of the raw material methanol is 0.5-7.0 h^-1(ii) a 2) The reaction product from the tube side enters the shell side of the reactor to contact with a shell side catalyst, the operation temperature is 330-380 ℃, the operation pressure is 0.1-3.5 Mpa, and the operation airspeed is 0.4-4.0 h^-1Is catalytically converted into C through a shell side₅ ⁺And (3) rectifying and separating the hydrocarbon liquid product to obtain aromatic hydrocarbon and non-aromatic hydrocarbon, and separating the gas product in the shell side product, wherein the low-carbon olefin is returned to the shell side of the reactor to continue the reaction. The process uses a fluidized bed reactor, a reactor tube side catalyst consists of 50-75% of modified ZSM-5, 5-30% of modified SAPO-34 and 10-20% of binder SB powder, and a shell side catalyst consists of 40-80% of modified ZSM-5 and 20-60% of binder SB powder, so that the contact between methanol and the active center of the catalyst is effectively strengthened, the yield of aromatic hydrocarbon products is improved, and the problem of low selectivity of xylene also exists.

The patent CN103864561B discloses a process for preparing aromatic hydrocarbon by methanol aromatization, which adopts a mode of connecting three reactors in series, raw material methanol is gasified and then enters a methanol-olefin aromatization reactor, methanol aromatization and olefin aromatization are simultaneously carried out, and then reaction products enter the reactorIntroducing into a non-aromatic hydrocarbon cracking reactor, separating to obtain dry gas and C₃ ⁺Non-aromatic and aromatic products, and then adding C₃ ⁺The non-aromatic hydrocarbon product is sent into a dehydrogenation reactor, and the dehydrogenated material returns to the aromatization reactor for continuous reaction. The process improves the yield of aromatic hydrocarbon and reduces the separation difficulty, but the flow is biased to be complex and the yield of dimethylbenzene is low.

The patent CN101671226A discloses a method for preparing dimethylbenzene by aromatizing methanol, which uses a metal-modified molecular sieve composite material as a catalyst, the reaction temperature is 350-650 ℃, the reaction pressure is 0.1-3.0 MPa, and the mass space velocity of methanol is 0.1-20.0 h^-1. By using methanol and C₁～C₁₂One or a plurality of mixtures in the xylene synthesis catalyst are subjected to aromatization reaction, so that the selectivity of a target product xylene is improved, but the reaction raw material cost is high, the reaction process is complex, and a xylene product (para position, ortho position or meta position) with a single structure cannot be flexibly prepared.

In summary, the aromatization of methanol as a technology with huge potential economic benefits has been advanced in recent years, but the current aromatization research mainly focuses on the aromatization reaction stage, the research on the subsequent treatment of aromatization products is less, the obtained products are mainly mixed aromatic hydrocarbons, the problems of low selectivity of xylene and low comprehensive utilization rate of byproducts generally exist, and at present, no method and process for realizing flexible regulation and control of xylene product types (para position, ortho position or meta position) exist.

Disclosure of Invention

Aiming at the defects of flexible regulation and control method and process of the type of the methanol aromatization product at the present stage and the problems in the methanol aromatization, the invention provides a system and a method for preparing dimethylbenzene and xylene isomer oriented conversion with high selectivity by taking methanol as a raw material. The system and the method can flexibly and effectively control the type of the xylene product, obtain the xylene isomer product with a single structure (para position, ortho position or meta position) or preset proportion according to requirements, and have the characteristics of complete process, low cost, high xylene yield and flexible product scheme.

The technical scheme adopted by the invention is as follows:

a system for high selectivity production of xylenes and the directional conversion of xylene isomers from methanol, the system comprising the following units and apparatus:

a methanol aromatization reaction unit (R-1) for subjecting a raw material methanol to aromatization reaction to generate an aromatization product, wherein the aromatization product comprises an aromatic hydrocarbon mixture of benzene, toluene, xylene and/or trimethylbenzene;

a three-phase separation unit (D-1) for separating the aromatization product produced by the methanol aromatization reaction unit into an aromatization gas phase product, an aromatization oil phase product and an aromatization water phase product;

the device comprises a debenzolization tower unit (T-1), a debenzolization tower unit (T-2) and a debenzolization tower unit (T-3), wherein the debenzolization tower unit (T-1), the debenzolization tower unit (T-2) and the debenzolization tower unit (T-3) are sequentially connected in series and used for sequentially sending the aromatized oil phase product separated by the three-phase separation unit (D-1) to the debenzolization tower unit (T-1), the debenzolization tower unit (T-2) and the debenzolization tower unit (T-3) for fractional separation so as to separate benzene, toluene, xylene and trimethylbenzene;

a benzene-toluene alkylation reaction unit (R-2) for carrying out a co-alkylation reaction of benzene, toluene and methanol to generate xylene;

a toluene-trimethylbenzene transalkylation reaction unit (R-3) for carrying out transalkylation reaction on toluene and trimethylbenzene to generate a xylene mixed isomer;

a xylene isomerization reaction unit (R-4) for the directed conversion of xylene isomers to xylene isomer products in single structures or mixed proportions.

Further, the tower top product of the debenzolization tower unit (T-1) is benzene, the tower top product of the debenzolization tower unit (T-2) is toluene, and the tower top and tower bottom products of the debenzolization tower unit (T-3) are xylene and trimethylbenzene respectively.

Further, the system also comprises a two-phase separation unit (D-2) which is used for sending the alkylation product generated by the benzene-toluene alkylation reaction unit (R-2) into the two-phase separation unit (D-2) for oil-water separation, and returning the separated oil phase product to the debenzolization tower unit (T-1) for benzene separation.

Further, the system also comprises an alcohol-water separation tower unit (T-4) which is used for leading the aromatization gas phase product separated by the three-phase separation unit (D-1) to be sent into the alcohol-water separation tower unit (T-4) for separating methanol and water, and the methanol as the overhead product is then merged into a methanol main pipe for recycling.

Further, the system also comprises a xylene separation tower unit (T-5) and a xylene isomer product tank (P), and the xylene isomer mixed product generated by the xylene isomerization reaction unit (R-4) is sent to the xylene separation tower unit (T-5) for separating xylene, the tower bottom product is sent to the xylene separation tower unit (T-5), and the tower top product is returned to the xylene separation tower unit (T-5).

Further, the system also comprises a condensing device matched with each reaction unit, each separation tower unit and each separation unit, and the condensing device is used for condensing the inflowing or extracted material flow.

The invention also provides a method for preparing xylene with high selectivity and directionally converting xylene isomers by using the system, which comprises the following steps:

(1) methanol aromatization reaction:

sending the aromatization product generated by the methanol aromatization reaction unit (R-1) into the three-phase separation unit (D-1) for gas-oil-water separation, carrying out light hydrocarbon treatment on the aromatization gas-phase product separated from the top of the tower, using the aromatization water-phase product separated from the bottom of the tower as industrial water, and carrying out the operation of the step (2) on the aromatization oil-phase product separated from the tower;

(2) fractionation of the aromatized oil phase product:

the aromatized oil phase product separated from the three-phase separation unit (D-1) is subjected to fractional separation sequentially through the debenzolization tower unit (T-1), the debenzolization tower unit (T-2) and the debenzolization tower unit (T-3), so that benzene, toluene, xylene and trimethylbenzene are separated sequentially;

(3) benzene-toluene alkylation reaction:

mixing benzene extracted from the top of the debenzolization tower unit (T-1) and partial toluene extracted from the top of the debenzolization tower unit (T-2), mixing the mixture with methanol from a methanol main pipe, and sending the mixture to the benzene-toluene alkylation reaction unit (R-2) for alkylation reaction to generate an alkylation product containing toluene, xylene and water;

(4) toluene-Trimethylbenzene transalkylation reaction:

mixing part of toluene extracted from the top of the demethanizer unit (T-2) and trimethylbenzene extracted from the bottom of the demethanizer unit (T-3), and then sending the mixture into the toluene-trimethylbenzene transalkylation reaction unit (R-3) for toluene-trimethylbenzene transalkylation reaction to generate a product containing xylene, toluene and trimethylbenzene;

(5) xylene isomerization reaction:

sending the mixed xylene isomer extracted from the top of the xylene removal tower unit (T-3) to the xylene isomerization reaction unit (R-4), and directionally converting the mixed xylene isomer into a xylene isomer product with a single structure or a mixed proportion.

Further, the debenzolization tower unit (T-1), the debenzolization tower unit (T-2) and the debenzolization tower unit (T-3) are sequentially connected in series to form a rectifying tower, so that the aromatized oil phase product separated by the three-phase separation unit (D-1) is firstly sent to the debenzolization tower unit (T-1) for rectification and debenzolization (tower top product), the material flow extracted from the tower bottom of the debenzolization tower unit (T-1) is sent to the debenzolization tower unit (T-2) for rectification and debenzolization (tower top product), the material flow extracted from the tower bottom of the debenzolization tower unit (T-2) is further sent to the debenzolization tower unit (T-3) for rectification and debenzolization (tower top product) and trimethylbenzene (tower bottom product), thereby realizing the fractional separation of the methanol aromatized oil phase product, ensures the conversion and utilization of the subsequent by-products, thereby improving the selectivity and yield of the dimethylbenzene.

Further, the step (1) also comprises the step of passing the liquid methanol raw materialSending the vaporized methanol into the methanol aromatization reaction unit (R-1), wherein the methanol aromatization reaction unit (R-1) adopts a fixed bed, a fluidized bed, a moving bed or a simulated moving bed, the reaction temperature is 435-500 ℃, the reaction pressure is 0.1-5.0 MPa, and the mass space velocity of the fed methanol is 0.1-5 h^-1。

Further, in the step (3), a fixed bed, a fluidized bed, a moving bed or a simulated moving bed is adopted for the benzene-toluene alkylation reaction, the reaction temperature is 350-520 ℃, the reaction pressure is 0.1-5.0 MPa, and the mass airspeed of feeding is 0.1-5 h^-1The molar ratio of benzene (benzene and toluene) alcohol fed is 0.1-10.

Further, in the step (4), the toluene-trimethylbenzene transalkylation reaction adopts a fixed bed, a fluidized bed, a moving bed or a simulated moving bed, the reaction temperature is 280-550 ℃, the reaction pressure is 2.0-4.0 MPa, and the feeding mass space velocity is 0.3-3 h^-1The molar ratio of the toluene to the trimethylbenzene in the raw materials is 0.1-10.

Further, in the step (4), the product taken out from the bottom of the toluene-trimethylbenzene transalkylation reaction unit (R-3) is returned to the three-phase separation unit (D-1) to be separated.

Further, in the step (5), if xylene isomers of a single structure are prepared, the xylene isomerization reaction unit (R-4) is packed with a corresponding isomerization molecular sieve catalyst, for example, an isomerization catalyst for preparing p-xylene (PX) employs a Ga-modified HZSM-5 molecular sieve having a silica-alumina ratio of 120, an isomerization catalyst for o-xylene (OX) employs a Co-modified HZSM-5 molecular sieve having a silica-alumina ratio of 95, an isomerization catalyst for m-xylene (MX) employs a Ga-Co-modified HZMS-5 molecular sieve, and the like.

Further, the catalyst for the methanol aromatization reaction adopts a ZSM-5 molecular sieve modified by any one or more than two metals of Zn, Ga and Cd, and the silicon-aluminum ratio is 8-100; the catalyst for benzene-toluene alkylation reaction adopts a ZSM-5 molecular sieve modified by Ni, P, Mg or La, and the silica-alumina ratio is 30-200; the catalyst for toluene-trimethyl benzene alkyl transfer reaction adopts SiO₂-Al₂O₃Or Al₂O₃-B₂O₃The solid acid catalyst of (2) or ZSM-5 molecular sieve, beta molecular sieve, mordenite and Y-type molecular sieve, wherein the silica-alumina ratio is 25-130; the catalyst for the xylene isomerization reaction is an HZSM-5 molecular sieve or an HZSM-5 molecular sieve modified by any one or more than two metals of Ga, Pt, Fe and Co, and the silica-alumina ratio is 40-240.

The invention has the beneficial effects that:

1. a process route is provided for producing a single structure xylene isomer product (para-xylene, ortho-xylene, or meta-xylene), as well as a predetermined ratio of xylene mixed isomer products, directly from a feedstock methanol.

2. Through the rectifying towers which are sequentially connected in series with the debenzolization tower unit (T-1), the debenzolization tower unit (T-2) and the debenzolization tower unit (T-3), the aromatized oil phase product separated by the three-phase separation unit (D-1) is subjected to multi-stage separation, the conversion and utilization of subsequent byproducts are ensured, and the selectivity and the yield of dimethylbenzene are improved.

3. Through the reaction unit for further converting the by-products, the comprehensive utilization rate of the by-products is improved, so that the total yield of the xylene products is obviously improved: a benzene-toluene alkylation reaction unit for effectively converting benzene and toluene into xylene; and the toluene-trimethylbenzene transalkylation reaction unit is used for converting the toluene and the trimethylbenzene into the dimethylbenzene through reaction.

4. The method realizes the directional conversion between xylene isomers through a xylene isomerization reaction unit and by means of specially developed different types of isomerization catalysts, and can flexibly and effectively control the type of a xylene product, thereby obtaining a xylene product (p-xylene, o-xylene or m-xylene) which is mainly in a certain single structure or a xylene isomer mixture product with a preset proportion according to requirements.

Drawings

In the drawings, like reference numerals refer to the same or similar parts or elements throughout the several views unless otherwise specified. The figures are not necessarily to scale. It is appreciated that these drawings depict only some embodiments in accordance with the disclosure and are therefore not to be considered limiting of its scope.

FIG. 1 is a schematic diagram of a process flow for the high selectivity preparation of xylene from methanol and the directional conversion of xylene isomers according to the present invention.

The reference numbers are as follows:

v-1-methanol tank

R-1-methanol aromatization reaction unit

R-2-benzene-toluene alkylation reaction unit

R-3-toluene-trimethylbenzene transalkylation reaction unit

R-4-xylene isomerization reaction unit

D-1-three-phase separation Unit

D-2-two-phase separation Unit

T-1-debenzolization tower unit

T-2-demethanizer unit

T-3-dimethyl benzene removing tower unit

T-4-alcohol-water separation tower unit

T-5-xylene separation column unit

P-xylene isomer product tank

Detailed Description

In the following, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

Examples

The invention is illustrated in detail below with reference to examples:

example 1

As shown in fig. 1, a system for the high selectivity production of xylene from methanol and the directional conversion of xylene isomers, the system comprises the following devices:

a methanol aromatization reaction unit (R-1) for carrying out aromatization reaction on the raw material methanol to generate aromatization products, wherein the aromatization products comprise aromatic hydrocarbon mixture of benzene, toluene, dimethylbenzene and/or trimethylbenzene;

a three-phase separation unit (D-1) for separating the aromatization product produced by the methanol aromatization reaction unit into an aromatization gas phase product, an aromatization oil phase product and an aromatization water phase product;

the device comprises a debenzolization tower unit (T-1), a debenzolization tower unit (T-2) and a debenzolization tower unit (T-3), the debenzolization tower unit (T-1), the debenzolization tower unit (T-2) and the debenzolization tower unit (T-3) which are sequentially connected in series, and is used for sequentially sending aromatization oil phase products separated by a three-phase separation unit (D-1) into the debenzolization tower unit (T-1), and performing fractional separation on the debenzolization tower unit (T-2) and the debenzolization tower unit (T-3) so as to separate benzene, toluene, xylene and trimethylbenzene;

a benzene-toluene alkylation reaction unit (R-2) for carrying out a co-alkylation reaction of benzene, toluene and methanol to generate xylene;

a toluene-trimethylbenzene transalkylation reaction unit (R-3) for carrying out transalkylation reaction on toluene and trimethylbenzene to generate a xylene mixed isomer;

a xylene isomerization reaction unit (R-4) for the directional conversion of xylene isomers to xylene isomer products in a single structure or mixed ratio;

the two-phase separation unit (D-2) is used for sending the alkylation product generated by the benzene-toluene alkylation reaction unit (R-2) into the two-phase separation unit (D-2) for oil-water separation, and returning the separated oil phase product to the debenzolization tower unit (T-1) for benzene separation;

and the alcohol-water separation tower unit (T-4) is used for feeding the aromatization gas phase product separated by the three-phase separation unit (D-1) into the alcohol-water separation tower unit (T-4) to separate methanol and water, and the methanol product at the top of the tower is then merged into a methanol main pipe to be recycled.

A xylene separation tower unit (T-5) and a xylene isomer product tank (P) for feeding the xylene isomer mixture product generated by the xylene isomerization reaction unit (R-4) into the xylene separation tower unit (T-5) for xylene separation, feeding the tower bottom product into the xylene separation tower unit (T-5), and returning the tower top product to the xylene separation tower unit (T-5).

The specific process using PX (paraxylene) as a target product is as follows:

(1) methanol aromatization reaction:

liquid methanol raw material in a methanol storage tank (V-1) is vaporized and then sent into a methanol aromatization reaction unit (R-1), aromatization products generated by the methanol aromatization reaction unit (R-1) are condensed and then sent into a three-phase separation unit (D-1) for gas-oil-water separation, aromatization gas-phase products separated from the top of the tower are subjected to light dydrocarbon treatment, aromatization water-phase products separated from the bottom of the tower are used as industrial water, and aromatization oil-phase products separated from the tower are subjected to the operation of the step (2);

the methanol aromatization reaction unit (R-1) adopts a fixed bed reactor, the reaction temperature is 450 ℃, the reaction pressure is normal pressure, and the mass space velocity of the fed methanol is 1h^-1The catalyst is Zn/ZSM-5 molecular sieve with the silica-alumina ratio of 14.

(2) Fractionation of the aromatized oil phase product:

and (3) carrying out fractional separation on the aromatized oil phase product separated from the three-phase separation unit (D-1) sequentially through a debenzolization tower unit (T-1), a debenzolization tower unit (T-2) and a debenzolization tower unit (T-3). The benzene removal tower unit (T-1), the toluene removal tower unit (T-2) and the toluene removal tower unit (T-3) are rectifying towers which are sequentially connected in series, so that an aromatized oil phase product separated by the three-phase separation unit (D-1) is firstly sent to the benzene removal tower unit (T-1) for rectifying and removing benzene (tower top product), a material flow extracted from the tower bottom of the benzene removal tower unit (T-1) is further sent to the benzene removal tower unit (T-2) for rectifying and removing toluene (tower top product), and a material flow extracted from the tower bottom of the benzene removal tower unit (T-2) is further sent to the toluene removal tower unit (T-3) for rectifying and removing xylene (tower top product) and trimethylbenzene (tower bottom product).

(3) Benzene-toluene alkylation reaction:

mixing benzene extracted from the top of the debenzolization tower unit (T-1) and partial toluene extracted from the top of the debenzolization tower unit (T-2), mixing the mixture with methanol from a methanol main pipe, and sending the mixture to a benzene-toluene alkylation reaction unit (R-2) for carrying out a co-alkylation reaction to generate an alkylation product containing toluene, xylene and water;

the alkylate product is condensed and sent into a two-phase separation unit (D-2) for water-oil separation, an oil phase product is mixed with an oil phase separated by the three-phase separation unit (D-1) and then sent into a debenzolization tower unit (T-1), the rest of the alkylate product enters an alcohol-water separation tower unit (T-4), a methanol separator at the top of the tower is merged into a methanol main pipe for recycling, and a water phase is sent into a water treatment unit;

the benzene-toluene alkylation reaction can adopt a fixed bed, a fluidized bed, a moving bed or a simulated moving bed, the reaction temperature is 500 ℃, the reaction pressure is normal pressure, and the feeding mass space velocity is 2h^-1The molar ratio of benzene (benzene and toluene) to alcohol in the feed is 1:1, and an HZSM-5 molecular sieve with the silica-alumina ratio of 30-200 is used as a catalyst.

(4) toluene-Trimethylbenzene transalkylation reaction:

mixing part of toluene extracted from the top of the toluene removing tower unit (T-2) and trimethylbenzene extracted from the tower bottom of the toluene removing tower unit (T-3), and then sending the mixture into a toluene-trimethylbenzene alkyl transfer reaction unit (R-3) for carrying out toluene-trimethylbenzene alkyl transfer reaction to generate a product containing xylene, toluene and trimethylbenzene;

returning a product extracted from the tower bottom of the toluene-trimethylbenzene transalkylation reaction unit (R-3) to the three-phase separation unit (D-1) for separation;

the toluene-trimethyl benzene transalkylation reaction adopts a moving bed reactor, the reaction temperature is 510 ℃, the reaction pressure is normal pressure, and the feeding mass space velocity is 0.5h^-1The molar ratio of toluene to trimethylbenzene in the raw material is 0.1-10. .

(5) Xylene isomerization reaction:

and sending the mixed xylene isomer extracted from the top of the xylene removal tower unit (T-3) to a xylene isomerization reaction unit (R-4) to directionally convert the mixed xylene isomer into a product containing the para-xylene isomer. Subsequently, the product containing the para-xylene isomer produced by the xylene isomerization reaction unit (R-4) is sent to a xylene separation column unit (T-5), the bottom product is PX (para-xylene), and the top product is returned to the xylene isomerization reaction unit (R-4);

the xylene isomerization reaction unit (R-4) adopts a fixed bed reactor, the reaction temperature is 450 ℃, the reaction pressure is normal pressure, and the feeding mass space velocity is 2.5h^-1The isomerization catalyst of p-xylene adopts Ga modified HZSM-5 molecular sieve with the silica-alumina ratio of 120.

Example 2

A system for the highly selective production of xylene from methanol and the directional conversion of xylene isomers was the same as in example 1.

The specific process steps (1) to (4) for targeting OX (o-xylene) were the same as in example 1.

Except that in step (5), the mixed xylene isomer withdrawn from the top of the xylylene removal column unit (T-3) is fed to a xylene isomerization reaction unit (R-4) to directionally convert the mixed xylene isomer into a product containing OX (ortho-xylene isomer). Subsequently, feeding the OX-containing product produced in the xylene isomerization reaction unit (R-4) to a xylene separation column unit (T-5), the bottom product being OX, and the top product being returned to the xylene isomerization reaction unit (R-4);

the xylene isomerization reaction unit (R-4) adopts a fixed bed reactor, the reaction temperature is 450 ℃, the reaction pressure is normal pressure, and the feeding mass space velocity is 2.5h^-1The isomerization catalyst of o-xylene (OX) adopts a Co modified HZSM-5 molecular sieve with a silica-alumina ratio of 95.

Example 3

A system for the highly selective production of xylene from methanol and the directional conversion of xylene isomers was the same as in example 1.

The specific process steps (1) - (4) with MX (m-xylene) as the target product are the same as in example 1.

Except that in the step (5), the mixed xylene isomer withdrawn from the top of the xylylene removal column unit (T-3) is fed to a xylene isomerization reaction unit (R-4) to directionally convert the mixed xylene isomer into a product containing MX (m-xylene isomer). Subsequently, a product containing MX produced in the xylene isomerization reaction unit (R-4) is sent to a xylene separation column unit (T-5), the bottom product is MX, and the top product is returned to the xylene isomerization reaction unit (R-4);

the xylene isomerization reaction unit (R-4) adopts a fixed bed reactor, the reaction temperature is 450 ℃, the reaction pressure is normal pressure, and the feeding mass space velocity is 2.5h^-1The isomerization catalyst of m-xylene (MX) adopts a Ga-Co modified HZMS-5 molecular sieve and the like.

Example 4

A system for the highly selective production of xylene from methanol and the directional conversion of xylene isomers was the same as in example 1.

The specific process steps (1) to (4) of the target product were the same as in example 1, with xylene mixed isomers having PX (p-xylene), OX (o-xylene) and MX (m-xylene) ratios of 25%, 10% and 65%, respectively.

The difference is that in step (5), the xylene mixture isomer withdrawn from the top of the xylylene removal column unit (T-3) is sent to the reaction unit (R-4) containing a PX (para-xylene) isomerization catalyst, PX (para-xylene) is produced in a 25% yield and then replaced with an OX (ortho-xylene) isomerization catalyst, OX (ortho-xylene) is produced in a 10% yield and then replaced with a MX (meta-xylene) isomerization catalyst, and MX (meta-xylene) is produced in a 65% yield.

The xylene isomerization reaction unit (R-4) adopts a fixed bed reactor, the reaction temperature is 450 ℃, the reaction pressure is normal pressure, and the feeding mass space velocity is 2.5h^-1The isomerization catalyst of paraxylene adopts HZSM-5 molecular sieve with the silica-alumina ratio of 120 as the catalyst, the isomerization catalyst of o-xylene (OX) adopts HZSM-5 molecular sieve with the silica-alumina ratio of 95, and the isomerization catalyst of m-xylene (MX) adopts HZMS-5 molecular sieve modified by Ga-Co.

The content of PX, OX and MX in the xylene mixed isomer is 25%, 10% and 65% respectively, and the xylene mixed isomer can be widely used as a solvent in the paint and dye industries.

Comparative example

Taking mixed xylene as a target product, gasifying liquid methanol from a methanol storage tank (V-1) through a gasification furnace (E-1), sequentially passing through a xylene isomerization reaction unit and a three-phase (gas, oil and water) separation unit thereof, using a Zn/ZSM-5 molecular sieve with a silica-alumina ratio of 14 as a catalyst, reacting at 450 ℃,the reaction pressure is normal pressure, the mass space velocity of the fed methanol is 1h^-1。

The gas phase product is sent to a light hydrocarbon processing unit; the water phase can be used as process water after being treated, and the oil phase directly enters a mixed xylene storage tank. The oil phase product mainly contains C₆、C₇、C₈And C₉The aromatic hydrocarbon comprises 85 mass percent of BTX aromatic hydrocarbon and 31 mass percent of PX.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, but any modifications or equivalent variations made according to the technical spirit of the present invention are still within the scope of the present invention as claimed.