阅读说明：本技术 通过氧化生产芳族二羧酸的能量和环境整合方法 (Energy and environment integrated process for producing aromatic dicarboxylic acids by oxidation ) 是由 J.G.金特罗巴拉雅斯 P.S.拉米雷斯索萨 A.埃斯科巴洛佩斯 V.梅迪纳拉伦西亚 A.布 于 2018-02-26 设计创作，主要内容包括：一种用于在一级鼓泡塔反应器中用压缩空气氧化二烷基取代的芳族化合物的连续方法；包括将三相反应介质的一部分移除至供应有压缩空气的后氧化鼓泡塔单元；将后氧化反应介质分离成塔顶气体和底流浆液；收集来自氧化反应器和脱气单元的塔顶气体并将经合并的塔顶气体引导至除水塔(WRC)；将来自所述脱气单元的所述底流浆液转移至蒸煮单元以实现进一步氧化而不向所述蒸煮单元添加空气；将塔顶气体移除至所述除水塔；使最终氧化浆液结晶；以及在旋转压力过滤器上过滤所述浆液；其中利用来自所述WRC的废气的一部分能量来驱动空气压缩机,以供应所述压缩空气用于氧化。(a continuous process for oxidizing a dialkyl-substituted aromatic compound with compressed air in a primary bubble column reactor; comprising removing a portion of the three-phase reaction medium to a post-oxidation bubble column unit supplied with compressed air; separating the post-oxidation reaction medium into a top gas and a bottom slurry; collecting the overhead gases from the oxidation reactor and the degassing unit and directing the combined overhead gases to a Water Removal Column (WRC); transferring the underflow slurry from the degassing unit to a cooking unit to effect further oxidation without adding air to the cooking unit; removing the overhead gas to the water removal column; crystallizing the final oxidized slurry; and filtering the slurry on a rotary pressure filter; wherein a portion of the energy of the exhaust gas from the WRC is utilized to drive an air compressor to supply the compressed air for oxidation.)

1. A continuous process for preparing an aromatic dicarboxylic acid, the process comprising:

Oxidizing a dialkyl-substituted aromatic compound with compressed air in an acetic acid reaction medium in a first bubble column reactor in the presence of a catalyst to obtain a three-phase reaction medium;

Removing a portion of the three-phase reaction medium containing catalyst from the primary bubble column reactor to a post-oxidation bubble column unit supplied with compressed air to obtain a post-oxidized reaction medium;

Transferring the post-oxidation reaction medium to a degassing unit and separating the post-oxidation reaction medium into an overhead gas and an underflow slurry;

Collecting overhead gas from each of the primary oxidation reactor and the post oxidation reactor with the overhead gas from the degassing unit and directing the combined overhead gas to a Water Removal Column (WRC);

Transferring the underflow slurry from the degassing unit to a cooking unit, wherein the temperature of the underflow slurry is raised to a temperature to at least partially dissolve precipitated solids and effect further oxidation of exposed intermediate oxidation products with air and catalyst present in the underflow slurry without adding air to the cooking unit to obtain a final oxidation slurry;

Removing overhead gas from the digestion unit to the water removal column;

Crystallizing the final oxidized slurry to obtain a slurry to be filtered of the aromatic dicarboxylic acid;

filtering the slurry to be filtered on a rotary pressure filter to obtain a mother liquor filtrate and a filter cake;

Wherein

the overhead gas passed to the water removal column is separated in the water removal column into a waste gas comprising steam and an underflow liquid comprising acetic acid removed from the top of the column,

Collecting and utilizing at least a portion of the energy of the off-gas comprising steam to drive an air compressor to supply the compressed air to the bubble column first stage reactor and the post-oxidation bubble column unit, and

controlling the water content of the continuous oxidation by removing water condensed from the water removal column off-gas.

2. The method of claim 1, further comprising:

Passing said off-gas comprising steam from said water removal column through at least one heat exchange steam generator to utilize the heat energy of said off-gas to produce process utility steam and a heat exchanged stream;

Collecting and removing condensed water from said heat-exchanged stream to obtain a pressurized vapor stream; and

Passing the pressurized vapor stream to a gas expander to drive the air compressor.

3. The process of claim 2, wherein the condensed water from the heat-exchanged stream is returned to the WRC or optionally removed as waste.

4. The method of claim 1, further comprising:

superheating said off-gas comprising steam from said water removal column;

Passing the highly heated exhaust gas to a gas expander to drive the air compressor; and

Passing the expanded stream from the expander to at least one heat exchange steam generator to produce process utility steam and a heat exchanged stream; and

Collecting and removing condensed water from the heat-exchanged stream.

5. the process of claim 4, wherein the condensed water from the heat-exchanged stream is returned to the WRC or optionally removed as waste.

6. The method of claim 1, further comprising:

Washing the filter cake with acetic acid;

flowing nitrogen through the acetic acid washed filter cake to obtain a solid filter cake;

Drying the solid filter cake to remove acetic acid;

(ii) reslurrying and purifying the dried filter cake of the aromatic dicarboxylic acid in an aqueous medium to obtain a purified dicarboxylic acid slurry;

filtering the purified aqueous slurry on a rotary pressure filter to obtain a final filter cake of the aromatic dicarboxylic acid and an aqueous mother liquor filtrate;

Membrane filtering the aqueous mother liquor filtrate to obtain a water permeate; and

Transferring the water permeate to the water removal column as water reflux.

7. the process of claim 6, wherein said acetic acid of said filter cake wash comprises acetic acid from said underflow liquid of said WRC.

8. The process of claim 6, wherein repulping and purifying the dried filter cake of the dicarboxylic acid comprises:

(ii) reslurrying said dried filter cake of said aromatic dicarboxylic acid in an aqueous medium;

Treating the aqueous slurry with hydrogen in the presence of a hydrogenation catalyst to obtain an aromatic dicarboxylic acid slurry to be crystallized;

Crystallizing the aromatic dicarboxylic acid in a series of at least two crystallization units;

filtering the crystallized aqueous slurry on a rotary pressure filter to obtain the final filter cake of the aromatic dicarboxylic acid and the aqueous mother liquor filtrate.

9. The process of claim 8, wherein the water of the reslurry aqueous medium is obtained from condensate from the overhead vapor of the WRC.

10. The method of claim 1, further comprising:

Washing the filter cake with water to remove acetic acid and catalyst;

flowing nitrogen through the water-washed filter cake to obtain a solid filter cake;

(ii) reslurrying and purifying the solid filter cake of the aromatic dicarboxylic acid in an aqueous medium to obtain a purified aromatic dicarboxylic acid slurry;

filtering the purified aqueous slurry on a rotary pressure filter to obtain a final filter cake of the aromatic dicarboxylic acid and an aqueous mother liquor filtrate;

membrane filtering the aqueous mother liquor filtrate to obtain a water permeate; and

Transferring the water permeate to the water removal column.

11. the process of claim 10, wherein repulping and purifying the dried filter cake of the dicarboxylic acid comprises:

(ii) reslurrying said solid filter cake of said aromatic dicarboxylic acid in an aqueous medium;

Treating the aqueous slurry with hydrogen in the presence of a hydrogenation catalyst to obtain an aromatic dicarboxylic acid slurry to be crystallized;

Crystallizing the aromatic dicarboxylic acid in a series of at least two crystallization units;

filtering the crystallized aqueous slurry on a rotary pressure filter to obtain the final filter cake of the aromatic dicarboxylic acid and the aqueous mother liquor filtrate.

12. The process of claim 11, wherein the water of the reslurry aqueous medium is obtained from the condensate from the overhead vapor of the WRC.

13. The process of claim 10, wherein said water used to wash said filter cake is water obtained from the condensation of said overhead vapor from said WRC.

14. The process of claim 1 wherein the dialkyl-substituted aromatic compound is para-xylene and the aromatic dicarboxylic acid is terephthalic acid.

Technical Field

The present invention relates to an energy efficient system and method for producing aromatic dicarboxylic acids by liquid phase oxidation of dialkyl substituted aromatic compounds that collects and recycles catalyst and reactants to produce aromatic dicarboxylic acids in an environmentally safe manner. The system, and thus the elements of the process, can be retrofitted into existing chemical plants to achieve increased energy and production efficiency while producing high quality products.

Background

Liquid phase oxidation reactions are often used for the oxidation of aldehydes to acids (e.g., propionaldehyde to propionic acid), cyclohexane to adipic acid, and alkylaromatics to alcohols, acids, or diacids. An important example of the oxidation of alkylaromatic compounds is the liquid phase catalytic oxidation of para-xylene to terephthalic acid, which is a feedstock for the production of polyethylene terephthalate ("PET"). PET is a well-known plastic that is used extensively throughout the world to make products such as bottles, fibers, and packaging.

In a liquid phase oxidation process, a liquid phase feed stream and a gas phase oxidant stream are introduced into a reactor and form a multi-phase reaction medium in the reactor. The liquid-phase feed stream introduced into the reactor contains at least one oxidizable organic compound, while the gas-phase oxidant stream contains molecular oxygen. At least a portion of the molecular oxygen introduced into the reactor as a gas dissolves into the liquid phase of the reaction medium to provide oxygen available for the liquid phase reaction. If the liquid phase of the multi-phase reaction medium contains an insufficient concentration of molecular oxygen (i.e., if some portion of the reaction medium is "oxygen deficient"), undesirable side reactions can produce impurities and/or a delay in the rate at which the intended reaction occurs.

If the liquid phase of the reaction medium contains too little oxidizable compound, the reaction rate may be undesirably low. Furthermore, if the liquid phase of the reaction medium contains an excessive concentration of oxidizable compound, additional undesirable side reactions can produce impurities. Therefore, in order to obtain a high purity product at the lowest cost, many efforts have been made to achieve efficient utilization of raw materials, including recycling of raw materials, lowest energy consumption, and lowest waste treatment costs.

to obtain a uniform distribution of the heterogeneous oxidation reaction medium, the liquid phase oxidation reactor may be equipped with agitation means to promote dissolution of molecular oxygen into the liquid phase of the reaction medium, to maintain a relatively uniform concentration of dissolved oxygen in the liquid phase of the reaction medium, and to maintain a relatively uniform concentration of the oxidizable organic compound.

thus, agitation of the reaction medium may be provided by mechanical agitation, such as provided in a continuously stirred reaction tank ("CSTR"). However, CSTRs have relatively high capital costs because they require expensive motors, fluid-tight bearings and drive shafts and/or complex agitation mechanisms. In addition, the rotating and/or oscillating mechanical components of conventional CSTRs require periodic maintenance. The labor and downtime associated with this maintenance increases the operating costs of the CSTR. However, even with regular maintenance, the mechanical agitation systems employed in CSTRs are prone to mechanical failure and may require replacement after a relatively short period of time.

The bubble column reactor provides agitation of the reaction medium without the need for expensive and unreliable mechanical equipment. Bubble column reactors typically comprise an elongated vertical reaction zone containing a reaction medium. Agitation of the reaction medium within the reaction zone is provided primarily by the natural buoyancy of gas bubbles rising through the liquid phase of the reaction medium. This natural buoyancy agitation provided in the bubble column reactor reduces capital and maintenance costs relative to mechanically agitated reactors. Furthermore, the substantial absence of moving mechanical components associated with the bubble column reactor provides an oxidation system that is less prone to mechanical failure relative to mechanically agitated reactors.

efficient manufacture of large volumes of oxidation products of interest, such as terephthalic acid, involves not only the oxidation process, but also the work-up and separation of the products, and often employs multiple unit operations in series or parallel in the overall manufacturing process. Each of these operations may require energy input or may be an energy source that may be captured and utilized. Furthermore, controlling the reaction variables and reactant stoichiometry to optimize product yield and purity while minimizing waste and environmental impact can be key to commercial success in operation.

terephthalic acid is conventionally produced by the liquid phase oxidation of paraxylene. In a typical process, a solvent liquid phase feed stream and a gas phase oxidant stream are introduced into a primary oxidation reactor having a catalyst system and form a multi-phase reaction medium in the reactor. The solvent present in the liquid phase typically comprises a low molecular weight organic acid such as acetic acid and water. In production systems where the solvent is recycled, the solvent may contain small amounts of impurities such as, for example, para-tolualdehyde (para-tolualdehyde), terephthaldehyde, 4-carboxybenzaldehyde (4-CBA), benzoic acid, para-toluic acid, para-tolualdehyde (para-tolualdehyde) (4-methylbenzaldehyde), alpha-bromo-para-toluic acid, isophthalic acid, terephthalic acid, trimellitic acid, polyaromatics, and/or suspended particulates.

the catalyst is a homogeneous liquid phase system comprising cobalt, bromine and manganese.

As noted above, the use of a bubble column reactor for the primary oxidation reaction provides many advantages over conventional continuously stirred reaction tanks, and oxidation processes employing bubble column reactors are disclosed in, for example, u.s.7,355,068, u.s.7,371,894, u.s.7,568,361, u.s.7,829,037, u.s.7,910,769, u.s.8,501,986, u.s.8,685,334, and u.s.8,790,601, the contents of which are incorporated herein by reference. Bubble column reactors typically comprise an elongated upright reaction zone containing a reaction medium and agitation of the reaction medium within the reaction zone is provided primarily by the natural buoyancy of gas bubbles rising through the liquid phase of the reaction medium. This natural buoyancy agitation provided in the bubble column reactor reduces utility power, investment and maintenance costs relative to mechanically agitated reactors.

the initial oxidation reactor system may include a primary oxidation reactor for oxidizing a substantial portion of the liquid-phase oxidizable compound and optionally at least one secondary oxidation reactor. The primary purpose of this secondary oxidation, also known as post oxidation or as early oxidative digestion, as in U.S.7,393,973 (incorporated herein by reference in its entirety), is to oxidize a larger portion of the liquid phase aromatic oxidation intermediate that proceeds from the primary oxidation to TPA prior to digestion into more severe oxidation conditions. This provides a useful reduction in the total amount of peroxidized carbon oxides that occur after the primary oxidation.

The product withdrawn from the primary oxidation system is typically a slurry comprising a particulate solid phase of Crude Terephthalic Acid (CTA) and a mother liquor. CTA contains relatively high levels of impurities (e.g., 4-carboxybenzaldehyde, p-toluic acid, fluorenones, and other color bodies), making it unsuitable as a feedstock for PET production. Thus, CTA is typically subjected to a purification process that converts CTA particles to Purified Terephthalic Acid (PTA) that can be suitable for the production of polyethylene terephthalate. Further purification of CTA may include oxidative digestion followed by hydrogenation.

Typically, a slurry of CTA particles in a mother liquor obtained from a primary oxidation system can contain from about 10 to about 50 weight percent solid CTA particles, with the remainder being primarily acetic acid mother liquor. The solid CTA particles present in the initial slurry withdrawn from the primary oxidation system can contain from about 400ppmw to about 15,000ppmw of 4-carboxybenzaldehyde (4-CBA).

CTA may be converted to PTA by oxidative digestion treatment in a series of additional oxidation reactors (often referred to as "digesters"), with further oxidation reactions being carried out at temperatures slightly to significantly higher than those used in the primary and secondary oxidation reactors. Optionally, the slurry of CTA particles may be subjected to a solvent exchange step prior to being forwarded to the digester unit, whereby the exchanged solvent has a reduced concentration of aromatic impurities and/or a modified concentration of catalyst and water, which is reconditioned to be more suitable for the oxidation catalyst in the digester unit. Optionally, the mass fraction of solids in the CTA slurry may also be adjusted with or without solvent exchange prior to entering the digester unit.

In order to make precipitated oxidation intermediate impurities available for oxidation in a series of digesters, the particles are exposed to higher temperatures than in primary oxidation to at least partially dissolve the CTA particles and expose the impurities to liquid phase oxidation containing additional molecular oxygen injected into the digesters. The high surface area, crystallization defects, and overbalanced impurity concentrations of the small CTA particles kinetically and thermodynamically favor the partial dissolution and ongoing recrystallization of terephthalic acid as the CTA slurry temperature is raised moderately above the temperature at which CTA is formed in the primary oxidation.

Further oxidation in the digester system is intended to reduce the concentration of 4-CBA in the CTA particles. The cooking temperature may be from 5 ℃ to about 90 ℃ above the primary oxidation temperature and may typically be from about 150 ℃ to about 280 ℃.

in a second effect of the digestion process, the terephthalic acid particles may undergo Ostwald ripening (Ostwald ripening), which tends to provide larger particles with a narrowed particle size distribution compared to CTA particles in the outlet stream of the primary oxidation.

in a third effect of the digestion process, the recrystallized terephthalic acid particles contain a reduced concentration of many impurities, such as polyaromatic carboxylic acid species, that are resistant to catalytic oxidative correction for forming terephthalic acid, including in particular many colored species, such as 2,6-DCF and 2,7-DCF, among others. The reason for this decrease is the more closely balanced distribution between the solid and liquid phases of the oxidation resistant impurities, which results from the hotter operating temperatures than in the initial oxidation and the extended recrystallization time during the cooking process. The reduction of the solid phase concentration of antioxidant impurities is further enhanced if the optional solvent exchange step uses a relatively purer solvent, such as, for example, distilled aqueous acetic acid from a solvent dehydration process for removing water produced by the oxidation of para-xylene.

After the digestion process, the purified product from oxidative digestion may be crystallized and collected in one or more crystallization units and separated by filtration into a mother liquor filtrate and a filter cake. The filter cake is washed thoroughly with a solvent to remove catalyst and other impurities, including methyl acetate, formed during the oxidation process.

The filter cake may then be purged to remove the remaining wash and mother liquor and dried in an oven system to remove residual solvent.

further purification can then be carried out using conventional hydrogenation processes. The dried, washed filter cake is reslurried in water and catalytically hydrogenated to convert the impurities to more desirable and/or easily separable compounds.

Terephthalic acid can be selectively precipitated from the hydrogenated solution via multiple crystallization steps and isolated.

the multiple systems required for primary oxidation, digestion, crystallization, filtration, drying and purification require energy management for thermal control of various operations, overhead systems for managing vent vapors from the oxidation and digestion systems, supply of air oxidant, and systems for collecting and recycling solvent and catalyst. Thus, there is a need to further integrate existing liquid phase oxidation systems for the oxidation of dialkyl aromatic compounds to reduce overall energy requirements while maximizing production efficiency and product yield. There is also a need to develop new liquid phase oxidation systems that provide efficient energy management, material recycling and waste minimization compared to the prior art.

Disclosure of Invention

It is therefore an object of the present invention to provide a process for integrating energy and material management in an existing liquid phase oxidation system for dialkyl aromatic compounds to provide overall reduced energy consumption and significantly improved production efficiency.

it is another object of the present invention to provide a new process and system for the liquid phase oxidation of dialkyl aromatic compounds having significantly reduced energy consumption and significantly improved production efficiency compared to conventional systems.

These and other objects are provided by the present invention, a first embodiment of which provides a continuous process for preparing an aromatic dicarboxylic acid, said process comprising:

Oxidizing a dialkyl-substituted aromatic compound with compressed air in an acetic acid reaction medium in a first bubble column reactor in the presence of a catalyst;

Removing a portion of the three-phase reaction medium containing catalyst from the primary bubble column reactor to a post-oxidation bubble column unit supplied with compressed air;

Transferring the post-oxidation reaction medium to a degassing unit and separating the post-oxidation reaction medium into an overhead gas and an underflow slurry;

collecting overhead gas from each of the primary oxidation reactor and the post oxidation reactor with the overhead gas from the degassing unit and directing the combined overhead gas to a water removal column;

Transferring the underflow slurry from the degassing unit to a cooking unit, wherein the temperature of the underflow slurry is raised to a temperature to at least partially dissolve precipitated solids and effect further oxidation of exposed intermediate oxidation products with air and catalyst present in the underflow slurry to obtain a final oxidation slurry;

Removing the overhead gas of the digestion unit to the water removal column;

Crystallizing the final oxidized slurry to obtain a slurry to be filtered of the aromatic dicarboxylic acid;

Filtering the slurry to be filtered on a rotary pressure filter to obtain a mother liquor filtrate and a filter cake;

wherein

the overhead gas passed to the water removal column is separated in the water removal column into a waste gas comprising steam and an underflow liquid comprising acetic acid removed from the top of the column,

Collecting and utilizing at least a portion of the energy of the off-gas comprising steam to drive an air compressor to supply the compressed air to the bubble column first stage reactor and the post-oxidation bubble column unit, and

controlling the water content of the continuous oxidation by removing water condensed from the water removal column off-gas.

In another aspect, the first embodiment may comprise: washing the filter cake with acetic acid;

flowing nitrogen through the acetic acid washed filter cake to obtain a solid filter cake;

drying the solid filter cake to remove solvent;

(ii) reslurrying and purifying the dried filter cake of the aromatic dicarboxylic acid in an aqueous medium to obtain a purified dicarboxylic acid slurry;

filtering the purified aqueous slurry on a rotary pressure filter to obtain a final filter cake of the aromatic dicarboxylic acid and an aqueous mother liquor filtrate;

membrane filtering the aqueous mother liquor filtrate to obtain a water permeate; and

Transferring the water permeate to the water removal column.

In another aspect, the first embodiment may comprise:

(ii) reslurrying said dried filter cake of said aromatic dicarboxylic acid in an aqueous medium;

Treating the aqueous slurry with hydrogen in the presence of a hydrogenation catalyst to obtain an aromatic dicarboxylic acid slurry to be crystallized;

Crystallizing the aromatic dicarboxylic acid in a series of at least two crystallization units;

Filtering the crystallized aqueous slurry on a rotary pressure filter to obtain a final filter cake of the aromatic dicarboxylic acid and an aqueous mother liquor filtrate;

Membrane filtering the aqueous mother liquor filtrate to obtain a water permeate; and

transferring the water permeate to the water removal column as water reflux.

In the second embodiment, the continuous oxidation process of the present invention further comprises:

Washing the filter cake with water to remove solvent and catalyst;

flowing nitrogen through the water-washed filter cake to obtain a solid filter cake;

(ii) reslurrying and purifying the solid filter cake of the aromatic dicarboxylic acid in an aqueous medium to obtain a purified aromatic dicarboxylic acid slurry;

filtering the purified aqueous slurry on a rotary pressure filter to obtain a final filter cake of the aromatic dicarboxylic acid and an aqueous mother liquor filtrate;

Membrane filtering the aqueous mother liquor filtrate to obtain a water permeate; and

Transferring the water permeate to the water removal column.

In another version of the second embodiment, repulping and purifying the dried cake of the dicarboxylic acid comprises:

(ii) reslurrying said solid filter cake of said aromatic dicarboxylic acid in an aqueous medium;

Treating the aqueous slurry with hydrogen in the presence of a hydrogenation catalyst to obtain an aromatic dicarboxylic acid slurry to be crystallized;

Crystallizing the aromatic dicarboxylic acid in a crystallization unit;

Filtering the crystallized aqueous slurry on a rotary pressure filter to obtain a final filter cake of the aromatic dicarboxylic acid and an aqueous mother liquor filtrate;

Membrane filtering the aqueous mother liquor filtrate to obtain a water permeate; and

Transferring the water permeate to the water removal column for use as a water reflux.

In a particular form of all of the above embodiments and aspects thereof, the dialkyl-substituted aromatic compound is para-xylene and the aromatic dicarboxylic acid is terephthalic acid.

The foregoing paragraphs have been provided by way of general introduction and are not intended to limit the scope of the claims below. The described embodiments, together with further advantages, may be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

Drawings

a more complete understanding of the present disclosure and many of the attendant advantages thereof will be more readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Fig. 1 shows a schematic diagram of a unit system employed in a method according to various embodiments of the present invention.

fig. 2 shows a schematic layout of a material supply and recycling unit according to an embodiment of the present invention.

fig. 3 shows a schematic layout of an oxidation unit according to an embodiment of the present invention.

fig. 4 shows a schematic layout of a water removal unit according to an embodiment of the invention.

Fig. 5 shows a schematic layout of an expander unit (dry expander) according to an embodiment of the invention.

fig. 6 shows a schematic layout of a compressed air supply unit according to an embodiment of the present invention.

Fig. 7 shows a schematic layout of an alternative expander unit (wet expander) according to an embodiment of the invention.

fig. 8 shows a schematic layout of a cooking unit according to an embodiment of the invention.

Fig. 9 shows a schematic layout of a first filtration unit (brown land) according to an embodiment of the present invention.

Fig. 10 shows a schematic layout of a first filtration unit (Greenfield) according to an embodiment of the present invention.

Fig. 11 shows a schematic layout of a purification unit according to an embodiment of the invention.

fig. 12 shows a schematic layout of a second filtration unit according to an embodiment of the invention.

Detailed Description

As noted above, the present invention relates to the integration of energy and material recycle in the commercial scale continuous liquid phase oxidation of dialkyl-substituted aromatic compounds to the corresponding aromatic dicarboxylic acids. The process described in detail in the following paragraphs describes the liquid phase oxidation of para-xylene (PX) to terephthalic acid (PTA), and this description cites various intermediates and impurities associated with the particular chemistry of PTA manufacture. However, the general integrated energy management and recycling system associated with continuous PX oxidation processes is applicable to the oxidation of any dialkyl-substituted aromatic compound.

throughout the following description, the words "a" and "an" and the like have the meaning of "one or more". The phrases "selected from the group consisting of," "selected from," and the like include mixtures of the specified materials. Unless specifically stated otherwise, terms such as "comprising" and the like are open-ended terms meaning "including at least. All references, patents, applications, tests, standards, documents, publications, manuals, texts, articles and the like mentioned herein are incorporated by reference. Where numerical limitations or ranges are stated, the endpoints are included. Moreover, all values and subranges within a numerical limit or range are specifically included as if explicitly written out.

when describing numerical content, the units are percentages by weight or ppm by weight unless otherwise indicated. The terms lowermost and uppermost, when used in describing a position within the reactor, mean that the reaction mixture is located within the upper 10% and lower 10% of the total height within the reactor.

An integrated oxidation, material recycling and energy management system according to various embodiments of the present invention will be described with reference to the associated drawings. It must be understood that the drawings are diagrammatic and illustrate the arrangement and interaction of the systems and unit operations employed. The actual spatial positioning and location of the system can vary greatly depending on the physical structure of the manufacturing facility and whether an existing system is retrofitted or a new system is constructed.

an integrated oxidation unit system according to an embodiment of the present invention is shown in fig. 1 and as shown comprises a material supply and recycle unit, an oxidation unit, a water removal unit, an expander unit, a compressed air supply unit, a digestion unit, a crystallizer unit, a first filtration unit, an optional drying unit, a purification unit, a second filtration unit, and a filtrate treatment unit. As understood by those skilled in the art, the overall system may include other auxiliary units to support and control the integration and performance of the described units, and the present invention is not intended to be limited to the units shown in fig. 1.

Each of the unit systems will be described with reference to appropriate drawings.

Fig. 2 shows a material supply unit including, as main components, a scrubbing acid tank, a filtrate tank, a catalyst tank containing a Co/Mn catalyst, and an HBr supply tank.

The wash acid tank serves as the primary collection point for the system to recycle acetic acid from multiple sources, as described in the following description. However, the main source of recycled acetic acid is the underflow (2) from the Water Removal Column (WRC). The scrubber acid tank is also used to collect solids-free and catalyst-free acid from the exhaust condenser and vacuum system (not shown in fig. 2). Fresh acetic acid may be added to this tank from an associated storage supply (1) in order to maintain sufficient levels of acetic acid to support multiple uses of the acetic acid in the overall integrated system. It is preferred to prevent contamination of the tank with solids or catalyst.

the wash acid may provide for washing of the primary product filter (brown) described below.

acetic acid from the scrubbed acid tank may be supplied to the top of the primary oxidation reactor as a jet reflux to prevent solids entrainment in the off-gas vent (fig. 3) and to promote water to reach the off-gas vent system as acetic acid/water vapor separation. A small amount of acetic acid was also supplied to the compressed air line feeding the primary and secondary oxidizers to wash the solids-free line (not shown).

Acetic acid from the wash acid tank is also supplied to the filtrate tank. The filtrate tank is a collection vessel for a recycle stream containing catalyst and/or solids and is supplied with cobalt, manganese and hydrogen bromide (HBr) from an associated catalyst supply tank.

Acetic acid from the wash acid tank can also be used as wash liquid for the filter cake in the rotary pressure filter of the first filtration unit (fig. 9).

As noted, the filtrate containing acetic acid, aqueous cobalt, manganese and bromine, as well as any other acetic acid stream containing solids, is recycled and collected in a filtrate tank.

the catalyst is a homogeneous liquid phase system comprising cobalt, bromine and manganese. The concentration of catalyst in the system can be controlled by monitoring the concentration of the component at a defined point and making adjustments as appropriate. Such monitoring and control will be understood by those skilled in the art.

the acetic acid concentration of the filtrate catalyst mixture fed to the primary oxidation reactor may be 83 to 96 wt%, preferably 85 to 94 wt%, and most preferably 88 to 93 wt% of the total filtrate feed weight.

The filtrate catalyst level is important for oxidation performance in terms of yield and quality. Excess catalyst should be avoided because once the catalyst is in the system, the loss rate can be quite low and can be quickly taken out of control.

In the overall system, the filtrate and scrubbed acid tanks are connected to a process vent scrubber (not shown) which recovers and recycles acetic acid from the vapor stream prior to venting to atmosphere.

The oxidation unit as shown in fig. 3 comprises a primary oxidation reactor, a secondary oxidation reactor and a deaerator.

during the continuous liquid phase oxidation feed of paraxylene, the catalyst-containing filtrate from the filtrate tank and air are fed to the primary oxidation reactor (fig. 3). The compressed air supplied to the primary oxidation reaction mixture may be fed through an air sparger-ring located in the lowermost region of the primary oxidation reactor, preferably within the lowermost 10% of the total height of the reaction medium in the primary bubble column oxidation reactor. The compressed air supplies the oxidant O required for the oxidation of p-xylene and for the agitation of the reaction mixture in the column₂。

the time-averaged concentration of oxygen in the gaseous effluent withdrawn from the reactor via the gas outlet is preferably in the range of from about 0.5 to about 9 mole percent, more preferably in the range of from about 1 to about 7 mole percent, and most preferably in the range of from 1.5 to 5 mole percent, on a dry weight basis.

the aerated reaction mixture may be substantially homogeneous and occupy about 60 to 98% w, preferably 80 to 96% w, and most preferably 85 to 94% w of the total volume of the primary oxidation reactor.

the purity of the para-xylene fed to the primary oxidation reaction mixture may be 99.5% or higher, preferably 99.6% or higher, and most preferably 99.7% or higher.

As previously described, a recycle solution of relatively catalyst-free weak acetic acid from a wash acid tank is fed through a nozzle in a vapor head space (vapor head space). The reflux flow rate can be adjusted to control the total reaction volume in the primary oxidizer. The maintenance reflux stream can be used to control the vapor flow to the water removal column described in the following paragraph. This flow disruption can lead to overloading of the water removal column and possible damage to the exhaust gas treatment system also described in the following paragraphs.

the combination of temperature, pressure and catalyst level produces near complete conversion of para-xylene to terephthalic acid in the primary oxidation reaction mixture. The operating parameters for the primary oxidation include a temperature of 125 ℃ to 200 ℃, preferably 140 ℃ to 180 ℃, and most preferably 150 ℃ to 170 ℃; a water content of 2 to 12 wt%, preferably 2 to 16 wt%, and most preferably about 3 wt%; a cobalt concentration of from 300 to 6000ppmw, preferably from 700 to 4200ppmw, and most preferably from 1200 to 3000 ppmw; a manganese content of from 20 to 1000ppmw, preferably from 40 to 500ppmw, and most preferably from 50 to 200 ppmw; a bromine content of from 300 to 5000ppmw, preferably from 600 to 4000ppmw, and most preferably from 900 to 3000 ppmw. The total solids content of the primary oxidation reaction mixture may be from 5 to 40 wt.%, preferably from 10 to 35 wt.%, and most preferably from 15 to 30 wt.%.

The side draw transfer tube located in the uppermost part of the primary oxidation reactor is connected to the secondary oxidation reactor (post-oxidizer) and allows the aerated reaction mixture to flow into the post-oxidizer where additional compressed air is fed through the bottom sparger loop. The reaction mixture obtained in the uppermost primary oxidation reaction medium comprises a particulate solid phase of Crude Terephthalic Acid (CTA) and a mother liquor. CTA contains relatively high levels of impurities (e.g., 4-carboxybenzaldehyde, p-toluic acid, fluorenones, and other color bodies). The solid CTA particles present in the slurry entering the secondary oxidation reactor from the primary oxidation reactor may contain about 15,000ppm of 4-carboxybenzaldehyde (4-CBA) and/or p-toluic acid.

Approximately 80% to 99% of the total compressed air supplied to the oxidation reaction medium of the present invention is supplied to the primary oxidation reactor, while the remaining approximately 1% to 20% is supplied to the post-oxidizer. According to an embodiment of the invention, no compressed air or oxygen is added to the system after the post-oxidizer.

The post-oxidizer is operated as a semi-plug flow (semi-plug flow) and is responsible for the reaction removal of liquid phase p-toluic acid from the oxidizer reaction mixture.

The post oxidizer is connected to the deaerator unit via a side draw transfer to the deaerator unit, and the aerated slurry from the post oxidizer is separated in the deaerator unit into a liquid slurry underflow and an overhead gas.

The CTA in the underflow from the post-oxidizer has a relatively high content of solid phase impurities such as 4-CBA. To further reduce the level of impurities, it is necessary to raise the temperature to redissolve the crystals and react to remove the impurities, which is the purpose of the digestion system in the digestion unit as described below. The underflow slurry from the secondary oxidation reactor is transferred to the digestion system via a degasser and the overhead vapor is sent to a water removal unit, as indicated in fig. 3.

the water removal unit as shown in figure 4 comprises a water removal tower.

The Water Removal Column (WRC) provides the primary means for removing water from the continuous process system as well as controlling the water content of the oxidation reaction mixture.

The oxidizer unit overhead gases from the primary oxidation reactor, secondary reactor and deaerator are passed to a water removal column. The WRC may be a distillation column equipped with trays and/or packing. The oxidation reactions of the primary and secondary oxidations are exothermic and the heat generated vaporizes acetic acid, water, and low boiling compounds from the reaction mixture slurry. This vapor, along with nitrogen, unreacted oxygen and small amounts of carbon monoxide and carbon dioxide obtained as overhead vapors from each of the primary oxidizer, post oxidizer and deaerator, is introduced into the bottom of the water removal column. The overhead vapor has sufficient thermal energy to operate the water removal column.

In addition to receiving overhead vapor from the oxidation unit, the WRC may also receive overhead vapor from the digestion unit and membrane water permeate from the membrane filters of the filtrate processing unit.

The underflow from the water removal column may comprise about 90% acetic acid and 10% water. The water content in the whole process is controlled at the bottom of the column. A portion of the water column bottoms stream can be pumped directly to the rotary pressure filter as acetic acid wash of the filter cake.

the excess underflow of wash liquid not used as filter cake may be passed through a series of steam generators or at least one steam generator (not shown) for power generation in a compressor steam turbine. After the steam generator, the underflow may be cooled in a cooling unit and sent to a scrubber acid tank for recycling back into the system, as previously described.

the remaining thermal energy of the underflow can be collected in a series of one or more heat exchange units (not shown) en route to the wash acid tank.

As indicated in fig. 5, the water removal column off-gas may be passed through one or more steam generators to convert steam heat energy into process steam. Only one generator is shown in fig. 1; however, multiple generators in series or parallel may be included to generate process steam from the exothermic energy of the oxidation process. The vapor may then be partially condensed in a condenser and the vapor and condensate collected in a WRC reflux drum where uncondensed flue gas and condensate may be separated. The condensate from the overhead vapor collected at this stage contains about 99 wt.% water, along with trace amounts of acetic acid and methyl acetate, and may be pumped back to the top of the water removal tower as reflux or may be discharged to a waste tank as wastewater.

the off-gas is scrubbed in a High Pressure Absorber (HPA) to recover any remaining para-xylene contained in the off-gas stream. After HPA, the off-gas is heated in one or more preheater units to 150 ℃ to 240 ℃, preferably 170 ℃ to 220 ℃, before being passed via a vapor-liquid expander to the off-gas expander system of the compressed air unit, in which the energy contained in the stream is recovered by expansion and used to move the compressor train.

Fig. 6 shows a schematic view of a compressed air unit.

An air compressor provides compressed process air to the primary and secondary oxidation reactors in accordance with the reaction requirements as previously described. Air is taken from the atmosphere through an inlet filter (not shown) and compressed in a multi-stage air compressor. One of ordinary skill will recognize that different numbers of compressor units may be used within the confines and boundaries of the present invention. After each stage, the compressed air is cooled by cooling water, and water condensed from the compressed air is separated in the inter-cooler heat exchanger. The normal operating conditions of the compressor are a discharge pressure of 301.325 to 2401.33kPaA, preferably 401.325 to 1601.33kPaA and most preferably 601.325 to 1201.33 kPaA.

the power required to compress the air is provided by a steam turbine and an exhaust gas expander that receives preheated exhaust gas from the HPA, both of which are mounted on the same shaft as the compressor. The steam used in the steam turbine may be generated within the process, including from the thermal energy of the overhead gas from the WRC as previously described, and from the thermal energy of the underflow of the WRC during transfer to the scrub acid tank as previously described.

In an alternative embodiment of the expander unit (dry expander) shown in fig. 5, the WRC off-gas may be treated as schematically shown in fig. 7 (wet expander).

The hot overhead vapor leaving the water removal column is at its dew point. Condensation of this stream can result in the formation of hydrobromic acid (HBr), which is highly corrosive. To avoid this problem and to efficiently recover and utilize the energy available in the waste gas stream, the waste gas stream from the WRC may first be superheated in one or more gas preheaters. The one or more flue gas preheaters may use high pressure steam or any other heat transfer medium. The superheated WRC exhaust gas may be directed through a vapor-liquid expander to a compressed air unit exhaust gas expander (turbo-expander) as shown in fig. 6 to directly recover the energy contained in the superheated stream.

After exiting the turboexpander, the exhaust gas is sent to one or more steam generators to generate low pressure steam. After the steam generator or generators, all the steam is partially condensed in the condenser and collected in the water removal reflux tank. The water may then be returned to the WRC as reflux liquid.

The motor generator may be used in a generator mode to generate electrical energy from the remaining energy available during normal operation of the oxidation process. During start-up of the compressor package, the motor-generator may be used as a drive motor.

in either the dry expander or wet expander embodiments, the energy generated in the exothermic oxidation reaction in the oxidation unit is harvested and used to drive at least the air compressor unit that supplies compressed air to the primary and secondary oxidation reactors.

The cooking unit is schematically shown in fig. 8.

As previously noted, the CTA of the underflow slurry obtained from the post-oxidizer via the deaerator unit contains moderately high levels of impurities that can be reacted via further oxidation to produce terephthalic acid. The post-oxidizer slurry from the degassing unit may be at a temperature of 125 ℃ to 200 ℃, preferably 140 ℃ to 180 ℃, and most preferably 150 ℃ to 170 ℃. To partially dissolve the CTA crystals, the slurry may be heated to a temperature of 180 ℃ to 240 ℃, preferably 190 ℃ to 220 ℃, and most preferably 200 ℃ to 216 ℃. One heater is shown in fig. 8. However, those skilled in the art will recognize that a series of heaters may be used at this stage.

As indicated in fig. 8, the heated post oxidizer slurry underflow may be pumped to a digestion unit. At elevated temperatures in the digester, the partial oxidation products of para-xylene (para-toluic acid and 4-CBA) may be oxidized to terephthalic acid, resulting in a more complete conversion of para-xylene to PTA. The main obstacle to achieving high conversion of para-xylene to PTA is the mass transfer limitation associated with oxygen diffusion to the 4-CBA and para-toluic acid contained in terephthalic acid. To achieve conversions greater than 99%, these mass transfer limitations need to be overcome. This may be accomplished by operating the digester unit at a temperature in the range of 180 ℃ to 240 ℃ and at a pressure of 790 to 2515KPa as previously described.

according to an embodiment of the invention, compressed air is not supplied to the digester to complete the oxidative digestion process. This may be contrasted with conventional cooking systems in which some form of oxygen is injected directly into the cooking reactor. The inventors have surprisingly found that under the control of the present invention as described above, sufficient residual oxygen is retained in the post oxidizer slurry underflow to drive oxidation to terephthalic acid by controlling the temperature and pressure within the digestion reactor. One or more digester reactors may be equipped with an agitation system comprising several shaft mounted blades on a stable bearing mounted shaft in order to provide sufficient agitation of the slurry.

off-gases from the digester unit may be directed to the WRC for water removal, acid recovery and capture for use with the heat energy present as previously described.

After treatment in the digester unit, the slurry may be transferred to a crystallization tank (crystallizer) where the temperature is reduced to a range of 130 ℃ to 200 ℃, preferably 150 ℃ to 180 ℃, and most preferably 160 ℃ to 170 ℃. The crystallizer may be agitated by an agitator to keep the solids suspended.

the off-gas from the crystallizer may be passed to a heat exchange heater to heat the steam used to heat the post-oxidizer slurry underflow en route to the cooking unit. Such thermal energy control for the production of steam may be accomplished by mechanical vapor recompression systems, the mechanisms of which are well known to those skilled in the art. This energy recapture is not indicated in fig. 8.

After treatment in the crystallization unit, the slurry may be transferred to a flash cooling system, which includes a Vacuum Flash Tank (VFT). In the flash cooling system, the slurry product from the crystallization unit is subjected to controlled cooling to avoid solids plugging the system.

the solids content of the slurry entering the flash cooling system may be 20 to 60 wt%, preferably 25 to 50 wt%, and most preferably 30 to 40 wt%.

In the flash drum, the temperature within the flash cooling system may be from 40 ℃ to 110 ℃, preferably from 50 ℃ to 100 ℃, most preferably from 60 ℃ to 90 ℃. In the flash drum, almost all insoluble material is precipitated or crystallized from solution. The vapor produced in the flash drum may be directed to a condenser system where the remaining acetic acid may be recovered. Any remaining non-condensable gases may be removed from the system. The auxiliary devices for the VFT are conventional devices known to those skilled in the art and are not shown in fig. 8.

the flash cooled product slurry may be passed to a first filtration unit where the solids formed in the crystallizer are separated from the mother liquor in a rotary pressure filter. The filter is pressurized and is made up of a plurality of active zones. In the pressure filter, PTA is separated from the slurry as a wet solid cake. The filtrate collected from the rotary pressure filter is transferred to a filtrate tank of a material supply unit.

as described in the above paragraph, in the process according to the present invention, the thermal energy generated as a result of the exothermic oxidation reaction may be captured to generate mechanical energy to operate at least the air compressors that supply compressed air to the primary and secondary oxidation reactors. Furthermore, the water content of the continuous oxidation, and thus the reactivity and efficiency of the oxidation, is controlled by removing at least a portion of the water condensed from the water removal column off-gas.

Accordingly, in a first embodiment, the present invention provides a continuous process for the preparation of an aromatic dicarboxylic acid, said process comprising:

Oxidizing a dialkyl-substituted aromatic compound with compressed air in an acetic acid reaction medium in a first bubble column reactor in the presence of a catalyst;

Removing a portion of the three-phase reaction medium containing catalyst from the primary bubble column reactor to a post-oxidation bubble column unit supplied with compressed air;

Transferring the post-oxidation reaction medium to a degassing unit and separating the post-oxidation reaction medium into an overhead gas and an underflow slurry;

Collecting overhead gas from each of the primary oxidation reactor and the post oxidation reactor with the overhead gas from the degassing unit and directing the combined overhead gas to a water removal column;

Transferring the underflow slurry from the degassing unit to a cooking unit comprising at least two cooking reaction tanks in series, wherein the temperature of the underflow slurry is raised to a temperature to at least partially dissolve precipitated solids and effect further oxidation of exposed intermediate oxidation products with air and catalyst present in the underflow slurry without adding air to the cooking unit to obtain a final oxidation slurry;

removing the overhead gas of the digestion unit to the water removal column;

crystallizing the final oxidized slurry to obtain a slurry to be filtered of the aromatic dicarboxylic acid;

Filtering the slurry to be filtered on a rotary pressure filter to obtain a mother liquor filtrate and a filter cake;

wherein

The overhead gas passed to the water removal column is separated in the water removal column into a waste gas comprising steam and an underflow liquid comprising acetic acid removed from the top of the column,

Collecting and utilizing at least a portion of the energy of the off-gas comprising steam to drive an air compressor to supply the compressed air to the bubble column first stage reactor and the post-oxidation bubble column unit, and

Controlling the water content of the continuous oxidation by removing water condensed from the water removal column off-gas.

In the aspect designated as the dry expander schematically shown in fig. 5, the energy of the exhaust gas containing steam collected and utilized to drive the air compressor can be obtained by the following steps: passing the off-gas from the water removal column comprising steam through at least one heat exchange steam generator to generate process utility steam and a heat exchanged stream using the thermal energy of the off-gas; collecting and removing condensed water from said heat-exchanged stream to obtain a pressurized vapor stream; and passing the pressurized vapor stream to a gas expander to drive an air compressor.

in the aspect designated as the wet expander schematically shown in fig. 7, the energy of the off-gas containing steam collected and utilized to drive the air compressor may be obtained by: superheating the steam-containing off-gas from the water removal column in at least one preheater; removing any; passing the superheated exhaust gas to a gas expander to drive an air compressor; and passing the expanded stream from the expander to at least one heat exchange steam generator to produce process utility steam and a heat exchanged stream; and collecting and removing condensed water from the heat-exchanged stream.

as previously noted, in one aspect of the first embodiment, the dialkyl-substituted aromatic compound is para-xylene and the aromatic dicarboxylic acid is terephthalic acid.

as schematically shown in fig. 9, in aspects of the first embodiment designated as brown-ground, the initial cake layer in the first filtration zone of the rotary pressure filter may be washed with multiple acetic acid washing operations to remove impurities and catalyst from the final product cake. The mother liquor containing the catalyst resulting from the filtration is collected and transferred to the filtrate tank in the material unit. These mother liquors may optionally be passed through a filter, such as a candle filter, to remove solids before being passed to a filtrate tank. The washing may be followed by treatment in a hot nitrogen drying zone of a rotary pressure filter to at least partially remove acetic acid and water present in the filter cake. The rotary pressure filter is pressurized and contains multiple active filtration, scrubbing and nitrogen feed zones. The filter cake may then be conveyed to a drying unit suitable for drying to remove acetic acid, such as, for example, a rotary hollow screw dryer (hold screw), in which the filter cake is heated with steam to evaporate substantially all of the acetic acid from the filter cake as it passes through the dryer. Vaporized acetic acid may be removed by a vent scrubber system conventional in the art, and the dried powder collected and transferred to a purification unit.

a second embodiment of a continuous oxidation process designated as a greenfield embodiment is schematically illustrated in fig. 10. According to this embodiment, the flash cooled product slurry from the VFT may be passed to a rotary pressure filter in a first filtration unit, where the solids formed in the crystallizer are separated from the mother liquor in the rotary pressure filter. The filter is pressurized and is made up of a plurality of active zones. However, unlike the brown field aspect, in the green field embodiment, the initial filter cake in the first filtration zone of the rotary pressure filter after mother liquor removal is washed with hot water (90 ℃ to 100 ℃) which is recovered from the oxidation overhead gas collected in the water removal column reflux drum. The water-washed filter cake is then treated in a drying zone arranged to partially dehydrate the filter cake using hot nitrogen gas passed through the cloth to the filter cake. The water-washed, partially water-depleted filter cake is discharged from the pressure filter and conveyed directly to the purification unit without any further drying operation.

the mother liquor filtrate collected from the rotary pressure filter is passed to a filtrate tank, optionally filtered on its way to the filtrate tank to remove solids. The washing water collected from the rotary pressure filter is transferred to the WRC.

As previously described, the filtrate receiver and transfer line are in communication with the scrubber system.

FIG. 11 shows a schematic of a purification unit used in both brown land and green land embodiments. In the brown process, the dried filter cake from the dryer is dissolved in a dissolver tank, whereas in the green process, the moist filter cake is dissolved in a dissolver. Two materials are designated collectively as TA cakes in fig. 11. A conventional hydrogenation process may be employed wherein a terephthalic acid cake is dissolved in water and the solution is subjected to catalytic hydrogenation to convert the retained impurities into more desirable and/or easily separable compounds. The hydrogenation can be carried out at 280 ℃ to 290 ℃ with the terephthalic acid in solution and the impurities retained available for the reaction. After the hydrogenation treatment, the dissolved terephthalic acid may be selectively precipitated from the hydrogenated solution via a plurality of crystallization steps, and the resulting crystal slurry is sent to a second filtration unit for final separation via filtration. One crystallizer is shown in FIG. 11; however, the number of crystallizers employed may vary depending on the design and control parameters of the process. Control of crystallization at each stage in the plurality of crystallization units may allow for a gradual temperature reduction to promote formation of particles of product of a targeted size and distribution in the final crystallization slurry that is sent to the second filtration unit for separation.

fig. 12 shows a schematic view of a second filter unit. The final crystalline terephthalic acid slurry may be filtered on a rotary pressure filter to isolate crystalline PTA from the filtrate. The various zones of the rotary pressure filter may operate as previously described for the rotary pressure filter of the first filtration unit. The filter cake may be washed and then purged with hot nitrogen to remove retained water before draining for utility in further synthesis. The mother liquor filtrate is collected and then passed through a filter to remove any solids, which pass through the filter and then are treated in a membrane system to obtain a water permeate which can be returned to the water removal column as reflux liquid.

As noted above, brown and green embodiments provide a significant reduction in process energy requirements by capturing the exothermic energy generated in the oxidation reaction to drive the compressor train via steam generation and controlled expansion of the overhead vapors. In addition, by recycling the aqueous condensate and filtrate to the WRC as described above, significant savings in water utilization are achieved. Furthermore, by controlling the process water content at the WRC, the efficiency of the oxidation process, as well as the quality and yield of the product, can be significantly improved.

The greenfield embodiment provides not only the energy and water savings of the brown field embodiment, but also additional energy savings by eliminating the energy intensive drying operation of the CTA filter cake used to remove acetic acid. Furthermore, the investment costs and operating costs of the drying unit are eliminated. Both embodiments provide the advantage of a bubble column reactor over a CSTR reactor in terms of energy savings and maintenance requirements.

The previous description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the preferred embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. The schematic diagrams shown in the figures illustrate the organization and arrangement of the primary devices used in various embodiments. However, one of ordinary skill in the art will recognize that additional auxiliary and support devices will be necessary in an actual operating system. Such functional devices for supporting the illustrated units are within the scope of embodiments of the present invention. In this regard, certain embodiments of the present invention may not exhibit all of the benefits of the present invention as broadly contemplated.