CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent

Application no. 62/768222, filed November 16, 2018, which is hereby incorporated herein by reference in its entirety.

FIELD

[0002] The present disclosure relates generally to processes for manufacturing aromatic carboxylic acids.

TECHNICAL BACKGROUND

[0003] Terephthalic acid and other aromatic carboxylic acids are widely used in manufacture of polyesters, commonly by reaction with ethylene glycol, higher alkylene glycols or combinations thereof, for conversion to fiber, film, containers, bottles and other packaging materials, and molded articles.

[0004] In commercial practice, aromatic carboxylic acids are commonly made by liquid- phase oxidation of methyl-substituted benzene and naphthalene feedstocks in an aqueous acetic acid solvent, in which the positions of the methyl substituents correspond to the positions of carboxyl groups in the desired aromatic carboxylic acid product, with air or another source of oxygen, which is normally gaseous, in the presence of a bromine- promoted catalyst comprising cobalt and manganese. The oxidation is exothermic and yields aromatic carboxylic acid together with by-products, including partial or intermediate oxidation products of the aromatic feedstock, and acetic acid reaction products, such as methanol, methyl acetate, and methyl bromide. Water is also generated as a by-product. The resulting aromatic carboxylic acid, typically accompanied by oxidation by-products of the feed-stock, is commonly formed as dissolved or as suspended solids in the liquid-phase reaction mixture and is commonly recovered by crystallization and solid-liquid separation techniques. The exothermic oxidation reaction is commonly conducted in a suitable reaction vessel at elevated temperature and pressure. A liquid-phase reaction mixture is maintained in the vessel and a vapor phase formed as a result of the exothermic oxidation is evaporated from the liquid phase and removed from the reactor to control reaction temperature. The vapor phase comprises water vapor, vaporized acetic acid reaction solvent and small amounts of by-products of the oxidation, including both solvent and feedstock by-products.

It usually also contains oxygen gas not consumed in oxidation, gaseous methyl bromide, minor amounts of unreacted feedstock, carbon oxides and, when the oxygen source for the process is air or another oxygen-containing gaseous mixture, nitrogen, carbon oxides and other inert gaseous components of the source gas. The vapor phase can be separated into one or more process streams for recovery or recycle of portions or components thereof.

[0005] Pure forms of aromatic carboxylic acids are often favored for manufacture of polyesters for important applications, such as fibers and bottles, because impurities, such as by-products generated from aromatic feedstocks in such oxidation processes and, more generally, various carbonyl-substituted aromatic species are known to cause or correlate with color formation in polyesters made from the acids and, in turn, off-color in polyester converted products. Aromatic carboxylic acids with reduced levels of impurities can be made by further oxidizing the crude products formed by the liquid-phase oxidation as described above at one or more, progressively lower temperatures and oxygen levels, and during crystallization to recover products of the oxidation, for conversion of feedstock partial oxidation products to the desired acid product. In commercial practice, liquid-phase oxidation of alkyl aromatic feed materials to crude aromatic carboxylic acid and purification of the crude product are often conducted in continuous integrated processes in which crude product from liquid-phase oxidation is used as starting material for purification.

[0006] In conventional processes, the composition of the crude products of the liquid- phase oxidation can vary, which as noted above are typically continuously provided as starting material for purification. Accordingly, the varying composition of the crude product must be continuously monitored, and the parameters for purification adjusted appropriately, to consistently provide a product having an acceptably reduced level of impurities.

[0007] Accordingly, there remains a need for a more efficient process of manufacturing aromatic carboxylic hydrocarbons with reduced levels of impurities.

SUMMARY

[0008] The scope of the present disclosure is not affected to any degree by the statements within the summary.

[0009] One aspect of the disclosure is a process for manufacturing an aromatic carboxylic acid, comprising:

oxidizing in a reaction zone a feedstock comprising a substituted aromatic hydrocarbon in the presence of an oxidation catalyst and monocarboxylic acid solvent under reaction conditions suitable to form a reaction mixture comprising the aromatic carboxylic acid and a gaseous effluent, the gaseous effluent being at least partially communicated to a first stage of a fractionation zone;

determining a water concentration of the reaction mixture (e.g., by direct measurement, or by calculation based on the reaction pressure, reaction temperature, and oxygen concentration of the gaseous effluent); separating at least part of the gaseous effluent in the first stage of the fractionation zone to form a gaseous overhead stream comprising steam and a bottoms stream, the bottoms stream being at least partially communicated to the reaction zone;

condensing at least part of the gaseous overhead stream to form a water-containing condensate; and

transferring at least part of the water-containing condensate to an upper portion of the first stage of the fractionation zone, wherein the rate of introduction of water (e.g., via the water- containing condensate) to the upper portion of the first stage of the fractionation zone is controlled (e.g., based at least in part on the calculated water concentration of the reaction mixture) to maintain a water concentration in the reaction zone in the range of 8 wt.% to 20 wt.% (e.g., in the range of 12 wt.% to 16 wt.%).

[0010] Other aspects of the disclosure will be apparent to those skilled in the art in view of the description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a process flow diagram for the manufacture and recovery of aromatic carboxylic acids in accordance with one embodiment of the present disclosure.

[0012] FIG. 2 is a process flow diagram of the fractionation zone shown in FIG. 1 , in accordance with one embodiment of the present disclosure.

[0013] FIG. 3 is a process flow diagram of the fractionation zone shown in FIG. 1 , in accordance with one embodiment of the present disclosure.

DEATILED DESCRIPTION

[0014] In various aspects, the processes of the disclosure provide an efficient manner of manufacturing aromatic carboxylic hydrocarbons with reduced levels of impurities.

[0015] Additional features of the processes of the disclosure will now be described in reference to the drawing figures.

[0016] The present inventors have noted that the water content of a reaction mixture can vary throughout the lifetime of a process for the continuous liquid-phase oxidation of a substituted aromatic hydrocarbon, which can affect catalyst activity and complicate the crystallization and/or purification of the aromatic carboxylic acid product. The present inventors have further noted that the gaseous effluent of the oxidation reaction comprises water, and can be condensed and returned to the reaction mixture to control the water content of the reaction mixture, which can in some embodiments be calculated from the temperature and pressure of the reaction mixture and the oxygen content of the gaseous effluent. [0017] Accordingly, one aspect of the disclosure provides a process for manufacturing an aromatic carboxylic acid comprising oxidizing in a reaction zone a feedstock comprising a substituted aromatic hydrocarbon in the presence of an oxidation catalyst and

monocarboxylic acid solvent under reaction conditions suitable to form a reaction mixture comprising the aromatic carboxylic acid and a gaseous effluent, the gaseous effluent being at least partially communicated to a first stage of a fractionation zone. The process further comprises separating at least part of the gaseous effluent in the first stage of the

fractionation zone to form a gaseous overhead stream comprising steam and a bottoms stream, the bottoms stream being at least partially communicated to the reaction zone. The process further comprises determining the water concentration in the reaction zone. The process further comprises condensing at least part of the gaseous overhead stream to form a water-containing condensate (e.g., in a second stage of the fractionation zone or in a condensing zone), and transferring at least part of the water-containing condensate to an upper portion of the first stage of the fractionation zone, wherein the rate of introduction of water to the upper portion of the first stage of the fractionation zone is controlled to maintain a water concentration in the reaction zone in the range of 8 wt.% to 20 wt.% (e.g., in the range of 12 wt.% to 16 wt.%).

[0018] FIG. 1 is a process flow diagram for manufacturing and recovering aromatic carboxylic acids in accordance with one embodiment of the present disclosure. FIG. 1 depicts a number of additional elements for use in processes according to certain embodiments of the disclosure. A system for performing a process 100 of FIG. 1 includes a reaction zone that includes an oxidation reactor 110 configured for liquid-phase oxidation of feedstock to provide a reaction zone effluent and a gaseous effluent; a crystallization zone 150 configured for forming solid crude aromatic carboxylic acid from the reaction zone effluent, and comprising one or more crystallizers in series; a solid/liquid separation device 190 configured for separating solid crude aromatic carboxylic acid (and oxidation by products) from liquid; a mixing zone including a purification reaction mixture make-up vessel 202 configured for preparing mixtures of crude aromatic carboxylic acid in purification reaction solvent; a purification zone including a hydrogenation reactor 210 configured for contacting the crude aromatic carboxylic acid with hydrogen in the presence of a catalyst to form a purified aromatic carboxylic acid; a recovery zone comprising a crystallization zone 220 including at least one crystallizer configured for forming a slurry stream comprising solid purified aromatic carboxylic acid and a vapor stream, wherein the vapor stream comprises steam and hydrogen; and a solid/liquid separation device 230 configured for separating solid purified aromatic carboxylic acid from liquid. [0019] The system further includes one or more stages of a fractionation zone 300 configured for fractionation of the gaseous effluent to provide a bottoms stream and an exit- gas stream; a condensing zone 350 configured for condensing the exit-gas stream to provide a water-containing condensate; a drum 372 configured for collecting the water- containing condensate and forming an exhaust gas stream; an absorber 380 configured for separating solvent monocarboxylic acid, substituted aromatic hydrocarbon, and reaction by products and forming a scrubbed gas stream 385 The scrubbed gas stream 385 is directed to emission control zone 390 and subsequently, to expander 400 attached to generator 420 (which can be directed to emission control zone 390 and, subsequently, to expander 400 attached to generator 420.

[0020] However, the person of ordinary skill in the art will appreciate that the integration of processes in FIG. 1 is meant to be purely representative, and various other integrated and non-integrated configurations may likewise be used.

[0021] Liquid and gaseous streams and materials used in the process represented in FIG. 1 may be directed and transferred through suitable transfer lines, conduits, and piping constructed, for example, from materials appropriate for process use and safety. It will be understood that particular elements may be physically juxtaposed and, where appropriate, may have flexible regions, rigid regions, or a combination of both. In directing streams of compounds, intervening apparatuses and/or optional treatments may be included. By way of example, pumps, valves, manifolds, gas and liquid flow meters and distributors, sampling and sensing devices, and other equipment (e.g., for monitoring, controlling, adjusting, and/or diverting pressures, flows and other operating parameters) may be present.

[0022] As described above, the feedstock includes a substituted aromatic hydrocarbon. Representative feedstock materials suitable for use in the processes of the disclosure include but are not limited to aromatic hydrocarbons substituted at one or more positions with at least one substituent that is oxidizable to a carboxylic acid group. In some

embodiments, the positions of the substituents correspond to the positions of the carboxylic acid groups of the aromatic carboxylic acid being prepared. In some embodiments, the oxidizable substituents include alkyl groups (e.g., methyl, ethyl, and/or isopropyl groups). In other embodiments, the oxidizable substituents include oxygen-containing groups, such as hydroxyalkyl, formyl, aldehyde, and/or keto groups. The substituents may be the same or different. The aromatic portion of feedstock compounds may be a benzene nucleus or it may be bi- or polycyclic (e.g., a naphthalene and/or anthracene nucleus). In some embodiments, the number of oxidizable substituents on the aromatic portion of the feedstock compound is equal to the number of sites available on the aromatic portion. In other embodiments, the number of oxidizable substituents on the aromatic portion of the feedstock is fewer than all such sites (e.g., in some embodiments 1 to 4 and, in some embodiments,

2). Representative feed compounds that may be used in accordance with the present teachings— alone or in combinations— include but are not limited to toluene; ethylbenzene and other alkyl-substituted benzenes; o-xylene; p-xylene; m-xylene; tolualdehydes, toluic acids, alkyl benzyl alcohols, 1-formyl-4-methylbenzene, 1-hydroxymethyl-4-methylbenzene; methylacetophenone; 1 ,2,4-trimethylbenzene; 1-formyl-2, 4-dimethyl-benzene; 1 , 2,4,5- tetramethylbenzene; alkyl-, formyl-, acyl-, and hydroxylmethyl-substituted naphthalenes (e.g., 2,6-dimethylnaphthalene, 2,6-diethylnaphthalene, 2,7-dimethylnaphthalene, 2,7- diethylnaphthalene, 2-formyl-6-methylnaphthalene, 2-acyl-6-methylnaphthalene, 2-methyl-6- ethylnaphthalene, and the like); and the like; and partially oxidized derivatives of any of the foregoing; and combinations thereof. In some embodiments, the substituted aromatic compound comprises a methyl-, ethyl-, and/or isopropyl-substituted aromatic hydrocarbon.

In some embodiments, the substituted aromatic compound comprises an alkyl-substituted benzene, o-xylene, p-xylene, m-xylene, or the like, or combinations thereof.

[0023] Aromatic carboxylic acids manufactured in accordance with the present disclosure are not restricted and include but are not limited to mono- and polycarboxylated species having one or more aromatic rings. In some embodiments, the aromatic carboxylic acids are manufactured by reaction of gaseous and liquid reactants in a liquid phase system. In some embodiments, the aromatic carboxylic acid comprises only one aromatic ring. In other embodiments, the aromatic carboxylic acid comprises a plurality (e.g., two or more) of aromatic rings that, in some embodiments, are fused (e.g., naphthalene, anthracene, etc.) and, in other embodiments, are not. In some embodiments, the aromatic carboxylic acid comprises only one carboxylic acid (e.g., -C0 ₂ H) moiety or a salt thereof (e.g., -C0 ₂ X, where X is a cationic species including but not limited to metal cations, ammonium ions, and the like). In other embodiments, the aromatic carboxylic acid comprises a plurality (e.g., two or more) of carboxylic acid moieties or salts thereof. Representative aromatic carboxylic acids include but are not limited to terephthalic acid, trimesic acid, trimellitic acid, phthalic acid, isophthalic acid, benzoic acid, naphthalene dicarboxylic acids, and the like, and

combinations thereof. In some embodiments, the present teachings are directed to manufacture of pure forms of terephthalic acid including purified terephthalic acid (PTA) and so-called medium purity terephthalic acids.

[0024] A representative type of oxidation that may be performed in the oxidation zone (e.g., oxidation reactor 110) is a liquid-phase oxidation that comprises contacting oxygen gas and a feed material comprising an aromatic hydrocarbon having one or more substituents oxidizable to carboxylic acid groups in a liquid-phase reaction mixture. In some

embodiments, the liquid-phase reaction mixture comprises a monocarboxyl ic acid solvent (e.g., acetic acid) and water in the presence of an oxidation catalyst comprising at least one heavy metal component (e.g., Co, Mn, V, Mo, Cr, Fe, Ni, Zi, Ce, Hf, or the like, and combinations thereof) and a promoter (e.g., halogen compounds, etc.). In some

embodiments, the oxidation is conducted at elevated temperature and pressure effective to maintain a liquid-phase reaction mixture and form a high temperature, high-pressure vapor phase. In some embodiments, oxidation of the aromatic feed material in the liquid-phase oxidation produces aromatic carboxylic acid as well as reaction by-products, such as partial or intermediate oxidation products of the aromatic feed material and/or solvent by-products. In some embodiments, the aromatic carboxylic acid comprises terephthalic acid, and the oxidizing comprises contacting para-xylene with gaseous oxygen in a liquid-phase oxidation reaction mixture that comprises acetic acid, water, and a bromine-promoted catalyst composition. The liquid-phase oxidation and associated processes may be conducted as a batch process, a continuous process, or a semi-continuous process. The oxidation may be conducted in the reaction zone, e.g., in one or more reactors.

[0025] In a representative embodiment, such as may be implemented as shown in FIG.

1 , liquid feed material comprising at least about 99 wt. % substituted aromatic hydrocarbon, aqueous acetic acid solution (e.g., containing about 70 to about 95 wt. % acetic acid), soluble compounds of cobalt and manganese (e.g., such as their respective acetates) as sources of catalyst metals, bromine (e.g., hydrogen bromide) as catalyst promoter, and air, as a source of oxygen, may be continuously charged to oxidation reaction vessel 110 through inlets, such as inlet 112. In some embodiments, vessel 110 is a pressure-rated, continuous-stirred tank reactor.

[0026] In some embodiments, stirring may be provided by rotation of an agitator 120, the shaft of which is driven by an external power source (not shown). Impellers mounted on the shaft and located within the liquid body are configured to provide forces for mixing liquids and dispersing gases within the liquid body, thereby avoiding settling of solids in the lower regions of the liquid body.

[0027] In some embodiments, para-xylene is oxidized in reaction zone, predominantly to terephthalic acid. By-products that may form in addition to terephthalic acid include but are not limited to partial and intermediate oxidation products (e.g., 4-carboxybenzaldehyde, 1 ,4- hydroxymethyl benzoic acid, p-toluic acid, benzoic acid, and the like, and combinations thereof). Since the oxidation reaction is exothermic, heat generated by the reaction may cause boiling of the liquid-phase reaction mixture and formation of a gaseous effluent that comprises vaporized monocarboxylic acid, water vapor, gaseous by-products from the oxidation reaction, carbon oxides, nitrogen from the air charged to the reaction, unreacted oxygen, and the like, and combinations thereof. [0028] As described above, in various aspects of the processes of the disclosure, the concentration of water present in the liquid-phase reaction mixture is determined. The concentration of water present in the liquid-phase reaction mixture can be determined, for example, by direct measurement. But in certain desirable embodiments of the methods of the disclosure, the concentration of water present in the liquid-phase reaction mixture is calculated based on measurement of other process conditions. For example, in certain such embodiments, the concentration of water present in the liquid-phase reaction mixture is calculated based on the temperature and pressure of the reaction mixture and the oxygen concentration of the gaseous effluent.

[0029] Accordingly, in certain embodiments as otherwise described herein, the process includes determining the reaction temperature and the reaction pressure in the reaction zone, and determining the oxygen concentration of the gaseous effluent. For example, in certain embodiments as otherwise described herein, the process includes directly measuring the temperature and/or pressure of the reaction zone. In other embodiments as otherwise described herein, the process includes measuring the temperature of the gaseous effluent in a zone other than the reaction zone (e.g., upstream of a fractionation zone) and applying a temperature bias to determine the reaction temperature, and/or measuring the pressure of the gaseous effluent in a zone other than the reaction zone (e.g., upstream of a fractionation zone) and applying a pressure bias to determine the reaction pressure. In certain embodiments as otherwise described herein, the oxygen concentration of the gaseous effluent (e.g., calculated on a dry basis) is measured at a point downstream of the reaction zone. In other embodiments as otherwise described herein, the oxygen concentration of the gaseous effluent is measured at a point downstream from a fractionation zone.

[0030] In certain embodiments as otherwise described herein, the calculation the water concentration of the reaction mixture is based on the mole fraction of water in the reaction mixture, for example, according to Formula I:

100 * x _{H 0}

wt. % o = - ₇ - ^ -

² X _Hz o + (100 - X _Hz0 ) * 60/18 in which X _Hz0 is the mole fraction of water. In such embodiments, the mole fraction of water can be determined based on reaction temperature and pressure, and the oxygen concentration of the gaseous effluent, for example, according to Formula II:

X _Hz o = (36.164 + 0.679 * P _R - 0.201 * T _R - 0.1616 * C _R ) ² in which P _R is the reaction pressure in barG, T _R is the reaction temperature in °C, and C _R is the oxygen concentration of the gaseous effluent in vol.%, calculated on a dry basis. In embodiments where, as noted above, the reaction pressure and/or reaction temperature are determined based on the respective properties of the gaseous effluent, the reaction pressure can be calculated, for example, according to Formula III:

PR = Pz + PB

in which P _z is the measured pressure of the gaseous effluent in barG and P _B is a pressure bias in barG, and the reaction temperature can be calculated, for example, according to Formula IV:

T _R = T _Z + T _B

in which T _z is the measured temperature of the gaseous effluent in °C and T _B is a temperature bias in °C.

[0031] For example, in certain embodiments, the water concentration of the reaction mixture is calculated according to Formulas I— IV, and P _B and T _B are 0 barG and in the range of 2-3 °C, respectively.

[0032] The gaseous effluent may be removed from the reactor through vent 116 and sent in a stream 111 to a first stage of a fractionation zone 330. The fractionation zone 330 is configured to substantially separate the monocarboxylic acid solvent and water of the gaseous effluent to provide a bottoms stream to the reactor in stream 321 and an exit-gas stream through gas removal outlet 334 to a condensing zone 350 in stream 337.

[0033] The fractionation zone can include one or more stages such as, for example, one or more distillation columns or one or more stages of a distillation column. An example of a fractionation zone 300 is depicted in schematic view in FIG. 2. A first distillation column 320 is configured to separate the gaseous effluent of stream 111 into a bottoms stream including monocarboxylic acid solvent and a gaseous overhead stream comprising steam. The water- rich gaseous overhead stream is removed from the distillation column 320 through gas removal outlet 324 to a second distillation column 330 in stream 323. In this embodiment, substantially all of the bottoms stream is returned to the reactor in stream 331. The distillation column 330 is configured to separate the gaseous overhead stream into a water- containing liquid condensate and an exit-gas stream. The water-containing condensate is returned to distillation column 320 at inlet 328 as reflux liquid in stream 321. The exit-gas stream is removed from the distillation column 330 through gas removal outlet 334 to a condensing zone 350 through stream 337. In certain embodiments, a water-rich liquid stream is supplied to the distillation column 330 at reflux inlet 336 (e.g., stream 355 from condensing zone 350). An outlet 345 is positioned intermediately relative to reflux inlets 336 and 334, and in certain embodiments can provide an additional water-rich liquid stream 353, which can be returned to the distillation column 330 at reflux inlet 336 (e.g., in stream 355). In certain embodiments, a mother-liquor stream (e.g., purification mother-liquor stream 233) is supplied to the distillation column 330 at reflux inlet 334. In certain embodiments, the flow of one or more of streams 321, 355, 233 are adjustable, to provide control over the rate of introduction of water to the distillation column 320.

[0034] Another example of a fractionation zone 300 is provided in FIG. 3. A distillation column 330 is configured to separate the gaseous effluent of stream 111 into a bottoms stream including monocarboxylic acid solvent and a gaseous overhead stream comprising steam. The water-rich gaseous overhead stream is removed from the distillation column 330 as exit gas, through gas removal outlet 334 to a condensing zone 350, through stream 337. The bottoms stream is returned to the reactor in stream 331. In certain embodiments, a water-rich liquid stream is supplied to the distillation column 330 at reflux inlet 336 (e.g., stream 355 from condensing zone 350). An outlet 345 is positioned intermediately relative to reflux inlets 336 and 334, and in certain embodiments can provide an additional water-rich liquid stream 353, which can be returned to the distillation column 330 at reflux inlet 336. In certain embodiments, a mother-liquor stream (e.g., purification mother-liquor stream 233) is supplied to the distillation column 330 at reflux inlet 334. In certain such embodiments, the flow of one or more of streams 355, 233 are adjustable, to provide control over the rate of introduction of water to the distillation column 320.

[0035] As described above, in various aspects of the processes of the disclosure, the concentration of water in the liquid-phase reaction mixture is maintained within in the range of 8 wt.% to 20 wt.%. For example, in certain embodiments, the concentration of water is maintained within the range of 8 wt.% to 18 wt.%, or 8 wt.% to 16 wt.%, or 8 wt.% to 14 wt.%, or 10 wt.% to 20 wt.%, or 12 wt.% to 20 wt.%, or 14 wt.% to 20 wt.%, or 10 wt.% to 18 wt.%, or 12 wt.% to 16 wt.%.

[0036] In various embodiments according to certain aspects of the present disclosure, the concentration of water (e.g., calculated as otherwise described herein) in the liquid- phase reaction mixture is controlled by controlling the rate of introduction of water (e.g., condensate of the gaseous overhead stream) to an upper portion of the first stage of a fractionation zone. As noted above, the bottoms stream of the first stage of the fractionation zone is at least partially communicated to the reaction zone. Notably, the water that is communicated to the upper portion of the first stage of the fractionation zone will be part of that bottoms stream, and so by controlling the amount of water that is communicated to the upper portion of the first stage of the fractionation zone the amount of water in the reaction zone can be controlled. In certain desirable embodiments, and as described above with respect to FIGS. 2 and 3, all of the bottoms stream of the first stage of the fractionation zone is communicated to the reaction zone. In other embodiments, only part of the bottoms stream of the first stage of the fractionation zone is communicated to the reaction zone; in certain desirable such embodiments, the fraction of the bottoms stream that is

communicated to the reaction zone is substantially constant.

[0037] As described above, in certain embodiments of the processes as described herein, the rate of introduction of water to the upper portion of the first stage of the fractionation zone is used to control the water concentration in the reaction zone.

Accordingly, in certain embodiments, the method includes changing the rate of introduction of water to the upper portion of the first stage of the fractionation zone in response to a change of water concentration in the reaction zone, for example, by increasing the rate of introduction of water to the upper portion of the first stage of the fractionation zone in response to a decrease in water concentration in the reaction zone, or by decreasing the rate of introduction of water to the upper portion of the first stage of the fractionation zone in response to an increase in water concentration in the reaction zone. The change in the rate of introduction of water to the upper portion of the first stage of the fractionation zone can be performed, for example, by changing the amount of the water-containing condensate that is transferred to the upper portion of the first stage of the fractionation zone. Additionally or alternatively, the change in the rate of introduction of water to the upper portion of the first stage of the fractionation zone can in some embodiments be performed by changing the concentration of water in the water-containing condensate that is transferred to the upper portion of the first stage of the fractionation zone, for example, by changing the condensation conditions in a second fractionation zone or in a condensation zone. The person of ordinary skill in the art can use conventional monitoring and process control techniques to perform the methods described herein.

[0038] In certain embodiments as otherwise described herein, the rate of introduction of water to the upper portion of the first stage of the fractionation zone is controlled by controlling a fraction of the water-containing condensate that is transferred to the to the upper portion of the first stage of the fractionation zone.

[0039] In certain embodiments as otherwise described herein, transferring at least part of the water-containing condensate to the upper portion of the first stage of the fractionation zone includes transferring at least part of the gaseous overhead stream to a condensing zone as an exit-gas stream; condensing at least part of the gaseous overhead stream in the condensing zone to form a water-containing reflux liquid; and transferring at least part of the reflux liquid to the upper portion of the first stage of the fractionation zone as the water- containing condensate. [0040] In certain embodiments as otherwise described herein, transferring at least part of the water-containing condensate to the upper portion of the first stage of the fractionation zone includes at least part of the water-containing condensate to the upper portion of the first stage of the fractionation zone includes transferring at least part of the gaseous overhead stream to a second stage of the fractionation zone; condensing a part of the gaseous overhead stream in the second stage of the fractionation zone to form a water- containing condensate and an exit-gas stream; transferring the exit-gas stream to a condensing zone; condensing at least part of the exit-gas stream to form a water-containing reflux liquid; and transferring at least part of the water-containing reflux liquid to an upper portion of the second stage of the fractionation zone. In certain such embodiments, the rate of introduction of water to the upper portion of the first stage of the fractionation zone is controlled by controlling a fraction of the water-containing reflux liquid that is transferred to the upper portion of the second stage of the fractionation zone. These methods can further include transferring a mother-liquor stream to an upper portion of the second stage of the fractionation zone; in certain such embodiments, the rate of introduction of water to the upper portion of the first stage of the fractionation zone is controlled by controlling a fraction of the mother-liquor stream that is transferred to the upper portion of the second stage of the fractionation zone.

[0041] For example, in the embodiment depicted in FIG. 2, the rate of introduction of water to the upper portion of distillation column 320 can be controlled by controlling the flow of stream 321 of a water-containing condensate formed in distillation column 330 (e.g., by condensing at least part of the gaseous overhead stream transferred from distillation column 320). Additionally or alternatively, the rate of introduction of water to the upper portion of distillation column 320 can be controlled by controlling the flow of stream 355 of a water-rich liquid that includes condensate formed in distillation column 330 (e.g., removed via outlet 345) and/or in condensing zone 350 (e.g., transferred from drum 372 in stream 373).

Additionally or alternatively, the rate of introduction of water to the upper portion of distillation column 320 can be controlled by controlling the flow of mother-liquor stream 233.

[0042] In another example, in the embodiment depicted in FIG. 3, the rate of introduction of water to the upper portion of distillation column 330 can be controlled by controlling the flow of stream 355 of a water-rich liquid that includes condensate formed in distillation column 330 (e.g., removed via outlet 345) and/or in condensing zone 350 (e.g., transferred from drum 372 in stream 373). Additionally or alternatively, the rate of introduction of water to the upper portion of distillation column 330 can be controlled by controlling the flow of mother-liquor stream 233. [0043] The exit gas may be removed from the fractionation zone through outlet 334 and sent in a stream 337 to condensing zone 350. The condensing zone 350 is configured to provide a water-rich liquid stream and an exhaust gas stream. As depicted in FIG. 1 , condensing zone 350 includes condensers 352 and 362, and disengagement drum 372. Condensation using two or more condensers in series using heat exchange fluids at successively lower temperatures allows for generation of steam at different pressures, thereby allowing for efficiencies in use of steam at the different pressures by matching with differing heat or energy inputs to operations in which steam is used. Following condensation in condenser 352, liquid and uncondensed gas is directed to condenser 362 in stream 361 for further condensation. Gas and liquid effluent from condenser 362 are directed in stream 363 to drum 372, in which condensate liquid comprising water is collected and removed in stream 373, which can be directed, for example, as water-rich liquid stream 355 to distillation column 330.

[0044] Uncondensed exhaust gas from condensation removed in stream 375 comprises non-condensable components such as unconsumed oxygen from oxidation, nitrogen from the air used as oxygen source to the oxidation, carbon oxides from such air as well as from reactions in oxidation, and in certain embodiments, traces of unreacted para-xylene and its oxidation by-products, as well as acetic acid, methyl acetate, and methanol, and methyl bromide formed from the bromine promoter used in oxidation. In certain embodiments, the uncondensed gas is substantially free of water vapor owing to substantially complete condensation into the condensate liquid recovered in the condenser.

[0045] The uncondensed exhaust gas from can be, for example, under pressure of about 10 to about 15 barg and can be transferred directly to a power recovery device or to a emission control device for removing corrosive and combustible species in advance of power recovery. In the embodiment of FIG. 1 , uncondensed gas is first directed to treatment to remove unreacted feed materials and traces of monocarboxylic acid solvent and/or reaction products thereof remaining in the gas. Thus, uncondensed gas is transferred in stream 375 to high-pressure absorber 380 for absorbing, in certain embodiments, para-xylene, acetic acid, methanol and methyl acetate without substantial loss of pressure. Absorber 380 is adapted for receipt of the substantially water-depleted gas remaining after condensation and for separation of para-xylene, solvent acetic acid and its reaction products from oxidation from the gas by contact with one or more liquid scrubbing agents. The absorber also includes an upper vent 382 from which a scrubbed gas under pressure comprising incondensable components of the inlet gas to the absorber is removed in stream 385 and a lower outlet 384 for removal of a liquid monocarboxylic acid solvent stream into which components from the gas phase comprising one or more of para-xylene, acetic acid, methanol and/or methyl acetate have been scrubbed. A bottoms liquid can be removed from a lower portion of the absorber and directed to the reaction zone for reuse of recovered components.

[0046] Pressurized gas from the condenser 362, or, as depicted in FIG. 1 , from the vent 382 from the high-pressure absorber, can be treated in pollution control zone 390, for example, to convert organic components and carbon monoxide in the gas from the condenser or the absorber to carbon dioxides and water. Such treatment can be performed, for example, using a catalytic oxidation unit adapted for receiving the gas, optionally heating it to promote combustion and directing the gas into contact with a high temperature-stable catalyst disposed on a cellular or other support. Overhead gas from absorber 380 can be, for example, directed to oxidation unit 394, optionally being preheated by one or more preheaters 392.

[0047] An oxidized high-pressure gas is directed from catalytic oxidation unit 394 to expander 400 which is connected to generator 420. Energy from the oxidized high-pressure gas can be converted to work in the expander 400 and such work is converted to electrical energy by generator 420. Expanded gas exits the expander and can be released to the atmosphere, preferably after caustic scrubbing and/or other treatments for appropriately managing such releases. Before being directed to the expander 400, some or all of the high-pressure gas can be directed to a bromine scrubber (not shown).

[0048] The person of ordinary skill in the art will appreciate that the condensing zone, absorber, and pollution control zone can be configured in a variety of manners. Examples of processing and treatment of the reaction off-gas stream, and sources of reflux fluids are more fully described in U.S. Pat. Nos. 5,723,656, 6,137,001 , 7,935,844, 7,935,845, and 8,173,834.

[0049] In some embodiments, solid crude product may be recovered from the reaction zone effluent by crystallization in one or more stages, such as in a crystallization zone 150, as shown in FIG. 1. In the embodiment shown in FIG. 1 , liquid-phase reaction mixture is removed from reaction vessel 110 through slurry outlet 114 and directed in stream 115 to one or more in-series crystallizers of crystallization zone 150, to form solid oxidation product. Cooling in the crystallizers may be accomplished by pressure release. One or more of the crystallizers may be vented to remove vapor resulting from pressure let down and generation of steam from the flashed vapor to a heat exchanger (not shown).

[0050] In certain embodiments of the processes as otherwise described herein, the aromatic carboxylic acid prepared by the process comprises terephthalic acid, and the substituted aromatic hydrocarbon of the feedstock comprises para-xylene. For example, in certain such embodiments, the substituted aromatic hydrocarbon of the feedstock is at least 99% by weight para-xylene.

[0051] A variety of process operations can be used in recovery of the crystallized carboxylic acid. In certain embodiments as otherwise described herein, at least a portion of an effluent of a last crystallizer of the crystallization zone is separated to form an aromatic carboxylic acid-rich stream and a solvent-rich stream. For example, in the process depicted in FIG. 1 , the crystallization zone 150 is in fluid communication with a solid/liquid separation device 190. The solid/liquid separation device 190 is configured to receive a slurry of solid product from the crystallization zone 150, and is further configured to separate the slurry of solid product to form an aromatic carboxylic acid-rich stream 197 and one or more solvent- rich streams (in FIG. 1 , 191). In a representative embodiment, such as may be implemented as shown in FIG. 1 , the slurry of solid product from crystallization zone 150 includes a solid crude aromatic carboxylic acid, a monocarboxylic acid solvent, and minor amounts of an oxidation catalyst.

[0052] A variety of process operations can be used in recovery of the crystallized carboxylic acid. In certain embodiments as otherwise described herein, at least a portion of an effluent of a last crystallizer of the crystallization zone is separated to form an aromatic carboxylic acid-rich stream and a solvent-rich stream. For example, in the process depicted in FIG. 1 , the crystallization zone 150 is in fluid communication with a solid-liquid separation device 190. The solid-liquid separation device 190 is configured to receive a slurry of solid product from the crystallization zone 150. In some embodiments, the solid-liquid separation device 190 is further configured to separate a crude solid product and by-products from the liquid. In some embodiments, the separation device 190 is a centrifuge, a rotary vacuum filter, a pressure filter, or the like, or a combination thereof. In some embodiments, the separation device 190 comprises a pressure filter configured for solvent exchange (e.g., by positive displacement under pressure of mother liquor in a filter cake with wash liquid comprising water). Suitable rotary pressure filters are sold by BHS-Sonthofen and are disclosed for example, in U.S. Pat. Nos. 2,741 ,369, 7,807,060, U.S. Pat. App. 20050051473, US Pat. App. 20150182890, and WO 2016/014830. The oxidation mother liquor resulting from the separation may exit separation device 190 in solvent-rich stream 191 for transfer to mother-liquor drum 192. A portion of the mother liquor and, in some embodiments, a major portion of the mother liquor, may be transferred from drum 192 to the reaction zone (e.g., to oxidation reactor 110). In such a way, monocarboxylic acid solvent, water, catalyst, and/or oxidation reaction by-products dissolved and/or present as fine solid particles in the mother liquor may be returned to the liquid-phase oxidation reaction. [0053] As shown in FIG. 1 , the aromatic carboxylic acid-rich stream 197 from the separation device 190 comprising crude solid product may be directed to a mixing zone including a reaction mixture make-up vessel 202. The crude solid product in stream 197 may be mixed and slurried in make-up vessel 202 with a make-up solvent entering vessel 202 through line 203 to form a purification reaction mixture comprising crude aromatic carboxylic acid. The purification reaction mixture prepared in vessel 202 is withdrawn through line 201. In some embodiments, the purification make-up solvent contains water. In some embodiments, the solvent line 203 connects to a holding vessel (not shown) for containing make-up solvent. In other embodiments, the solvent comprises fresh

demineralized water. In other embodiments, the solvent is supplied from another part of the integrated process 100. For example, in one embodiment, the solvent comprises liquid- phase component 373 of condensing zone 350. In another embodiment, the solvent comprises the liquid-phase stream 233 exiting solid-liquid separator 230. Sources of purification make-up solvent are more fully described, for example, in U.S. Pat. Nos.

5,723,656, 6,137,001 , 7,935,844, 7,935,845, and 8,173,834.

[0054] In certain embodiments as otherwise described herein, at least a portion of the aromatic carboxylic acid-rich stream is purified in a purification zone comprising a

hydrogenation catalyst under reaction conditions suitable to form a purification effluent comprising purified aromatic carboxylic acid. For example, in the process depicted in FIG. 1 , purification reaction mixture exiting vessel 202 through stream 201 enters purification reactor 210 of the purification zone. The purification zone may further include a pump and one or more heat exchangers (not shown) configured to pre-heat the purification mixture exiting vessel 202 before it enters purification reactor 210. In some embodiments, the purification reactor 210 is a hydrogenation reactor and purification in the purification reactor 210 comprises contacting the purification reaction mixture comprising crude aromatic carboxylic acid with hydrogen in the presence of a hydrogenation catalyst. In some embodiments, at least a portion of a purification effluent comprising purified aromatic carboxylic acid may be continuously removed from hydrogenation reactor 210 in stream 211 and directed to a crystallization zone 220 downstream of the purification zone. Crystallization zone 220 may comprise a plurality of crystallizers. In some embodiments, in crystallization zone 220, purified aromatic carboxylic acid and reduced levels of impurities may be crystallized from the reaction mixture. The resulting solid/liquid mixture comprising purified carboxylic acid solids formed in crystallization zone 220 may be fed, in stream 221 , to a solid-liquid separation device 230, configured to separate the solid/liquid mixture into a liquid-phase stream 233 and an aromatic carboxylic acid-rich stream 231 comprising solid purified aromatic carboxylic acid. [0055] Various aspects and embodiments of the present disclosure are set out in the following embodiments, which can be combined in any number and in any combination that is not technically or logically inconsistent:

Embodiment 1. A process for manufacturing an aromatic carboxylic acid, comprising: oxidizing in a reaction zone a feedstock comprising a substituted aromatic hydrocarbon in the presence of an oxidation catalyst and monocarboxylic acid solvent under reaction conditions suitable to form a reaction mixture comprising the aromatic carboxylic acid and a gaseous effluent, at least a portion of the gaseous effluent being communicated to a first stage of a fractionation zone;

determining the reaction temperature and the reaction pressure in the reaction zone; and

determining the oxygen concentration of the gaseous effluent,

determining the water concentration of the reaction mixture based on the

temperature and pressure of the reaction mixture and the oxygen concentration of the gaseous effluent;

separating at least part of the gaseous effluent in the first stage of the fractionation zone to form a gaseous overhead stream comprising steam and a bottoms stream, at least a portion of the bottoms stream being communicated to the reaction zone;

condensing at least a portion of the gaseous overhead stream to form a water- containing condensate; and

transferring at least part of the water-containing condensate to an upper portion of the first stage of the fractionation zone, wherein the rate of introduction of water to the upper portion of the first stage of the fractionation zone is controlled to maintain a water concentration in the reaction zone in the range of 8 wt.% to 20 wt.%.

Embodiment 2. The process according to embodiment 1 , wherein the rate of introduction of water to the upper portion of the fractionation zone is controlled to maintain a water concentration in the reaction zone in the range of 12 wt.% to 16 wt.%.

Embodiment 3. The process according to embodiment 1 , wherein the rate of introduction of water to the upper portion of the first stage of the fractionation zone is controlled by controlling a fraction of the water-containing condensate that is transferred to the upper portion of the first stage of the fractionation zone. Embodiment 4. The process according to any of embodiments 1-3, wherein determining the reaction pressure comprises directly measuring the pressure of the reaction zone.

Embodiment 5. The process according to any of embodiments 1-3, wherein determining the reaction pressure comprises measuring the pressure of the gaseous effluent in a zone other than the reaction zone.

Embodiment 6. The process according to any of embodiments 1-5, wherein determining the reaction temperature comprises directly measuring the temperature of the reaction zone.

Embodiment 7. The process according to any of embodiments 1-5, wherein determining the reaction temperature comprises measuring the temperature of the gaseous effluent in a zone other than the reaction zone.

Embodiment 8. The process according to any of embodiments 1-7, wherein the oxygen concentration of the gaseous effluent is determined at a point upstream from the fractionation zone.

Embodiment 9. The process according to any of embodiments 1-7, wherein the oxygen concentration of the gaseous effluent is determined at a point downstream from the fractionation zone.

Embodiment 10. The process according to any of embodiments 1-9, wherein the water concentration of the reaction mixture does not vary by more than 15% (e.g., by more than 12.5%, or by more than 10%, or by more than 7.5%) over a time period of 8 hours.

Embodiment 11. The process according to any of embodiments 1-10, wherein transferring at least part of the water-containing condensate to the upper portion of the first stage of the fractionation zone comprises

transferring at least part of the gaseous overhead stream to a condensing zone as an exit-gas stream;

condensing at least part of the gaseous overhead stream in the condensing zone to form a water-containing reflux liquid; and

transferring at least part of the reflux liquid to the upper portion of the first stage of the fractionation zone as the water-containing condensate. Embodiment 12. The process according to any of embodiments 1-10, wherein transferring at least part of the water-containing condensate to the upper portion of the first stage of the fractionation zone comprises

transferring at least part of the gaseous overhead stream to a second stage of the fractionation zone;

condensing a part of the gaseous overhead stream in the second stage of the fractionation zone to form a water-containing condensate and an exit-gas stream;

transferring the exit-gas stream to a condensing zone;

condensing at least part of the exit-gas stream to form a water-containing reflux liquid; and

transferring at least part of the water-containing reflux liquid to an upper portion of the second stage of the fractionation zone.

Embodiment 13. The process according to embodiment 12, wherein the rate of introduction of water to the upper portion of the first stage of the fractionation zone is controlled by controlling a fraction of the water-containing reflux liquid that is transferred to the upper portion of the second stage of the fractionation zone.

Embodiment 14. The process according to embodiment 12 or 13, further comprising transferring a mother-liquor stream to an upper portion of the second stage of the

fractionation zone.

Embodiment 15. The process according to embodiment 14, wherein the rate of introduction of water to the upper portion of the first stage of the fractionation zone is controlled by controlling a fraction of the mother-liquor stream that is transferred to the upper portion of the second stage of the fractionation zone.

Embodiment 16. The process according to any of embodiments 1-15, wherein:

the aromatic carboxylic acid comprises terephthalic acid; and

the substituted aromatic hydrocarbon of the feedstock comprises para-xylene.

Embodiment 17. The process according to embodiment 16, wherein the feedstock comprises at least 99% para-xylene.

[0056] The entire contents of each and every patent and non-patent publication cited herein are hereby incorporated by reference, except that in the event of any inconsistent disclosure or definition from the present specification, the disclosure or definition herein shall be deemed to prevail.

[0057] The foregoing detailed description and the accompanying drawings have been provided by way of explanation and illustration, and are not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.

[0058] It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims can, alternatively, be made to depend in the alternative from any preceding claim— whether independent or dependent— and that such new combinations are to be understood as forming a part of the present specification.