Methods for recovering oxidation byproducts

Abstract

The present invention relates to a method for recovering byproducts of substituted aromatics oxidation reactions, the method comprising cooling one or more of a gaseous stream directed to a high-pressure absorber (380), a solvent-rich wash stream (381) directed to the high-pressure absorber, and a water-rich liquid stream (383) directed to a solvent recovery zone by heat exchange with cooled waste wash liquid taken from a low-pressure scrubber (430).

Description

Technical Field

[0001] This disclosure generally relates to methods for recovering oxidation byproducts. More specifically, this disclosure relates to methods for recovering byproducts from the oxidation of substituted aromatic hydrocarbons. Background Technology

[0002] Terephthalic acid and other aromatic carboxylic acids are commonly used in the manufacture of polyesters through reactions with ethylene glycol, higher alkylene glycols, or combinations thereof, to transform them into fibers, films, containers, bottles and other packaging materials, as well as molded articles.

[0003] In commercial practice, aromatic carboxylic acids are typically produced by liquid-phase oxidation in an aqueous monocarboxylic acid solvent (e.g., acetic acid) with air or another, typically gaseous, oxygen source, in the presence of a bromine-assisted catalyst containing cobalt and manganese. The oxidative process is exothermic and produces a crude reaction mixture containing the aromatic carboxylic acid along with byproducts, including partial or intermediate oxidation products of the aromatic feed, water, acetic acid, and acetic acid reaction products such as methanol, methyl acetate, and methyl bromide. Specifically, terephthalic acid is typically produced using a feed containing p-xylene.

[0004] Byproducts can be recovered from various process streams, such as gaseous and liquid effluents from oxidation reactors and downstream crystallizers, purification reactors, and solid-liquid separators. While recovery efficiency can be improved by lowering the temperature of such streams, the temperatures achievable in conventional manufacturing processes are limited to a few degrees higher than the cooling water used elsewhere in the process. Furthermore, the equipment and operating costs associated with separate chilled water loops significantly outweigh the benefits of lowering the recovery temperature.

[0005] Therefore, there remains a need for improved methods for recovering byproducts from the oxidation of substituted aromatics. Summary of the Invention

[0006] The scope of this disclosure is not affected in any way by the statements in the description of the invention.

[0007] On one hand, this disclosure provides a method for recovering byproducts of substituted aromatic hydrocarbon oxidation reactions, the method comprising:

[0008] In a low-pressure scrubber, a first water-rich scrubbing stream is contacted with a first gaseous stream containing bromine to form a cooled waste stream and a first scrubbed gaseous stream, the first scrubbed gaseous stream containing a reduced amount of bromine relative to the first gaseous stream.

[0009] The method further includes one or both of the following:

[0010] a) In a high-pressure absorber, a second gaseous stream containing one or more byproducts of the oxidation reaction of substituted aromatics is contacted with a second solvent-rich washing stream to form a second washed gaseous stream, the second washed gaseous stream containing a reduced amount of one or more byproducts relative to the second gaseous stream.

[0011] Specifically, before being introduced into the high-pressure absorber, at least one of the second gaseous stream and the second solvent-rich washing stream is cooled by heat exchange with at least a portion of the cooled waste stream; and

[0012] b) In the solvent recovery zone, at least a portion of the water-rich liquid stream containing one or more byproducts of the substituted aromatic hydrocarbon oxidation reaction is separated by reverse osmosis to form a byproduct stream and a purified stream, the purified stream containing a reduced amount of the one or more byproducts relative to the water-rich liquid stream.

[0013] The water-rich liquid stream is cooled by heat exchange with at least a portion of the cooled waste stream before being introduced into the solvent recovery zone.

[0014] In some embodiments further described herein, the method also includes transferring (e.g., directly or indirectly) at least a portion of the liquid effluent from the high-pressure absorber (which contains one or more byproducts of the substituted aromatics oxidation reaction) to a reaction zone capable of carrying out the substituted aromatics oxidation reaction.

[0015] In some other embodiments described herein, the method further includes contacting the second gaseous stream with a second water-rich washing stream in the high-pressure absorber.

[0016] In some other embodiments described herein, the method includes:

[0017] The second gaseous stream is cooled to form a cooled second gaseous stream by heat exchange with at least a portion of the cooled waste stream; then

[0018] The cooled second gaseous stream is brought into contact with a second solvent-rich washing stream in the high-pressure absorber.

[0019] In some other embodiments described herein, the method further includes:

[0020] In the reaction zone, the feed containing substituted aromatics is oxidized in the presence of an oxidation catalyst and a monocarboxylic acid solvent, under reaction conditions suitable for the formation of crude aromatic carboxylic acids;

[0021] In the fractionation zone, at least a portion of the gaseous effluent from the reaction zone is separated to form a bottom stream and a top stream, the top stream containing water vapor and one or more additional byproducts of the oxidation of substituted aromatics.

[0022] In the condensation zone, a portion of the gas-phase column overhead stream is condensed to form a water-rich condensate; and

[0023] At least a portion of the gaseous effluent from the condensation zone (which contains one or more byproducts) is cooled to form the second gaseous stream.

[0024] In some embodiments further described herein, cooling at least a portion of the gaseous effluent comprises heat exchange with a coolant stream at a temperature at least 2°C (e.g., at least 3°C) higher than the temperature of the cooled waste stream.

[0025] In some other embodiments described herein, the method includes:

[0026] The second solvent-rich wash stream is cooled to form a cooled second solvent-rich wash stream by heat exchange with at least a portion of the cooled waste stream; then

[0027] The second gaseous stream is brought into contact with a cooled, second solvent-rich washing stream in the high-pressure absorber.

[0028] In some embodiments further described herein, the method further includes cooling at least a portion of the liquid effluent from the solvent drum (which contains, for example, acetic acid) to form the second solvent-rich wash stream.

[0029] In some embodiments further described herein, cooling at least a portion of the liquid effluent comprises exchanging heat with a coolant stream at a temperature at least 2°C (e.g., at least 3°C) higher than the temperature of the cooled waste stream.

[0030] In some other embodiments described herein, the method includes

[0031] The water-rich liquid stream is cooled to form a cooled water-rich liquid stream by heat exchange with at least a portion of the cooled waste stream; then

[0032] The cooled, water-rich liquid stream is separated by reverse osmosis in the solvent recovery zone.

[0033] In some embodiments further described herein, the method also includes transferring at least a portion of the byproduct stream (which contains one or more byproducts of the substituted aromatics oxidation reaction) to a reaction zone capable of carrying out the substituted aromatics oxidation reaction.

[0034] In some other embodiments described herein, the method further includes:

[0035] In the reaction zone, the feed containing substituted aromatics is oxidized in the presence of an oxidation catalyst and a monocarboxylic acid solvent, under reaction conditions suitable for the formation of crude aromatic carboxylic acids;

[0036] In the fractionation zone, at least a portion of the gaseous effluent from the reaction zone is separated to form a bottom stream and a top stream, the top stream containing water vapor and one or more additional byproducts of the oxidation of substituted aromatics.

[0037] In the condensation zone, a portion of the gas-phase column overhead stream is condensed to form a water-rich condensate containing one or more byproducts; and

[0038] At least a portion of the water-rich condensate containing one or more byproducts is cooled to form the water-rich liquid stream.

[0039] In some other embodiments described herein, the first gas stream includes at least a portion of the second washed gas stream.

[0040] In some other embodiments described herein, the method further includes:

[0041] In the preheating zone, at least a portion of the second-washed gaseous stream is heated to form a preheated gaseous stream;

[0042] In an oxidation apparatus, at least a portion of the preheated gaseous stream is oxidized to produce an oxidized high-pressure gaseous stream; and

[0043] In an expander, at least a portion of the oxidized high-pressure gaseous stream is expanded to form the first gaseous stream.

[0044] In some other embodiments described herein, the method further includes releasing at least a portion of the first washed gaseous stream into the atmosphere.

[0045] In some other embodiments described herein, the first water-rich washing stream has a temperature of 32-43°C.

[0046] In some other embodiments described herein, the temperature of the cooled waste stream is at least 2°C (e.g., at least 3°C) lower than the temperature of the first water-rich washing stream.

[0047] In some embodiments further described herein, the substituted aromatic hydrocarbon oxidation reaction is the oxidation of p-xylene to form terephthalic acid.

[0048] In some embodiments further described herein, the one or more byproducts include acetic acid, methyl acetate, methanol, and / or p-xylene.

[0049] On the other hand, this disclosure provides a system for recovering byproducts of substituted aromatic hydrocarbon oxidation reactions, the system comprising:

[0050] A low-pressure scrubber that can contact a first water-rich scrubbing stream with a first gaseous stream containing bromine to form a cooled waste stream and a first scrubbed gaseous stream, the first scrubbed gaseous stream containing a reduced amount of bromine relative to the first gaseous stream.

[0051] The system also includes one or both of the following:

[0052] a) A high-pressure absorber capable of contacting a second gas stream containing one or more byproducts of the oxidation reaction of substituted aromatics with a second solvent-rich scrubbing stream to form a second scrubbed gas stream, the second scrubbed gas stream containing a reduced amount of one or more byproducts relative to the second gas stream, and

[0053] at least one of the following

[0054] A heat exchanger that cools the second gaseous stream by exchanging heat with at least a portion of the cooled waste stream before introducing it into the high-pressure absorber.

[0055] But; and

[0056] A heat exchanger capable of cooling the second solvent-rich washing stream by heat exchange with at least a portion of the cooled waste stream before it is introduced into the high-pressure absorber; and

[0057] b) A reverse osmosis unit capable of separating at least a portion of the water-rich liquid stream containing one or more byproducts of the substituted aromatic hydrocarbon oxidation reaction by reverse osmosis to form a byproduct stream and a purified stream, the purified stream containing a reduced amount of the one or more byproducts relative to the water-rich liquid stream, and

[0058] A heat exchanger that cools the water-rich liquid stream by exchanging heat with at least a portion of the cooled waste stream before introducing it into the recycling zone. Attached Figure Description

[0059] Figure 1 It is a process flow diagram depicting an integrated method including the recovery of byproducts from the oxidation reaction of substituted aromatics according to certain embodiments of this disclosure.

[0060] Figure 2This describes the effect of feed temperature on the efficiency of acetic acid recovery via reverse osmosis according to certain embodiments of the present disclosure. Detailed Implementation

[0061] In various respects, the methods disclosed herein provide improved methods for recovering one or more byproducts from substituted aromatic hydrocarbon oxidation reactions.

[0062] Other features of the methods of this disclosure will now be described with reference to the accompanying drawings.

[0063] The inventors have determined that certain byproducts of substituted aromatic hydrocarbon oxidation reactions (e.g., acetic acid, methyl acetate, p-xylene) can be recovered more efficiently by cooling one or more streams directed to a high-pressure absorber (e.g., configured to wash a portion of the gas-phase overhead from an oxidation reaction) or a solvent recovery zone (e.g., configured to separate the condensate from the gas-phase overhead of the oxidation reaction via reverse osmosis) through heat exchange with waste scrubbing liquid drawn from a low-pressure scrubber (e.g., configured to wash process exhaust gases). Advantageously, due to partial evaporation in the low-pressure scrubber, the temperature of the waste scrubbing liquid can be several degrees lower than the temperature of the coolant used elsewhere in the process (e.g., for cooling the scrubbing liquid directed to the low-pressure scrubber). Using the waste scrubbing liquid as a coolant elsewhere in the integrated method can advantageously improve the recovery of one or more useful compounds (e.g., for recycling back to the aromatic hydrocarbon oxidation reaction).

[0064] Therefore, one aspect of this disclosure provides a method for recovering byproducts of a substituted aromatics oxidation reaction, the method comprising: in a low-pressure scrubber, contacting a water-rich scrubbing stream with a first gaseous stream containing bromine to form a cooled waste stream and a first scrubbed gaseous stream, the first scrubbed gaseous stream containing a reduced amount of bromine relative to the first gaseous stream. The method further includes one or both of the following: (a) in a high-pressure absorber, contacting a second gaseous stream containing one or more byproducts of the substituted aromatics oxidation reaction with a second solvent-rich wash stream to form a second washed gaseous stream, the second washed gaseous stream containing a reduced amount of one or more byproducts relative to the second gaseous stream, wherein at least one of the second gaseous stream and the second solvent-rich wash stream is cooled by heat exchange with at least a portion of the cooled waste stream before being introduced into the high-pressure absorber; and (b) in a solvent recovery zone, separating at least a portion of a water-rich liquid stream containing one or more byproducts of the substituted aromatics oxidation reaction by reverse osmosis to form a byproduct stream and a purified stream, the purified stream containing a reduced amount of the one or more byproducts relative to the water-rich liquid stream, wherein the water-rich liquid stream is cooled by heat exchange with at least a portion of the cooled waste stream before being introduced into the solvent recovery zone. For example, in some embodiments further described herein, the method includes the contact step (a) in the high-pressure absorber described above. In some embodiments further described herein, the method includes the separation step (b) in the solvent recovery zone described above. In some embodiments further described herein, the method includes both the contact step (a) in the high-pressure absorber described above and the separation step (b) in the solvent recovery zone described above.

[0065] When used herein, the term "byproduct" in the oxidation of substituted aromatics includes any component in the reaction mixture other than the desired reaction product (e.g., an aromatic carboxylic acid). Therefore, as will be appreciated by those skilled in the art, the oxidation of substituted aromatics can include aromatic carboxylic acid reaction products and byproducts such as water, solvents (e.g., monocarboxylic acids such as acetic acid), solvent reaction products, starting materials (e.g., substituted aromatics), partial and intermediate oxidation products, and catalysts. For example, byproducts of the oxidation of p-xylene can include p-xylene, acetic acid, and acetic acid reaction products (e.g., methanol, methyl acetate, methyl bromide).

[0066] The "high-pressure absorber" is configured to operate at a higher pressure than the "low-pressure washer," for example, at least 2 barg or 3 barg higher. In some embodiments further described herein, the "low-pressure washer" operates at a pressure in the range of 0-0.5 barg. In some embodiments further described herein, the "high-pressure absorber" operates at a pressure in the range of 6-15 barg (e.g., 9-12 barg).

[0067] Figure 1 This is a process flow diagram depicting an integrated method for manufacturing and recovering aromatic carboxylic acids, including the recovery of byproducts from the oxidation reaction of substituted aromatic hydrocarbons, according to one embodiment of this disclosure. Used for execution Figure 1 The system of method 100 includes: a reaction zone comprising an oxidation reactor 110 configured for liquid-phase oxidation of the feed to provide a liquid effluent and a gaseous effluent; a crystallization zone 150 configured for forming a solid crude aromatic carboxylic acid from the liquid effluent and comprising one or more crystallizers in series; a solid / liquid separation device 190 configured for separating the solid crude aromatic carboxylic acid (and oxidation byproducts) from the liquid; a mixing zone comprising a purification reaction mixture make-up vessel 200 configured for preparing a mixture of the crude aromatic carboxylic acid in a purification reaction solvent; a purification zone comprising a hydrogenation reactor 210 configured for contacting the crude aromatic carboxylic acid with hydrogen in the presence of a catalyst to form purified aromatic carboxylic acid; a recovery zone comprising a crystallizer 220 configured for forming a slurry stream and a gaseous stream containing the solid purified aromatic carboxylic acid; and a solid / liquid separation device 230 configured for separating the solid purified aromatic carboxylic acid from the liquid.

[0068] Figure 1 The system also includes: a fractionation zone comprising a distillation column 170 configured to separate the gaseous effluent from the reaction zone to provide a bottom stream and a top gaseous stream; a condensation zone comprising condensers 352, 362 and a drum 372 configured to condense the top gaseous stream to provide a condensate containing water and a gaseous effluent; and a high-pressure absorber 380 (e.g. configured to operate at a pressure of 6-15 barg) configured to recover byproducts of the oxidation reaction from the gaseous effluent of drum 372 and form a washed gaseous stream. The system further includes: an emission control zone comprising a preheater 392 and an oxidation device 394 configured to form a high-pressure oxidizing gas; an expander 400 connected to a generator 420 configured to convert energy from the high-pressure oxidizing gas into electrical energy and form an expanded gas; and a low-pressure scrubber 430 (e.g. configured to operate at a pressure of 0-0.5 barg) configured to recover byproducts of the oxidation reaction from the expanded gas.

[0069] However, those skilled in the art will recognize that, Figure 1 The integration of the methods described is intended to be purely representative, and various other integrated and non-integrated configurations can also be used. Figure 1 The liquid and gaseous streams and materials used in the methods described herein can be guided and transferred via suitable transfer lines, conduits, and tubing constructed of materials suitable for process application and safety. It should be understood that specific components may be physically juxtaposed and, where appropriate, may have flexible zones, rigid zones, or a combination of both. Intermediate devices and / or optional treatments may be included in the flow of the guided compound. For example, pumps, valves, mains, gas and liquid flow meters and distributors, sampling and detection devices, and other equipment (e.g., for monitoring, controlling, regulating, and / or redirecting pressure, flow, and other operating parameters) may be present.

[0070] As mentioned above, Figure 1 The integrated method includes an emission control zone comprising a low-pressure scrubber 430. During operation, a first gaseous stream 421 containing bromine (e.g., a gaseous effluent containing expander 400) is contacted in the low-pressure scrubber 430 with a first water-rich scrubbing stream 435 to form a first scrubbed gaseous stream 433 (containing a reduced amount of bromine relative to the first gaseous stream 421) and a cooled waste stream 431. In some embodiments further described herein, the first water-rich scrubbing stream is contacted with the first gaseous stream at a pressure not exceeding 0.5 barg (e.g., 0–0.25 barg). In some embodiments further described herein, the first scrubbed gaseous stream is released to the atmosphere.

[0071] exist Figure 1 In some embodiments, the first water-rich washing stream 435 includes a portion of cooled waste stream 431, which is combined with one or more supplementary streams 437, 439 (e.g., including water and one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium bromide, sodium formate, sodium sulfite, etc.). In some embodiments, a portion of the cooled waste stream 431 is transferred (not shown) to a wastewater treatment area (e.g., including one or more of aerobic and anaerobic treatment) to produce a treated wastewater stream that can be released into the environment.

[0072] In some embodiments further described herein, the temperature of the first water-rich wash stream (e.g., at the inlet of a low-pressure washer) is at least 30°C, for example, at least 32°C. For example, in some such embodiments, the temperature of the first water-rich wash stream is in the range of 32–43°C, 32–39°C, or 32–37°C. For example, in some such embodiments, the water-rich wash stream is cooled to 32–43°C by heat exchange with a coolant containing process cooling water at a temperature of 30–40°C.

[0073] The inventors have noted that, due to partial evaporation in the low-pressure scrubber, the temperature of the waste scrubbing liquid can be several degrees lower than the temperature of the coolant used elsewhere in the process (e.g., for cooling the scrubbing liquid directed to the low-pressure scrubber), and thus can be used to cool one or more process streams to temperatures lower than those achievable using typical process cooling water. Therefore, in some embodiments further described herein, the temperature of the cooled waste stream is at least 2°C (e.g., at least 3°C) lower than the temperature of the first water-rich scrubbing stream.

[0074] In some embodiments further described herein, the first water-rich wash stream is substantially water (e.g., containing at least 80 wt%, at least 90 wt%, or at least 95 wt% water). In some embodiments, the first water-rich wash stream contains water present in an amount of at least 90 wt% (e.g., at least 95 wt%), and one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium bromide, sodium formate, and sodium sulfite present in a combined amount of at least 0.5 wt% (e.g., 1–5 wt%). In some embodiments further described herein, the cooled waste stream contains at least 80 wt%, for example, at least 90 wt%, or at least 95 wt% water.

[0075] Now return to Figure 1 The integrated method involves oxidizing a reaction mixture comprising a feed including a substituted aromatic hydrocarbon, a monocarboxylic acid solvent, water, an oxidation catalyst, and a co-catalyst with oxygen in an oxidation reactor 110 under conditions sufficient to cause the substituted aromatic hydrocarbon to be oxidized to an aromatic carboxylic acid. In some embodiments further described herein, the temperature and pressure of the oxidation reaction are sufficient to maintain a liquid-phase reaction mixture and a high-temperature, high-pressure gas phase in the reaction zone. In some embodiments further described herein, the reaction zone comprises one or more continuously stirred tank reactors at rated pressure.

[0076] The feed comprising substituted aromatic hydrocarbons is introduced into oxidation reactor 110 through one or more inlets, such as inlet 112. In some embodiments further described herein, the feed comprises an aromatic hydrocarbon substituted at one or more sites, wherein at least one substituent can be oxidized to a carboxylic acid group. In some embodiments, the position of the substituent corresponds to the position of the carboxylic acid group of the aromatic carboxylic acid being prepared. In some embodiments, the oxidizable substituent comprises an alkyl group (e.g., methyl, ethyl, and / or isopropyl). In other embodiments, the oxidizable substituent comprises an oxygen-containing group, such as hydroxyalkyl, formyl, aldehyde, and / or ketone. The substituents may be the same or different. The aromatic moiety of the feed compound may be a benzene ring, or it may be bicyclic or polycyclic (e.g., naphthalene ring and / or anthracene ring). In some embodiments, the number of oxidizable substituents on the aromatic moiety of the feed compound is equal to the number of available sites on the aromatic moiety. In other embodiments, the number of oxidizable substituents on the aromatic moiety of the feed is less than all such sites (e.g., 1 to 4 in some embodiments, 2 in some embodiments). In some embodiments further described herein, the feed comprises one or more compounds selected from the following: toluene; ethylbenzene and other alkyl-substituted benzenes; o-xylene; p-xylene; m-xylene; tolueneformaldehyde, methylbenzene, alkylbenzyl alcohol, 1-formyl-4-toluene, 1-hydroxymethyl-4-toluene; methylacetylbenzene; 1,2,4-trimethylbenzene; 1-formyl-2,4-dimethylbenzene; 1,2,4,5-tetramethylbenzene; alkyl, formyl, acyl, and hydroxymethyl 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, etc.); and their partially oxidized derivatives.

[0077] In some embodiments, the substituted aromatic compounds include methyl, ethyl, and / or isopropyl-substituted aromatics. In some embodiments, the substituted aromatic compounds include alkyl-substituted benzenes, o-xylenes, p-xylenes, m-xylenes, and combinations thereof. In some preferred embodiments, the feed comprises p-xylene, and the aromatic carboxylic acid reaction product is terephthalic acid. For example, in some embodiments further described herein, a feed comprising at least 99 wt% p-xylene is continuously charged into the oxidation reactor.

[0078] Water, a monocarboxylic acid solvent, a catalyst, a co-catalyst, and an oxygen source are also introduced into the oxidation reactor 110 via one or more inlets, such as inlet 112 (e.g., individually or in any combination). In some embodiments further described herein, the monocarboxylic acid solvent is acetic acid. In some such embodiments, an aqueous solution of acetic acid (e.g., containing 70–95 wt% acetic acid) is continuously fed into the oxidation reactor. In some embodiments further described herein, the oxidation catalyst comprises at least one heavy metal component (e.g., selected from Co, Mn, V, Mo, Cr, Fe, Ni, Zi, Ce, Hf, etc.). For example, in some embodiments, the oxidation catalyst comprises soluble compounds of cobalt and manganese (e.g., cobalt acetate and manganese acetate). In some such embodiments, cobalt acetate and manganese acetate are continuously fed into the oxidation reactor. In some embodiments further described herein, the co-catalyst comprises a halogen (e.g., bromine). In some such embodiments, hydrogen bromide is continuously fed into the oxidation reactor. In some embodiments further described herein, the oxygen source is air. In some such embodiments, air is continuously fed into the oxidation reaction vessel.

[0079] exist Figure 1 In this embodiment, stirring is provided by the rotation of a mixer 120, the shaft of which is driven by an external power source (not shown). An impeller mounted on the shaft and located within the liquid is configured to provide forces for mixing the liquid and dispersing gas within the liquid, thereby preventing solids from depositing in the lower region of the liquid.

[0080] As described above, the oxidation of the substituted aromatic hydrocarbon yields an aromatic carboxylic acid. In some embodiments further described herein, the aromatic carboxylic acid is a monocarboxylic acid or polycarboxylate having one or more aromatic rings. In some embodiments, the aromatic carboxylic acid contains only one aromatic ring. In other embodiments, the aromatic carboxylic acid contains multiple (e.g., two or more) aromatic rings, which are fused in some embodiments (e.g., naphthalene, anthracene, etc.) and not fused in others. In some embodiments, the aromatic carboxylic acid contains only one carboxylic acid (e.g., -CO2H) component or a salt thereof (e.g., -CO2X, where X is a cationic substance, including but not limited to metal cations, ammonium ions, etc.). In other embodiments, the aromatic carboxylic acid contains multiple (e.g., two or more) carboxylic acid components or salts thereof. In some embodiments further described herein, the aromatic carboxylic acid is selected from terephthalic acid, trimellitic acid, trimellitic acid, phthalic acid, isophthalic acid, benzoic acid, naphthalenedicarboxylic acid, and combinations thereof.

[0081] In some embodiments further described herein, the substituted aromatic hydrocarbon is p-xylene, and the oxidation product is terephthalic acid. In some such embodiments, the oxidation reaction produces one or more partial or intermediate oxidation products, such as 4-carboxybenzaldehyde, 1,4-hydroxymethylbenzoic acid, p-methylbenzoic acid, and benzoic acid. In some such embodiments, the high-temperature, high-pressure gas phase contained in the reactor comprises one or more of the following: a monocarboxylic acid solvent (e.g., acetic acid) and its reaction products (e.g., methyl acetate, methanol), water vapor, p-xylene and its partial or intermediate oxidation products, bromine and its reaction products (e.g., methyl bromide), carbon oxides, nitrogen (e.g., air supplied to the reactor), and unreacted oxygen.

[0082] exist Figure 1 In one embodiment, the liquid reaction mixture 115 is removed from the reaction vessel 110 through the slurry outlet 114 and transferred to one or more crystallizers in series in the crystallization zone 150 to form a solid oxidation product. Conventional methods can be used for the operation of the crystallization zone. Cooling in the crystallizer may be accompanied by pressure relief. One or more crystallizers may be vented to remove the gas phase generated by pressure drop and water vapor from flash vapor phase to heat exchanger (not shown). Various different process operations can be used to recover the carboxylic acid from the crystallization. In some embodiments further described herein, at least a portion of the effluent from the last crystallizer in the crystallization zone is separated to form a stream rich in aromatic carboxylic acids and a stream rich in solvent.

[0083] The slurry stream 151, comprising solid product, from crystallization zone 150 is transferred to a solid-liquid separation device 190 and separated to form a solvent-rich stream 191 and a stream 197 containing crude solid product and rich in aromatic carboxylic acids. In some embodiments, the separation device is a centrifuge, a rotary vacuum filter, or a pressure filter. In some embodiments, the separation device includes a pressure filter configured for solvent exchange (e.g., by positively displacing the mother liquor in the filter cake under pressure with a washing liquid containing water).

[0084] The solvent-rich stream 191 is collected in the mother liquor drum 192. The aromatic carboxylic acid-rich stream 197 is directed to a mixing zone including a reaction mixture replenishment container 202. Stream 197 is mixed and slurried in the replenishment container 202 with a replenishment solvent stream 203 introduced into the container 202 to form a purified reaction mixture 205 containing crude aromatic carboxylic acids. In some embodiments, the replenishment solvent contains water. In some embodiments further described herein, the solvent comprises a portion of a water-rich condensate formed in a condensation zone. In other embodiments, the solvent comprises a liquid phase stream formed in a downstream solid-liquid separator.

[0085] The purified reaction mixture 205 is introduced into the purification reactor 210 of the purification zone. The purification zone may also include a pump and one or more heat exchangers (not shown) configured to preheat the purified mixture introduced into the purification reactor. In some embodiments, the purification reactor is a hydrogenation reactor, and purification in the reactor involves contacting the purified reaction mixture containing crude aromatic carboxylic acids with hydrogen in the presence of a hydrogenation catalyst.

[0086] The purified effluent 211, containing purified aromatic carboxylic acids, is removed from the hydrogenation reactor 210 and transferred to a crystallizer 220 in the crystallization zone downstream of the purification zone. In some embodiments, the crystallization zone comprises two or more crystallizers connected in series. In some embodiments, purified aromatic carboxylic acids and reduced levels of impurities are crystallized from the purified effluent.

[0087] The solid / liquid mixture 221 containing purified carboxylic acid solids formed in the crystallization zone 220 is transferred to the solid-liquid separation device 230 and separated to form a liquid stream 233 and an aromatic carboxylic acid-rich stream 235 containing the purified aromatic carboxylic acid solid.

[0088] A gaseous effluent 111 containing one or more byproducts of the oxidation reaction of substituted aromatic hydrocarbons is removed from the oxidation reactor 110 through an exhaust port 116. In some embodiments further described herein, the gaseous effluent contains one or more byproducts selected from monocarboxylic acid solvents and their reaction products, water vapor, p-xylene and its partial or intermediate oxidation products, bromine and its reaction products, carbon oxides, nitrogen, and unreacted oxygen. For example, in some embodiments, the gaseous effluent contains one or more byproducts selected from acetic acid, methyl acetate, methanol, water vapor, p-xylene and its partial or intermediate oxidation products, methyl bromide, carbon oxides, nitrogen, and unreacted oxygen.

[0089] The gaseous effluent 111 is introduced into distillation column 170 and separated to produce a bottom stream 171 and a gaseous overhead stream 174 containing water vapor and one or more additional byproducts of the oxidation of substituted aromatics. In some embodiments further described herein, the bottom stream contains a monocarboxylic acid. In some such embodiments, the bottom stream contains acetic acid. For example, in some embodiments further described herein, the bottom stream contains at least 70 wt% (e.g., at least 75 wt%, or at least 80 wt%, or at least 85 wt%, or at least 90 wt% or at least 95 wt%) of acetic acid. In some embodiments, the bottom stream also contains up to 25 wt% water (e.g., 5–20 wt%, or 10–20 wt%, or 15–20 wt% water). In some embodiments, the bottom stream further comprises up to 5 wt% (e.g., up to 2.5 wt% or up to 1 wt%) of one or more additional byproducts selected from monocarboxylic acid solvent reaction products, p-xylene and its partial or intermediate oxidation products, and bromine and its reaction products. For example, in some embodiments further described herein, the bottom stream comprises at least 70 wt% (e.g., at least 75 wt% or at least 80 wt%) of acetic acid, up to 25 wt% (e.g., 5–20 wt% or 15–20 wt%) of water, and up to 1 wt% (e.g., 0.1–1 wt% or 0.1–0.5 wt%) of methyl acetate. In some such embodiments, the bottom stream comprises up to 0.5 wt% of methanol and / or methyl bromide.

[0090] In some embodiments further described herein, the gas-phase overhead stream comprises water vapor and one or more additional byproducts selected from monocarboxylic acid solvents and their reaction products, p-xylene and its partial or intermediate oxidation products, bromine and its reaction products, carbon oxides, nitrogen, and unreacted oxygen. For example, in some embodiments, the gas-phase overhead stream comprises water vapor and one or more additional byproducts selected from acetic acid, methyl acetate, methanol, p-xylene and its partial or intermediate oxidation products, methyl bromide, carbon oxides, nitrogen, and unreacted oxygen. In some embodiments further described herein, the gas-phase overhead stream comprises 20–80 wt% (e.g., 40–80 wt% or 45–70 wt%) of water vapor. In some embodiments further described herein, the gas-phase overhead stream comprises one or more of nitrogen, oxygen, carbon oxides, p-xylene, methyl acetate, methanol, and acetic acid, present in a combined amount of 20–80 wt% (e.g., 20–60 wt% or 30–55 wt%) of the stream. For example, in some such embodiments, the gas column overhead stream contains water in an amount of 40–80 wt% (e.g., 45–70 wt%), one or more of nitrogen, oxygen, and carbon oxides in a combined amount of 20–60 wt% (e.g., 30–55 wt%), and one or more of acetic acid, methyl acetate, p-xylene, and methanol in a combined amount of 0.1–10 wt% (e.g., 0.5–5 wt%).

[0091] The bottom stream 171 is returned to the oxidation reactor 110. In the condensation zone, the vapor-phase top stream 174 is partially condensed in the first condenser 352 and then in the second condenser 362 to form a stream 363 containing a water-rich condensate and an uncondensed vapor phase, which is collected in drum 372. In some embodiments further described herein, at least 50 wt% (e.g., at least 60 wt%, 70 wt%, 80 wt%, or 90 wt%) of water vapor present in the vapor-phase top stream is condensed in the condensation zone. In some embodiments further described herein, the water-rich condensate contains at least 80 wt% (e.g., at least 90 wt% or 95 wt%) of water. In some embodiments further described herein, the water-rich condensate contains a monocarboxylic acid solvent (e.g., acetic acid). For example, in some such embodiments, the water-rich condensate contains 1–20 wt% (e.g., 1–15 wt%, 1–10 wt%, or 1–5 wt%) of acetic acid. In some embodiments, the water-rich condensate further comprises one or more monocarboxylic acid solvent reaction products (e.g., methyl acetate and / or methanol). In some such embodiments, the water-rich condensate comprises 1–10 wt% (e.g., 1–7.5 wt% or 1–5 wt%) of methyl acetate and / or methanol.

[0092] exist Figure 1 In one embodiment, the gaseous effluent 375 extracted from drum 372 is cooled in heat exchanger 376 to form a second gaseous stream 377. Therefore, in some embodiments further described herein, the second gaseous stream comprises at least a portion of the gaseous effluent from a condensation zone. In some embodiments further described herein, the second gaseous stream comprises one or more byproducts of substituted aromatic hydrocarbon oxidation reactions selected from monocarboxylic acid solvents and their reaction products, p-xylene and its partial or intermediate oxidation products, bromine and its reaction products, carbon oxides, nitrogen, and unreacted oxygen. For example, in some embodiments, the second gaseous stream comprises one or more byproducts selected from acetic acid, methyl acetate, methanol, p-xylene and its partial or intermediate oxidation products, methyl bromide, carbon oxides, nitrogen, and unreacted oxygen. In some embodiments further described herein, the second gaseous stream comprises one or more of p-xylene, methyl acetate, and acetic acid, present in a combined amount of 1–20 wt% (e.g., 5–20 wt%, 5–15 wt%, 10–20 wt%, or 15–20 wt%) of the stream. In some embodiments further described herein, the second gaseous stream is substantially free of water vapor (e.g., contains less than 1 wt%, less than 0.5 wt%, or even less than 0.1 wt% water vapor).

[0093] In some embodiments further described herein, cooling at least a portion of the gaseous effluent comprises heat exchange with a coolant stream whose temperature is at least 2°C (e.g., at least 3°C) lower than the temperature of the cooled waste stream. In some embodiments, the coolant stream comprises process cooling water at a temperature of 30–40°C (e.g., 30–36°C or 30–34°C). The inventors note that such temperatures typically present in process cooling water limit the achievable temperature of the second gaseous stream to above 30°C, for example, 32–43°C, 32–39°C, or 32–37°C.

[0094] Advantageously, the inventors have determined that cooling the second gaseous stream by exchanging heat with a cooled waste stream from a low-pressure scrubber can improve the recovery of byproducts (e.g., acetic acid, methyl acetate, p-xylene) from the gaseous stream in a high-pressure absorber. Therefore, in some embodiments further described herein, the method includes cooling the second gaseous stream to form a cooled second gaseous stream by exchanging heat with at least a portion of the cooled waste stream, and then contacting the cooled second gaseous stream with a second solvent-rich scrubbing stream in the high-pressure absorber. In some such embodiments, the temperature of the cooled second gaseous stream is at most 30°C (e.g., 22–29°C, 22–28°C, or 22–27°C).

[0095] In some embodiments further described herein, the heated waste stream (i.e., containing the heat-exchanged product of the cooled waste stream) is recycled to the low-pressure scrubber (e.g., to low-pressure scrubber 430 as a supplementary stream 439). In other embodiments, the heated waste stream is transferred to a wastewater treatment area.

[0096] exist Figure 1 In this embodiment, solvent drum 160 contains a solvent-rich liquid fraction. The condensed overhead vapor stream (not shown) from one or more crystallizers in crystallization zone 150, the condensed overhead vapor stream from mother liquor drum 192, and / or supplemental solvent can be transferred as streams 161, 163, 165 to solvent drum 160 (in... Figure 1 In some embodiments, the condensed overhead gas stream and the makeup solvent are transferred to the solvent drum. The liquid effluent 165 from the solvent drum 160 is combined with the effluent 193 from the mother liquor drum 192 and then transferred to the oxidation reactor 110. Therefore, in some embodiments further described herein, the solvent drum contains a solvent monocarboxylic acid (e.g., acetic acid). In some such embodiments, the solvent drum also contains one or more additional byproducts selected from monocarboxylic acid solvent reaction products, water, p-xylene and its partial or intermediate oxidation products, and bromine and its reaction products. For example, in some embodiments further described herein, the solvent drum contains acetic acid, methyl acetate, methyl bromide, and water.

[0097] The liquid effluent 167 extracted from solvent drum 160 is cooled in heat exchanger 162 to form a cooled solvent stream 169, a portion of which is directed as a second solvent-rich wash stream 381 to high-pressure absorber 380. Therefore, in some embodiments further described herein, the second solvent-rich wash stream comprises the liquid effluent from the solvent drum (e.g., containing acetic acid).

[0098] In some embodiments further described herein, the second solvent-rich wash stream comprises at least 80 wt% (e.g., at least 85 wt%, at least 90 wt%, or at least 95 wt%) of acetic acid. In some such embodiments, the second solvent-rich wash stream also comprises one or more additional byproducts selected from monocarboxylic acid solvent reaction products, water, p-xylene and its partial or intermediate oxidation products, and bromine and its reaction products, present in a combined amount of up to 20 wt% (e.g., 1–10 wt%, 5–15 wt%, or 10–20 wt%) of the second solvent-rich wash stream. For example, in some embodiments further described herein, the second solvent-rich wash stream comprises acetic acid, methyl acetate, methyl bromide, and water, present in a combined amount of at least 85 wt% (e.g., at least 90 wt%, at least 95 wt%, or at least 97.5 wt%) of the second solvent-rich wash stream.

[0099] In some embodiments further described herein, the method includes cooling at least a portion of the liquid effluent from the solvent drum (e.g., containing acetic acid) to form the second solvent-rich wash stream. In some embodiments further described herein, cooling at least a portion of the liquid effluent from the solvent drum includes heat exchange with a coolant stream at a temperature at least 2°C (e.g., at least 3°C) higher than the temperature of the cooled waste stream. In some embodiments, the coolant stream comprises process cooling water at a temperature of 30–40°C (e.g., 30–36°C or 30–34°C). The inventors note that such temperatures typically present in process cooling water limit the achievable temperature of the second solvent-rich wash stream to above 30°C, for example, 32–43°C, 32–39°C, or 32–37°C.

[0100] Advantageously, the inventors have determined that cooling the second solvent-rich wash stream by exchanging heat with a cooled waste stream from a low-pressure scrubber can improve the recovery of byproducts (e.g., acetic acid, methyl acetate, p-xylene) from the gaseous stream in a high-pressure absorber. Therefore, in some embodiments further described herein, the method includes cooling the second solvent-rich wash stream by exchanging heat with at least a portion of the cooled waste stream, and then contacting the second gaseous stream with the cooled second solvent-rich wash stream in the high-pressure absorber. In some such embodiments, the temperature of the cooled second gaseous stream is at most 30°C (e.g., 22–29°C, 22–28°C, or 22–27°C). In some such embodiments, the second gaseous stream is also cooled by exchanging heat with at least a portion of the cooled waste stream. In some other embodiments described herein, the contact is performed at a pressure in the range of 6–15 barg (e.g., 6–9 barg, 8–11 barg, 10–13 barg, or 12–15 barg).

[0101] In some embodiments further described herein, the heated waste stream (i.e., containing the heat-exchanged product of the cooled waste stream) is recycled to the low-pressure scrubber (e.g., to low-pressure scrubber 430 as a supplementary stream 439). In other embodiments, the heated waste stream is transferred to a wastewater treatment area.

[0102] exist Figure 1In some embodiments, a portion of the liquid effluent 373 drawn from drum 372 is directed as a second water-rich wash stream 383 to high-pressure absorber 380. Therefore, in some embodiments further described herein, the second water-rich wash stream introduced into the high-pressure absorber comprises at least a portion of water-rich condensate formed in the condensation zone. In some embodiments further described herein, the second water-rich wash stream comprises at least 85 wt% (e.g., at least 90 wt%, at least 95 wt%, or at least 97.5 wt%) of water. In some embodiments further described herein, the second water-rich wash stream comprises one or more byproducts selected from the oxidation of substituted aromatic hydrocarbons, including acetic acid, methyl acetate, and methanol. In some embodiments further described herein, the second water-rich wash stream comprises one or more of methyl acetate, methanol, and acetic acid, present in a combined amount of 1–10 wt% (e.g., 1–8 wt%, 1–6 wt%, or 1–4 wt%) of the stream.

[0103] The second gas stream 377, optionally further cooled in a second heat exchanger (not shown) through indirect contact with at least a portion of the cooled waste stream 187, the second solvent-rich wash stream 381, optionally further cooled in a second heat exchanger (not shown) through indirect contact with at least a portion of the cooled waste stream 187, and the water-liquid stream 383 are introduced into the high-pressure absorber. In the high-pressure absorber 380, the second gas stream 377 is contacted with the second solvent-rich wash stream 381 and the second water-rich wash stream 383 to form a second washed gas stream 385, which contains a reduced amount of one or more byproducts of the substituted aromatics oxidation reaction (i.e., relative to the second gas stream 377).

[0104] In some embodiments further described herein, the second washed gas stream contains reduced amounts of one or more byproducts of the oxidation of substituted aromatic hydrocarbons, selected from monocarboxylic acid solvents and their reaction products, and p-xylene and its partial or intermediate oxidation products. For example, in some such embodiments, the second washed gas stream contains reduced amounts of one or more byproducts selected from acetic acid, methyl acetate, methanol, p-xylene, and its partial or intermediate oxidation products. In some embodiments further described herein, the combined amount of acetic acid, methyl acetate, and p-xylene in the second washed gas stream is at most 20% (e.g., at most 15%, at most 10%, or at most 5%) of the combined amount of acetic acid, methyl acetate, and p-xylene present in the second gas stream.

[0105] The liquid effluent 387 from the high-pressure absorber 380, containing one or more byproducts of the oxidation of substituted aromatics, can be transferred (not shown) to the oxidation reactor 110. Therefore, in some embodiments further described herein, at least a portion of the liquid effluent from the high-pressure absorber containing one or more byproducts of the oxidation of substituted aromatics is transferred to a reaction zone capable of carrying out the substituted aromatics reaction. In some such embodiments, the liquid effluent is transferred directly to the reaction zone. Of course, in other embodiments, the liquid effluent is transferred indirectly to the reaction zone. For example, in some such embodiments, the liquid effluent is transferred to a mother liquor drum, and then the effluent from the mother liquor drum is transferred to the reaction zone.

[0106] The second washed gaseous stream 385 is heated in a preheater 392 to form a preheated stream 393, which is then oxidized in an oxidation unit 394 to produce an oxidized high-pressure gaseous stream 395. The inventors note that unrecovered byproducts of the oxidation reaction of substituted aromatics, including starting materials, solvents, and solvent reaction products (e.g., acetic acid, methyl acetate, and p-xylene), present in the second washed gaseous stream, are effectively removed from the manufacturing process by oxidation and therefore must be “replenished” with fresh feed. The inventors also note that, therefore, by cooling one or more streams directed to a high-pressure absorber as described herein to improve the recovery of such byproducts, the amount of starting materials and / or replenishing solvents required for the process can ideally be reduced.

[0107] The energy from the high-pressure gas stream 395 from oxidation is successfully converted in the expander 400, and the work is converted into electrical energy by the generator 420. The expanded gas from the expander is transferred as a first gaseous stream 421 to a low-pressure scrubber 430 and contacted with a first water-rich scrubbing stream 435 to form a first scrubbed gaseous stream 433 containing a reduced amount of bromine (e.g., suitable for release into the atmosphere) and a cooled waste stream 431 (e.g., suitable for cooling one or more process streams to temperatures below those achievable using typical process cooling water).

[0108] exist Figure 1In one embodiment, a portion of the liquid effluent 373 drawn from drum 372 is cooled in heat exchanger 374 to form a water-rich liquid stream 461. Therefore, in some embodiments further described herein, the water-rich liquid stream introduced into the solvent recovery zone comprises at least a portion of water-rich condensate formed in the condensation zone. In some embodiments further described herein, the water-rich liquid stream comprises at least 85 wt% (e.g., at least 90 wt%, at least 95 wt%, or at least 97.5 wt%) of water. In some embodiments further described herein, the water-rich liquid stream comprises one or more byproducts selected from the oxidation of substituted aromatic hydrocarbons using monocarboxylic acid solvents and their reaction products. For example, in some embodiments, the water-rich liquid stream comprises one or more byproducts selected from acetic acid, methyl acetate, and methanol. In some embodiments further described herein, the water-rich liquid stream comprises one or more of methyl acetate, methanol, and acetic acid, present in a combined amount of 1–10 wt% (e.g., 1–8 wt%, 1–6 wt%, or 1–4 wt%) of the stream.

[0109] In some embodiments further described herein, cooling at least a portion of the water-rich condensate involves heat exchange with a coolant stream at a temperature at least 2°C (e.g., at least 3°C) higher than the temperature of the cooled waste stream. In some embodiments, the coolant stream comprises process cooling water at a temperature of 30–40°C (e.g., 30–36°C or 30–34°C). The inventors note that such temperatures typically present in process cooling water limit the achievable temperature of the water-rich liquid stream to above 30°C, for example, 32–43°C, 32–39°C, or 32–37°C.

[0110] Advantageously, the inventors have determined that cooling the water-rich liquid stream by exchanging heat with a cooled waste stream from a low-pressure scrubber can improve the recovery of byproducts (e.g., acetic acid, methyl acetate) from the water-rich liquid stream in a reverse osmosis unit. Therefore, in some embodiments further described herein, the method includes cooling the water-rich liquid stream to form a cooled water-rich liquid stream by exchanging heat with at least a portion of the cooled waste stream, and then separating the cooled water-rich liquid stream by reverse osmosis in the solvent recovery zone. In some such embodiments, the temperature of the cooled water-rich liquid stream is at most 30°C (e.g., 22–29°C, 22–28°C, or 22–27°C).

[0111] In some embodiments further described herein, the heated waste stream (i.e., containing the heat-exchanged product of the cooled waste stream) is recycled to the low-pressure scrubber (e.g., to low-pressure scrubber 430 as a supplementary stream 439). In other embodiments, the heated waste stream is transferred to a wastewater treatment area.

[0112] The water-rich liquid stream 461 (which is optionally further cooled in a second heat exchanger (not shown) by indirect contact with at least a portion of the cooled waste stream 187) is separated in a reverse osmosis unit 460 to form a byproduct stream 463 and a purified stream 465, the latter containing a reduced amount of one or more byproducts of the substituted aromatics reaction (i.e., relative to the water-rich liquid stream 461).

[0113] In some embodiments further described herein, the purified feed stream contains reduced amounts of one or more byproducts selected from the oxidation of substituted aromatic hydrocarbons using monocarboxylic acid solvents and their reaction products. For example, in some embodiments, the purified feed stream contains one or more byproducts selected from acetic acid, methanol, and methyl acetate. In some embodiments further described herein, the combined amount of acetic acid, methanol, and methyl acetate contained in the second washed gaseous feed stream is at most 15% (e.g., at most 12.5%, at most 10%, or at most 5%) of the combined amount of acetic acid, methanol, and methyl acetate present in the second gaseous feed stream. In some embodiments further described herein, the purified feed stream contains at least 95 wt% (e.g., at least 97.5 wt%, at least 99 wt%, or at least 99.5 wt%) of water.

[0114] In some embodiments further described herein, one or more byproducts selected from the oxidation of substituted aromatic hydrocarbons, including acetic acid, methanol, and methyl acetate, are present in the byproduct stream in a combined amount of at least 90 wt% (e.g., at least 95 wt% or at least 99 wt%).

[0115] In some embodiments further described herein, at least a portion of a byproduct stream containing one or more byproducts of a substituted aromatics oxidation reaction is transferred to a reactor zone capable of carrying out the substituted aromatics reaction.

[0116] Byproduct stream 463 (not shown) can be transferred to oxidation reactor 110. Therefore, in some embodiments further described herein, at least a portion of the byproduct stream containing one or more byproducts of the substituted aromatics oxidation reaction is transferred to a reaction zone capable of carrying out the substituted aromatics reaction. In some such embodiments, the byproduct stream is transferred directly to the reaction zone. Of course, in other embodiments, the byproduct stream is transferred indirectly to the reaction zone. For example, in some such embodiments, the byproduct stream is transferred to a mother liquor drum, and then the effluent from the mother liquor drum is transferred to the reaction zone.

[0117] The purified feed stream 465 (not shown) can be transferred to a wastewater treatment zone (e.g., including one or more of aerobic and anaerobic treatment) to produce a treated wastewater stream that can be released into the environment. The inventors note that unrecovered substituted aromatic hydrocarbon oxidation byproducts present in the purified feed stream, including starting materials, solvents, and solvent reaction products (e.g., acetic acid, methyl acetate, and p-xylene), are effectively removed from the manufacturing process by wastewater treatment (e.g., including aerobic or anaerobic digestion) and therefore must be “replenished” with fresh feed. The inventors also note that, therefore, by cooling the feed stream directed to a solvent recovery zone, including a reverse osmosis unit, as described herein, to improve the recovery of such byproducts, the amount of starting materials and / or replenishment solvent required for the process can ideally be reduced.

[0118] Example

[0119] The following examples illustrate specific embodiments of the invention and its various uses. They are described for illustrative purposes only and are not intended to limit the invention.

[0120] Example 1. High-pressure absorption using a cooled feed stream

[0121] The recovery of p-xylene and methyl acetate from the gaseous stream in the high-pressure absorber was modeled using ASPEN Plus (Aspen Technology Inc., Bedford, MA). In runs 1–9, the temperatures of the gaseous stream and the acetic acid wash stream introduced into the absorber were changed independently. The amounts of p-xylene and methyl acetate remaining in the washed gaseous stream removed from the top of the absorber are shown in Table 1 below, normalized relative to run 1.

[0122] Table 1. High-pressure absorber recovery

[0123]

[0124] As shown in Table 1, further cooling of the gaseous feed stream and / or acetic acid wash stream introduced into the high-pressure absorber improves the recovery of reaction byproducts, including methyl acetate and p-xylene, from the oxidation of substituted aromatics.

[0125] Example 2. Reverse osmosis separation with cooled feed stream

[0126] Historical data on acetic acid recovery from water-rich feed streams were compiled and analyzed to determine the impact of feed stream temperature on reverse osmosis acetic acid recovery. Figure 2 The results shown confirm that by reducing the temperature of the water-rich feed stream (e.g., to 30°C), the acetic acid recovery rate can be increased to greater than 90%.

[0127] Other aspects of this disclosure are provided by the embodiments listed below, which may be combined in any number and in any manner that are not technically or logically inconsistent.

[0128] Implementation Method 1. A method for recovering byproducts of substituted aromatic hydrocarbon oxidation reactions, the method comprising:

[0129] In a low-pressure scrubber, a first water-rich scrubbing stream is contacted with a first gaseous stream containing bromine to form a cooled waste stream and a first scrubbed gaseous stream, the first scrubbed gaseous stream containing a reduced amount of bromine relative to the first gaseous stream; and

[0130] In a high-pressure absorber, a second gaseous stream containing one or more byproducts of the oxidation reaction of substituted aromatics is contacted with a second solvent-rich washing stream to form a second washed gaseous stream, the second washed gaseous stream containing a reduced amount of one or more byproducts relative to the second gaseous stream.

[0131] Prior to being introduced into the high-pressure absorber, at least one of the second gaseous stream and the second solvent-rich washing stream is cooled by heat exchange with at least a portion of the cooled waste stream.

[0132] Implementation 2. The method of Implementation 1 further includes transferring (e.g., directly or indirectly) at least a portion of the liquid effluent from the high-pressure absorber (which contains one or more byproducts of the substituted aromatics oxidation reaction) to a reaction zone where the substituted aromatics oxidation reaction can take place.

[0133] Implementation method 3. The method of implementation method 1 or implementation method 2, further comprising contacting the second gas phase feed stream with the second water-rich washing feed stream in the high-pressure absorber.

[0134] Implementation method 4. The method described in any one of implementation methods 1-3, comprising:

[0135] The second gaseous stream is cooled to form a cooled second gaseous stream by heat exchange with at least a portion of the cooled waste stream; then

[0136] The cooled second gaseous stream is brought into contact with a second solvent-rich washing stream in the high-pressure absorber.

[0137] Implementation method 5. The method of implementation method 4, further comprising:

[0138] In the reaction zone, the feed containing substituted aromatics is oxidized in the presence of an oxidation catalyst and a monocarboxylic acid solvent under reaction conditions suitable for the formation of crude aromatic carboxylic acids.

[0139] In the fractionation zone, at least a portion of the gaseous effluent from the reaction zone is separated to form a bottom stream and a top stream, the top stream containing water vapor and one or more additional byproducts of the oxidation of substituted aromatics.

[0140] In the condensation zone, a portion of the gas-phase column overhead stream is condensed to form a water-rich condensate; and

[0141] At least a portion of the gaseous effluent from the condensation zone (which contains one or more byproducts) is cooled to form the second gaseous stream.

[0142] Embodiment 6. The method of Embodiment 5, wherein cooling at least a portion of the gaseous effluent comprises exchanging heat with a coolant stream whose temperature is at least 2°C (e.g., at least 3°C) higher than the temperature of the cooled waste stream.

[0143] Implementation Method 7. The method described in any one of Implementation Methods 1-3, comprising:

[0144] The second solvent-rich wash stream is cooled to form a cooled second solvent-rich wash stream by heat exchange with at least a portion of the cooled waste stream; then

[0145] The second gaseous stream is brought into contact with a cooled, second solvent-rich washing stream in the high-pressure absorber.

[0146] Embodiment 8. The method of Embodiment 7 further includes cooling at least a portion of the liquid effluent (which contains, for example, acetic acid) from the solvent drum to form the second solvent-rich washing stream.

[0147] Embodiment 9. The method of Embodiment 8, wherein cooling at least a portion of the liquid effluent comprises exchanging heat with a coolant stream whose temperature is at least 2°C (e.g., at least 3°C) higher than the temperature of the cooled waste stream.

[0148] Implementation 10. The method of any one of Implementations 1-9, wherein the first gaseous stream comprises at least a portion of the second washed gaseous stream.

[0149] Implementation method 11. The method of implementation method 10, further comprising:

[0150] In the preheating zone, at least a portion of the second washed gaseous stream is heated to form a preheated gaseous stream;

[0151] In the oxidation unit, at least a portion of the preheated gaseous stream is oxidized to produce an oxidized, high-pressure gaseous stream; and

[0152] In an expander, at least a portion of the oxidized high-pressure gaseous stream is expanded to form the first gaseous stream.

[0153] Implementation method 12. The method of any one of implementation methods 1-11, further comprising:

[0154] In the solvent recovery zone, at least a portion of an aqueous-rich liquid stream containing one or more byproducts of the substituted aromatic hydrocarbon oxidation reaction is separated by reverse osmosis to form a byproduct stream and a purified stream, the purified stream containing a reduced amount of the one or more byproducts relative to the aqueous-rich liquid stream.

[0155] The water-rich liquid stream is cooled by heat exchange with at least a portion of the cooled waste stream before being introduced into the recycling area.

[0156] Implementation Method 13. A method for recovering byproducts of substituted aromatic hydrocarbon oxidation reactions, the method comprising:

[0157] In a low-pressure scrubber, a first water-rich scrubbing stream is contacted with a first gaseous stream containing bromine to form a cooled waste stream and a first scrubbed gaseous stream, the first scrubbed gaseous stream containing a reduced amount of bromine relative to the first gaseous stream; and

[0158] In the solvent recovery zone, at least a portion of an aqueous-rich liquid stream containing one or more byproducts of the substituted aromatic hydrocarbon oxidation reaction is separated by reverse osmosis to form a byproduct stream and a purified stream, the purified stream containing a reduced amount of the one or more byproducts relative to the aqueous-rich liquid stream.

[0159] The water-rich liquid stream is cooled by heat exchange with at least a portion of the cooled waste stream before being introduced into the recycling area.

[0160] Embodiment 14. The method of Embodiment 12 or Embodiment 13 further includes transferring at least a portion of the byproduct stream (which contains one or more byproducts of the substituted aromatic oxidation reaction) to a reaction zone capable of carrying out the substituted aromatic oxidation reaction.

[0161] Implementation method 15. The method of any one of implementation methods 12-14, further comprising:

[0162] In the reaction zone, the feed containing substituted aromatics is oxidized in the presence of an oxidation catalyst and a monocarboxylic acid solvent under reaction conditions suitable for the formation of crude aromatic carboxylic acids.

[0163] In the fractionation zone, at least a portion of the gaseous effluent from the reaction zone is separated to form a bottom stream and a top stream, the top stream containing water vapor and one or more additional byproducts of the oxidation of substituted aromatics.

[0164] In the condensation zone, a portion of the gas-phase column overhead stream is condensed to form a water-rich condensate containing one or more byproducts; and

[0165] At least a portion of the water-rich condensate containing one or more byproducts is cooled to form the water-rich liquid stream.

[0166] Embodiment 16. The method of Embodiment 15, wherein cooling at least a portion of the water-rich condensate comprises exchanging heat with a coolant stream whose temperature is at least 2°C (e.g., at least 3°C) higher than the temperature of the cooled waste stream.

[0167] Implementation 17. The method of any one of Implementations 1-16, further comprising releasing at least a portion of the first washed gaseous stream into the atmosphere.

[0168] Embodiment 18. The method of any one of Embodiments 1-17, wherein the first water-rich washing stream has a temperature of 32–43°C.

[0169] Embodiment 19. The method of any one of Embodiments 1-18, wherein the temperature of the cooled waste stream is at least 2°C (e.g., at least 3°C) lower than the temperature of the first water-rich washing stream.

[0170] Embodiment 20. The method of any one of Embodiments 1-19, wherein the substituted aromatic hydrocarbon oxidation reaction is the oxidation of p-xylene to form terephthalic acid.

[0171] Embodiment 21. The method of any one of Embodiments 1-20, wherein one or more byproducts include acetic acid, methyl acetate, methanol and / or p-xylene.

[0172] Implementation Method 22. A system for recovering byproducts of substituted aromatic hydrocarbon oxidation reactions, the system comprising:

[0173] A low-pressure scrubber that can contact a first water-rich scrubbing stream with a first gaseous stream containing bromine to form a cooled waste stream and a first scrubbed gaseous stream, the first scrubbed gaseous stream containing a reduced amount of bromine relative to the first gaseous stream.

[0174] A heat exchanger capable of cooling the second solvent-rich wash stream by exchanging heat with at least a portion of the cooled waste stream to form a cooled second solvent-rich wash stream; and

[0175] A high-pressure absorber is capable of contacting a second gaseous stream containing one or more byproducts of the oxidation reaction of substituted aromatic hydrocarbons with the cooled second solvent-rich washing stream to form a second washed gaseous stream, the second washed gaseous stream containing a reduced amount of one or more byproducts relative to the second gaseous stream.

[0176] Implementation Method 23. A system for recovering byproducts of substituted aromatic hydrocarbon oxidation reactions, the system comprising:

[0177] A low-pressure scrubber that can contact a first water-rich scrubbing stream with a first gaseous stream containing bromine to form a cooled waste stream and a first scrubbed gaseous stream, the first scrubbed gaseous stream containing a reduced amount of bromine relative to the first gaseous stream.

[0178] A heat exchanger capable of cooling a second gaseous stream containing one or more byproducts of a substituted aromatics oxidation reaction by exchanging heat with at least a portion of the cooled waste stream to form a cooled second gaseous stream; and

[0179] A high-pressure absorber is capable of contacting the cooled second gas stream with a second solvent-rich washing stream to form a second washed gas stream, the second washed gas stream containing a reduced amount of one or more byproducts relative to the second gas stream.

[0180] Implementation Method 24. A system for recovering byproducts of substituted aromatic hydrocarbon oxidation reactions, the system comprising:

[0181] A low-pressure scrubber that can contact a first water-rich scrubbing stream with a first gaseous stream containing bromine to form a cooled waste stream and a first scrubbed gaseous stream, the first scrubbed gaseous stream containing a reduced amount of bromine relative to the first gaseous stream.

[0182] A heat exchanger capable of cooling a water-rich liquid stream containing one or more byproducts of a substituted aromatic hydrocarbon oxidation reaction by exchanging heat with at least a portion of the cooled waste stream, to form a cooled water-rich liquid stream; and

[0183] A reverse osmosis unit capable of separating at least a portion of the cooled, water-rich liquid stream by reverse osmosis to form a byproduct stream and a purified stream, the purified stream containing a reduced amount of one or more byproducts relative to the water-rich liquid stream.

[0184] The above detailed description and accompanying drawings are provided by way of explanation and illustration and are not intended to limit the scope of the claims. Many variations of the presently preferred embodiments shown herein will be apparent to those skilled in the art and remain within the scope of the claims and their equivalents.

[0185] It should be understood that the elements and features recited in the claims can be combined in different ways to produce new claims that also fall within the scope of this disclosure. Therefore, although dependent claims are subordinate to only a single independent or dependent claim, it should be understood that such dependent claims may be optionally subordinated to any prior independent or dependent claim in alternative schemes, and such new combinations should be understood to form part of this specification.

Claims

1. A process for recovering byproducts of a substituted arene oxidation reaction, the process comprising: contacting a first water-rich scrubbing stream with a first gas phase stream comprising bromine in a low pressure scrubber operating at a pressure in the range of 0-0.5 barg to form a cooled waste stream and a first scrubbed gas phase stream comprising a reduced amount of bromine relative to the first gas phase stream, wherein the temperature of the cooled waste stream is at least 2°C lower than the temperature of the first water-rich scrubbing stream; the process further comprising one or both of: a) contacting a second gas phase stream comprising one or more byproducts of a substituted arene oxidation reaction with a second solvent-rich scrubbing stream in a high pressure absorber to form a second scrubbed gas phase stream comprising a reduced amount of the one or more byproducts relative to the second gas phase stream, wherein at least one of the second gas phase stream and the second solvent-rich scrubbing stream is cooled by heat exchange with at least a portion of the cooled waste stream prior to introduction to the high pressure absorber; and b) separating at least a portion of a water-rich liquid stream comprising one or more byproducts of a substituted arene oxidation reaction by reverse osmosis in a solvent recovery zone to form a byproduct stream and a purified stream comprising a reduced amount of the one or more byproducts relative to the water-rich liquid stream, wherein the water-rich liquid stream is cooled by heat exchange with at least a portion of the cooled waste stream prior to introduction to the recovery zone.

2. The process of claim 1, further comprising diverting at least a portion of a high pressure absorber liquid effluent comprising one or more byproducts of a substituted arene oxidation reaction to a reaction zone capable of carrying out a substituted arene oxidation reaction.

3. The process of claim 1, further comprising contacting the second gas phase stream with a second water-rich scrubbing stream in the high pressure absorber.

4. The process of any one of claims 1-3, comprising: cooling the second gas phase stream by heat exchange with at least a portion of the cooled waste stream to form a cooled second gas phase stream; then contacting the cooled second gas phase stream with the second solvent-rich scrubbing stream in the high pressure absorber.

5. The process of claim 4, further comprising: oxidizing a feed comprising a substituted arene in the presence of an oxidation catalyst and a monocarboxylic acid solvent in a reaction zone under reaction conditions suitable to form a crude aromatic carboxylic acid; separating at least a portion of a gas phase effluent of the reaction zone in a fractionation zone to form a bottoms stream and a gas phase overhead stream comprising water vapor and one or more additional byproducts of a substituted arene oxidation reaction; condensing a portion of the gas phase overhead stream in a condensation zone to form a water-rich condensate; and cooling at least a portion of the condensation zone gas phase effluent comprising one or more byproducts to form the second gas phase stream.

6. The process of claim 5, wherein cooling at least a portion of the gas phase effluent comprises heat exchange with a coolant stream having a temperature at least 2 °C greater than a temperature of the cooled waste stream.

7. The process of any one of claims 1-3, comprising: cooling the second solvent-rich scrubbing stream by heat exchange with at least a portion of the cooled waste stream to form a cooled second solvent-rich scrubbing stream; and then contacting the second gas phase stream with the cooled second solvent-rich scrubbing stream in the high pressure absorber.

8. The process of claim 7, further comprising cooling at least a portion of a liquid effluent of a solvent drum to form the second solvent-rich scrubbing stream.

9. The process of claim 8, wherein cooling at least a portion of the liquid effluent comprises heat exchange with a coolant stream having a temperature at least 2 °C greater than a temperature of the cooled waste stream.

10. The process of claim 1, comprising: cooling the water-rich liquid stream by heat exchange with at least a portion of the cooled waste stream to form a cooled water-rich liquid stream; then separating the cooled water-rich liquid stream by reverse osmosis in the solvent recovery zone.

11. The process of claim 10, further comprising diverting at least a portion of the byproduct stream comprising one or more byproducts of a substituted aromatic hydrocarbon oxidation reaction to a reaction zone capable of performing a substituted aromatic hydrocarbon oxidation reaction.

12. The process of claim 10 or claim 11, further comprising: oxidizing a feed comprising a substituted aromatic hydrocarbon in the presence of an oxidation catalyst and a monocarboxylic acid solvent at reaction conditions suitable for forming a crude aromatic carboxylic acid in a reaction zone; separating at least a portion of a gas phase effluent of the reaction zone to form a bottoms stream and a gas phase overhead stream comprising water vapor and one or more additional byproducts of a substituted aromatic hydrocarbon oxidation reaction in a fractionation zone; condensing a portion of the gas phase overhead stream to form a water-rich condensate comprising one or more byproducts in a condensation zone; and cooling at least a portion of the water-rich condensate comprising one or more byproducts to form the water-rich liquid stream.

13. The process of claim 12, wherein cooling at least a portion of the water-rich condensate comprises heat exchange with a coolant stream having a temperature at least 2 °C greater than a temperature of the cooled waste stream.

14. The process of any one of claims 1-3, wherein the first gas phase stream comprises at least a portion of the second scrubbed gas phase stream.

15. The process of claim 14, further comprising: heating at least a portion of the second scrubbed gas phase stream to form a preheated gas phase stream in a preheating zone; oxidizing at least a portion of the preheated gas phase stream to produce an oxidized high pressure gas phase stream in an oxidation device; and expanding at least a portion of the oxidized high pressure gas phase stream to form the first gas phase stream in an expander. ​ 16. The process of any one of claims 1-3, further comprising releasing at least a portion of the first scrubbed gas phase stream to the atmosphere.

17. The process of any one of claims 1-3, wherein the first water-enriched scrubbing stream has a temperature of 32-43 °C.

18. The process of any one of claims 1-3, wherein the temperature of the cooled waste stream is at least 3 °C lower than the temperature of the first water-enriched scrubbing stream.

19. The process of any one of claims 1-3, wherein the substituted arene oxidation reaction is oxidation of para-xylene to form terephthalic acid.

20. The process of any one of claims 1-3, wherein the one or more byproducts comprise acetic acid, methyl acetate, methanol, and / or para-xylene.

21. A system for recovering byproducts of a substituted arene oxidation reaction, the system comprising: a low pressure scrubber operating at a pressure in the range of 0-0.5 barg and capable of contacting a first water-enriched scrubbing stream with a first gas phase stream comprising bromine to form a cooled waste stream and a first scrubbed gas phase stream, the first scrubbed gas phase stream comprising a reduced amount of bromine relative to the first gas phase stream, wherein the temperature of the cooled waste stream is at least 2 °C lower than the temperature of the first water-enriched scrubbing stream; the system further comprising one or both of: a) a high pressure absorber capable of contacting a second gas phase stream comprising one or more byproducts of a substituted arene oxidation reaction with a second solvent-enriched scrubbing stream to form a second scrubbed gas phase stream, the second scrubbed gas phase stream comprising a reduced amount of the one or more byproducts relative to the second gas phase stream, and at least one of a heat exchanger capable of cooling the second gas phase stream prior to introduction to the high pressure absorber by heat exchange with at least a portion of the cooled waste stream; and a heat exchanger capable of cooling the second solvent-enriched scrubbing stream prior to introduction to the high pressure absorber by heat exchange with at least a portion of the cooled waste stream; and b) a recovery zone comprising a reverse osmosis device capable of separating at least a portion of the water-enriched liquid stream comprising one or more byproducts of a substituted arene oxidation reaction by reverse osmosis to form a byproduct stream and a purified stream, the purified stream comprising a reduced amount of the one or more byproducts relative to the water-enriched liquid stream, and a heat exchanger capable of cooling the water-enriched liquid stream prior to introduction to the recovery zone by heat exchange with at least a portion of the cooled waste stream. ​ ​

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