Process for removal of benzoic acid from an oxidizer purge stream

The present invention relates to the removal of impurities, in particular benzoic acid, from a mother liquor produced in the synthesis of carboxylic acid, usually terephthalic acid. The present invention further relates to the removal of impurities, in particular benzoic acid, from the benzoic acid containing stream produced in the synthesis of carboxylic acid.

BACKGROUND OF THE INVENTION [0002] Terephthalic acid is industrially produced by oxidation of para-xylene in the presence of a catalyst such as, for example, Co, Mn, Br and a solvent. Terephthalic acid used for the production of fibers, films and polyester resins must be further treated to remove impurities formed as a result of para-xylene oxidation.

[0003] Terephthalic acid (TPA) is an intermediate in the production of polyesters for plastics and applications in fibers. In industrial ways

0 In the production of TPA, heavy metal-catalyzed p-xylene oxidation is often used, usually with a bromide promoter in acetic acid as a solvent. Due to the limited solubility of TPA in acetic acid under practical oxidation conditions, a TPA crystal suspension is usually formed in the oxidation reactor. The TPA slurry in the oxidation reactor is usually removed from the reactor and

5 solid TPA is separated from the mother liquor from the oxidation reactor by conventional solid-liquid separation methods. The mother liquor from the oxidation reactor, containing most of the catalyst and promoter used in this process, is recycled to the oxidation reactor. In addition to the catalyst and promoter, the mother liquor stream from the oxidation reactor also contains dissolved TPA and many

0 by-products and impurities. These by-products and impurities are partly formed from the fine impurities present in the p-xylene feed stream. Other impurities result from incomplete oxidation of p-xylene, resulting in partially oxidized products. Still other by-products are formed as a result of competitive side reactions occurring during the oxidation of p-xylene to terephthalic acid.

[0004] Solid TPA undergoes a solid-liquid separation that uses fresh solvent to remove most of the liquid components from the mother liquor from the oxidation reactor. After drying, solid TPA is contaminated by impurities that were present in the mother liquor from the oxidation reactor because they can pass to solid TPA. Impurities also occur as occlusions in the TPA crystal structure and as a result of incomplete removal of mother liquor from the oxidation reactor by washing with fresh solvent.

[0005] Many of the impurities in the recycle stream of mother liquor from the oxidation reactor are relatively inert to further oxidation.

Such impurities include, for example, isophthalic acid, phthalic acid and trimellitic acid. There are also impurities that can undergo further oxidation, such as, for example, 4-carboxybenzaldehyde, p-toluylic acid and p-tolualdehyde. Non-oxidative impurities usually accumulate in the mother liquor from the oxidation reactor upon recycling. The concentration of these inert impurities increases in the mother liquor from the oxidation reactor until equilibrium is reached, whereby the rate of removal of each impurity by the TPA product balances the rate of formation and the rate of addition to the oxidation process. The typical level of pollution in industrial raw TPA prevents its direct

0 use in most applications in polymers.

[0006] Typically, crude TPA is purified by conversion of dimethyl ester or by dissolution in water with subsequent hydrogenation over standard hydrogenation catalysts. Later, additional oxidation treatment was used to produce TPA of polymer-grade quality. It is desirable

5 minimizing the concentration of impurities in the mother liquor and thus facilitating subsequent TPA purification. In some cases, it is not possible to produce purified TPA of polymer-grade quality if certain methods for removing impurities from the mother liquor stream from the oxidation reactor are not used. [0007] WO 9730963 (A1) discloses a method for producing an aromatic carboxylic acid comprising oxidizing an aromatic carboxylic acid precursor in an aqueous liquid phase containing a lower aliphatic carboxylic acid in the presence of a heavy metal catalyst system, removing the aromatic carboxylic acid suspension from the reaction mixture in the mother liquor containing mainly aliphatic acid, subjecting the suspension to separation of solids from liquids to recover crystals of aromatic carboxylic acid, recycling of the first fraction of the mother liquor obtained to the oxidation reaction, concentration of the second fraction of the separated mother liquor to remove the aliphatic acid and removal or processing of the concentrated residue, characterized in that the second fraction mother liquor is subjected to separation of solids from liquid before its concentration.

[0008] GB 2067563 (A) discloses a method for the synthesis of terephthalic acid comprising oxidizing p-xylene with oxygen in an acetic acid solution in the presence of a catalyst system, separating solid terephthalic acid from the mother liquor from the reaction, treating the mother liquor to reduce the water content therein, and concentrating at least part of the lye obtained to remove 70 to 90% of the acetic acid it contains, in which said mother liquor is cooled below the toilet, for precipitation of the solid phase, the solid phase is separated from the remaining liquid phase containing organic impurities and at least part of the solid phase is recycled to the synthesis zone; the remaining liquid phase is extracted with water or an aqueous acetic acid solution in the presence of a co-adjuvant selected from p-xylene, isobutyl acetate and sec-butyl acetate to form a heavy phase that separates, and at least part of the heavy phase is recycled to the synthesis zone.

[0009] One method for removing impurities from the recycle stream, which is often used in the chemical processing industry, is to isolate or remove some of the recycle stream. The removed stream is usually discarded or, if economically justified, subjected to various treatments to remove unwanted impurities, isolating valuable components. One example of such a method is US Pat. No. 4,939,297. The amount of material removed to control contamination depends on the method; however, 10-40 wt.% removal is usually sufficient to produce TPA suitable as a raw material for industrial polymer production. total mother liquor stream from the oxidation reactor. In the production of TPA, the percentage of mother liquor stream removed from the oxidation reactor necessary to maintain an acceptable concentration of impurities, combined with the economic value of the metal catalyst and solvent components in the stream removed from the oxidation reactor, makes simple ejection of the stream removed from the oxidation reactor economically disadvantageous . There is therefore a need for a process in which substantially all of the valuable metal catalyst and acetic acid contained in the stream removed from the oxidation reactor are recovered, and most of the impurities contained in the stream removed from the oxidation reactor are removed. The metal catalyst can be recovered in active form suitable for reuse by directly recycling to the p-xylene oxidation step.

[0010] One of the benefits of the present invention is the energy and cost savings compared to the extraction removal method described earlier.

[0011] Another benefit of the present invention is its performance over extraction methods using extraction in relation to the utility of the stream or solvent streams recycled to the TPA process. The main reason for using the liquid extraction process is based on the assumption that the introduction of any aromatic impurities into the oxidation process of p-xylene to produce terephthalic acid has an adverse effect on the quality of powdered terephthalic acid (e.g., yellow color). It was therefore assumed that it was necessary to remove a wide range of aromatic impurities such as those obtained by the extraction of liquids to obtain the appropriate quality of terephthalic acid powder.

[0012] In one embodiment of the present invention, however, a relatively simple method of separating benzoic acid from the aqueous solvent has been used. The yield of the process relative to benzoic acid is high because benzoic acid has a higher volatility (higher vapor pressure) than most identified aromatic impurities in the production of carboxylic acid, usually terephthalic acid. Down

0 These aromatic impurities include trimellitic acid, isophthalic acid, stilbenes and anthraquinones. It is therefore quite surprising that removal of benzoic acid and leaving other known impurities that have a natural color is sufficient to produce carboxylic acid, usually terephthalic acid, of suitable quality.

SUMMARY OF THE INVENTION [0013] In a first embodiment of the present invention, a method of producing a benzoic acid stream is provided. This method includes:

0 (a) subjecting the stream removed from the oxidation reactor to evaporation in a main evaporation zone, forming a vapor stream and a highly concentrated removed slurry;

(b) filtration of the highly concentrated suspension removed in the solid-liquid separation zone, forming a filter cake and mother liquor, said solid-liquid separation zone comprising at least one device selected from the group consisting of pressure belt filters, filter presses, centrifuges, pressure plate filters and cross flow filters;

(c) washing the filter cake with a washing stream in said solid-liquid separation zone, forming a washed cake and filtrate after washing;

(d) subjecting the mother liquor to evaporation in a evaporation zone, forming high-solvent vapors; and (e) subjecting the high-solvent vapor to distillation in a separation zone, forming a high-solvent stream and a high-benzoic acid stream.

[0014] In another embodiment of the present invention there is provided a method of producing a benzoic acid stream.

[0015] This method includes:

(a1) subjecting the stream removed from the oxidation reactor to evaporation in a first evaporation zone, forming a vapor stream and concentrated removed slurry;

(a2) subjecting the concentrated removed suspension to evaporation in a second evaporation zone, forming a stream with a high solvent content and a highly concentrated removed suspension;

0 (b) filtration of the highly concentrated suspension removed in the solid-liquid separation zone, forming a filter cake and mother liquor, said solid-liquid separation zone comprising at least one device selected from the group consisting of pressure belt filters, filter presses, centrifuges, pressure plate filters and cross flow filters;

5 (c) washing the filter cake with a washing stream in a solid-liquid separation zone to form a washed filter cake and a filtrate after washing, the solid-liquid separation zone comprising at least one pressure filtration device;

(d) subjecting the mother liquor to evaporation in a evaporation zone, forming

0 high solvent content vapors; and (e) subjecting the high solvent vapor to distillation in a separation zone, forming a high solvent stream and a high benzoic acid stream; wherein the high benzoic acid stream contains at least 60% by weight of benzoic acid.

BRIEF DESCRIPTION OF THE DRAWINGS [0016]

Figure 1 illustrates various embodiments of the invention, showing a method for recovering benzoic acid from stream 101 removed from the oxidation reactor.

Figure 2 shows an embodiment of the process taking place in the solid-liquid separation zone 151, wherein the solid-liquid separation zone comprises a filtration zone

153, a washing zone 155 and optionally a drainage zone 157.

Figure 3 shows an embodiment of the invention in which a rotary drum pressure filter is used in the solid-liquid separation zone.

Figure 4 shows an embodiment of the invention, showing a method for recovering benzoic acid from stream 101 removed from the oxidation reactor and using the main evaporation zone 125.

Figure 5 shows an embodiment not in accordance with the invention in which recovery of benzoic acid from stream 347 containing benzoic acid is shown.

0 DESCRIPTION OF THE INVENTION:

[0017] In one embodiment of the present invention, a method of separating benzoic acid from stream 101 removed from the oxidation reactor is provided, as shown in figure 1.

[0018] Step (a) comprises subjecting the stream 101 removed from the oxidation reactor to evaporation in a first evaporation zone 121, forming a steam stream 104 and a concentrated removed suspension 105.

[0019] In an embodiment of the invention, the stream 101 removed from the oxidation reactor is removed from the carboxylic acid synthesis process by oxidation. Stream 101 removed from

0 The oxidation reactor is a stream fed into this process. In an embodiment of the invention, the stream 101 removed from the oxidation reactor contains at least one carboxylic acid, at least one solvent, at least one metal catalyst, and impurities. The impurities contain at least one impurity selected from the group consisting of organic bromides, oxidized metals, by-products of the oxidation of p-xylene, and impurities resulting from impurities of p-xylene. Organic bromides can be used as promoters in the oxidation reaction. Examples of oxidized metals are iron and chromium compounds that inhibit, reduce or completely destroy the activity of the metal catalyst. In addition to the catalyst and promoter, stream 101 removed from the oxidation reactor also contains by-products and impurities. These by-products and impurities are partly formed from the fine impurities present in the p-xylene feed stream. Other impurities result from incomplete oxidation of p-xylene, resulting in partially oxidized products. Still other by-products are formed as a result of competitive side reactions occurring during the oxidation of p-xylene to terephthalic acid.

[0020] Carboxylic acids include any aromatic carboxylic acids produced by controlled oxidation of an organic substrate. Such aromatic carboxylic acids include compounds having at least one carboxylic acid group attached to a carbon atom that is part of an aromatic ring, preferably having at least 6 carbon atoms, even more preferably having only carbon atoms. Suitable examples of such aromatic rings include benzene, biphenyl, terphenyl, naphthalene and other fused carbon aromatic rings. Examples of suitable carboxylic acids include

0 terephthalic acid, benzoic acid, p-toluic acid, isophthalic acid, trimellitic acid, naphthalene dicarboxylic acid, 2,5-diphenyl terephthalic acid and mixtures thereof.

[0021] Suitable solvents include aliphatic monocarboxylic acids, preferably containing 2 to 6 carbon atoms, or benzoic acid and mixtures thereof, and mixtures of these compounds with water. The solvent is preferably acetic acid in a mixture with water in a ratio of about 5: 1 to about 25: 1, preferably from about 8: 1 to about 20: 1. Throughout the description, acetic acid will be referred to as the solvent. However, it should be understood that any other suitable solvents, for example previously disclosed, may also be used.

[0022] In the first step of the present method, the stream 101 removed from the oxidation reactor is concentrated by conventional methods in a first evaporation zone 121 comprising at least one evaporator, forming a vapor stream 104 and a concentrated removed suspension 105. In an embodiment of the invention the evaporator operates at atmospheric pressure or slightly higher from atmospheric, usually from 1x10⁵ Pa (1 atmosphere) up to 1x10⁶ Bye (10 atmospheres). The vapor stream 104 mostly contains water and solvent, and the concentrated slurry removed 105 contains the remaining water and solvent that was not removed from stream 101 removed from the oxidation reactor. In this document, "most" means above 50% by weight. In an embodiment of the invention, 50% by weight is removed by evaporation. (weight percent) up to 80 wt. solvent and water, usually acetic acid and water, present in stream 101 removed from the oxidation reactor.

[0023] Step (a1) comprises subjecting the concentrated removed suspension 105 to evaporation in a second evaporation zone 150, forming a high solvent stream

144 and highly concentrated suspension removed 145.

[0024] In an embodiment of the invention, the second evaporation zone 150 comprises at least one evaporator operating under vacuum. In an embodiment of the invention, the evaporation may take place at a temperature of 20 ° C to 70 ° C; another range is 30 ° C to 50 ° C. In an embodiment of the invention, the combination of evaporators 121 and 150 operates such that the stream removed from the oxidation reactor, which shows stream 101, is concentrated to a state in which 75 wt.% Of stream 101 removed from the oxidation reactor is removed. up to 99 wt. solvent and water, usually acetic acid and water, forming a highly concentrated suspended suspension 145. In another embodiment of the invention, the other operating range of the combination of evaporators 121 and 150 operates in such a way that the stream removed from the oxidation reactor, which shows stream 101, is concentrated to a state in which 85 wt.% Of stream 101 removed from the oxidation reactor is removed. up to 99 wt. solvent and water, usually acetic acid and water, forming a highly concentrated suspended suspension 145.

[0025] In another embodiment of the invention, the first evaporation zone 121 and the second evaporation zone may be combined into a main evaporation zone 125, as shown in figure 4. The main evaporation zone 125 comprises at least one evaporator. The evaporator or evaporators in the main evaporation zone 125 operate at a temperature and pressure sufficient to remove at least a total of 75% by weight of the solvent and water from stream 101 removed from the oxidation reactor. In another embodiment of the invention, the evaporator or evaporators in the main evaporation zone 125 operate at a temperature and pressure sufficient to remove at least a total of 85% by weight of the solvent and water from the stream removed from the oxidation reactor. In another embodiment of the invention, the evaporator or evaporators in the main evaporation zone 125 operate at a temperature and pressure sufficient to remove at least a total of

90% by weight of the solvent and water from stream 101 removed from the oxidation reactor. In another embodiment of the invention, the evaporator or evaporators in the main evaporation zone 125 operate at a temperature and pressure sufficient to remove at least a total of 95% by weight of the solvent and water from the stream removed from the oxidation reactor.

[0026] The ranges given in the present disclosure and the following claims should be understood to specifically disclose the entire scope, not just the endpoint or points. For example, disclosure of the range 0 to 10 should be understood to specifically disclose 2, 2.5, 3.17 and all other numbers in the range, not just 0 and 10.

[0027] In an embodiment of the invention, the state of the highly concentrated slurry being removed 145 may be a mixture of solids and a liquid containing only enough solvent to be pumpable.

[0028] Step (b) comprises filtering the highly concentrated removed suspension 145 in the solid-liquid separation zone 151, forming a filter cake 154 and mother liquor 147, said solid-liquid separation zone comprising at least one device selected from the group consisting of from pressure belt filters, filter presses, centrifuges, pressure plate filters and cross-flow filters.

[0029] Step (c) comprises washing the filter cake 154 with a washing stream 149 in a solid-liquid separation zone 151 to form a washed cake

0 filtration filter 146 and the filtrate after washing 148, the solid-liquid separation zone 151 comprising at least one pressure filtration device.

[0030] In an embodiment of the invention, the highly concentrated removed suspension 145 is introduced into the solid-liquid separation zone 151, wherein the solid-liquid separation zone comprises a filtration zone 153, a washing zone 155 and optionally a drying zone 157, as shown in figure 2. The filtration zone 153 comprises a filtration chamber or a series of filtration chambers positioned so as to allow the distribution of the filter cake 154 on the surface of the filtration chamber and impede or prevent the flow of washing stream 149 through the filter cake 154.

[0031] Suitably, a filter cake 154 with a depth of at least 0.64 cm (0.25 inches) to 20 cm (8 inches), preferably with a depth of at least 1.3 cm (0.5 inches), more preferably with a depth of at least 3 cm (1 inch) and even more preferably about 5 to about 10 cm (2 to 4 inches) deep is distributed over the surface of the filter chamber. The washed cake 146 can be recovered or further processed, recycled and / or sent to a waste disposal installation.

[0032] After obtaining a filter cake 154 of suitable or preferred height, the filter cake 154 leaves the filtration zone 153 containing the filter or a series of filters and is introduced into the washing zone 155, in which the filter cake 154 contacts the washing stream 149. In one embodiment of the invention, there is sufficient pressure across the filter cake 154 to create a certain volume or accumulation of wash stream 149 above the filter cake 154 of a suitable depth, preferably a minimum depth of 0.64 cm (0.25 inches). A pressure gradient of at least 3.4 kPa (0.5 psi) can be applied between filter cake 154 and volume of wash stream 149, preferably from 3x10⁴ Pa (5 psi) up to 45x10⁴

Pa (65 psi) to allow any solutes to pass from filter cake 154 to wash stream 149.

[0033] A filter cake 154 with a depth of at least 1.3 cm (0.5 inch) is suitable to obtain a filter cake 154 with sufficient compactness such that a washing system is obtained, i.e. a filter cake 154 from which by washing by displacement, it is possible to efficiently remove the washing filtrate 148 containing solutes from filter cake 154. If the depth of filter cake 154 is less than 0.64 cm (0.25 inch), washing stream 149 may be directed through only one place in filter cake 154, which causes uneven washing of filter cake 154.

[0034] Because of the reduction in washing efficiency by displacing contaminants from filter cake 154, a minimum depth of filter cake 154 of purified terephthalic acid of at least 0.64 cm (0.25 inches) is preferred.

[0035] A minimum liquid height above the filter cake 154 is necessary to achieve displacement washing. This height must be sufficient to provide complete coverage of the filter cake 154 with wash stream 149. If the surface of filter cake 154 is not covered with wash stream 149, side flow of wash stream 149 may occur without sufficient displacement of solutes from filter cake 154. Due to the irregularity of the filter cake surface 154 above the surface of filter cake 154 there is a preferred minimum liquid height of 0.64 cm (0.25 inch).

[0036] It has been found that the displacement of solutes from the filter cake 154 by high pressure washing stream 149 allows efficient separation of catalytic metals from the filter cake 154. Another benefit of high pressure is the reduction of the washing stream 149 necessary to recover cobalt, which show examples.

[0037] The use of additional stages in the solid-liquid separation zone 151 may limit the amount of washing stream 149 necessary to reduce the total amount of metal catalyst retained in the filter cake 154. It is therefore convenient to use the appropriate number of positive displacement washing stages, whereby the total volume of washing stream 149 used for the displacement washing is minimized and the need for further waste disposal installations is reduced.

[0038] It should be understood that many stages in the displacement washing procedure can replace a single stage in the displacement washing procedure, wherein the amount of washing stream 149 is sufficient to provide a recovery of at least 80 wt. a metal catalyst from the highly concentrated suspension 145 to mother liquor 147 and the filtrate after washing 148. In addition, a procedure in which multiple scrubbing steps are used under countercurrent conditions can be useful if the benefits of reducing the amount of scrubbing stream 149 are found.

[0039] In the method of the present invention, the highly concentrated suspension 145 is introduced into one or more of a series of filter chambers, physically positioned so as to allow the appropriate thickness of filter cake 154 to grow. After reaching the minimum height of filter cake 154, about 0.64 cm to about 10 cm (0.25 to 4 inches), filter cake 154 leaves the filter or a series of filters and is introduced into wash zone 155 where the filter cake

154 it is washed with wash stream 149. You can then apply pressure to wash stream 149 to displace solutes (i.e., liquid and any compounds dissolved in the filter cake, e.g. metal catalyst) from filter cake 154. After displacement of the solutes by the stream to washing cake filter cake 154 can be removed from filtration zone 155 by any suitable method and the cycle repeated. In an embodiment of the invention, the ratio of wash stream 149 to removed filter cake 154 is in the range of from about 1:20 to about 20: 1 to reduce the level of metal catalyst in the filter cake by more than 95% by weight.

[0040] Devices for carrying out a suitable washing cycle may comprise a series of filtration chambers held in position, thereby allowing the volume of the washing stream 149 to rise above the filtration chambers. In one embodiment of the invention, suitable devices may include a rotary pressure drum filter with multiple filtration chambers, equipped with a system for removing the washed cake 146 from the filtration chambers. The filter cake 154 can be washed as many times as necessary to obtain the minimum metal catalyst concentration in the washed cake 146 before removing the washed cake 146 from the filter device.

[0041] A suitable pressure filter that can be adapted to the requirements of the method of the present invention is the BHSFEST rotary drum pressure filter^™, BHS-WERK, Sonthofen, D-8972, Sonthofen, West Germany, but other pressure filters can be used to operate as required. Devices that can be used in the 151 solid-liquid separation zone include pressure belt filters, filter presses, centrifuges, pressure plate filters, and cross-flow filters.

The pressure filter can operate at a temperature and pressure sufficient to obtain a recovery of at least 80 wt. metal catalyst from substances soluble in mother liquor 147. The pressure filter can advantageously be operated at a temperature of 25 ° C to 160 ° C and a pressure of 1 x 10⁵ Pa (1 atmosphere) up to 5 x 10⁶ Pa (50 atmospheres).

[0042] Operation of the BHS-FEST filter^™ consists in the fact that the rotary drum comprises a series of filtration chambers located on the periphery of the rotary drum. As the drum rotates, the highly concentrated removed suspension 145 flows into the filter cartridges and the filter cake 154 rises to the appropriate depth. The filtration liquor 147 is the result of filtration of the highly concentrated suspended suspension 145. During the drum rotation, the filter cake 154 enters the washing zone 155, in which the volume of the washing stream 149 increases above the filter cake 154, reaching the appropriate depth. The pressure exerted on the volume of the washing stream forces water to flow through the filter cake 154 and displace the solutes (with dissolved metal catalyst) retained in the highly concentrated removed suspension 145, resulting in a washed cake 146. When the drum continues rotating, the washing cycle can be repeated if necessary at least three times in the counter-current system, after which the pressure in the system releases and the temperature decreases to the value in the environment. The washed cake 146 can optionally be dewatered in the drainage zone 157 by means of vapors through conduit 152, resulting in a dehydrated cake 159 and moist vapors 160. The resulting dehydrated cake 159 can then be removed from the drum by any conventional method.

[0043] Figure 3 shows an embodiment of the invention in which a rotary drum pressure filter is used as the filtration device in the process. In an embodiment of the invention, the rotary drum pressure filter includes a filtration zone 153, a washing zone 155, optionally a drainage zone 157, a drainage zone 164 and a washing zone through fabric 162. The fabric wash zone of Figure 3 is an embodiment of the invention in which the rotary pressure drum filter includes a fabric wash zone 162, the filters being washed after removal of the dehydrated cake 159.

[0044] The filtrate after washing 148 is produced by washing the filter cake by washing stream 149. The filter cake 154 in the solid-liquid separation zone 151 is extracted with a metal catalyst by introducing the washing stream 149, forming the filtrate after washing

148. In an embodiment of the invention, at least 80 wt.% Of the filtrate after washing 148 and mother liquor 147 is recovered. metal catalyst. In an embodiment of the invention, at least 90 wt.% Of the filtrate is washed after washing 148 and mother liquor 147. metal catalyst. The washing stream 149 contains water and optionally an additional solvent for oxidation.

0 [0045] Perhaps the most surprising is that if as a wash stream

149 water with a temperature in the range 20 ° C to 70 ° C, preferably 30 ° C to 50 ° C will be used, a sufficient amount of oxidized metal is retained in dehydrated cake 159, that it is not necessary to remove oxidized metal, by other means methods. Dehydrated cake 159, which is solid in addition to the catalyst

5 metallic, can be removed from the system.

[0046] Step (d) involves subjecting the mother liquor 147 to evaporation in the evaporation zone 210, forming a high solvent content vapor stream 202 and a filtrate residue after washing 201.

[0047] The evaporation zone 210 comprises at least one evaporator. In an embodiment of the invention, the evaporator operates at atmospheric pressure or slightly above atmospheric, usually from about 1 x 10⁵ Pa (1 atmosphere) to about 1 x 10⁶ Bye (10 atmospheres). The high solvent vapors 202 contain mostly water and solvent, and the washing filtrate residue 201 contains the remaining water and solvent that was not removed from mother liquor 147, and most of the catalyst. 90% by weight is removed by evaporation. up to 99 wt. solvent and water from the combined stream in conduit 147, typically acetic acid and water, found in the filtrate after washing 148, as well as most of the benzoic acid in mother liquor 147. "Most" herein means more than 50% by weight.

[0048] Step (e) involves subjecting the high solvent content vapor stream 202 to conventional distillation in a distillation zone 220, forming stream 203 with a high benzoic acid content and stream 204 with a high solvent content.

[0049] The separation zone 220 comprises at least one liquid vapor separator. In an embodiment of the invention, the separator operates at atmospheric pressure or slightly above atmospheric, usually from 1 x 10⁵ Pa (1 atmosphere) up to 1 x 10⁶ Bye (10 atmospheres). The liquid-vapor separator contains at least one theoretical degree of equilibrium between vapor and liquid. Examples of liquid-vapor separators include flash condensers and distillation columns.

[0050] In an embodiment of the invention, the benzoic acid content in the stream 203 with a high benzoic acid content is over 5 wt. In another embodiment of the invention, the benzoic acid content in stream 203 with a high benzoic acid content is over 15 wt. In another embodiment of the invention, the benzoic acid content in stream 203 with a high benzoic acid content is above

0 30 wt. In another embodiment of the invention, the benzoic acid content of the stream

203 with a high benzoic acid content is over 50 wt. In another embodiment of the invention, stream 203 having a high benzoic acid content contains about 5 wt. up to 75% by weight benzoic acid. In another embodiment of the invention, stream 203 having a high benzoic acid content contains about 5 wt. up to 50%

5 wt. benzoic acid. In another embodiment of the invention, stream 203 having a high benzoic acid content contains about 5 wt. up to 35% by weight benzoic acid. In another embodiment of the invention, stream 203 having a high benzoic acid content contains about 15 wt. up to 30% by weight benzoic acid.

[0051] Step (f) optionally comprises recycling at least a portion of stream 204 o

0 high solvent content to the oxidation reactor in the oxidation process of aromatic compounds.

[0052] At least a portion of the high solvent content stream may be recycled to the oxidation reactor in the oxidation process. "At least part" may mean that at least 5 wt.%, At least 15 wt.%, At least 30 wt.%, At least 50 wt.%, At least 75 wt.% or all of the high solvent content stream 204 is recycled to the oxidation reactor.

[0053] An example of an oxidation process for aromatic compounds is disclosed in US Patent Application Ser. Am. North 10 / 156.312.

[0054] Although the composition of the various streams in the process varies depending on the process conditions, the typical composition of the streams, determined on the basis of a model using computer simulation (ASPEN, version 12.1) of the process, is shown in Tables 1a and 1b. In the tables 1a and 1b in the left column the ingredients are given, and in the column whose number corresponds to the stream number in figure 1, the contents of these ingredients in each stream in figure 1 are given.

[0055] In another embodiment, a method is disclosed in figure 5 which is not in accordance with the invention.

Table 1A

<td colspan="8">PROCESS SIMULATION USING THE ASPEN PROGRAM</td>

<td></td><td>101 % MASS</td><td>104 % MASS</td><td>105 % MASS</td><td>144 % MASS</td><td>145 % MASS</td><td>146 % MASS</td><td>147 % MASS</td>

<td>WATER</td><td> 7,7</td><td> 8,9</td><td> 4,3</td><td> 6,0</td><td> 2,7</td><td> 20,0</td><td> 3,5</td>

<td>ACETIC ACID</td><td> 88,4</td><td> 91,1</td><td> 80,2</td><td> 94,0</td><td> 66,7</td><td> 0,0</td><td> 86,6</td>

<td>ACID terephthalic</td><td> 2,9</td><td> 0,0</td><td> 11,4</td><td> 0,0</td><td> 22,7</td><td> 74,0</td><td> 2,3</td>

<td>OTHER ORGANIC COMPOUNDS</td><td> 0,6</td><td> 0,1</td><td> 2,0</td><td> 0,0</td><td> 4,0</td><td> 5,9</td><td> 3,1</td>

<td>ACID benzoic acid</td><td> 0,3</td><td> 0,0</td><td> 1,1</td><td> 0,0</td><td> 2,1</td><td> 0,0</td><td> 2,8</td>

<td>METALS AND COMPLEX BROMINE</td><td> 0,2</td><td> 0,0</td><td> 0,9</td><td> 0,0</td><td> 1,8</td><td> 0,1</td><td> 1,7</td>

<td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>FLOW TOTAL kg / h</td><td> 10000</td><td> 7500</td><td> 2500</td><td> 1241</td><td> 1259</td><td> 351</td><td> 894</td>

<td>TEMPERATURE ° C</td><td> 121,2</td><td> 123,5</td><td> 123,5</td><td> 49,4</td><td> 49,4</td><td> 83,0</td><td> 49,4</td>

Table 1B

<td></td><td>148 % MASS</td><td>149 % MASS</td><td>201 % MASS</td><td>202 % MASS</td><td>203 % MASS</td><td>204 % MASS</td>

<td>WATER</td><td> 89,8</td><td> 100,0</td><td> 0,0</td><td> 3,7</td><td> 1,2</td><td> 3,9</td>

<td>ACETIC ACID</td><td> 8,1</td><td> 0,0</td><td> 1,7</td><td> 91,7</td><td> 47,0</td><td> 94,4</td>

<td>ACID terephthalic</td><td> 0,7</td><td> 0,0</td><td> 40,2</td><td> 0,0</td><td> 0,0</td><td> 0,0</td>

<td>OTHER ORGANIC COMPOUNDS</td><td> 0,3</td><td> 0,0</td><td> 27,1</td><td> 1,6</td><td> 20,3</td><td> 0,5</td>

<td>ACID benzoic acid</td><td> 0,3</td><td> 0,0</td><td> 0,7</td><td> 2,9</td><td> 31,5</td><td> 1,2</td>

<td>METALS AND COMPLEX</td><td> 0,9</td><td> 0,0</td><td> 30,2</td><td> 0,0</td><td> 0,1</td><td> 0,0</td>

<td>BROMINE</td><td></td><td></td><td></td><td></td><td></td><td></td>

<td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>FLOW TOTAL kg / h</td><td> 801</td><td> 787</td><td> 51</td><td> 843</td><td> 48</td><td> 795</td>

<td>TEMPERATURE ° C</td><td> 60,0</td><td> 70,9</td><td> 272,1</td><td> 272,1</td><td> 159,5</td><td> 159,5</td>