Process for removal of benzoic acid from an oxidizer purge stream

BACKGROUND OF THE INVENTION

Terephthalic acid is produced commercially by the oxidation of paraxylene in the presence of a catalyst, such as e.g. Co, Mn, Br, and a solvent. Terephthalic acid used in the production of polyester fibers, films and resins must be further processed to remove impurities resulting from the oxidation of paraxylene.

Terephthalic acid (TPA) is an intermediate product in the production of polyesters used in the plastics and textile industry. Commercial processes used in the production of TPA are often based on the oxidation of heavy metal-catalysed p-xylene, usually with the use of bromide (promoter) in acetic acid (solvent). Due to the limited solubility of TPA in acetic acid under practical oxidation conditions, a TPA crystal suspension is typically formed in the oxidation reactor. Typically, the TPA oxidant suspension is removed from the reactor and the TPA crystals are separated from the mother liquor of the oxidant using conventional solid-liquid separation techniques. The oxidant mother liquor, containing most of the catalyst and promoter used in the process, is recycled to the oxidation reactor. In addition to the catalyst and promoter, the oxidant mother liquor also contains dissolved TPA and many byproducts and impurities. These by-products and impurities are formed partly from impurities present in the feedstock stream, p-xylene. Other impurities arise due to the incomplete oxidation of p-xylene resulting in the appearance of partially oxidized products. Still other by-products are formed in competitive side reactions occurring as a result of oxidation of p-xylene to terephthalic acid. Other impurities arise due to the incomplete oxidation of p-xylene resulting in the appearance of partially oxidized products. Still other by-products are formed in competitive side reactions occurring as a result of oxidation of p-xylene to terephthalic acid. Other impurities arise due to the incomplete oxidation of p-xylene resulting in the appearance of partially oxidized products. Still other by-products are formed in competitive side reactions occurring as a result of oxidation of p-xylene to terephthalic acid.

The TPA crystals are subjected to separation of the solid from the liquid in which the fresh solvent is used to replace the major part of the liquid component of the oxidant mother liquor. After drying, the TPA crystals are contaminated with substances that have been present in the oxidant mother liquor, because these impurities can be incorporated into the TPA crystals. Impurities also occur due to occlusion in the TPA crystal structure and incomplete removal of the mother liquor of the oxidant by washing with fresh solvent.

Many impurities in the oxidant matrix stock stream that are recycled are relatively inert for 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-toluene acid and p-tolualdehyde. Impurities that are inert to oxidation tend to accumulate in the mother liquor of the oxidant when recycled. The concentration of these inert impurities will increase in the oxidant stock solution until equilibrium is reached as the rate of removal of each contaminant from the TPA product will be equivalent to the rate of formation and the rate of addition to the oxidation process. The normal level of contamination in commercial, untreated TPA makes it unsuitable for direct use in most polymer applications.

In a conventional manner, untreated TPA was purified by conversion of dimethyl ester or by dissolution in water followed by hydrogenation using standard hydrogenation catalysts. Recently, a secondary oxidation treatment was used to produce TPA suitable for polymer applications. It is desirable to minimize the concentration of impurities in the mother liquor, thereby facilitating the subsequent purification of TPA. In some cases, it is not possible to produce a purified TPA suitable for polymer-related applications unless specific methods for removing impurities from the parent oxidant solution stream are used.

GB 892,766 describes improvements in the production of aromatic acids, in particular the recovery of oxidation catalysts used for liquid phase oxidation of aromatic compounds substituted with aliphatic groups or aromatic compounds with linked rings to aromatic carboxylic acids. The method includes extracting the lower fraction in a liquid or solid state using a solvent mixture, such as water and low-saturated paraffin and naphthenic monocarboxylic acids, to separate oxidation catalysts from insoluble oxidation byproducts.

WO 97/30963 relates to a mother liquor derived from the primary separation process of solids from the liquid used to separate the aromatic carboxylic acid crystals from their suspension in the mother liquor. More specifically, the mother liquor is divided into a recycle fraction and the fraction being dropped, the recycle fraction returning to the reactor in which the aromatic carboxylic acid is formed.

The technique of removing contaminants from the recycle stream commonly used in the chemical industry consists in discharging or "dropping" a part of the recycle stream. Usually, the dropped stream is simply recycled or, if economically justified, subjected to a variety of treatments to remove undesirable impurities and recover valuable components. An example of such a process is set forth in U.S. Patent No. 4,939,297. The dropped amount required to control the contaminants depends on the process; however, the amount dropped is 10-40 wt%. the total oxidizer mother liquor stream is usually sufficient to provide a TPA which is a suitable raw material for the commercial production of polymers. In the production of TPA, the percentage of the oxidant solution mother liquor required to maintain acceptable concentrations of impurities, combined with the economic value of the metal catalyst and solvent components in this stream, make its normal disposal unprofitable. Therefore, there is a need for a method that substantially recover all of the valuable metal catalysts and acetic acid contained in the oxidant stream to be released while removing most of the impurities present therein. The metal catalyst can be recovered in an active form suitable for reuse by direct recycling to the oxidation step of p-xylene. in combination with the economic value of the metal catalyst and solvent components in this stream, its normal disposal is unprofitable. Therefore, there is a need for a method that substantially recover all of the valuable metal catalysts and acetic acid contained in the oxidant stream to be released while removing most of the impurities present therein. The metal catalyst can be recovered in an active form suitable for reuse by direct recycling to the oxidation step of p-xylene. in combination with the economic value of the metal catalyst and solvent components in this stream, its normal disposal is unprofitable. Therefore, there is a need for a method that substantially recover all of the valuable metal catalysts and acetic acid contained in the oxidant stream to be released while removing most of the impurities present therein. The metal catalyst can be recovered in an active form suitable for reuse by direct recycling to the oxidation step of p-xylene. Therefore, there is a need for a method that substantially recover all of the valuable metal catalysts and acetic acid contained in the oxidant stream to be released while removing most of the impurities present therein. The metal catalyst can be recovered in an active form suitable for reuse by direct recycling to the oxidation step of p-xylene. Therefore, there is a need for a method that substantially recover all of the valuable metal catalysts and acetic acid contained in the oxidant stream to be released while removing most of the impurities present therein. The metal catalyst can be recovered in an active form suitable for reuse by direct recycling to the oxidation step of p-xylene.

An advantage of the present invention is energy efficiency and economy compared to the previously described purification process using extraction.

A further advantage of the present invention is the efficiency compared to the purification process by extraction in terms of the suitability of solvent streams returned to the TPA process. The basic justification of the liquid extraction process is based on the assumption that the introduction of any aromatic impurities in the oxidation of p-xylene in the production of terephthalic acid has a negative effect on the quality of the terephthalic acid powder (eg yellow color). Therefore, it has been assumed that the removal of the aromatic impurities in a wide range, provided by liquid extraction, is necessary to achieve an appropriate quality of terephthalic acid powder.

In one embodiment of the present invention, however, a relatively simple process for the separation of benzoic acid and aqueous solvent has been used. The process efficiency for benzoic acid is high because benzoic acid is more volatile (higher vapor pressure) than most of the identified aromatic impurities in the production of carboxylic acid, typically terephthalic acid. These aromatic impurities include trimellitic acid, isophthalic acid, stilbenes and anthraquinones. It is therefore quite surprising that the removal of benzoic acid for other known impurities characterized by natural color is sufficient for the production of a carboxylic acid, usually terephthalic acid, of good quality.

SUMMARY OF THE INVENTION

The present invention relates to a method as defined in claim 1.

Preferred embodiments are defined in claims 2 to 14 based on this method.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates a method for recovering benzoic acid from a dropped oxidant stream 101.

Fig. 2 illustrates an embodiment of the process occurring in the solid-liquid separation zone 151, wherein the solid-liquid separation zone consists of a filtration zone 153, a rinse zone 155 and, optionally, a dewatering zone 157.

Fig. 3 illustrates an embodiment in which a pressure rotary drum filter is used in the solid-liquid separation zone.

Fig. 4 illustrates an embodiment, the method for recovering benzoic acid from a dropped oxidant stream 101 using a primary evaporation zone 125.

Fig. 5 illustrates the present invention, wherein a method for recovering benzoic acid from a benzoic acid-containing stream 347 is provided.

DESCRIPTION OF THE INVENTION:

A method for the separation of benzoic acid from the oxidant stream 101 shown in Fig. 1 is disclosed.

Step (a) considers submitting the oxidant flow 101 to evaporate in the first evaporation zone 121 to obtain a liquid vapor stream 104 and a concentrated dropped slurry 105.

In an exemplary embodiment, the oxidant stream 101 is derived from a process for the synthesis of a carboxylic acid by oxidation. The oxidant stream 101 thus obtained is a feed stream in the present process. In an embodiment, the oxidant stream 101 comprises at least one carboxylic acid, at least one solvent, at least one metal catalyst and impurities. At least one pollutant selected from the group consisting of: organic bromides, corrosive metals, byproducts of oxidation of p-xylene and impurities from impurities present in p-xylene belongs to impurities. Organic bromides can be used as promoters in the oxidation reaction. Examples of corrosive metals include iron and chromium compounds that inhibit, limiting or completely eliminating the activity of the metal catalyst. In addition to the catalyst and promoter, the oxidant solution 101 also contains by-products and impurities. These by-products and impurities are formed partly from impurities present in the feedstock stream, p-xylene. Other impurities arise due to the incomplete oxidation of p-xylene resulting in the appearance of partially oxidized products. Still other by-products are formed in competitive side reactions during the oxidation of p-xylene to terephthalic acid. Other impurities arise due to the incomplete oxidation of p-xylene resulting in the appearance of partially oxidized products. Still other by-products are formed in competitive side reactions during the oxidation of p-xylene to terephthalic acid. Other impurities arise due to the incomplete oxidation of p-xylene resulting in the appearance of partially oxidized products. Still other by-products are formed in competitive side reactions during the oxidation of p-xylene to terephthalic acid.

The carboxylic acids include any aromatic carboxylic acids produced by controlled oxidation of the organic substrate. Such aromatic carboxylic acids include compounds with at least one carboxylic acid group attached to a carbon atom that is part of an aromatic ring, preferably containing at least 6 carbon atoms, and more preferably consisting exclusively of carbon atoms. Suitable examples of such aromatic rings include benzene, biphenyl, terphenyl, naphthalene and other carbon-based combined aromatic rings. Examples of suitable carboxylic acids include terephthalic acid, p-toluene acid, isophthalic acid, trimellitic acid, naphthalene dicarboxylic acid, acid

2,5-diphenyl-terephthalic acid and mixtures thereof.

Suitable solvents include aliphatic monocarboxylic acids, preferably containing from 2 to 6 carbon atoms, or benzoic acid and mixtures thereof, and mixtures of these compounds with water. Preferably, the solvent is acetic acid mixed with water in a ratio of about 5: 1 to about 25: 1, preferably about 8: 1 to about 20: 1. Within this specification, acetic acid will be referred to as a solvent. However, it should be noted that other suitable solvents may also be used, such as the solvents disclosed earlier.

In the first step of the present method, the oxidant solution 101 is concentrated by conventional methods in a first evaporation zone 121 containing at least one evaporator to obtain a liquid vapor stream 104 and a concentrated liquid suspension 105. In an embodiment, the evaporator operates under atmospheric or slightly higher pressure conditions. in general, from 1 x 100,000 Pa (1 atmosphere) to 1 x 000,000 Pa (10 atmospheres). The vapor stream of liquid 104 contains most of the water and solvent, whereas the concentrated dropped slurry 105 contains residual water and solvent that have not been removed from the oxidant flow 101. The term "majority" as used herein means above 50 wt%. In an embodiment, evaporation removes from about 50% by weight. (weight percent) to about 80% by weight solvent and water, typically acetic acid and water, present in the oxidant stream 101.

Step (b) takes into account the concentration of the dropped suspension of the evaporation in the second evaporation zone 150 in order to obtain a high solvent stream 144 and a highly concentrated dropped slurry 145.

In an embodiment, the second evaporation zone 150 comprises at least one evaporator operating under vacuum conditions. In an embodiment of the present invention, the evaporation can be carried out at a temperature of about 20 ° C to about 70 ° C; another range is from about 30 ° C to about 50 ° C. In an embodiment, the combination of evaporators 121 and 150 is operated in such a way as to concentrate the oxidant stream provided by stream 101 to a state in which from about 75 wt.%. up to about 99% by weight The solvent and water, typically acetic acid and water, are removed from the oxidant stream 101 to provide a highly concentrated dropped slurry 145. In a further embodiment, a different range of operating parameters for the evaporator combinations 121 and 150 is used to concentrate the oxidant stream 101 to be concentrated to a state where from about 85 wt.%. up to about 99% by weight The solvent and water, typically acetic acid and water, are removed from the oxidant stream 101 to give a highly concentrated dropped slurry 145.

In a further embodiment, the first evaporation zone 121 and the second evaporation zone can be combined to form a primary evaporation zone 125 as shown in Fig. 4. The primary evaporation zone 125 comprises at least one evaporator. The evaporator or evaporators in the main vaporization zone 125 are operated using a temperature and pressure sufficient to remove a total of at least 75% by weight. Solvent and water originating from a dropped oxidant stream 101. In a further embodiment, the evaporator or evaporators in the main evaporation zone 125 are operated using temperature and pressure sufficient to remove a total of at least 85% by weight. solvent and water coming from the oxidant stream dropped. In a further embodiment, the evaporator or evaporators in the main vaporization zone 125 are operated using a temperature and pressure sufficient to remove a total of at least 90% by weight. Solvent and water originating from a dropped oxidant stream 101. In a further embodiment, the evaporator or evaporators in the main vaporization zone 125 are operated using temperature and pressure sufficient to remove a total of at least 95% by weight. solvent and water coming from the oxidant stream dropped. In a further embodiment, the evaporator or evaporators in the main vaporization zone 125 are operated using a temperature and pressure sufficient to remove a total of at least 95% by weight. solvent and water coming from the oxidant stream dropped. In a further embodiment, the evaporator or evaporators in the main vaporization zone 125 are operated using a temperature and pressure sufficient to remove a total of at least 95% by weight. solvent and water coming from the oxidant stream dropped.

The ranges given in this disclosure and the appended claims are to be understood as disclosing the entire specified scope, and not just its endpoints. For example, disclosing a range from 0 to 10 means disclosing a value of 2; 2.5; 3.17 and all other numbers included in this range, not just values ​​0 and 10.

In an embodiment, the highly concentrated dropped slurry 145 may be in the form of a mixture of a solid and a liquid, with a sufficient solvent content to allow it to be pumped.

Step (c) takes into account the filtration of the highly concentrated dropped slurry 145 in the solid-liquid separation zone 151 to form a filter cake 154 and a mother liquor 147.

Step (d) takes into account washing of the filter cake 154 with a rinse agent 149 in the solid-liquid separation zone 151 to obtain a washed cake 146 and wash filtration 148 and optionally dewatering the washed cake 146 in the solid-liquid separation zone 151 to obtain dehydrated cake 159; wherein the separation zone of solids from liquid 151 comprises at least one pressure filter device.

In an embodiment, the highly concentrated dropped slurry 145 is introduced into the solid-liquid separation zone 151, wherein the solid-liquid separation zone comprises a filtering zone 153, a washing zone 155 and, optionally, a drying zone 157 as shown in Fig. 2. The filtration zone 153 includes a filter chamber or a series of filter chambers positioned to allow distribution of the filter cake 154 on the surface of the filter chamber, obstructing or preventing the formation of rinsing agent channels 149 through the filter cake 154.

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

After obtaining the appropriate or preferred height of the filter cake 154, the filter cake 154 exits the filtration zone 153 containing the filter or series of filters and passes to the washing zone 155, where the filter cake 154 is contacted with the scrubbing agent 149. In one embodiment, the pressure within the filter cake 154 it is sufficient to allow the reservoir or the rinsing agent layer 149 to form over the filter cake 154 at the appropriate depth, preferably at a minimum depth of 0.64 cm (0.25 inches). A pressure gradient of at least 3.4 kPa (0.5 psi), preferably from 3 x 10 kPa (5 psi) to 45 x 10 kPa (65 psi), within the filter cake 154 and the reservoir of the rinse agent 149 may be used,

A filter cake depth of at least 1.3 cm (0.5 inches) is suitable to obtain a filter cake 154 with sufficient firmness to provide a washing substrate, i.e. a filter cake 154, from which the filtrate 148 containing the substances dissolved from the cake The filter 154 can be effectively removed by washing with displacement. If the depth of the filter cake 154 is less than 0.64 cm (0.25 in), the channels of the rinsing agent 149 may be formed in the filter cake 154, resulting in a non-uniform washing of the filter cake 154.

Because of the loss of washing efficiency with displacement of the filter cake 154, a minimum depth of filter cake 154 of at least 0.64 cm (0.25 in) of purified terephthalic acid is preferred.

A minimum liquid height above the surface of the filter cake 154 is required to ensure washing with displacement. This height must be sufficient to ensure complete coverage of the surface of the filter cake 154 with rinsing agent 149. If the surface of the filter cake 154 is not covered with the scrubbing agent 149, the flushing medium 149 can flow without proper displacement of the solutes from the filter cake 154. unevenness of the surface of the filter cake 154, a minimum liquid height of 0.64 cm (0.25 inches) above the surface of the filter cake 154 is preferred.

It has been found that displacing the solute from the filter cake 154 by the high pressure scrubbing agent 149 allows efficient separation of the catalytic metals from the filter cake 154. A further advantage provided by the high pressure is the reduction of the scrubbing agent 149 required to recover the cobalt as shown in the examples.

The use of additional steps in the solid and liquid separation zone 151 may allow to reduce the amount of scrubbing agent 149 required to reduce the total amount of metallic catalyst remaining in the filter cake 154. Conveniently, therefore, a number of displacement washing steps should be used to reduce the total amount of scrubbing agent 149 used displacement washing in order to reduce the need for additional sewage treatment installations in the further part of the system.

It is contemplated that many stages of the positive displacement washing procedure may replace a one-stage displacement washing procedure in which the amount of scrubbing agent 149 is sufficient to recover at least 80 wt.%. a metal catalyst from the highly concentrated slurry 145 to the mother liquor 147 and the wash filtrate 148. Furthermore, it may be useful to use multiple stages of the countercurrent washing procedure if it is judged that reducing the amount of scrubbing agent 149 is beneficial.

As part of this process, a highly concentrated dropped slurry 145 is introduced into one or more physically arranged filter chambers arranged in series so as to allow the formation of a filter cake 154 with the required thickness. After obtaining a minimum height of the filter cake 154, from 0.64 cm (0.25 inches) to 10 cm (4 inches), the filter cake 154 is discharged from the filter or a series of filters and is introduced into the scrubbing zone 155 in which the filter cake 154 is washed using a rinse agent 149. A pressure may then be applied to the scrubbing agent 149 to displace the solute (i.e., liquid and any dissolved compounds, such as a metal catalyst in the filter cake) from the filter cake 154. After the displacement of the solute using the scrubbing agent, the filter cake 154 can be drained from the filtering zone 155 using any suitable means, and then the cycle repeated. In an embodiment, the ratio of the scrubbing agent 149 to the substances discharged from the filter cake 154 is in the range of from 1:20 to 20: 1 to reduce the level of the metal catalyst in the filter cake by more than 95% by weight.

The equipment for carrying out the required rinsing cycle may comprise a plurality of filter chambers held in a suitable position to allow the reservoir of rinsing agent 149 to form on the filter chambers. In one embodiment of the present invention, suitable equipment may include a pressurized rotary drum filter with multiple filter chambers equipped with a mechanism for discharging the washed cake 146 from the filter chambers. The filter cake 154 may be washed any number of times required to provide a minimum concentration of metal catalyst in the washed cake 146 prior to removing the washed cake 146 from the filter device.

A suitable pressure filter that can be adapted to the requirements of the invented process is a pressurized rotary drum filter BHS-FEST ™, BHS-WERK, Sonthofen, D-8972, Sonthofen, West Germany, but other pressure filters that provide the required action can also be used. Examples of other devices that can be used in the solid and liquid separation zone 151 include pressure belt filters, filter presses, centrifuges, pressure plate filters and crossflow filters. The pressure filter can operate under temperature and pressure conditions sufficient to recover at least 80% by weight. a metal catalyst from a dissolved mother liquor substance 147.

The principle of operation of the BHS-FEST ™ filter is as follows: the rotating drum contains a series of filter chambers located on the periphery of the rotary drum. As the drum rotates, the highly concentrated dropped slurry 145 is introduced into the filter chambers and the filter cake 154 is formed to the required depth. The mother liquor 147 is produced by filtration of the highly concentrated dropped slurry 145. As the drum rotates, the filter cake 154 is introduced into the scrubbing zone 155, in which a reservoir of rinsing agent 149 is formed on the filter cake 154 to the desired depth. Under the influence of the pressure applied to the reservoir of the rinsing agent, water is directed to the filter cake 154, to displace the solute (with dissolved metal catalyst) contained in the highly concentrated dropped slurry 145 to form a washed cake 146. When the drum is still rotating, the washing cycle can be repeated at least three times, if necessary countercurrently, followed by reduction of pressure in the system along with a decrease in temperature to the ambient conditions. Optionally, the washed cake 146 may be dehydrated in the dewatering zone 157 using liquid vapor by means of a conduit 152 to obtain a dewatered cake 159 and a liquid wet steam 160. The resulting dewatered cake 159 may then be drained from the drum using any conventional means. the washing cycle can be repeated at least three times, if necessary countercurrently, after which the pressure in the system decreases with the temperature being reduced to the ambient conditions. Optionally, the washed cake 146 may be dehydrated in the dewatering zone 157 using liquid vapor by means of a conduit 152 to obtain a dewatered cake 159 and a liquid wet steam 160. The resulting dewatered cake 159 may then be drained from the drum using any conventional means. the washing cycle can be repeated at least three times, if necessary countercurrently, after which the pressure in the system decreases with the temperature being reduced to the ambient conditions. Optionally, the washed cake 146 may be dehydrated in the dewatering zone 157 using liquid vapor by means of a conduit 152 to obtain a dewatered cake 159 and a liquid wet steam 160. The resulting dewatered cake 159 may then be drained from the drum using any conventional means.

Figure 3 shows an embodiment in which a pressurized rotary drum filter was used as the filter device in the process. In an embodiment, the pressurized rotary drum filter comprises a filter zone 153, a wash zone 155, optionally a drainage zone 157, a drainage zone 164 and a fabric wash zone 162. The fabric wash zone shown in Figure 3 is part of an embodiment in which the pressurized rotary drum filter comprises a zone washing the fabrics 162, in which the filters are washed after draining the dehydrated cake 159.

The washing filter 148 is obtained by washing the displacement filter cake with a rinsing agent 149. The filter cake 154 in the solid and liquid separation zone 151 is subjected to extraction of the metal catalyst by introducing the scrubbing agent 149 to obtain a wash filtrate 148. In the embodiment of this invention At least 80% by weight of the invention The metal catalyst is recovery in a wash filtrate 148 and a mother liquor 147. In an embodiment of the present invention, at least 90 wt. The metal catalyst is recovery in a wash filtrate 148 and a mother liquor 147. The scrubbing agent 149 contains water and optionally an additional oxidation solvent.

Surprisingly, when using water as a scrubbing agent 149 at a temperature in the range of about 20 ° C to about 70 ° C, preferably up to about 30 ° C to about 50 ° C, a sufficient amount of corrosion metal is retained in the dehydrated cake 159, which eliminates the need to remove the corrosive metal using other means. The dehydrated cake 159, which contains solids without a metal catalyst, can be removed from the system.

In step (e), optionally the mother liquor 147 and optionally the washing wash filtrate 148 are subjected to evaporation in the vaporization zone 210 to obtain a vapor of liquid with a high solvent content 202 and washed sludge of the filtrate 201.

In the evaporation zone 210 there is at least one evaporator. In an embodiment, the evaporator operates at atmospheric pressure or slightly higher than atmospheric pressure, generally from 1 x 100 kPa (1 atmosphere) to 1 x 1000 kPa (10 atmospheres). The high solvent vapor pair 202 consists of most of the water and solvent, and the wash filtrate sludge pellet 201 consists of the rest of the water and solvent not removed from the mother liquor 147 and most of the catalyst. In the evaporation process, 90% by weight is removed. up to 99% by weight solvent and water from the combined stream in line 147, typically acetic acid and water, which are present in the wash filtrate 148, and the majority of benzoic acid in the mother liquor 147.

In step (f), a high solvent vapor stream of liquid 202 is subjected to conventional distillation in the distillation zone 220 to obtain a high benzoic stream 203 stream and a high solvent solvent stream 204.

In the separation zone 220 there is at least one liquid and liquid vapor separator. In an embodiment, the distributor operates at atmospheric pressure or slightly higher than atmospheric pressure, generally from 1 χ 100 kPa (1 atmosphere) to 1 χ 1000 kPa (10 atmospheres). The liquid and liquid vapor distributor comprises at least one theoretical equilibrium liquid-liquid vapor. Examples of liquid and liquid vapor separators are e.g. instant capacitors and distillation columns.

In an embodiment, the high content benzoic acid stream 203 contains more than 5 wt. benzoic acid. In another embodiment, the high content benzoic acid stream 203 contains more than 15 wt. benzoic acid. In another embodiment, the high content stream of benzoic acid 203 contains more than 30 wt%. benzoic acid. In another embodiment, the high content benzoic acid stream 203 contains more than 50 wt%. benzoic acid. In another embodiment, the high content benzoic acid stream 203 contains from about 5 wt.%. up to 75% by weight benzoic acid, in another embodiment, the high content benzoic acid stream 203 contains from about 5 wt.% up to 50% by weight benzoic acid. In another embodiment, the high content benzoic acid stream 203 contains from about 5 wt.%. up to 35% by weight benzoic acid. In another embodiment, the high content benzoic acid stream 203 contains from about 15 wt.%. up to 30% by weight benzoic acid.

In step (g), optionally at least a portion of the high solvent stream 204 is reprocessed in the oxidation reactor in the oxidation of the aromatic compound.

At least a portion of the high solvent stream can be recycled in the oxidation reactor by an oxidation process. The term "at least a portion" can mean that at least 5 wt.%, At least 15 wt.%, At least 30 wt.%, At least 50 wt.%, At least 75 wt.%. or the entire high solvent stream 204 is recycled in the oxidation reactor.

An example of an aromatic compound oxidation process is disclosed in US Patent Application No. 10 / 156,312.

Although the composition of different process streams varies depending on the process conditions, typical stream compositions, determined using a computer-simulated model (ASPEN, version 12.1) of the process, are shown in Tables 1a and 1b. In Tables 1a and 1b, the ingredients are given in the left-hand column, and the amount of these components in each stream in Figure 1 is given in a column labeled with the number corresponding to the number of the stream in Figure 1.

The present invention relates to the method shown in Figure 5.

In step (a), the stream containing benzoic acid 347 is subjected to evaporation in the evaporation zone 310 to obtain a liquid vapor with a high content of solvent 302 and a precipitate of the filtrate from the wash 301.

In the evaporation zone 310 there is at least one evaporator. The stream containing benzoic acid 347 consists of water and benzoic acid. In an embodiment of the present invention, the evaporator operates at atmospheric pressure or slightly higher than atmospheric pressure, generally from 1 χ 100 kPa (1 atmosphere) to 1 χ 1000 kPa (10 atmospheres). The high liquid solvent vapor 302 consists of the majority of water and solvent, and the wash 301 filtrate precipitate consists of the remaining water and solvent not removed from the benzoic acid containing stream 347. In another embodiment of the present invention, the evaporator removes from about 90% by weight . up to about 99% by weight solvent and water from a stream containing benzoic acid 347, typically acetic acid and water.

The benzoic acid-containing stream is a stream produced by the oxidation of the para-xylene aromatic compound to terephthalic acid. An example of a method for oxidizing an aromatic compound is disclosed in U.S. Patent Application No. 10, 156,312.

For example, during the oxidation reaction, the exothermic heat energy of the reaction mixture and the water produced by the oxidation of the dialkyl aromatic compound is removed from the reactor by vaporizing part of the liquid reaction medium. These liquid vapor, referred to as the reactor effluent gas, contain an aqueous solvent containing from five to thirty percent by weight of water and a low oxygen process gas containing small amounts of decomposition products, including a catalyst sludge. The exit gas from the reactor can be used as a stream containing benzoic acid.

In an embodiment of the present invention, the evaporation zone 310 operates at atmospheric pressure or slightly higher than atmospheric pressure, generally from 1 x 100 kPa (1 atmosphere) to 1 x 1000 kPa (10 atmospheres). The high solvent vapor liquid stream 302 contains benzoic acid, and the filtrate of the 301 rinse filtrate contains solids not captured in the solid and liquid separation zone, including all residual catalytic metals.

In step (b), a high solvent vapor stream 302 is subjected to distillation in the separation zone 320 to obtain a high benzoic stream 303 stream and a high solvent content stream 304.

In the separation zone 320 there is at least one liquid and liquid vapor separator. In an embodiment of the present invention, the liquid and liquid vapor separator operates at atmospheric or slightly higher than atmospheric pressure, generally from 1 x 100 kPa (1 atmosphere) to 1 x 1000 kPa (10 atmospheres). The liquid and liquid vapor distributor comprises at least one theoretical equilibrium liquid-liquid vapor. Examples of liquid and liquid vapor separators are e.g. instant capacitors and distillation columns.

The high benzoic acid stream 303 contains at least 5 wt. benzoic acid. In another embodiment of the present invention the stream with a high content of benzoic acid contains more than 15% by weight. benzoic acid.

In another embodiment of the present invention, the high content benzoic acid stream 303 contains more than 30 wt%. benzoic acid. In another embodiment of the present invention, the high content benzoic acid stream 303 contains more than 50 wt. benzoic acid. In another embodiment of the present invention, the high content benzoic acid stream 303 comprises from 5 wt% up to 75% by weight benzoic acid; in another embodiment of the present invention, the high content benzoic acid stream 303 contains from 5 wt% up to 50% by weight benzoic acid. In another embodiment of the present invention, the high content benzoic acid stream 303 comprises from 5 wt% up to 35% by weight benzoic acid. In another embodiment of the present invention, the high content stream of benzoic acid 303 contains from 15 wt% up to 30% by weight benzoic acid.

In step (c), optionally at least a portion of the high solvent stream 304 is recycled in the oxidation reactor in the oxidation of the aromatic compound.

At least a portion of the high solvent stream can be recycled in the oxidation reactor by an oxidation process. The term "at least a portion" can mean that at least 5 wt.%, At least 15 wt.%, At least 30 wt.%, At least 50 wt.%, At least 75 wt.%. or the entire high solvent stream 304 is recycled in the reactor.