KR20140102761A - Process for producing terephthalic acid - Google Patents

Abstract

A process and apparatus for producing terephthalic acid using a p-xylene stream rich in p-toluic acid are disclosed. The apparatus includes first and second reactor zones. The reactor zone may be in the same reactor or in a different reactor.

Description

PROCESS FOR PRODUCING TEREPHTHALIC ACID [0002]

STATEMENT OF PRIORITY

This application claims priority from U.S. Serial Nos. 13 / 340,132 and 13 / 340,122, filed December 29, 2011.

Field of invention

The present invention relates to a terephthalic acid composition, and to a process for preparing terephthalic acid from a feedstock comprising p-xylene. More particularly, the present invention relates to a process and apparatus for the oxidation of a p-toluene-rich p-xylene stream to produce terephthalic acid.

Oxidation of alkylaromatic compounds such as toluene and xylene is an important commercial process. A variety of oxidation products can be obtained, including aromatic carboxylic acids used in the polymer industry, such as terephthalic acid (1,4-benzenedicarboxylic acid) and isophthalic acid (1,3-benzenedicarboxylic acid).

It is known that oxidation products such as aromatic alcohols, aromatic aldehydes, aromatic ketones and aromatic carboxylic acids can be solidified or crystallized under oxidizing conditions and / or as the reaction mixture is cooled. Thus, a mixture of oxidation products may be generated that requires further processing to increase the purity of a given product. For example, in the preparation of terephthalic acid, the oxidation product is sometimes referred to as crude terephthalic acid, since it contains a color body and an intermediate oxidation product, especially 4-carboxybenzaldehyde (4-CBA). In order to obtain polymer grade or purified terephthalic acid, it is advantageous to carry out the steps of washing the crude terephthalic acid with water and / or solvent, further oxidation or crystallization steps, and dissolving in hydrogenation conditions generally comprising palladium and carbon- Various purification steps are known in the art including the reaction of a solution of crude terephthalic acid with hydrogen. Often several purification steps are used.

US 2,833,816 discloses an oxidation process of aromatic compounds into corresponding aromatic carboxylic acids. The liquid phase oxidation process for alkylaromatics uses oxygen molecules, metal or metal ions, and bromine or bromide ions in the presence of an acid. The metal may comprise cobalt and / or manganese. Exemplary acids are lower aliphatic monocarboxylic acids containing from 1 to 8 carbon atoms, especially acetic acid.

US 6,355,835 discloses a process for the preparation of benzene dicarboxylic acids by liquid oxidation of xylene isomers using oxygen or air by oxidation in the presence of acetic acid as solvent, cobalt salt as catalyst and initiator. After the oxidation step, the reaction mixture is flashed to remove volatiles, and the material is cooled and filtered to obtain crude benzene dicarboxylic acid and filtrate as a solid product. Recrystallizing the crude benzene dicarboxylic acid to obtain a purity of 99% or more and recirculating the filtrate is also disclosed.

US 7,094,925 discloses a process for the preparation of alkylaromatics. The process comprises mixing an oxidizing agent or a sulfur compound in the presence of an ionic liquid. Any other form of air, dioxygen, peroxide, superoxide or active oxygen, nitrite, nitrate and other oxides of nitric acid or nitrogen or oxyhalides (hydrates or anhydrides) may be used as the oxidizing agent. The process is typically carried out under Bronsted acidic conditions. The oxidation is preferably carried out in an ionic liquid containing an acid promoter such as methanesulfonic acid. The product is preferably a carboxylic acid or ketone or an intermediate compound in oxidation such as an aldehyde or an alcohol.

US 7,985,875 discloses a process for preparing aromatic polycarboxylic acids by liquid phase oxidation of disubstituted or trisubstituted benzene or naphthalene compounds. The process involves contacting the aromatic compound with an oxidizing agent in the presence of a carboxylic acid solvent, a metal catalyst and an accelerator in the reaction zone. The accelerator is an ionic liquid comprising an organic cation and a bromide or iodide anion. Accelerator is used in a concentration range of 10-50,000 ppm (based on the solvent), and the preferred range is 10-1,000 ppm. Other accelerators such as bromine containing compounds need not be used in the process. The above process produces crude terephthalic acid (CTA) with 1.4-2.2% of 4-CBA. Purification of CTA is required to obtain purified terephthalic acid (PTA).

US 2010/0174111 describes a process for the purification of aryl carboxylic acids such as terephthalic acid. The non-pure acid is dissolved or dispersed in the ionic liquid. The non-solvent (defined as a molecular solvent in which the ionic solvent has a high solubility and the aryl carboxylic acid has little or no solubility) is added to the solution to precipitate the purified acid.

US 7,692,036, US 2007/0155985, US 2007/0208193 and US 2010/0200804 disclose processes and apparatus for effecting liquid phase oxidation of oxidizable compounds. Liquid phase oxidation is carried out in a bubble column reactor which provides high efficiency reactions at relatively low temperatures. When the oxidized compound is p-xylene, the product from the oxidation reaction is CTA which must be purified. It is said that purification is easier than conventional high temperature processes.

The present invention provides a process for the oxidation of p-xylene to terephthalic acid. It has been found that the present invention can be used in the preparation of terephthalic acid compositions having different amounts of contaminants relative to those observed in conventional processes. In some embodiments, the terephthalic acid composition produced by the method has a low impurity concentration, thus reducing the cost of purification. In some embodiments, polymer grade or purified terephthalic acid is produced in the present invention without the use of catalytic hydrogenation.

One aspect of the present invention is a method for producing terephthalic acid. In one embodiment, the method comprises providing a p-xylene stream rich in p-toluic acid; Toluene-rich p-xylene stream, a solvent comprising an ionic liquid, a bromine source, a catalyst and an oxidant to produce a product comprising terephthalic acid. In one aspect, the step of providing a p-xylene stream rich in p-toluic acid comprises contacting a first solvent comprising p-xylene, a carboxylic acid, a first bromine source, a first catalyst and a first oxidant in a first reaction zone Lt; RTI ID = 0.0 > p-xylene < / RTI > stream.

Another aspect of the invention includes an apparatus for the oxidation of alkyl-aromatics. In one embodiment, the apparatus comprises a first reaction zone having at least one inlet and at least one outlet; A second reaction zone having at least one inlet and at least one outlet, wherein at least one second reaction zone inlet is in fluid communication with the at least one first reaction zone outlet; And a purification zone having at least one inlet and at least one outlet, wherein at least one purification zone inlet is in fluid communication with at least one second reaction zone outlet and wherein at least one purification zone outlet is in fluid communication with the at least one first reaction zone inlet, And a purification zone in fluid communication with the reaction zone inlet or both.

In another embodiment, the process comprises providing a p-xylene stream comprising p-toluene acid, wherein the p-xylene stream comprises a p-xylene stream formed from p-toluene acid in a concentration of at least 5% A step formed by a process of retaining a material; Contacting a solvent comprising an ionic liquid, a bromine source, a catalyst, a p-xylene stream in the providing step and an oxidizing agent to produce a product comprising terephthalic acid.

In another embodiment, the method comprises contacting p-xylene, a first solvent, a first bromine source, a first catalyst and a first oxidant to form a p-toluene rich p-xylene stream; maintaining p-toluic acid so that the concentration of p-toluene-rich p-xylene stream is at least 5 wt%; And a p-xylene stream rich in p-toluic acid, a second solvent comprising an ionic liquid, a second bromine source, a second catalyst, and a second oxidant to produce a product comprising terephthalic acid.

Figure 1 is a diagram of the reaction for the oxidation of p-xylene.
Figure 2 is a general process flow diagram for one embodiment of a process for preparing purified oxidized alkylaromatics.
Figure 3 is a general process flow diagram for another embodiment of a process for preparing purified oxidized alkylaromatics.
Figure 4 is a process flow diagram for an embodiment having a single reactor.
Figure 5 is an illustration of one embodiment of a two zone continuous stirred tank reactor.
Figure 6 is an illustration of one embodiment of a two-zone plug flow bubbling reactor.
7 is a graph showing the influence of the starting material on the impurity concentration.

In general, the present invention relates to a terephthalic acid composition, and to a process for the oxidation of p-xylene to terephthalic acid. In a broad sense, the present invention relates to a process for preparing terephthalic acid from a p-xylene stream rich in p-toluic acid.

As discussed below, when the starting material was p-toluene, which is not p-xylene, the production of 4-CBA was found to be much lower. As a result, it was determined that the p-toluene-rich starting p-xylene feed stream was desirable.

Also shown in Figure 1 is a general reaction diagram for the preparation of terephthalic acid via liquid phase oxidation of p-xylene. In a series of reactions, the preparation of p-toluic acid from p-xylene is faster in acetic acid than in ionic liquids. However, the subsequent reaction in an ionic liquid / acetic acid mixture rather than acetic acid alone is faster and more selective.

The p-toluene rich p-xylene stream can be obtained in any suitable manner including but not limited to oxidation, alkylation, and the like. For example, a stream having the desired p-toluene acid content can be produced as a product stream in a petroleum or chemical treatment complex as described below. If the initial product stream does not have the required purity, it can be purified to the desired concentration using known methods.

The p-xylene stream rich in p-toluic acid contains not less than 5 wt% and less than 90 wt% p-toluene acid. It is typically at least 10 wt%, or at least 15 wt%, or at least 20 wt%, or at least 25 wt%, or at least 30 wt%, or at least 35 wt%, or at least 40 wt% Or 50 wt% or more, or 55 wt% or more, or 60 wt% or more, or 65 wt% or more, or 70 wt% or more, or 75 wt% or more. Less than 85 wt%, alternatively less than 80 wt%, alternatively less than 75 wt%, alternatively less than 70 wt%, alternatively less than 65 wt%, alternatively less than 60 wt%, alternatively less than 55 wt%, alternatively less than 50 wt% , Or less than 40% by weight.

The p-toluic acid concentration is maintained in solution, as a colloid, or as a slurry.

The basic steps of the process involve contacting the (obtained) p-toluene rich p-xylene stream, a solvent comprising an ionic liquid, a bromine source, a catalyst and an oxidant to produce a product comprising terephthalic acid.

The contact step (s) can be carried out in laboratory scale experiments through full scale commercial operation. The method may be operated in a batch, continuous or semi-continuous mode. The contacting step can be carried out in various ways. The order of addition of the components (e.g. p-xylene stream rich in p-toluic acid, solvent, bromine source, catalyst and oxidant) is not important. For example, the ingredients may be added separately, or two or more ingredients may be added or mixed prior to combining or combining with the other ingredients.

Figure 2 is a general process flow diagram for one embodiment of a process for preparing purified oxidized alkylaromatics.

The feed 200 is introduced into the oxidation zone 210 along with the oxidant 215. The overhead condenser 225 removes heat from the reflux stream to control the temperature of the reaction zone and the absorption zone 230 and dewatering zone 235 remove offgas and water from the reaction zone.

The effluent 240 from the oxidation zone 210 is transferred to the crystallization zone 300 to complete the crystallization process. The crystallization zone 300 may comprise at least one pre-reaction zone and / or at least one crystallizer. If an entire reaction zone is needed to further increase the conversion rate, additional oxidant is needed. The entire reaction zone can be operated at lower pressure and lower temperature to aid crystallization. One or more crystallizers are used to complete crystallization of the product, such as terephthalic acid, at lower temperatures. Care should be taken not to simultaneously crystallize the impurities. The solvent comprising the ionic liquid provides a medium in which impurities and / or intermediates remain in the solvent or are further oxidized with terephthalic acid to not substantially reduce simultaneously crystallized impurities.

The crystallized product is separated from the solvent in separator zone 305. The separator zone 305 may comprise one or more of filters, centrifuges and dryers as known in the art.

The solvent 310 is used to clean the product crystals in the separator zone 305. The purified product 315 is dried and stored in a product silo. Additional separation equipment may be required to ensure that the product meets product specifications before storage.

The cleaned mother liquor 320 is transferred to the solvent separator zone 325. The solvent separation may include one or more of evaporators, distillation and / or fractionation columns, membrane separators, etc., as known to those skilled in the art. The ionic liquid 260 is recirculated back to the oxidation zone 210. A make-up ionic liquid 265 can be added as needed.

The catalyst 330 is transported for catalyst recovery.

The carboxylic acid solvent (335) is dehydrated in the dehydration zone (340). The carboxylic acid solvent 205 may be recycled back to the oxidation zone 210. The constituent carboxylic acid solvent (220) can be added as needed. The wastewater 345 is removed.

Figure 3 is a general process flow diagram for an embodiment having two reaction zones.

In some embodiments, any type of process may be utilized in the first reaction zone. For example, any of the commercially available processes discussed in the above or other patents may be used where necessary.

In another embodiment, an oxidation process as described is used.

A feed 200 comprising p-xylene, a carboxylic acid solvent, a catalyst, a bromine source and, if present, an oxidant 215 enters the first reaction zone 210. The overhead condenser 225 removes heat from the reflux stream to control the temperature of the reaction zone and the absorption zone 230 and dewatering zone 235 remove offgas and water from the reaction zone.

 The product from the first reaction zone, which is a p-toluene rich p-xylene stream, is used as feed 240 to the second oxidation reaction zone 245. The feed may comprise a carboxylic acid solvent, an ionic liquid solvent, a catalyst, and a bromine source. The feed to the second oxidation reaction zone 245 also includes an oxidant 250 and a recycled ionic liquid stream 260. The ionic liquid solvent stream 260 may include not only the constituent ionic liquid 265 but also the recovered ionic liquid.

The solvent in the second oxidation reaction zone 245 may include a carboxylic acid solvent and an ionic liquid. Compared to conventional processes, when using an ionic liquid to avoid excess solvent volume, the amount of carboxylic acid solvent is reduced.

The overhead condenser 270 removes heat from the reflux stream of the second oxidation reaction zone 245 to control the reactor temperature and the absorption zone 275 and dehydration zone 280 remove offgas and water from the reaction zone do.

The second oxidation reaction zone 245 may include a stream 285 directed to the heat exchanger 290, returning to the second oxidation reaction zone 245. Depending on the design of the reaction zone, the cooler recycle stream can be returned to the vapor space, the upper stage of the reaction zone, or the appropriate location in the plug-flow reaction zone.

The effluent mixture 295 from the second oxidation reaction zone 245 is transferred to the crystallization zone 300 to complete the crystallization process. The crystallization zone 300 may comprise at least one pre-reaction zone and / or at least one crystallizer. If an entire reaction zone is needed to further increase the conversion rate, additional oxidant is needed. The entire reaction zone can be operated at lower pressure and lower temperature to aid crystallization. One or more crystallizers are used to complete the crystallization of terephthalic acid at lower temperatures.

The crystallized product is separated from the solvent in separator zone 305. The separator zone 305 may comprise one or more of filters, centrifuges and dryers as known in the art.

The solvent 310 is used to clean the product crystals in the separator zone 305. The purified product 315 is dried and stored in a product silo. Additional separation equipment may be required to ensure that the product meets product specifications before storage.

The cleaned mother liquor 320 is transferred to the solvent separator zone 325. The ionic liquid 260 is returned to the second oxidation reaction zone 245 and optionally to the first oxidation reaction zone depending on the process used in the first reactor. The constituent ionic liquid 265 can be added as needed.

The catalyst 330 is transported for catalyst recovery.

The carboxylic acid solvent (335) is dehydrated in the dehydration zone (340). The carboxylic acid solvent 205 may be recycled back to the first oxidation reaction zone 210. The constituent carboxylic acid solvent (220) can be added as needed. The wastewater 345 is removed.

The first and second reaction zones may be present in different reactors if desired. However, the additional processing cost of the second titanium reactor is greatly increased. Also, adding a second reactor to an existing plant may not be readily possible.

Thus, the first and second reaction zones may be present in a single reactor if desired. As shown in FIG. 4, the two reaction zones 210 ', 245' are two zones within a single reactor 350. By properly designing the two zones, the same result can be obtained.

Figure 5 shows an embodiment of a continuous stirred tank reactor (CSTR) 400 in which two zones are designed. Feed 405 enters a first reaction zone 410, such as an annulus. Feed 405 comprises an alkyl aromatic compound with a catalyst and a carboxylic acid as a solvent. The oxidant 415 enters the first reaction zone 410 through the gas distributor ring 420 if necessary. After a short residence time, e.g., less than 10 minutes to 40 minutes, the reactants and products 425 from the first reaction zone 410 overflow and enter the second reaction zone 430. When p-xylene is used as the starting material, the main product from the first reaction zone 410 must be p-toluic acid, which will react further in the second reaction zone 430 to produce terephthalic acid. The overhead carboxylic acid and water will condense in the condenser 435 to return 440 to the first reaction zone 410. The condenser 435 is located at the top of the reactor 400 to minimize the carryover. The reaction time in the second reaction zone is typically longer in the first reaction zone, for example over 10 minutes. The reaction conditions in the first and second reaction zones are similar to those discussed below.

The concentration of the second reaction zone 430 is controlled. There is a second distribution ring 445 for introducing the oxidant 450 into the second reaction zone 430. Vapor from the second reaction zone 430 generates bubbles through the first reaction zone 410 to provide proper mixing in the first reaction zone 410. The mother liquor and ionic liquid solvent 455 enter the bottom of the second reaction zone 430 and mix with the feed 425 coming from the first reaction zone 410. The product 460 of the second reaction zone 430 exits through an internal or external air remover 465. In order to control the ionic liquid to carboxylic acid ratio, a specific amount of carboxylic acid from the condenser 420 can be returned to the second reaction zone 430 with the constituent carboxylic acid 475, if necessary.

The CSTR reactor includes an impeller 480 having a baffle 485 for mixing the contents of the second reaction zone 430.

FIG. 6 illustrates a two-zone plug flow bubbling reactor 500 including a first reaction zone 505 and a second reaction zone 510. A feed 515 comprising an alkyl aromatic compound, a carboxylic acid solvent and a catalyst enters the first reaction zone 505. An oxidant is added to the first reaction zone (505). The first reaction zone 505 is located above the second reaction zone 510. Reactants and products 520 flow from the top of the first reaction zone 505 to the second reaction zone 510. A feed 525 for a second reaction zone 510 containing an ionic liquid solvent and mother liquor is introduced near the top of the second reaction zone 510. The overhead acetic acid and water are condensed in the condenser 530 to return 535 to the first reaction zone 505.

A distribution ring 550 is present to introduce the oxidant 55 into the second reaction zone 510. Vapor from the second reaction zone 510 generates bubbles through the first reaction zone 505 to provide proper mixing in the first reaction zone 505. The product 560 of the second reaction zone 510 exits through the inner or outer air remover 465 in the middle of the second reaction zone 510. To control the ionic liquid to carboxylic acid ratio, the carboxylic acid 540 from the condenser 530 can be returned to the second reaction zone 510 with the constituent carboxylic acid 545 if necessary.

The product recovery process and equipment may be similar to those described above for the two reactor systems.

The solvent includes at least one ionic liquid. If necessary, two or more ionic liquids can be used.

Generally, an ionic liquid is a non-aqueous organic salt composed of ions in which the cation is balanced with the anion. These materials often have melting points as low as 100 占 폚 or less, have an undetectable vapor pressure, and have good chemical and thermal stability. The cationic charge of the salt is polarized throughout the heteroatom, and the anion can be any inorganic, organic or organometallic species.

Most ionic liquids are formed from cations that do not contain acidic protons. The synthesis of ionic liquids can generally be divided into two parts: the formation of certain cations, and the formation of certain products by anion exchange. For example, quaternization of amines or phosphines is an early step in the synthesis of cations of ionic liquids. If it is impossible to directly form a predetermined anion by the quaternization reaction, an additional step is required.

Hundreds of thousands of simple ion combinations for producing ionic liquids, and a nearly infinite (10 ¹⁸ ) number of possible ionic liquid mixtures are estimated. This means that it should be possible to design an ionic liquid having certain characteristics to suit the particular application by selecting the anion, cation and mixture concentration. The ionic liquid may be adjusted or adjusted to provide a specific melting point, viscosity, density, hydrophobicity, miscibility, etc. for a particular application. The thermodynamics and the reaction kinetics of the processes carried out in ionic liquids are different from those in conventional media. This creates new opportunities for catalysis, separation, combined reaction / separation processes, heat transfer agents, hydraulic fluids, paint additives, electrochemical applications, as well as many others. Ionic liquids do not release volatile organic compounds (VOCs), providing a basis for clean manufacturing, such as "green chemistry. &Quot;

Organic cations may include linear, branched, or cyclic heteroalkyl units. The term "heteroalkyl" refers to a cation that contains at least one heteroatom selected from nitrogen, oxygen, sulfur, boron, arsenic, boron, antimony, aluminum or phosphorus capable of forming a cation. Hetero atoms may be part of a pyridinyl, imidazole ring which may have a ring formed with one or more other heteroatoms, such as substituted or unsubstituted straight or branched chain alkyl moieties attached thereto. In addition, the cation may be a single heteroatom wherein a sufficient number of substituted or unsubstituted straight or branched chain alkyl units are attached to the heteroatom to form a cation.

Non-limiting examples of heterocyclic and heteroaryl units that may be alkylated to form a cationic unit include imidazole, pyrazole, thiazole, isothiazole, azathiazole, oxothiazole, oxazine, oxazoline, And examples of the organic solvent include dicyclohexylcarbodiimide, dicyclohexylcarbodiimide, dicyclohexylcarbodiimide, dicyclohexylcarbodiimide, dicyclohexylcarbodiimide, dicyclohexylcarbodiimide, dicyclohexylcarbodiimide, Include furan, benzothiophene, dibenzothiophene, thiadiazole, pyridine, pyrimidine, pyrazine, pyridazine, piperazine, piperidine, morpholine, pyran, anoline, phthalazine, quinazoline and quinoxaline do.

The anion portion of the ionic liquid may comprise an inorganic, organic or organic metal moiety. Non-limiting examples of anions include inorganic anions: halogens (e.g., F, Cl, Br, and I); Of borides, BX ₄ (formula, X is a halogen (e.g., BF _4, BCl _4), and the like; phosphate _{(V), PX 6; PF} 6 , and the like; arsenate _{(V), AsX 6; AsF} 6 , and the like; antimonate (V) (antimony), SbX _6; SbF _6, such ^{_{as; CO 3 2-; NO 2 1-}} , NO 3 1-, SO 4 2-, PO 4 3-, (CF 3) SO 3 1- and their Derivatives.

Other non-limiting examples of ionic liquid anions include substituted azolates, a 5-membered heterocyclic aromatic ring (imidazolylate) having a nitrogen atom at positions 1 and 3; A 5-membered heterocyclic aromatic ring (1,2,3-triazololate) having nitrogen atoms at 1, 2 and 3 positions; Or a 5-membered heterocyclic aromatic ring (1,2,4-triazolate) having nitrogen atoms at 1, 2 and 4 positions. It includes groups, and NH ₂ (amino), NO ₂ (nitro) substitution of a ring is a CN (cyano) addition takes place at a position (these being carbon position) are not on the nitrogen position, the heterocyclic azole rate Core .

Further non-limiting examples of anions include substituted or unsubstituted borides: B (R) ₄ ; Substituted or unsubstituted sulphate: (RO) S (= O) ₂ O; Substituted or unsubstituted acyl units RCO ₂ such as acetate CH ₃ CO ₂ , propionate, CH ₃ CH ₂ CO ₂ , butyrate CH ₃ CH ₂ CH ₂ CO ₂ and benzylate, C ₆ H ₅ CO ₂ ; Substituted or unsubstituted phosphates: (RO) ₂ P (= O) O; Substituted or unsubstituted carboxylate: (RO) C (= O) O; Substituted or unsubstituted azolates, wherein the azolate may be substituted on the carbon atom in units selected from cyano, nitro and amino. R can be an organic, inorganic, or organometallic group. Non-limiting examples of R are hydrogen; Substituted or unsubstituted straight, branched or cyclic alkyl; Substituted or unsubstituted straight, branched or cyclic alkoxy; Substituted or unsubstituted aryl; Substituted or unsubstituted aryloxy; A substituted or unsubstituted heterocyclic ring; Substituted or unsubstituted heteroaryl; Acyl; Silyl; Boryl; Phosphino; Amino; Thio; And seleno.

In one embodiment, the ionic liquid suitable for use includes, but is not limited to, one or more of an imidazolium ionic liquid, a pyridinium ionic liquid, a tetraalkylammonium ionic liquid, and a phosphonium ionic liquid. More than one ionic liquid may be used. The imidazolium, pyridinium and ammonium ionic liquids have a cation containing at least one nitrogen atom. The phosphonium ionic liquid has a cation containing one or more phosphorus atoms. In one embodiment, the ionic liquid comprises a cation selected from alkyl imidazolium, di-alkyl imidazolium, and combinations thereof. In another embodiment, the ionic liquid comprises anions selected from halides, acetic acid salts, carboxylic acid salts and combinations thereof. The ionic liquid was prepared by dissolving 1-butyl 3-methyl imidazolium acetate (BMImOAc), 1-butyl 3-methyl imidazolium bromide (BMImBr), 1-hexyl 3-methyl imidazolium acetate and 1-hexyl 3- Zolybromide. ≪ / RTI >

An ionic liquid may be provided, or it may be generated from the same system from a suitable precursor, or both. When this is produced in situ, the solvent comprises at least one precursor of the ionic liquid. Ionic liquid precursors include cationic precursors such as alkylimidazoles, alkylpyridines, alkylamines, alkylphosphines, and the like, and anionic precursors such as alkyl or aryl halides or acetic acid salts. In one embodiment, the precursors are methyl imidazole and butyl bromide.

The manner of introduction of the ionic liquid precursor may depend on the nature of the alkylaromatics to be oxidized and on the nature and purity of the desired product. In a further embodiment, a cation precursor and an anion precursor (generally liquid at room temperature and pressure) are mixed with a carboxylic acid (e.g., acetic acid) solvent and introduced into the oxidation reactor (s). In other additional embodiments, the ionic liquid precursor may be mixed with an alkyl aromatic feed and introduced into an oxidation reactor. In other further embodiments, both the cationic and anionic ionic liquid precursor components may be introduced into the bottom of the reactor without premixing with any other oxidation reactor component, such as a feedstock, a carboxylic acid solvent, and a catalyst package.

The solvent may also include a carboxylic acid. When a carboxylic acid is used in a solvent, the amount of the carboxylic acid is reduced as compared with the conventional process in order to avoid an excessive solvent volume. The carboxylic acid preferably has 1 to 7 carbon atoms. In one embodiment, the carboxylic acid comprises acetic acid. The solvent may contain more than one carboxylic acid. For example, the solvent may further comprise benzoic acid. In another embodiment, the carboxylic acid of the solvent is acetic acid.

In one embodiment, the solvent is selected such that the ratio of carboxylic acid to ionic liquid is from 1:16 to 16: 1 by weight, or from 1: 9 to 9: 1 by weight, or from 3:17 to 17: 3 by weight, Or from 1: 4 to 4: 1 by weight, or from 1: 3 to 3: 1 by weight, or from 3: 7 to 7: 3 by weight, or from 7: Based on weight of 2: 3 to 3: 2, or 9: 11 to 11: 9 on weight basis, or 1: 1 on weight basis. In one embodiment, the solvent comprises more than 5 weight percent ionic liquid, or more than 6 weight percent ionic liquid, or more than 10 weight percent ionic liquid, or more than 15 weight percent ionic liquid, or more than 20 weight percent ionic liquid, Or at least 30% by weight of ionic liquid, or at least 35% by weight of ionic liquid, or at least 40% by weight of ionic liquid, or at least 45% by weight of ionic liquid. When present in the amount of the ionic liquid, the ionic liquid precursor is included. Any ionic solid or material capable of forming an ionic salt in the solution discussed below is included in the amount of ionic liquid.

Optionally, ionic solids such as ammonium acetate (NH ₄ OAc) and / or ammonium bromide (NH ₄ Br) can be added to the mixture. Alternatively, a substance capable of forming an ionic salt in solution may be added. The material can form ionic salts in solution in combination with ions present in the solution. For example, in a solution containing bromide (e.g. in the form of HBr) or acetic acid salt (e.g. in the form of acetic acid), the ammonia may be combined with bromide or acetate ion to form ammonium bromide or ammonium acetate. The use of materials capable of forming ionic salts in one or more ionic solids or solutions has provided an additional reduction in impurity concentration.

In one embodiment, the amount of material capable of forming an ionic salt in the ionic solid and solution is in the range of 5 wt% to 45 wt%, or 10 wt% to 45 wt%, based on the weight of the solvent. Solvents include carboxylic acids, ionic liquids and / or ionic liquid precursors, any ionic solid or materials capable of forming ionic salts in solution and any water.

Optionally, the solvent may further comprise water. Water may be added to the mixture, or water may be produced in the mixture during the oxidation process. In one embodiment, the amount of water ranges from 0.01% to 5% by weight relative to the weight of the carboxylic acid. The amount of water may range from 0.1 wt% to 2 wt% based on the weight of the carboxylic acid.

In one embodiment, the ratio of solvent to p-toluene rich p-xylene stream in the mixture is from 1: 1 to 10: 1 by weight, or from 1.5: 1 to 6: 1 by weight, or from 2: 1 to 4: 1. Solvents include carboxylic acids, ionic liquids and / or ionic liquid precursors, any ionic solid or materials capable of forming ionic salts in solution and any water.

The catalyst includes at least one of cobalt, manganese, titanium, chromium, copper, nickel, vanadium, iron, molybdenum, tin, cerium and zirconium. In one embodiment, the catalyst comprises cobalt and manganese. The metal may be in the form of an inorganic or organic salt. For example, the metal catalyst may be in the form of a carboxylate salt, such as a metal acetate salt and its hydrate. Exemplary catalysts include individual or combined cobalt (II) acetate dihydrate and manganese acetate (II). In one embodiment, the amount of manganese (II) acetate is less than the amount of cobalt (II) acetic acid dihydrate on a weight basis.

The amount of catalyst used in the present invention can vary widely. For example, the amount of cobalt may range from 0.001 wt% to 2 wt% with respect to the weight of the solvent. In one embodiment, the amount of cobalt ranges from 0.05% to 2% by weight relative to the weight of the solvent. The amount of manganese may range from 0.001 wt% to 2 wt% with respect to the weight of the solvent. In one embodiment, the amount of manganese ranges from 0.05% to 2% by weight relative to the weight of the solvent. In another embodiment, the ratio of cobalt to manganese ranges from 3: 1 to 1: 2 by weight on an elemental metal basis.

Bromine source and is generally recognized in the art as a catalyst promoter, bromine, ionic bromide such as HBr, NaBr, KBr, NH ₄ Br; And / or organic bromides known to provide bromide ions under oxidizing conditions, such as benzyl bromide, mono and di-bromoacetic acid, bromoacetyl bromide, tetrabromomethane, ethylene bromide. In one embodiment, the bromine source comprises, or consists essentially of, or consists of hydrogen bromide. The amount of hydrogen bromide may range from 0.01 wt% to 5 wt% with respect to the weight of the solvent. In other embodiments, the amount of hydrogen bromide ranges from 0.05 wt% to 2 wt%, based on the weight of the solvent. Solvents include carboxylic acids, ionic liquids, any ionic solid or materials capable of forming ionic salts in solution and any water.

Suitable oxidizing agents for the process provide a source of oxygen atoms to oxidize p-xylene and / or p-toluic acid, and / or other intermediate oxidation products under the oxidizing conditions employed. Examples of the oxidizing agent include oxygen-containing nitrogen compounds such as peroxides, excess oxides, and nitric acid. In one embodiment, the oxidizing agent is a gas comprising oxygen, such as air, carbon dioxide and oxygen molecules. The gas may be a mixture of gases. The amount of oxygen used in the process preferably exceeds the stoichiometric amount required for the given oxidation process. In one embodiment, the amount of oxygen contacted with the mixture ranges from 1.2 times the stoichiometric amount to 100 times the stoichiometric amount. Optionally, the amount of oxygen contacted with the mixture can range from two times the stoichiometric amount to 30 times the stoichiometric amount.

At least a portion of the components provide a liquid phase, although dissolution of one or more of the mixtures may not be complete at any or some time during the process. The liquid phase can be formed by mixing the components under ambient conditions. In another embodiment, the liquid phase is formed while increasing the temperature of the mixture to the oxidation temperature. The mixture of components may be formed prior to the oxidation step in the same or different vessel as used in the oxidation step. In other embodiments, the mixture of components is formed in an oxidation reactor, for example, while the various streams of the components are added individually and / or in combination to a continuous or semi-continuous oxidation reactor. The various streams of combined ingredients and / or ingredients may be heated prior to mixing together.

Many conventional alkylaromatic oxidation processes are typically performed in mixed phases and often include three phases (e.g., solids, gases and liquids), but they are sometimes referred to in the art as " Because the oxidation conditions are maintained to provide at least a portion of < RTI ID = 0.0 > It is also known in the art that the number of phases present can vary over time during the process. The process according to the invention can also be carried out in liquid or mixed phase in the same manner as is known in the art.

Conventional liquid phase oxidation reactors known in the art can be used in the practice of the present invention. Examples include containers capable of having at least one mechanical stirrer and various bubble column reactors such as those described in US 7,692,036. It is also known to design, manipulate and control such reactors and oxidation reactions for the oxidizing conditions employed, including temperature, pressure, liquid and gas volume, and, if applicable, liquid and gaseous corrosion. See, for example, US 7,692,036 and US 6,137,001.

The contacting step (s) can be carried out under oxidizing conditions if necessary. Suitable oxidation conditions generally include a temperature in the range of 125 캜 to 275 캜, and a pressure in the atmospheric pressure range, i.e., a residence time in the range of 0 MPa (g) to 6 MPa (g), and 5 seconds to 2 weeks. That is, the mixture has a temperature and pressure within this range and can be maintained within this range for this period of time within this residence time range. In another embodiment, the temperature is in the range of 175 [deg.] C to 225 [deg.] C; The temperature may range from 190 캜 to 235 캜. In one embodiment, the pressure ranges from 1.2 MPa (g) to 6.0 MPa (g); The pressure may range from 1.5 MPa (g) to 6.0 MPa (g). In a further embodiment, the residence time ranges from 10 minutes to 12 hours. The oxidation temperature, pressure and residence time can be varied based on various factors including, for example, the reactor configuration, size, and whether the process is batch, continuous, or semi-continuous. Oxidation conditions can also be varied on the basis of different oxidation conditions. For example, the use of a specific temperature range may enable the use of different residence time ranges.

In one embodiment, the terephthalic acid produced by the present invention can be precipitated, crystallized or solidified under oxidizing conditions and / or in a liquid mixture while the mixture is being cooled. Accordingly, the mixture according to the present invention may further comprise solid terephthalic acid. Other compounds, including chromophores and other oxidation products, may be solidified with the solid oxidation product or entrapped therein to reduce the purity of a given product. In one embodiment, the mixture comprises a liquid phase. The mixture may contain a gas phase, such as when the oxidant is added as a gas. The mixture may comprise a solid phase, such as a mixture component, and the oxidation products or by-products are not dissolved or solidified in the mixture. In one embodiment, the mixture comprises a liquid phase, a solid phase and optionally a gaseous phase. In another embodiment, the mixture comprises a liquid phase and a gaseous phase.

As described above and discussed below, it has been found that the present invention can be used to produce oxidation products with different amounts of contaminants as compared to those observed in conventional processes. The present invention also provides a new way to control the concentration of various contaminants in the oxidation products. In one embodiment, the process according to the present invention further comprises the step of forming an oxidation product which is formed as a solid, optionally under oxidizing conditions, to produce a solid oxidation product and a mother liquor. The solid oxidation product can be separated from the mother liquor, i.e. the liquid phase, and the mother liquor of the process can be recycled, or reused in the contact step or other stages of the process described below.

The process according to the invention may comprise at least one further oxidation step. In one embodiment, the second oxidation step comprises a second oxidation temperature that is lower than the temperature of the first oxidation step. The method according to the present invention may comprise the further contacting step of the invention as described herein and / or the invention may be combined with other oxidation steps, such as conventional oxidation steps known in the art . Multiple contact and / or oxidation steps may be performed sequentially and / or concurrently, and may be combined with other processing steps such as the purification steps described herein.

In another embodiment, the present invention further comprises the step of purifying the oxidation product. Tablets may include one or more additional steps for isolating and purifying the oxidation product. Examples of purification steps include separation to separate oxidation products from the mother liquor or other liquid phase, such as filtration and / or centrifugation; Cleaning to clean the oxidation product with, for example, water and / or other solvent components; Drying of the oxidation product; And a hydrogenation process. Although the hydrogenation process can be used for purification, it is less desirable than other purification methods due to cost. These additional processing steps are described in the general literature and are well known to those skilled in the art to be used in various combinations for the purification of the oxidation products of the present invention. See, for example, the references listed in this application and the techniques described therein.

The purification step of the present invention may further comprise at least one solvent-contacting step. The solvent contacting step may comprise contacting the oxidation product comprising the solid oxide product washed or dried with at least one of water, a carboxylic acid, an ionic liquid and / or an ionic liquid precursor and a mother liquor to produce a purified oxidation product Lt; RTI ID = 0.0 > solvent. ≪ / RTI > In one embodiment, the solvent in the solvent contacting step contains an ionic liquid and a carboxylic acid, and optionally a mother liquor. The composition of the solvent for the solvent contacting step may be as described above for the contacting step.

The solvent contact can remove impurities from the solid oxidation product, and / or can partially or completely dissolve the oxidation product in the solvent. The solvent contact conditions include the solvent contact temperature. The solvent contact temperature may be lower than the oxidation temperature. In one embodiment, the solvent contact temperature is at least 20 占 폚 lower than the oxidation temperature. The solvent contact may be carried out, for example, in one or more crystallizers following the oxidation reactor in some conventional processes. The oxidation product can be solidified, precipitated or crystallized in the solvent in the solvent contacting step.

The products produced by the original process or produced according to one or more additional oxidation and / or purification steps are less than 2500 ppm of 4-CBA, or less than 2000 ppm of 4-CBA, or less than 1500 ppm of 4-CBA, or Less than 4 ppm of 4-CBA, or less than 750 ppm of 4-CBA, or less than 500 ppm of 4-CBA, or 250 ppm of 4-CBA, or less than 100 ppm of 4-CBA, , Or less than 25 ppm of 4-CBA.

It should be noted that the terms "first", "second" and "third" are used to distinguish one component, or composition, or step, or zone, or reactor, The " second "step or zone does not necessarily follow the" first "step or zone, e.g., physically or temporally. Depending on the context, it may be before or after, as will be understood by those skilled in the art.

Example

Embodiments are provided to further illustrate some aspects and advantages of the present invention, which should not be considered as limiting the scope of the present invention.

Example 1: Experimental procedure: A fume hood was charged with a Parr reactor having a specified amount of constituent for the given experiment and the reactor was sealed. The Fare reactor included a gas distributor to distribute the gas through the 1.6 mm opening to the liquid, a mechanical gas catch stirrer, and a baffle ensuring thorough mixing. The FARR reactor was installed in the heater assembly at room temperature, the gas feed line connected to the reactor, and the condenser connected to the reactor outlet. During operation, gas was discharged from the reactor through the condenser, then through the trap, and then through the back pressure regulator. A safety vent and a thermocouple with rupture discs were connected to the reactor. The coolant re-circulator was connected to the condenser and the coolant was recycled. A pressure test was performed on the Parr reactor at room temperature and 1.4 MPa (g) (200 psig) using nitrogen until no pressure drop persists for 15 minutes. The back pressure regulator on the outlet of the reactor was set to the experimental pressure and the reactor was subjected to a pressure test under a nitrogen atmosphere.

The temperature of the reactor was raised to the experimental temperature in a nitrogen atmosphere. I always followed all instructions for a particular reactor, including temperature and pressure limits. When the reactor reached a predetermined temperature, it began to add air at an experimental rate and monitored the reactor temperature and pressure for the duration of the test. During the test, maintaining the air flow entering the reactor to 2500 standard cm ³ per minute, and maintaining the pressure at 4.1 MPa (g), which was maintained with a stirrer with 1600 rpm. At the end of the test, the heater was turned off, the air flow was shut off, and the reactor was allowed to cool. When the reactor was cooled below 35 ° C, the back pressure valve was opened, the cooling water was stopped, the reactor was removed and emptied to obtain solid oxidation product and mother liquor.

The mother liquor and the product were filtered under vacuum to separate the solid and liquid. The solids were then mixed with 100 cc of deionized water at room temperature and decanted. Deionized water mixing and decanting at room temperature were repeated two more times. Washed four times with deionized water, heated to 95 DEG C for 30 minutes, and then filtered. Before analysis, the solids were dried at 80 DEG C for 8-24 hours.

Example 2-3: Example 2-3 was a separate test performed using the equipment and procedures provided in Example 1. [ g, operating temperature, time and air flow, and results are provided in Table 1 below.

Example 2: p-xylene was used as the starting material under oxidizing conditions.

Example 3: The same oxidation conditions as in Example 2 were used, except that p-toluic acid was used as a starting material. As shown in FIG. 7, the amount of 4-CBA and p-toluic acid in the product was considerably lower and benzoic acid was slightly lowered. Recovery and selectivity increased.

While the invention has been described in detail and with reference to specific embodiments thereof, it is evident that modifications and variations are possible without departing from the scope of the invention as defined in the claims. More specifically, while some aspects of the invention have been identified herein as being preferred or particularly advantageous, it should be understood that the invention is not necessarily limited to such preferred aspects of the invention.

Claims (10)

providing a p-xylene stream rich in p-toluic acid; And
contacting a p-toluene rich p-xylene stream, a solvent comprising an ionic liquid, a bromine source, a catalyst and an oxidant to produce a product comprising terephthalic acid
≪ / RTI > The process of claim 1, wherein the step of providing a p-xylene stream enriched in p-toluic acid comprises providing a p-xylene stream comprising p-toluene acid, wherein the p-xylene stream is formed from p- Xylene stream at a concentration of at least 5 wt%. ≪ Desc / Clms Page number 12 > The method of claim 1, wherein the step of providing a p-xylene stream enriched in p-toluic acid comprises contacting p-xylene, a first solvent, a first bromine source, a first catalyst and a first oxidant to form p- To produce a xylene stream. 4. The method according to any one of claims 1 to 3, wherein the solvent further comprises a carboxylic acid. 5. The method of claim 4, wherein the solvent has a ratio of carboxylic acid to ionic liquid in the range of from 1:16 to 16: 1 by weight. 4. The process according to any one of claims 1 to 3, wherein the catalyst comprises at least one of cobalt, titanium, manganese, chromium, copper, nickel, vanadium, iron, molybdenum, tin, cerium and zirconium. 4. The method according to any one of claims 1 to 3, wherein the ionic liquid is formed in situ from at least one ionic liquid precursor. 4. The method according to any one of claims 1 to 3, wherein the cation of the ionic liquid is selected from the group consisting of imidazole, pyrazole, thiazole, isothiazole, azathiazole, oxothiazole, oxazine, oxazoline, oxazaborol oxazaborole), dithiazole, triazole, celenosol, oxaphosphole, pyrrole, boron, furan, thiophene, phosphol, pentazole, indole, indoline, oxazole, isothiazole, Pyridine, pyrrolidine, morpholine, pyran, annoline, phthalazine, pyridine, pyrimidine, pyrazine, pyridazine, piperazine, piperidine, morpholine, , Quinazoline, quinoxaline, or a combination thereof. 4. The method according to any one of claims 1 to 3, wherein the anion of the ionic liquid is selected from the group consisting of halides, borides, phosphates, arsenates, stibates, acetates, carboxylates, azolates, Acyl unit, CO ₃ ^2- , NO ₂ ^1- , NO ₃ ^1- , SO ₄ ^2- , PO ₄ ^3- , (CF ₃ ) SO ₃ ^1- , derivatives thereof, or combinations thereof. A first reaction zone having at least one inlet and at least one outlet;
A second reaction zone having at least one inlet and at least one outlet, wherein at least one second reaction zone inlet is in fluid communication with the at least one first reaction zone outlet; And
Claims 1. A purification zone having at least one inlet and at least one outlet, wherein at least one inlet of the purification zone is in fluid communication with at least one outlet of the second reaction zone and at least one outlet of the purification zone comprises at least one inlet of the first reaction zone, A purification zone in fluid communication with the zone entrance or both
≪ / RTI > of the alkyl-aromatic compound.

Images