CN1332714A - Purification and production method of high-purity aromatic polycarboxylic acid and derivatives thereof - Google Patents

Abstract

The present invention provides a process for the solvent extraction purification of aromatic polycarboxylic acids or derivatives thereof, having a purity which meets or exceeds the polymerization grade specifications. The process comprises dissolving a crude aromatic polycarboxylic acid or a derivative thereof (e.g., methyl ester) in a basic compound, removing impurities and an excess of the basic compound, and also removing residual basic compound when recovering the product. This purification process not only removes impurities from the crude acid or derivative thereof, but also simultaneously removes residual base compounds from the final product that contaminate the product. The salt in the percolated cake is converted to the product by acid substitution, pyrolysis, or electrolysis. The process uses an alkaline extraction solvent to extract the alkaline compounds and impurities from the salt. Then, the residual alkali compounds in the recovered product are removed by leaching, stripping, electromagnetic wave thermal agitation, or pyrolysis evaporation. The purification process eliminates the need for crystallizers and equipment for drying and gas delivery. Finally, combining this purification process with the oxidation and solvent recovery of the currently known technology, one can reduce the two current process steps for the production of aromatic polycarboxylic acids or derivatives to one, thereby significantly reducing the production costs.

Description

Purification and production method of high-purity aromatic polycarboxylic acid and derivatives thereof

scope of invention

The present invention relates to high-purity aromatic polycarboxylic acids and derivatives thereof, and in particular to improved purification and methods for producing high-purity aromatic polycarboxylic acids or derivatives thereof (such as esters).

Background of the invention

Aromatic polycarboxylic acids are prepared by oxidizing the corresponding alkyl groups on aromatic compounds. Examples of such acids are: Pure Terephthalic Acid (PTA), Isophthalic Acid (IPA), Phenylbenzene Trimellitic Acid (TMA), 2,6-Naphthalene Dicarboxylic Acid (2,6-Naphthalene Dicarboxylic Acid,, 2,6-NDA), 2,7-Naphthalene Dicarboxylic Acid (2,7-NDA), etc. . Since PTA is the most typical method, it will be used to illustrate the present invention. However, the purification and production methods of the present invention are also applicable to all aromatic polycarboxylic acids and derivatives thereof.

The main production method of PTA is to produce crude terephthalic acid (CrudeTerephthalic Acid, CTA) in the following steps.

1) Oxidation: P-xylene (PX) is oxidized with air in a liquid phase at 150-230°C and 150-425 psia, using cobalt-manganese-bromine as a catalyst and acetic acid as a solvent to form terephthalic acid.

2) Crystallization: The effluent from the oxidation reactor is crystallized under reduced pressure and temperature through 3 to 5 large crystallizers to precipitate terephthalic acid from the mother liquor.

3) Filtration: The crude acid is separated from the mother liquor via centrifugation/filtration. Treated or untreated mother liquor is recycled to the oxidation step.

4) Drying: Dry the crude acid with inert gas, and the acetic acid carried by the inert gas is recovered by the scrubber. The dried crude terephthalic acid is transported by air to the storage silo, so a large amount of nitrogen, or air separation equipment is required.

5) Solvent and catalyst recovery: Solvents and catalysts can be recovered through many different methods.

CTA with about 0.5% impurity was hydrogenated to produce polymer grade PTA containing about 25PPM 4-p-acid benzaldehyde (4-CBA), 150PPM p-toluic acid and 0-50PPM benzoic acid. Similar to the above-mentioned CTA process, the PTA purified by the hydrogenation reaction must also be recovered through similar procedures of crystallization, filtration, and drying. Therefore, to remove about 0.5% of impurities from the reactor effluent and purify the product to about 0.025% impurities, the current process requires the following expensive steps:

1) Two sets of process steps of crystallization, centrifugation/filtration, drying and gas delivery.

2) Purification by means of expensive chemical reactions. In addition to the equipment cost of the expensive hydrogenation unit, high production costs are also required due to the operation at high pressure and high temperature and the use of noble metal catalysts.

3) Relatively long crystallization residence time. CTA needs about 3-5, and PTA needs about 5 large crystallizers to recover the product from the mother liquor. In addition, due to the highly corrosive bromine and acetic acid environment, some crystallizers must use expensive corrosion-resistant materials, such as titanium-lined equipment.

4) Step procedure of drying and gas delivery to make the final product.

5) The product, while meeting polymer grade specifications, still contained about 0.01% impurities.

High-purity PTA and its derivatives must be used in the manufacture of polyester fibers, films, and molding resins. The reason why terephthalic acid is difficult to purify is mainly because of its low solubility in most solvents, high boiling point, and similar physical and chemical properties of products and impurities.

Another method of purification is solvent extraction to remove impurities. Solvent extraction, attractive for its lower cost, dates back to 1953 (US Patent 2,664,440), or possibly earlier. Solvents suggested earlier were unstable, reactive with the product, toxic, or did not purify the CTA to the required degree. Subsequently, Iwane (US Patent 5,344,969) and Hirowatari (US Patent 5,565,609) disclosed methods using more stable solvents. These methods are outlined below.

1) Dissolving crude acid: Aromatic polycarboxylic acid and many basic compounds will form salts, and this salt can be dissolved in many dissolving solvents, such as warming water or alcohol.

2) Removal of impurities: Some impurities can be easily separated by pretreatment of the solution, such as using activated carbon to adsorb colorants. However, impurities whose properties are close to those of acids must be cooled to at least 30°C and separated from the mother liquor in the form of crystallization.

3) Product recovery: Hirowatari thermally decomposes the pretreatment solution by heat treatment, or in the presence of ethylene glycol, heats and decomposes by contacting the steam with the concentrated solution. Iwane precipitated the salt, washed it, and converted it to a purified product by thermally decomposing it, or adding an acid-substituting solvent to replace the product acid in the salt. Iwane also recovered the product by adding an acid-substituting solvent directly into the solution.

Both Iwane and Hirowatari use amine compounds containing only nitrogen as a heteroatom, such as aliphatic, alicyclic, aromatic, or heterocyclic amines. Iwane used alcohol as a dissolving solvent to purify crude NDA from oxidation. Hirowatari uses water as a dissolving solvent to recover aromatic dicarboxylic acids from hydrolyzed polyester resins. Since the only impurities contained are additives and colorants, which can be easily recovered and separated by activated carbon, this method does not separate the purified salt by crystallization. Therefore, this method is only suitable for the purification of highly purified PTA (which only contains additives and colorants that are easily separated), and is not suitable for the purification of crude aromatic dicarboxylic acids containing oxidized impurities that are difficult to separate.

For pyrolysis, Iwane added salts to paraffins, alkylbenzenes, alkylnaphthalenes, or alkylbiphenyls and heated without using steam. But the selected high boiling point solvent will remain in the product as another pollutant. Hirowatari heated and refluxed the pretreatment solution to decompose the amine salt, or concentrated the solution by distillation, and then contacted with steam to decompose and remove the amine compound. Ethylene glycol is mainly used to increase the reflux temperature, but reflux will increase the residual amount of alkali compounds in the product, and the distillation method must evaporate more than 50% of the water, so a large amount of energy is required.

Iwane was able to improve the purity of 2,6-NDA from 97.2% to about 99.8%, while Hirowatari was able to recover PTA with a purity of about 99.9% from hydrolyzed polyester resin. Iwane was only able to purify crude NDA from the reactor effluent, which was less pure than CTA, to a degree close to CTA using his method. Although the above two methods can improve the purity of the product, they still cannot reach the specification (>99.98%) of polymer grade PTA.

Another method is Lee (US Patent No. 5,767,311 ), which directly dissolves CTA in N-methylpyrrolidone (NMP) at 140-190° C. without using a dissolving solvent. The solution is cooled to 5-50°C to precipitate crystals. The precipitate was filtered and washed to bring the PTA to polymer grade. Experiments using this method have shown, however, that there is still considerable salt contamination of the product. The formation of this contamination may be due to its failure to understand that in this method, PTA and NMP will form salts. Lee thought the precipitate from the solution was PTA, but in fact it was still a salt. During the wash, the salt is converted to product by the wash solvent, such as methanol or water. However, a large amount of salt remains unconverted because washing alone cannot convert all the salt to product. This method of dissolution and solvent recovery is expensive. Compared with amine compounds or morpholine, NMP is about 2-3 times more expensive, and needs to use 3-5 times the amount to dissolve crude acid. Moreover, the boiling point of the solvent is high, and a large amount of heat energy must be spent for recovery. Additionally, Lee incorrectly believed that CTA was soluble in non-aqueous morpholine solutions. Regardless of the solution temperature, unless water is present, its solubility is negligibly small. Even if morpholine is able to dissolve CTA, the end product will not be PTA but a salt because methanol cannot convert the precipitate of morpholine salt into PTA. The distinction between NMP and morpholinium salts will be discussed in more detail later, and the present invention will take advantage of them. The present invention will use a new crystallization method and washing solvent to improve the quality of the product of this method.

Even with all the advantages mentioned above, no commercial use of solvent extraction purification has been found. One of the main problems is that the residual alkali compound remaining in the final product turns out to be a pollutant. All of the proposed organic base compounds contain nitrogen which will cause color and some other problems in the manufacture of polyester, and there is no prior art disclosing this problem and how to remove the base compound from the product.

Crystals usually contain residual solution upon crystallization. With some known crystallization methods, it may contain more than 0.1% residual lye, which is close to the level of impurities in CTA. In order to be suitable for the production of polyester, the residual alkali compound must be removed to the level of about a few million, which is close to the level of PTA impurities. Thus, known solvent extraction techniques remove impurities from the crude acid, but contaminate the product with residual alkali compounds, making it unsuitable for the manufacture of polyesters.

All known methods do not attempt to remove residual base from the final product. Iwane teaches the use of acid solvents, Hirowatari teaches the use of water to wash the base compounds in the filter end product cake, and Lee teaches the use of NMP, p-xylene, acetone, methyl ethyl ketone, or methanol to wash the filter cake. Experiments using a 100:1 ratio of water to wash and leach the filter cake for 10 hours produced a purified product that still contained significant amounts of base compounds. This shows that once the alkali compound is contained in the product crystal, it is difficult to be removed. Because the known literature does not discuss this problem, or it is known but still to be solved by those who are familiar with the art.

In the known solvent extraction purification methods, all explicitly or implicitly teach replacing the hydrogenation unit with solvent extraction, and using CTA as the feed, only Lee is an exception. He mistakenly believed that high levels of CTA could be recovered by direct filtration of the reactor effluent without the use of crystallizers or other methods. But with direct filtration, most of the CTA is still present in the mother liquor in the reactor effluent, which requires a rather long residence time to precipitate the CTA. There is a reason why the current process uses 3-5 large crystallizers to recover CTA. The present invention proposes the use of flash and evaporation to reduce residence time.

The solvent extraction purification method itself also requires crystallization, filtration, drying and gas delivery. Therefore, the known solvent extraction purification technology also requires two sets of process steps to produce PTA. Therefore, all known solvent extraction methods for the purification of aromatic polycarboxylic acids have the following disadvantages:

1) Containing residual alkali compound in the crystal, which contaminates the final product.

2) Two sets of equipment for crystallization, centrifugation/filtration, drying and gas delivery are required.

3) The final product still contains obvious detectable impurities.

4) Requires considerable residence time to crystallize, thus requiring several large crystallizers.

5) Drying and gas delivery are required to make the final product.

Therefore, several objectives of the present invention are:

1) Provide a set of solvent extraction purification methods to remove impurities from crude acid to meet or exceed the specifications of aromatic polycarboxylic acid polymer grades.

2) Removal of alkali compounds in the final product to make it suitable for use in the manufacture of polyester fibers, films, molding resins, or other applications.

3) To provide a method for producing polymeric-grade aromatic polycarboxylic acids, which requires only one set of process steps, thereby substantially reducing investment and production costs.

4) Reduce the number of crystallizers, or even eliminate them altogether.

5) Production of aromatic polycarboxylic acids that can be directly used in the manufacture of polyester without the use of drying and gas delivery steps.

The solvent extraction method disclosed in the present invention is unexpectedly and surprisingly found that it can remove impurities to a level that cannot be detected by current standard HPLC, so further advantages will be more obvious.

Summary of the invention

The present invention provides a method for solvent extraction and purification of aromatic polycarboxylic acid or its derivatives, the purity of which can meet or exceed the specification of polymer grade. The process involves dissolving crude aromatic polycarboxylic acid or derivatives thereof (such as methyl ester) in a base compound, removing impurities and excess base compound, and removing residual base compound when recovering the product. This purification process not only removes impurities from the crude acid or its derivatives, but also simultaneously removes residual base compounds that contaminate the product from the final product. Salts in the filter cake are converted to products by acid substitution, pyrolysis, or electrolysis. This method uses a base extraction solvent to extract base compounds and impurities from the salt. Then, the residual alkali compound in the recovered product is removed by leaching, steam stripping, electromagnetic wave thermal agitation, or pyrolysis evaporation. This purification method avoids the use of crystallizers and equipment for drying and gas delivery. Finally, combining the purification method with the oxidation and solvent recovery of the currently known technology can reduce the current two sets of process steps for the production of aromatic polycarboxylic acids or derivatives to one set, thereby significantly reducing production costs.

Detailed description of the invention

The invention provides a set of solvent extraction and purification methods for aromatic polycarboxylic acid or its derivatives, the purity of which can meet or exceed the polymerization level. This method is applicable to any polycarboxylic acid, such as PTA, IPA, TMA, 2,6-NDA, 2,7-NDA, etc. The method is also applicable to derivatives of the acid, including esters such as dimethyl terephthalate (DMT), dimethyl 2,6-naphthalene dicarboxylate (2,6-NDC), hydrolyzed polyesters, and the like. The process involves dissolving crude aromatic polycarboxylic acid or its derivatives in a base compound; removing impurities and excess base compound; and removing residual base compound when producing a purified product. Preferred base compounds are bases containing oxygen and nitrogen heteroatoms, such as morpholine or NMP, and others discussed in more detail below. Salts in the filter cake can be converted back to product by acid substitution of solvent, pyrolysis, or electrolysis.

In addition to removing impurities from the crude acid or its derivatives, this method uses a base extraction solvent to extract base compounds and impurities from the salt and recover the product. Residual alkali compounds in the recovered product can be further removed by leaching, stripping, thermal agitating with electromagnetic waves, or evaporation with thermal decomposition. The residual base compound is not an impurity, but a contaminant introduced by the purification process. The purification method can avoid the use of crystallizers and drying or gas delivery equipment, thereby reducing costs. Finally, this purification method will combine traditional oxidation and solvent extraction techniques (both of which use two sets of purification process steps), and only use one set of process steps to produce aromatic polycarboxylic acids.

The crystals of the aromatic polycarboxylic acid purified by solvent extraction can be adsorbed on the surface of the crystal; trapped in cracks, crevices, or aggregated; and contained in a liquid bag containing the alkali compound and other solvents used. Alkaline compounds in crystals are not necessarily liquid, but may form solid salts with crystalline acids. Washing or pyrolysis only makes it possible to remove a part of the adsorbed or trapped solvent, but not those contained in the product crystals having a melting point of about 300-425°C. It is extremely difficult to remove these residual alkali compounds from the product crystals.

Known techniques use inert gases to avoid oxidation of the base compound causing discoloration and deterioration of the product, but this only hides the problems caused by the presence of the base compound. Standard HPLC analytical methods can only measure impurities and not non-aromatic bases; product color measurements cannot detect bases unless they are intentionally oxidized to reveal their presence. A simple method to detect residual alkali compounds is to oxidize the final product to a non-white color by heating at high temperature for a long time, measure its chroma with the current color measurement method, and compare it with PTA purified by hydrogenation.

The base compound not bound to the carboxylic acid function in the purified salt is the base compound in excess. Mere removal of excess base compound from the salt does not completely avoid contact with the base compound during product recovery, since the base compound is still a component of the salt. Therefore, an additional method is required, which is extremely difficult and non-obvious, to remove the residual alkali compound contained in the recovered product crystals.

The present invention has discovered that base extraction solvents are capable of extracting base compounds and impurities from salts and recovered products. A suitable base extraction solvent is any compound that does not contain nitrogen and has low solubility for target crystals or can convert salts into product acids; has high solubility for base compounds and impurities; and is easy to separate from the product, or does not need to be separated. Such solvents may contain hydroxyl, carbonyl, ether, ketone, ester or other functional groups.

Unless stated otherwise, the solvent extraction method is carried out under a predetermined pressure at a temperature ranging from the freezing point to the highest boiling point of the solution, and preferably the temperature used is from the cooling water temperature to the highest boiling point. The operating pressure is not particularly limited; it may be 0 to 100 absolute atmospheres, and preferably 0.001 to 5 absolute atmospheres.

The purification method for removing impurities and residual alkali compounds comprises the following steps.

Soluble crude acid or derivatives

The crude aromatic polycarboxylic acid or its derivative forms a salt with a base compound and dissolves. If the salt is soluble in the dissolving solvent, the dissolving agent can be used to increase the solubility and thereby reduce the cost of dissolution. Otherwise, no solvent is used. This also includes the rare case where certain crude acids or derivatives are soluble in base compounds but do not form salts.

The crude aromatic polycarboxylic acid or derivatives thereof may be from any source containing any impurities. It can come from oxidation reactors, intermediate or final product streams of many processes, such as intermediates in the manufacture of DMT or dimethyl 2,6-naphthalene dicarboxylate (NDC), hydrolyzed polyesters, etc. Alkali compounds include oxygen-containing and oxygen-free alkali compounds. The oxygen-containing base compound includes any base compound containing oxygen and nitrogen as heteroatoms, such as morpholine compounds, amide compounds, inorganic bases and the like. Alkaline compounds not containing oxygen include amine compounds and ammonia. Base compounds include aliphatic, alicyclic, aromatic, and heterocyclic compounds. The amount of base compound used is 0.5-100 moles per mole of carboxyl or substituted carboxyl functional groups in the aromatic polycarboxylic acid or its derivatives, and the usual amount is 1-2 moles per mole of carboxyl functional groups in the crude aromatic polycarboxylic acid. Dissolving solvents include water, alcohols, ethers, ketones, and esters, among others. The amount of dissolving solvent can be 0-100 moles per mole of carboxyl functional groups in the crude aromatic polycarboxylic acid, and the usual amount is 1-10 moles.

The known techniques all use traditional heating method to transfer energy through solvent molecules to salt ions so that they can overcome the gravitational force to dissolve the crude acid. In addition to the traditional heating method, the present invention can also use electromagnetic wave heat stirring method to dissolve crude acid or ester. The thermal agitation of ions under electromagnetic waves is different from conventional heating or microwave heating. Electromagnetic waves provide thermal agitation to both solvent molecules and salt ions. However, salt ions receive greater stirring energy than solvent molecules, allowing ions to heat other molecules, unlike traditional heating methods. Therefore, the thermal agitation method of electromagnetic waves has remarkable characteristics, such as solubility, solvent evaporation, and crystallization phenomena. For example, because salt ions receive more energy to dissolve, but may also be pyrolyzed back to the original acid or ester molecules faster, and have different solubility; due to higher vapor evaporation, better crystallization efficiency; There are different precipitation mechanisms as energetic ions may pyrolyze a portion of the salt back to the product acid or ester. Its main advantage is to effectively save energy and time for dissolution. Less dissolution time reduces solvent degradation or reaction with impurities.

Iwane and Hirowatari used oxygen-free amine compounds, while Lee used pyrrolidones, cycloaliphatic amide compounds that have both carbonyl and amine functional groups. Other preferred oxygen-containing base compounds are morpholine compounds having the character of ether and amine functional groups. Oxygen-containing and oxygen-free organic base compounds have significantly different properties in terms of basicity, dielectric constant, dipole moment, or hygroscopicity with the solvent in which they are dissolved. The present invention will take advantage of these characteristics and advantages to remove base compounds and impurities from the final product.

Oxygen-containing salts are called base salts while those without oxygen are called regular salts. Most common salts are soluble in many solvents such as water and alcohols. Salts containing ether will be called ether base salts and most are soluble in water but many are insoluble in other solvents such as alcohols. Salts containing carbonyl groups will be referred to as carbonyl base salts and are mostly insoluble in solvents including water and alcohols. Alkaline extraction solvent is a solvent with low solubility to salt or can reduce salt to product acid, and has high solubility to alkali compound and impurities, so as to purify salt and product. The inventors found that the carbonyl base salts have weaker bonds. It is thus easier to reduce the salt to the product, and remove the base compound from the product, but such salts are more difficult to form and more expensive to dissolve, whereas the opposite is true for ether base salts. Thus, the base compound separates the impurities from the crude acid, while the base extraction solvent separates the base compound and impurities from the purified salt and final product.

More specifically, aromatic polycarboxylic acids are those containing one or more fused rings, wherein two or more carboxylic acid groups may be in any position on the aromatic or fused rings, and any hydrogen may be replaced by any other functional group. replace. Examples of polycarboxylic acids containing one aromatic ring include, but are not limited to, terephthalic acid, isophthalic acid, orthophthalic acid, trimellitic acid, hemimellitic acid, trimellitic acid (trimesic acid), pyromellitic acid, and mellitic acid. Examples of polycarboxylic acids containing two aromatic rings include, but are not limited to, 2,6-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid, 1,7-naphthalene dicarboxylic acid, 1,8-naphthalene dicarboxylic acid, 2 , 3,6-naphthalenetricarboxylic acid, 1,4,5,8-naphthalenetetracarboxylic acid, and 2,3,6,7-naphthalenetetracarboxylic acid. Examples of polycarboxylic acids containing three aromatic rings include, but are not limited to, 2,6-anthracene dicarboxylic acid, 2,7-anthracene dicarboxylic acid, 2,8-anthracene dicarboxylic acid, 2,9-anthracene dicarboxylic acid, 1,9-anthracenedicarboxylic acid, 2,3,6-anthracenetricarboxylic acid, 1,4,5,8-anthracenetetracarboxylic acid, and 2,3,6,7-anthracenetetracarboxylic acid. Aromatic polycarboxylic acids also include aromatic polycarboxylic acids mixed in any proportion, for example, a mixture of 2,6-naphthalene dicarboxylic acid and 2,7-naphthalene dicarboxylic acid.

As for the base compound, the nitrogen atom on the base compound may have trivalent or pentavalent. The base compound includes all combinations of heteroatoms and carbon atoms in any different positions, and saturated or unsaturated compounds with one or more hydrogen atoms, which may be substituted by alkyl, aryl, or acyl groups, or all Ammonium salts derived from these compounds. An aqueous solution of the alkali compound may be used if it is in a solid or gaseous state under normal conditions. Alkaline compounds also include mixtures in any proportion. The inorganic base can be sodium hydroxide, potassium hydroxide, etc.

Morpholine compounds include morpholine, N-methylmorpholine, N-ethylmorpholine, N-propylmorpholine, N-isopropylmorpholine, N-methylmorpholine oxide, N-phenyl Morpholine, 4-morpholinepropionitrile, 1-morpholine-1-cyclohexene, etc. Other basic compounds containing ether functional groups also include monoheterocyclic compounds with 3 to 8 atoms containing nitrogen and oxygen atoms in the ring, which include oxazocines, oxazepines ), oxazines, oxazoles, isoxazoles, oxadiazetes, oxazirines, etc.

Amide compounds include aliphatic amides such as dimethylformamide, dimethylacetamide, acetamide, acetamide, and the like. Alicyclic amides include pyrrolidone, N-methylpyrrolidone, N-ethyl-pyrrolidone, N-alkyl-2-pyrrolidone, N-mercaptoalkyl-2-pyrrolidone, N-mercaptoethyl-2-pyrrolidone, N -Alkyl-2-thiopyrrolidone, N-methyl-2-thiopyrrolidone, N-hydroxyalkyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, lactam, etc. Aromatic amides include phenylacetamide, phenylene terephthalamide and the like.

Aliphatic amines include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, n-propylamine, di-n-propylamine, tri-n-propylamine, isopropylamine, diisopropylamine, triisopropylamine, ethylenediamine , N-methylethylenediamine, N,N-dimethylethylenediamine, N,N'-diethylethylenediamine, N,N'-dimethylethylenediamine, N,N,N' - Trimethylethylenediamine, N, N, N', N'-tetramethylethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, monoethanolamine, diethanolamine, triethanolamine, Dimethylacetamide, dimethylformamide, etc. Alicyclic amines include methylcyclohexylamine, N-methylcyclohexylamine, N,N-dimethylcyclohexylamine, ethylcyclohexylamine, N-ethylcyclohexylamine, N,N-diethylcyclohexylamine Cyclohexylamine, isopropylcyclohexylamine, N-isopropylcyclohexylamine, N,N-diisopropylcyclohexylamine, ethyleneimine, propyleneimine, etc. Aromatic amines include N,N-dimethylaniline, N,N-diethylaniline, N,N-dibutylaniline, N,N-dimethyltoluidine, N,N-diethyltoluidine wait. Heterocyclic amines include pyridine, piperidine, N-methylpiperidine, N-methylpyrrolidine, and the like.

The more commonly used base compounds are morpholine, NMP, trimethylamine, triethylamine or triethanolamine.

Alcohols include aliphatic monohydric alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, tert-butanol, n-pentanol, isoamyl alcohol, sec-pentanol, t- Pentanol, neopentyl alcohol, hexanol, heptanol, octanol, nonanol, and decyl alcohol; alicyclic monoalcohols such as cyclopentanol and cyclohexanol; aliphatic linear diols such as ethylene glycol, diol Ethylene glycol, propylene glycol, butanediol, and pentanediol; alicyclic dihydric alcohols such as 1,2-cyclopentanediol, 1,3-cyclopentanediol, 1,2-cyclohexanediol, 1, 3-cyclohexanediol, 1,4-cyclohexanediol; and aliphatic polyhydric alcohols such as glycerol, pentaerythritol, and the like. Preferred are aliphatic monohydric alcohols having 3 carbon atoms or less or aliphatic dihydric alcohols having 4 carbon atoms or less. The alcohol may be a mixture of the various alcohols mentioned above in any proportion. Preferred alcohols are methanol, ethanol, or alkylene glycols.

Ethers include dimethyl ether, dipentyl ether, diethyl ether, isopropyl ether, n-butyl ether, n-hexyl ether, chlorodimethyl ether, anisole, diphenyl ether, ethylene oxide, dioxane, trioxane alkanes, furan, tetrahydrofuran, methyl-tetrahydrofuran, tetrahydropyran, methyl-tetrahydropyran, etc. Ketones include acetone, methyl ethyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, methyl amyl ketone, methyl acetone, 2-methylcyclopentanone, cyclopentanone, cyclohexanone, etc. other. Esters include ethylene glycol methyl ether, diethylene glycol methyl ether, ethylene glycol ethyl ether, diethylene glycol ethyl ether, ethylene glycol propyl ether, ethylene glycol butyl ether, ethylene glycol benzene Methyl ether, diethylene glycol, triethylene glycol, alkyl formate, alkyl acetate, alkyl propionate, oxalate, alkyl lactate, carbonate, benzoate, etc.

Removal of impurities and excess alkali compounds

This step removes impurities through pretreatment, precipitation, separation, and washing of the filter cake. Currently known techniques have taught that impurities can be removed by solution pretreatment and cooling crystallization. In addition, the present invention will provide new methods to remove impurities and excess alkali compounds in the washed filter cake.

The purpose of solution pretreatment is to remove impurities that are easily separated from the solution, such as adsorbing colorants or additives with activated carbon, filtering insoluble impurities, flowing out or scraping off drifting impurities, etc. Methods for separating such impurities are well known, and the present invention is not intended to be limited to any particular method. If there are no such impurities in the crude acid, no solution pretreatment is required.

The purpose of crystallization is to remove impurities that are difficult to separate and whose physical and chemical properties are very close to those of the product. Under a certain temperature and solution composition, the solubility of the impurity salt is either lower or higher than that of the product salt. Thus by changing the temperature and/or composition of the solution, impurities with low solubility will precipitate first and be separated from the other substances. Precipitated product salts can then be separated from those highly soluble impurities in the mother liquor.

Currently known technology uses cooling to separate impurities by crystallization, while salts are separated by common methods, such as filtration or centrifugation. Several very large crystallizers are required because of the long residence time required for crystal growth in the mother liquor. Another approach is to control the solution composition and cool it down to reduce the required residence time. After the crude acid is completely dissolved and before crystallization, a predetermined amount of solvent is removed by common methods, such as evaporation or distillation, so that the cooled slurry still has a sufficient amount of mother liquor to separate impurities. This method can reduce but still require a relatively long crystallization residence time. Both of these approaches attempt to keep as many impurities as possible in the mother liquor to separate from the purified salt.

Current known techniques generally use alkaline compounds to wash filter salts, since the dissolving agent will immediately dissolve the salts. Due to the high viscosity of the salt, the washing efficiency is very low. In addition, this method will make the salt contain more base compounds, thereby increasing the content of base compounds in the final product. Other known techniques teach the use of aliphatic or aromatic hydrocarbons as scrubbing solvents. This method simply replaces the solvent in the crystal with the washing solvent, without any extraction ability, and its residue may contaminate the final product.

The present invention uses a base extraction solvent to remove excess base compounds and impurities from the salt. The new method includes washing and leaching with a base extraction solvent, crystallization of the salt in the presence of a base extraction solvent, precipitation of the product acid in the presence of a base extraction solvent, direct extraction of the salt, resalination crystallization, and base salt substitution.

Most base extraction solvents will not convert the salt back to the acid, but will if the solvent is used to wash the carbonyl base salt. However, if the base extraction solvent for converting the salt is mixed with a base compound, the conversion of the salt can be reduced. For example, washing filter salt with 50% methanol and NMP mixed solvent can greatly reduce the conversion of salt. The present invention wishes to keep the washing cake in the form of salt as much as possible.

More specifically, the base extraction solvent may be water, hydrogen peroxide, alcohols, ethers, phenols, ketones, esters, and the like. Alcohols, ethers, ketones, and esters have been defined previously. Alkaline extraction solvent can be used alone, or a mixture of two or more solvents mixed in any proportion, and the solvent can be used in liquid or vapor form. Preferred base extraction solvents are water, methanol, ethanol, alkylene glycol, acetone, tetrahydrofuran, or tetrahydropyran. Although the crystallization in this step is a purified salt, so the dissolving solvent is excluded as the base extraction solvent. But the crystallization of the next step is the product acid or its derivatives, then the dissolving agent may include the base extraction solvent used.

Most impurity salts are non-white in color, and excess alkali compounds have an ammonia odor. Filter cakes washed or leached with alkaline extraction solvents have significantly improved color and odor compared to salts washed with other washing solvents such as alkaline compounds or hydrocarbons. By definition, leaching is not the same as washing the filter cake (Perry's Handbook of Chemical Engineering, 6th Edition, 19-48). Methods of washing and leaching are well known, and the present invention is not limited to the use of any particular method.

After the crude acid is completely dissolved, an alkaline extraction solvent can also be added to the solution. During the crystallization process, the presence of the base extraction solvent can reduce the base compound contained in the crystal, and also extract impurities and bases from the salt. Additionally, the presence of a base extractive solvent in solution may also alter crystallization mechanisms such as shape, size, and rate. For example, the addition of methanol, acetone, or tetrahydrofuran changes the shape and increases the crystal size of the NMP-PTA salt.

In the presence of a base extraction solvent, the pure product acid can be precipitated by adding an acid substitution solvent. The presence of the base extraction solvent can extract impurities and base compounds from the precipitate. The present invention finds that, for carbonyl base salts, water can be a base extraction solvent but also an acid substitution solvent, because it can directly precipitate the product acid from a saturated solution, but other base extraction solvents, such as methanol, are in some Salts can be precipitated within the range of solution composition. However, 4-CBA and NMP salts are about 10 times less soluble in water than methanol. Compared with the prior art of salt conversion by washing, the product acid is precipitated in a solution in the presence of an alkali extraction solvent, and the salt conversion and crystal size of the precipitated product can be better controlled by controlling temperature, agitation, composition, and residence time. Known techniques add an acid instead of a solvent directly into solution to precipitate the product without using a base to extract the solvent. Because most of the impurities will precipitate together with the product, reducing the product purity.

If most or all of the solvent is removed from the solution by evaporation or flash evaporation, a solid salt or slurry is obtained. Since the impurities do not evaporate under normal operating conditions, they will all remain in the salt. Currently known techniques all avoid this situation, and crystallize in solution to leave impurities in the separated mother liquor. However, the present inventors have surprisingly and surprisingly discovered that base extraction solvents are capable of directly extracting impurities and excess base compounds from such salts. This eliminates the crystallization residence time requirement. The product recovery efficiency depends on the solubility of the salt in the base extraction solvent and the amount of solvent left in the slurry. Unlike prior art crystallization, this direct extraction from salt does not require cooling of the solution to crystallize. Before adding the alkaline extraction solvent, the mother liquor in the slurry can be separated or not. The extracted solution is separated from the salt by the usual separation method.

If the precipitate is redissolved in a solvent or alkali compound, and recrystallized one or more times, it will be possible to reach the level of impurities that cannot be detected by the current standard HPLC, or to purify the crude acid containing higher impurities to meet the requirements of polymerization. Grade Specifications. Thus, resalting crystallization includes crystallization of salt from crude acid solution; separation, washing, and redissolution of salt; recrystallization of salt from solution; separation and washing of salt in the usual way. Preferably, the salt is completely dissolved before crystallization. If the wash cake is crystallized under electromagnetic waves or washed with a base extraction solvent that converts the salt to an acid, it may contain the product acid. The acid in the wash cake may or may not be separated from the salt, or redissolved with an alkaline compound. Any of the crystallization methods discussed above can be used for crystallization and precipitation, but the method of crystallization and recrystallization by direct extraction of salt is preferred. Precipitation of the product under a base extraction solvent is preferred for the final crystallization step. The number of times of recrystallization is not particularly limited, preferably 1-2 times.

The above method can use different types of alkaline extraction solvents in different steps to remove impurities. The amount of base extraction solvent can be 0.1-100 moles, preferably 1-10 moles, per mole of carboxyl functional groups. Methanol or ethanol are preferred base extraction solvents for ether base salts, while alkylene glycols, acetone, tetrahydrofuran, or tetrahydropyran are preferred base extraction solvents for carbonyl base salts.

Salt-base substitution is a method in which a base in a salt is replaced by another base to increase product recovery. As mentioned earlier, carbonyl base salts are more difficult to form and more expensive to dissolve, but easier and less expensive to recover. For example, making NMP-PTA salt is several times more expensive than making morpholine-PTA salt, but it can be recovered with less expensive water. The present invention finds that the base compound of a salt can be replaced by another base compound with a high boiling point, so that an ether base salt or a conventional salt can be converted into a carbonyl base salt. Thus, it enables the manufacture of a purified salt from a more economical base compound, which is then converted into another salt which is easier and less expensive to recover. The converted salt is mixed with the substituting base, with or without the addition of a dissolving agent. The substituted base compound and/or dissolving agent are then separated from the solution by conventional heating or electromagnetic wave methods, using common solution separation methods, such as evaporation or distillation. The substituted salt can be precipitated by cooling in the presence or absence of a base extraction solvent, or can be obtained by direct extraction from the salt. A solvent, such as water, can be used to dissolve the unconverted salt, which can then be recovered, or the conversion can be continued in a series of steps. Salt-base substitution also includes changing the crystallization of a salt, such as shape or size, in the presence of another base compound. The amount of the substituting base can be 0.1-100 moles, preferably 1-10 moles, per mole of carboxyl functional groups.

In addition to washing the filter cake with a base extraction solvent that does not convert the salt to an acid, the filter cake can also be washed with a base extraction solvent that converts the salt to an acid or with an acid replacement solvent. This can be viewed as a combined wash with the acid substitution method discussed next, which is also the method used by Lee. However, washing has only little control over salt conversion and product properties. The present invention thinks that the better method is to precipitate the purified product acid before filtration, or to separate the purified salt by precipitation, and then convert the salt to the product acid in the method discussed in the next step, because both of the conversion of the salt, from the product The extraction of impurities and alkali compounds, as well as the size of product particles, all have good controllability. For certain base salts, the size of the salt particles can affect the size of the product particles, and the size of the salt particles can be controlled by spray drying, adjusting composition, residence time, temperature, agitation, or otherwise.

Therefore, the methods for removing impurities include solution pretreatment, cooling crystallization, solution composition control and cooling crystallization, precipitation of salts in the presence of alkali extraction solvents, precipitation of products in the presence of alkali extraction solvents, direct extraction of salts, resalination crystallization, alkali salts Substitution, washing with a base extraction solvent, leaching with a base extraction solvent, or all possible combinations of the above. In addition to removing impurities from the crude acid or its derivatives, this step also removes excess base compounds from the filter cake to reduce residual base compounds in the final product produced in the following steps.

     Manufacture of purified products while removing residual base compounds

The purpose of this step is to recover the product from the salt, if the filter cake contains a sufficient amount of salt, and/or to remove residual alkali compounds before making the final product. Methods for recovering product from purified salts include acid displacement, pyrolysis, or electrolysis. The product is preferably recovered in the presence of an extractive solvent. Because the solution composition, temperature, stirring, and residence time will affect the shape and size of the product particles, these factors should cooperate with the extraction of alkali and impurities to achieve the best condition.

Acid substitution

To convert the salt to the product, an acid displacement solvent is added to displace and precipitate the product acid from the salt. The salt can first be mixed with the base extraction solvent. A better method is to completely dissolve the ether alkali salt or conventional salt in a dissolving agent before adding the acid to replace the solvent, and the preferred dissolving agent is water, methanol, ethanol, alkylene glycol, or a mixture thereof. Carbonyl base salts are insoluble in most solvents and water is the preferred acid substitution solvent for the salts. A preferred method is to add water in the presence of a base extraction solvent such as methanol, ethanol, acetone, tetrahydrofuran, or tetrahydropyran. Acid substitution can be performed under electromagnetic waves. Acid substitution in the presence of a base extraction solvent reduces the inclusion of residual base compounds and impurities in the recovered product.

Acid-substituted solvents may be aliphatic carboxylic acids, mineral acids, water, and the like. The aliphatic carboxylic acid can be formic acid, acetic acid, propionic acid, butyric acid, hydroxyacetic acid, lactic acid, malic acid, tartaric acid, meso-tartaric acid, citric acid, monochloroacetic acid, monobromoacetic acid, mononitro acid, tris Fluoroacetic acid, and trichloroacetic acid; while the inorganic acid may be nitric acid, hydrochloric acid, hydrogen bromide, hydrogen iodide, sulfuric acid, phosphoric acid, and perchloric acid. As previously discussed, water or base extraction solvents can be acid substitution solvents for carbonyl base salts. The acid-substituted solvent can be a mixture of the above-mentioned acids in any proportion, or a mixture with a dissolving agent or a base extraction solvent in any proportion, and the proportion of the acid is greater than 1% by weight. Preferred acid substitution solvents for ether base or conventional salts are aliphatic carboxylic acids, with acetic acid being most preferred. The carbonyl base salt is preferably water. The acid-substituted solvent is used in an amount of 0.5-100 moles per mole of carboxylic acid functional groups in the aromatic polycarboxylic acid. The usual amount is slightly more than the number of moles of carboxylic acid functional groups. Pyrolysis

Adding heat to the purified salt can thermally decompose the alkali compound in the salt at a temperature range of 50-350°C. Salts can also be mixed with base extraction solvents having the desired boiling point which can be pressure controlled. Preferred base extraction compounds are water, steam, or alcohols. Heat may be applied by thermal transfer means, such as heat conduction, or by direct contact with a heat medium.

In addition to the traditional heating methods mentioned above, salt can also be heated and decomposed under electromagnetic waves. The preferred method is to mix the salt with a base extraction solvent, such as water, steam, or alcohol, in any proportion, and the solvent can dissolve the salt or acid-substituted salt, and can absorb electromagnetic waves to assist the decomposition of the salt. Electromagnetic waves can thermally stir these molecules and separate them from crystallized products that cannot absorb electromagnetic waves, and the solution is thus pyrolyzed into a mixture of converted products and unconverted salts. If the solvent concentration and temperature are maintained in an appropriate range, the solution can be continuously decomposed by electromagnetic waves. It is also possible to add a base extraction solvent to the mixture in a subsequent step to continue the decomposition. The unconverted salt can also be dissolved in a dissolving solvent to separate from the product, and the filtrate can be recycled, or the filtrate can be further pyrolyzed by electromagnetic waves in a series of steps. Therefore, this method can be used in batch or continuous mode. Compared with traditional methods, electromagnetic wave pyrolysis uses less energy and processing time. For example, this method requires only 0.04-0.6 hours compared to conventional methods that require 2-12 hours of dwell time. In addition, the thermal agitation from the inside out will reduce the chance of including alkali compounds in the crystals.

The decomposed base compound can be separated from the product by commonly used methods, such as evaporation, vacuum absorption, distillation, absorption by absorbent, or transport away with inert gas, vapor, or solvent.

For carbonyl alkali salts, a better method is to make the salt directly contact with steam or use water or steam as the base extraction solvent, and then pyrolyze and replace the salt with acid at the same time through the action of electromagnetic waves. In this case, the product particle size will be determined by the more easily controlled salt particle size. In addition, using alkylene glycol as a solvent to pyrolyze the residual salt and evaporate the solvent can avoid the use of filtration, drying and gas transfer procedures, which will be discussed later.

electrolysis

By passing an electric current through the solution formed by dissolving the purified salt in the base extraction solvent, the cathode will attract base cations and the anode will attract acid anions. If the applied current is high enough, the product acid will precipitate around the anode. Alternative methods are to replace the solvent with acid or apply heat near this electrode to precipitate the product acid, while using an electric field to separate the base cations to reduce the chance of the product acid being contained in the base compound. Electrodes are designed in the usual way to reduce the interference of ions surrounding other electrodes. This electrolytic method is similar to the well-known electrolytic production methods of metal elements, but the present invention is not limited to any specific method. The amount of current used is not particularly limited and depends on the desired yield and the electric field to separate the ions. Materials that do not react with ions and do not dissolve into solution to contaminate the product, or that deposit ions on the electrodes, are used as electrodes. Preferred base extraction solvents are methanol, ethanol, alkylene glycols, or mixtures of these solvents.

The recovered product can be separated by the commonly used methods at present, and its filter cake can be washed with an alkali extraction solvent, an acid replacement solvent, or a solvent mixture in any mixing ratio. Some recovered products can be used directly for polymerization without isolation if the following procedure is used.

Currently known techniques only remove residual alkali compounds or convert salts into products by washing, which is not enough to remove alkali compounds in the final product to an ideal level. The reasons for these final products containing relatively high residual base compounds are that the washed cake still contains too much base compound, the residual base compound is not extracted from the crystallization when the product is recovered, the solution containing a high base compound concentration is directly pyrolyzed, the The base compound is refluxed into the pyrolysis solution, or the washing solution is used as an acid replacement solvent to convert the salt, leaving many unconverted salts in the product, etc.

On the other hand, the present invention will remove excess alkali compounds in the salt as much as possible, and extract residual alkali compounds from recovered products to reduce the residual amount. However, since the base compound is a component of the salt, contact with the base cannot be completely avoided when recovering the product. Therefore, these can only be reduced, but not completely removed from the recovered product. Some of the alkali removal steps mentioned above can be omitted, but the amount of residual alkali compounds will be increased. Since the residual alkali compound is difficult to remove, the content of the alkali compound should be reduced as much as possible in each step.

The following will provide a new method of the present invention for removing residual alkali compounds in the recovered product, so that it can be applied to the manufacture of polyester. The new method includes leaching, stripping, thermal agitation with electromagnetic waves, evaporative pyrolysis, or a combination of the above procedures.

The product is recovered by leaching with an alkali extraction solvent within a predetermined amount and time, and the leaching times can be one or more times. Methods of leaching or stripping residual solvent from filter cakes are well known, and the present invention is not limited to any particular method. However, leaching or stripping can only remove some of the alkali compounds that are adsorbed or trapped, but cannot remove those alkali compounds contained in the crystals.

Electromagnetic wave thermal agitation can apply electromagnetic waves to the recovered product or its mixture with the base extraction solvent. This method is similar to the method of electromagnetic pyrolysis of salt, but its focus is on removing residual alkali compounds contained in the recovered product. The electromagnetic wave has no effect on the product crystal, but it can cause the residual alkali compound and solvent to stir and generate heat, so that the alkali ion and solvent adsorbed on the surface or contained in the crystal are separated from the crystal. Decomposed base compounds and other solvents are separated as gas, liquid adsorption, or leached by the base extraction solvent around the crystals. The base extraction solvent can be added continuously or in batches to assist in the decomposition of residual salts. This method removes residual alkali compounds and simultaneously dries the product.

Evaporative pyrolysis is to evaporate the residual solvent, such as water or acetic acid, and pyrolyze the residual alkali compound. The operating temperature can be 50-350°C, preferably 90-210°C. The recovered product is mixed with a monomer, such as an alkylene glycol, or with an oligomer (oligomer) obtained by polymerizing the product acid with the monomer (the size of the oligomer chain is 1-100 basic units), or Mix with an alkaline extraction solvent such as warmed water. High boiling alkylene glycols or oligomers are used to pyrolyze residual salts and evaporate residual solvents from solution. In addition, alkylene glycol is the building block of polyester, and the solution or filter cake can be directly used to produce polyester, thus eliminating the steps of drying and gas delivery. If the polyester plant and the purification plant are not co-located, the method can be performed at either. It is best to heat by heat transfer or electromagnetic wave thermal agitation to avoid the introduction of other ingredients. The evaporated residual solvent is removed by vacuum suction or other suitable means. The amount of alkylene glycol used is preferably that amount required for polymerization so that the treated solution can be used directly to make polyester. This step can also be applied to the existing manufacturing method by mixing the undried end product with the alkylene glycol so as to avoid the steps of drying and gas delivery. The solution obtained in this way is different from the pyrolysis solution of the product recovery mentioned above, because it contains relatively high alkali compounds and other solvents, so it is not suitable for the manufacture of polyester.

Alkaline extraction solvents used for product recovery, washing, leaching, stripping, electromagnetic wave thermal agitation, or evaporative pyrolysis are not necessarily of the same kind. The amount of base extraction solvent used is not particularly limited, and is usually 0.5-1000 mol per mol of carboxylic acid functional group.

If the residual alkali compound is not removed by evaporative pyrolysis of the alkylene glycol, if necessary, the residual solution can also be dried by the current commonly used flowing inert gas, or by the aforementioned electromagnetic wave.

The purification method by solvent extraction can be operated under air, steam, inert gas (such as nitrogen, argon, helium), or reducing gas (such as hydrogen or lower molecular weight hydrocarbon gas). This process can be batch, semi-batch, or continuous.

Recycling can improve product recovery and solvent usage efficiency. For example, the filtrate can be recycled to a previous step or used for washing or leaching to reduce solvent requirements and improve product recovery. The recycled filtrate may or may not be treated. The filtrate can be treated by any suitable method, such as distillation, filtration, centrifugation, settling, evaporation, cooling, addition of additional solvent, or any combination of the above. Methods of recycling to improve efficiency are well known, and the present invention is not limited to any particular method.

The purity of the product obtained by the above purification method is unexpected and surprisingly found that the impurity cannot be detected by the current standard HPLC measurement method. Compared with the product purity of the prior art, it is about one hundred times purer. The color of the product baked at high temperature can reach the current standard, which indicates that the alkali compound has been removed to a satisfactory degree. Low-impurity PTA offers many advantages: increased polymer molecular weight, stronger and finer fibers, lower oxygen permeability for plastic bottles, increased spinning speed for increased yield, and many other advantages that have yet to be discovered.

Combining the above purification methods with oxidation and solvent and catalyst recovery methods of the presently known technology can provide a new set of methods which reduce investment and production costs considerably. This method can be applied to the production of all aromatic polycarboxylic acids produced by oxidation of the corresponding alkyl groups, such as PTA, IPA, TMA, 2,6-NDA, 2,7-NDA and the like. PTA is the most typical example that will be used to illustrate this new method.

This combination can reduce the two sets of process steps for the current production of high-purity aromatic polycarboxylic acid into one set, which mainly brings into full play the following characteristics and advantages in the new purification method of the present invention.

1) In addition to using CTA as a feed, the new purification method can also directly use the reactor effluent as a feed without using currently known techniques to separate CTA. The effluent contains components such as catalyst (including catalyst promoters) and acetic acid which can be separated from the purification process described above. This allows reducing the currently used two sets of process steps into one, significantly reducing investment and production costs.

2) The current technology must consider the following factors, such as viscosity, particle size, product recovery, and crystal impurities, etc., and the crystallization method of the above-mentioned salt direct extraction can not consider these factors. In addition, the base extraction solvent can also be used to adjust the slurry viscosity for separation and transfer.

3) The new purification method can remove more impurities than the current hydrogenation method. This allows the oxidation reactor to operate under more economical conditions, such as lower hydrocarbon burn rates and catalyst consumption rates.

4) The new purification method may not require a crystallizer for crystallization.

5) The new purification method can use alkylene glycol for evaporative pyrolysis to avoid the steps of drying and gas delivery.

6) The new purification method uses a physical separation method instead of a chemical reaction method to remove impurities, so the investment and production costs for purification are relatively low.

7) The new purification method can produce a product with higher purity than the current one. This offers many of the aforementioned potential advantages.

The present invention exploits these mutually synergistic advantages and non-obvious features to provide a set of previously unsuggested combinations which can reduce investment and production costs considerably. The new combined method includes oxidation, dissolution of crude acid, removal of impurities and base compounds from the purified salt, removal of residual base compounds while recovering product from the salt, and recovery of solvent and catalyst. The step-by-step procedure of this process is described as follows:

Oxidation

This step oxidizes the corresponding alkyl groups on aromatic compounds to produce aromatic polycarboxylic acids. Oxidation of such aromatic polycarboxylic acids has been extensively studied over the past 50 years, and the present invention may use any of the previous methods and is not limited to any particular method.

The method developed by Medieval Company is an oxidation method widely used at present. It uses acetic acid as solvent to assist the mixing and circulation of slurry; heavy metals, such as cobalt and manganese, as catalysts; and bromine-containing compounds as accelerators. The reaction conditions are usually at 175-230°C and 1500-3000kPa.

Feeds may include recycled reflux, which may contain catalyst, reactor solvent, or intermediates from steps such as dissolution of crude acid and base compounds, removal of impurities and base compounds from purified salt, and solvent and catalyst recovery, among others.

Soluble crude acid or derivatives

The dissolution of the crude aromatic polycarboxylic acid or its derivatives in the base compound has been described previously. It was also mentioned previously that the new purification process can use either the reactor effluent or the CTA of the current process as the crude acid feed. Therefore, there are many options between these two extremes to produce crude acid. For example, if the slurry after flash evaporation of the reactor effluent is used as the crude acid, the reactor solvent and catalyst will appear along with the impurities in the filtrate of the solvent extraction purification process, which is then recovered in the solvent and catalyst recovery step. Other options are to separate the reactor solvent and catalyst from the crude acid by methods taught by known techniques such as flash evaporation, evaporation, heating/cooling, crystallization, filtration, centrifugal clarifiers , distillation, classification tower, hydrocyclone, cyclone separator, settling, replacement of mother liquor with water, membrane osmosis, or any intermediate step in the current manufacturing method of CTA. The separated mother liquor can be returned to the reactor or sent to the steps of solvent and catalyst recovery. The present invention is not limited to any particular method for separating the reactor effluent. The preferred method, however, is to evaporate most of the mother liquor in the flash reactor effluent and to recycle a small portion of the catalyst-containing mother liquor separated from the crude acid. Evaporation can also operate under electromagnetic waves. This method recovers most of the crude acid from the reactor effluent without using a crystallizer.

Another possible source of crude acid is from treated or untreated reflux filtrate, or from solvent and catalyst recovery steps.

      Remove impurities and excess alkali compounds

How to remove impurities has been described above. As mentioned earlier, controlling the composition for cooling crystallization can reduce the number of crystallizers required, and direct salt extraction crystallization can eliminate the use of crystallizers.

The treated or untreated filtrate can be recycled to other steps, or sent to solvent and catalyst recovery steps. Some impurities must be removed from this step to avoid further accumulation, and this can be done by any suitable method. One example is to evaporate the filtrate containing a large amount of impurities, and return the bottom residue to the reactor, or to convert the impurity salts into impurities by the method of product recovery before reflux.

     Residual alkali compounds are also removed while producing purified products

This step has been described previously. If alkylene glycols are used to remove residual base compounds by evaporative pyrolysis, the current drying or gas delivery steps may not be required.

Compared with the particle size obtained by the current PTA method, the product particles recovered by the acid substitution method are generally smaller, but more uniform. If the residual alkali compounds are removed with alkylene glycol, the treated mixture can be directly used for the manufacture of PET. However, if necessary, it can be redissolved and recrystallized to adjust the bulk density of PTA. This can be accomplished by various methods known to date. The bulk density of PTA after recrystallization will not only be the same as that of the currently commercially available PTA, but also the purity will be higher and contain less impurities.

Solvent and catalyst recovery

In addition to recovering the reactor solvent, water, and catalyst using currently known methods, this step also recovers base compounds, base extraction solvent, acid substitution solvent (if it is used to recover product and is different from the reactor solvent), and solvent (as it is used and different from water). Additionally, recycle filtrates from some purification steps may also contain residual impurities and products.

Not all components have to be recovered to their original purity. Some components can be recovered as a mixture. For example, in the step of dissolving the crude acid, a mixture of a base compound and a dissolving agent may be used. Furthermore, if the mixture contained some acid in place of the solvent, it had no significant effect on the purification efficiency.

In all solvents, some solvents may form azeotropes. If acid substitution is used to recover the product, the base compound and the acid substitution solvent may form an electrolyte. However, methods for separating these components are well known, such as distillation, filtration, centrifugation, settling, evaporation, pyrolysis, cooling, membrane permeation, substitution with a stronger base, substitution with a stronger acid, addition of another Substances to break azeotropes, etc. The present invention can also use electromagnetic waves for evaporation, distillation, and pyrolysis, etc.

in conclusion

Thus, the purification method of the present invention not only removes impurities in the crude aromatic polycarboxylic acid or its derivatives, but also simultaneously provides a means of removing the base compound used for purification, which would otherwise contaminate the final product. The present invention solves previously unsolved or unknown problems, and it makes the solvent extraction purification method practical.

New purification methods reduce the number of crystallizers used for crystallization, or eliminate them entirely. The use of alkylene glycols to separate residual base compounds eliminates the drying and gas delivery steps required by current techniques.

Compared with the currently known technology, the new purification method can produce a pure product with an impurity content that cannot be measured by standard HPLC methods, which is an improvement of about one hundred times. High purity offers many potential advantages such as being able to create stronger and finer new fibers, increasing spinning speeds to increase the yield of PET fibers, reducing oxygen permeability to provide new uses for PET plastic bottles, and many others yet to be discovered The advantages.

The invention makes full use of some special characteristics and advantages found in the new purification method, and combines with the current method of oxidation, solvent and catalyst recovery, and can reduce the current two sets of method steps into one set. This previously unmentioned combination can substantially reduce the investment and production costs of high purity aromatic polycarboxylic acids.

In addition to aromatic polycarboxylic acids, this purification method can be used to purify any organic acid or its derivatives containing similar physical and chemical impurities. These derivatives may contain any number of acid functional groups; acid groups substituted by other functional groups; acid groups in different positions; or acid groups in the same position but with hydrogens replaced by other functional groups, such as methyl groups and the like.

Accordingly, the scope of the invention should be determined by the appended claims and their legal equivalents rather than by the specific examples described. The present invention will be illustrated below.

Reference Example

Table 1 shows the impurity content of crude terephthalic acid (CTA) produced by the PTA method used in the experiments: Table 1 4-CBA benzoic acid p-toluic acid PTA (ppmw) 2436 1097 515

Where ppmw means parts per million by weight.

Comparative Example 1

Table 2 shows that the CTA with the same composition as Table 1 is purified by the traditional hydrogenation purification method of the prior art, and the PTA product with the impurity content shown in Table 2 is obtained: Table 2 4-CBA benzoic acid p-toluic acid PTA (ppmw) 15 not detected 141 Likewise, Table 3 shows the impurity levels of PTA products obtained from other sources: table 3 4-CBA benzoic acid p-toluic acid PTA (ppmw) 25 52 150

The impurity content of the purified product was typical of commercial polymer grade terephthalic acid.

   Comparative Example 2 (removal of impurities but not removal of alkali compounds)

150 grams of the CTA sample described in Table 1 was mixed with 198 grams of morpholine and 180 grams of water. The solution was heated to 100°C to completely dissolve the CTA, then cooled to room temperature to precipitate it. The slurry was filtered to separate from the mother liquor, and the filter cake was washed with morpholine to obtain 196 grams of wet cake. The recovered solid was then mixed with 84 grams of water and 22 grams of morpholine. The temperature of the solution was raised to 110°C to evaporate 57 ml of condensate, and then the solution was cooled to room temperature to allow precipitation. Then, the filter cake was washed with morpholine to obtain 145 g of pure salt. The salt was then mixed with 235 grams of acetic acid and 14 grams of water to precipitate the PTA. The filter cake was subsequently washed with about 600 grams of water, and the wet cake was dried in an oven at about 275° C. for 4 hours to obtain 40 grams of dry PTA. Table 4 shows the results of HPLC analysis of impurities, but the B value of the color measurement filter cake is 6.5, which is about 4 times higher than the standard value of 1.6. This shows that PTA contains a significant amount of morpholine. Table 4 4-CBA benzoic acid p-toluic acid PTA (ppmw) not detected not detected not detected

   Comparative Example 3 (by directly adding acetic acid to precipitate the product)

3 grams of the CTA sample described in Table 1 was completely dissolved in a solution containing 5.010 grams of triethylamine and 9.047 grams of methanol at room temperature. Then 7.570 g of acetic acid was added to precipitate crystals, and then filtered and dried to obtain 2.179 g of terephthalic acid. HPLC analysis showed that the acid contained impurities as shown in Table 5. table 5 4-CBA benzoic acid p-toluic acid PTA (ppmw) 2471 844 471

Example 1 (direct extraction crystallization method from leached sediment)

40 grams of the CTA sample described in Table 1 was mixed with 52 grams of morpholine and 48 grams of water. The solution was heated to 110° C. to dissolve the CTA and evaporate about 29 ml of condensate, which was subsequently cooled to room temperature to allow precipitation. The filter cake was washed with methanol and leached to yield 55 g of wet cake. The wet cake was mixed with 30 grams of methanol, and then 85 grams of acetic acid was added to the solution to precipitate terephthalic acid. The wet cake was then washed with about 35 grams of methanol and leached three times with 35 grams of methanol to yield a 31.5 grams wet cake. The wet cake was dried in an oven at about 250°C for 4 hours to yield 24 grams of dry cake. The B-value of the cake was 2.73, which was still higher than the standard value, and HPLC analysis showed that the PTA contained the impurities in Table 6. Table 6 4-CBA benzoic acid p-toluic acid PTA (ppmw) 20.8 not detected not detected

Example 2 (Crystalization method of resalination by evaporative pyrolysis)

925 grams of a CTA sample as described in Table 1 were mixed with 1103 grams of morpholine and 1205 grams of water. The solution was heated to 110° C. and about 404 ml of condensate evaporated and stopped before flash crystallization. The solution was then cooled to room temperature and allowed to stand for 4 hours to precipitate crystals. 250 grams of ethanol was added to dilute the slurry and the filter cake was washed and leached with approximately 750 grams of ethanol to yield 1455 grams of salt. Take 1005 grams of salt and dissolve in 465 grams of water. The solution was heated to 109°C and crystallized rapidly after evaporation of about 280 ml of condensate. The salt was leached with 650 grams of ethanol and the filter cake was washed with 250 grams of ethanol to yield 702 grams of pure salt. 35 g of salt was dissolved in 40 g of water and 40 g of ethanol, and 60 g of acetic acid was added to the solution to precipitate the product crystals. The filter cake was then washed and leached three times with approximately 200 grams of water to obtain 27.5 grams of wet cake. It is then mixed with 130 grams of EG. The solution was heated to 150-160°C at atmospheric pressure until no condensed brown liquid separated from the solution. The hot liquid was immediately filtered, washed with 300 g of water and leached to give 15.4 g of wet cake. The wet cake on a sorbent was heated in a microwave oven at moderate power for 20 minutes and then dried in an oven at about 250°C for 4 hours to yield 11.6 grams of dry cake. The B-value of the cake was 1.58, which met the standard value, and HPLC analysis showed that the PTA contained the impurities shown in Table 7. Table 7 4-CBA benzoic acid p-toluic acid PTA (ppmw) not detected not detected not detected

Example 3 (conditions and leaching of simulated reactor effluent)

A 150 g sample of CTA as described in Table 1 was mixed at room temperature with a solution having a composition similar to that of the reactor effluent flashed. The solution contained 202 grams of morpholine, 191 grams of water, 29 grams of 48% hydrobromic acid, 0.23 grams of cobalt acetate tetrahydrate, 0.3 grams of magnesium acetate tetrahydrate, and 60 grams of acetic acid. The temperature of the solution was heated to 110° C. to dissolve the CTA and evaporate 79 ml of condensate. The solution was then cooled to room temperature to precipitate, and the filter cake was washed with methanol and leached to obtain 278 g of a wet cake. The wet cake was mixed with 133 grams of water, and the temperature of the solution was heated to 110° C. to evaporate 88 ml of condensate, and the solution was cooled to room temperature to precipitate. The filter cake was washed with methanol and leached to yield 160 g of a wet cake. The wet cake was then mixed with 160 grams of methanol followed by the addition of 180 grams of acetic acid to precipitate terephthalic acid. The wet cake was washed and leached with 500 grams of water and leached 3 times with 35 grams of methanol to give 123 grams of wet cake. The wet cake on an adsorbent was heated in a microwave oven at moderate power for 20 minutes, followed by drying in an oven at about 250°C for 4 hours to yield 73 grams of dry cake. The cake had a B-value of 2.22, all metal contents were below specified standards, and HPLC analysis showed the impurity content of the PTA as shown in Table 8. Table 8 4-CBA benzoic acid p-toluic acid PTA (ppmw) not detected not detected not detected

Example 4 (pyrolysis with electromagnetic waves)

A 10.05 gram sample of the pure salt of Example 2 was dissolved in 6 grams of water. The solution was heated in a 600 watt microwave oven for 3 minutes, and the residual mixture contained about 9.29 grams of solids. 6.27 grams of water were mixed with the solid and heated in the microwave for 3 minutes to give 8.82 grams of solid. Then, 6.66 grams of water were mixed with the solid and heated for 3 minutes to obtain 8.49 grams of solid. The solid was then mixed with 10.85 grams of water and heated in a microwave oven for 4 minutes to give 8.14 grams of solid. The solid was further mixed with 9.59 grams of water and heated in the microwave for 3 minutes to give 7.82 grams of solid. In each of the above steps, the weight loss comes from the decomposition of the salt.

Embodiment 5 (crude NDC)

A 150 gram sample of crude dimethyl 2,6- and 2,7-naphthalene dicarboxylate (NDC) was mixed with 161 grams of morpholine and 180 grams of water. The temperature of the solution was then heated to 110°C to evaporate 86 ml of solvent. The solution was then cooled to precipitate crystals and filtered to separate from the mother liquor. The filter cake was washed with a mixture of morpholine containing 10 wt% water to give 186 grams of wet cake. The wet cake was redissolved in 72 grams of water and 18 grams of morpholine, and the solution was heated to evaporate about 35 ml of condensate. The solution was then cooled to precipitate, filtered, and washed with a solvent mixture of morpholine containing 10 wt% water to yield 158 grams of a wet cake. A mixture of 16 grams of water and 158 grams of acetic acid was then added to the purified salt to precipitate the product acid. After filtering, washing with water and drying, 85 grams of purified acid were obtained. The crude NDC was purified to 99.993% purity. The capillary electrophoresis analysis of crude acid showed 11 peaks, the time and area of which were at (8.86, 3.824), (8.92, 2.891), (8.92, 5.518), (9.06, 10.038), (9.18, 36.226), ( 9.45, 18.536), (9.52, 13.944), (9.57, 8.298), (11.87, 0.106), (11.99, 0.598). The capillary electrophoresis of the purified acid showed two peaks whose time and area were at (9.49, 99.993) and (9.55, 0.007), respectively. Example 6 (dissolved by electromagnetic waves and crystallized in ethanol using NMP)

12.5 grams of a CTA sample as described in Table 1 was mixed with 60 grams of NMP, which was preheated in a 600 watt microwave oven for 30 seconds. The CTA was then microwaved on low power for about 3.5 minutes to completely dissolve. Then 13 grams of ethanol was added to the solution during crystallization and placed in an ice bath for about 60 minutes to cool the solution. The salt was then filtered and washed with a mixed solvent of 50% ethanol and 50% NMP to obtain 26.2 g of the salt. The salt was then mixed with 31 grams of NMP and heated in a microwave oven at low power for 2.7 minutes to dissolve completely. An additional 15 grams of ethanol was added to the solution during crystallization and placed in an ice bath for about 60 minutes to cool the solution. Then the salt was filtered and washed with a mixed solvent of 50% ethanol and 50% NMP to obtain 16 g of pure salt. 3 grams of pure salt were placed between a stack of absorbent paper filters. And the microwave oven is set at low power to heat and decompose the pure salt until the weight does not change any more to obtain 1.2 grams of PTA. Table 9 shows the impurities analyzed by this HPLC. Table 9 4-CBA benzoic acid p-toluic acid PTA (ppmw) not detected not detected not detected

The above examples are mainly used to help the understanding of the method of the present invention, but not to limit the scope of the present invention to a specific compound or processing step. The scope of the invention is defined by the book.

Claims (38)

1. A method for the manufacture of pure organic acids or derivatives thereof, comprising: dissolving the crude organic acid or its derivatives in the base compound; remove impurities; and Upon recovery of the pure organic acid or the derivative, residual base compounds are removed. 2. The method of claim 1, wherein the crude organic acid or the derivative is dissolved by thermal agitation under electromagnetic waves. 3. The method of claim 1, wherein the crude organic acid or the derivative is a crude aromatic polycarboxylic acid. 4. The method of claim 1, wherein the crude organic acid or the derivative is dissolved in the base compound and a dissolving agent. 5. The method of claim 1, wherein removing impurities also removes excess base compound. 6. A method for the manufacture of pure organic acids or derivatives thereof comprising: Dissolving salts formed from crude organic acids or their derivatives and base compounds; Impurities and excess base compounds are removed from the salt of the crude organic acid or derivative thereof by one or more methods selected from the group consisting of: pretreatment, crystallization by cooling, composition by controlled cooling and crystallization, salt crystallization in the presence of a base extraction solvent, precipitation of a product in the presence of a base extraction solvent, salt direct extraction crystallization, resalination crystallization, salt-alkali substitution, washing with a base extraction solvent, and leaching with a base extraction solvent; and The pure organic acid or its derivatives are recovered from the salt, while residual base compounds are removed. 7. The method of claim 6, wherein the crude organic acid or derivative thereof is crude aromatic polycarboxylic acid. 8. The method of claim 7, wherein the crude aromatic polycarboxylic acid is terephthalic acid or isophthalic acid. 9. The method of claim 7, wherein the crude aromatic polycarboxylic acid is 2,6-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid or mixed naphthalene dicarboxylic acids. 10. The method of claim 6, wherein the salt is dissolved by thermal agitation under electromagnetic waves. 11. The method of claim 6, wherein the base compound is an oxygen-containing base compound. 12. The method of claim 6, wherein the salt is dissolved in the base compound and a dissolving agent. 13. The method of claim 6, wherein the base compound is morpholine, and the salt is dissolved in water. 14. The method of claim 6, wherein the base compound is trimethylamine, triethylamine, or triethanolamine, and the salt is dissolved in water or alcohol. 15. The method of claim 6, wherein the base compound is an amide compound. 16. The method of claim 15, wherein the amide compound is N-methyl-pyrrolidone. 17. The method of claim 6, wherein the base compound is an amide compound, and the salt is dissolved in a dissolving solvent. 18. The method of claim 6, wherein the impurities are removed using a base extraction solvent, and the base extraction solvent comprises water, methanol, ethanol, alkylene glycol, acetone, tetrahydrofuran, or tetrahydropyran. 19. The method of claim 7, wherein pure organic acid is recovered from the salt by adding an acid displacement solvent in the presence of a base extraction solvent. 20. The method of claim 7, wherein pure organic acid is recovered from the salt by pyrolysis using electromagnetic waves. 21. The method of claim 7, wherein the residual base compound is removed from the pure organic acid by one or more methods selected from the group consisting of: leaching, stripping, electromagnetic thermal agitation, and heat of vaporization untie. 22. A method for the manufacture of pure organic acids or derivatives thereof comprising: Dissolving salts formed from crude organic acids or their derivatives and base compounds; Impurities are removed from the salt by one or more methods selected from the group consisting of direct extraction crystallization of the salt, crystallization of the salt in the presence of a base extraction solvent, precipitation of the product in the presence of a base extraction solvent, use of base extraction Solvent re-salting crystallization, salt-alkali substitution, and alkali extraction solvent leaching. 23. The method of claim 22, wherein the crude organic acid or derivative thereof is crude aromatic polycarboxylic acid. 24. The method of claim 22, wherein the salt is dissolved by thermal agitation under electromagnetic waves. 25. The method of claim 22, wherein the salt is dissolved in a dissolving agent. 26. The method of claim 22, wherein the base compound is an oxygen-containing base compound. 27. The method of claim 22, further comprising recovering the pure organic acid or its derivatives from the salt by acid substitution, pyrolysis, or electrolysis. 28. The method as claimed in claim 27, which further comprises adopting one or more methods selected from the following, when recovering the pure organic acid or its derivatives from the salt, simultaneously removing the residual alkali compound, said Methods include: leaching, steam stripping, electromagnetic wave thermal agitation, and evaporation by pyrolysis. 29. A method for preparing a purified solution of an aromatic polycarboxylic acid or a derivative thereof and a monomer or oligomer, comprising: mixing an aromatic polycarboxylic acid or derivative thereof containing residual solvent with a monomer or oligomer; and Increase the temperature to 50°C-350°C to remove residual solvent. 30. The method of claim 29, wherein the monomer is an alkylene glycol. 31. The method of claim 29, wherein the residual solvent is removed by heating under electromagnetic waves. 32. A method for the manufacture of pure aromatic polycarboxylic acids or derivatives thereof comprising the steps of: Oxidation of alkyl groups on aromatic compounds in the presence of catalysts and solvents to produce crude aromatic polycarboxylic acids or derivatives; dissolving a salt formed from the crude aromatic polycarboxylic acid or its derivative and a base compound; removing impurities in the crude aromatic polycarboxylate or derivative salt thereof; When recovering the pure aromatic polycarboxylic acid or its derivatives from the salt, the residual base compound is simultaneously removed; and Recover solvent and catalyst. 33. The method of claim 32, wherein the salt is dissolved in the base compound and a dissolving agent. 34. The method of claim 32, wherein the crude aromatic polycarboxylic acid or derivative thereof is prepared by flashing and evaporation. 35. A process for the preparation of pure organic acids or derivatives thereof comprising: dissolving the crude organic acid or derivative containing impurities in the base compound by thermal agitation under electromagnetic waves; and This impurity is removed. 36. The method of claim 35, wherein the crude organic acid or derivative thereof is dissolved in the base compound and a dissolving agent. 37. The method of claim 35, further comprising recovering the pure organic acid or derivative thereof. 38. The method of claim 36, wherein the residual base compound is simultaneously removed while recovering the pure organic acid or derivative thereof.