JPS596184B2 - How to recover oxidation catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering a liquid phase oxidation catalyst used in the production of benzene polycarboxylic acid.

It is well known to air oxidize polyalkylbenzenes in acetic acid with heavy metals such as cobalt, manganese, and bromine compounds as catalysts to produce the corresponding benzene polycarboxylic acids, including terephthalic acid, isophthalic acid, trimellitic acid, pyromellitic acid, etc. Acids and the like are produced on an industrial scale by this method.

Among these, terephthalic acid is particularly produced on a large scale as a raw material for polyester. Since the catalyst used is expensive, repeated use is essential for economically producing benzene polycarboxylic acid. However, the catalyst used in the reaction coexists with impurities that inhibit the reaction in the mother liquor from which benzene polycarboxylic acid is separated from the reaction mixture. It is not desirable to simply circulate the reaction residue (reaction mother liquor concentrate) from which a portion of the acetic acid has been distilled off to the reaction system. For this reason, various efforts have been made for catalyst recovery.

Examples include a method in which the reaction residue is extracted with water and then the heavy metals are precipitated and separated in the form of carbonate, and a method in which the residue is incinerated and the heavy metals are eluted from the ash. Although these methods can recover relatively high-purity catalysts, they not only require complicated steps, but also require a large amount of alkali or acid, and have the disadvantage that almost all of the bromine among the catalyst components is lost. be. Another method is to pass the reaction mother liquor or the aqueous extract of the residue through a cation exchange resin to adsorb heavy metals, recover hydrogen bromide by evaporating the passed liquid, and recover the heavy metals by passing hydrobromic acid through the cation exchange resin. Although this method has been proposed, in addition to the serious problem of corrosion of the equipment, it is necessary to evaporate a large amount of solvent in order to recover high-boiling hydrogen bromide. The present inventors have arrived at the present invention as a result of research into a method for recovering bromine, which has not been recovered satisfactorily by conventional methods, and for recovering a catalyst at low cost with almost no reduction in activity.

That is, according to the present invention, benzene polycarboxylic acid is removed from a reaction mother liquor by solid-liquid separation from a reaction product mixture obtained by oxidizing polyalkylbenzene with molecular oxygen-containing gas in acetic acid containing a heavy metal and a bromine compound as a catalyst. To recover the catalyst component, the reaction mother liquor is concentrated, mixed with water, insoluble substances are removed, and the resulting aqueous solution is treated with a strongly basic anion exchange resin in which the hydroxyl group has been substituted with a strong acid counter anion. By treating with , the catalyst activity can be recovered and the bromine catalyst can be recovered effectively and inexpensively.

According to the method of the present invention, water-insoluble organic substances are first removed when the catalyst is extracted with water from the reaction residue.

At this time, most of the tar-like substances and colored substances that inhibit the reaction are also removed, but the aqueous layer still contains reaction inhibitors, and these are effectively removed by the strongly basic anion exchange resin layer. , resulting in the majority of heavy metal catalyst components and bromine compounds being present in the flowthrough. The method of the present invention is particularly valuable as a catalyst recovery method for producing terephthalic acid for direct polymerization by one-step oxidation of paraxylene. Terephthalic acid for direct polymerization is required to be so-called high-purity terephthalic acid with few impurities such as 4-carboxybenzaldehyde (hereinafter abbreviated as 4-CBA) and coloring substances, and in order to produce such high-purity terephthalic acid, It is necessary to reduce as much as possible the amount of reaction inhibitors mixed into the catalyst to be recovered and reused, and the method of the present invention easily achieves this objective. In the present invention, polyalkylbenzenes include paraxylene, paracymene, paradiisopropylbenzene, metaxylene, pseudocumene, diyurene, etc., and benzene polycarboxylic acids include terephthalic acid, isophthalic acid, trimellitic acid, pyromellitic acid, etc. .

The heavy metal catalyst is a compound of metals such as cobalt, manganese, nickel, and cerium, and these are used alone or in combination of two or more. Bromine compounds include alkali metal salts such as sodium bromide and potassium bromide, inorganic bromine compounds such as molecular bromine, hydrogen bromide, cobalt bromide, and manganese bromide, as well as tetrabromoethane, bromoform, and paramethylbenzyl bromide. Organic bromine compounds such as bromine compounds are also included, but since accumulation of alkali metals is undesirable, when additional bromine compounds are used, hydrogen bromide, cobalt bromide, and tetrabromoethane are preferred. The molecular oxygen-containing gas is oxygen, air, or air diluted with an inert gas such as nitrogen. The method of the present invention includes
It can be applied to a reaction mother liquor obtained by solid-liquid separation of benzene polycarboxylic acid from a reaction product obtained by oxidizing the above polyalkylbenzene with a molecular oxygen-containing gas in acetic acid containing the above heavy metal and bromine compound as a catalyst.

The reaction conditions such as the reaction temperature during the polyalkylbenzene oxidation reaction, the concentration of each substance, the method of separating benzene polycarboxylic acid and its conditions, etc. are not limited. The separated reaction mother liquor is distilled to recover the acetic acid solvent, and the catalyst is taken out as a residue.

The amount of free acetic acid contained in the residue is preferably 50% by weight or less. Note that free acetic acid is acetic acid excluding those present in the form of metal salts. This residue contains not only organic impurities but also impurities of metal compounds such as iron, chromium, copper, etc., and is separated into a filthy residue and a catalyst solution by a water extraction operation.

That is, the residue and water are mixed, the catalyst is extracted into the aqueous layer, and then the insoluble residue is separated and removed from the aqueous extract by a known method such as centrifugation, vacuum filtration, or decanting. In this case, metals that have an adverse effect on oxidation reactions, such as iron, chromium, and copper, are mostly removed together with insoluble residues. The appropriate amount of water used for water extraction is 2 to 10 parts by weight per 1 part by weight of the residue, but it should be adjusted so that the concentration of free acetic acid in the extracted water is 30% by weight or less, especially 10% by weight or less. is preferable. When the free acetic acid concentration increases, the water-impossible organic residue becomes more likely to elute into water, which causes a decrease in the adsorption capacity of the anion exchange resin used in the next step. The temperature at which the intractable residue is separated is preferably as low as possible for the purpose of reducing the solubility of the organic residue, but is not particularly limited. The strongly basic anion exchange resin used in the present invention is a resin having a quaternary ammonium group as an exchange group, and includes what is generally known as type I and type strongly basic anion exchange resins. Type I strongly basic anion exchange resin is one that has a copolymer of styrene and divinylbenzene as a base and has a group shown by formula 1 as an exchange group, and the type has a group shown by the formula as an exchange group. It is. In the present invention, it is necessary that the type I and type hydroxyl groups be substituted with a counteranion of a strong acid, such as chloride ion, bromide ion, iodide ion, sulfate ion, nitrate ion, etc.

This is because the hydroxyl group type has low heat resistance, and if it comes into contact with catalyst metals such as coloreto, it deposits metal hydroxide on the resin surface and reduces efficiency, and it also absorbs bromide ions in the initial stage of use. However, this results in a decrease in the bromine recovery efficiency, which is one of the characteristics of the method of the present invention.
However, even if it is a hydroxyl type, it becomes substantially a bromine type with repeated use. Among the above substituted anions, chlorine ion and bromide ion are more preferred, and bromide ion is most preferred. In the following description, a type I resin in which the hydroxyl group is substituted with a bromide ion is referred to as a type I bromine type strongly basic anion exchange resin, and when simply referred to as an anion exchange resin, all of these are included. The anion exchange resin may be either a gel type resin having only micropores or a porous type resin in which physical macropores are formed in the gel type resin, and even if it is generally spherical,
It may also be in the form of a sheet known as an ion exchange membrane.
The treatment operation using an anion exchange resin can be carried out either batchwise or continuously.

When using a spherical anion exchange resin, it is preferable to pack it into a column and pass the catalyst extract through the column as a downward flow or an upward flow. In this case, the flow rate of the catalyst extract depends on the operating temperature and the concentrations of the catalyst, free acetic acid and organic impurities in the catalyst extract, but is generally preferably in the range of 0.5 to 5 hr-1 in space velocity. Since the catalyst extract usually contains yellow colored impurities, the adsorption breakthrough point can be determined by measuring the degree of coloration of the passing liquid, and it is particularly convenient to use the change in absorbance between 300 and 400 nm. be. The adsorption operation can be carried out in a wide temperature range from 5°C to 80°C, but the higher the temperature, the faster the deterioration of the anion exchange resin, and conversely, the lower the temperature, the more organic substances that gradually precipitate from the catalyst extract will cause ion exchange. Since the adsorption effect of the resin tends to decrease, it is preferable to carry out the reaction at a temperature in the range of 20 to 60°C. The catalyst treatment capacity per anion exchange resin 11 varies greatly depending on various factors, but in general, the amount of catalyst required to produce polycarboxylic acids 10 to 200k9 can be treated with the anion exchange resin 11. The anion exchange resin that has reached its breakthrough point can be used repeatedly by washing it with water or water containing 50% by weight or less of acetic acid, and then performing a regeneration treatment. As a regeneration method, cleaning with acetic acid is particularly effective. The acetic acid used may contain up to 50% by weight of water, preferably up to 30% by weight. Generally, as the moisture content in acetic acid increases, the regeneration efficiency decreases. Further, it is preferable to degas the regeneration solvent such as acetic acid in advance. Organic impurities adsorbed on the anion exchange resin are removed by regeneration treatment. The solvent used in the regeneration process is recovered by evaporation, and the residue is subjected to a process such as incineration together with the insoluble residue separated in the water extraction process. As adsorption and regeneration are repeated, the adsorption capacity of anion exchange resin gradually decreases, but
In such cases, after cleaning with mineral acid and alkali,
If necessary, the substituted anion exchange resin can be regenerated by passing an aqueous solution containing a predetermined anion therethrough. The catalyst liquid treated with the anion exchange resin is recycled again as an oxidation reaction catalyst after replenishing the missing catalyst components and adjusting the water content by evaporation or the like if necessary.

Generally, part of the bromine component of the catalyst escapes from the system as hydrogen bromide during the oxidation reaction, so the amount of replenishment is larger than that of a heavy metal catalyst. When the method of the present invention is adopted and the catalyst is repeatedly used for recovery and circulation, alkali, etc. used for cleaning the reaction equipment etc. may accumulate in the catalyst.
In such a case, it is preferable to appropriately extract a portion of the catalyst from the circulation system and carry out an operation for removing alkali and the like so that the accumulated amount does not exceed the permissible limit. The present invention will be specifically explained below using examples. In the examples, % is by weight unless otherwise specified. Example 1 1 kg of 4% hydrous acetic acid in which 0.15% of cobalt acetate tetrahydrate, 0.105% of manganese acetate tetrahydrate, and 0.13% of sodium bromide were dissolved as a catalyst was charged into a 21 titanium autoclave and heated at 200°C. , 231<g/c! While introducing air at a rate of 10 NI/min under Ii, paraxylene was introduced at a rate of 1.8 y/min for 2 hours, and an oxidation reaction was carried out with stirring.

After stopping the supply of paraxylene, air was continued to be introduced for 10 minutes to complete the reaction, and then the reactor was cooled and the contents were taken out, and the terephthalic acid was poured out. The solution was concentrated under reduced pressure to obtain 8.69 g of an organic residue containing the catalyst. Water 309 was added to the residue and stirred at room temperature for 4 hours to extract the catalyst with water, followed by vacuum filtration and the cake was washed with water 209.
The weight of the cake was 1.89, and the combined weight of the water extract and washing liquid was 56y. Separately, use a river-type chlorine-type strong basic anion exchange resin (Diaion SA2OA8 manufactured by Mitsubishi Chemical Industries, Ltd.) 20a with an inner diameter of 1.5c! After passing 1 N sodium hydroxide 200 WLI 1 water 200 a and 11 N hydrobromic acid 200 a in order, distilled water was further passed until halogen ions were barely detected.
It was made into a bromine type strongly basic anion exchange resin.

2 of the previously obtained catalyst extract 56y was added to the column containing the resin.
The liquid was passed through at a rate of 60 ml/hour at 5°C, and then 107 ml of water was added.
The catalyst was washed through 7L1 until no catalyst remained in the column. The catalyst components contained in the passing liquid are 94% cobalt and 9% manganese, based on the amount charged in the autoclave.
5%, bromide ion 76%, and sodium 96%.
The reason why the recovery rate of bromide ions is low is that some of the bromine is converted into organic bromine compounds. After concentrating the permeate under reduced pressure and adjusting the water content, the deficient catalyst components are replenished in the form of cobalt acetate, manganese acetate, sodium acetate, and hydrobromic acid, and an acetic acid solution of the catalyst to be used in the oxidation reaction 1 is prepared.
kg was prepared. 5CI! Absorbance ε340 at a wavelength of 340 nm for the acetic acid solution using a quartz cell of
was measured with a spectrometer and found to be 0.05.

On the other hand, the anion exchange resin is vacuum degassed acetic acid (water content 4%).
) 40d was washed and regenerated by passing liquid through it for 30 minutes.

The first 20 ml of Rakude acetic acid is yellow, and the next 20 ml
Sample No. 1 was slightly yellow. Next, 20 d of water was passed through, this liquid was combined with the regeneration treatment liquid, and acetic acid was added to this to make 11<9.
When the absorbance at 340 nm was measured using a 5 cm quartz cell, it was 0.48. The catalyst components contained in the regenerated solution are 0.2 to 0.3% of cobalt, manganese, and sodium, 0.5% of bromide ion, and 1.4% of total bromine based on the amount charged in the autoclave. % (Total bromine was measured by burning the evaporation residue in oxygen, converting it to bromine ions with hydrogen peroxide, and titrating with silver nitrate.) By concentrating the regenerated solution under reduced pressure, 1.35y of yellow organic matter was obtained. The anion exchange resin was used as is for the next adsorption operation. The obtained recovered catalyst acetic acid solution was charged into the autoclave again, and a second oxidation reaction was carried out under the same conditions as the first.

Table 1 shows changes in the quality of terephthalic acid obtained by repeating the reaction and catalyst recovery in this manner. In Table 1, the degree of coloration of terephthalic acid is 4f! It represents the absorbance at an optical path length of 5 cm and a wavelength of 340 nm, which was measured by dissolving 2N potassium hydroxide in 50ml of 1&C. The lower the 4-CBA concentration and the degree of coloration, the higher the purity of terephthalic acid, which is suitable as terephthalic acid for direct polymerization.

Comparative Example 1 The catalyst aqueous solution was recovered and the reaction was repeated in the same manner as in Example 1 except that the treatment with the anion exchange resin was not performed.

The degree of coloration of the catalyst solution used in the third reaction is ε340=0
．． 64, and the coloring degree of terephthalic acid after reaction is 0.1
The 1,4-CBA concentration was 360 PPI [l, and the activity of the catalyst was significantly reduced.

Example 2 Catalyst recovery was carried out in the same manner as in Example 1, using type I chlorine type strongly basic anion exchange resin (Diaion SAlOA8 manufactured by Mitsubishi Chemical Industries, Ltd.) instead of the ... type bromine type anion exchange resin in Example 1. Table 2 shows the results of repeated reaction experiments.

Example 3 Oxidation was carried out using the same catalyst and other reaction conditions as in Example 1, except that meta-xylene was used instead of para-xylene in Example 1.

Claims (1)

[Claims] 1. Benzene polycarboxylic acid is removed from the reaction product mixture obtained by oxidizing polyalkylbenzene with molecular oxygen-containing gas in acetic acid containing heavy metals and bromine compounds as catalysts by solid-liquid separation, and the catalyst component is recovered from the reaction mother liquor. After concentrating the reaction mother liquor and mixing it with water, insoluble substances are removed, and the resulting aqueous solution is passed through a strongly basic anion exchange resin in which the hydroxyl group has been substituted with a counter anion of a strong acid to remove the catalyst. A method for recovering an oxidation catalyst, the method comprising recovering the oxidation catalyst as a permeate.