JPS636268B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for stabilizing catalysts used in the production of terephthalic acid and recovered. More specifically, terephthalic acid is separated and removed from the reaction mixture obtained by oxidizing paraxylene with molecular oxygen in the presence of a catalyst containing cobalt and manganese in acetic acid, and then substantially acetic acid is removed by distillation or the like. The present invention relates to a method for stabilizing cobalt and manganese carbonates recovered from a solution in which the reaction mother liquor concentrate obtained by removing the reaction mother liquor is calcined and the calcined product is dissolved in sulfuric acid. As a method for industrially producing terephthalic acid,
Using paraxylene as a raw material, a cobalt compound and a manganese compound as a catalyst, and acetic acid as a solvent,
A method of liquid phase oxidation using a molecular oxygen-containing gas is generally practiced. In this method, terephthalic acid is separated from the reaction mixture of the liquid phase oxidation reaction by filtration, centrifugation, etc., and then acetic acid is recovered from the reaction mother liquor by distillation, etc. The residue (reaction mother liquor concentrate) from which acetic acid has been substantially removed contains cobalt and manganese used in the reaction, as well as reaction intermediates p-toluic acid, 4-carboxybenzaldehyde, and other organic impurities. Contains metals such as iron, nickel, chromium, molybdenum, copper, and lead resulting from corrosion of equipment. It is essential to recover cobalt and manganese from the reaction mother liquor and reuse them in the liquid phase oxidation reaction of paraxylene in order to economically produce terephthalic acid. As a method for recovering the used catalyst, the reaction mother liquor concentrate is calcined, the calcined product is dissolved in sulfuric acid, the precipitate precipitated by neutralization is separated, and carbonate ions are added to remove cobalt and manganese. A method of recovering carbonate as carbonate is known. When the cobalt and manganese carbonates recovered by this method are left in the air or stored in an aerated state, they take on a bright purple color immediately after production, but their appearance gradually changes. turns brown to black, and when it is dissolved in an acetic acid aqueous solution for reuse as a liquid phase oxidation catalyst for paraxylene, a brown precipitate is deposited. This precipitate mainly consists of oxides of cobalt and manganese, but it clogs the flow path of the equipment and causes fluctuations in the flow rate of the catalyst. This alteration phenomenon of cobalt and manganese carbonates is thought to be due to autooxidation of some of the cobalt and manganese into higher-order oxides of trivalent or higher valence. The inventors of the present invention have arrived at the present invention as a result of intensive studies on methods for preventing such alteration phenomena of cobalt and manganese carbonates. That is, according to the present invention, paraxylene is oxidized with molecular oxygen in the presence of a cobalt and manganese catalyst in acetic acid, and the reaction mother liquor concentrate obtained by substantially removing terephthalic acid and acetic acid from the resulting reaction mixture is calcined. After dissolving the resulting calcined product in sulfuric acid, the precipitate that precipitates by neutralization is separated and removed, and then carbonate ions are added to precipitate cobalt and manganese, and the precipitate is recovered as carbonate. By adding 0.001 part by weight or more of an inorganic acid or an organic acid or a mixture thereof per 1 part by weight of the carbonate to the cobalt and manganese catalyst, stable cobalt and manganese carbonates that do not cause the above-mentioned deterioration phenomenon can be obtained. Salt crystals can be obtained. The reaction mother liquor concentrate is usually calcined at a temperature of 300 to 1500°C, preferably 400 to 1200°C, and may be in the presence of air (combustion) or in its absence (carbonization). Next, the baked product is dissolved in sulfuric acid, but at this time, inorganic compounds such as salts containing chlorine ions and bromine ions, hydrogen peroxide, and sulfites, and organic compounds such as formic acid, oxalic acid, aldehydes, starch, and glucose are dissolved. A reducing agent may be used in combination. Further, the sulfuric acid used to dissolve the fired product may contain almost no water or may contain water. Although the fired product contains water-soluble salts, they may be removed by washing with water in advance, or the above-mentioned sulfuric acid solution may be applied without washing with water. By selecting the heating temperature and time in this melting process,
Can dissolve over 95% of cobalt and manganese. Usually, the temperature range is 50 to 100°C and the time is selected from the range of 1 to 50 hours. If impurities such as iron, chromium, copper, etc. are present in the sulfuric acid solution in excess of the limit, it can be treated by known methods.
Perform its removal. That is, for iron and chromium,
A method is used in which the iron is removed as a precipitate at a pH of 4 to 6, and if necessary, the iron is changed from bivalent to trivalent with hydrogen peroxide or air to completely remove the precipitate. Further, copper can be removed as copper sulfide by adding alkali sulfide or the like. Cobalt and manganese carbonates are obtained by adding alkali carbonate or alkali bicarbonate to the solution of cobalt and manganese thus obtained. Representative alkali carbonates or alkali bicarbonates include sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate. In this case, the cobalt and manganese solutions may be added to the alkali carbonate or bicarbonate solution, or both solutions may be simultaneously introduced into the stirring tank. Cobalt and manganese carbonates precipitate and are separated out by a suitable solid-liquid separation method, such as centrifugation or filtration, and washed with water if necessary. The washing may be carried out by centrifugation, by sprinkling water on the cake, or by pouring it into water again to form a slurry. In the method of the present invention, the obtained cobalt and manganese carbonate contains 1 part by weight of the carbonate.
At least 0.001 parts by weight, preferably at least 0.01 parts by weight, of inorganic or organic acids or mixtures thereof are added. If the amount is less than 0.001 part by weight, almost no effect of stabilizing the catalyst can be expected. If the amount added is 0.001 part by weight or more, a certain effect can be obtained depending on the amount added, but even if the amount added exceeds 0.05 part by weight, no further effect can be expected, and rather, the effect will be long-term. Inconveniences such as changes in the form of the catalyst may occur during storage. Specific methods for adding inorganic or organic acids include adding these acids as they are or as an aqueous solution and stirring them, or absorbing them in gaseous form into cobalt or manganese carbonates. In this case, if necessary, air drying or heat drying using a dryer or the like is performed to remove part of the moisture. Alternatively, when the above-mentioned cobalt and manganese carbonates are separated into solid and liquid, a method may be used in which they are sprinkled on the cake. Examples of acids that can be used for this purpose include inorganic acids such as hydrobromic acid, sulfuric acid, phosphoric acid, and boric acid, and organic acids such as carboxylic acids such as oxalic acid, propionic acid, butyric acid, and benzoic acid. Even if cobalt and manganese carbonate crystals treated in this way are left in the air or in an air-containing state for a long period of time, for example, for about a year, they will retain the same purple appearance as they did immediately after production, and will remain brown to brown. It does not turn black and hardly forms an insoluble precipitate even when dissolved in acetic acid aqueous solution. The gist of the present invention is that cobalt and manganese carbonates obtained by reaction with alkali carbonate from a sulfuric acid solution of cobalt and manganese can be stored for a long time by a very simple operation of adding a small amount of acid. The advantage is that it can be made into a stable product that does not show any deterioration. Next, the present invention will be explained in more detail with reference to Examples. In Examples and Comparative Examples, % is a value based on weight. Example 1 Acetic acid is used as a solvent, and cobalt acetate, manganese acetate (metal weight ratio of Mn/Co is 0.95) and sodium bromide (weight ratio of Br/Co is 2.80) as catalysts.
Terephthalic acid was produced by air oxidation of para-xylene in liquid phase using the following method, and the reaction mother liquor from which terephthalic acid was separated from the reaction mixture was distilled to recover acetic acid to obtain a reaction mother liquor concentrate. 500g of this reaction mother liquor concentrate
is baked at approximately 500℃ in an air atmosphere to produce 105g of baked product.
I got it. When this was washed with water and dried, it weighed 42 g. Add 33g of this to dilute sulfuric acid, add a small amount of starch, heat to 60℃ to dissolve, and adjust the pH with soda carbonate.
After adjusting the concentration to 4.5, it was filtered to obtain 540 g of liquid. The cobalt concentration in this liquid is 2.2%, and the manganese concentration is 1.4.
It was %. Add a 15% sodium carbonate aqueous solution to this to adjust the pH to 8.2, filter it through Nutsuchie, and then
Rinse water was added for washing, and 59 g of wet cake was obtained.
This wet cake was allowed to absorb HBr vapor at room humidity.
The amount of HBr absorbed was 1.2 g when a portion of this was dissolved in dilute sulfuric acid and measured. The color and amount of dissolved residue immediately after production and after 6 months were as shown in Table 1. The amount of dissolved residue was measured as follows.
Put 45g of water and 45ml of acetic acid into a 200ml Erlenmeyer flask.
Cobalt and manganese carbonate with stirring at 87℃
After adding 20g and stirring at the same temperature for 120 minutes,
Pass through NO5C paper, wash the precipitate with water, and combine the washings with the liquid to quantify the Co and Mn contents.
The precipitate is heated and dissolved in concentrated hydrochloric acid, and the contents of Co and Mn are determined. Table 1 shows the ratio of the precipitated portion to the total of both quantitative values expressed in %. Example 2 47 g of a 5% aqueous sulfuric acid solution was added to 59 g of a wet cake obtained in the same manner as in Example 1 and stirred to form a slurry. Air dry this and
Part of the water was evaporated to obtain 55 g of cake. The properties of this product are shown in Table 1. Example 3 8.9 g of a 20% aqueous propionic acid solution was added to 59 g of a wet cake obtained in the same manner as in Example 1, stirred to make it almost uniform, and a portion of the water was air-dried to reduce the moisture content. 25% cobalt, manganese carbonate
Obtained 55g. The properties of this product are shown in Table 1. Comparative Example In Example 1, the properties of the wet cake were as shown in Table 1 when no HBr vapor was absorbed. 【table】

Claims (1)

[Claims] 1. Oxidize paraxylene with molecular oxygen in the presence of cobalt and manganese catalysts in acetic acid, and calcinate the reaction mother liquor concentrate obtained by substantially removing terephthalic acid and acetic acid from the resulting reaction mixture. After dissolving in sulfuric acid, the precipitate that precipitates by neutralization is separated and removed, and then carbonate ions are added to precipitate cobalt and manganese to obtain a precipitate. The cobalt and manganese catalysts are recovered as carbonates. , an inorganic acid or an organic acid, or a mixture thereof per part by weight of the carbonate.
A method for stabilizing a recovered oxidation catalyst, characterized by adding 0.001 part by weight or more.