JPH07258152A - Production of 4-halophthalic acid - Google Patents

Abstract

PURPOSE:To obtain 4-halophthalic acid which can be formed into crystals of high filterability and cause no adverse effect on the filterability, even when they are reused in the reaction with halogen. CONSTITUTION:In the production of 4-halophthalic acid where phthalic acid is allowed to react with halogen in an aqueous system, the formed halophthalic acid is crystallized out, the crystals are separated, the remaining mother liquor is subjected to reduction treatment in the presence of an alkali and a Pd catalyst to convert the halogenated phthalic acids into phthalic acid and the phthalic acid is precipitated with acid, the amount of 3,4,3',4'-bisphenylteracarboxylic acid in the mother liquor is adjusted to less than 1% based on the phthalic acid.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing 4-halophthalic acid. More specifically, it relates to a method for converting halogenated phthalic acid, which is a by-product during the production of 4-halophthalic acid by reacting phthalic acid with halogen, to phthalic acid for recovery. Further, the present invention relates to a method for avoiding difficulties in producing 4-halophthalic acid from recovered phthalic acid as a raw material.

[0002]

The reaction of phthalic acid with halogens in aqueous media to produce 4-halophthalic acid is known.
In this reaction, in addition to 4-halophthalic acid, halogenated phthalic acids such as 3-halophthalic acid, 3,4-dihalophthalic acid, and 4,5-dilophthalic acid are by-produced. Treatment with a reducing agent in the presence of a platinum group metal supported catalyst can convert it to phthalic acid. Therefore, in the production of 4-halophthalic acid, other halogenated phthalic acid produced as a by-product can be recovered as phthalic acid and used again for the reaction with halogen.

[0003]

In order to recover phthalic acid from a reaction solution which has been converted into phthalic acid by treating halogenated phthalic acid with a reducing agent in the presence of a platinum group metal-supported catalyst in an aqueous alkaline solution, first of all, The platinum group metal-supported catalyst is removed from the reaction solution, an acid is then added to the reaction solution to precipitate phthalic acid crystals, and the precipitated phthalic acid is recovered by filtration. At this time, what is important is to precipitate crystals having good filterability. Crystals with poor filterability require a long time for filtration and also contain a large amount of impurities. Further, when 4-halophthalic acid is produced by reacting phthalic acid having poor filterability with halogen, it often takes a long time to filter 4-halophthalic acid crystals from the reaction solution. Therefore, the present invention provides a method for recovering phthalic acid crystals from a halogenated phthalic acid, which are easy to filter and give 4-halophthalic acid crystals having good filterability when used as a raw material for 4-halophthalic acid. Is.

[0004]

According to the present invention, halogenated phthalic acid is converted to phthalic acid by reacting a halogenated phthalic acid with a reducing agent in the presence of a platinum group metal-supported catalyst in an aqueous medium containing an alkali. When converting, 3,4,3 ', 4'
-Suppressing the formation of biphenyltetracarboxylic acid to form a phthalate solution having a ratio of 3,4,3 ', 4'-biphenyltetracarboxylic acid to phthalic acid of 1.0% by weight or less, and then producing this solution. By precipitating phthalic acid crystals by acid precipitation according to a conventional method, the subsequent filtration operation can be easily performed. Further, when the phthalic acid thus recovered is reacted with halogen to produce 4-halophthalic acid, crystals of 4-halophthalic acid having good filterability are obtained.

Explaining the present invention in detail, the present invention solves a difficulty in recovering phthalic acid from a halogenated phthalic acid produced as a by-product and reusing it as a raw material in a method for producing 4-halophthalic acid. is there. It is known to produce 4-halophthalic acid by reacting phthalic acid with a halogen. This reaction is carried out by dissolving phthalic acid in an aqueous medium containing caustic and introducing halogen into it. Normally, chlorine is used as halogen to generate 4-chlorophthal, so that this case will be described below as an example. The caustic alkali present in the aqueous medium is for neutralizing hydrogen chloride by-produced in the reaction, and caustic soda is usually used, but caustic potash may be used. The caustic alkali is used in an equimolar amount or more with respect to phthalic acid. Chlorine is usually used in an amount of 0.5 to 2 times the molar amount of phthalic acid. When the amount of chlorine used is less than equimolar, a considerable amount of unreacted phthalic acid remains, and conversely, when it is more than equimolar, the amount of chlorinated phthalic acid other than 4-chlorophthalic acid increases by-product.
However, in the present invention, since unreacted phthalic acid and chlorinated phthalic acid other than 4-chlorophthalic acid can be recovered and reused as phthalic acid, the ratio of chlorine used to phthalic acid can be selected from a wide range. The temperature of the chlorination reaction is usually 20 to 100 ° C, preferably 50 to 80 ° C.

The reaction time is about 0.5 to 10 hours. In addition, the pH of the liquid due to hydrogen chloride produced as a by-product during the reaction.
If the pH drops, add caustic and add
To 4-6. After completion of the reaction, the crystals of 4-chlorophthalic acid are separated by filtration. Since the solubility of 4-chlorophthalic acid becomes lower at lower temperatures, it is desirable to carry out crystal separation at a lower temperature in order to increase the recovery rate of 4-chlorophthalic acid. However, at low temperatures, the solubility of unreacted phthalic acid and other chlorinated phthalic acids also decreases, so that the purity of 4-chlorophthalic acid obtained decreases. Usually 5 to 70
The temperature of the precipitation-filtration of the crystals is determined in consideration of the recovery rate of 4-chlorophthalic acid and the required purity of the recovered 4-chlorophthalic acid from the range of 20 ° C., particularly 20 to 50 ° C.

The mother liquor after the crystal separation contains monochlorophthalic acids and dichlorophthalic acids in addition to unreacted phthalic acid. In the present invention, this mother liquor is treated with a reducing agent in the presence of a platinum group metal supported catalyst to convert chlorinated phthalic acid to phthalic acid. As the platinum group metal of the catalyst, palladium, rhodium, ruthenium, platinum, iridium and the like are used, and palladium is particularly preferable. Further, as a carrier for supporting these metals, activated carbon, silica, alumina, silica-alumina, zeolite, titania, magnesia, diatomaceous earth, grafide, asbestos, ion exchange resin, barium carbonate, a conventional catalyst carrier such as calcium carbonate. It can be used, and activated carbon is particularly preferable. The amount of the metal loaded on the carrier is usually 0.1 to 20% by weight, preferably 0.5 to 10% by weight.

The conversion reaction of chlorinated phthalic acid to phthalic acid is carried out by suspending the platinum group metal catalyst in the above mother liquor and adding a reducing agent thereto. Hydrogen, formic acid, hydrazine and the like are used as the reducing agent, and hydrogen is particularly preferable. That is, the mother liquor is 40 to 100 ° C., especially 50 to 80 ° C.
It suffices to keep the temperature at 0 ° C. and blow hydrogen gas into it. The pressure of hydrogen gas may be normal pressure, but it may be increased if desired. The reaction time is 0.1 to 10 hours. Since hydrogen chloride is produced in this reaction, it is necessary to allow an alkali such as caustic soda or caustic potash to be present as an acid binder.

The amount of alkali is the stoichiometric amount required to capture hydrogen chloride generated by the reaction from organic chlorine, in addition to the amount required to convert phthalic acid and chlorinated phthalic acid in the mother liquor into alkali salts. 1 to 10 times the amount may be used. If the amount of alkali is too small, the conversion of chlorinated phthalic acid to phthalic acid will not proceed smoothly. On the contrary, even if the amount of alkali is excessive, the reaction results do not change, and alkali and acid are wasted, which is economically disadvantageous.

In the reduction treatment of this mother liquor, 3,4 produced by dechlorination dimerization of 4-chlorophthalic acid
It is necessary to minimize the by-product of 3 ', 4'-biphenyltetracarboxylic acid. 3, 4, 3 ',
4'-biphenyltetracarboxylic acid is a substance having extremely low solubility in water, and 3,4,3 ', 4'-biphenyltetracarboxylic acid present in the mother liquor after the reduction treatment is almost eliminated in the next acid precipitation step. The whole amount is mixed in the phthalic acid crystals. When biphenyltetracarboxylic acid is mixed in the phthalic acid crystals, its filterability is significantly deteriorated. Also,
If phthalic acid containing 3,4,3 ′, 4′-biphenyltetracarboxylic acid is used as a raw material for 4-chlorophthalic acid, the filterability of the produced 4-chlorophthalic acid deteriorates.
Therefore, the amount of 3,4,3 ', 4'-biphenyltetracarboxylic acid in the mother liquor after the reduction treatment needs to be 1% by weight or less of phthalic acid, preferably 0.5% by weight or less. is there. In order to suppress the by-production of 3,4,3 ′, 4′-biphenyltetracarboxylic acid during the reduction treatment, it is preferable to carry out the reduction reaction at a low temperature and complete the reaction in a short time. The time required to complete the reaction depends on the reaction temperature, reaction pressure, stirring conditions, etc.
It is necessary to set these conditions appropriately according to the allowable production amount of 3 ', 4'-biphenyltetracarboxylic acid.

The mother liquor after the reduction treatment is first filtered to remove the suspended catalyst, and then acid is added to precipitate phthalic acid. As the acid, hydrochloric acid, sulfuric acid, phosphoric acid or the like is used. The amount of the acid added may be equal to or more than the amount of the remaining alkali and phthalic acid alkali salt. The temperature of acid precipitation is 10
A temperature of ~ 50 ° C is suitable. After the acid precipitation, if at least a part of the crystal is heated to dissolve and then cooled to be recrystallized, the crystal grain size becomes large and the content of impurities also decreases. The precipitated phthalic acid crystals are filtered and separated from the mother liquor. The filtration temperature is usually 5 to 40 ° C. The separated crystals are washed with water and dried if desired, then mixed with fresh phthalic acid and subjected to the reaction again.

[0012]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. In the following description, parts and% mean parts by weight and% by weight unless otherwise specified.

Example 1 A stainless steel autoclave was charged with 1200 g of a solution having the composition shown in Table 1. Pd / activated carbon catalyst (5% Pd loading, 57% water content)
7.9 g and 103% 47% aqueous sodium hydroxide solution were added. While stirring at 650 rpm, hydrogen was blown in so that the liquid temperature was maintained at 70 ° C. and the pressure was 8 kg / cm ² . Hydrogen is absorbed by the reaction and the pressure is 7 kg / cm ²
Then, hydrogen was blown again to restore the pressure to 8 kg / cm ² . Although the absorption of hydrogen was completed in about 30 minutes, the temperature was maintained at the same temperature for 30 minutes, then cooled to room temperature and released. The catalyst was separated by filtration and the filtrate was analyzed by liquid chromatography. No chlorinated phthalic acid was detected. The ratio of 3,4,3 ', 4'-biphenyltetracarboxylic acid to phthalic acid was 0.04%.

In a glass flask, 280 g of demineralized water and 35
% 175 g of hydrochloric acid was charged, and the filtrate obtained above was added dropwise at 40 to 45 ° C. with stirring. The temperature was raised to 95 ° C. to dissolve the precipitated crystals, the temperature was cooled to 40 ° C., and the precipitated crystals were filtered. The filterability was extremely good, and the water content of the recovered crystals was 10%. According to microscopic observation, the crystals were not aggregated with rod-shaped primary particles, and their sizes were 200 μm in major axis and 80 μm in minor axis on average.

[0015]

[Table 1] Table 1 Disodium phthalate 0.067 mmol / g Disodium chlorophthalate 0.309 mmol / g Disodium dichlorophthalate 0.066 mmol / g Caustic soda 0.318 mmol / g

Example 2 The reaction and acid precipitation were carried out in exactly the same manner as in Example 1 except that the reaction temperature was 80 ° C. and the stirring speed was 580 rpm. The time required for absorbing hydrogen was 120 minutes. No chlorinated phthalic acid was detected in the filtrate after the catalyst separation, and the ratio of 3,4,3 ', 4'-biphenyltetracarboxylic acid to phthalic acid was 0.4.
It was 2%. Further, the filterability of the phthalic acid crystals after the acid precipitation was good, and the water content of the recovered crystals was 12%.
Crystals are rod-shaped primary particles with a long diameter of 100μ and a short diameter of 50μ,
A small amount of secondary particles, which had agglomerated with each other and grew to around 200 μm, were mixed.

Comparative Example 1 The reaction and acid precipitation were carried out in the same manner as in Example 1 except that the reaction temperature was 100 ° C. and the stirring speed was 570 rpm. The time required for absorbing hydrogen was 110 minutes. No chlorinated phthalic acid was detected in the filtrate after the catalyst separation, and the ratio of 3,4,3 ', 4'-biphenyltetracarboxylic acid to phthalic acid was 1.
It was 1%. Further, the filterability of the phthalic acid crystals after acid precipitation was poor, and the water content of the recovered crystals was 22%.
Most of the crystals were secondary particles that agglomerated fine particles and grew to around 200 μm.

Example 3 In a glass-lined reactor equipped with a stirrer and a chlorine gas supply pipe, demineralized water 4562 was added.
Parts, 1374 parts of phthalic anhydride and 1100 parts of 47% aqueous sodium hydroxide solution were charged and heated to 75 ° C. with stirring to obtain a uniform solution. Cool to 70 ° C., adjust the pH of the solution to 5 with a 47% aqueous sodium hydroxide solution, and add 7% chlorine gas.
56 parts were fed at a rate of 195 parts / hour and continued for 30 minutes. Then, the pH of the solution was adjusted to 4.5 with 35% hydrochloric acid, and then gradually cooled to 38 ° C. and kept for 2 hours. After filtration, 1492 parts of crystals of 4-chlorophthalic acid were recovered.
The time required for filtration was 9.5 hours, and the water content of the recovered crystals was 20.3%. The composition of the recovered 4-chlorophthalic acid is shown in Table 2.

[0019]

[Table 2] Table 2 4-chlorophthalic acid 77.0 mol% phthalic acid 12.3 mol% 3-chlorophthalic acid 1.8 mol% 3,4-dichlorophthalic acid 0.5 mol% 4,5-dichlorophthalic acid Acid 8.4 mol%

Example 4 The procedure of Example 3 was repeated except that 1374 parts of phthalic anhydride was replaced with a mixture of 995 parts of phthalic anhydride and 470 parts of recovered phthalic acid having the composition shown in Table 3. Then, chlorination and filtration of crystals were performed. The time required for filtration was 9.5 hours, the amount of crystals recovered was 1479 parts, and the water content was 20.2%. Also,
The composition of the recovered 4-chlorophthalic acid is shown in Table 4.

[0021]

[Table 3] Table 3 Phthalic acid 90.3% 3,4,3 ', 4'-biphenyl 0.01% Tetracarboxylic acid water 5.6%

[0022]

[Table 4] Table 4 4-chlorophthalic acid 77.1 mol% phthalic acid 9.2 mol% 3-chlorophthalic acid 1.4 mol% 3,4-dichlorophthalic acid 0.7 mol% 4,5-dichlorophthalic acid Acid 11.5 mol%

Comparative Example 2 Example 3 was repeated except that a mixture of 1095 parts of phthalic anhydride and 349 parts of recovered phthalic acid having the composition shown in Table 5 was used in place of 1374 parts of phthalic anhydride.
Chlorination and filtration of crystals were performed in exactly the same manner as in. The time required for filtration was 15 hours, and the amount of crystals collected was 1
The water content of 966 parts was 37.8%. The composition of the recovered 4-chlorophthalic acid is shown in Table 6.

The difference in the reaction results between Examples 3 and 4 and Comparative Example 2 even though the chlorination conditions were the same was considered to be due to changes in the reaction conditions such as the chlorine gas supply rate. To be Further, in Comparative Example 2, since the water content of the crystal is high, there is a possibility that a large amount of the component that normally remains in the mother liquor is contained in the crystal.

[0025]

[Table 5] Table 5 Phthalic acid 89.4% 3,4,3 ', 4'-biphenyl 1.29% Tetracarboxylic acid water 8.7%

[0026]

[Table 6] Table 6 4-chlorophthalic acid 73.4 mol% phthalic acid 12.7 mol% 3-chlorophthalic acid 3.9 mol% 3,4-dichlorophthalic acid 1.4 mol% 4,5-dichlorophthalic acid Acid 8.6 mol%

[0027]

EFFECTS OF THE INVENTION According to the present invention, the filterability when recovering the softened halogenated phthalic acid into phthalic acid is good,
Therefore, there are effects such as shortening of filtration time and reduction of impurity mixing rate. In addition, by reacting the recovered phthalic acid with chlorine, 4
Even when producing -halophthalic acid, the filterability of 4-halophthalic acid crystals is good.

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Claims (4)

[Claims] 1. A method of reacting a halogenated phthalic acid with a reducing agent in the presence of a platinum group metal-supported catalyst in an alkaline aqueous solution to convert the halogenated phthalic acid to phthalic acid, and the generated phthalic acid. In a method of recovering phthalic acid from halogenated phthalic acid, which comprises the step of reacting an aqueous solution with an acid to precipitate and recover phthalic acid crystals,
A method comprising carrying out a reduction reaction such that the content of 3 ', 4'-biphenyltetracarboxylic acid is 1.0% by weight or less with respect to phthalic acid. 2. A step of reacting phthalic acid with a halogen in an aqueous medium to produce 4-halophthalic acid, a step of recovering crystals of 4-halophthalic acid from a reaction solution, and a halogenated phthalic acid after crystal separation. A step of converting a halogenated phthalic acid into phthalic acid by reacting a reducing agent with a solution in the presence of an alkali and a platinum group metal-supported catalyst, and reacting an aqueous solution containing the generated phthalic acid with an acid to precipitate phthalic acid crystals. In the process for producing 4-halophthalic acid in which the recovered phthalic acid is reused for the reaction with halogen, the 3,4,3 ′, 4′-biphenyltetracarboxylic acid A method comprising carrying out a reduction reaction such that the content thereof is 1.0% by weight or less with respect to phthalic acid. 3. The method according to claim 1, wherein the platinum group metal-supported catalyst comprises palladium supported on activated carbon, and the reducing agent is hydrogen. 4. The reduction reaction is carried out such that the content of 3,4,3 ′, 4′-biphenyltetracarboxylic acid is 0.5% by weight or less with respect to phthalic acid. 4. The method according to any one of 3 to 3.