RU2402524C1 - Method of obtaining monochloracetic acid - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: invention relates to chemical technology and specifically to methods of producing monochloroacetic acid used in production of carboxymethylcellulose, pharmaceutical preparations, pesticides and ethylene diamine tetraacetic acid. The method of producing monochloroacetic acid involves crystallisation in a solvent and separation of monochloroacetic acid crystals from the mother solution through filtration, extraction of the solvent from the mother solution and returning to the crystallisation step, where the solvent used is carbon tetrachloride or perchloroethylene as commercial-grade as well as recycled, wherein crystallisation is carried out for 6-8 hours at weight ratio of molten crude monochloroacetic acid : solvent equal to 1:2-2.5. The initial crystallisation temperature is 38C and the final crystallisation temperature is equal to 05C. ^ EFFECT: improved process of producing monochloroacetic acid which is expressed in intensification of the crystallisation process, improvement of quality factors of monochloroacetic acid and improved technical and economical factors of production. ^ 4 cl, 1 tbl, 8 ex

Description

The invention relates to chemical technology, and in particular to methods for the isolation of monochloroacetic acid (MCA) used in the production of carboxymethyl cellulose, pharmaceuticals, pesticides, ethylenediaminetetraacetic acid.

Monochloracetic acid obtained by chlorination of acetic acid (AC) in the presence of catalysts (acetyl chloride, acetic anhydride) contains non-convertible acetic acid and products of deeper chlorination (di- and trichloroacetic acids) as impurities.

Removing impurities can be accomplished by two main methods of crystallization and hydrogenation.

The process of obtaining MCA, including the stage of hydrogenation of impurities (di- and trichloroacetic acids), is represented quite widely [US Patent No. 3,304,325, Germany No. 1816931, Cl. С07С 51/42, 1976, German patent No. 1668023, Cl. C07C 51/42, 1973].

According to the descriptions, it can be carried out in the gas and liquid phases in the presence of a fixed or suspended catalyst based on noble metals of Group VIII of the periodic table, among which priority is given to metallic palladium on inert carriers. The process is conducted in a wide temperature range from 60 ° C to 240 ° C and a large excess of hydrogen, sometimes under pressure. The disadvantages of this method of obtaining improved quality MCA (dichloroacetic acid (DCA) content <0.5%) are the use of an expensive palladium catalyst, the possibility of its tarring, which limits its useful life and difficulties in its regeneration. In addition, the removal of MCC from a unit volume of the catalyst is small, which requires the use of large contact devices with a well-organized heat removal system. Severe process temperature conditions with extremely high corrosiveness of the media require the use of expensive equipment using silver or steel - silver bimetal.

The method of isolation of monochloracetic acid by crystallization is implemented under industrial conditions [L. Oshin Industrial organochlorine products. Directory. - M: Chemistry, 1978].

In a number of industries, crystallization of raw MCC is carried out in bulk reactors with a jacket for cooling. In this case, heat is removed by supplying water, and the concentration of the solid phase in the suspension is controlled by mixing the reaction mass obtained after chlorination of acetic acid with the mother liquor from the filtration stage. The temperature of the suspension is gradually lowered from 70 ° C to 20 ° C. Due to the inlaid surface of the crystallizer, the crystallization process is time-consuming, while the DCA content in the finished product reaches 2%, the UK - 1%, and the removal of the product does not exceed 300 kg with 1 m ^{3 the} working volume of the reactor.

A known method of the so-called thermal crystallization of the reaction mass MHUK [Initial data of the Research Institute "Synthesis" for the design of technical re-equipment of the production of MHUK, Moscow, 1983]. The process is carried out in tubular-type heat exchangers.

Significant disadvantages of such crystallization are extremely high costs for the manufacture of crystallizers and their bulkiness; in this case, only graphite or titanium can be used as materials for equipment. The method requires ensuring the constancy of the composition of the reaction mixture and precise control of the temperature regime; accompanied by the formation of two mother liquors (warm and cold), one of which is in recycling, the second requires an additional recycling scheme.

It should also be noted that the method of thermal crystallization of MCA does not allow to concentrate DCC to a concentration optimal for its subsequent processing.

A known method for the allocation of commodity MCC from the reaction mixture [US Patent No. 3365493, CL. 260-539, 1968], obtained by chlorination of glacial acetic acid, containing 90-99% of MCA, 0-5% of DCA, less than 1% of AC and 0.01-0.5% of water, diluted with an inert solvent (methylene chloride) in a weight ratio 1: 5. The content of MCA in the selected crystals is in the range of 0.2-0.5%, however, this result is achieved through the use of the initial reaction mixture with a very low content of impurities, which is extremely difficult to ensure when chlorinating acetic acid, taking into account recycling of the mother liquor real in the number of all impurities associated with MCA, especially DCA and CC.

The noted shortcomings do not allow us to recognize the proposed method for the production of MCCs suitable for industrial use.

A known method of crystallization of a chloro mixture containing MCC in an organic solvent [RF Patent No. 2084443, Cl. C07C 53/16, 51/43, B01D 9/02, 1997]. It is proposed to use two compounds as solvents - chloroethyl and freon-113. Crystallization is carried out at a weight ratio of the starting components of 1: 1 in two stages, on the first crystallization of the raw material, on the second - the mother liquor. At both steps, the crystals are washed with the solvent used. The method allows to obtain MCA with the content of DCA 0.12-0.2% in the first stage and 0.65-0.45% in the second. The main disadvantage of the process is the use of expensive solvents, their enormous losses due to high volatility (boiling point of chloroethyl + 12.3 ° C, cold-113 -47.5 ° C), complex technical solutions to develop a method for capturing them.

The closest in technical essence to the proposed one is a method of crystallization of a chlorine mixture containing MCC in an organic solvent (Patent GB 949393, publ. 12.02.64.), Which consists in adding to this mixture a chlorinated hydrocarbon having no more than two carbon atoms, cooling the resulting mixture from +20 to -5 ° C for crystallization of monochloracetic acid from the mixture. The amount of chlorinated hydrocarbon added should be sufficient to provide an easily shakeable mixture after crystallization. The crystals are then separated from the mother liquor and recycled, if necessary, to the entire mother liquor to most of the initial mixture in at least one cycle, until the percentage of dichloroacetic acid in the mother liquor after separation of the crystals is at least equal to the percentage of monochloracetic acid there (preferably 10-50 wt.%) and then part of the described mother liquor is sent for recycling.

The disadvantage of this method is the presence in the process of a significant amount of circulating mother liquor, which must be periodically removed and disposed of, which leads to the loss of a significant amount of MCA with it. All this greatly complicates the process and reduces its technical and economic indicators. In addition, monochloracetic acid of poor quality is obtained.

The technical result of the present invention is to improve the process of obtaining MCC, expressed in the intensification of the crystallization process, to improve the quality parameters of the MCC and increase the technical and economic indicators of production.

The technical result is achieved by obtaining myochloroacetic acid, which includes crystallization in a solvent and separating crystals of monochloracetic acid from the mother liquor by filtration, removing the solvent from the mother liquor and returning to the crystallization stage. Carbon tetrachloride or perchlorethylene, both commercial and regenerated, are used as the solvent, and crystallization carried out for 6-8 hours at a weight ratio of the raw melt of monochloracetic acid: solvent 1 : 2-2.5, while the initial crystallization temperature is 38 ° C, the final 0 ± 5 ° C.

The mother liquor is subjected to washing with water in a weight ratio of 10-15: 1, followed by separation from the aqueous acid layer and returning the solvent to the crystallization stage.

The aqueous acid layer is evaporated to a residual moisture content of not more than 1.5 wt.%, And then crystallized in the solvent used to obtain a technical product containing monochloracetic acid of at least 95 wt.%. While crystallization is subjected to raw monochloracetic acid or its mixture with technical monochloracetic acid, allocated at the stage of disposal of the mother liquor.

The proposed method allows to obtain high-quality MCC and to increase the yield of marketable products, as well as to provide a simple technological method for the regeneration of the solvent and its further use in the process, practically eliminating its loss.

The proposed method is illustrated by the following examples.

Example 1. In a volumetric type reactor equipped with a reflux condenser, a thermometer and a jacket for heat dissipation, 200 g of carbon tetrachloride are poured and 100 g of a raw monochloracetic acid melt with a temperature of 70 ° C of the following composition, wt.%, Are metered with stirring: MCC - 90 60, DCAA - 5.1, CC - 3.6, water - 0.5, other impurities - 0.15. The dosage rate ensures the temperature of the crystallization mass is not higher than 50 ° C. During cooling, the temperature difference between the contents of the reactor and the refrigerant is maintained no more than 5 ° C. The crystallization process begins at a temperature of 38 ° C. The stage of crystal growth takes 6 hours, during which the reaction mass is cooled to a temperature of + 5 ° C.

The resulting suspension is filtered on a centrifuge, isolating 78.5 g of crystalline MCA composition, wt.%: MCA - 99.5, DCA - 0.2, UK - 0.08, water - 0.16, other impurities - 0.06.

The yield of purified acid is 86.21%; in addition, 221.5 g of filtrate is obtained, to which 22 g of water is added. After mixing and sludge, 200.3 g of carbon tetrachloride (CFC) and 43.2 g of an aqueous acid layer are isolated. CHC is returned to the cycle for the subsequent crystallization operation, and 25.9 g of water are evaporated from the aqueous acid layer. 34.5 g of CFCs are added to the dehydrated sludge and crystallization is carried out in the mode described above. After filtration, 9.00 g of technical MHUK of the composition are obtained, wt.%: MHUK - 96.1, DHUK - 3.05, UK - 0.46, water - 0.32, other impurities - 0.07, which is used during subsequent crystallization operation.

Example 2. Under the conditions of example 1, 200 g of regenerated carbon tetrachloride, 91 g of raw melt and 9 g of technical monochloracetic acid of the compositions described in example 1 are charged to crystallization.

The resulting solution was cooled from a temperature of 50 ° C to -5 ° C for 8 hours. After filtering the suspension, 82.3 g of crystalline MCAA composition are obtained, wt.%: MCAA - 99.1, DCAA - 0.45, CC - 0.11, water - 0.25, other impurities - 0.01. The yield of purified acid is 89.5%.

22 g of water is added to 217.7 g of the mother liquor, after separation of the layers, 200.5 g of CFCs and 39.1 g of an aqueous acid layer are obtained, from which 25.1 g of water with an admixture of acetic acid are evaporated. 30 g of CFCs are added to the dehydrated residue and crystallization is carried out. After filtration, 6.66 g of technical MHUK of the composition are obtained, wt.%: MHUK - 95.9, DHUK - 3.3 UK - 0.50, water - 0.19, other impurities - 0.12.

From the presented examples it follows that crystallization of a chlorine mixture consisting of MCC, DCA and CC in a medium of carbon tetrachloride or perchlorethylene makes it possible to obtain MCC with a content of at least 99.0% with a content of DCC 0.2-0.5%. The experimental data are presented in table 1.

The proposed crystallization modes are optimal, as they provide high quality and yield of the target MCC. A decrease in the crystallization temperature leads to an increase in the content of DCA in the commercial product, and its increase to a decrease in yield. The effect of the amount of solvent used is similar.

Claims (4)

1. A method of producing monochloroacetic acid, including crystallization in a solvent and separating crystals of monochloracetic acid from the mother liquor by filtration, removing the solvent from the mother liquor and returning to the crystallization stage, in which carbon tetrachloride or perchlorethylene is used either as commodity or regenerated, different the fact that crystallization is carried out for 6-8 hours at a weight ratio of the raw melt of monochloracetic acid: solvent 1: 2-2.5, while total crystallization temperature 38 ° С, final 0 ± 5 ° С. 2. The method according to claim 1, characterized in that the mother liquor is washed with water in a weight ratio of 10-15: 1, followed by separation of the solvent from the aqueous-acid layer and its return to the crystallization stage. 3. The method according to claim 2, characterized in that the aqueous acid layer is evaporated to a residual moisture content of not more than 1.5 wt.%, And then crystallized in the solvent used to obtain a technical product containing at least 95 wt.% Monochloracetic acid . 4. The method according to claim 3, characterized in that the raw material is subjected to crystallization of monochloracetic acid or a mixture thereof with technical monochloracetic acid, allocated at the stage of disposal of the mother liquor.