Method Of Producing High-Purity Monochloroacetic Acid

Abstract

A method has been disclosed of obtaining high purity, colourless monochloroacetic acid encompassing the chlorination of acetic acid with chlorine in the presence of a catalyst, followed by the recovery of the catalyst through vacuum distillation and purification of the obtained liquid raw product by its hydrodehalogenation by hydrogen in the presence of a palladium catalyst and then vacuum distillation.

Claims

1. The method of obtaining high purity, colourless monochloroacetic acid encompassing the chlorination of acetic acid with chlorine in the presence of a catalyst, followed by the recovery of the catalyst through vacuum distillation and purification of the remaining liquid raw product by its hydrodehalogenation in the presence of a palladium catalyst and then vacuum distillation, characterised in that a. hydrolysis is conducted of anhydrides and acid chlorides which are present in the stream of the liquid product obtained after the stage of recovery of the catalyst, whereby hydrolysis is conducted with such a continuous excess of water with respect to the content of chlorides and anhydrides that the concentration of water in the mixture leaving to the next stage is between 0.05 and 5% by weight, in a temperature of between from 50 to 160? C. and then b. the excess water is removed by a reaction with acid chlorides so that the concentration of water in the reaction mixture entering the hydrodehalogenation process is less than 2%.

2. The method according to claim 1, characterised in that the hydrolysis of the anhydrides and acid chlorides is conducted in the reactor or an intermediate tank or in a cascade of reactors with an overall retention time of between 30 minutes and 12 hours.

3. The method according to claim 1, characterised in that the concentration of water in the reaction mixture entering the hydrodehalogenation process is less than 1% by weight.

4. The method according to claim 1, characterised in that the hydrodehalogenation is conducted by of the raw product with hydrogen in the presence of a catalyst containing metal from group X of the periodic table of elements.

5. The method according to claim 4, characterised in that the catalyst is seated on a medium in the form of powder, granules or extrusions of activated carbon, silica or zeolite.

6. The method according to claim 1, characterised in that the hydrodehalogenation process takes place in a liquid or gaseous phase.

7. The method according to claim 1, characterised in that the hydrodehalogenation process is conducted in the liquid phase in a reactor with a fixed catalyst bed.

8. The method according to claim 1, characterised in that the hydrodehalogenation process is conducted in the liquid phase in a circulation reactor.

9. The method according to claim 1, characterised in that the hydrodehalogenation process is conducted in the gaseous phase in a reactor with a fixed catalyst bed.

10. The method according to claim 1, characterised in that the reactor or cascade of reactors, in which the hydrolysis of the anhydrides is conducted enables the liquid in it to mix.

11. The method according to claim 1, characterised in that during the stage of hydrolysis of the anhydrides, the excess water is within the range of 0.2 to 5% by weight.

12. The method according to claim 11, characterised in that during the stage of hydrolysis of the anhydrides, the excess water is within the range of 0.3 to 0.7% by weight.

13. The method according to claim 1, characterised in that the concentration of water in the reaction mixture entering the hydrodehalogenation process is less 0.01% by weight.

14. The method according to claim 1, characterised in that the hydrodehalogenation is conducted by of the raw product with hydrogen in the presence of a catalyst containing palladium or platinum.

Description

EXAMPLE 1. (COMPARATIVE EXAMPLE)

[0047] A reaction mixture from the chlorination of acetic acid with chlorine gas has been analysed without derivatization by gas chromatography with a flame ionization detector (GC-FID) and HPLC. The composition of the mixture is 68% MCAA, 4.5% DCAA, 21.2% acetic acid and 2.6% acetyl chloride, 1.8% chloroacetyl chloride, 1.2% acetic anhydride and 0.7% hydrogen chloride. The mixture was subjected to gas stripping with hydrogen chloride to separate the acid chlorides. To achieve this, the mixture was fed into the top of the stripping column at a flow rate of 3 kg/h. At the same time, hydrogen chloride gas was fed into the column from the bottom. The pressure in the process was 2.5 bar (a) and the temperature was 130? C. The flow of hydrogen chloride was set at 1.5 kg/h.

[0048] The mixture at the exit from the stripping column contained 71.9% MCAA, 4.8% DCAA, 21.6% acetic acid and 0.2% acetyl chloride, 0.3% chloroacetyl chloride, 0.3% acetic anhydride and 0.9% HCl. The product obtained after stripping was passed through a static mixer at a rate of approximately 3 kg/h, into which water was also dosed in quantities of 100 g/h, after which the mixture containing water was directed to the hydrodehalogenation process. The hydrodehalogenation system was equipped with a thermally insulated column reactor filled with a heterogeneous catalyst (1% palladium on granular activated carbon). The volume of the catalyst bed was 6 litres, while its height was 3 m. The mixture leaving the column in which water was mixed was continuously dosed at the top of the hydrodehalogenation column. The GC-FID and HPLC analysis of the mixture after adding water, but before hydrogenation showed that this mixture contains 72.3% MCAA, 4.8% DCAA, 18.9% acetic acid, 0.2% acetic anhydride and 0.6% HCl, as well as 3.2% water.

[0049] The hydrodehalogenation process was conducted continuously at a temperature of 140? C., measured at the top of the column for 72 hours. The reactor was supplied from the bottom with hydrogen in a quantity of 120 Nm.sup.3/h. After a single passage through the column, the mixture contained 0.9% DCAA. The HPLC and GC-FID analyses found the presence of an ester of chloroacetic and glycolic acid (GAMA) in a quantity of 0.9% and glycolic acid (GA) in a quantity of 0.4% in the product after hydrogenation.

[0050] The reaction mixture after hydrogenation was yellow, while the gaseous effluents from the hydrodehalogenation stage passing through the alkaline scrubber removing hydrogen chloride coloured the solution yellow. Minimal quantities of acetaldehyde (120 ppm) were found in the reaction mixture, but it was not possible to precisely measure the concentration of this compound because of its volatility and reactivity.

[0051] The mixture was subjected to vacuum distillation after hydrodehalogenation, at which stage acetic acid was distilled off. The distillation was repeated to distil off pure monochloroacetic acid. The product (MCAA) was collected as a colourless distillate. The colour on the PtCo scale was 10 units. Distillation was stopped when the residue in the column bottom blocked further operation and the distillate started to take on a yellow colour. 11 kg of a tar-like substance, of a content of approximately 45% MCAA was obtained as a residue of the distillation. The rest was polymeric fraction, the composition of which was not analysed. The ratio of the quantity of heavy residues to the quantity of product received is 0.051.

EXAMPLE 2

[0052] A sample of a mixture of a composition as in the case of the mixture used in example 1 was subjected to the distillation process under reduced pressure in order to recover volatile fractions containing acid chlorides. After distillation, the mixture had the following composition: MCAA 75.1%, DCAA 5.2%, AcOH 17.0%, acetyl chloride 0.2%, chloroacetyl chloride 0.4%, acetic anhydride 1.9% and HCl 0.2%. A mixture of this composition was passed through a static mixer at a flow rate of approximately 3 kg/h, into which water was also dosed in quantities of 30 g/h, after which the mixture containing water was taken to the container with an agitator of an operating volume of 7 litres. After two hours of hydrolysis, a sample was taken and the mixture was analysed for water content. It was found that the concentration of water was 0.54%. Next, the process mixture from the hydrolysis tank started to be added continuously to the receiver, which was equipped with an agitator and outlet for gaseous effluent, keeping a constant level of liquid in the hydrolysis tank. The hydrolysis time was 2 hours, while a temperature of 130? C. was maintained in the tank. The mixture's water content was determined at the end of the hydrolysis. The concentration of water was 0.53%, whereby no presence of acid chlorides and anhydrides was found in the water. The mixture in the receiver was treated with acetyl chloride in a quantity of 23.6 g/kg of liquid and the water and acetyl chloride content were determined after thorough mixing. The water content was 60 ppm, while no presence of acid chlorides was found. Next, liquid started to be added for hydrodehalogenation in the same way and under the same conditions as in example 1.

[0053] The product obtained from hydrodehalogenation was straw-coloured, which is related to the formation of negligible quantities of acetaldehyde. However, the product contained only 0.015% GAMA and less than 100 ppm glycolic acid.

[0054] The hydrodehalogenation process was completed after 80 hours and the products mixture that was obtained was subjected to vacuum distillation to separate the acetic acid, after which the distillation was repeated to distil off MCAA. The product (MCAA) was collected as a colourless distillate. The colour on the PtCo scale was 10 units.

[0055] At the same time, 1320 g of a tar-like substance, of a content of approximately 50% MCAA, was obtained as a residue of the distillation. The ratio of the quantity of heavy residues to the quantity of product received is 0.0055.

EXAMPLE 3

[0056] A sample of the mixture used in examples 1 and 2 was subjected to a reaction with water under the same conditions as in example 2. The mass of the sample was 2000 g. Hydrolysis was also conducted for 120 minutes. The excess water was measured after this time. It was 0.51%. 64.5 g chloroacetyl chloride was measured and added to the mixture, after which it was stirred for approximately 10 minutes. The water content measured in the mixture obtained was 20 ppm. The mixture prepared in this way was then subjected to hydrodehalogenation. The conditions of the hydrodehalogenation were the same as in examples 1 and 2. The product obtained had a light yellow colour. The product did not contain GAMA or glycolic acid in quantities enabling the concentration of these impurities to be determined.

[0057] After conducting vacuum distillation to separate the excess acetic acid, the product was subjected to final vacuum distillation. The product (MCAA) was collected as a colourless distillate. The colour on the PtCo scale was 10 units. The liquid taken, in a quantity of 80 g was a tan-coloured mixture with a low viscosity. The MCAA content of the liquid taken was 87.5%. The ratio of the quantity of heavy residues to the quantity of product obtained was 0.01 (per waste in the form of heavy fractions of a content of 50% MCAA).

EXAMPLE 4

[0058] The mixture obtained in example 1 containing 68% MCAA, 4.5% DCAA, 21.2% acetic acid and 2.6% acetyl chloride, 1.8% chloroacetyl chloride, 1.2% acetic anhydride and 0.7% hydrogen chloride was subjected to vacuum distillation to separate the volatile fractions containing acid chlorides. The concentration of the individual chlorides and anhydrides in the mixture was determined. The acetyl chloride content was 0.2%, chloroacetyl chloride 0.4%, acetic anhydride 1.7% and HCl 0.16%. A series of four experiments in accordance with the description in example 3 were conducted using the mixture obtained. The hydrolysis stage and the reaction of the excess water with acetyl chloride were conducted such that the following concentrations of water were obtained in the mixture before hydrodehalogenation in 4 successive attempts: experiment 190 ppm, experiment 275 ppm, experiment 394 ppm, experiment 450 ppm. An ultra-pure colourless product (MCAA) was obtained after conducting the double vacuum distillation to separate the acetic acid and distil off the final product.