RU2391331C2 - Method of obtaining monochloracetic acid - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to an improved method of obtaining monochloracetic acid (MCA) and can be used in chemical industry. MCA is an essential product in production of carboxymethyl cellulose, various pesticides and medicinal agents. The method involves a step for chlorinating acetic acid with molecular chlorine in a bubbling reactor in the presence of a homogeneous catalyst, hydrogenolysis of chlorination products in the presence of a fixed-bed catalyst based on palladium and extraction of the end product through rectification under vacuum, where the hydrogenolysis step is carried out in film mode with direct-flow movement of liquid and gas.

EFFECT: lower consumption indices of raw material, higher quality of the obtained MCA and increased amount of recycled material.

4 cl, 1 dwg, 1 tbl, 5 ex

Description

The invention relates to an improved method for producing monochloroacetic acid (MCC) and can be used in the chemical industry. MCA is a valuable product for the production of carboxymethyl cellulose, various pesticides and medicines.

A known method of producing MCC, including continuous liquid-phase catalytic chlorination of acetic acid (CC) and the allocation of MCC by crystallization, followed by centrifugation. The liquid phase (mother liquor) separated from the MCC crystals returns to the chlorination stage. [Industrial organochlorine products. Handbook Ed. L.A. Oshina. - M .: Chemistry, 1978, p.85].

The chlorination of acetic acid is carried out at 100-120 ° C. Chlorination products contain about 75% wt. MHUK, 18% wt. UK and 7% wt. dichloroacetic acid (DCAA). The resulting products at 50 ° C are fed to the crystallization stage, which is carried out by cooling the product to 20-25 ° C. The resulting suspension of crystals of MCCA mixed with acetic and dichloroacetic acids is subjected to separation, for example, by centrifugation. The solid phase is a commercial product, and the liquid phase (mother liquor) is returned to chlorination.

From the description of the known method for producing MCA, it can be seen that supplying the mother liquor to the chlorination stage leads to the accumulation of DCC in the scheme, which will require the withdrawal of part of the mother liquor for destruction. In addition, a high concentration of DCA reduces the performance of the crystallization step. In this regard, the disadvantage of this method is the need to destroy part of the mother liquor, which leads to high consumption coefficients of the feedstock, as well as low productivity of the periodic crystallization stage due to the high content of DCA in the raw monochloracetic acid.

A known method of producing MCC, including the stage of continuous liquid phase chlorination of CC with molecular chlorine at 110 ° C and a 10% molar excess of chlorine relative to CC in the presence of a catalyst - acetic anhydride (12.4% by weight in the initial mixture with CC), periodic a stage of catalytic hydrogenolysis of chlorination products in the presence of a heterogeneous catalyst - palladium on activated carbon at 140 ° C and a seven-fold molar excess of hydrogen with respect to DCA, and a crystallization stage with the isolation of a commercial product. Received commodity MHUK contains up to 0.5% wt. DHUK and 0.5% wt. Criminal Code [RU 2059602].

Consumption coefficients of reagents (per 1 ton of MCC) are: UK - 0.98 t / t; chlorine - 1.38 t / t.

The main disadvantage of this method is the high consumption rates of the reagents, the use of low-productivity periodic stages of hydrogenolysis and crystallization, as well as the high content of DCA and CC in the commercial product.

The closest in technical essence is the method of obtaining MCC, including the stage of chlorination of MC with molecular chlorine in a bubble column, the stage of hydrogenolysis of chlorinated products in the presence of a stationary catalyst layer based on palladium and the stage of separation of the target product by distillation under vacuum [US 7135597 B2, US 2005272953 A1] .

The main disadvantage of this method is that at the stage of hydrogenolysis there is not only the conversion of DCA to MCA, but also the conversion of MCA to CC, and, as a result, high consumption rates of reagents.

The technical objective of the method is to reduce the expenditure coefficients for raw materials, reduce the number of recycled products and improve the quality of commodity MHUK.

This problem is solved by the method of obtaining MCC, including the stages of chlorination of acetic acid with molecular chlorine, hydrogenolysis of chlorinated products in the presence of a stationary catalyst layer based on palladium and isolation of the commercial product by distillation under vacuum, in which the hydrogenolysis stage is carried out in film mode with direct flow of liquid and gas.

The chlorination process can be carried out in a single bubble reactor. However, it is preferable that the chlorination process be carried out in a cascade of bubble reactors with fractional (dispersed) supply of chlorine and catalyst through the cascade reactors.

As a catalyst for the chlorination process, UA and acetyl chloride (AH) can be used. However, it is preferable to use a mixture of AA with acetyl chloride (AX) as a catalyst in the chlorination step.

Palladium supported on an inert support, in particular activated carbon, can be used as a hydrogenolysis catalyst.

The following examples illustrate the method.

Example 1

The process is carried out on the installation shown in the drawing.

Chlorination Stage

The process of chlorination of acetic acid with molecular chlorine is carried out continuously in two successive reactors P1 and P2, which are steel enamelled columns with a volume of 8.5 m ³ , equipped with shirts to remove the heat of the chemical reaction. Acetic anhydride is used as a catalyst.

Acetic acid is dosed at a rate of 1022.60 kg / h, part of the catalyst at a rate of 53.69 kg / h (35% of the total amount of catalyst), and through a bubbler, part of the chlorine at a rate of 856.81 kg is dosed through the fittings located at the bottom of the reactor through the fittings located at the bottom of the reactor / hour (56% of the total). The reactor P1 maintains a temperature in the range of 105-115 ° C and a pressure of 1-3 atm. The conversion of acetic acid in the reactor P1 is about 55%, the conversion of chlorine is ~ 97%.

Liquid reaction products from the upper part of the reactor P1 are sent to the lower part of the reactor P2, where additional (remaining) amounts of chlorine and catalyst are fed.

The chlorination process in the second reactor P2 is carried out at 115-125 ° C and a pressure of 1-2 MPa. The conversion of acetic acid in reactor P2 is about 98%, the conversion of chlorine is ~ 98%.

The total feed rate of the reagents and catalyst in the reactors P1 and P2 was: UK - 1022.60 kg / h; chlorine - 1530.01 kg / hour; catalyst (UA) - 153.39 kg / hour.

Liquid reaction products from the upper part of reactor P2 are sent to apparatus P3, in which the catalyst is decomposed with deionized (desalted) water.

Raw monochloracetic acid (MCCA raw) from apparatus P3 after decomposition of the catalyst with water is collected in a container E1, from which MCCA raw is fed to the hydrogenation stage of dichloroacetic acid.

Gaseous streams generated in reactors P1 and P2 and containing hydrogen chloride, chlorine, acetic acid, monochloroacetic acid and a catalyst are sent to separate for each chlorination reactor two-stage condensation systems T1-T2 and T3-T4, cooled by circulating water and a refrigerant with temperature 0 ÷ - 5 ° C.

The condensate formed is returned to the chlorination reactors in full, and non-condensed gaseous reaction products containing mainly hydrogen chloride and chlorine (~ 5% wt.) Are sent to the stage of thermal neutralization, in which hydrogen chloride is purified from chlorine and organic impurities.

DHA hydrogenation step

Hydrogenation of raw MCC containing 6.4% wt. DCAA is carried out in film mode at 130-135 ° C and a 3-5-fold molar excess of hydrogen in a reactor P4, which is a column-type steel enamelled apparatus filled with an IK-53-1 palladium catalyst containing 1% wt. palladium on a carbon support with a particle size of the catalyst from 2.5 to 3.2 mm

Raw MCC and hydrogen are fed to the upper part of reactor P4 from tank E1 at a rate of 2113.86 kg / h and 8.54 kg / h, respectively. As a result of the chemical hydrogenation reaction, the dichloroacetic acid contained in the MCC raw is converted to monochloracetic acid. Hydrogenation products are removed from the lower part at a rate of 2073.04 kg / h, which, in addition to MCC, contain no more than 0.26% wt. DHUK and not more than 5.7% wt. Criminal Code, which is collected in a container E2, and then sent to the stage of purification - rectification.

Gaseous reaction products containing hydrogen, hydrogen chloride and monochloracetic acid vapors are sent to a T5 condenser cooled by a refrigerant. Condensate is collected in a container E2, and non-condensed gases, mainly consisting of hydrogen and hydrogen chloride, are sent for cleaning by burning.

Rectification Stage

The products of the hydrogenation reaction from tank E2 go to the stage of isolating the commercial form of monochloracetic acid, which is carried out by rectification in a packed column K1 with a diameter of 0.8 m under vacuum at a column top pressure of 0.3-0.4 kgf / cm ² . The column contains several layers of the nozzle (Rashig ring size 35 × 35 mm). The total height of the packed layer is 9.0 m.

A distillate is taken off the top of the column and sent to the chlorination step (recycling). From the bottom of the column, in the form of steam, a flow of commodity MHUK (1875.17 kg / h) is selected, composition,% wt .: MHUK - 99.72; DHUK - 0.27; UK - 0.01, which is condensed and collected in the capacity of a commercial product E3. From the cube of the column (as resinous compounds accumulate), a small amount of heavy products is taken, which are sent for disposal (burning).

Consumption ratios for UK, chlorine and hydrogen amounted to 0.63, 0.82 and 0.005 tons per 1 ton of commodity MHUK, respectively. The amount of recycled substances was 9.4% wt. of the total amount of hydrogenate fed to the rectification.

The main material flows of example 1 are shown in the table.

Example 2

The process is carried out analogously to example 1, but the chlorination of the UK is carried out in a single reactor with a volume of 8.5 m ³ at a temperature of 100-125 ° C, and the process of hydrogenolysis at 110-120 ° C in the presence of a catalyst containing 5% wt. Pd on activated carbon AG-3.

Consumption ratios for UK, chlorine and hydrogen were 0.83, 1.1 and 0.02 tons per 1 ton of commodity MHUK, respectively. The amount of recycled substances was 16.4% wt. of the total amount of hydrogenate fed to the rectification.

Example 3

The process is carried out analogously to example 1, but hydrogenolysis is carried out at 110-140 ° C in the presence of a catalyst containing 2% wt. Pd on Al ₂ O _3, when applying a liquid raw MHUK and hydrogen into the lower part of the reactor.

Consumption ratios for UK, chlorine and hydrogen were 0.79, 0.90 and 0.1 tons per 1 ton of commodity MHUK, respectively. The amount of recycled substances was 12.2% wt. of the total amount of hydrogenate fed to the rectification.

Example 4

The process is carried out analogously to example 1, but as a catalyst at the stage of chlorination using a mixture of acetic anhydride and acetyl chloride in a molar ratio of 1: 1.

Consumption ratios for UK, chlorine and hydrogen were 0.63, 0.80 and 0.01 tons per 1 ton of commodity MHUK, respectively. The amount of recycled substances was 9.9% by weight of the total amount of hydrogenate fed to the rectification.

Example 5

The process is carried out analogously to example 1, but the distillation is carried out at a pressure in the upper part of the column of 0.5-0.6 kgf / cm ² .

Consumption ratios for UK, chlorine and hydrogen were 0.83, 0.90 and 0.01 tons per 1 ton of commodity MHUK, respectively. The amount of recycled substances was 22.8% wt. of the total amount of hydrogenate fed to the rectification.

Thus, the process of the claimed method allows to reduce the expenditure coefficients for raw materials (t per 1 t MHUK): UK - from 0.98 to 0.63-0.83; chlorine - from 1.38 to 0.80-1.10; hydrogen - from 0.012 to 0.005-0.01, and also reduce the amount of recycled substances from 38% to 9.4-22.8% of the total amount of substances supplied for rectification. The amount of impurities (UK and DHUK) in the resulting commodity MCA did not exceed 0.03% wt. (UK) and 0.35% wt. (DCAA).

Table. Material flows of reagents and consumption ratios for raw materials. Method steps Prototype Example 1 Chlorination Filed Cl ₂ kg / hr 331.76 1530.01 Filed UK, kg / h 202.25 1022.60 Catalyst fed, kg / h 33.60 153.39 Recycle from the isolation stage, kg / h
including kg / h 149.24 194.93 MHUK 74.56 77.87 DHUK 4.40 0.26 UK 70.28 116.80 Received chlorination products, kg / h
including kg / h 396.00 2113.86 MHUK 297.00 1866.13 DHUK 27.72 134.58 UK 71.28 113.15 Hydrogenolysis Hydrogen supplied, kg / h 3.00 8.54 Received hydrogenolysis products, kg / h
including kg / h 390.03 2073.04 MHUK 313.35 1948.58 DHUK 5.40 5.38 UK 71.28 119.08 Selection Received commodity MHUK kg / hour
including kg / h 240.79 1875.17 MHUK 238.39 1869.86 DHUK 1.20 5.12 UK 1.20 0.19 Sent for recycling kg / hour
including kg / h 149.24 194.93 MHUK 74.56 77.87 DHUK 4.40 0.26 UK 70.28 116.80 Consumption ratios, t / t UK and catalyst 0.98 0.63 Cl ₂ 1.38 0.82 H ₂ 0.012 0.005

Claims (4)

1. A method of producing monochloracetic acid, comprising the steps of chlorinating acetic acid with molecular chlorine in a bubbler reactor in the presence of a homogeneous catalyst, hydrogenolysis of the chlorinated products in the presence of a stationary palladium-based catalyst layer and isolating the product by distillation under vacuum, characterized in that the hydrogenolysis stage is carried out in film mode with direct-flow motion of liquid and gas. 2. The method according to claim 1, characterized in that a mixture of acetic anhydride and acetyl chloride is used as a catalyst in the stage of chlorination of acetic acid. 3. The method according to claim 1, characterized in that the chlorination stage is carried out in a cascade of bubble reactors with fractional (dispersed) supply of chlorine and catalyst through the reactors of the cascade. 4. The method according to claim 1, characterized in that the rectification stage is carried out at a residual pressure in the upper part of the column equal to 0.3-0.4 kgf / cm ² .

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