Method for purifying crude chloroacetic acid

Abstract

The invention belongs to the technical field of synthesis of organic compounds, and particularly relates to a method for purifying a crude chloroacetic acid product. The method comprises the following steps: S1, impregnating activated carbon with chloropalladic acid to prepare a catalyst precursor; the preparation method comprises the following steps: blending a catalyst precursor, a dispersing agent, a reducing agent, poly (N-vinyl caprolactam) and (S, S)-(+)-N, N '-bis (3, 5-di-tert-butyl salicylidene)-1, 2-cyclohexanediamine, carrying out a reduction reaction to prepare a palladium-carbon catalyst, and passivating to prepare a passivated palladium-carbon catalyst; s2, the heated crude chloroacetic acid product and hydrogen are introduced into a micro-interface generator to be mixed, then hydrogenation reaction is carried out under the action of a passivated palladium-carbon catalyst, gas-liquid separation and rectification are carried out after the reaction is completed, and the chloroacetic acid product is prepared. By improving the problems of insufficient selectivity and conversion rate of dichloroacetic acid impurities in the chloroacetic acid crude product purified by the existing palladium-carbon catalyst, the content of the dichloroacetic acid impurities in the chloroacetic acid crude product after catalytic hydrogenation is effectively reduced.

Description

Technical Field

[0001] This invention belongs to the field of organic compound synthesis technology, specifically relating to a method for purifying crude chloroacetic acid. Background Technology

[0002] Due to the high electronegativity of the chlorine atom in chloroacetic acid, it exhibits higher acidity and stronger reactivity compared to acetic acid. The chlorine atom in chloroacetic acid can undergo substitution reactions with various groups such as hydroxyl, mercapto, and cyano groups to generate new compounds. Therefore, chloroacetic acid is an important raw material for the synthesis of drugs such as barbiturates. In addition, chloroacetic acid has wide applications in petroleum, pesticides, and daily chemical industries.

[0003] Currently, chloroacetic acid is commonly synthesized by the catalytic chlorination of acetic acid, which involves the reaction of acetic acid and chlorine gas to produce chloroacetic acid under the action of a catalyst. However, the product often contains a variety of byproducts, among which dichloroacetic acid is one of the main byproducts, which has a significant impact on the performance of chloroacetic acid. The dichloroacetic acid can be converted into chloroacetic acid by using a catalytic hydrogenation process, which removes dichloroacetic acid and reduces waste and environmental pollution.

[0004] Currently, the common catalytic hydrogenation process for crude chloroacetic acid typically involves adding crude chloroacetic acid and hydrogen separately into a hydrogenation tower. After mixing within the tower, the crude chloroacetic acid and hydrogen react in a palladium-carbon catalyst bed fixed inside the tower, converting dichloroacetic acid in the crude chloroacetic acid into chloroacetic acid. However, this process has a problem: due to the turbulent hydrogen flow, crude chloroacetic acid easily generates a large amount of foam at the palladium-carbon catalyst bed. During the bursting process, the hydrogen foam cannot fully contact the crude chloroacetic acid, requiring a higher hydrogen feed rate and pressure to achieve sufficient contact. This results in significant hydrogen waste and high energy consumption.

[0005] To address this issue, one improvement method is to install a micro-interface generator. This allows crude chloroacetic acid and hydrogen to be mixed in the micro-interface generator before entering the hydrogenation tower for the hydrogenation reaction. The micro-interface generator's function is to use specific mechanical microstructures to thoroughly mix the crude chloroacetic acid and hydrogen before the next hydrogenation reaction, significantly increasing the gas-liquid phase mass transfer efficiency and effectively alleviating the problem of poor contact between crude chloroacetic acid and hydrogen. However, in actual use, it was found that simply adding the micro-interface generator, with other parameters unchanged, resulted in a significantly higher catalytic activity and poorer catalytic selectivity in the palladium-carbon catalyst. This could lead to excessive reduction of dichloroacetic acid to acetic acid or partial hydrogenation and dechlorination of chloroacetic acid to acetic acid.

[0006] Chinese patent CN115160124A discloses a method for hydrodechlorinating a feed containing dichloroacetic acid. In this method, the hydrodechlorination is carried out in a vertical tubular reactor. The liquid stream containing dichloroacetic acid and hydrogen gas preferably flow in parallel downwards at a heterogeneous catalyst. The heterogeneous catalyst is preferably housed in a fixed bed and is preferably a solid heterogeneous hydrogenation catalyst of one or more Group VIII metals of the periodic table deposited on a support. The Group VIII metals are preferably selected from ruthenium, rhodium, palladium, and / or platinum, most preferably from those containing palladium, and sulfur or sulfur compounds. The support is selected from activated carbon, silica, alumina, zirconium oxide, and titanium oxide, most preferably activated carbon. The catalyst used in this patent is a conventional catalyst, and problems such as excessive reduction of dichloroacetic acid leading to acetic acid impurities still exist.

[0007] How to address the issues of high catalytic activity and poor catalytic selectivity in catalysts after the addition of a micro-interface generator, in order to reduce the over-reduction of dichloroacetic acid and improve the purity of chloroacetic acid after catalytic hydrogenation, is one of the important research topics in the field. Summary of the Invention

[0008] The purpose of this invention is to provide a method for purifying crude chloroacetic acid, which improves upon the shortcomings of insufficient catalyst selectivity and conversion rate in the existing crude chloroacetic acid purification hydrogenation process, and effectively reduces the content of dichloroacetic acid impurities in the crude chloroacetic acid after catalytic hydrogenation.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The method for purifying crude chloroacetic acid according to the present invention includes the following steps: S1. Activated carbon is impregnated with chloropalladium acid to obtain a catalyst precursor; the catalyst precursor, dispersant, reducing agent, poly(N-vinylcaprolactam) and (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylene)-1,2-cyclohexanediamine are mixed and subjected to a reduction reaction to obtain a palladium-on-carbon catalyst; a passivating agent is added to the palladium-on-carbon catalyst for passivation treatment to obtain a passivated palladium-on-carbon catalyst. S2. The crude chloroacetic acid is heated to obtain heated crude chloroacetic acid. The heated crude chloroacetic acid is mixed with hydrogen in a micro-interface generator to obtain a mixture. The mixture is subjected to hydrogenation reaction under the action of a passivated palladium carbon catalyst. After gas-liquid separation and distillation, the chloroacetic acid product is obtained.

[0010] in: In S1, palladium chloride is prepared by reacting palladium chloride with hydrochloric acid; the reaction temperature is 38~45℃, the reaction time is 15~20min; the molar ratio of palladium chloride to hydrochloric acid is 1:(2.1~2.5), and the average diameter of activated carbon is 1~5mm.

[0011] In S1, the dispersant is a mixture of sodium polyacrylate and water, and the reducing agent is tetraethylene glycol.

[0012] In S1, the ratio of the amount of catalyst precursor, tetraethylene glycol, sodium polyacrylate and water is 450:(350~500):(120~150):(1500~2000), wherein the amount of catalyst precursor is in g, and the amount of tetraethylene glycol, sodium polyacrylate and water is in mL.

[0013] In S1, the mass ratio of the catalyst precursor, poly(N-vinylcaprolactam), and (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylyl)-1,2-cyclohexanediamine is 450:(60~120):(12~18).

[0014] In S1, the reduction reaction temperature is 150~160℃ and the reduction reaction time is 2.5~3.5h.

[0015] In S1, the passivating agent is prepared from tetrasodium iminodisuccinate, silver nitrate and water, and the ratio of tetrasodium iminodisuccinate, silver nitrate and passivating agent is (20~25):(12~18):(650~850). The tetrasodium iminodisuccinate and silver nitrate are both expressed in g, and the passivating agent is expressed in mL.

[0016] In S1, the ratio of palladium-carbon catalyst to passivating agent is 450:(650~850), the passivating agent is in mL and the palladium-carbon catalyst is in g; the passivation temperature is 125~140℃, the passivation time is 30~40min, and the palladium loading on the palladium-carbon catalyst is 5.39~5.90 wt%.

[0017] In S2, the heating temperature is 140~160℃.

[0018] In step S2, the hydrogen inlet pressure is 0.15~0.20 MPa, and the hydrogen flow rate is 155~165 m³ / h. 3 / h; the flow rate of the heated crude chloroacetic acid is 4.5~5.6t / h; the hydrogenation reaction temperature is 140~160℃.

[0019] The apparatus used in the method for purifying crude chloroacetic acid according to the present invention includes a crude chloroacetic acid feed pipeline connected to a heater. The heater, micro-interface generator, hydrogenation tower and gas-liquid separator are connected in sequence. A hydrogen feed pipeline is provided on the micro-interface generator.

[0020] The passivated palladium-on-carbon catalyst is packed into a fixed bed, which is then installed in a hydrogenation tower. The hydrogenation reaction takes place in the hydrogenation tower, and the mixture enters from the bottom of the tower. The fixed bed comprises three catalyst layers, each with a thickness of 180-300 mm; adjacent catalyst layers are separated by ceramic ball layers with a thickness of 300-400 mm.

[0021] The beneficial effects of this invention are as follows: The main reason for the poor selectivity of conventional palladium-on-carbon catalysts in the purification of crude chloroacetic acid is the problem of the uniformity of the active site structure. This is because Pd particles have a wide size distribution and various crystal plane configurations and point and surface defects. The Pd atoms at these point and surface defects have high coordination unsaturation and excessive adsorption of C-Cl bonds. In addition, the amount of chloroacetic acid in crude chloroacetic acid is much greater than that of impurities such as dichloroacetic acid. Therefore, some chloroacetic acid will be dechlorinated due to over-adsorption. At the same time, the adsorption of chloroacetic acid occupies the active sites of the palladium-on-carbon catalyst, which also leads to a decrease in the conversion rate of impurities such as dichloroacetic acid.

[0022] Sodium polyacrylate, as an anionic polyelectrolyte, has its carboxyl group reacting with Pd in ​​the initial stage of reduction. 2+ Dynamic coordination is formed, slowing down the reduction rate and preventing explosive nucleation; poly(N-vinylcaprolactam) can undergo a thermo-induced hydrophobic transition at high temperatures, forming micelle structures that can encapsulate Pd. 2+ The dynamic coordination compound with sodium polyacrylate, through the confinement effect of the micelle structure, allows sodium polyacrylate to adsorb onto the newly formed Pd cores and micelle surface. Through electrostatic repulsion (negative charge layer), it prevents the aggregation of Pd cores and micelles, providing the preconditions for the monodisperse growth of Pd cores, further restricting the growth rate of Pd particles and reducing the generation of defect sites.

[0023] Finally, sodium polyacrylate and poly(N-vinylcaprolactam) were used to treat Pd 2+ The ordering and subsequent monodispersity of Pd cores provide a favorable adsorption microenvironment for (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylyl)-1,2-cyclohexanediamine (referred to as chiral ligand). The rigid planar structure and chiral cavity of the chiral ligand enable it to selectively adsorb onto specific crystal planes of the Pd core. The imine nitrogen and phenolic oxygen atoms in the chiral ligand effectively bind to the unsaturated sites (defects) in the Pd core, thereby inducing the reduction of unsaturated sites (defects) during Pd core growth, forming Pd particles with regular atomic arrangement and low surface energy, suppressing the tendency for excessive adsorption of C-Cl bonds, and thus reducing the phenomenon of excessive dechlorination to generate acetic acid byproducts.

[0024] Through coordination with silver nitrate, tetrasodium iminodisuccinate can be effectively deposited on the inner wall of the pores of the palladium-carbon catalyst, improving the mass transfer resistance of hydrogen at the phase interface (gas, liquid, solid) on the surface of the palladium-carbon catalyst. At the same time, the deposition of tetrasodium iminodisuccinate can further cover the rough defects and chemical inhomogeneities on the surface of the palladium-carbon catalyst, smoothing the surface of the palladium-carbon catalyst, which is conducive to the desorption of reaction products and reduces the probability of over-hydrogenation. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the apparatus used in the present invention to purify crude chloroacetic acid; In the diagram: 1. Crude chloroacetic acid feed line; 2. Heater; 3. Hydrogen feed line; 4. Micro-interface generator; 5. Hydrogenation tower; 6. Gas-liquid separator. Detailed Implementation

[0026] The present invention will now be described and illustrated in detail with reference to the embodiments.

[0027] The raw materials used in the following examples and comparative examples are all commercially available products. The crude chloroacetic acid product is a chloroacetic acid product that has undergone preliminary refining and contains a variety of impurities, including acetic acid accounting for 0.10 wt% and dichloroacetic acid accounting for 2.30 wt%.

[0028] Example 1 Preparation of passivated palladium-carbon catalyst: 180g of palladium chloride was mixed with 1000mL of 2.5mol / L hydrochloric acid solution and heated in a water bath at 38℃ for 20min to obtain chloropalladic acid; 500g of activated carbon particles (average diameter 3mm) were weighed and placed in 800mL of 0.2mol / L hydrochloric acid solution and stirred and acid-washed for 20min, filtered to obtain a wet filter cake, and the wet filter cake was vacuum-dried at 80℃ for 40min and then removed; the acid-washed activated carbon particles were impregnated with all the obtained chloropalladic acid for 22min, filtered, and vacuum-dried at 80℃ for 40min to obtain the catalyst precursor; 450 g of catalyst precursor, 500 mL of tetraethylene glycol, 120 mL of sodium polyacrylate, and 1.5 L of water were mixed, and then 60 g of poly(N-vinylcaprolactam) and 15 g of (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylic acid)-1,2-cyclohexanediamine were added. The mixture was heated in an oil bath at 155 °C and refluxed for 3 min. After filtration, washing three times with an ethanol-water solution, and vacuum drying at 80 °C for 1 h, a palladium-on-carbon catalyst with a palladium loading of 5.90 wt% was obtained. 20g of tetrasodium iminodisuccinate and 12g of silver nitrate were dissolved in water and diluted to a final volume to prepare 680mL of passivating agent. 450g of palladium-on-carbon catalyst was impregnated with 680mL of passivating agent for 30min. Then, the catalyst was added to a rotary evaporator and rotary evaporated at 135℃ for 40min. The catalyst was washed three times with an ethanol-water solution and then placed in an infrared drying oven under a nitrogen atmosphere at 90℃ for 12h to obtain the passivated palladium-on-carbon catalyst.

[0029] Purified crude chloroacetic acid: like Figure 1 As shown, the apparatus used in the method for purifying crude chloroacetic acid includes a crude chloroacetic acid feed line 1, which is connected to a heater 2. The heater 2, micro-interface generator 4, hydrogenation tower 5, and gas-liquid separator 6 are connected in sequence. A hydrogen feed line 3 is provided on the micro-interface generator 4.

[0030] 4.5 kg of passivated palladium-on-carbon catalyst was loaded into a fixed bed, which was then installed in hydrogenation tower 5. The fixed bed consisted of three layers, each including a 180 mm thick catalyst layer and a 300 mm thick ceramic ball layer, with adjacent catalyst layers separated by ceramic ball layers. Crude chloroacetic acid was fed into heater 2 via crude chloroacetic acid feed line 1 and heated to 140°C. It was then fed into micro-interface generator 4 at a flow rate of 4.5 t / h, simultaneously via hydrogen feed line 3 at a flow rate of 155 m³ / h. 3 Hydrogen gas is introduced into the micro-interface generator 4 at a flow rate of [flow rate] / h and a feed pressure of 0.2 MPa. The hydrogen gas mixes with crude chloroacetic acid in the micro-interface generator 4 to form a mixture. This mixture then enters the hydrogenation tower 5, where a hydrogenation reaction is carried out at 140°C. After hydrogenation, the mixture enters the gas-liquid separator 6 for gas-liquid separation. The tail gas is discharged from the top of the separator, and the liquid phase containing chloroacetic acid is distilled to obtain the chloroacetic acid product. The content of dichloroacetic acid and acetic acid in the chloroacetic acid product is analyzed; the dichloroacetic acid content is 0.12 wt%, and the acetic acid content is 0.13 wt%.

[0031] Example 2 Preparation of passivated palladium-carbon catalyst: 180g of palladium chloride was mixed with 1000mL of 2.1mol / L hydrochloric acid solution and heated in a water bath at 45℃ for 15min to obtain chloropalladic acid; 500g of activated carbon particles (average diameter 1mm) were weighed and placed in 800mL of 0.2mol / L hydrochloric acid solution and stirred and acid-washed for 20min, and filtered to obtain a wet filter cake. The wet filter cake was vacuum-dried at 80℃ for 40min and then removed; the acid-washed activated carbon particles were impregnated with all the obtained chloropalladic acid for 22min, filtered, and vacuum-dried at 80℃ for 40min to obtain the catalyst precursor.

[0032] 450 g of catalyst precursor, 420 mL of tetraethylene glycol, 150 mL of sodium polyacrylate and 1.2 L of water were mixed and then 85 g of poly(N-vinylcaprolactam) and 18 g of (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylic acid)-1,2-cyclohexanediamine were added and mixed. The mixture was heated in an oil bath at 160 °C and refluxed for 2.5 min. After filtration, washing three times with an ethanol-water solution and vacuum drying at 80 °C for 1 h, palladium-on-carbon catalyst with a palladium loading of 5.39 wt% was obtained.

[0033] 25g of tetrasodium iminodisuccinate and 18g of silver nitrate were dissolved in water and diluted to a final volume to prepare 850mL of passivating agent. 450g of palladium-on-carbon catalyst was impregnated with 850mL of passivating agent for 30min. Then, it was added to a rotary evaporator and rotary evaporated at 125℃ for 36min. The catalyst was washed three times with an ethanol-water solution and then placed in an infrared drying oven and allowed to stand at 90℃ for 12h under a nitrogen atmosphere to obtain the passivated palladium-on-carbon catalyst.

[0034] Purified crude chloroacetic acid: The apparatus used in the method for purifying crude chloroacetic acid is as follows: Figure 1 As shown, it is the same as in Example 1.

[0035] 8.4 kg of passivated palladium-on-carbon catalyst was loaded into a fixed bed, which was then installed in hydrogenation tower 5. The fixed bed consisted of three layers, each including a 300 mm thick catalyst layer and a 350 mm thick ceramic ball layer, with adjacent catalyst layers separated by ceramic ball layers. Crude chloroacetic acid was fed into heater 2 via crude chloroacetic acid feed line 1 and heated to 150°C. It was then fed into micro-interface generator 4 at a flow rate of 5 t / h, simultaneously via hydrogen feed line 3 at a flow rate of 160 m³ / h. 3 Hydrogen gas is introduced into the micro-interface generator 4 at a flow rate of / h and a feed pressure of 0.15MPa. The hydrogen gas mixes with crude chloroacetic acid in the micro-interface generator 4 to form a mixture. This mixture then enters the hydrogenation tower 5, where a hydrogenation reaction is carried out at 150℃. After hydrogenation, the mixture enters the gas-liquid separator 6 for gas-liquid separation. The tail gas is discharged from the top of the separator, and the liquid phase containing chloroacetic acid is distilled to obtain the chloroacetic acid product. The content of dichloroacetic acid and acetic acid in the chloroacetic acid product is analyzed; the dichloroacetic acid content is 0.10wt%, and the acetic acid content is 0.12wt%.

[0036] Example 3 Preparation of passivated palladium-carbon catalyst: 180g of palladium chloride was mixed with 1000mL of 2.3mol / L hydrochloric acid solution and heated in a water bath at 42℃ for 18min to obtain chloropalladic acid; 500g of activated carbon particles (average diameter 5mm) were weighed and placed in 800mL of 0.2mol / L hydrochloric acid solution and stirred and acid-washed for 20min, and filtered to obtain a wet filter cake. The wet filter cake was vacuum-dried at 80℃ for 40min and then removed; the acid-washed activated carbon particles were impregnated with all the obtained chloropalladic acid for 22min, filtered, and vacuum-dried at 80℃ for 40min to obtain the catalyst precursor.

[0037] 450g of catalyst precursor, 350mL of tetraethylene glycol, 140mL of sodium polyacrylate and 1L of water were mixed and then 120g of poly(N-vinylcaprolactam) and 12g of (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylic acid)-1,2-cyclohexanediamine were added and mixed. The mixture was heated in an oil bath at 150℃ and refluxed for 3.5min. After filtration, washing three times with an ethanol-water solution and vacuum drying at 80℃ for 1h, palladium-on-carbon catalyst with a palladium loading of 5.73wt% was obtained.

[0038] 22g of tetrasodium iminodisuccinate and 14g of silver nitrate were dissolved in water and diluted to a final volume to prepare 650mL of passivating agent. 450g of palladium-on-carbon catalyst was impregnated with 650mL of passivating agent for 30min. Then, the catalyst was added to a rotary evaporator and rotary evaporated at 140℃ for 30min. The catalyst was washed three times with an ethanol-water solution and then placed in an infrared drying oven and allowed to stand at 90℃ for 12h under a nitrogen atmosphere to obtain the passivated palladium-on-carbon catalyst.

[0039] Purified crude chloroacetic acid: The apparatus used in the method for purifying crude chloroacetic acid is as follows: Figure 1 As shown, it is the same as in Example 1.

[0040] Passivated palladium-carbon catalyst was loaded into a fixed bed, which was then installed in hydrogenation tower 5. The fixed bed consisted of three layers, each including a 250 mm thick catalyst layer and a 400 mm thick ceramic ball layer, with adjacent catalyst layers separated by ceramic ball layers. Crude chloroacetic acid was fed into heater 2 via crude chloroacetic acid feed line 1 and heated to 160°C. It was then fed into micro-interface generator 4 at a flow rate of 5.6 t / h, simultaneously via hydrogen feed line 3 at a flow rate of 165 m... 3Hydrogen gas is introduced into the micro-interface generator 4 at a flow rate of [flow rate] / h and a feed pressure of 0.17 MPa. The hydrogen gas mixes with crude chloroacetic acid in the micro-interface generator 4 to form a mixture. This mixture then enters the hydrogenation tower 5, where a hydrogenation reaction is carried out at 160°C. After hydrogenation, the mixture enters the gas-liquid separator 6 for gas-liquid separation. The tail gas is discharged from the top of the separator, and the liquid phase containing chloroacetic acid is distilled to obtain the chloroacetic acid product. The content of dichloroacetic acid and acetic acid in the chloroacetic acid product is analyzed; the dichloroacetic acid content is 0.09 wt%, and the acetic acid content is 0.14 wt%.

[0041] Comparative Example 1 The poly(N-vinylcaprolactam) was replaced with an equal mass of water, and the remaining steps were the same as in Example 1. The content of dichloroacetic acid and acetic acid in the chloroacetic acid product was tested. The content of dichloroacetic acid was 1.24 wt%, and the content of acetic acid was 0.85%.

[0042] Comparative Example 2 The sodium polyacrylate was replaced with an equal volume of water, and the remaining steps were the same as in Example 1. The content of dichloroacetic acid and acetic acid in the chloroacetic acid product was tested. The content of dichloroacetic acid was 1.07%, and the content of acetic acid was 0.89%.

[0043] Comparative Example 3 (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicyl)-1,2-cyclohexanediamine was replaced with an equal volume of water, and the remaining steps were the same as in Example 1. The content of dichloroacetic acid and acetic acid in the chloroacetic acid product was tested. The content of dichloroacetic acid was 0.98%, and the content of acetic acid was 1.13%.

[0044] Comparative Example 4 Without adding tetrasodium iminodisuccinate, the remaining steps were the same as in Example 1. The content of dichloroacetic acid and acetic acid in the chloroacetic acid product was tested, and the content of dichloroacetic acid was 0.84% ​​and the content of acetic acid was 0.53%.

[0045] Comparative Example 5 Without adding silver nitrate, the remaining steps were the same as in Example 1. The content of dichloroacetic acid and acetic acid in the chloroacetic acid product was tested, and the content of dichloroacetic acid was 0.66% and the content of acetic acid was 0.68%.

Claims

1. A method for purifying crude chloroacetic acid, characterized in that, Includes the following steps: S1. Activated carbon is impregnated with chloropalladium acid to obtain a catalyst precursor; the catalyst precursor, dispersant, reducing agent, poly(N-vinylcaprolactam) and (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylene)-1,2-cyclohexanediamine are mixed and subjected to a reduction reaction to obtain a palladium-on-carbon catalyst; a passivating agent is added to the palladium-on-carbon catalyst for passivation treatment to obtain a passivated palladium-on-carbon catalyst. S2. The crude chloroacetic acid is heated to obtain the heated crude chloroacetic acid. The heated crude chloroacetic acid is mixed with hydrogen in a micro-interface generator (4) to obtain a mixture. The mixture is subjected to hydrogenation reaction under the action of passivated palladium carbon catalyst. After gas-liquid separation and distillation, the chloroacetic acid product is obtained.

2. The method for purifying crude chloroacetic acid according to claim 1, characterized in that, In S1, palladium chloride is prepared by reacting palladium chloride with hydrochloric acid; the reaction temperature is 38~45℃, the reaction time is 15~20min; the molar ratio of palladium chloride to hydrochloric acid is 1:(2.1~2.5); the average diameter of activated carbon is 1~5mm; the dispersant is a mixture of sodium polyacrylate and water, and the reducing agent is tetraethylene glycol.

3. The method for purifying crude chloroacetic acid according to claim 2, characterized in that, In S1, the ratio of catalyst precursor, tetraethylene glycol, sodium polyacrylate and water is 450:(350~500):(120~150):(1500~2000), where the catalyst precursor is expressed in g, and the tetraethylene glycol, sodium polyacrylate and water are expressed in mL.

4. The method for purifying crude chloroacetic acid according to claim 1, characterized in that, In S1, the mass ratio of the catalyst precursor, poly(N-vinylcaprolactam) and (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylene)-1,2-cyclohexanediamine is 450:(60~120):(12~18).

5. The method for purifying crude chloroacetic acid according to claim 1, characterized in that, In S1, the reduction reaction temperature is 150~160℃ and the reduction reaction time is 2.5~3.5h.

6. The method for purifying crude chloroacetic acid according to claim 1, characterized in that, In S1, the passivating agent is prepared from tetrasodium iminodisuccinate, silver nitrate and water. The ratio of tetrasodium iminodisuccinate, silver nitrate and passivating agent is (20~25):(12~18):(650~850). Tetrasodium iminodisuccinate and silver nitrate are expressed in g, and passivating agent is expressed in mL.

7. The method for purifying crude chloroacetic acid according to claim 1, characterized in that, In S1, the ratio of palladium-on-carbon catalyst to passivator is 450:(650~850), with the passivator measured in mL and the palladium-on-carbon catalyst measured in g; the passivation temperature is 125~140℃, the passivation time is 30~40 min, and the palladium loading on the palladium-on-carbon catalyst is 5.39~5.90 wt%.

8. The method for purifying crude chloroacetic acid according to claim 1, characterized in that, In S2, the heating temperature is 140~160℃.

9. The method for purifying crude chloroacetic acid according to claim 1, characterized in that, In S2, the hydrogen inlet pressure is 0.15~0.20 MPa, and the hydrogen flow rate is 155~165 m³ / h. 3 / h.

10. The method for purifying crude chloroacetic acid according to claim 1, characterized in that, The flow rate of the heated crude chloroacetic acid was 4.5~5.6 t / h; the hydrogenation reaction temperature was 140~160℃.

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