Method for refining and purifying waste catalyst generated in the production process of difluoromonochloromethane

Abstract

The present invention provides a method for refining and purifying waste catalysts generated in the process of producing difluorochloromethane, the method comprising: pre-separating the waste catalysts, rectifying the chloroform phase containing antimonide, and reactivating the antimonide obtained by rectification. The present invention regenerates antimony pentachloride with catalytic activity from the waste catalysts by separation, rectification and reactivation; and at the same time, condensation recovery is provided to recover chloroform, hydrogen fluoride and other substances generated in the process of refining and reactivating the waste catalysts. Through this process scheme, the reactivation ratio of the waste catalysts is about 80%, achieving the purpose of reducing the discharge of three wastes and reducing production costs.

Description

Technical Field

[0001] The invention relates to the field of organic fluorine chemical industry, and in particular to a method for refining and purifying waste catalysts generated in the production process of difluoromonochloromethane. Background Art

[0002] Chlorodifluoromethane, also known as chlorodifluoromethane, Freon-22, abbreviated as HCFC-22, has a chemical formula of CHClF2. It is a hydrogen-containing chlorofluorocarbon, a colorless gas with a slightly sweet odor. It is mainly used as a raw material for the production of tetrafluoroethylene and a raw material for the production of refrigerants, sprays, and pesticides. As an important chemical intermediate in the organic fluorine industry, it is currently generally produced by using hydrogen fluoride and chloroform under the catalysis of antimony pentachloride to produce chlorodifluoromethane and other by-products.

[0003] HF+SbCl5=SbCl4F+HCl①

[0004] HF+SbCl4F=SbCl3F2+HCl②

[0005] CHCl3+SbCl4F=CHCl2F+SbCl5 ③

[0006] CHCl2F+SbCl4F=CHClF2+SbCl5 ④

[0007] CHCl3+SbCl3F2=CHCl2F+SbCl4F ⑤

[0008] CHCl2F+SbCl3F2=CHClF2+SbCl4F ⑥

[0009] Antimony pentachloride will be converted into fluoroantimonate SbCl in this reaction. x F y , x+y=5 exists as an intermediate, but due to the following reasons:

[0010] 1. Antimony pentachloride itself is a perchloride and is unstable;

[0011] 2. When antimony pentachloride participates in the reaction in the form of fluoroantimonic acid, part of the fluoroantimonic acid will over-react with hydrogen fluoride to become antimony fluoride, resulting in the deactivation of the catalyst;

[0012] 3. The cumulative effect of introducing trace amounts of water into the reactants causes the catalyst to denature and become inactivated;

[0013] 4. During the reaction, the interaction between carbon cations generates long-chain hydrocarbons, which increases the viscosity of the reaction system and reduces the interaction between the reactants, resulting in a decrease in reaction capacity.

[0014] Therefore, chlorine needs to be introduced intermittently during the reaction to ensure the activity of the catalyst. At the same time, the reactor needs to be cleaned regularly and the waste catalyst (mainly composed of chloroform, hydrogen fluoride, antimony fluoride, antimony trichloride and antimony pentachloride) in the reactor needs to be discharged.

[0015] At present, the main method for disposing such waste catalysts in the industry is to generate antimony oxide through water alkali washing and oxidation drying, converting the liquid waste catalyst, which is a hazardous waste, into solid powder. However, due to the limitations of the water alkali washing and oxidation process, the solid antimony oxide produced has the following disadvantages:

[0016] 1. The product is impure, contains impure salts, and is mostly gray-black in color. This is caused by the long-chain hydrocarbons produced during the reaction entering the oxidation drying system;

[0017] 2. The crystal form is impure, and antimony pentoxide and antimony trioxide exist simultaneously in the product.

[0018] Most of the solid powder produced can only be treated as solid hazardous waste. At the same time, this process route produces a large amount of wastewater, which has a high content of metal antimony ions and low conversion efficiency. Summary of the invention

[0019] In view of the problems existing in the prior art, the present invention provides a method for refining and purifying waste catalyst generated in the production process of difluoromonochloromethane.

[0020] The invention provides a method for refining and purifying waste catalysts generated in the production process of difluorochloromethane, comprising: pre-separating the waste catalysts, rectifying a chloroform phase containing antimonide, and reactivating the antimonide obtained by the rectification.

[0021] The invention uses separation, distillation and reactivation methods to regenerate antimony pentachloride with catalytic activity from waste catalysts. The antimony pentachloride has high purity and can be recycled, thereby reducing production costs. In addition, the method has less three waste emissions and is superior to traditional water alkali washing and oxidation processes.

[0022] Furthermore, during distillation, the bottom of the tower is fed with materials, the bottom temperature is controlled at 70-75°C, the bottom pressure is controlled at 3-10 kPa, and the pressure difference of the whole tower is controlled at 1.5-2 kPa.

[0023] Furthermore, during distillation, a condenser is provided at the top of the tower to recover chloroform and hydrogen chloride.

[0024] Furthermore, the condenser is a full condenser, and the discharge temperature is controlled at -27 to -23° C. The present invention can recover chloroform at a high recovery rate, which can be directly sent back to the fluorination reactor for use, thereby maximizing resource utilization and reducing environmental pollution.

[0025] Furthermore, in the reactivation process, chlorine gas is introduced, and the temperature is controlled at 30-80° C. and the pressure is controlled at 10-50 kPa.

[0026] In a specific embodiment of the present invention, the pre-separation adopts filtering to separate the low-density, high-viscosity long-chain hydrocarbons and insoluble antimony fluoride from the chloroform solution rich in antimonide and hydrogen fluoride.

[0027] Furthermore, filtration was performed using a 100-10000 mesh tetrafluoroethylene filter membrane.

[0028] Preferably, the specific implementation comprises the following steps:

[0029] (1) filtering the spent catalyst using a 100-10000 mesh tetrafluoroethylene filter membrane to separate low-density, high-viscosity long-chain hydrocarbons and insoluble antimony fluoride from a chloroform solution rich in antimonide and hydrogen fluoride;

[0030] (2) the chloroform phase separated in step (1) is introduced into a distillation tower for separation, the tower bottom temperature is controlled at 70-75° C., the pressure is 3-10 kPa, and the pressure difference of the whole tower is controlled at 1.5-2 kPa. The chloroform and hydrogen fluoride separated from the top of the tower are cooled by a refrigerant to become liquid chloroform and gaseous hydrogen fluoride, and the antimonide in the tower bottom is then introduced into the next step;

[0031] (3) The antimonide phase in step (2) is sent to a reactivation system, and chlorine gas is introduced at 30-80° C. and 10-50 kPa for reactivation.

[0032] In the step (1), negative pressure filtration is preferably used for filtration, and chlorine-containing waste gas and chloroform gas will be obtained by filtration.

[0033] In another specific embodiment of the present invention, the pre-separation is carried out by heating at 30-50°C and -200 to -50Pa to evaporate part of the chloroform and chlorine in the waste catalyst and convert the residual antimony pentachloride in the waste catalyst into antimony trichloride.

[0034] Furthermore, the method also includes: treating the insoluble solids produced during the refining and purification process by using a traditional water alkali washing oxidation-reduction method.

[0035] Furthermore, the method further comprises: sending the waste gas generated during the refining and purification process into a VOCs (volatile organic compounds) treatment system. For example, in the first embodiment, the chlorine-containing waste gas and chloroform gas generated during the negative pressure filtration in step (1) can be sent to the VOCs treatment system.

[0036] Furthermore, the method can achieve a waste catalyst recovery rate of 80%.

[0037] The present invention provides a method for refining and purifying waste catalysts generated in the process of producing difluoromonochloromethane, wherein the waste catalysts are separated, distilled and reactivated to generate antimony pentachloride with catalytic activity; and condensation recovery is provided to recover chloroform, hydrogen fluoride and other substances generated in the process of refining and reactivating the waste catalysts. Through this process scheme, the reactivation ratio of the waste catalysts is about 80%, achieving the purpose of reducing the discharge of three wastes and reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic flow diagram of a method for refining and purifying waste catalyst generated in the production process of difluorochloromethane in Example 1 of the present invention;

[0039] Figure 2 The figure is a schematic flow chart of a method for refining and purifying waste catalyst generated in the production process of difluorochloromethane in Example 2 of the present invention. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention is clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] Unless otherwise specified, the experimental reagents and materials used in the embodiments of the present invention can be obtained commercially.

[0042] Unless otherwise specified, the technical means used in the embodiments of the present invention are conventional means well known to those skilled in the art.

[0043] Example 1

[0044] This embodiment provides a method for refining and purifying the waste catalyst generated in the production process of difluoromonochloromethane. The specific process is as follows: Figure 1 As shown, the steps are as follows:

[0045] The waste catalyst (Liquid 1) is filtered in a filter (F) using a special tetrafluoroethylene filter membrane of 800 mesh under negative pressure filtration (~100 Pa). The chlorine-containing waste gas and chloroform gas (Gas 1) obtained by filtration enter the VOCs treatment system, and the liquid phase (chloroform solution rich in antimonide and hydrogen fluoride) (Liquid 2) enters the distillation tower (T).

[0046] The distillation tower is set as a plate tower, with a feed temperature of 50°C, a feed pressure of 5-10kPa, a tower bottom feed, a tower bottom temperature controlled at 70-75°C, a tower bottom pressure controlled at 3-10kPa, a full tower pressure difference controlled at 1.5-2kPa, a tower top condenser as a full condenser, and a discharge temperature controlled at -23 to -27°C. Among the tower bottom discharge products, the recovery rate of antimony chloride can reach 98%, and the recovery rate of chloroform (Liquid 4) at the top of the tower can reach 82%, which can be directly sent back to the fluorination reactor for use.

[0047] Antimony chloride (Liquid 3) containing a trace amount of chloroform is then sent to the activation reactor (R), and chlorine gas (Gas 2) is introduced at 30-80°C and 10-50kPa for reactivation.

[0048] The comprehensive recovery rate of the spent catalyst is about 80%, wherein the comprehensive recovery rate = the content of antimonide after activation (in terms of antimony element) / the content of antimonide entering the distillation tower (in terms of antimony element).

[0049] The filter residue obtained from the first filtration is then treated by conventional water-alkali washing and oxidation-reduction methods (the catalyst recovered from this part is not included in the previous comprehensive recovery rate).

[0050] Example 2

[0051] This embodiment provides a method for refining and purifying the waste catalyst generated in the production process of difluoromonochloromethane. The specific process is as follows: Figure 2 As shown, the steps are as follows:

[0052] The waste catalyst (Liquid 1) enters the preheater (EH) and is heated at 30-50°C and -200 to -50Pa to slowly evaporate a large amount of chloroform and chlorine contained in the waste catalyst, and the gas phase (Gas 1) enters the VOCs treatment system; at the same time, most of the residual antimony pentachloride in the waste catalyst is converted into antimony trichloride; when the chloroform content in the preheater is lower than a certain value (the classic value of the chloroform: catalyst weight ratio in the waste catalyst in the industry is 2:1; here it is necessary to reduce the ratio of chloroform to the total material to about 10-30% to avoid high energy consumption caused by excessive chloroform, and to avoid tower coking and equipment damage caused by too little chloroform), the residual liquid phase (Liquid 2) is sent to the distillation tower (T). The feed pressure of the distillation tower is 5-10kPa, the feed to the tower kettle, the tower kettle temperature is controlled at 70-75℃, the tower kettle pressure is controlled at 3-10kPa, the pressure difference of the whole tower is controlled at 1.5-2kPa, the top condenser is a full condenser, and the discharge temperature is controlled at -23~-27℃. After the distillation is completed, the material is extracted from the middle of the tower kettle; the chloroform (Liquid 4) at the top of the tower can be directly sent back to the fluorination reactor for use, with a recovery rate of 82%; the long-chain hydrocarbons in the tower kettle and the insoluble solids at the bottom are treated by traditional water alkali washing oxidation-reduction methods; the material (Liquid 3) extracted from the middle of the tower kettle is then sent to the activation reactor (R), and chlorine (Gas 2) is introduced under the working conditions of 30-80℃ and 10-50kPa for reactivation.

[0053] The overall recovery rate of spent catalyst is about 78%.

[0054] This embodiment adopts the discharge of the middle part of the tower kettle, which has stricter requirements on operation control, and at the same time, the cleaning of the tower kettle in the later stage is more complicated. Therefore, the method in Example 1 is preferably adopted in the two embodiments, and only the filter membrane needs to be replaced, and the whole equipment does not need to be cleaned.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for refining and purifying waste catalyst generated in the production process of difluoromonochloromethane, characterized in that: include: After pre-separation of the spent catalyst, the chloroform phase containing the antimonide is distilled, and the antimonide obtained by distillation is reactivated; The pre-separation adopts a heating method, and is heated at 30-50°C and -200 to -50Pa to evaporate part of the chloroform and chlorine in the waste catalyst, and convert the residual antimony pentachloride in the waste catalyst into antimony trichloride; During distillation, the tower bottom is fed with materials, the tower bottom temperature is controlled at 70-75°C, the tower bottom pressure is controlled at 3-10kPa, and the pressure difference of the whole tower is controlled at 1.5-2kPa; during distillation, a condenser is set at the top of the tower to recover chloroform and hydrogen chloride, the condenser is a full condenser, and the discharge temperature is controlled at -27 to -23°C.

2. The method for refining and purifying waste catalyst generated in the production process of difluorochloromethane according to claim 1, characterized in that: In the reactivation process, chlorine gas is introduced, and the temperature is controlled at 30-80° C. and the pressure is controlled at 10-50 kPa.

3. The method for refining and purifying waste catalyst generated in the production process of difluorochloromethane according to claim 1, characterized in that: The pre-separation adopts filtering mode to separate the low-density, high-viscosity long-chain hydrocarbons and the insoluble antimony fluoride from the chloroform solution rich in antimonide and hydrogen fluoride.

4. The method for refining and purifying waste catalyst generated in the production process of difluorochloromethane according to claim 3, characterized in that: Filter using a 100-10000 mesh tetrafluoroethylene filter.

5. The method for refining and purifying the waste catalyst generated in the production process of difluorochloromethane according to any one of claims 1 to 3, characterized in that: The method further comprises: treating the insoluble solids produced in the refining and purification process by using a conventional water alkali washing oxidation-reduction method.

6. The method for refining and purifying waste catalyst generated in the production process of difluorochloromethane according to claim 5, characterized in that: The method can achieve a recovery rate of 80% for the spent catalyst.

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