A method for preparing 1-chloro-1,1-difluoroethane by gas phase catalysis

Abstract

The invention discloses a method for preparing 1-chloro-1,1-difluoroethane by gas phase catalysis, wherein the method uses 1,1-difluoroethane and chlorine as raw materials, and prepares the 1-chloro-1,1-difluoroethane by gas phase chlorination reaction under the action of a chlorination catalyst, wherein the chlorination catalyst is selected from a Lewis acid catalyst. The invention has the advantages of high single-pass conversion rate, high product selectivity, low production cost, continuous reaction, and suitability for industrial application.

Description

Technical Field

[0001] The invention relates to the field of fluorine chemical industry, and in particular to a method for preparing 1-chloro-1,1-difluoroethane by gas phase catalysis in the presence of a chlorination catalyst, using 1,1-difluoroethane and chlorine as raw materials. Background Art

[0002] 1-Chloro-1,1-difluoroethane, commonly known as difluorochloroethane, Freon-142b, codenamed HCFC-142b or R142b, is a colorless, slightly aromatic gas that is easily soluble in oil but difficult to dissolve in water. R142b is an important organic intermediate, mainly used in the production of vinylidene fluoride (VDF) and then in the preparation of polyvinylidene fluoride resin (PVDF).

[0003] At present, the synthesis methods of 1-chloro-1,1-difluoroethane mainly include: 1,1,1-trichloroethane direct fluorination method, VDC addition fluorination method and 1,1-difluoroethane photochlorination method based on raw materials.

[0004] (1) 1,1,1-Trichloroethane direct fluorination method

[0005] Using 1,1,1-trichloroethane and hydrogen fluoride as raw materials, a fluorination reaction is carried out under specific conditions. The reaction equation is as follows:

[0006] CH3CCl3+HF→CH3CFCl2+HCl

[0007] CH3CFCl2+HF→CH3CF2Cl+HCl

[0008] Atto Chemicals' patent CN1030746A discloses a method for preparing 1,1-difluoro-1-chloroethane by liquid phase fluorination reaction using 1,1,1-trichloroethane or 1,1-dichloro-1-fluoroethane and hydrofluoric acid as raw materials and perfluoroalkylsulfonic acid (trifluoromethanesulfonic acid) as catalyst. The method has a 98.5% conversion rate of 1,1,1-trichloroethane and a 64.4% selectivity for 1,1-difluoro-1-chloroethane. However, since the trichloromethyl group of 1,1,1-trichloroethane itself is very active, fluorination reaction can occur even in the absence of a catalyst, and the degree of reaction is difficult to control, resulting in many by-products and complicated subsequent treatment. If the reaction does not use a catalyst, the required reaction temperature is too high; excessive hydrogen fluoride will result in excessive by-products in the reaction product; too little hydrogen fluoride will result in a reduced reaction rate and a prolonged reaction time.

[0009] (2) VDC addition fluorination method

[0010] The process of using 1,1-dichloroethylene (VDC) and hydrogen fluoride as raw materials to carry out addition fluorination reaction under specific conditions to obtain 1-chloro-1,1-difluoroethane can be divided into a one-step method and a two-step method. The one-step method is to place the addition reaction and the fluorination reaction in the same reactor to obtain the target product; the two-step method is to divide the reaction into two stages. The first stage is to directly carry out addition reaction of VDC and hydrogen fluoride to obtain 1-fluoro-1,1-dichloroethane, and the second stage is to separate and purify the product obtained in the first stage to obtain 1-fluoro-1,1-dichloroethane with higher purity and then carry out fluorination reaction with hydrogen fluoride to generate 1-chloro-1,1-difluoroethane. The reaction equation is as follows:

[0011] CH2=CCl2+HF→CH3CCl2F

[0012] CH3CCl2F+HF→CH3CF2Cl+HCl

[0013] Patent CN1171837C of Suzhou Lianfu Chemical Co., Ltd. discloses a method for preparing R124b by a one-step liquid phase reaction using VDC and hydrogen fluoride as raw materials and SnCl4 and CF3(CF2)3COF as catalysts. The selectivity of R142b in this method reaches 95.2%, but the heat release is intense during the experiment and the utilization rate of hydrogen fluoride is low.

[0014] Zhejiang University patent CN1927790A discloses a method for synthesizing and separating difluorochloroethane using VDC and hydrogen fluoride as raw materials, SnCl4 as a catalyst for liquid phase reaction, and a cyclic reaction distillation method in the same device. The method improves the yield of HCFC-142b and the selectivity of HCFC-142b to HCF-143a, but the method has a significant amplification effect. During the industrialization process, VDC is very likely to undergo self-polymerization and cracking reactions to generate a large amount of polymers and tar-like substances, resulting in a decrease in reaction yield, a rapid decrease in catalyst activity, and pipeline blockage.

[0015] (3) 1,1-Difluoroethane Photochlorination

[0016] The process of using 1,1-difluoroethane and chlorine as raw materials to obtain 1-chloro-1,1-difluoroethane by gas phase or liquid phase chlorination reaction in a photochlorination reactor under the action of ultraviolet light. Depending on whether there is a spraying facility in the photochlorination reactor, it can be divided into wet photochlorination and dry photochlorination. The reaction proceeds according to the free radical process and is often catalyzed by heat, light and free radical initiation. It is an exothermic reaction. The equation is as follows:

[0017] CH3CHF2+Cl2→CH3CF2Cl+HCl

[0018] Shandong Huaan New Materials Co., Ltd. patent CN106431819A discloses a method for preparing difluoromonochloroethane using difluoroethane and chlorine as raw materials through steps such as vaporization, multi-stage photochlorination reaction, water alkali washing, compression, dehydration, and rectification. The method is a wet photochlorination reaction under ultraviolet light, and the heat released by the reaction is taken away by internal spray water, and the generated hydrogen chloride gas is also absorbed by washing in the photochlorination tower, and the byproduct sodium hypochlorite solution produced by the subsequent alkali washing has a low hydrochloric acid content, but the method has a large reactor amplification effect and low production efficiency.

[0019] At present, in actual industrial production, the preparation of difluorochloroethane mainly adopts VDC addition fluorination method and 1,1-difluoroethane photochlorination method, but the price of VDC raw materials has been at a high level, and the photochlorination reactor has a significant amplification effect, which is prone to the risk of material leakage due to damage to the light tube, and the production scale is limited. Summary of the invention

[0020] In order to solve the above technical problems, the present invention proposes a method for preparing 1-chloro-1,1-difluoroethane by gas phase catalysis, which has high single-pass conversion rate, high product selectivity, low production cost, can realize continuous reaction and is suitable for industrial application.

[0021] The objective of the present invention is achieved through the following technical solutions:

[0022] A method for preparing 1-chloro-1,1-difluoroethane by gas phase catalysis, the method comprising: using 1,1-difluoroethane and chlorine as raw materials, preparing the 1-chloro-1,1-difluoroethane by gas phase chlorination reaction under the action of a chlorination catalyst, wherein the chlorination catalyst is selected from a Lewis acid catalyst, and the reaction equation is as follows:

[0023] CH3CHF2+Cl2→CH3CF2Cl+HCl

[0024] The reaction of 1,1-difluoroethane and chlorine is relatively easy to proceed. Under the action of a highly active catalyst, if the reaction conditions are not properly controlled, it is easy to cause an overreaction to form by-products. Therefore, the existing technology often uses photocatalysis.

[0025] The Lewis acid catalyst of the present invention comprises a carrier and an active component, wherein the active component is at least one of zinc chloride, magnesium chloride or calcium chloride, and the active component accounts for 10 to 30% of the total mass of the Lewis acid catalyst. Preferably, the active component is zinc chloride, and accounts for 15 to 20% of the total mass of the Lewis acid catalyst.

[0026] The Lewis acid catalyst of the present invention comprises a carrier and an active component, wherein the carrier is at least one of activated carbon, alumina or aluminum fluoride. Preferably, the carrier is activated carbon.

[0027] The reaction temperature of the gas phase chlorination reaction of the present invention is 200-300° C., the reaction pressure is 0-0.05 MPa, and the molar ratio of chlorine to 1,1-difluoroethane is 0.33-5:1, preferably 1-3:1.

[0028] The reaction of 1,1-difluoroethane and chlorine is an exothermic reaction, but the reaction must be heated to give the reactants a certain activation energy in order for the reaction to proceed smoothly. If the heating temperature is too low, the reactants cannot reach an activated state; if the heating temperature is too high, the side reactions will be aggravated, resulting in a low yield of the target product. Therefore, the reaction temperature of the present invention is controlled at 200 to 300°C, preferably 250 to 300°C.

[0029] The material molar ratio of 1,1-difluoroethane and chlorine has little effect on the reaction. As the chlorine ratio increases, the conversion rate of 1,1-difluoroethane increases. Therefore, the molar ratio of chlorine to 1,1-difluoroethane in the present invention is 0.33 to 5:1, and in order to reduce the difficulty of chlorine separation in the later stage, it is preferably 1 to 3:1.

[0030] The chlorination catalyst of the present invention is subjected to activation treatment, and the activation treatment step comprises:

[0031] A1. Calcination step: calcining under a nitrogen atmosphere, the calcination temperature is 300 to 350 ° C, and the calcination time is 2 to 5h;

[0032] A2. Activation step: introduce chlorine gas and maintain at 150-200°C for 0.5-2h, then raise the temperature to 200-300°C and continue activation for 0.5-2h to obtain an activated chlorination catalyst.

[0033] The mixed raw gas of 1,1-difluoroethane and chlorine reacts with the activated chlorination catalyst in a gas phase chlorination reaction, and the space velocity of the mixed raw gas is 240h -1 ~720h -1 .

[0034] The space velocity of 1,1-difluoroethane and chlorine on the catalyst also has a great influence on the reaction. If the contact time between the material and the catalyst is too short, the conversion rate of 1,1-difluoroethane is low; if the contact time between the material and the catalyst is too long, deep chlorination reaction is likely to occur, and the number of by-products increases. Therefore, the space velocity of the reaction material on the catalyst of the present invention is 240~720h -1 , preferably 360~720h -1 .

[0035] The crude product of the gas phase chlorination reaction of the present invention is washed with water, compressed, dehydrated and distilled to obtain a high-purity 1-chloro-1,1-difluoroethane product. The 1,1-difluoroethane separated by the distillation operation can be reused as a raw material.

[0036] Under the chlorination catalyst and reaction conditions of the present invention, the raw material single-pass conversion rate is high, the product selectivity is high, and it is not easy to cause overreaction to form over-chlorination by-products. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements and equivalents within the scope of the claims.

[0038] Preparation Example 1

[0039] 20 mL of catalyst was loaded into an Incon material reaction tube with an inner diameter of 19 mm and a length of 800 mm. The catalyst carrier was activated carbon, and the active component was zinc chloride, which accounted for 15% of the total mass. The reaction tube was heated to 300°C, calcined for 2 h with nitrogen, and then cooled to 200°C. Chlorine was introduced at a feed rate of 11.4 g / h to activate the catalyst. After half an hour of activation, the temperature was raised to 300°C and the activation was continued for half an hour to obtain an activated chlorination catalyst, which was recorded as Cat1.

[0040] Preparation Example 2

[0041] The operation process of this preparation example is the same as that of Preparation Example 1, with the only difference being that the active components are calcium chloride, magnesium chloride, copper chloride, and nickel chloride, respectively, and the obtained catalysts are respectively recorded as Cat2, Cat3, Cat4, and Cat5.

[0042] Preparation Example 3

[0043] 20 mL of catalyst was loaded into an Inconel material reaction tube with an inner diameter of 19 mm and a length of 800 mm. The catalyst carrier was alumina and the active component was zinc chloride, which accounted for 15% of the total mass. The reaction tube was heated to 300°C and calcined for 2 h with nitrogen. Then the temperature was lowered to 200°C and chlorine was introduced at a feed rate of 11.4 g / h to activate the catalyst. After half an hour of activation, the temperature was raised to 300°C and the activation was continued for half an hour to obtain an activated chlorination catalyst, which was recorded as Cat6.

[0044] Preparation Example 4

[0045] The operation process of this preparation example is the same as that of Preparation Example 3, with the only difference being that the carrier is aluminum fluoride and the obtained catalyst is denoted as Cat7.

[0046] Example 1

[0047] The chlorine feed rate was 11.4 g / h and the 1,1-difluoroethane feed rate was 10.6 g / h. After mixing, they were introduced into a fixed bed reactor (filled with Cat1). The reaction temperature was controlled at 300 °C, the molar ratio of chlorine to 1,1-difluoroethane was 1:1, and the space velocity was 360 h -1 The reaction products are sequentially passed through a water alkali washing device, a compression device, a drying and dehydration device, and a distillation device, and are sampled and analyzed from the sampling port at the reactor outlet. The conversion rate of 1,1-difluoroethane and the selectivity of 1-chloro-1,1-difluoroethane are shown in Table 1 below.

[0048] Example 2-3

[0049] The operation of this embodiment is the same as that of embodiment 1, except that the reaction temperatures are controlled at 275° C. and 250° C., respectively. The reaction results are shown in Table 1 below:

[0050] Table 1

[0051] Example Reaction temperature / ℃ 1,1-Difluoroethane conversion R142b Selectivity Example 1 300 95.0％ 93.5％ Example 2 275 91.3％ 94.0％ Example 3 250 86.2％ 94.2％

[0052] Embodiment 4-5

[0053] The operation of this embodiment is the same as that of embodiment 1, except that the ratio of chlorine to 1,1-difluoroethane is controlled at 0.33:1 and 3:1 respectively. The reaction results are shown in Table 2 below:

[0054] Table 2

[0055] Example Chlorine and 1,1-difluoroethane ratio 1,1-Difluoroethane conversion R142b Selectivity Example 1 1:1 95.0％ 93.5％ Example 4 0.33:1 50.3％ 93.3％ Example 5 3:1 97.8％ 87.2％

[0056] Embodiment 6-7

[0057] The operation of this embodiment is the same as that of embodiment 1, except that the chlorine feed rate is 7.5 g / h, the 1,1-difluoroethane feed rate is 6.9 g / h, and the space velocity is 240 h -1 ; Chlorine feed flow rate 22.7g / h, 1,1-difluoroethane feed flow rate 21.1g / h, space velocity 720h -1 The reaction results are shown in Table 3 below:

[0058] Table 3

[0059] Example <![CDATA[Air speed / h -1 > 1,1-Difluoroethane conversion R142b Selectivity Example 1 360 95.0％ 93.5％ Example 6 240 75.1％ 93.3％ Example 7 720 95.5％ 84.9％

[0060] Embodiment 8-11

[0061] The operation of this embodiment is the same as that of embodiment 1, except that the catalysts are Cat2, Cat3, Cat6, and Cat7, respectively. The reaction results are shown in Table 4 below:

[0062] Table 4

[0063] Example catalyst 1,1-Difluoroethane conversion R142b Selectivity Example 1 Cat1 95.0％ 93.5％ Example 8 Cat2 90.1％ 93.3％ Example 9 Cat3 94.5％ 91.3％ Example 10 Cat6 40.2％ 90.2％ Embodiment 11 Cat7 93.2％ 32.2％

[0064] Comparative Example 1-2

[0065] The chlorine feed rate was 11.4 g / h and the 1,1-difluoroethane feed rate was 10.6 g / h. After mixing, they were introduced into a fixed bed reactor (filled with Cat4 and Cat5, respectively). The reaction temperature was controlled at 300 °C, the molar ratio of chlorine to 1,1-difluoroethane was 1:1, and the space velocity was 360 h -1 The reaction product passes through a water alkali washing device, a compression device, a drying and dehydration device, and a distillation device in sequence, and is sampled and analyzed from the sampling port at the reactor outlet. The conversion rate of 1,1-difluoroethane and the selectivity of 1-chloro-1,1-difluoroethane are shown in Table 5 below:

[0066] Table 5

[0067] Example catalyst 1,1-Difluoroethane conversion R142b Selectivity Comparative Example 1 Cat4 82.5％ 74.8％ Comparative Example 2 Cat5 50.3％ 65.5％

Claims

1. A method for preparing 1-chloro-1,1-difluoroethane by gas phase catalysis, characterized in that: The 1-chloro-1,1-difluoroethane is prepared by using 1,1-difluoroethane and chlorine as raw materials and in the presence of a chlorination catalyst through a gas phase chlorination reaction. The reaction temperature of the gas phase chlorination reaction is 200-300° C. The molar ratio of chlorine to 1,1-difluoroethane is 1-3:

1. The chlorination catalyst is selected from a Lewis acid catalyst, which comprises a carrier and an active component. The active component is at least one of zinc chloride, calcium chloride or magnesium chloride. The carrier is activated carbon.

2. The method for preparing 1-chloro-1,1-difluoroethane by gas phase catalysis according to claim 1, characterized in that: The active components of the Lewis acid catalyst account for 10-30% of the total mass of the Lewis acid catalyst.

3. The method for preparing 1-chloro-1,1-difluoroethane by gas phase catalysis according to claim 2, characterized in that: The active component is zinc chloride, which accounts for 15-20% of the total mass of the Lewis acid catalyst.

4. The method for preparing 1-chloro-1,1-difluoroethane by gas phase catalysis according to claim 1, characterized in that: The reaction pressure is 0~0.05MPa.

5. The method for preparing 1-chloro-1,1-difluoroethane by gas phase catalysis according to claim 1, characterized in that: The chlorination catalyst is subjected to activation treatment, and the activation treatment step comprises: A1. Calcination step: calcining under a nitrogen atmosphere, the calcination temperature is 300 to 350 ° C, and the calcination time is 2 to 5h; A2. Activation step: introduce chlorine gas and maintain at 150-200°C for 0.5-2h, then raise the temperature to 200-300°C and continue activation for 0.5-2h to obtain an activated chlorination catalyst.

6. The method for preparing 1-chloro-1,1-difluoroethane by gas phase catalysis according to claim 5, characterized in that: The mixed raw gas of 1,1-difluoroethane and chlorine reacts with the activated chlorination catalyst in a gas phase chlorination reaction, and the space velocity of the mixed raw gas is 240h -1 ~720h -1 .

7. The method for preparing 1-chloro-1,1-difluoroethane by gas phase catalysis according to claim 6, characterized in that: The crude product of the gas phase chlorination reaction is washed with water, compressed, dehydrated and distilled to obtain a high-purity 1-chloro-1,1-difluoroethane product.