A process for the preparation of 2,3,3,3-tetrafluoropropene in a two-step process

Abstract

A method for preparing 2,3,3,3-tetrafluoropropene by a two-step method, the method comprising: A1. a telomerization step: preparing 3-chloro-1,1,1,2-tetrafluoropropane by pressure telomerization reaction of monofluoromonochloromethane and trifluoroethylene under the action of a telomerization catalyst; the telomerization catalyst is a Lewis acid catalyst or a mixed catalyst of a Lewis acid catalyst and dichloromethane; A2. a dehydrochlorination step: 3-chloro-1,1,1,2-tetrafluoropropane is dehydrochlorinated under the catalysis of activated carbon to obtain 2,3,3,3-tetrafluoropropene. The present application has the advantages of simple process, high product selectivity, mild reaction conditions and the like.

Description

[0001] This invention is a divisional application of Chinese invention patent application filed on April 15, 2021, with application number CN202110404625.4 and invention title “A two-step method for preparing 2,3,3,3-tetrafluoropropylene”. Technical Field

[0002] This invention relates to the preparation of 2,3,3,3-tetrafluoropropylene, and particularly to a method for preparing 2,3,3,3-tetrafluoropropylene using trifluoroethylene as a raw material through a two-step reaction of telomerization and dehydrochlorination. Background Technology

[0003] 2,3,3,3-Tetrafluoropropylene has an ODP of zero, a GWP of 4, and lower life-cycle climate performance (LCCP) than the conventional refrigerant HFC-134a. Its system refrigeration performance is superior to HFC-134a, and its atmospheric decomposition products are the same as HFC-134a. It is considered the most promising alternative to automotive refrigerants and has been accepted by several major automakers. Currently, the preparation routes for 2,3,3,3-tetrafluoropropylene include the following:

[0004] I. Hexafluoropropylene route:

[0005] The preparation of 2,3,3,3-tetrafluoropropylene from hexafluoropropylene involves four steps: (1) hydrogenation of hexafluoropropylene and hydrogen to prepare 1,1,1,2,3,3-hexafluoropropane (HFC-236ea); (2) dehydrofluorination of HFC-236ea under the action of a catalyst to prepare 1,1,1,2,3-pentafluoropropylene (HFO-1225ye); (3) hydrogenation of HFO-1225ye with hydrogen to prepare 1,1,1,2,3-pentafluoropropane (HFC-245eb); and (4) dehydrofluorination of HFC-245eb under the action of a catalyst to prepare 2,3,3,3-tetrafluoropropylene.

[0006] US Patent US20070179324A, Chinese Patents CN101544536A, CN102267869A, and CN102026947A all disclose methods for preparing 2,3,3,3-tetrafluoropropylene from hexafluoropropylene through a four-step reaction involving hydrogenation, dehydrofluorination, rehydrogenation, and redehydrofluorination. These methods are characterized by simple processes and mature technology. However, they involve multiple reaction steps, require the separation and purification of various intermediate products, and suffer from problems such as complex process steps, large equipment investment, low reaction yield, high separation cost, and high energy consumption.

[0007] To address the shortcomings of the aforementioned patented technologies, Chinese patent CN103449963B discloses a method for synthesizing 2,3,3,3-tetrafluoropropylene via a multi-step continuous reaction using hexafluoropropylene as a raw material. This method enables the continuous production of intermediate products such as HFC-236ea, HFO-1225ye, and HFC-245eb without separation. However, the lack of separation and purification of intermediate products means that impurities will continuously accumulate and be added to the reactants, ultimately affecting the yield of the target product, 2,3,3,3-tetrafluoropropylene. It also increases the difficulty of distilling and separating the 2,3,3,3-tetrafluoropropylene product.

[0008] II. Tetrachloropropylene (TCP) route:

[0009] Patent CN101395108B discloses a method for preparing 2,3,3,3-tetrafluoropropylene from 1,1,2,3-tetrachloropropene via a three-step reaction. The reaction steps include: (1) 1,1,2,3-tetrachloropropene and HF undergo a gas-phase fluorination reaction to prepare 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf), with a selectivity of 80-96%. When using Cr2O3 and FeCl3 / AC catalysts, the selectivity reaches 96%, and the conversion rate is only 20%; (2) HCFO-1233xf undergoes an addition reaction with HF to generate 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb), with SbCl5 as the catalyst; (3) HCFC-244bb undergoes a gas-phase dehydrochlorination reaction under the action of an activated carbon catalyst to obtain the target product 2,3,3,3-tetrafluoropropylene. The process involves complex reaction steps, which is detrimental to industrial production, and also suffers from problems such as low conversion rate and high reaction temperature.

[0010] US Patent 20090099396 discloses a two-step method for preparing 2,3,3,3-tetrafluoropropylene from 1,1,2,3-tetrachloropropene as a raw material. The reaction steps include: (1) liquid-phase fluorination of 1,1,2,3-tetrachloropropene and HF to prepare 1,1,1,2,3-pentafluoropropane (HFC-245eb), with SbCl5 as the catalyst. The TCP conversion rate can reach 100%, but the selectivity of HFC-245eb is only 53-59%, and a large number of by-products are generated; (2) HFC-245eb undergoes liquid-phase defluorination under the action of alkali metal hydroxide to generate the target product 2,3,3,3-tetrafluoropropene. This process has the advantages of fewer reaction steps and less equipment investment, but the intermediate product HFC-245eb has low selectivity and the separation of by-products is difficult.

[0011] III. Trifluoropropylene Route:

[0012] Patent CN101979364A discloses a method for preparing 2,3,3,3-tetrafluoropropylene using 3,3,3-trifluoropropylene as a raw material. The reaction is carried out in four steps: (1) 3,3,3-trifluoropropylene reacts with chlorine under photocatalysis to generate 1,2-dichloro-3,3,3-trifluoropropane, with a raw material conversion rate of 95% and a selectivity of 90%; (2) 1,2-dichloro-3,3,3-trifluoropropane undergoes a liquid-phase dehydrochlorination reaction under the action of alkali metal hydroxide to generate 2-chloro-3,3,3-trifluoropropylene (HCFO- 1233xf), the conversion rate and selectivity both reached 90%; (3) HCFO-1233xf and HF underwent an addition reaction to generate 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb), the catalysts were SnCl4 and TiCl4 fluorosulfonic acid, the raw material conversion rate reached 95%, and the selectivity was 90-96%; (4) HCFC-244bb underwent a liquid-phase dechlorination reaction under the action of an alkali metal catalyst to prepare the target product CF3CF=CH2, the raw material conversion rate was 95%, and the selectivity was 90-95%. The synthesis route of this process is long, the first step of the chlorination reaction has high equipment requirements, the two steps of the dehalogenation reaction generate a lot of waste liquid, the overall reaction yield is low, and the synthesis cost is high.

[0013] IV. Other routes:

[0014] Asahi Glass's patent WO2011162341A discloses a method for preparing 2,3,3,3-tetrafluoropropene from 1,1-dichloro-2,3,3,3-tetrafluoropropene (CFO-1214ya) via hydrogenation reduction in the presence of a palladium catalyst. However, this method is difficult to control the degree of hydrogenation reduction, easily generating intermediates or over-reduction products such as 1-chloro-2,3,3,3-tetrafluoropropene (HCFO-1224yd), 1-chloro-2,3,3,3-tetrafluoropropane (HCFC-244eb), and 2,3,3,3-tetrafluoropropane (HFC-254eb). The product selectivity is low, post-processing is complex, and the byproduct HFC-254eb is prone to further dehydrofluorination during alkaline washing to generate 3,3,3-trifluoropropene (HFO-1243zf), which has a boiling point close to that of HFO-1234yf, further increasing the difficulty of impurity separation. Although the above problems can be improved by controlling the reaction temperature of the catalyst bed and the absorption temperature of the alkaline washing, the improvement is not significant, and the process conditions are difficult to control, making it unsuitable for industrial scale-up. Summary of the Invention

[0015] To address the aforementioned technical problems, this invention proposes a two-step method for preparing 2,3,3,3-tetrafluoropropylene, which features a simple process, mild reaction conditions, high product selectivity, and suitability for industrial production.

[0016] The objective of this invention is achieved through the following technical solution:

[0017] A two-step method for preparing 2,3,3,3-tetrafluoropropylene, the method comprising:

[0018] A1. Telogenization step: 3-chloro-1,1,1,2-tetrafluoropropane is prepared by pressurized telogenization reaction of monofluorochloromethane and trifluoroethylene under the action of a telogenization catalyst; the telogenization catalyst is a Lewis acid catalyst or a mixed catalyst of Lewis acid catalyst and dichloromethane.

[0019] A2. Dehydrochlorination step: 3-chloro-1,1,1,2-tetrafluoropropane is dehydrochlorinated under the catalysis of activated carbon to obtain 2,3,3,3-tetrafluoropropene.

[0020] The reaction equation for the two-step preparation of 2,3,3,3-tetrafluoropropylene according to this invention is as follows:

[0021] CH2FCl+CF2=CHF→CF3CHFCH2Cl→CF3CHF=CH2

[0022] The Lewis acid catalyst of this invention is selected from at least one halide of Al, Sb, Ti, Zr, and Hf. Preferably, the Lewis acid catalyst is selected from at least one of ZrCl4, HfCl4, TiCl4, AlCl3, AlF3, and SbF5. More preferably, the Lewis acid catalyst is ZrCl4 or HfCl4.

[0023] The telomerization reaction of the raw materials monofluorochloromethane and trifluoroethylene in this invention is carried out under pressure. Under the reaction conditions, the raw material monofluorochloromethane partially or completely forms a liquid. In addition, the 3-chloro-1,1,1,2-tetrafluoropropane produced by the telomerization reaction is a liquid. Therefore, step A1 of this invention preferably adopts a solvent-free reaction to reduce the separation steps of intermediates and / or products.

[0024] The telomerization catalyst described in this invention can be a single Lewis acid catalyst or a mixed catalyst of a Lewis acid catalyst and dichloromethane. When a mixed catalyst is used, the Lewis acid catalyst dissociates and activates monofluorochloromethane to form F... - CH2Cl + Cl - CH2F + Plasma; dichloromethane inhibits the formation of F2+ from dissociation. - CH2Cl + Cl - CH2F + Plasma recombines, thereby ensuring F - CH2Cl +Ions undergo a directional telomerization reaction with trifluoroethylene to selectively produce the telomerization product CF3CHFCH2Cl.

[0025] In chemical reactions, the ratio of raw materials, the ratio of raw materials to catalysts, reaction temperature, and reaction time all affect the reaction results. In particular, the combination of multiple variables can have a significant impact on the reaction outcome.

[0026] In the telomerization step described in this invention, the molar ratio of monofluorochloromethane to trifluoroethylene is 1:0.1 to 1:10; more preferably, the molar ratio of monofluorochloromethane to trifluoroethylene is 1:1 to 1:5. The amount of Lewis acid catalyst is 0.01 to 50 wt% of the mass of monofluorochloromethane; more preferably, the amount of Lewis acid catalyst is 0.1 to 10 wt% of the mass of monofluorochloromethane. When a mixed catalyst of Lewis acid catalyst and dichloromethane is used, the molar ratio of dichloromethane to monofluorochloromethane is 1:0.01 to 1:10; more preferably, the molar ratio of dichloromethane to monofluorochloromethane is 1:0.1 to 1:5.

[0027] The telomerization step described in this invention is carried out under pressure, with a reaction temperature of -30 to 100°C, a reaction pressure of 0.5 to 5.0 MPa, and a reaction time of 1 to 50 h. More preferably, the reaction temperature is 0 to 50°C, the reaction pressure is 0.8 to 3.0 MPa, and the reaction time is 5 to 10 h.

[0028] The dehydrochlorination step of the present invention is carried out under the catalytic action of activated carbon, which is selected from fruit shell activated carbon, coal-based activated carbon or wood-based activated carbon, preferably fruit shell activated carbon.

[0029] The reaction temperature for the dehydrochlorination step is 200–500°C, preferably 300–350°C.

[0030] To further improve the purity of 2,3,3,3-tetrafluoropropylene and reduce the difficulty of post-processing, the 3-chloro-1,1,1,2-tetrafluoropropane obtained from the telomerization step is used for the dehydrochlorination step after being separated by distillation.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] This invention uses monofluorochloromethane and trifluoroethylene as raw materials. Under the action of Lewis acid catalyst or a mixed catalyst of Lewis acid catalyst and dichloromethane, 3-chloro-1,1,1,2-tetrafluoropropane obtained by pressure telomerization is used to prepare 2,3,3,3-tetrafluoropropylene under the catalysis of activated carbon. It has the advantages of simple process, mild reaction conditions, high selectivity of telomerization products and target products, and suitability for industrial scale-up. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternatives, improvements, and equivalents that may be included within the scope of the claims.

[0034] Example 1

[0035] This embodiment proposes a two-step method for preparing 2,3,3,3-tetrafluoropropylene, including a telomerization step and a dehydrochlorination step, as detailed below:

[0036] I. Aggregation Steps

[0037] A1. Using a 250mL Inconel alloy autoclave as the reactor, 3.0g HfCl4 and 20.0g dichloromethane were added to the autoclave respectively. After sealing the autoclave, nitrogen gas at 1.0MPa was introduced to replace the air in the autoclave. This process was repeated three times.

[0038] A2. After the air in the reactor is completely replaced, 19.9 g (0.29 mol) of monofluorochloromethane and 24.6 g (0.30 mol) of trifluoroethylene are introduced successively.

[0039] A3. Set the reaction temperature to 10℃, the stirring speed to 300rpm, the initial reaction pressure to 0.9MPa, and gradually reduce the pressure as the reaction proceeds. The reaction time is 10h.

[0040] A4. After the reaction is complete, collect the unreacted gaseous raw materials trifluoroethylene and / or monofluorochloromethane, as well as a small amount of telomerization products and dichloromethane; perform solid-liquid separation treatment such as filtration or distillation on the materials in the reactor. The solid part is Lewis acid catalyst (HfCl4), and the liquid part is dichloromethane and telomerization products. After distillation, 3-chloro-1,1,1,2-tetrafluoropropane with a purity of 99.9% is obtained and used for dehydrochlorination reaction.

[0041] Unreacted gaseous feedstock and the separated Lewis acid catalyst can be returned to the telomerization step for reuse.

[0042] Gas chromatography was used to analyze the gas and liquid phase materials. The conversion rate of monofluorochloromethane was 76.5%, the selectivity of 3-chloro-1,1,1,2-tetrafluoropropane was 81.2%, the main byproduct was 1-chloro-1,1,2,3-tetrafluoropropane with a selectivity of 15.3%, and there were a small amount of other byproducts.

[0043] II. Dehydrochlorination Steps

[0044] B1. An Inconel alloy reaction tube with an inner diameter of 19 mm and a length of 800 mm was used as a fixed-bed reactor. 20 mL of coconut shell activated carbon with a particle size of 10-20 mesh was filled into the middle of the fixed-bed reactor. The reaction pipeline was connected and nitrogen was introduced for purging. The nitrogen flow rate was 100 mL / min.

[0045] B2. Set the reaction temperature to 350℃ and the heating rate to 5℃ / min, and start heating the reactor.

[0046] B3. After the catalyst bed reaches the reaction temperature, adjust the nitrogen flow rate to 20 mL / min, and simultaneously continuously introduce 3-chloro-1,1,1,2-tetrafluoropropane with a purity of 99.9% into the fixed-bed reactor at a rate of 5.0 g / h to start the reaction;

[0047] B4. Online GC and GC / MS analysis of the gas mixture effluent from the reactor showed that the conversion of 3-chloro-1,1,1,2-tetrafluoropropane was 99.6%, and the selectivity of the product 2,3,3,3-tetrafluoropropene was 99.3%.

[0048] Example 2

[0049] This embodiment proposes a method for preparing 2,3,3,3-tetrafluoropropylene. The operation is the same as in Example 1, except that in the telomerization step, ZrCl4 is used instead of HfCl4, and the amount is 4.0 g; the amount of monofluorochloromethane is increased to 39.7 g (0.58 mol), and the amount of trifluoroethylene is increased to 71.3 g (0.87 mol), while other conditions remain unchanged.

[0050] Gas chromatography analysis of the gas and liquid phase materials in the polymerization step showed that the conversion rate of monofluorochloromethane was 99.0%, the selectivity of 3-chloro-1,1,1,2-tetrafluoropropane was 89.9%, the main byproduct was 1-chloro-1,1,2,3-tetrafluoropropane with a selectivity of 5.3%, and there were also a small amount of other byproducts.

[0051] Example 3

[0052] This embodiment proposes a method for preparing 2,3,3,3-tetrafluoropropylene. The operation is the same as in Example 2, except that dichloromethane is not used in the telomerization step, the amount of trifluoroethylene is increased to 95.1 g (1.16 mol), the reaction temperature is increased to 30 °C, the initial reaction pressure is increased to 1.5 MPa, and other conditions remain unchanged.

[0053] Gas chromatography analysis of the gas and liquid phase materials in the polymerization step showed that the conversion rate of monofluorochloromethane was 99.5%, the selectivity of 3-chloro-1,1,1,2-tetrafluoropropane was 88.1%, the main byproduct was 1-chloro-1,1,2,3-tetrafluoropropane with a selectivity of 4.1%, and there were also a small amount of other byproducts.

[0054] Example 4

[0055] This embodiment proposes a method for preparing 2,3,3,3-tetrafluoropropylene. The operation is the same as in Example 2, except that: in the telomerization step, AlCl3 is used instead of ZrCl4, and the amount remains the same at 4.0g; at the same time, dichloromethane is not used, and the amount of trifluoroethylene is reduced to 52.5g (0.64mol), while other conditions remain unchanged.

[0056] Gas chromatography analysis of the gas and liquid phase materials in the polymerization step showed that the conversion rate of monochlorofluoromethane was 99.6%, the selectivity of 3-chloro-1,1,1,2-tetrafluoropropane was 75.5%, the main byproduct was 1-chloro-1,1,2,3-tetrafluoropropane with a selectivity of 15.9%, and there were also a small amount of other byproducts.

[0057] Example 5

[0058] This embodiment proposes a method for preparing 2,3,3,3-tetrafluoropropylene. The operation is the same as in Example 1, except that in step A2 of the telomerization step, after chlorofluoromethane and trifluoroethylene are introduced into the autoclave in sequence, high-purity high-pressure nitrogen is used to pressurize the autoclave, increasing the pressure inside the autoclave from 0.9 MPa to 3.0 MPa, while keeping other conditions unchanged.

[0059] Gas chromatography analysis of the gas and liquid phase materials in the polymerization step showed that the conversion rate of monofluorochloromethane was 99.8%, the selectivity of 3-chloro-1,1,1,2-tetrafluoropropane was 88.6%, the main byproduct was 1-chloro-1,1,2,3-tetrafluoropropane with a selectivity of 7.6%, and there were also a small amount of other byproducts.

[0060] Example 6

[0061] This embodiment proposes a method for preparing 2,3,3,3-tetrafluoropropylene. The operation steps are the same as in Example 1, except that in the dehydrochlorination step, 10-20 mesh coal-based activated carbon is used instead of coconut shell activated carbon.

[0062] Chromatographic analysis of the dehydrochlorination product showed that the conversion rate of 3-chloro-1,1,1,2-tetrafluoropropane was 99.2%, and the selectivity of the product 2,3,3,3-tetrafluoropropene reached 95.1%.

[0063] Example 7

[0064] This embodiment proposes a method for preparing 2,3,3,3-tetrafluoropropylene, which is the same as in Example 1, except that the reaction temperature is reduced to 300°C in the dehydrochlorination step.

[0065] Chromatographic analysis of the dehydrochlorination product showed that the conversion rate of 3-chloro-1,1,1,2-tetrafluoropropane was 75.8%, and the selectivity of the product 2,3,3,3-tetrafluoropropene was 99.2%.

[0066] Example 8

[0067] This embodiment proposes a method for preparing 2,3,3,3-tetrafluoropropylene, which is the same as in Example 1, except that the reaction temperature is reduced to 320°C in the dehydrochlorination step.

[0068] Chromatographic analysis of the dehydrochlorination product showed that the conversion rate of 3-chloro-1,1,1,2-tetrafluoropropane was 86.9%, and the selectivity of the product 2,3,3,3-tetrafluoropropene was 99.1%.

[0069] Comparative Example 1

[0070] This comparative example presents a method for preparing 2,3,3,3-tetrafluoropropylene, which is the same as in Example 1, except that chloroform is used instead of dichloromethane, and the amount is 20.0 g, while other conditions remain unchanged.

[0071] Chromatographic analysis of the material after the telomerization step showed that the conversion rate of monofluorochloromethane was 86.9%, the selectivity of 3-chloro-1,1,1,2-tetrafluoropropane was 46.2%, a large amount of dichloromethane, a disproportionation product of monofluorochloromethane, was produced with a selectivity of 40.3%, and a small amount of other telomerization byproducts were also produced.

[0072] Comparative Example 2

[0073] This comparative example presents a method for preparing 2,3,3,3-tetrafluoropropylene. The operation is the same as in Example 1, except that ZnCl2 is used instead of HfCl4, and the amount is 3.0 g, while other conditions remain unchanged.

[0074] Chromatographic analysis of the material after the telomerization step showed that the conversion rate of monofluorochloromethane was 20.8%, and no target product 3-chloro-1,1,1,2-tetrafluoropropane was produced.

[0075] Comparative Example 3

[0076] This comparative example presents a method for preparing 2,3,3,3-tetrafluoropropylene, which is the same as in Example 1, except that HfCl4 and dichloromethane are not added, while other conditions remain unchanged.

[0077] Chromatographic analysis of the material after the polymerization step showed that the conversion rate of monofluorochloromethane was 7.7%, with no target product 3-chloro-1,1,1,2-tetrafluoropropane produced, and only a small amount of dichloromethane, a disproportionation product of monofluorochloromethane, was produced.

Claims

1. A two-step method for preparing 2,3,3,3-tetrafluoropropylene, characterized in that: The method includes: A1. Telogenization step: 3-chloro-1,1,1,2-tetrafluoropropane is prepared by pressurized telogenization reaction of monofluorochloromethane and trifluoroethylene under the action of a telogenization catalyst; the telogenization catalyst is a mixed catalyst of Lewis acid catalyst and dichloromethane; the Lewis acid catalyst is selected from at least one of ZrCl4, HfCl4, TiCl4, AlCl3, and AlF3; A2. Dehydrochlorination step: 3-chloro-1,1,1,2-tetrafluoropropane is dehydrochlorinated under the catalysis of activated carbon to obtain 2,3,3,3-tetrafluoropropene.

2. The two-step method for preparing 2,3,3,3-tetrafluoropropylene according to claim 1, characterized in that: The molar ratio of monofluorochloromethane to trifluoroethylene is 1:0.1 to 1:

10.

3. The two-step method for preparing 2,3,3,3-tetrafluoropropylene according to claim 1, characterized in that: The Lewis acid catalyst is 0.01 to 50 wt% of monofluorochloromethane.

4. The two-step method for preparing 2,3,3,3-tetrafluoropropylene according to claim 1, characterized in that: The molar ratio of dichloromethane to monochlorofluoromethane is 1:0.01 to 1:

10.

5. The two-step method for preparing 2,3,3,3-tetrafluoropropylene according to claim 1, characterized in that: The pressurized polymerization reaction is carried out at a temperature of -30 to 100°C and a pressure of 0.5 to 5.0 MPa for a reaction time of 1 to 50 h.

6. The two-step method for preparing 2,3,3,3-tetrafluoropropylene according to claim 1, characterized in that: The activated carbon is selected from fruit shell activated carbon, coal-based activated carbon, or wood-based activated carbon.

7. The two-step method for preparing 2,3,3,3-tetrafluoropropylene according to claim 1, characterized in that: The reaction temperature for the dehydrochlorination step is 200–500 °C.

8. The two-step method for preparing 2,3,3,3-tetrafluoropropylene according to claim 1, characterized in that: The 3-chloro-1,1,1,2-tetrafluoropropane obtained through the telomerization step was used for the dehydrochlorination step after being separated by distillation.