A method for preparing cis-1,3,3,3-tetrafluoropropene

Abstract

The invention belongs to the technical field of organic chemistry, and in particular to a method for preparing cis-1,3,3,3-tetrafluoropropylene. The method for preparing cis-1,3,3,3-tetrafluoropropylene provided by the present invention, comprises the following steps: using trans-1,3,3,3-tetrafluoropropylene as raw material, under the action of light source and silicon dioxide supported phosphomolybdic heteropoly acid catalyst, promoting trans-1,3,3,3-tetrafluoropropylene to undergo photochemical reaction, and obtaining cis-1,3,3,3-tetrafluoropropylene. The method for preparing cis-1,3,3,3-tetrafluoropropylene provided by the present invention is simple to operate, and thermodynamic limitations can be broken through by photoreaction, so that the conversion rate of trans-1,3,3,3-tetrafluoropropylene is high, and the selectivity and yield of cis-1,3,3,3-tetrafluoropropylene are high, and the service life of the silicon dioxide supported phosphomolybdic heteropoly acid catalyst obtained by the present invention is relatively long, which is conducive to continuous production.

Description

Technical Field

[0001] The invention belongs to the technical field of organic chemistry, and particularly relates to a method for preparing cis-1,3,3,3-tetrafluoropropylene. Background Art

[0002] Growing concerns about global warming, and the associated possible adverse climate impacts, have led to an increasing number of developed countries agreeing to reduce greenhouse gas emissions. Considering the relatively high global warming potential (GWP) of most hydrofluorocarbons (HFCs), different countries are taking multiple actions to reduce the use of these fluids. For example, the recent F-Gas Regulation in the European Union specifies mandatory GWP values ​​for refrigerants used as working fluids in almost all air conditioners and refrigerators starting in 2020. Some refrigerants with GWP values ​​exceeding 150 used today will be gradually replaced.

[0003] The fourth generation of HFO series refrigerants, such as cis-1,3,3,3-tetrafluoropropene (cis-HFO-1234ze, CF3CH=CHF), has a double bond structure between carbon and carbon in the molecule. Because of its high reactivity with hydroxyl radicals, it has extremely low global warming potential (GWP), less burden on the environment, and is flame retardant and non-toxic. Cis-1,3,3,3-tetrafluoropropene has an ODP value of 0, a GWP100 value of <1, and an atmospheric life of only 9 days. It is considered to be one of the most promising alternative refrigerants and has good application prospects in refrigeration cycles, heat pumps, and organic Rankine cycles (ORC).

[0004] Cis-HFO-1234ze is rarely prepared in the prior art. However, the physical and chemical properties of cis-HFO-1234ze and trans-HFO-1234ze are different. The boiling point of cis-HFO-1234ze is 9°C, and the boiling point of trans-HFO-1234ze is -19°C. In some applications, cis-HFO-1234ze has a better use effect.

[0005] In the prior art, when preparing trans-HFO-1234ze by isomerization reaction, metal fluoride is usually used as an isomerization catalyst. However, when metal fluoride is used as a catalyst for the isomerization reaction of trans-HFO-1234ze to generate cis-HFO-1234ze, more by-products will be produced and carbon deposition will be serious. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the object of the present invention is to provide a method for preparing cis-1,3,3,3-tetrafluoropropene.

[0007] The technical solution of the present invention is:

[0008] A method for preparing cis-1,3,3,3-tetrafluoropropene comprises the following steps: using trans-1,3,3,3-tetrafluoropropene as a raw material, promoting a photochemical reaction of trans-1,3,3,3-tetrafluoropropene under the action of a light source and a silicon dioxide-supported phosphomolybdic heteropoly acid catalyst to obtain cis-1,3,3,3-tetrafluoropropene;

[0009] The preparation method of the silicon dioxide-supported phosphomolybdic heteropoly acid catalyst is as follows:

[0010] S1, stirring and heating ammonium molybdate, disodium hydrogen phosphate and deionized water, adding hydrochloric acid solution dropwise until crystals are completely precipitated, filtering and separating, then recrystallizing with water, and then drying to obtain phosphomolybdic heteropoly acid;

[0011] S2, mixing the silicon source, deionized water, anhydrous ethanol and the phosphomolybdic heteropoly acid obtained in step S1, reflux at 35-45° C., then heating to 75-85° C. and continuing to stir and reflux, then vacuum drying, and finally high-temperature calcination, and after cooling, a silica-supported phosphomolybdic heteropoly acid catalyst is obtained.

[0012] Preferably, in step S1, the mass ratio of ammonium molybdate, disodium hydrogen phosphate and deionized water is 1:0.1-0.5:2-3;

[0013] Further preferably, the mass ratio of ammonium molybdate, disodium hydrogen phosphate and deionized water is 1:0.2-0.3:2-3;

[0014] Particularly preferably, the mass ratio of the ammonium molybdate, disodium hydrogen phosphate and deionized water is 1:0.2-0.25:2-2.5.

[0015] Preferably, the heating temperature in step S1 is 75-85° C., and the concentration of the hydrochloric acid solution is 36-38%.

[0016] Preferably, in step S1, the drying temperature is 70-80° C. and the drying time is 10-15 h.

[0017] Preferably, the silicon source in step S2 is one of ethyl orthosilicate, water glass and silica sol;

[0018] Further preferably, the silicon source is one of tetraethyl orthosilicate and silica sol;

[0019] Particularly preferably, the silicon source is tetraethyl orthosilicate.

[0020] Preferably, the mass ratio of the silicon source, deionized water, anhydrous ethanol and phosphomolybdic heteropoly acid in step S2 is: 1:1-2:0.5-2.3:0.05-0.2;

[0021] Further preferably, the mass ratio of the silicon source, deionized water, anhydrous ethanol and phosphomolybdic heteropoly acid is: 1:1-1.8:0.5-2:0.05-0.15;

[0022] Particularly preferably, the mass ratio of the silicon source, deionized water, anhydrous ethanol and phosphomolybdic heteropoly acid is: 1:1-1.5:0.5-1.5:0.05-0.1.

[0023] Preferably, in step S2, the reaction mixture is refluxed at 35-45° C. for 1-1.5 h, or refluxed at 75-85° C. for 1-2 h.

[0024] Preferably, in step S2, the vacuum drying temperature is 50-60°C, the drying time is 20-30 h, the high temperature calcination temperature is 280-330°C, and the calcination time is 2-4 h.

[0025] Preferably, the specific steps of photochemically reacting the trans-1,3,3,3-tetrafluoropropene to obtain cis-1,3,3,3-tetrafluoropropene are as follows:

[0026] In a fixed bed reactor, a built-in light source is introduced, and trans-1,3,3,3-tetrafluoropropylene is converted into cis-1,3,3,3-tetrafluoropropylene under the catalytic action of a silica-supported phosphomolybdic heteropoly acid catalyst.

[0027] Preferably, during the photochemical reaction, the reaction temperature is 40-80°C and the reaction space velocity is 20-100 h -1 ;

[0028] More preferably, the reaction temperature is 40-60°C and the reaction space velocity is 30-80 h -1 ;

[0029] Particularly preferably, the reaction temperature is 40-55°C and the reaction space velocity is 40-70 h -1 ;

[0030] Preferably, the light source in the photochemical reaction process is one of a xenon lamp light source, an ultraviolet lamp light source and a high-pressure mercury lamp light source;

[0031] Further preferably, the light source is one of an ultraviolet lamp light source and a high-pressure mercury lamp light source;

[0032] Particularly preferably, the light source is an ultraviolet lamp light source.

[0033] The invention provides a method for preparing cis-1,3,3,3-tetrafluoropropene, which adopts a gas-solid phase reaction mode for continuous production, takes trans-1,3,3,3-tetrafluoropropene as a raw material, promotes a photochemical reaction of trans-1,3,3,3-tetrafluoropropene under the action of a specific light source and a silicon dioxide-supported phosphomolybdic heteropoly acid catalyst, and obtains cis-1,3,3,3-tetrafluoropropene.

[0034] The present invention provides a silicon dioxide-supported phosphomolybdic heteropoly acid catalyst, wherein the phosphomolybdic heteropoly acid is supported on a silicon dioxide carrier, and the two can be reacted by SiOH 2+ The interaction between the groups and the oxygen atoms outside the phosphomolybdic heteropoly acid fixes the heteropoly acid on the silicon source to form a relatively stable multiphase catalyst. After the phosphomolybdic heteropoly acid is fixed on the silica, the hydrogen bond interaction between the hydroxyl groups on the silica and the oxygen atoms of the phosphomolybdic heteropoly acid is beneficial to reduce the deactivation of the proton site, thereby improving the stability and activity of the catalyst and increasing the service life of the catalyst.

[0035] At the same time, the phosphomolybdic heteropoly acid catalyst prepared by the present invention is used to carry out a photocatalytic olefin isomerization reaction, and by controlling the light source, temperature, reaction space velocity and other conditions of the reaction, the C=C double bond can be transformed, breaking through the thermodynamic limitation, and transforming from the thermodynamically stable E type to the thermodynamically unstable Z type, thereby causing a photochemical reaction of trans-1,3,3,3-tetrafluoropropylene to obtain cis-1,3,3,3-tetrafluoropropylene.

[0036] Compared with the prior art, the method for preparing cis-1,3,3,3-tetrafluoropropene provided by the present invention has the following advantages:

[0037] The preparation method of cis-1,3,3,3-tetrafluoropropene provided by the present invention is simple to operate, and the thermodynamic limitation can be broken by the light reaction, so that the conversion rate of trans-1,3,3,3-tetrafluoropropene is high, the selectivity and yield of cis-1,3,3,3-tetrafluoropropene are high, and the energy consumption is greatly reduced. In addition, the phosphomolybdic heteropolyacid catalyst prepared by the present invention has a long service life and can be used continuously for more than 500 hours, and the frequency of catalyst regeneration can be effectively reduced, which is conducive to the continuous production by gas-solid phase reaction mode in the process, improves the continuity and stability of the production process and the production efficiency, effectively increases the output, and reduces the cost. DETAILED DESCRIPTION

[0038] The present invention is further illustrated below through the description of specific implementation methods, but this is not a limitation of the present invention. Those skilled in the art can make various modifications or improvements based on the basic idea of ​​the present invention, but as long as they do not deviate from the basic idea of ​​the present invention, they are all within the protection scope of the present invention.

[0039] In the following examples and comparative examples, reagents not otherwise specified are conventional reagents and can be purchased from conventional reagent production and sales companies. The methods used are all prior art unless otherwise specified.

[0040] Example 1

[0041] A method for preparing cis-1,3,3,3-tetrafluoropropene, using trans-1,3,3,3-tetrafluoropropene as a raw material, and performing a photochemical reaction to obtain cis-1,3,3,3-tetrafluoropropene. The specific steps are as follows:

[0042] In a fixed bed reactor, a xenon lamp light source was built in, and a silicon dioxide-supported phosphomolybdic acid catalyst was added. Trans-1,3,3,3-tetrafluoropropylene was introduced, and the light source was started. At a reaction temperature of 40 °C and a reaction space velocity of 20 h -1 Under the conditions of , the reactants are irradiated to carry out continuous photoisomerization reactions to generate cis-1,3,3,3-tetrafluoropropene.

[0043] The preparation method of the silicon dioxide-supported phosphomolybdic heteropoly acid catalyst is as follows:

[0044] S1. Add ammonium molybdate, disodium hydrogen phosphate and deionized water into a 500 mL three-necked flask, stir and heat to 75°C, then add a 36% hydrochloric acid solution dropwise to the solution until crystals are completely precipitated, separate the phosphomolybdic heteropoly acid, recrystallize with water, and then dry in an oven at 70°C for 15 h to obtain the phosphomolybdic heteropoly acid; the mass ratio of the ammonium molybdate, disodium hydrogen phosphate and deionized water is 1:0.1:2.

[0045] S2. In a 500 mL three-necked flask equipped with a condenser reflux tube, water glass, deionized water, anhydrous ethanol and the phosphomolybdic heteropoly acid obtained in step S1 are mixed (the mass ratio of the water glass, deionized water, anhydrous ethanol and phosphomolybdic heteropoly acid is 1:1:0.5:0.05), refluxed at 35°C for 1.5 h, then heated to 75°C, stirred and refluxed for 2 h, vacuum dried at 50°C for 30 h, and finally placed in a high-temperature furnace for calcination at 280°C for 4 h, and cooled to obtain a silica-supported phosphomolybdic heteropoly acid catalyst.

[0046] Example 2

[0047] A method for preparing cis-1,3,3,3-tetrafluoropropene, using trans-1,3,3,3-tetrafluoropropene as a raw material, and performing a photochemical reaction to obtain cis-1,3,3,3-tetrafluoropropene. The specific steps are as follows:

[0048] In a fixed bed reactor, a built-in ultraviolet light source was added, and a silica-supported phosphomolybdic acid catalyst was added. Trans-1,3,3,3-tetrafluoropropylene was introduced, and the light source was started. At a reaction temperature of 60 °C and a reaction space velocity of 70 h -1 Under the conditions of , the reactants are irradiated to carry out continuous photoisomerization reactions to generate cis-1,3,3,3-tetrafluoropropene.

[0049] The preparation method of the silicon dioxide-supported phosphomolybdic heteropoly acid catalyst is as follows:

[0050] S1. Add ammonium molybdate, disodium hydrogen phosphate and deionized water into a 500 mL three-necked flask, stir and heat to 80°C, then drop a 37% hydrochloric acid solution into the solution until crystals are completely precipitated, separate the phosphomolybdic heteropoly acid, recrystallize with water, and then dry in an oven at 75°C for 12 h to obtain the phosphomolybdic heteropoly acid; the mass ratio of the ammonium molybdate, disodium hydrogen phosphate and deionized water is 1:0.25:2.5.

[0051] S2. In a 500 mL three-necked flask equipped with a condenser reflux tube, tetraethyl orthosilicate, deionized water, anhydrous ethanol and the phosphomolybdic heteropoly acid obtained in step S1 are mixed (the mass ratio of tetraethyl orthosilicate, deionized water, anhydrous ethanol and phosphomolybdic heteropoly acid is 1:1.5:1.2:0.08), refluxed at 40°C for 1.2 h, then heated to 80°C, stirred and refluxed for 1.5 h, vacuum dried at 50°C for 24 h, and finally placed in a high-temperature furnace for calcination at 300°C for 3 h, and cooled to obtain a silica-supported phosphomolybdic heteropoly acid catalyst.

[0052] Example 3

[0053] A method for preparing cis-1,3,3,3-tetrafluoropropene, using trans-1,3,3,3-tetrafluoropropene as a raw material, and performing a photochemical reaction to obtain cis-1,3,3,3-tetrafluoropropene. The specific steps are as follows:

[0054] In a fixed bed reactor, a built-in ultraviolet light source was added, and a silica-supported phosphomolybdic acid catalyst was added. Trans-1,3,3,3-tetrafluoropropylene was introduced, and the light source was started. At a reaction temperature of 55 °C and a reaction space velocity of 80 h -1 Under the conditions of , the reactants are irradiated to carry out continuous photoisomerization reactions to generate cis-1,3,3,3-tetrafluoropropene.

[0055] The preparation method of the silicon dioxide-supported phosphomolybdic heteropoly acid catalyst is as follows:

[0056] S1. Add ammonium molybdate, disodium hydrogen phosphate and deionized water into a 500 mL three-necked flask, stir and heat to 80°C, then drop a 37% hydrochloric acid solution into the solution until crystals are completely precipitated, separate the phosphomolybdic heteropoly acid, recrystallize with water, and then dry in an oven at 75°C for 13 h to obtain the phosphomolybdic heteropoly acid; the mass ratio of the ammonium molybdate, disodium hydrogen phosphate and deionized water is 1:0.2:2.2.

[0057] S2. In a 500 mL three-necked flask equipped with a condenser reflux tube, tetraethyl orthosilicate, deionized water, anhydrous ethanol and the phosphomolybdic heteropoly acid obtained in step S1 are mixed (the mass ratio of tetraethyl orthosilicate, deionized water, anhydrous ethanol and phosphomolybdic heteropoly acid is 1:1.8:1.5:0.1), refluxed at 42°C for 1.3 h, then heated to 82°C, stirred and refluxed for 1.5 h, vacuum dried at 55°C for 24 h, and finally placed in a high-temperature furnace for calcination at 310°C for 3 h, and cooled to obtain a silica-supported phosphomolybdic heteropoly acid catalyst.

[0058] Example 4

[0059] A method for preparing cis-1,3,3,3-tetrafluoropropene, using trans-1,3,3,3-tetrafluoropropene as a raw material, and performing a photochemical reaction to obtain cis-1,3,3,3-tetrafluoropropene. The specific steps are as follows:

[0060] In a fixed bed reactor, a high-pressure mercury lamp light source was built in, and a silicon dioxide-supported phosphomolybdic acid catalyst was added. Trans-1,3,3,3-tetrafluoropropylene was introduced, and the light source was started. At a reaction temperature of 80 °C and a reaction space velocity of 100 h -1 Under the conditions of , the reactants are irradiated to carry out continuous photoisomerization reactions to generate cis-1,3,3,3-tetrafluoropropene.

[0061] The preparation method of the silicon dioxide-supported phosphomolybdic heteropoly acid catalyst is as follows:

[0062] S1. Add ammonium molybdate, disodium hydrogen phosphate and deionized water into a 500 mL three-necked flask, stir and heat to 85°C, then drop a 38% hydrochloric acid solution into the solution until crystals are completely precipitated, separate the phosphomolybdic heteropoly acid, recrystallize with water, and then dry in an oven at 80°C for 10 h to obtain the phosphomolybdic heteropoly acid; the mass ratio of the ammonium molybdate, disodium hydrogen phosphate and deionized water is 1:0.5:3.

[0063] S2. In a 500 mL three-necked flask equipped with a condenser reflux tube, silica sol, deionized water, anhydrous ethanol and the phosphomolybdic heteropoly acid obtained in step S1 are mixed (the mass ratio of the silica sol, deionized water, anhydrous ethanol and phosphomolybdic heteropoly acid is 1:2:2.3:0.2), refluxed at 45°C for 1 h, then heated to 85°C, stirred and refluxed for 1 h, vacuum dried at 60°C for 20 h, and finally placed in a high-temperature furnace for calcination at 330°C for 2 h, and cooled to obtain a silica-supported phosphomolybdic heteropoly acid catalyst.

[0064] Comparative Example 1

[0065] Compared with Example 2, the difference is that in the photochemical reaction process using trans-1,3,3,3-tetrafluoropropene as raw material, the ultraviolet light source is replaced by a sodium light source, and other parameters and operations are the same as those in Example 2.

[0066] Comparative Example 2

[0067] Compared with Example 2, the difference is that the silica-supported phosphomolybdic heteropoly acid catalyst in the photochemical reaction process is replaced by a silica-supported phosphotungstic heteropoly acid catalyst, and the preparation method of the silica-supported phosphotungstic heteropoly acid catalyst is as follows:

[0068] S1. Add sodium tungstate, disodium hydrogen phosphate and deionized water into a 500 mL three-necked flask, stir and heat to 80°C, then drop 37% hydrochloric acid solution into the solution until crystals are completely precipitated, separate phosphotungstic heteropoly acid, recrystallize with water, and then dry in an oven at 75°C for 12 h to obtain phosphotungstic heteropoly acid; the mass ratio of sodium tungstate, disodium hydrogen phosphate and deionized water is 1:0.25:2.5;

[0069] S2. In a 500 mL three-necked flask equipped with a condenser reflux tube, tetraethyl orthosilicate, deionized water, anhydrous ethanol and the phosphotungstic heteropoly acid obtained in step S1 are mixed (the mass ratio of tetraethyl orthosilicate, deionized water, anhydrous ethanol and phosphotungstic heteropoly acid is 1:1.5:1.2:0.08), refluxed at 40°C for 1.2 h, then heated to 80°C, stirred and refluxed for 1.5 h, vacuum dried at 50°C for 24 h, and finally placed in a high-temperature furnace for calcination at 300°C for 3 h, and after cooling, a silica-supported phosphotungstic heteropoly acid catalyst is obtained.

[0070] Other parameters and operations are the same as those in Example 2.

[0071] Comparative Example 3

[0072] Compared with Example 2, the difference is that the silicon dioxide-supported phosphomolybdic heteropoly acid catalyst in the photochemical reaction process is replaced by a titanium dioxide-supported phosphomolybdic heteropoly acid catalyst, and the preparation method of the titanium dioxide-supported phosphomolybdic heteropoly acid catalyst is as follows:

[0073] S1. Add ammonium molybdate, disodium hydrogen phosphate and deionized water into a 500 mL three-necked flask, stir and heat to 80°C, then drop a 37% hydrochloric acid solution into the solution until crystals are completely precipitated, separate the phosphomolybdic heteropoly acid, recrystallize with water, and then dry in an oven at 75°C for 12 h to obtain the phosphomolybdic heteropoly acid; the mass ratio of the ammonium molybdate, disodium hydrogen phosphate and deionized water is 1:0.25:2.5;

[0074] S2. In a 500 mL three-necked flask equipped with a condenser reflux tube, titanium dioxide powder, deionized water, anhydrous ethanol and the phosphomolybdic heteropoly acid obtained in step S1 are mixed (the mass ratio of the titanium dioxide powder, deionized water, anhydrous ethanol and phosphomolybdic heteropoly acid is 1:1.5:1.2:0.08), stirred evenly with a glass rod, vacuum dried at 50°C for 30h, and finally placed in a high-temperature furnace for calcination at 280°C for 4h, and after cooling, a titanium dioxide-supported phosphomolybdic heteropoly acid catalyst is obtained.

[0075] Other parameters and operations are the same as those in Example 2.

[0076] Test Example 1: Selectivity and service life test of cis-1,3,3,3-tetrafluoropropene prepared by the method of the present invention

[0077] The products obtained by the preparation methods of Examples 1 to 4 of the present invention and Comparative Examples 1 to 3 were subjected to gas chromatography analysis to obtain the conversion rate (%) of trans-1,3,3,3-tetrafluoropropene and the selectivity (%) of cis-1,3,3,3-tetrafluoropropene as shown in Table 1.

[0078] When the catalysts prepared in Examples 1 to 4 of the present invention and Comparative Examples 1 to 3 were used continuously for 500 h, the products after the reaction were subjected to gas chromatography analysis to obtain the conversion rate (%) of trans-1,3,3,3-tetrafluoropropene and the selectivity (%) of cis-1,3,3,3-tetrafluoropropene, as shown in Table 2.

[0079] Table 1

[0080] Group Conversion rate of trans-1,3,3,3-tetrafluoropropene (%) Selectivity of cis-1,3,3,3-tetrafluoropropene (%) Example 1 69.5 98.6 Example 2 73.2 99.3 Example 3 72.5 99.1 Example 4 70.7 99.2 Comparative Example 1 15.6 88.5 Comparative Example 2 57.5 85.9 Comparative Example 3 63.4 95.1

[0081] Table 2

[0082] Group Conversion rate of trans-1,3,3,3-tetrafluoropropene (%) Selectivity of cis-1,3,3,3-tetrafluoropropene (%) Example 1 61.3 97.1 Example 2 68.4 98.3 Example 3 67.2 97.9 Example 4 65.9 98.0 Comparative Example 1 14.2 83.3 Comparative Example 2 51.7 80.6 Comparative Example 3 17.5 66.2

[0083] As can be seen from Table 1, the products prepared by the methods of Examples 1 to 4 of the present invention were subjected to gas chromatography analysis, and the selectivity of cis-1,3,3,3-tetrafluoropropene obtained was all above 98%. It can be seen that the silica-supported phosphomolybdic heteropolyacid catalyst prepared by Examples 1 to 4 of the present invention can effectively improve the selectivity of cis-1,3,3,3-tetrafluoropropene.

[0084] As shown in Table 2, after the silicon dioxide-supported phosphorus molybdenum heteropoly acid catalysts prepared in Examples 1 to 4 of the present invention were continuously catalyzed for 500 h, the selectivity of cis-1,3,3,3-tetrafluoropropylene was still above 97%. After the silicon dioxide-supported phosphorus molybdenum heteropoly acid catalysts prepared in Comparative Examples 1 to 3 were used to catalyze trans-1,3,3,3-tetrafluoropropylene for 500 h, the selectivity of cis-1,3,3,3-tetrafluoropropylene obtained decreased to varying degrees, especially in Comparative Example 3, when the carrier of the catalyst was changed, the selectivity of cis-1,3,3,3-tetrafluoropropylene obtained decreased to a greater extent, indicating that the silicon dioxide-supported phosphorus molybdenum heteropoly acid catalysts prepared by the method of the present invention have a long service life, which is conducive to reducing the regeneration frequency of the catalyst in the production process.

[0085] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing cis-1,3,3,3-tetrafluoropropene, characterized in that: The method comprises the following steps: using trans-1,3,3,3-tetrafluoropropylene as a raw material, promoting a photochemical reaction of trans-1,3,3,3-tetrafluoropropylene under the action of a light source and a silicon dioxide-supported phosphomolybdic heteropoly acid catalyst to obtain cis-1,3,3,3-tetrafluoropropylene; The light source is one of a xenon lamp, an ultraviolet lamp and a high-pressure mercury lamp; During the photochemical reaction, the reaction temperature is 40-80°C and the reaction space velocity is 20-100 h -1 ; The preparation method of the silicon dioxide-supported phosphomolybdic heteropoly acid catalyst is as follows: S1, stirring and heating ammonium molybdate, disodium hydrogen phosphate and deionized water, adding hydrochloric acid solution dropwise until crystals are completely precipitated, filtering and separating, then recrystallizing with water, and then drying to obtain phosphomolybdic heteropoly acid; S2, mixing a silicon source, deionized water, anhydrous ethanol and the phosphomolybdic heteropoly acid obtained in step S1, refluxing at 35-45° C., then heating to 75-85° C. and continuing to stir and reflux, then vacuum drying, and finally high-temperature calcining, and cooling to obtain a silicon dioxide-supported phosphomolybdic heteropoly acid catalyst; the silicon source in step S2 is one of tetraethyl orthosilicate, water glass and silica sol.

2. The method for preparing cis-1,3,3,3-tetrafluoropropene according to claim 1, characterized in that: In the step S1, the mass ratio of ammonium molybdate, disodium hydrogen phosphate and deionized water is 1:0.1-0.5:2-3.

3. The method for preparing cis-1,3,3,3-tetrafluoropropene according to claim 1, characterized in that: The heating temperature in step S1 is 75-85° C., and the concentration of the hydrochloric acid solution is 36-38%; the drying temperature in step S1 is 70-80° C., and the drying time is 10-15 h.

4. The method for preparing cis-1,3,3,3-tetrafluoropropene according to claim 1, characterized in that: The mass ratio of the silicon source, deionized water, anhydrous ethanol and phosphomolybdic heteropoly acid in step S2 is 1:1-2:0.5-2.3:0.05-0.

2.

5. The method for preparing cis-1,3,3,3-tetrafluoropropene according to claim 1, characterized in that: In the step S2, reflux is performed at 35-45° C. for 1-1.5 h, and reflux is performed at 75-85° C. for 1-2 h.

6. The method for preparing cis-1,3,3,3-tetrafluoropropene according to claim 1, characterized in that: In the step S2, the vacuum drying temperature is 50-60°C, the drying time is 20-30 h, and the high temperature calcination temperature is 280-330°C, and the calcination time is 2-4 h.

7. The method for preparing cis-1,3,3,3-tetrafluoropropene according to claim 1, characterized in that: The specific steps of photochemically reacting trans-1,3,3,3-tetrafluoropropene to obtain cis-1,3,3,3-tetrafluoropropene are as follows: In a fixed bed reactor, a built-in light source is introduced, and trans-1,3,3,3-tetrafluoropropylene is converted into cis-1,3,3,3-tetrafluoropropylene under the catalytic action of a silica-supported phosphomolybdic heteropoly acid catalyst.