Method for preparing 1, 2-difluoroethylene from dichloromethane

Abstract

The invention discloses a method for preparing 1, 2-difluoroethylene from dichloromethane, which comprises the following steps: carrying out fluoridation reaction on dichloromethane and hydrogen fluoride under the action of a catalyst I to obtain a first mixture, rectifying to obtain a second mixture containing monochlorofluoromethane (HCFC-31, R31), converting the monochlorofluoromethane from R31 to R1132 under the action of a cracking catalyst, and separating the first mixture from the second mixture to obtain the 1, 2-difluoroethylene. The preparation method is high in yield, the selectivity of the fluorination reaction to R31 is high, and the selectivity of the cracking reaction to the product R1132 is high. Meanwhile, the method also can realize co-production of difluoromethane, so that fluorine elements and carbon elements in the raw materials are efficiently utilized in a stepped manner, the atom economy is remarkably improved, and co-production from the cheap raw material dichloromethane to a high-added-value refrigerant (R32) and a fluorine-containing monomer (R1132) is realized.

Description

Technical Field

[0001] This invention relates to the field of fluorine compound preparation technology, specifically to a method for preparing 1,2-difluoroethylene from dichloromethane. Background Technology

[0002] 1,2-Difluoroethylene (HFO-1132 or R1132), with the molecular formula C2H2F2, has both cis and trans isomers. HFO-1132 is not only a polymer monomer, but its refrigeration efficiency (COP) and freezing capacity are comparable to the widely used high GWP refrigerants R410A and R32 for residential air conditioning and R134a for automotive air conditioning. It has a low boiling point, moderate flammability, and low toxicity, making it a potential replacement for HFCs such as R410A. Meanwhile, 1,2-difluoroethylene has an ODP value of 0 and a GWP100 value below 2. Its molecular structure does not contain perfluoroalkyl groups, it is not a PFAS substance, and its degradation products in the atmospheric environment do not contain trifluoroacetic acid (TFA), thus avoiding secondary pollution and meeting the requirements for fifth-generation ODS replacements. Furthermore, compositions of HFO-1132 with HFO-1234yf can be used as automotive air conditioning refrigerants in hybrid vehicles, electric vehicles, or hydrogen-powered vehicles. Therefore, HFO-1132 is a hot research topic in the context of increasingly stringent ozone layer protection.

[0003] There are many existing methods for synthesizing HFO-1132, including gas / liquid phase defluorination, thermal decomposition, isomerization, fluorine-chlorine exchange, and dehalogenation. Among the reported synthesis methods, the process of obtaining (E / Z)-HFO-1132 by gas-phase defluorination of 1,1,2-trifluoroethane (R143) as a raw material has the potential for industrialization.

[0004] Chinese patent document CN120698844A discloses a method for manufacturing general formula (1): CX with a high selectivity. 1 X 2 =CX 3 X 4 (where X) 1 X 2 X 3 and X 4 A method for manufacturing fluorinated olefins (represented by the same or different hydrogen or fluorine atoms) comprising: making a general formula (2): CX 1 X 2 FCX 3 X 4 H (where X is in the formula) 1 X 2 X 3 and X 4The defluorination process is carried out by contacting the fluorinated carbon (as described above) with a metal catalyst. The defluorination process is carried out in the gas phase in the presence of water. The concentration of water is less than 500 ppm relative to the fluorinated carbon shown in the general formula (2). The fluorinated olefin shown in the general formula (1) is at least one selected from 1,2-difluoroethylene (HFO-1132) and trifluoroethylene (HFO-1123). The fluorinated carbon shown in the general formula (2) is at least one selected from 1,1,2-trifluoroethane (HFC-143) and 1,1,1,2-tetrafluoroethane (HFC-134a).

[0005] Chinese patent document CN112105594A discloses a catalyst mainly composed of chromium, aluminum, iron, nickel, and magnesium, used to synthesize (E / Z)-HFO-1132 via gas-phase defluorination of hydrogen using R143. The conversion rate of R143 can reach over 90%, the selectivity of E-HFO-1132 is approximately 30%, and the selectivity of Z-HFO-1132 is approximately 60%.

[0006] It is worth noting that a certain amount of oxygen is added to this reaction, primarily to remove the carbon deposits generated during the reaction, thereby extending the catalyst's lifespan. However, excess oxygen and carbon dioxide produced from the reaction with carbon will enter the crude product. Furthermore, according to publicly available information, the synthesis of HFO-1132 generates various organic impurities, including methane, trifluoromethane, vinylidene fluoride, fluoromethane, and 1,1,1-trifluoroethane. Therefore, the coexistence of multiple types of impurities, and the potential for some impurities to form azeotropes, hinders the separation and purification of HFO-1132.

[0007] Therefore, there is an urgent need to find a preparation method that can improve the purity and yield of HFO-1132. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a method for preparing 1,2-difluoroethylene from dichloromethane. The method involves a fluorination reaction of dichloromethane and hydrogen fluoride under the action of catalyst I to obtain a first mixture. After distillation, a second mixture containing monochlorofluoromethane (HCFC-31, R31) is obtained. The monochlorofluoromethane is then converted from R31 to R1132 under the action of a cracking catalyst. This preparation method exhibits high yield and high selectivity for the product R1132.

[0009] A method for preparing 1,2-difluoroethylene from dichloromethane includes the following steps: (1) Dichloromethane and hydrogen fluoride are fed into the first reactor and fluorinated under the action of catalyst I to obtain a first mixture. The first mixture is then fed into the first distillation column for distillation. The top component of the column is fed into the first deHCl column to separate hydrogen chloride. The bottom of the column yields a second mixture containing monochlorofluoromethane (HCFC-31, R31), wherein the proportion of R31 in the first mixture is ≥70 mol% (2) The second mixture is fed into the second reactor and reacted under the action of the cracking catalyst to obtain the third mixture. The third mixture is then fed into the second deHCl tower, the alkali washing tower and the drying tower in sequence for deacidification and drying. Subsequently, it is fed into the second distillation tower for distillation. After the components at the top of the tower are separated, 1,2-difluoroethylene is obtained.

[0010] The specific reaction route is as follows: The reaction in the first reactor: CH2Cl2+HF→CH2FCl(R31)+HCl CH2Cl2+2HF→CH2F2(R32)+2HCl The reaction in the second reactor: 2CH2FCl→CF=CF(R1132)+2HCl In this invention, a first mixture is obtained by fluorination of dichloromethane and hydrogen fluoride under the action of catalyst I. After distillation, a second mixture containing monochlorofluoromethane (HCFC-31, R31) is obtained. The proportion of R31 in the second mixture can reach more than 70 mol%. R31 and R32 are converted to R1132 under the action of cracking catalyst. However, the conversion rate of R32 is low. This preparation method has a high yield and high selectivity for product R1132.

[0011] Preferably, in step (1), the catalyst I is chromium fluoride or chromium oxide.

[0012] In this invention, after being subjected to the reaction conditions of this invention (especially contact with hydrogen fluoride), chromium fluoride and chromium oxide form a moderate Lewis acid strength on their surfaces. This catalyzes the substitution of the first chlorine atom with fluorine (generating R31), but is insufficient to strongly adsorb the R31 molecule and allow it to further react to generate R32. This makes it easier for R31 to desorb from the catalyst surface once it is generated, reducing the selectivity of R32, and consequently resulting in a much higher R31 content than R32 in the prepared first mixture.

[0013] Preferably, in step (1), the molar ratio of dichloromethane to hydrogen fluoride is 1:1 to 10.

[0014] In this invention, in order to control the hot spot of the reaction from being too high, hydrogen fluoride should be used to remove heat in excess, and increasing the concentration of hydrogen fluoride is beneficial to the conversion of dichloromethane. However, this results in a large post-processing load and high energy consumption. Therefore, the molar ratio of dichloromethane to hydrogen fluoride in this invention is 1:1 to 10.

[0015] More preferably, the molar ratio of dichloromethane to hydrogen fluoride is 1:3 to 8.

[0016] Preferably, in step (1), the fluorination reaction is carried out at a temperature of 150~240 °C and a pressure of 0.1~1.5 MPa.

[0017] Excessive reaction temperature increases energy consumption and accelerates catalyst carbonization, leading to accelerated catalyst deactivation; excessively low reaction temperature results in low dichloromethane conversion. Therefore, the reaction temperature in this invention is 150–240 °C. Increasing pressure can increase the contact time between the reactants and the catalyst, which is beneficial for improving the conversion rate, but excessive pressure places high demands on the reactor material and increases equipment investment. Therefore, the reaction pressure in this invention is controlled at 0.1–1.5 MPa.

[0018] More preferably, the fluorination reaction is carried out at a temperature of 180~220 °C and a pressure of 0.3~1 MPa.

[0019] Preferably, in step (1), the space velocity of the fluorination reaction is 500~1500 h⁻¹. -1 .

[0020] In this invention, increasing the space velocity of the reaction decreases the conversion rate of dichloromethane. Conversely, decreasing the space velocity increases the conversion rate of dichloromethane, but reduces the catalyst yield per unit time, thus decreasing the economic efficiency of the reaction. Therefore, the space velocity in this invention is 500~1500 h⁻¹. -1 Preferably 800~1200 h -1 .

[0021] Preferably, the proportion of R31 in the first mixture is 70-80 mol.

[0022] Preferably, in step (1), the first mixture is a mixture of monochlorofluoromethane, difluoromethane (R32), hydrogen fluoride, hydrogen chloride and dichloromethane.

[0023] More preferably, the proportion of difluoromethane in the first mixture is 15-26 mol.

[0024] Preferably, in step (2), the cracking catalyst is an oxide-supported metal catalyst, wherein the oxide is at least one of aluminum oxide, magnesium oxide, zirconium oxide, cerium oxide, lanthanum oxide, and silicon oxide, and the metal comprises a first metal and a second metal, wherein the first metal is at least one of group IA metals and group IIA metals, and the second metal is at least one of transition metals.

[0025] More preferably, in the cracking catalyst, the first metal accounts for 0.1-5% of the total mass of the catalyst, the second metal accounts for 1-30% of the total mass of the catalyst, and the molar ratio of the first metal to the second metal is 1:1-20.

[0026] More preferably, the first metal in the cracking catalyst is one of K, Na, Ba, Ca, and Sr, and the second metal is one of Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Pt, Rh, Ag, and Au.

[0027] Preferably, in step (2), the reaction temperature is 400~700 ℃ and the pressure is 0.1~1.5 MPa.

[0028] Excessive temperature leads to increased byproducts and catalyst deactivation due to carbon deposition, while insufficient temperature results in incomplete pyrolysis. Therefore, the reaction temperature in this invention is 400–700 °C. Increasing pressure increases the contact time between the reactants and the catalyst, which is beneficial for improving the conversion rate; however, excessive pressure places high demands on the reactor material and increases equipment investment. Therefore, the reaction pressure in this invention is controlled at 0.1–1.5 MPa.

[0029] More preferably, the reaction temperature is 500~700 ℃ and the pressure is 0.3~1 MPa.

[0030] Preferably, in step (2), the space velocity of the reaction is 50~1500 h⁻¹. -1 .

[0031] In this invention, the pyrolysis reaction temperature is controlled at 400~700 ℃, and the acid sites of the pyrolysis catalyst are regulated by the type and amount of the first metal added, thereby reducing carbon deposition, reducing the deactivation of the pyrolysis catalyst, extending the continuous operation cycle of the pyrolysis catalyst to more than 500 h, and reducing equipment start-up and shutdown losses.

[0032] Preferably, in step (2), the third mixture further contains difluoromethane.

[0033] In this invention, the difluoromethane molecule has a stable structure and a high CF bond energy, which increases the difficulty of the defluorination reaction. Within the cracking process parameter range of this invention, the conversion rate of this defluorination reaction is extremely low, with only a small or even trace amount of reaction occurring; and from the reaction pathway perspective, even if a small amount of conversion occurs, the product is the target product, 1,2-difluoroethylene. The trace amounts of HF generated during the reaction can be efficiently absorbed and removed by an alkaline washing tower in a subsequent process unit, thereby obtaining high-purity 1,2-difluoroethylene.

[0034] More preferably, the proportion of difluoromethane in the third mixture is 14-20 mol.

[0035] In this invention, unreacted difluoromethane and the product 1,2-difluoroethylene can be separated after distillation in the second distillation column.

[0036] More preferably, the proportion of 1,2-difluoroethylene in the third mixture is 70-81 mol.

[0037] Preferably, in step (2), the bottom product of the second distillation column is monochlorofluoromethane, which is returned to the second reactor.

[0038] Preferably, in step (2), the top component of the second distillation column further includes difluoromethane.

[0039] The preparation method of the present invention can also achieve the co-production of difluoromethane, enabling the efficient utilization of fluorine and carbon elements in the raw materials in a stepwise manner, significantly improving atom economy, and realizing the co-production from inexpensive raw material dichloromethane to high-value-added refrigerant (difluoromethane, R32) and fluorine-containing monomer (1,2-difluoroethylene, R1132).

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) High raw material utilization rate, achieving joint production and efficiency improvement. Using dichloromethane and anhydrous HF as initial raw materials, two fluorine-containing substances, R32 and R31, are generated simultaneously through a one-step fluorination reaction. The R31 stream is then converted into high-value R1132 through cracking, enabling the efficient utilization of fluorine and carbon elements in the raw materials in a stepwise manner and significantly improving atom economy.

[0041] (2) Optimize process conditions and balance energy consumption and stability The fluorination reaction is carried out under low-temperature gas phase conditions of 150~240 ℃, which reduces energy consumption compared with traditional high-temperature fluorination processes. By controlling the proportion of raw materials and the amount of catalyst used in the fluorination reaction, the products of the fluorination reaction are kept in R31 as much as possible. The cracking reaction temperature is controlled at 400~700 ℃, and carbon deposition and catalyst deactivation are reduced by controlling the acid sites of the catalyst, so that the continuous operation cycle of the cracking catalyst is extended to more than 500 h, reducing equipment start-up and shutdown losses.

[0042] (3) The catalyst system has strong adaptability and excellent reaction efficiency. Chromium fluoride or chromium oxide is selected as the fluorination catalyst, which has high selectivity for the formation of R32 and R31, and the conversion rate of dichloromethane is stable at 93%~97%. In the cracking stage, oxide-supported metal catalysts are used to synergistically improve the cracking activity of R31 and the selectivity of R1132. Attached Figure Description

[0043] Figure 1 The system used in the preparation method of the present invention includes: 1 is a first reactor, 2 is a first distillation column, 3 is a first deHCl column, 4 is a second reactor, 5 is a second deHCl column, 6 is an alkaline washing column, 7 is a drying column, and 8 is a second distillation column. Detailed Implementation

[0044] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited to the following embodiments.

[0045] All raw materials used in this invention are commercially available.

[0046] The system used in this invention is as follows Figure 1 As shown, dichloromethane and hydrogen fluoride are fed into the first reactor 1 and undergo a fluorination reaction under the action of catalyst I to obtain a first mixture. The first mixture is then fed into the first distillation column 2 for distillation. The top component of the column is then fed into the first deHCl column 3 to separate hydrogen chloride. The bottom of the column yields a second mixture containing monochlorofluoromethane (HCFC-31, R31). The second mixture is then fed into the second reactor 4 and reacted under the action of a cracking catalyst to obtain a third mixture. The third mixture is then fed into the second deHCl column 5, the alkali washing column 6, and the drying column 7 in sequence for deacidification and drying. Subsequently, it is fed into the second distillation column 8 for distillation. The top component of the column is separated to obtain 1,2-difluoroethylene. The bottom product of the first distillation column 2 can be returned to the first reactor 1; The bottom product of the second distillation column 8 can be returned to the second reactor 4.

[0047] Example 1 use Figure 1The system shown has 100 mL of chromium oxide catalyst in the first reactor and 100 mL of cracking catalyst #1 in the second reactor. The specific steps are as follows: (1) Dichloromethane and hydrogen fluoride are fed into the first reactor and fluorinated under the action of chromium oxide catalyst to obtain a first mixture, wherein monochlorofluoromethane (R31) accounts for 78.2% of the first mixture. The first mixture is fed into the first distillation column for distillation. The top component of the column is fed into the deHCl column to separate hydrogen chloride. The bottom of the column is then filled with a second mixture containing monochlorofluoromethane and difluoromethane (R32). (2) The second mixture is fed into the second reactor and reacted under the action of cracking catalyst 1# to obtain the third mixture, in which R1132 accounts for 71.6%; the third mixture is fed into the deHCl tower, the alkali washing tower and the drying tower in sequence for deacidification and drying, and then fed into the second distillation tower for distillation. After the components at the top of the tower are separated, 1,2-difluoroethylene (R1132) and difluoromethane are obtained. The remaining R31 at the bottom of the tower can be returned to the first and second reactors for further reaction. The yields of 1,2-difluoroethylene (R1132) and difluoromethane are 16.2% and 71.6%, respectively.

[0048] The specific reaction conditions are shown in Table 1. Table 1: Reaction conditions, material composition and proportion at reactor outlet in Example 1 The preparation method of cracking catalyst 1# is as follows: Pour 500 mL of deionized water into a 1000 mL beaker and place it on a thermostatic magnetic stirrer. Set the temperature to 35°C and the stirring speed to 250 r / min. Slowly add 1.3 g of potassium nitrate and stir until completely dissolved. Then add 76.9 g of chromium nitrate and continue stirring for 10 min. During this time, the temperature can be increased to 40°C to accelerate dissolution. Finally, a clear and transparent potassium nitrate is obtained. + -Cr 3+ Mixed metal salt solutions; Slowly pour 84.8 g of γ-Al2O3 powder into the above metal salt solution, while increasing the stirring speed to 400 r / min to ensure that the carrier powder is evenly dispersed in the solution and to avoid agglomeration. 25 wt% ammonia solution was slowly added dropwise using a constant pressure dropping funnel at a rate of 1.2 mL / min. The pH of the solution was monitored in real time with a pH meter during the addition process, and flocculent precipitate was observed to form. Ammonia solution was added dropwise until the pH reached 8.2-8.5. After the addition was stopped, the stirring speed was maintained at 400 r / min and stirring was continued for 30 min to ensure that the precipitation reaction was complete. After the precipitation reaction is complete, the suspension is transferred to a Buchner funnel, connected to a vacuum filtration device, and filtered for separation. The solution is then washed with deionized water until the pH of the washing solution is approximately 7.0. The washed filter cake was transferred to an oven and dried at a low temperature of 80 °C for h, then the temperature was increased to 120 °C and dried for another 8 h to completely remove the water of crystallization. It was then calcined at 400 °C to obtain Cr-K / γ-Al2O3 catalyst powder; the powder was then pressed into tablets to obtain cracking catalyst #1.

[0049] Example 2 use Figure 1 The system shown has 100 mL of chromium fluoride catalyst in the first reactor and 100 mL of cracking catalyst #2 in the second reactor. The specific steps are as follows: (1) Dichloromethane and hydrogen fluoride are fed into the first reactor and fluorinated under the action of chromium fluoride catalyst to obtain a first mixture, wherein monochlorofluoromethane (R31) accounts for 76.9% of the first mixture. The first mixture is fed into the first distillation column for distillation. The top component of the column is fed into the first deHCl column to separate hydrogen chloride. The bottom of the column is then filled with a second mixture containing monochlorofluoromethane and difluoromethane (R32). (2) The second mixture is fed into the second reactor and reacted under the action of cracking catalyst 2# to obtain the third mixture, in which R1132 accounts for 74.1%; the third mixture is fed into the second deHCl tower, the alkali washing tower and the drying tower in sequence for deacidification and drying, and then fed into the second distillation tower for distillation. After separation of the components at the top of the tower, 1,2-difluoroethylene (R1132) and difluoromethane are obtained. The remaining R31 at the bottom of the tower can be returned to the first and second reactors for further reaction. The yields of 1,2-difluoroethylene (R1132) and difluoromethane are 15.4% and 74.1%, respectively.

[0050] The specific reaction conditions are shown in Table 2. Table 2: Reaction conditions and material composition at reactor outlet in Example 2 The preparation method of cracking catalyst #2 is as follows: Pour 500 mL of deionized water into a 1000 mL beaker and place it on a thermostatic magnetic stirrer. Set the temperature to 35°C and the stirring speed to 250 r / min. Slowly add 3.7 g of sodium nitrate and stir until completely dissolved. Then add 74.3 g of nickel nitrate and continue stirring for 10 min. During this time, the temperature can be increased to 40°C to accelerate dissolution. Finally, a clear and transparent Na₂SO₄ solution is obtained. + -Ni 3+ Mixed metal salt solutions; Slowly pour 89.1 g of ZrO2 powder into the above metal salt solution, while increasing the stirring speed to 400 r / min to ensure that the carrier powder is evenly dispersed in the solution and to avoid agglomeration. 25 wt% ammonia solution was slowly added dropwise using a constant pressure dropping funnel at a rate of 1.2 mL / min. The pH of the solution was monitored in real time with a pH meter during the addition process, and flocculent precipitate was observed to form. Ammonia solution was added dropwise until the pH reached 8.2-8.5. After the addition was stopped, the stirring speed was maintained at 400 r / min and stirring was continued for 30 min to ensure that the precipitation reaction was complete. After the precipitation reaction is complete, the suspension is transferred to a Buchner funnel, connected to a vacuum filtration device, and filtered for separation. The solution is then washed with deionized water until the pH of the washing solution is approximately 7.0. The washed filter cake was transferred to an oven and dried at a low temperature of 80 °C for h, then the temperature was increased to 120 °C and dried for another 8 h to completely remove the water of crystallization. Then it was calcined at 400 °C to obtain Ni-Na / ZrO2 catalyst powder; the powder was pressed into tablets to obtain cracking catalyst #2.

[0051] Example 3 use Figure 1 The system shown has 100 mL of chromium oxide catalyst in the first reactor and 100 mL of cracking catalyst #3 in the second reactor. The specific steps are as follows: (1) Dichloromethane and hydrogen fluoride are fed into the first reactor and fluorinated under the action of chromium oxide catalyst to obtain a first mixture, wherein monochlorofluoromethane (R31) accounts for 74.4% of the first mixture. The first mixture is fed into the first distillation column for distillation. The top component of the column is fed into the first deHCl column to separate hydrogen chloride. The bottom of the column is then filled with a second mixture containing monochlorofluoromethane and difluoromethane (R32). (2) The second mixture is fed into the second reactor and reacted under the action of cracking catalyst 3# to obtain the third mixture, in which R1132 accounts for 74.9%; the third mixture is fed into the second deHCl tower, the alkali washing tower and the drying tower in sequence for deacidification and drying, and then fed into the second distillation tower for distillation. After the components at the top of the tower are separated, 1,2-difluoroethylene (R1132) and difluoromethane are obtained. The remaining R31 at the bottom of the tower can be returned to the first and second reactors for further reaction. The yields of 1,2-difluoroethylene (R1132) and difluoromethane are 20.2% and 74.9%, respectively.

[0052] The specific reaction conditions are shown in Table 3. Table 3: Reaction conditions and material composition at reactor outlet in Example 3 The preparation method of cracking catalyst #3 is as follows: Pour 500 mL of deionized water into a 1000 mL beaker and place it on a thermostatic magnetic stirrer. Set the temperature to 35°C and the stirring speed to 250 r / min. Slowly add 6.1 g of barium nitrate and stir until completely dissolved. Then add 144.7 g of ferric nitrate and continue stirring for 10 min. During this time, the temperature can be increased to 40°C to accelerate dissolution. Finally, a clear and transparent Ba2O3 solution is obtained. 2+ -Fe 3+ Mixed metal salt solutions; Slowly pour 69.7 g of CeO2 powder into the above metal salt solution, while increasing the stirring speed to 400 r / min to ensure that the carrier powder is evenly dispersed in the solution and to avoid agglomeration; 25 wt% ammonia solution was slowly added dropwise using a constant pressure dropping funnel at a rate of 1.2 mL / min. The pH of the solution was monitored in real time with a pH meter during the addition process, and flocculent precipitate was observed to form. Ammonia solution was added dropwise until the pH reached 8.2-8.5. After the addition was stopped, the stirring speed was maintained at 400 r / min and stirring was continued for 30 min to ensure that the precipitation reaction was complete. After the precipitation reaction is complete, the suspension is transferred to a Buchner funnel, connected to a vacuum filtration device, and filtered for separation. The solution is then washed with deionized water until the pH of the washing solution is approximately 7.0. The washed filter cake was transferred to an oven and dried at a low temperature of 80 °C for 8 hours, then the temperature was increased to 120 °C and dried for another 8 hours to completely remove the water of crystallization. It was then calcined at 400 °C to obtain Fe-Ba / CeO2 catalyst powder; the powder was then pressed into tablets to obtain cracking catalyst #3.

[0053] Example 4 use Figure 1 The system shown has 100 mL of chromium oxide catalyst in the first reactor and 100 mL of cracking catalyst #4 in the second reactor. The specific steps are as follows: (1) Dichloromethane and hydrogen fluoride are fed into the first reactor and fluorinated under the action of chromium oxide catalyst to obtain a first mixture, wherein monochlorofluoromethane (R31) accounts for 72.5% of the first mixture. The first mixture is fed into the first distillation column for distillation. The top component of the column is fed into the first deHCl column to separate hydrogen chloride. The bottom of the column is then filled with a second mixture containing monochlorofluoromethane and difluoromethane (R32). (2) The second mixture is fed into the second reactor and reacted under the action of cracking catalyst 4# to obtain the third mixture, in which R1132 accounts for 77.7%; the third mixture is fed into the second deHCl tower, the alkali washing tower and the drying tower in sequence for deacidification and drying, and then fed into the second distillation tower for distillation. After separation of the components at the top of the tower, 1,2-difluoroethylene (R1132) and difluoromethane are obtained. The remaining R31 at the bottom of the tower can be returned to the first and second reactors for further reaction. The yields of 1,2-difluoroethylene (R1132) and difluoromethane are 22.6% and 77.7%, respectively.

[0054] The specific reaction conditions are shown in Table 4. Table 4: Reaction conditions and material composition at reactor outlet in Example 4 The preparation method of cracking catalyst #4 is as follows: Pour 500 mL of deionized water into a 1000 mL beaker and place it on a thermostatic magnetic stirrer. Set the temperature to 35°C and the stirring speed to 250 r / min. Slowly add 0.81 g of calcium nitrate and stir until completely dissolved. Then add 12.5 g of palladium nitrate and continue stirring for 10 min. During this time, the temperature can be increased to 40°C to accelerate dissolution. Finally, a clear and transparent Ca2+ solution is obtained. 2+ -Pd 2+ Mixed metal salt solutions; Slowly pour 48.5 g of Al2O3 and 48.5 g of SiO2 powder into the above metal salt solution, while increasing the stirring speed to 400 r / min to ensure that the carrier powder is evenly dispersed in the solution and to avoid agglomeration. 25 wt% ammonia solution was slowly added dropwise using a constant pressure dropping funnel at a rate of 1.2 mL / min. The pH of the solution was monitored in real time with a pH meter during the addition process, and flocculent precipitate was observed to form. Ammonia solution was added dropwise until the pH reached 8.2-8.5. After the addition was stopped, the stirring speed was maintained at 400 r / min and stirring was continued for 30 min to ensure that the precipitation reaction was complete. After the precipitation reaction is complete, the suspension is transferred to a Buchner funnel, connected to a vacuum filtration device, and filtered for separation. The solution is then washed with deionized water until the pH of the washing solution is approximately 7.0. The washed filter cake was transferred to an oven and dried at a low temperature of 80 °C for h, then the temperature was increased to 120 °C and dried for another 8 h to completely remove the water of crystallization. Then it was calcined at 400 °C to obtain Ca-Pd / Al2O3 / SiO2 catalyst powder; the powder was then pressed into tablets to obtain cracking catalyst #4.

[0055] Example 5 use Figure 1The system shown has 100 mL of chromium fluoride catalyst in the first reactor and 100 mL of cracking catalyst #5 in the second reactor. The specific steps are as follows: (1) Dichloromethane and hydrogen fluoride are fed into the first reactor and fluorinated under the action of chromium fluoride catalyst to obtain a first mixture, wherein monochlorofluoromethane (R31) accounts for 70.1% of the first mixture. The first mixture is fed into the first distillation column for distillation. The top component of the column is fed into the first deHCl column to separate hydrogen chloride. The bottom of the column is then filled with a second mixture containing monochlorofluoromethane and difluoromethane (R32). (2) The second mixture is fed into the second reactor and reacted under the action of cracking catalyst 5# to obtain the third mixture, in which R1132 accounts for 80.3%; the third mixture is fed into the second deHCl tower, the alkali washing tower and the drying tower in sequence for deacidification and drying, and then fed into the second distillation tower for distillation. After separation of the components at the top of the tower, 1,2-difluoroethylene (R1132) and difluoromethane are obtained. The remaining R31 at the bottom of the tower can be returned to the first and second reactors for further reaction. The yields of 1,2-difluoroethylene (R1132) and difluoromethane are 25.9% and 80.3%, respectively.

[0056] The specific reaction conditions are shown in Table 5. Table 5: Reaction conditions and material composition at reactor outlet in Example 5 The preparation method of cracking catalyst #5 is as follows: Pour 500 mL of deionized water into a 1000 mL beaker and place it on a thermostatic magnetic stirrer. Set the temperature to 35°C and the stirring speed to 250 r / min. Slowly add 10.2 g of strontium nitrate and stir until completely dissolved. Then add 95.1 g of copper nitrate and continue stirring for 10 min. During this time, the temperature can be increased to 40°C to accelerate dissolution. Finally, a clear and transparent Sr solution is obtained. 2+ -Cu 2+ Mixed metal salt solutions; Slowly pour 41 g of La2O3 and 41 g of MgO powder into the above metal salt solution, while increasing the stirring speed to 400 r / min to ensure that the carrier powder is evenly dispersed in the solution and to avoid agglomeration. 25 wt% ammonia solution was slowly added dropwise using a constant pressure dropping funnel at a rate of 1.2 mL / min. The pH of the solution was monitored in real time with a pH meter during the addition process, and flocculent precipitate was observed to form. Ammonia solution was added dropwise until the pH reached 8.2-8.5. After the addition was stopped, the stirring speed was maintained at 400 r / min and stirring was continued for 30 min to ensure that the precipitation reaction was complete. After the precipitation reaction is complete, the suspension is transferred to a Buchner funnel, connected to a vacuum filtration device, and filtered for separation. The solution is then washed with deionized water until the pH of the washing solution is approximately 7.0. The washed filter cake was transferred to an oven and dried at a low temperature of 80 °C for 8 hours, then the temperature was increased to 120 °C and dried for another 8 hours to completely remove the water of crystallization. Then it was calcined at 400 °C to obtain Cu-Sr / La2O3 / MgO catalyst powder; the powder was then pressed into tablets to obtain cracking catalyst #5.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing 1,2-difluoroethylene from dichloromethane, characterized in that, Includes the following steps: (1) Dichloromethane and hydrogen fluoride are fed into the first reactor and fluorinated under the action of catalyst I to obtain a first mixture. The first mixture is then fed into the first distillation column for distillation. The top component of the column is fed into the first deHCl column to separate hydrogen chloride. The bottom of the column yields a second mixture containing monochlorofluoromethane, wherein the proportion of monochlorofluoromethane in the first mixture is ≥70 mol% (2) The second mixture is fed into the second reactor and reacted under the action of the cracking catalyst to obtain the third mixture. The third mixture is then fed into the second deHCl tower, the alkali washing tower and the drying tower in sequence for deacidification and drying. Subsequently, it is fed into the second distillation tower for distillation. After the components at the top of the tower are separated, 1,2-difluoroethylene is obtained.

2. The method for preparing 1,2-difluoroethylene from dichloromethane according to claim 1, characterized in that, In step (1), the catalyst I is chromium fluoride or chromium oxide.

3. The method for preparing 1,2-difluoroethylene from dichloromethane according to claim 1, characterized in that, In step (1), the molar ratio of dichloromethane and hydrogen fluoride is 1:1~10.

4. The method for preparing 1,2-difluoroethylene from dichloromethane according to claim 1, characterized in that, In step (1), the fluorination reaction is carried out at a temperature of 150~240 ℃ and a pressure of 0.1~1.5 MPa.

5. The method for preparing 1,2-difluoroethylene from dichloromethane according to claim 1, characterized in that, In step (1), the space velocity of the fluorination reaction is 500~1500 h⁻¹. -1 .

6. The method for preparing 1,2-difluoroethylene from dichloromethane according to claim 1, characterized in that, In step (1), the first mixture is a mixture of monochlorofluoromethane, difluoromethane, hydrogen fluoride, hydrogen chloride and dichloromethane.

7. The method for preparing 1,2-difluoroethylene from dichloromethane according to claim 1, characterized in that, In the first mixture, the proportion of difluoromethane is 15-26 mol.

8. The method for preparing 1,2-difluoroethylene from dichloromethane according to claim 1, characterized in that, In step (2), the cracking catalyst is an oxide-supported metal catalyst, wherein the oxide is at least one of aluminum oxide, magnesium oxide, zirconium oxide, cerium oxide, lanthanum oxide, and silicon oxide, and the metal comprises a first metal and a second metal, wherein the first metal is at least one of group IA metals and group IIA metals, and the second metal is at least one of transition metals.

9. The method for preparing 1,2-difluoroethylene from dichloromethane according to claim 8, characterized in that, The first metal in the pyrolysis catalyst is one of K, Na, Ba, Ca, and Sr, and the second metal is one of Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Pt, Rh, Ag, and Au.

10. The method for preparing 1,2-difluoroethylene from dichloromethane according to claim 8 or 9, characterized in that, In the aforementioned cracking catalyst, the first metal accounts for 0.1-5% of the total mass of the cracking catalyst, the second metal accounts for 1-30% of the total mass of the cracking catalyst, and the molar ratio of the first metal to the second metal is 1:1-20.

11. The method for preparing 1,2-difluoroethylene from dichloromethane according to claim 1, characterized in that, In step (2), the space velocity of the reaction is 50~1500 h⁻¹. -1 .

12. The method for preparing 1,2-difluoroethylene from dichloromethane according to claim 1, characterized in that, In step (2), the reaction temperature is 400~700 ℃ and the pressure is 0.1~1.5 MPa.

13. The method for preparing 1,2-difluoroethylene from dichloromethane according to claim 1, characterized in that, In step (2), the third mixture also contains difluoromethane.

14. The method for preparing 1,2-difluoroethylene from dichloromethane according to claim 13, characterized in that, In step (2), the proportion of difluoromethane in the third mixture is 14~20 mol.

15. The method for preparing 1,2-difluoroethylene from dichloromethane according to claim 1, characterized in that, In step (2), the bottom product of the second distillation column is chlorofluoromethane, which is returned to the second reactor.

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