Method for preparing 1, 1-difluoroethylene through resource utilization of 1, 1-difluoro-2-chloroethane

Abstract

The invention discloses a method for preparing 1, 1-difluoroethylene through resource utilization of 1, 1-difluoro-2-chloroethane, and the method comprises the following steps: by taking a mixture containing 1, 1-difluoro-2-chloroethane as a raw material, carrying out catalytic cracking under the action of a modified molecular sieve to obtain 1, 1-difluoroethylene; the active component of the modified molecular sieve is an oxide of at least one of Zn, Fe, Cu, Ni, Co and Ru, and the mass content is 1-50wt%; the molecular sieve is selected from at least one of ZSM-5, Beta, X, Y, 5A or L type zeolite molecular sieves. The method has the advantages of simple process, mild reaction, high conversion rate, good selectivity, good catalyst stability, suitability for industrial application and the like.

Description

Technical Field

[0001] The present invention relates to resource utilization of 1,1-difluoro-2-chloroethane, and in particular to a method for preparing 1,1-difluoroethylene by catalytic cracking using a mixture containing 1,1-difluoro-2-chloroethane as a raw material. Background Art

[0002] 2-Chloro-1,1-difluoroethane (R142), an isomer of 1-chloro-1,1-difluoroethane (R142b), is a byproduct of the industrial production of R142b. Currently, it has no direct industrial application value, and the large amount of byproduct R142 poses certain pressures on companies regarding environmental protection, storage, and conversion. 1,1-Difluoroethylene, also known as "vinylidene fluoride," or VDF for short, is an intermediate in the synthesis of polyvinylidene fluoride (PVDF). Converting byproduct R142 into 1,1-difluoroethylene has significant application value.

[0003] Jia Wenzhi et al. (Catalytic Pyrolysis of 2-Chloro-1,1-difluoroethane to Synthesize Vinylidene Fluoride over the Potassium-Promoted Carbon Catalysts) disclose a method for preparing vinylidene fluoride by cracking R142 over an activated carbon-supported potassium catalyst. When the potassium loading reaches 1%, the K / C catalyst exhibits excellent catalytic performance, achieving an R142 conversion of 47.7% and a VDF selectivity of 48.4% at 600°C. However, the R142 conversion and VDF selectivity in this method are both low, failing to meet requirements. The catalyst's service life is also not disclosed.

[0004] Zhejiang University of Technology patent CN109180420A discloses a method for preparing 1,1-difluoroethylene by catalytic cracking of 1,1-difluoro-2-chloroethane (R142) in the presence of a composite catalyst of alkaline earth metal fluorides. The BaSrF4 catalyst has a high selectivity for VDF, reaching 85%, but the R142 conversion rate is too low, only 38%.

[0005] Sanaifu patent CN110776394A discloses a method for preparing VDF by catalytic cracking of 1,1-difluoro-2-chloroethane under the action of a fluoride-loaded activated carbon catalyst, wherein the fluoride is selected from aluminum fluoride, chromium fluoride, potassium fluoride, magnesium fluoride, calcium fluoride, etc., at a reaction temperature of 400-700°C and a space velocity of 200-3000h -1The reaction was carried out under conditions of 0.1-1.0 MPa pressure. The activated carbon catalyst loaded with aluminum fluoride showed the best reaction performance, with an R142 conversion of 97.8% and a VDF selectivity of 86.6%. This method achieved good conversion and selectivity, but no catalyst life evaluation experiments were conducted. According to those skilled in the art, aluminum fluoride is a strong Lewis acid catalyst, which is prone to active site deactivation and catalyst sintering at high temperatures, resulting in poor catalyst stability and a short service life.

[0006] In summary, the current resource utilization process for by-product R142 uses pure R142 as the raw material. However, the R142 content in the by-product of industrial production of R142b is generally greater than 80%, and obtaining pure R142 requires multi-stage distillation. Moreover, the above-mentioned R142 preparation process for VDF may suffer from low reaction conversion rate, low target selectivity, high reaction temperature, poor catalyst stability, and short service life. In order to achieve efficient utilization of the by-product 1,1-difluoro-2-chloroethane, it is necessary to conduct in-depth research on the process for preparing 1,1-difluoroethylene from 1,1-difluoro-2-chloroethane. Summary of the Invention

[0007] In order to solve the above technical problems, the present invention proposes a method for preparing 1,1-difluoroethylene by resource utilization of 1,1-difluoro-2-chloroethane, which is simple to operate, has a high single-pass conversion rate, few side reactions, and the catalyst is resistant to impurity interference and has a long service life, and can achieve continuous industrialization.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A method for preparing 1,1-difluoroethylene by resource utilization of 1,1-difluoro-2-chloroethane, comprising: using a mixture containing 1,1-difluoro-2-chloroethane as a raw material, catalytically cracking the mixture under the action of a modified molecular sieve to obtain 1,1-difluoroethylene; the chemical reaction formula is as follows:

[0010]

[0011] The modified molecular sieve comprises an active component of at least one oxide selected from the group consisting of Zn, Fe, Cu, Ni, Co, and Ru, with a mass content of 1 to 50 wt%. The molecular sieve is selected from at least one of ZSM-5, Beta, X, Y, 5A, or L zeolite molecular sieves, and the balancing cation is selected from at least one of hydrogen ion, alkali metal ion, alkaline earth metal ion, transition metal ion, or rare earth metal ion.

[0012] Currently, 1,1-difluoro-2-chloroethane is produced as a byproduct of the industrial production of R142b, resulting in a mixture containing 1,1-difluoro-2-chloroethane. Typically, the mixture contains at least 80% by weight of 1,1-difluoro-2-chloroethane, with the remainder being at least one of dichlorodifluoroethylene, monochlorodifluoroethylene, and monofluorodichloroethane. Furthermore, the mixture can contain 90-100% by weight of 1,1-difluoro-2-chloroethane.

[0013] Of course, a higher content of 1,1-difluoro-2-chloroethane in the mixture is more conducive to the reaction and reduces by-products. However, this requires separating and treating the mixture containing 1,1-difluoro-2-chloroethane obtained directly from the R142b device, adding operations such as distillation, and increasing the complexity of the process.

[0014] Moreover, 1,1-difluoro-2-chloroethane is prone to undergoing 1,2-FCl exchange reaction. If a suitable catalyst is not selected and the reaction conditions are not properly controlled, it is easy to cause a large number of by-products and low product selectivity. Therefore, most of the existing R142 is treated as a useless by-product.

[0015] Based on this, the present application proposes a modified molecular sieve catalyst, which can not only avoid the influence of other impurities in the mixture on the reaction, but also maintain excellent single-pass conversion rate while maintaining product selectivity, and improve the stability and service life of the catalyst.

[0016] In order to further improve the selectivity of the dehydrochlorination reaction and inhibit the rearrangement reaction, the active component of the modified molecular sieve is preferably an oxide of at least one of Zn, Fe, Cu, and Ni, with a mass content of 5 to 20 wt%. The molecular sieve is selected from at least one of ZSM-5, Beta, or L-type zeolite molecular sieves, and the Si / Al ratio of the zeolite molecular sieve is 50 to 300. More preferably, the active component of the modified molecular sieve is selected from at least one of Zn, Cu, and Ni, the molecular sieve is selected from at least one of ZSM-5 and Beta, the Si / Al ratio is 50 to 200, and the balancing cation is selected from K + 、Na + , Ca 2+ 、Ba 2+ 、H + Most preferably, the balancing cation is selected from Ca 2+ 、Ba 2+ 、H + At least one of .

[0017] The mixture of the present invention is preheated and vaporized in a preheater before reacting, and the preheating temperature is 100-300° C., preferably 150-200° C. The preheating improves the temperature distribution in the reaction tube and reduces carbon deposition during the reaction.

[0018] The modified molecular sieve of the present invention is activated and then reacted. Calcination activation can remove moisture from the catalyst, change the catalyst pore structure, and improve the reaction effect. The activation step specifically includes:

[0019] A1. The modified molecular sieve is calcined under a nitrogen atmosphere at a temperature of 400 to 600 ° C for 2 to 5 h; preferably, the calcination temperature is 400 to 500 ° C and the calcination time is 2 to 3 h;

[0020] A2. A preheated mixture containing 1,1-difluoro-2-chloroethane is introduced and maintained at 200-400°C for 0.5-2h, then the temperature is raised to 300-500°C and activation is continued for 0.5-2h to obtain an activated modified molecular sieve for catalytic cracking reaction; preferably, the calcined modified molecular sieve is first maintained at 200-300°C for 0.5-1h, then the temperature is raised to 300-400°C and activation is continued for 1-1.5h.

[0021] The cracking of 1,1-difluoro-2-chloroethane is an endothermic reaction. If the heating temperature is too low, the activation energy required for the reaction cannot be achieved and the reaction cannot proceed. If the heating temperature is too high, it will not only promote the F-Cl rearrangement reaction of 1,1-difluoro-2-chloroethane, reducing the catalyst effect, but also shorten the catalyst life.

[0022] The space velocity has little effect on the reaction results. If the space velocity is too short, the reaction carbon deposition rate will be accelerated.

[0023] Therefore, the reaction temperature of the catalytic cracking reaction of the present invention is 300-500°C, and the space velocity is 100-1000h -1 , reaction pressure 0.1~1.0MPa. Preferably, the reaction temperature is 300~400℃, and the space velocity is 360~720h -1 .

[0024] The catalytic cracking reaction of the present invention is carried out in a fixed bed reactor, and the reactor material is selected from monel alloy, inconel alloy or hastelloy alloy.

[0025] The product obtained by the cracking reaction of the present invention may contain, in addition to 1,1-difluoroethylene, at least one of 1-fluoro-2-chloroethylene, 1,2-difluoroethylene, and 1-fluoro-1-chloroethylene. The product can be subjected to water alkali washing, compression, dehydration, and separation to obtain the 1,1-difluoroethylene product.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention can directly convert a mixture containing 1,1-difluoro-2-chloroethane into 1,1-difluoroethylene with high industrial application value by using a modified molecular sieve catalyst. The operation is simple, the single-pass conversion rate is high, the selectivity is good, the catalyst is resistant to impurity interference, has good stability and a long service life, and is very suitable for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The life evaluation results of the catalyst in Example 1 of the present invention are as follows;

[0029] Figure 2 The life evaluation results of the catalyst in Example 11 of the present invention are as follows;

[0030] Figure 3 This is the life evaluation result of the catalyst in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements and equivalents within the scope of the claims.

[0032] The reactor used in the embodiment of the present invention is a heating furnace (the inner diameter of the furnace is 30 mm and the height is 600 mm), the inner diameter of the reaction tube is 19 mm and the length is 700 mm, the material is Inconel 600 alloy, and the catalyst loading amount is 20 mL.

[0033] Example 1

[0034] This embodiment provides a method for preparing 1,1-difluoroethylene by resource utilization of 1,1-difluoro-2-chloroethane. The reaction raw material is 100% 1,1-difluoro-2-chloroethane, the catalyst is a NiO / ZSM-5 modified molecular sieve, the content of the active component NiO is 10wt%, the molecular sieve is a ZSM-5 molecular sieve, the Si / Al ratio is 50, and the balancing cation is selected from H + .

[0035] The method comprises the following steps:

[0036] S1. NiO / ZSM-5 modified molecular sieve was loaded into the reaction tube, the heating furnace was set at 400 ° C, and calcined under a nitrogen atmosphere for 2h. After calcination, the temperature was lowered to 200 ° C;

[0037] S2. The reaction raw materials preheated and vaporized at 150 ° C were introduced at a feed rate of 20.0 g / h, maintained at 250 ° C for 0.5 h, then raised to 350 ° C and continued to activate for 1 h;

[0038] S3. Set the reaction temperature to 400 ° C, feed the reaction raw materials at a feed rate of 32.3 g / h, and the space velocity is 360h -1 , sampling was performed from the reactor outlet for analysis, and the raw material conversion rate and product selectivity are shown in Table 1. The reaction product was sequentially passed through a water alkali washing device, a compression device, a drying and dehydration device, and a distillation device to obtain pure VDF.

[0039] Example 2

[0040] The operation of this embodiment is the same as that of Example 1, except that the catalyst uses ZnO / ZSM-5 modified molecular sieve, and other conditions remain unchanged. The reaction results are shown in Table 1 below.

[0041] Example 3

[0042] The operation of this embodiment is the same as that of Example 1, except that the catalyst uses CuO / ZSM-5 modified molecular sieve, and other conditions remain unchanged. The reaction results are shown in Table 1 below.

[0043] Example 4

[0044] The operation of this embodiment is the same as that of Example 1, except that the catalyst uses Fe2O3 / ZSM-5 modified molecular sieve, and other conditions remain unchanged. The reaction results are shown in Table 1 below.

[0045] Example 5

[0046] The operation of this embodiment is the same as that of Example 1, except that the catalyst uses NiO / Beta modified molecular sieve, and other conditions remain unchanged. The reaction results are shown in Table 1 below.

[0047] Example 6

[0048] The operation of this embodiment is the same as that of Example 1, except that the reaction temperature is lowered to 300° C. during the reaction, and other conditions remain unchanged. The reaction results are shown in Table 1 below.

[0049] Example 7

[0050] The operation of this embodiment is the same as that of Example 1, except that the reaction temperature is increased to 500° C. during the reaction, and other conditions remain unchanged. The reaction results are shown in Table 1 below.

[0051] Example 8

[0052] The operation of this embodiment is the same as that of embodiment 1, except that the feed rate of the reaction raw materials is increased to 34.1 g / h, and the space velocity is 480 h -1 , other conditions remain unchanged, and the reaction results are shown in Table 1 below.

[0053] Example 9

[0054] The operation of this embodiment is the same as that of embodiment 1, except that the feed rate of the reaction raw materials is increased to 64.6 g / h, and the space velocity is 720 h -1 , other conditions remain unchanged, and the reaction results are shown in Table 1 below.

[0055] Example 10

[0056] The operation of this embodiment is the same as that of embodiment 1, except that the content of the active component NiO is increased to 20 wt %. Other conditions remain unchanged. The reaction results are shown in Table 1 below.

[0057] Example 11

[0058] The operation of this embodiment is the same as that of Example 1, except that the content of 1,1-difluoro-2-chloroethane in the reaction raw materials is 90%, and the rest is difluorodichloroethylene, difluoromonochloroethylene and dichloromonofluoroethane. Other operations remain unchanged. The reaction results are shown in Table 1 below.

[0059] Example 12

[0060] The operation of this example is the same as that of Example 1, except that the content of 1,1-difluoro-2-chloroethane in the reaction raw materials is 95%, and the rest is difluorodichloroethylene, difluoromonochloroethylene and dichloromonofluoroethane. Other operations remain unchanged. The reaction results are shown in Table 1 below.

[0061] Comparative Example 1

[0062] The operation of this comparative example is the same as that of Example 1, except that the catalyst is a ZSM-5 molecular sieve without active components. Other operations remain unchanged. The reaction results are shown in Table 1 below.

[0063] Comparative Example 2

[0064] The operation of this comparative example is the same as that of Example 1, except that the active component is Al2O3, and the content is 10wt%. Other operations remain unchanged. The reaction results are shown in Table 1 below.

[0065] Comparative Example 3

[0066] The operation of this comparative example is the same as that of comparative example 2, except that the content of 1,1-difluoro-2-chloroethane in the reaction raw materials is 90%, and the rest are difluorodichloroethylene, difluoromonochloroethylene and dichloromonofluoroethane. Other operations remain unchanged. The reaction results are shown in Table 1 below.

[0067] Table 1 Reaction results

[0068]

[0069] The present invention is attached Figure 1-3 The life evaluation results of the catalyst in Example 1, the catalyst in Example 11, and the catalyst in Comparative Example 2 are given respectively. Figure 1-3 It can be seen that the feedstock conversion and product selectivity of the catalysts of Examples 1 and 11 of the present invention remained unchanged after about 168 hours of reaction, but the feedstock conversion and selectivity of the catalyst of Comparative Example 2 decreased significantly after about 80 hours of reaction. Therefore, the stability of the modified molecular sieve catalyst of the present invention is significantly improved.

Claims

1. A method for preparing 1,1-difluoroethylene by resource utilization of 1,1-difluoro-2-chloroethane, characterized in that: A mixture containing 1,1-difluoro-2-chloroethane is used as raw material, and 1,1-difluoroethylene is obtained by catalytic cracking under the action of a modified molecular sieve; the active component of the modified molecular sieve is an oxide of at least one selected from Zn, Fe, Cu, Ni, Co, and Ru, with a mass content of 1 to 50 wt%.

2. The method for preparing 1,1-difluoroethylene by resource utilization of 1,1-difluoro-2-chloroethane according to claim 1, characterized in that: The active component is selected from at least one oxide of Zn, Fe, Cu and Ni, and its mass content is 5-20 wt%.

3. The method for preparing 1,1-difluoroethylene by resource utilization of 1,1-difluoro-2-chloroethane according to claim 1, characterized in that: The molecular sieve is selected from at least one of ZSM-5, Beta, X, Y, 5A or L-type zeolite molecular sieves, and the balance cation is selected from at least one of hydrogen ion, alkali metal ion, alkaline earth metal ion, transition metal ion or rare earth metal ion.

4. The method for preparing 1,1-difluoroethylene by resource utilization of 1,1-difluoro-2-chloroethane according to claim 3, characterized in that: The molecular sieve is selected from at least one of ZSM-5, Beta or L-type zeolite molecular sieves, and the Si / Al ratio of the zeolite molecular sieve is 50-300.

5. The method for preparing 1,1-difluoroethylene by resource utilization of 1,1-difluoro-2-chloroethane according to claim 3 or 4, characterized in that: The counter cation is selected from K + 、Na + , Ca 2+ 、Ba 2+ 、H + At least one of .

6. The method for preparing 1,1-difluoroethylene by resource utilization of 1,1-difluoro-2-chloroethane according to claim 1, characterized in that: The mixture contains at least 80% by mass of 1,1-difluoro-2-chloroethane, and the remainder is at least one of dichlorodifluoroethylene, monochlorodifluoroethylene, and dichlorofluoroethane.

7. The method for preparing 1,1-difluoroethylene by resource utilization of 1,1-difluoro-2-chloroethane according to claim 6, characterized in that: The mixture contains 90 to 100% by mass of 1,1-difluoro-2-chloroethane.

8. The method for preparing 1,1-difluoroethylene by resource utilization of 1,1-difluoro-2-chloroethane according to any one of claims 1 to 7, characterized in that: The mixture is preheated and vaporized in a preheater before reacting, and the preheating temperature is 100-300°C.

9. The method for preparing 1,1-difluoroethylene by resource utilization of 1,1-difluoro-2-chloroethane according to claim 8, characterized in that: The modified molecular sieve is activated and then reacted, and the activation step includes: A1. The modified molecular sieve was calcined under a nitrogen atmosphere at a temperature of 400 to 600°C for 2 to 5 hours; A2. A preheated mixture containing 1,1-difluoro-2-chloroethane is introduced and maintained at 200-400°C for 0.5-2 hours. The temperature is then raised to 300-500°C and activation is continued for 0.5-2 hours to obtain an activated modified molecular sieve for catalytic cracking reaction.

10. The method for preparing 1,1-difluoroethylene by resource utilization of 1,1-difluoro-2-chloroethane according to claim 9, characterized in that: The reaction temperature of the catalytic cracking reaction is 300-500℃, and the space velocity is 100-1000h -1 , reaction pressure 0.1~1.0MPa.

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