A mixed crystal form AlF3 catalyst and its application in the fluorine-chlorine exchange reaction

Abstract

The present invention discloses a mixed crystalline form AlF3 catalyst and its application in the fluorine-chlorine exchange reaction. The mixed crystalline form AlF3 catalyst comprises: 30-70% of β-AlF3, 10-40% of θ-AlF3 and 10-50% of α-AlF3. When the mixed crystalline form AlF3 catalyst is used in the fluorine-chlorine exchange reaction of trifluoromethane and chloroform, it has good catalytic activity and stability, high raw material conversion rate and long catalyst life, and is suitable for industrial application.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and particularly to a mixed-crystalline AlF3 catalyst and its application in the fluorine-chlorine exchange reaction. Background Art

[0002] Trifluoromethane (CHF3, HFC-23) is an inevitable by-product in the industrial production of dichlorofluoromethane (CHClF2, HFC-22), and its global warming potential is about 14,800 times that of carbon dioxide. At present, the main way to reduce the emission of CHF3 is through high-temperature incineration (above 1200 °C). However, the incineration treatment cost is high and there is a waste of resources. Therefore, the resource conversion of trifluoromethane is of great significance.

[0003] US Patent US2003 / 0166981A discloses a method for the pyrolysis reaction of trifluoromethane and HCFC-22 to produce pentafluoroethane, heptafluoropropane, tetrafluoroethylene and hexafluoropropene at a temperature of 690 - 775 °C using gold as a catalyst. However, the catalyst required by this method is too expensive, and the reaction temperature is relatively high, resulting in excessive energy consumption.

[0004] Patent EP2172441A discloses a method for preparing CHClF2 by the fluorine-chlorine exchange reaction of trifluoromethane and chloroform. The reaction mainly uses substances with Lewis acid such as fluorides and fluoroxides of Mg, Al, Zn, Cr as catalysts. However, the yield of the target product is low, and the catalyst is prone to carbon deposition and deactivation.

[0005] Patent CN112979410A discloses that under the catalytic action of a main catalyst and a metal oxide, trifluoromethane and a halogenated hydrocarbon undergo a fluorine-chlorine exchange reaction. The main catalyst is a chromium, aluminum, magnesium-based catalyst or a chromium, aluminum, magnesium supported on activated carbon / graphite catalyst, and the metal oxide is selected from at least one metal oxide of K, Na, Fe, Co, Cu, Ni, Zn or Ti. This catalyst is suitable for general fluorine-chlorine exchange reactions, but has low reactivity when used in the fluorine-chlorine exchange reaction of trifluoromethane and is difficult to activate stable CHF3.

[0006] Patent CN109772377A discloses a catalyst for the fluorine-chlorine exchange reaction and a preparation method. By adding a surfactant during the preparation process, the prepared catalyst has a multi-sided prismatic structure. When used in the fluorine-chlorine exchange reaction of trifluoromethane, it has high selectivity, high conversion rate and good stability. However, the preparation method of this catalyst is complex and costly, making it difficult to achieve industrial application.

[0007] Patent CN104628513A discloses a method for converting trifluoromethane and chloroform into HCFC-22 under the action of a Lewis acid catalyst. Although this method realizes the conversion of trifluoromethane at a relatively low temperature (below 400°C), due to the use of a strong Lewis acid catalyst, there is an obvious deactivation phenomenon of the catalyst caused by carbon deposition and sintering during the reaction process.

[0008] Therefore, it is of great significance to study a catalyst that takes into account both activity and stability. Summary of the Invention

[0009] To solve the above technical problems, the present invention proposes a mixed-crystalline AlF3 catalyst that simultaneously has high catalytic activity and catalyst stability and its application in the fluorine-chlorine exchange reaction.

[0010] The object of the present invention is achieved by the following technical solutions:

[0011] A mixed-crystalline AlF3 catalyst, the mixed-crystalline AlF3 catalyst comprises 30-70% of β-AlF3, 10-40% of θ-AlF3 and 10-50% of α-AlF3.

[0012] Preferably, the mixed-crystalline AlF3 catalyst comprises: 40-60% of β-AlF3, 20-30% of θ-AlF3 and 20-40% of α-AlF3.

[0013] The inventor of the present invention has found through research that α-AlF3 has a close-packed structure, and the Al atoms with L acid active sites are tightly surrounded by F atoms, shielding some of the active sites, with poor reaction activity but the best stability; the structure of β-AlF3 is relatively open, with more exposed Al atoms. Theoretically, it is more conducive to the adsorption of CHCl3 than α-AlF3, with better reaction activity and the second-best stability; the structure of θ-AlF3 is the most open, with more exposed Al atoms, more exposed Al atoms than β-AlF3 and α-AlF3. Therefore, the reaction activity is the best, but the stability is the worst. Through the synergistic effect of the three different crystal forms of α-AlF3, β-AlF3 and θ-AlF3, the phenomena of catalyst sintering and carbon deposition can be effectively reduced, while taking into account high catalytic activity and stability.

[0014] Within the scope of the distribution of different crystal forms of AlF3 in the present invention, when it is used in the fluorine-chlorine exchange reaction, it can have good catalytic activity and catalyst stability.

[0015] The present invention also provides an application of a mixed-crystalline AlF3 catalyst in the fluorine-chlorine exchange reaction. In particular, using trifluoromethane and chloroform as raw materials and any one of the above-mentioned mixed-crystalline AlF3 as a catalyst, dichlorofluoromethane and chlorodifluoromethane are obtained through the fluorine-chlorine exchange reaction.

[0016] The molar ratio of trifluoromethane to chloroform is 1:1 to 1:5, the reaction temperature is 300 to 400 °C, and the reaction pressure is 0 to 0.50 MPa. Preferably, the molar ratio of trifluoromethane to chloroform is 1:2 to 1:3, the reaction temperature is 320 to 380 °C, and the reaction pressure is 0.1 to 0.40 MPa.

[0017] The present invention also provides a method for preparing the mixed crystal form AlF3 catalyst described above, and the preparation method includes: stirring and dissolving an aluminum source and a fluorine-containing polymer in a mixed solution of a solvent and a surfactant to form a gel, then drying to remove the solvent, and subjecting the dried solid to a roasting treatment in a muffle furnace roasting atmosphere, and obtaining the mixed crystal form AlF3 catalyst after cooling.

[0018] The aluminum source is selected from at least one of aluminum nitrate, aluminum isopropoxide, aluminum hydroxide, aluminum chloride hexahydrate, aluminum sulfate, or aluminum acetate.

[0019] The fluorine-containing polymer is selected from at least one of polyvinylidene fluoride, polytrifluorochloroethylene, polyvinyl fluoride, or polytetrafluoroethylene, and preferably polyvinylidene fluoride.

[0020] The solvent is at least one of tetrahydrofuran, propylene glycol, isopropyl acetate, dimethyl sulfoxide, or dimethylformamide.

[0021] The surfactant is at least one of polyvinyl alcohol, polyethylene glycol, or TX-100.

[0022] The volume ratio of the surfactant to the solvent is 1:4 to 1:10.

[0023] The mass ratio of the aluminum source to the fluorine-containing polymer is 1:2.5 to 1:3.5. Under this ratio, an AlF3 catalyst can be prepared, including: 40 to 60% of β-AlF3, 20 to 30% of θ-AlF3, and 20 to 40% of α-AlF3.

[0024] Furthermore, the aluminum source and the fluorine-containing polymer are stirred and dissolved in the mixed solution of the solvent and the surfactant at a temperature of 60 to 90 °C. The drying temperature after forming the gel is 100 to 180 °C, preferably 120 to 160 °C. The roasting atmosphere is at least one of air, oxygen, or nitrogen, the roasting heating rate is 1 to 5 °C / min, the roasting temperature is 300 to 450 °C, and the roasting time is 5 to 15 h.

[0025] Specifically, the preparation of the mixed crystal form AlF3 catalyst includes the following steps:

[0026] Dissolve the aluminum source in a mixed solution of a solvent and a surfactant under heating and stirring conditions. Then, add a fluorine-containing polymer as a fluorinating agent to this solution and stir until completely dissolved to form a gel. Next, place the gel in a drying oven to dry and remove the organic solvent. The completely dried solid is calcined in a muffle furnace under a calcination atmosphere, and finally cooled naturally to obtain a mixed crystal form AlF3 catalyst.

[0027] Under the action of the surfactant in the present invention, by adjusting the mass ratio of the aluminum source and the fluorine-containing polymer, the composition and content of different crystal forms can be effectively adjusted. During the calcination process, the aluminum source decomposes to generate Al2O3, the solvent adsorbed on the surface of the aluminum species decomposes, and at the same time, part of the fluorine-containing polymer decomposes and releases HF. HF gradually fluorinates Al2O3 into AlF3, and the remaining fluorine-containing polymer in the sample plays a role in restricting the growth of crystals and particles. As the mass ratio of the aluminum source to the fluorine-containing polymer increases from low to high, more and more fluorinating agents are left in the sample to interfere with the growth of AlF3 crystals, so different crystal forms of AlF3 are formed.

[0028] Compared with the prior art, the beneficial effects of the present invention include:

[0029] Under the action of the surfactant in the present invention, through the adjustment of the ratio of the aluminum source and the fluorine-containing polymer, as well as steps such as drying and calcination, a mixed crystal form AlF3 catalyst with a specific content distribution can be prepared. It can avoid the problems that the existing α-AlF3 has good stability but low activity, while β-AlF3 or θ-AlF3 has high activity but poor stability. When it is used in the fluorochlorination exchange reaction of trifluoromethane and trichloromethane, it not only has a high trifluoromethane conversion rate, but also has a long catalyst life and is suitable for industrial application. Description of the Drawings

[0030] Figure 1 The XRD diagrams of the mixed crystal form AlF3 catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention are given;

[0031] Figure 2 The XPS Al2p fine spectrum diagram of the mixed crystal form AlF3 catalyst prepared in Example 1 of the present invention is given. Detailed Embodiments

[0032] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternative, improved, and equivalent solutions that may be included within the scope of the claims.

[0033] Example 1

[0034] Dissolve 20 g of aluminum nitrate in 40 mL of tetrahydrofuran and 8 mL of polyvinyl alcohol, add 60 g of polyvinylidene fluoride, stir in a water bath at 80 °C until it becomes gel-like, and dry it by foaming at 150 °C for 3 h. Place the gel in a muffle furnace, heat it to 380 °C at a heating rate of 3 °C / min and hold for 10 h, then cool it to room temperature to obtain a mixed-crystalline AlF3 catalyst, denoted as Cat 1. After tableting at 15 MPa, crush it into 10-20 mesh particles for standby.

[0035] Figure 1 and Figure 2 gives the XRD and XPS Al2p fine spectrum characterization results of this catalyst. It can be seen from Figure 2 that by calculating the area of each spectral peak, in the mixed-crystalline AlF3 catalyst, 50% is β-AlF3, 24% is θ-AlF3, and 26% is α-AlF3.

[0036] Example 2

[0037] The operation of this example is the same as that of Example 1, except that: aluminum isopropoxide is used as the aluminum source, and the dosage remains unchanged. In the prepared mixed-crystalline AlF3 catalyst, 45% is β-AlF3, 24% is θ-AlF3, and 31% is α-AlF3, denoted as Cat 2.

[0038] Example 3

[0039] The operation of this example is the same as that of Example 1, except that: aluminum hydroxide is used as the aluminum source, and the dosage remains unchanged. In the prepared mixed-crystalline AlF3 catalyst, 41% is β-AlF3, 21% is θ-AlF3, and 38% is α-AlF3, denoted as Cat 3.

[0040] Comparative Example 1

[0041] The operation of this example is the same as that of Example 1, except that: the dosage of polyvinylidene fluoride (fluorinating agent) is increased to 100 g, and the mass ratio of aluminum source to fluorinating agent is 1:5. In the prepared mixed-crystalline AlF3 catalyst, 40% is β-AlF3 and 60% is α-AlF3, denoted as Cat B1.

[0042] Comparative Example 2

[0043] The operation of this example is the same as that of Example 1, except that: the dosage of polyvinylidene fluoride (fluorinating agent) is reduced to 40 g, and the mass ratio of aluminum source to fluorinating agent is 1:2. In the prepared mixed-crystalline AlF3 catalyst, 80% is β-AlF3 and 20% is θ-AlF3, denoted as Cat B2.

[0044] Comparative Example 3

[0045] The operation of this example is the same as that of Example 1, except that: the dosage of polyvinylidene fluoride (fluorinating agent) is increased to 160 g, and the mass ratio of aluminum source to fluorinating agent is 1:8. In the prepared mixed-crystalline AlF3 catalyst, the content of α-AlF3 reaches more than 98%, denoted as Cat B3.

[0046] Comparative Example 4

[0047] The operation of this example is the same as that of Example 1, except that: the dosage of polyvinylidene fluoride (fluorinating agent) is increased to 80 g, and the mass ratio of aluminum source to fluorinating agent is 1:4. In the prepared mixed-crystalline AlF3 catalyst, the content of β-AlF3 reaches more than 98%, denoted as Cat B4.

[0048] Comparative Example 5

[0049] The operation of this example is the same as that of Example 1, except that: the dosage of polyvinylidene fluoride (fluorinating agent) is reduced to 20 g, and the mass ratio of aluminum source to fluorinating agent is 1:1. In the prepared mixed-crystalline AlF3 catalyst, the content of θ-crystalline form reaches more than 98%, denoted as Cat B5.

[0050] Comparative Example 6

[0051] The operation of this example is the same as that of Example 1, except that: the surfactant polyvinyl alcohol is not added. In the prepared mixed-crystalline AlF3 catalyst, 25% is β-AlF3, 5% is θ-AlF3, and 70% is α-AlF3, denoted as Cat B6.

[0052] Example 4

[0053] This example provides a method for the resource utilization of trifluoromethane, including:

[0054] Using CHF3 and CHCl3 as raw materials, a fluoro-chloro exchange reaction is carried out under the action of Cat1 - Cat3, CatB1 - CatB6. The specific steps are as follows:

[0055] Load 8 mL of the catalyst into a fixed-bed reactor, which is a stainless-steel tube with an inner diameter of 20 mm and a length of 800 mm for the tubular reactor. The reaction temperature is 360 °C, the pressure is 0.1 MPa, the molar ratio of trifluoromethane to trichloromethane is 1:2, and the residence time is 6 s. Qualitative and quantitative analysis is carried out on the reaction products, and the analysis results are shown in Table 1 below.

[0056] Table 1 also gives the results of the activity evaluation of Cat1 - Cat3, CatB1 - CatB6 under the above conditions.

[0057] Table 1 Catalyst Reaction Evaluation Results of Each Example

[0058]

[0059]

[0060] As can be seen from Table 1 above, for the single or two mixed crystal forms of the AlF3 catalyst (Comparative Examples 3 to 5), when the CHF3 conversion rate is relatively good, the catalyst stability is poor; when the catalyst stability is good, the CHF3 conversion rate is low. Without using a surfactant (Comparative Example 6), the content of α-AlF3 in the mixed crystal form is relatively high, the catalyst stability is good, but the CHF3 conversion rate is low.

[0061] When the mixed crystal form AlF3 catalyst provided by the method of the present invention is used in the fluorochlorination exchange reaction of trifluoromethane and trichloromethane (Examples 1 to 3), a mixed crystal form AlF3 within a certain ratio range can be prepared. The three crystal forms play a synergistic role. While ensuring a large number of active sites, it can effectively inhibit the phenomena of catalyst sintering and carbon deposition, achieving the effect of taking into account both good catalyst activity and stability, and is suitable for industrial production scale-up.

Claims

1. A mixed crystal form AlF3 catalyst, characterized in that: The mixed crystalline form AlF₃ catalyst comprises: 30 - 70% of β-AlF₃, 10 - 40% of θ-AlF₃ and 10 - 50% of α-AlF₃.

2. The mixed crystalline form AlF3 catalyst according to claim 1, wherein: The mixed crystalline form AlF₃ catalyst is 40 - 60% of β-AlF₃, 20 - 30% of θ-AlF₃ and 20 - 40% of α-AlF₃.

3. Application of a mixed crystal form AlF3 catalyst in a fluorine-chlorine exchange reaction, characterized in that: Using trifluoromethane and chloroform as raw materials, and the mixed crystalline form AlF₃ described in Claim 1 or 2 as the catalyst, difluorochloromethane and chlorodifluoromethane are obtained through a fluorine-chlorine exchange reaction.

4. Use of the mixed crystalline form AlF3 catalyst according to claim 3 in the fluorine-chlorine exchange reaction, characterized in that: The molar ratio of the trifluoromethane to the chloroform is 1:1 - 1:5, the reaction temperature is 300 - 400 °C, and the reaction pressure is 0 - 0.50 MPa.

5. The preparation method of the mixed crystal form AlF3 catalyst according to claim 1 or 2, characterized in that: The aluminum source and the fluorine-containing polymer are stirred and dissolved in a mixed solution of a solvent and a surfactant to form a gel, and then the solvent is removed by drying. The dried solid is calcined in a muffle furnace roasting atmosphere, and the mixed crystalline form AlF₃ catalyst is obtained after cooling; The fluorine-containing polymer is selected from at least one of polyvinylidene fluoride, polychlorotrifluoroethylene, polyvinyl fluoride or polytetrafluoroethylene; the mass ratio of the aluminum source to the fluorine-containing polymer is 1:2.5 - 1:3.5; The solvent is at least one of tetrahydrofuran, propylene glycol, isopropyl acetate, dimethyl sulfoxide or dimethylformamide; the surfactant is at least one of polyvinyl alcohol, polyethylene glycol or TX-100; the volume ratio of the surfactant to the solvent is 1:4 - 1:10; The roasting atmosphere is at least one of air, oxygen or nitrogen, the roasting heating rate is 1 - 5 °C / min, the roasting temperature is 300 - 450 °C, and the roasting time is 5 - 15 h.

6. The preparation method of the mixed crystal form AlF3 catalyst according to claim 5, characterized in that: The aluminum source is selected from at least one of aluminum nitrate, aluminum isopropoxide, aluminum hydroxide, aluminum chloride hexahydrate, aluminum sulfate or aluminum acetate.

7. The preparation method of the mixed crystal form AlF3 catalyst according to claim 5, characterized in that: The aluminum source and the fluorine-containing polymer are stirred and dissolved in the mixed solution of the solvent and the surfactant at a temperature of 60 - 90 °C.

8. The preparation method of the mixed crystal form AlF3 catalyst according to claim 5, characterized in that: The drying temperature after forming the gel is 100 - 180 °C.

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