Process for the preparation of 1,1,1-trifluoroethane

Abstract

The application provides a preparation method of 1,1,1-trifluoroethane (HFC-143a), which is prepared by liquid phase fluorination reaction of hydrogen fluoride and HCFC-142b in the presence of a composite catalyst, wherein the reaction temperature is 10-50 DEG C, preferably 10-40 DEG C, the weight ratio of HF to HCFC-142b is 1:4-5.5, preferably 1:4.5-5, the composite catalyst is a mixture of antimony halide and rare earth oxide, the rare earth metal is preferably neodymium or yttrium, and the molar ratio of antimony halide to rare earth oxide is 20-200:1, preferably 20-150:1. According to the method, the conversion rate of HFC-143a prepared by liquid phase fluorination of HF and HCFC-142b can reach more than 99.5%, and the conversion rate can still be kept more than 98% after 1000h continuous reaction, thereby prolonging the service life of the catalyst.

Description

Technical Field

[0001] This invention relates to a method for preparing 1,1,1-trifluoroethane (HFC-143a), specifically a method for preparing HFC-143a by a gas-phase fluorination reaction. Background Technology

[0002] HFC-143a is a major raw material for refrigerants, and 1,1,1-trifluoroethane is used in refrigerants, foaming agents, propellants, cleaning agents, and other fields. It is well known in the art that 1,1,1-trifluoroethane has no ozone-depleting effect (its ozone depletion potential (ODP) is 0). In particular, mixtures with other substances are used to replace F22 in refrigerators, air conditioners, and other applications. Currently, there are two main preparation methods: liquid-phase and gas-phase. The liquid-phase method inevitably causes corrosion to equipment; therefore, the gas-phase method is relatively less corrosive than the liquid-phase method.

[0003] There are already several gas-phase methods for preparing HFC-143a.

[0004] CN100526271C protects a method for preparing at least one hydrofluorocarbon selected from difluoromethane (HFC-32), 1,1,1-trifluoroethane (HFC-143a), and 1,1-difluoroethane (HFC-152a): 1. providing a reaction vessel; 2. providing activated carbon impregnated with a strong Lewis acid fluorination catalyst in the reaction vessel, wherein the strong Lewis acid catalyst is selected from halides of As, Sb, Al, Tl, In, V, Nb, Ta, Ti, Zr, and Hf; 3. passing the activated carbon impregnated with the strong Lewis acid fluorination catalyst through anhydrous hydrogen fluoride gas and... 4. In a reaction vessel containing the activated catalyst, hydrogen fluoride is contacted in vapor form with one or more halogenated hydrocarbons selected from chlorofluoromethane, dichloromethane, 1,1,1-trichloroethane, vinyl chloride, 1,1-dichloroethylene, 1,2-dichloroethylene, 1,2-dichloroethane, and 1,1-dichloroethane at a certain temperature for a certain period of time to prepare a product stream containing hydrofluorocarbon products corresponding to the chlorinated hydrocarbon reactants, as well as one or more of hydrogen chloride, unreacted chlorinated hydrocarbon reactants, underfluorinated intermediates, and unreacted hydrogen fluoride; 5. The hydrofluorocarbon products are separated from the product stream. This method is less corrosive and has better selectivity.

[0005] CN101028990B protects a method for preparing 1,1,1-trifluoroethane, using hydrogen fluoride and 1,1,1-trichloroethane as raw materials, in the presence of a chromium-based fluorination catalyst, via a gas-phase fluorination reaction to prepare 1,1,1-trifluoroethane. The reaction temperature is 150℃~280℃, the contact time is 2 seconds~15 seconds, the molar ratio of hydrogen fluoride to 1,1,1-trichloroethane is 3~10:1, and the chromium-based fluorination catalyst is either antimony trioxide bulk or supported catalyst, with aluminum fluoride or magnesium fluoride as the support. This method addresses the problems of severe reactor corrosion and numerous byproducts in existing liquid-phase methods for preparing 1,1,1-trifluoroethane. It provides a preparation method with a low reaction temperature, long catalyst lifetime, and high yield.

[0006] CN1279008C protects a method for preparing 1,1,1-trifluoroethane, which involves vaporizing vinylidene chloride and anhydrous hydrofluoric acid and then mixing them for a gas-phase fluorination reaction under the action of a chromium-based fluorination catalyst to obtain 1,1,1-trifluoroethane. The reaction temperature is 140–380℃, the reaction pressure is 0.3–1.8 MPa, the reactor space velocity is 300 h⁻¹–2200 h⁻¹, and the ratio of anhydrous hydrofluoric acid to vinylidene chloride is 4:1–30:1. The conversion rate and selectivity of the reaction both reach 99%.

[0007] While gas-phase methods have been studied, they still suffer from drawbacks such as high reaction temperatures and stringent reaction conditions. Liquid-phase methods, on the other hand, involve significantly lower reaction temperatures than gas-phase methods. Improving the reaction lifetime of the catalyst system could potentially enhance the convenience of industrial production. Summary of the Invention

[0008] This invention provides a liquid-phase synthesis method for preparing HFC-143a with low reaction temperature, long catalyst lifetime, and high yield.

[0009] An unexpected discovery was made that, in the presence of a composite catalyst, hydrogen fluoride and 1,1-difluoro-1-chloroethane HCFC-142b undergo a liquid-phase fluorination reaction at 10-50°C, and HFC-143a can be obtained in high yield with a continuous reaction time of 1000 h.

[0010] Rare earth metals, also known as rare earth elements, are a collective term for 17 elements in Group IIIB of the periodic table, including scandium, yttrium, and the lanthanides, commonly represented by R or RE. From the discovery of the first rare earth element, yttrium, in 1794, to the discovery of promethium in nature in 1972, it took 178 years for all 17 rare earth elements to be found in nature. The luster of rare earth metals is between that of silver and iron. Rare earth metals are highly chemically reactive. The atomic structure of rare earth elements can be represented as 4fx5d16s2, where x ranges from 0 to 14. When rare earth elements transform from metals into ions, the outer edge of the 4f orbital still surrounds a 5s25p6 electron cloud. They lose a 6s2 electron and one electron from either the 5d1 or 4f orbital, forming a 4fx5s25p6 electronic structure. In rare earth metals, 6s electrons and 5d electrons form the conduction band, while 4f electrons are localized in the atom. This localization and incomplete filling of 4f electrons will be reflected in their various physical properties.

[0011] Rare earth element oxides refer to the oxides of 15 lanthanide elements with atomic numbers 57 to 71 in the periodic table, as well as the oxides of scandium (Sc) and yttrium (Y), which have similar chemical properties to the lanthanides, making a total of 17 elements.

[0012] The research and development of rare earth catalytic materials have provided an effective way for the high-quality and efficient utilization of abundant light rare earth elements such as La and Ce. Rare earth elements have characteristics such as unfilled 4f orbitals and lanthanide contraction, which give them unique catalytic performance when used as active components or supports for catalysts.

[0013] This invention discloses a method for preparing HFC-143a, using hydrogen fluoride and HCFC-142b as raw materials, and preparing HFC-143a through a liquid-phase fluorination reaction in the presence of a composite catalyst. The weight ratio of hydrogen fluoride to HCFC-142b is 1:4-5.5. The composite catalyst is a mixture of antimony halide and rare earth oxide Ln2O3, where Ln represents a rare earth metal. The molar ratio of antimony halide to rare earth oxide is 20-200:1, and the rare earth metal is preferably a lanthanide rare earth metal. The mass ratio of HF to the composite catalyst is 5-25:1.

[0014] Preferably, the reaction temperature is 10-50℃. More preferably, the reaction temperature is 10-40℃.

[0015] The preferred mass ratio of hydrogen fluoride to HCFC-142b is 1:4.5-5.

[0016] Preferably, the rare earth metal is neodymium or yttrium.

[0017] Preferably, the molar ratio of antimony halide to rare earth oxide is 20-150:1.

[0018] Preferably, the reaction pressure is 0.3-1.0 MPa. More preferably, the reaction pressure is 0.3-0.5 MPa.

[0019] Preferably, the antimony halide is antimony pentahalide or a fluorinated chloride of pentavalent antimony.

[0020] According to the method of the present invention, HFC-143a is prepared by liquid-phase fluorination of HF and HCFC-142b with a conversion rate of over 99.5%, and the conversion rate can still be maintained at over 98% after continuous reaction for 1000 hours, thus extending the service life of the catalyst. Detailed Implementation

[0021] Example 1

[0022] 25 kg of HF and 1 kg of composite catalyst were added to a conventional fluorination reactor equipped with a condenser. Then, HF and HCFC-142b were continuously introduced at room temperature, with the weight ratio of HF to HCFC-142b controlled at 1:5. When the pressure reached 0.3 MPa, the reaction gas was continuously discharged through the condenser while maintaining the reaction pressure and temperature at 10 °C. The discharged reaction gas was washed to remove HCl and HF, and the composition of organic matter was analyzed by gas chromatography. The reaction results at different times are shown in Table 1.

[0023] The composite catalyst is a mixture of antimony pentachloride and neodymium oxide in a molar ratio of 50:1.

[0024] Example 2

[0025] The composite catalyst is a mixture of antimony pentachloride and neodymium oxide in a molar ratio of 150:1, and the other aspects are the same as in Example 1.

[0026] Example 3

[0027] The mass ratio of hydrogen fluoride to HCFC-142b was 1:4, and other parameters were the same as in Example 1.

[0028] Example 4

[0029] The rare earth metal is yttrium, and the other elements are the same as in Example 1.

[0030] Comparative Example 1

[0031] The catalyst was only antimony pentachloride, and everything else was the same as in Example 1.

[0032] Comparative Example 2

[0033] The catalyst was only neodymium oxide, and the rest was the same as in Example 1.

[0034] Table 1. Results of reactions in the examples and comparative examples.

[0035]

Claims

1. The use of antimony pentachloride and neodymium oxide as a composite catalyst in the preparation of 1,1,1-trifluoroethane to maintain a high yield of continuous reaction for 1000 h. 25 kg of HF and 1 kg of the composite catalyst are added to a conventional fluorination reactor equipped with a condenser. Then, HF and HCFC-142b are continuously introduced at room temperature, controlling the weight ratio of HF to HCFC-142b to be 1:

5. When the pressure reaches 0.3 MPa, the reaction gas is continuously discharged through the condenser while maintaining the reaction pressure. The temperature is controlled at 10 °C. The discharged reaction gas is washed to remove HCl and HF, and the organic composition is analyzed by gas chromatography. The composite catalyst is a mixture of antimony pentachloride and neodymium oxide in a molar ratio of 50:1; The conversion rate of HCFC-142b was 99.6% after 100 hours. The conversion rate of HCFC-142b was 99.5% after 500 hours; After 1000 hours, the conversion rate of HCFC-142b was 98.5%.

2. The application of antimony pentachloride and yttrium oxide as a composite catalyst in the preparation of 1,1,1-trifluoroethane to maintain a high yield of continuous reaction for 1000 h. 25 kg of HF and 1 kg of the composite catalyst are added to a conventional fluorination reactor equipped with a condenser. Then, HF and HCFC-142b are continuously introduced at room temperature, controlling the weight ratio of HF to HCFC-142b to be 1:

5. When the pressure reaches 0.3 MPa, the reaction gas is continuously discharged through the condenser while maintaining the reaction pressure. The temperature is controlled at 10 °C. The discharged reaction gas is washed to remove HCl and HF, and the organic composition is analyzed using a gas chromatograph. The composite catalyst is a mixture of antimony pentachloride and yttrium oxide in a molar ratio of 50:1; The conversion rate of HCFC-142b was 99.6% after 100 hours. The conversion rate of HCFC-142b was 99.6% after 500 hours; After 1000 hours, the conversion rate of HCFC-142b was 98.5%.

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