Highly Selective Dehydrochlorination of 1,1,1,2‐Tetrafluoro‐2‐chloropropane to 2,3,3,3‐Tetrafluoropropene over Alkali Metal Fluoride Modified MgO Catalysts

Abstract

Gas‐phase selective dehydrochlorination of 1,1,1,2‐tetrafluoro‐2‐chloropropane (HCFC‐244bb) to 2,3,3,3‐tetrafluoropropene was investigated over various K and Cs halides modified MgO catalysts. The reaction proceeded in the absence of additives such as air and HF. High dehydrochlorination selectivity (>97 %) with moderate activity (>14 μmol h−1 m−2) was achieved on KF and CsF modified MgO catalysts, in which the dehydrofluorination process was inhibited. Compared with alkali metal modified MgO, the dehydrofluorination product, 2‐chloro‐3,3,3‐trifluoropropene increased over Zr and Al modified MgO and fluorinated MgO catalysts (sel. of 20–76 %). XRD and energy‐dispersive‐spectrometry results revealed that surface chlorination and fluorination occurred on the MgO‐based catalysts during the reaction. Introducing alkali metal fluorides into the catalyst can reduce the fluorination of MgO and the deposition of chlorine species, thus improving the dehydrochlorination activity and stability of MgO. The NH3 temperature‐programmed desorption (TPD) results show that decreasing the surface acidity of catalyst benefits the dehydrochlorination of HCFC‐244bb, whereas the relationship between the basicity of the catalyst and its dehydrohalogenation behavior is complicated as shown by the CO2 TPD results. According to the hard–soft acid–base principle, the dehydrohalogenation selectivity can be correlated with the surface chemical hardness of the catalyst.

Fluorocarbon Refrigerants and their Syntheses: Past to Present

“…887 Lu et al investigated the thermal dehydrochlorination of 244bb over various metal oxide catalysts, reporting that this reaction is an endothermic equilibrium (ΔH = +17 kcal/mol, ΔG = +4.4 kcal/mol), and thus favored by increasing temperature. 888 The dehydrofluorination is slightly less endothermic (ΔH = +16.2 kcal/mol, ΔG = +3.8 kcal/mol). Furthermore, on the basis of these figures, the theoretical conversion should be nearquantitative at >170 °C, a reckoning not at all borne out empirically.…”

Manufacture of hydrofluorocarbons and hydrofluoroolefins as the CFCs-alternatives: from fundamental of catalytic reaction to commercialization

“…第三步反应为HCFC-244bb选择性脱HCl 生成目标产物HFO-1234yf. HCFC-244bb分子中α碳原 子上同时具有Cl、F两个离去基团, 热力学计算表明, 气相脱HCl与脱HF的反应能垒接近(图3), 难以实现选 择性脱HCl [36] . HCFC-244bb脱HCl还是强吸热反应, 在 高温(大于450℃)下才可获得一定的转化率.…”

“…http://engine.scichina.com/doi/10.1360/N032017-00105 图 2 TCP气相氟化合成HCFO-1233xf反应历程 [34] 图 3 HCFC-244bb气相脱卤化氢反应(网络版彩图) [36]…”

“…图 4 F-Cr2O3催化剂表面Cr2p结合能谱图 [54] 图 5 Cr/AlF3催化剂表面活性物种示意图 [55] HF反应, 碱性位发生脱HCl反应. 据此构建了以碱中 心为活性位的Mg基催化剂, 实现了气相选择性脱HCl 制备HFO-1234yf [36] .…”

Facile Preparation of BaClxFy for the Catalytic Dehydrochlorination of 1-Chloro-1,1-Difluoroethane to Vinylidene Fluoride

“…At present, in industry, VDF is usually produced via the dehydrochlorination of 1,1-difluoro-1-chloroethane (HCFC-142b) at reaction temperatures above 650 • C [3,4]. Dehydrochlorination is an efficient route for the preparation of 1, 1-dichloroethylene (VDC), vinyl chloride monomer (VCM), 2,3,3,3-tetrafluoropropene (HFO-1234yf), and ethylene oxychlorination [5][6][7][8]. As the dehydrochlorination of HCFC-142b is a highly endothermic reaction, very long reaction tubes are adopted to supply the reaction heat.…”