A BaF(p-BDC)0.5catalyst was prepared by solid state reaction at room temperature with Ba(OH)2as precursor, NH4F as F source, and H2(p-BDC) as organic ligand. The calcined samples were used as catalysts for dehydrochlorination of 1-chloro-1,1-difluoroethane to generate vinylidene fluoride (VDF) at 350 °C. Commercial production of VDF is carried out at 600–700 °C. Clearly, pyrolysis of the BaF(p-BDC)0.5catalyst provided a promising way to prepare VDF at low temperatures. Prior to calcination, the activity of the BaF(p-BDC)0.5catalyst was low. Following calcination at high temperatures, BaF(p-BDC)0.5decomposed to BaF2and BaCO3, and then the catalyst was chlorinated and fluorinated to BaClF, which showed high activity and stable VDF selectivity for dehydrochlorination of 1-Chloro-1,1-Difluoroethane to VDF.Keywords:barium fluoride;catalytic pyrolysis;dehydrochlorination;1-chloro-1,1-difluoroethane;vinylidene fluoride
Wei Yu,Wenfeng Han,Yongnan Liu,Jiaqin Lu,Hong Yang,Bing Liu,Haodong Tang,Aimin Chen,Ying Li
BaClxFyas well as BaF2and BaClF catalysts were prepared by solid-state reaction at room temperature with Ba(OH)2as the precursor and NH4F/NH4Cl as the F and Cl sources. The catalysts were applied for the dehydrochlorination of 1-chloro-1,1-difluoroethane to vinylidene fluoride at 350 °C. The industrial manufacture of vinylidene fluoride (VDF) is carried out at 600–700 °C, whereas the BaClxFycatalysts provided a promising pathway to produce VDF at much lower temperatures. Unfortunately, the selectivity of VDF over BaF2decreased from 94% to 84% along with the deactivation of the BaF2catalyst monotonically. In the presence of small amounts of Cl in BaF2, stabilized selectivity was achieved. Over BaCl0.05F0.95, BaCl0.1F0.9and BaCl0.25F0.75, no decrease in VDF selectivity was observed. Clearly, the presence of small amounts Cl during solid-state preparation inhibited the growth of BaF2crystalline significantly. Far smaller particles were achieved. The particle size, or more precisely, the crystal size of the barium catalyst played a major role in the catalytic performance. In addition to the crystal growth, the presence of small amounts of Cl during catalyst preparation changed the chemical state of Ba, and therefore the adsorption and activation of the C–Cl bond for HCFC-142b were altered.Keywords:barium chlorofluoride;catalytic pyrolysis;barium fluoride;dehydrochlorination;1-chloro-1,1-difluoroethane;vinylidene fluoride
Uniform, free-standing and cubic SrF2 microparticles were successfully fabricated by a facile hydrothermal method with ethylenediaminetetraacetic acid (EDTA) as the chelating agent. The influences of preparation conditions, such as the pH value, amount of EDTA and hydrothermal time, on the formation of SrF2 crystals were investigated. The formation mechanism of cubic SrF2 particles was proposed based on the experimental results. Following calcination in air at 500 °C, SrF2 particles were evaluated as the catalyst for the pyrolysis of 1-chloro-1,1-difluoroethane (HCFC-142b, CH3CClF2) to vinylidene fluoride (VDF, CH2CF2) at 350 °C and a space velocity of 600 h−1. The results indicate that SrF2 cubes exhibit high catalytic activity with a HCFC-142b conversion of about 70% and a selectivity to VDF of 80–87%. No significant deactivation was observed within the time on stream of 30 h. With the reaction temperature increased to 450 °C, the conversion of HCFC-142b is close to 94%, while the selectivity to VDF remains almost unchanged. Although the SrF2 catalyst prepared by the conventional precipitation method also shows high conversion, its selectivity to VDF is only around 50–70%. We suggest that the surface acidity and specific surface area play major roles in the catalytic performance. Compared with the temperatures for industrial manufacture of VDF of 650–700 °C, the SrF2 catalysts provide a promising pathway to produce VDF at much lower temperatures.
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