Aluminum-based Catalysts For Vapor-phase Dehydrofluorination Of 1,1,1,3,3-Pentafluoropropane To 1,3,3,3-Tetrafluoropropene

Hydrofluorocarbons(HFCs)such as 1,1,1,2-tetrafluoroethane(HFC-134a)have been widely used as refrigerants,solvents and polishes.However,due to its the high global warming potential(GWP)and the long climatic performance,it becomes a great challenge to its continuous application.On the contrary,as new environmental benign alternatives of HFCs,hydrofluoroolefins(HFOs)such as 1,3,3,3-tetrafluoropropene(HFO-1234ze)have been extensively used as refrigerants,aerosol agent and detergents for its outstanding performance parameters such as low toxicity,large refrigeration capacity,high energy efficiency,good compatibility with other materials,high efficiency and non-flammable safety.Thus,it is of great importance to synthesize eco-friendly and valuable HFOs compounds via HFCs compounds.The synthesis of HFO-1234ze via catalytic dehydrofluorination of 1,1,1,3,3-pentafluoropropane(HFC-245fa)has good potential in practical industrial application owing to its simple reaction process,high yield and easy operation,which is therefore regarded as an ideal route for the production of HFO-1234ze.Aluminum-based catalysts are main catalysts for defluorination reaction with high activity and low environmental pollution.However,the catalysts are easy to deactivate.In this thesis,aluminum-based catalyst with high catalytic activity and stability were tested for the dehydrofluorination of HFC-245fa to synthesize HFO-1234ze.The effects of additives loading,preparation method and pretreatment conditions on the catalytic performance were investigated.Various characterizations were conducted to illustrate the phase composition,specific surface area and catalyst deactivation.The detailed contents of this work are as follows:1.AIF3 catalysts were synthesized and tested for gas phase dehydrofluorination of HFC-245fa to HFO-1234ze.It was found that AIF3 pretreated at high temperature and N2 atomsphere were active,and high reaction temperature was also beneficial for the activity.Furthermore,supported Rh/AlF3 catalysts with different Rh contents were prepared by an impregnation method.It showed that the addition of Rh could improve the catalytic performance of HFC-245fa which was related to the enhancement of surface acidity.Furthermore,the addition of Rh in the catalyst improved the catalyst stability,which was due to the reduced surface carbon deposition during the reaction.2.High surface area AlF3(denoted as C-AlF3)was synthesized by a sol-gel method using aluminum isopropoxide as the precursor,and tested for catalytic dehydrofluorination of HFC-245fa.It was found that the catalytic activity declined with decreasing surface area of the C-AIF3 catalyst,which was due to its higher thermal treatment temperature and possible hydrolysis of AIF3 at high temperature.Also,it was found that compared to the commercial AIF3,the C-AIF3 catalyst showed much better stability,as the conversion of HFC-245fa drastically decreased from 79.6%to 47.8%in 100 h reaction while the C-AlF3 showed stable conversion in 90 h reaction.These findings indicated that the aluminum fluoride catalyst prepared by this method had great reaction stability due to its higher specific surface area and highly active ?-phase structure.