Gas-phase dehydrohalogenation of 2-chloro-1,1,1,2-tetrafluoropropene over magnesium fluoride-based catalysts
JIA Zhao-hua1,2, MAO Wei1,2, BAI Yan-bo1,2, LV Jian1,2
1. Xi'an Modern Chemistry Research Institute, Xi'an 710065, China; 2. State Key Laboratory for Efficient Development and Utilization of Fluorine & Nitrogen Chemicals, Xi'an 710065, China
Abstract: A series of magnesium fluoride-based catalysts (M/MgF2) modified by different metal ions (Mn+) are prepared by equal volume impregnation method and their catalytic performances are investigated in the gas-phase catalytic dehydrochlorination of 1,1,1,2-tetrafluoro-2-chloropropane (HCFC-244bb) to make 2,3,3,3-tetrafluoropropylene (HFO-1234yf),a new generation of environment-friendly refrigerant.It is found that both dehydrofluorination and dehydrochlorination reactions occur on the pure MgF2 catalyst,with dehydrofluorination as the main reaction.More importantly,the dehydrochlorination selectivity to HFO-1234yf is only 8.8%,and the selectivity to 2-chloro-3,3,3-trifluropropylene (HCFO-1233xf) is as high as 87.7%.The catalyst modified by Al3+exhibits higher activity,however,the un-expected dehydrofluorination selectivity to HCFO-1233xf increases to around 90% over the catalyst modified by Al3+,although.The dehydrochlorination selectivity to HFO-1234yf over 3%Fe/MgF2 or 3%Zr/MgF2 catalysts increases,but still less than 20%.High dehydrochlorination selectivity can be achieved over the MgF2 catalysts modified by K or Cs halides,reaching 76.4% and 86.6% respectively,however,the activities of these catalysts are lower than the pure MgF2 catalyst.The structure and surface acidity of prepared catalysts are characterized by means of XRD,NH3-TPD and N2 physical adsorption measurements,which are then correlated with catalytic performance.The results show that decreasing the surface acidity of catalyst can benefit the dehydrochlorination of HCFC-244bb.
[1] Velders G J M,Reimann S.Preserving montreal protocol climate benefits by limiting HFCs[J].Science,2012,335(6071):922-923. [2] Tsai W T.An overview of environmental hazards and exposure risk of hydrofluorocarbons (HFCs)[J].Chemosphere,2005,61(11):1539-1547. [3] Mao W,Bai Y,Wang B,et al.A facile sol-gel synthesis of highly active nano α-aluminum fluoride catalyst for dehydrofluorination of hydrofluorocarbons[J].Applied Catalysis B Environmental,2017,206:65-73. [4] Lu M C,Tong J R,Wang C C.Investigation of the two-phase convective boiling of HFO-1234yf in a 3.9 mm diameter tube[J].International Journal of Heat & Mass Transfer,2013,65(7):545-551. [5] Nappa M J,Lousenberg R D,Jackson A.Synthesis of 1234YF by selective dehydrochlorination of 244BB:US,8263817[P].2012-09-11. [6] Mao W,Wang B,Ma Y,et al.Selective gas-phase catalytic fluorination of 1,1,2,3-tetrachloropropene to 2-chloro-3,3,3-trifluoropropene[J].Catalysis Communications,2014,49(5):73-77. [7] Teinz K,Wuttke S,Börno F,et al.Highly selective metal fluoride catalysts for the dehydrohalogenation of 3-chloro-1,1,1,3-tetrafluorobutane[J].Journal of Catalysis,2011,282(1):175-182. [8] Parr R G,Pearson R G.ChemInform abstract:Absolute hardness:Companion parameter to absolute electronegativity[J].Chemischer Informationsdienst,1984,15(13):7512-7516. [9] Koch E.Acid-base interactions in energetic materials:Ⅰ.The hard and soft acids and bases (HSAB) principle-insights to reactivity and sensitivity of energetic materials[J].Propellants Explosives Pyrotechnics,2010,30(1):5-16.