Efficient synthesis of fluoroethylene carbonate via phase transfer catalysis using[bmim][BF4]
As one of the key components in lithium battery electrolyte additives,fluoroethylene carbonate(FEC)is primarily produced industrially using the halogen exchange process.During the FEC synthesis,a substitution reaction between potassium fluoride(KF)and chloroethylene carbonate(CEC)occurs,the rate of which has been limited by the interphase mass transfer of KF.Meanwhile,the CEC is susceptible to an elimination reaction to form by-product of vinylene carbonate.To address these issues,the effect of phase transfer catalyst(PTC)structure on the interphase mass transfer of KF and reaction energy barriers were investigated.It was revealed that the optimized conditions consist of[bmim][BF4](1-butyl-3-methylimidazolium tetrafluoroborate)as the PTC,acetonitrile as the solvent,a reaction temperature of 81.6℃,and a KF∶CEC molar ratio of 2.5∶1.Under the optimized reaction conditions,an unprecedently high yield of FEC(91.94%,molar fraction)was achieved.Density functional theory calculations suggested that the[bmim][BF4]can form complexes with the KF in acetonitrile to increase the nuclear distance between K+and F-and decrease the free energy of solvation of KF.As a result,the interphase mass transfer of KF was facilitated and the energy barrier of the substitution reaction between KF and CEC was reduced,which contributed to the efficient production of FEC from CEC.
ionic liquidsphase transfer catalysiscomplexesmass transferfluoroethylene carbonatedensity functional theory
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