Study On Performance Of Transition Metal Phosphides For Thioetherification Of Isoprene And Butanethiol

Thioetherification between mercaptan and diolefin is an efficient process to remove mercaptans in FCC gasoline at mild condition,during which selective hydrogenation of diolefin to monoolefin is also expected.Here,SiO₂ supported transition metal?Fe,Co,Ni,Mo and W?phosphides,x%MoP/SiO₂ with different MoP loadings and K promoted 25%MoP/SiO₂ were investigated for the thioetherification of isoprene and butanethiol on a fixed-bed reactor at 120°C and 1.5 MPa H₂,and their structure before and after reaction was characterized by means of XRD,HRTEM,N₂sorption,CO chemisorption,NH₃-TPD,XPS and TG.For comparison,Ni/Si O₂ and P_xO_y/SiO₂ were also tested.It was found that,among different metal phosphides,MoP/SiO₂ showed the best performance,and the optimal MoP loading was 25%.Apart from the nature of metal,the density of metal and acid sites determined the catalyst performance.Metal site was mainly responsible for hydrogenation of isoprene,while acid site dominantly contributed to thioetherification and polymerization of olefins.Moreover,a balance between metallic and acidic functions is required to arrive at a desired performance.Excessive metal sites or acid sites led to over-hydrogenation of isoprene or severe polymerization of olefins,respectively.25%MoP/SiO₂ was tested for 37 h time on stream,and butanethiol conversion maintained at 100%;although isoprene conversion remarkably decreased,the selectivity to isopentenes exceeded 80%after reaction for 11h.We suggest that the deactivation of MoP/SiO₂ is mainly due to butanethiol poisoning and carbonaceous deposit,where butanethiol poisoning is the main reason.The introduction of K species promoted the dispersion of MoP and significantly reduced acid amount.As K content increased,the CO uptakes of 25%MoP-K-x first increased and then remarkably decreased.The latter case is related to that too much amount of K covered the Mo sites.With increasing K content,although the selective hydrogenation was promoted and the olefin polymerization was inhibited on 25%MoP-K-x,the conversions of isoprene and butanethiol decreased.On the whole,K is not a good promoter for 25%MoP inthioetherification.