Study On Design And Preparation Of Catalysts For Selective Oxidation Of Isobutylene

Isobutene is mainly derived from the by-product C4 fraction of petroleum crackers,and the main utilization route is to produce methyl tert-butyl ether（MTBE）,which is widely used in gasoline as a fuel additive.In September 2017,15 departments（incl.the National Development and Reform Commission,the National Energy Administration,and the Ministry of Finance,etc.）jointly issued the"Implementation Plan for Expanding Production of Biofuel Ethanol and Promoting the Use of Ethanol Gasoline for Vehicles".Ethanol gasoline for vehicles requires no artificial addition of oxygenated organic compounds,and MTBE,which is an oxygenated organic compound,will be banned,resulting in much lower sales of MTBE.Therefore,the capacity of isobutene,the upstream of its industry,is greatly overcapacity,and how to effectively utilize isobutene has a strong practical significance.The goal of this paper is to convert and utilize isobutylene into chemical substances with high added value and to improve the utilization and economic efficiency of isobutylene.Therefore,isobutylene and air were chosen as reactants for the catalytic reaction by using a fixed-bed reactor at atmospheric pressure and a certain temperature.The catalyst for the selective oxidation reaction of isobutylene was designed to oxidize isobutylene to methacrolein or methacrylic acid.At atmospheric pressure and 450℃,93%conversion of isobutylene and 81%selectivity of methacrolein were obtained when Mo-V-Te-Ce was used as catalyst.The surface morphology,pore size distribution and specific surface area of different catalysts were not significantly different by SEM and TEM characterization and BET test.By XRD,FT-IR and Raman tests,it was found that Mo₆V₉O₄₀ phase was formed in the catalyst;by XPS tests,it was found that the percentage of Mo⁶⁺in the Mo of the catalyst increased after the doping of Ce,which was thought to be the reason for the improved selectivity of methacrolein.At atmospheric pressure and 450℃,90%conversion of isobutylene and 71%selectivity of methacrylic acid were obtained when Mo-V-Te-Cs was used as catalyst.The characterization results of SEM,TEM,BET,XRD,FT-IR and Raman showed that the morphology,pore size distribution,specific surface area and surface topography of Mo-V-Te-Cs catalysts were not much different from Mo-V-Te-Ce catalysts,but the higher percentage of strongly acidic sites in Mo-V-Te-Cs catalysts was found by NH₃-TPD test,which was considered to be the reason for the improved selectivity of methacrylic acid.In the presence of Mo-V-Te-Cs catalyst,isobutylene was first oxidized to methacrolein,and then methacrolein was further oxidized to methacrylic acid.