Study On Design,Preparation And Performance Of Catalysts For Transformation Of Mixed Propane And C₄ Hydrocarbons To Ethene And Propane

In order to convert liquefied petroleum gas(LPG)to propylene and ethylene,multifunctional catalysts were designed and the structure-activity relationship was studied.New clues for the utilization of LPG are expected.Acidity tuning,mesopore building of HZSM-5 and improvement of mass transfer.Hierarchical HZSM-5 was prepared by NaOH treatment and loaded 10%Cr2O3.The acid amount,the acid strength and the Cs+ selectivity were reduced.The activity for LPG conversion was obviously lowered.Hierarchical HZSM-5 was prepared by TPAOH treatment and loaded 10%Cr2O3.The surface acidity and the mesoporosity was adjusted owing to secondary crystallization.The weak-acid amount,strength and the mesoporosity were increased.With treatment concentration of 0.15 mol/L and treatment time for 96 h,the selectivity of C2=+C3= was 49.30%.The total conversion of LPG was reduced by 30%.Improvement in catalytic activity by adjusting surface acid and introducing mesopores.The SAPO-1(shell)/HZSM-5(core)composite molecular sieve was prepared and loaded 10%Cr2O3.The weak-acid amount and the acid strength were increased.Using the liquid-solid ratio of 20 mL/g and crystallization time of 24 h,the selectivity of C2=+C3= reached 65.89%and the total conversion of LPG was 45%.Compared with alkali-treated HZSM-5,the total conversion was increased by 15%and the selectivity of C2=+C3= was increased by 17%.Influence of the pore size of the shell.The SAPO-5/HZSM-5 composite molecular sieve was prepared.The selectivity of C2=+C3= was 62.56%at the total conversion of LPG of 72.22%.Compared with SAPO-11/HZSM-5,the conversion of LPG was improved due to enhanced diffusion of molecules in larger pores of the shell.Influence of the acidity of the core-shell.Composite molecular sieves were prepared with different silica sol amounts and SiO2/Al2O3 ratios of HZSM-5 core.For SAPO-11/HZSM-5,appropriate silica sol loading was 0.6(Si/Al)and SiO2/Al2O3 100.For SAPO-5/HZSM-5,proper silica sol loading was 0.4(Si/Al)and SiO2/Al2O3 50.The acidity of the core improves the transformation of intermediates while the acidity of the shell inhibit heavy component.Influence of the reaction conditions.Over SAPO-11/HZSM-5 at 600? and space velocity of 15 g·h/mol,the total conversion of LPG was 65%,the selectivity of C2O=+C3= was 68%,and remained stable with time-on-stream reaction for 240 h.There existed the interplay between the component transformation of LPG.