Hzsm - 5 / Sapo - 34 Composite Molecular Sieve Catalyst In Propylene Ethanol System Research

Propylene is one of fundamental chemicals in the petrochemical industry. Propylene is mainly produced from the steam cracking and fluid catalytic cracking (FCC) of naphtha at present. In recent years, since the need of propylene derivates grows fast, the production of propylene from these units cannot meet the market demand of propylene. In addition, other routes such as methanol to olefins/methanol to propylene (MTO/MTP), olefin disproportionation and propane dehydrogenation are limited by production capacity, high emission, soaring energy consumption or high cost. It is desirable to search an alternative route to increase the quantity of propylene.The conversion of ethanol to propylene (ETP), especially from bio-ethanol by the fermentation of biomass, has attracted increasing attention. ETP is considered to be a carbon-neutral process by the use of renewable biomass sources, and can reduce the dependence of the fossil energy resources.In this work, HZSM-5/SAPO-34composites were prepared by hydrothermal synthesis and mechanical mixture. The effect of the catalyst preparation method and composition were investigated. ETP on these composites was investigated under different reaction conditions. The physicochemical properties of these catalysts were appropriately characterized by N2isothermal adsorption-desorption, Powder X-ray diffraction (XRD), Infrared spectroscopy (IR), Scanning electronic microscopy (SEM) and NH3temperature-programmed desorption (NH3-TPD). The correlation between their acidity properties and catalytic performance was discussed, and the possible reaction pathway for ethanol conversion on such catalyst was proposed based on the reaction results. The main research results are shown as follows:(1) Under the optimal reaction conditions of0.1MPa、500℃、PC2H5OH=18kPa and W/F=0.00625g/(mL/min), ZS(25)-MM-4(mechanical mixture, HZSM-5/SAPO-34=4weigh ratio, Si/Al2=25molar ratio) showed the highest34.5wt%yield of propylene. ZS (25)-HS-1(hydrothermal synthesis, HZSM-5/SAPO-34=1weigh ratio, Si/Al2=25molar ratio) exhibited the best catalytic stability.(2) The physicochemical properties of these catalysts were characterized by N2isothermal adsorption-desorption, XRD, IR, SEM and NH3-TPD. It can deduce that SAPO-34 might at least partially overlap on HZSM-5in HZSM-5/SAPO-34composite prepared by hydrothermal synthesis. HZSM-5/SAPO-34ratio of the HZSM-5/SAPO-34composite zeolite catalyst played significant influence on the acidity of these catalysts. HZSM-5/SAPO-34ratio modified the concentration and distribution of acid sites, which in turn determined the reactivity of HZSM-5/SAPO-34catalyst.(3) The acidity played great influences on the yield of propylene and catalytic stability. For achieving the higher propylene yield and better catalytic stability, the catalyst should possess the moderate concentration and distribution of acid sites.(4) It was found that the yield of C2H4, C3H6and C4H8showed the similar tendency as the variety of the contact time. These results imply that C2H4, C3H6and C4H8might be produced through the parallel pathway and the common intermediate on the catalyst.