Mesopore-modified mordenites as catalysts for catalytic pyrolysis of biomass and cracking of vacuum gasoil processes

摘要

Mesopore-modified mordenite zeoljtic materials with different Si/AI ratios have been prepared and tested in the biomass pyrolysis and catalytic cracking of vacuum gasoil. Alkaline treatment was carried out to generate mesoporosity. Severity of alkaline treatment was found to be of paramount importance to tune the generated mesoporosity, while it significantly affected the crystallinity of treated mordenites. It was moreover observed that the alkaline treatment selectively extracted Si decreasing the Si/AI ratio of treated samples. Catalytic activity of parent and alkaline treated mordenites was studied in the pyrolysis of biomass. All zeolitic based materials produced less amounts of bio-oil but of better quality (lowering the oxygen content from ~40% to as much as 21%) as compared to the non-catalytic pyrolysis experiments. On the other hand, it was found that the combination of mesopore formation and high surface area after alkaline treatment of the mordenite with a high Si/AI ratio resulted in the enhancement of its catalytic activity, despite the reduction of its acidity. The increment of the decarboxylation and dehydration reactions, combined with a reduction of carbon deposition on the catalyst, resulted in a remarkable decrease in the oxygen content in the organic fraction and therefore, resulted in a superior quality liquid product. Alkaline treated mordenites were additionally acid treated targeting dealumination and removal of the extra framework debris, thus generating mesopore-modified mordenite samples with stronger acid sites and higher total acidity, as candidate catalysts for catalytic cracking of vacuum gasoil. Desilicated and especially desilicated and dealuminated mordenites exhibited the highest activity and selectivity towards LCO with the best olefinicity in gases and higher bottoms conversion. Therefore, an optimized desilicated-dealuminated mordenite additive could be an interesting candidate as a component of the FCC catalyst for a high LCO yield.