Product distribution control and reaction mechanism study of isobutanol conversion into aromatics

摘要

Isobutanol can be produced in large scale by biomass fermentation as a renewable energy source. Production of low-carbon olefins and light aromatic hydrocarbons using isobutanol as the raw material is a very promising process. In this work, the conversion pathway of isobutanol to olefins and aromatics was studied over parent and Ga impregnated ZSM-5 zeolites. In contrast to olefins, the selectivity of aromatics and alkanes can be increased byreducing the Si/Al ratio and increasing the residence time. The results showed that isobutanol were firstly dehydrated to isobutene on ZSM-5 zeolite, and then polymerized to form high-carbon alkenes which can be further converted to aromatics and alkanes through hydrogen transfer route. This reaction mechanism was confirmed byintermediate species detected with in-situ FT-IR method. After Ga_2O_3 loading, the aromatics selectivityincreased, which suggested that the high-carbon alkenes produced by polymerization from low-carbon olefin were preferentially dehydrogenated into aromatics with the presence of Ga species.On the other side, the cracking activity to form ethylene and propylene was weakened. The amount of Bronsted acid sites in the Ga impregnated samples decreased because the Ga species replaced the H~+ on Bronsted acid sites at the surface of zeolite, forming BAS-Ga structure and promoting the dehydrogenation route through the synergistic effect.