Catalytic conversion of biomass-derived feedstocks into olefins and aromatics with ZSM-5: the hydrogen to carbon effective ratio

TLDR

Coke forms via both homogeneous and heterogeneous reactions during biomass conversion. The study demonstrates that the H/Ceff ratio of the feed governs conversion of biomass‑derived feedstocks into aromatics and olefins using zeolite catalysts. The authors performed gas‑phase flow‑fixed‑bed catalytic conversion of ten biomass‑derived feedstocks with varying H/Ceff ratios over a ZSM‑5 catalyst. Increasing the H/Ceff ratio raises aromatic and olefin yields, lowers coke production and catalyst deactivation, and shifts the olefin‑to‑aromatic ratio upward, with a maximum in CO/CO₂ yields and an inflection at H/Ceff = 1.2, while very low ratios (<0.15) cause excessive coke (>12 wt %).

Abstract

Catalytic conversion of ten biomass-derived feedstocks, i.e.glucose, sorbitol, glycerol, tetrahydrofuran, methanol and different hydrogenated bio-oil fractions, with different hydrogen to carbon effective (H/Ceff) ratios was conducted in a gas-phase flow fixed-bed reactor with a ZSM-5 catalyst. The aromatic + olefin yield increases and the coke yield decreases with increasing H/Ceff ratio of the feed. There is an inflection point at a H/Ceff ratio = 1.2, where the aromatic + olefin yield does not increase as rapidly as it does prior to this point. The ratio of olefins to aromatics also increases with increasing H/Ceff ratio. CO and CO2 yields go through a maximum with increasing H/Ceff ratio. The deactivation rate of the catalyst decreases significantly with increasing H/Ceff ratio. Coke was formed from both homogeneous and heterogeneous reactions. Thermogravimetric analysis (TGA) for the ten feedstocks showed that the formation of coke from homogeneous reactions decreases with increasing H/Ceff ratio. Feedstocks with a H/Ceff ratio less than 0.15 produce large amounts of undesired coke (more than 12 wt%) from homogeneous decomposition reactions. This paper shows that the conversion of biomass-derived feedstocks into aromatics and olefins using zeolite catalysts can be explained by the H/Ceff ratio of the feed.