A Little Help from Hydrogen: Biomass may one day displace petroleum as the chemical industry's primary feedstock. Currently, though, the primary hurdle for incorporating plant-derived material into existing process feeds is the high proportion of oxygen in its molecular frameworks. Rapid heating of the biomass followed by high-temperature treatment with zeolite catalysts can yield tractable quantities of useful commodity compounds such as ethylene and benzene, but much of the carbon is wasted in the process—diverted either toward gaseous CO and CO ₂ , or solid coke. Vispute et al. (p. 1222 ) show that an intermediate step, in which hydrogen is catalytically incorporated into the heated material prior to zeolite treatment, can substantially raise the yield of useful products by reducing susceptibility to coking.

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/C_eff) 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/C_eff ratio of the feed. There is an inflection point at a H/C_eff 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/C_eff ratio. CO and CO₂ yields go through a maximum with increasing H/C_eff ratio. The deactivation rate of the catalyst decreases significantly with increasing H/C_eff 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/C_eff ratio. Feedstocks with a H/C_eff 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/C_eff ratio of the feed.