Processing biomass-derived oxygenates in the oil refinery: Catalytic cracking (FCC) reaction pathways and role of catalyst

The catalytic cracking of glycerol and sorbitol, as representative of biomass-derived oxygenates, was studied at 500–700 °C with six different catalysts, including a fresh fluid catalytic cracking (FCC) catalyst (FCC1), an equilibrium FCC catalyst with metal impurities (ECat), a mesoporous Al2O3, a USY zeolite (Y), a ZSM5-based FCC additive (ZSM5), and an inert silicon carbide (SiC). In this process, oxygen is removed from the feed as H2O, CO, or CO2. Repeated dehydration and hydrogen transfer allows the production of olefins, paraffins, and coke. Aromatics (in yields up to 20 molar carbon%) are formed by Diels–Alder and condensation reactions of olefins and dehydrated species, and the different reaction pathways are discussed. Sorbitol and glycerol gave similar product distributions, with the primary difference being that sorbitol produces more CO than glycerol. Glycerol can also be converted when fed together with vacuum gasoil without significantly altering the product selectivity, suggesting that biomass-derived products can be co-fed with petroleum-derived streams in an industrial FCC reactor. When glycerol is fed together with a vacuum gasoil, interactions between the hydrocarbon components and the glycerol reaction intermediates occur, resulting in final selectivities better than those calculated by considering a simple additive effect.