From biomass to bio-gasoline by FCC co-processing: effect of feed composition and catalyst structure on product quality

Due to a worldwide demand for biofuels, a need has emerged to develop new processes. Co-processing of bio-oils in refinery units is a promising alternative, especially by Fluid Catalytic Cracking (FCC). In order to promote biofuel production by co-processing a detailed mechanistic study is required based on comparison with pure vacuum gasoil (VGO) processing. Three different porous materials containing micropores and/or mesopores were tested (FCC, HY and HZSM-5). The co-processing of hydrodeoxygenated pyrolysis oil (HDO-oil) with VGO in a lab test FCC unit leads to lower product formation rates than the processing of VGO alone, except for the coke formation and the formation of more unsaturated components (essentially aromatics). The data for both VGO cracking and co-processing follow the published trends with acid site density. These results are explained by the restricted access of the oxygenated molecules into the zeolite pores and coke formation on the outside surface leading to pore blocking. Another key mechanistic feature, explaining the observed effects of co-processing on the product quality, is the competition for the zeolite acid sites between the cracking route and the deoxygenation of the oxygenated components on the outer surface. Lignocellulosic biomass can be transformed into biofuels through co-processing in a FCC unit. The mechanism of cracking of oxygenated species is quite different than that of hydrocarbons requiring new catalysts.