Catalytic conversion of biomass pyrolysis vapours with zinc oxide

Conversion of pyrolysis vapours of pine sawdust was studied in micro and bench scales with zinc oxide catalyst. Three different zinc oxides were screened in a gas chromatograph system using an injection port as a fixed-bed catalytic converter in order to find appropriate reaction conditions by emphasising a high yield of bio-oil. Catalytically treated pyrolysis oils were produced in a side stream of an atmospheric fluidised bed pyrolyser (1 kg h⁻¹) at the catalyst temperature of 400°C. The oils with silicon carbide treatment and without any catalyst were used as references. The aim was to study the catalytic effect of zinc oxide on the composition and on the stability of the oil. The pyrolysis liquids produced were homogeneous one-phase oils. The ZnO proved to be a mild catalyst and the liquid yields were not substantially reduced. It had no effect on the water-insoluble fraction (lignin-derived), but it decomposed the diethyl ether-insoluble fraction (water-soluble anhydrosugars and polysaccharides). Some indications of catalyst deactivation were observed. The oil samples were aged thermally and the variation of viscosity and water content were determined. The increase in the viscosity was significantly lower for the ZnO-treated oil (55%) than for the reference oil without any catalyst (129%). The results indicated an improvement in the stability of the ZnO-treated oil.