Flash pyrolysis of rapeseed cake: Influence of temperature on the yield and the characteristics of the pyrolysis liquid

Biomass waste is a promising source of renewable fuels and value-added chemicals. Rapeseed cake, the solid waste after pressing of rapeseed, is a biomass with such a potential. In this study, the possibilities of flash pyrolysis to convert rapeseed cake into a liquid form are investigated. Flash pyrolysis experiments are performed at four constant temperatures (350, 400, 450 and 550 °C) using a home-built lab-scale semi-continuous reactor. It is found that higher pyrolysis temperature results in a higher yield of pyrolysis liquid, while the yield of char (solid residue) decreases. At each investigated temperature, the pyrolysis liquid separates spontaneously into an oil and a water fraction. At 550 °C, the oil fraction reaches a maximum yield of 42.1 wt%, contains only 6.7 wt% water and has a high calorific value of 32.8 MJ/kg. All oil fractions are characterized with complementary analytical techniques. GC/MS analysis shows compounds related to triglycerides in the rapeseed cake as the major compounds at all temperatures, together with a minor amount of oxygenated compounds. GPC and HPLC analyses indicate that the increased yield of the oil fraction at higher pyrolysis temperature is mainly caused by enhanced flash distillation of the triglycerides with only a small degree of degradation into fatty acids. This is confirmed by FTIR and 1H NMR spectroscopy.