Selective production of light oil by biomass pyrolysis with feedstock-mediated recycling of heavy oil

This paper proposes pyrolysis of biomass with recycling of a heavier portion of bio-oil [heavy oil (HO)] and reports results of the experimental simulation of this process, employing chipped cedar as not only the feedstock but also the sorbent/carrier of HO. Repetition of 10 pyrolysis runs in sequence simulated recycling of HO. In the nth run, HO-loaded cedar that had been prepared in the (n - 1)th run was pyrolyzed at 500 °C. The volatiles, i.e., gas, steam, light oil (LO), and HO, were formed and sent to the HO sorber, in which fresh cedar sorbed HO selectively. The resultant HO-loaded cedar was subjected to the pyrolysis in the (n + 1)th run. HO loading on the cedar became steady around 0.4 kg of HO/kg of dry cedar. Recycled HO was converted mainly by self-pyrolysis with once-through conversion of about 40%. Conversion of the recycled HO resulted in increases in char and LO yields without significant increases in the gas and water yields. The HO recycling increased the LO yield from 0.16 to 0.26 kg/kg of dry cedar (excluding water). LO from the last run was highly volatile that 99.8 wt % of its portion was evaporated in heating to 250 °C. The LO consisted mainly of compounds with a carbon number (number of carbon atoms per molecule) of 1-12. The proposed pyrolysis thus enabled selective production of LO with full recycling of HO.