Negative-carbon pyrolysis of biomass (NCPB) over CaO originated from carbide slag for on-line upgrading of pyrolysis gas and bio-oil

Abstract In this study, the feasibility and reaction mechanism of using CaO derived from calcined carbide slag in biomass pyrolysis to realize negative-carbon emission was investigated in a fixed bed reactor. The results showed that 0.06 g CO2/g biomass was fixed when the mass ratio of calcined carbide slag/biomass was 1:1. Further increasing the amount of calcined carbide slag increased a little on the yield of fixed-CO2, but the utilization efficiency of carbide slag reduced and large amounts of coke formed. As to the effect on pyrolysis products, calcined carbide slag increased the content of combustible component in pyrolysis gas (H2, CO and CH4) through CO2 absorption, catalytic decarbonylation and cracking effect, increasing the lower heating value (LHV) of pyrolysis gas. Meanwhile, calcined carbide slag favored the dehydration of sugars and furans to cyclopentanones, ketonization of acids to linear ketones, and cracking of heavy compounds to light phenols. As a result, the content of low-oxygen containing compounds in bio-oil increased at the cost of high-oxygen containing compounds. Overall, biomass pyrolysis with calcined carbide slag is a promising negative-carbon technology, which can realize negative-carbon emission and upgrade the quality of pyrolysis products at the same time.