Biomass pyrolysis in a circulating fluidized bed reactor: Evaluating two strategies for the reduction of oxygen content in bio-oil

The use of a circulating fluidised bed (CFB) reactor promotes higher heat transfer to the biomass pyrolysis process and has the advantage of being energy self-sufficient through the continuous burning of biochar. CFB's similarity with the fluidised catalytic cracking (FCC) of fossil streams represents a promising scenario of integration of lignocellulosic biomass in a conventional refining scheme. In this paper, two approaches were studied to enhance the deoxygenation reactions of biomass components in a pilot pyrolysis CFB reactor. First, in a noncatalytic pyrolysis, a lignocellulosic biomass was cofed with hydrogen-rich compounds produced in the oil refinery (methane and propane). In the second part, using a ZSM-5 catalyst in the bed, the effect of different catalyst-to-biomass ratios (CTB) in the bio-oils' properties was evaluated. Compared with conventional pyrolysis, the cofeeding of methane or propane produced bio-oils with less oxygen content. The use of propane achieved better performance in terms of hydrocarbon concentrations in bio-oils, hence increasing benzene, toluene and xylene (BTX) production and being comparable with the results of catalytic pyrolysis. It was also shown that the increase of CTB in catalytic pyrolysis led to the enhancement of deoxygenation reactions, producing more O-free compounds. Both strategies were promising for improving the quality of bio-oil. Issues such as the cost of the catalyst and gases must be evaluated for possible integration into a conventional refining process.