Catalytic pyrolysis of lignocellulosic biomass : a review of variations in process factors and system structure

Increasing global energy demand and concerns of carbon emissions have driven the utilisation of renewable sources such as biomass. Biomass pyrolysis in the presence of catalyst, i.e., biomass catalytic pyrolysis (CP), is one of the most efficient routes for generating renewable hydrocarbon fuels or commodity chemicals. Most previous review papers on biomass CP focused on the summary of catalyst classification, properties and performance based on product yields and oil quality. Information on biomass CP process especially effects of different reaction atmospheres has not been reviewed or discussed in sufficient detail. This paper aims to provide a review and insights of the essential process factors and system structure of the lignocellulosic biomass CP with emphasis on process performance indexes such as bio-oil's effective hydrogen to carbon ratio, deoxygenation degree, carbon efficiency and energy efficiency. The paper sections are organised in order of biomass CP catalysts, biomasss CP assessment, modification of essential process factors (e.g., biomass pre-treatment, co-feeding with other materials, atmosphere and temperature) and variations in the system structure (e.g., heat source alternatives, staged catalysis and process integration). Variations in process factors and system structure can possibly tailor the products and improve the economic attraction. A number of questions about biomass CP are still unclear. The current status, challenges and future research directions of biomass CP are also discussed in the paper. The comprehensive review and insights of the biomass CP process in this work will provide reference for the research and industrialisation of biomass CP for renewable fuel production.