Recent advances in improving lignocellulosic biomass-based bio-oil production

Developing pyrolysis technology to produce bio-oil from lignocellulosic biomass is a promising pathway for diversifying energy supply and controlling carbon emissions. Improving bio-oil production is a key research topic due to low-quality and low cost feedstock, and high demand for products. Understanding the multiscale complexity in the conversion process including biomass structure and the interactive reactions is crucial for designing a feasible and cost-effective pyrolysis process. This review provides a fundamental summary for the current knowledge. Biomass structure and its pyrolysis behaviors are firstly discussed to understand fundamental reaction chemistry in this process. Effects of pyrolysis process parameters on product yield and distribution are then reviewed. By analyzing recent studies, effects of different pretreatment techniques including torrefaction, hydrothermal pretreatment, and acid pretreatment on improving bio-oil production are reviewed. An emphasis is placed on the advanced catalytic pyrolysis for selective production of valuable products. Based on zeolite and metal oxide catalysts, chemical compositions of bio-oils can be more clearly understood and selective production of desirable products is more reliable. Co-pyrolysis of biomass with polymers to improve the bio-oil yield and quality is also summarized. The challenges and future research directions for effective pyrolysis processes are also proposed, which may lead to future important breakthroughs.