Thermochemical Conversion of Lignocellulosic Biomass into Mass-Producible Fuels: Emerging Technology Progress and Environmental Sustainability Evaluation

Lignocellulosic biomass is increasingly recognized as a carbon-neutral resource rather than an organic solid waste nowadays. It can be used for the production of various value-added chemicals and biofuels like bio-oil. However, the undesirable properties of bio-oil such as chemical instability, low heating value, high corrosivity, and high viscosity are greatly restricting the utilization of bio-oil as a drop-in fuel. As a consequence, bio-oil should be upgraded. Recently, several emerging methods, such as electrocatalytic hydrogenation, atmospheric distillation, and plasma-assisted catalysis, have been developed for improving the bio-oil quality under mild conditions. Here, we overview the new knowledge on the molecular structure of lignocellulosic biomass gained over the past years and discuss the future challenges and opportunities for further advances of the bio-oil production and upgrading from lignocellulosic biomass. The development of sustainable biomass resource recycle systems with improved efficiency and minimized environmental impacts is analyzed in details. Also, their environmental impacts and sustainability are evaluated. Lastly, the remaining knowledge gaps are identified, and the future research needs that may lead to massive production of biofuels from lignocellulosic biomass are highlighted.