Lignocellulosic biomass pyrolysis for aromatic hydrocarbons production: Pre and in-process enhancement methods

Rapid consumption of petroleum and concerns about carbon emissions have promoted utilization of renewable energy such as biomass. Pyrolysis of biomass is one of effective sustainable routes for aromatic hydrocarbons production. However, it has not been applied commercially on a large scale. One of the biggest challenges is inferior characteristics of biomass, including complex crosslinking structure, high content of alkali and alkaline earth metals (AAEMs), and low hydrogen to carbon effective ratio (H/C_eff). Main objective of this review is to investigate main methods that enhance aromatic hydrocarbons production, while screening out option to maximize aromatic hydrocarbons production, taking economic analysis and technical application progress as a reference. Results show that pre enhancement methods including physical, thermal, chemical and biological biomass pretreatments are mainly used to break crosslinking structure and remove AAEMs. The most significantly influential factor limiting biomass conversion is low H/C_eff, and thus in-process enhancement methods including deoxidation via catalysis, and hydrogenation via co-pyrolysis and atmosphere regulation are more effective for improving aromatic hydrocarbons. Industrial problems, existed in co-pyrolysis (great characteristics differences, etc.) and atmosphere regulation (high investment cost, etc.), have not been solved yet. By comparison, development of catalysts is relatively mature, and there are successful commercial cases. Total production cost of catalytic pyrolysis of biomass is only 67% of petroleum refining route, showing best economic potential. Accurate design and construction of catalysts with high activity and long life based on biomass characteristics is the most feasible and promising development direction.