Depolymerization of Lignin with Supercritical Fluids: A Review

Abstract

Biomass has attracted keen interest as a renewable resource and an environmental friendly material that is essential to realize a sustainable world. Lignin as biomass has been long labeled with waste material. But now the innate chemistry of lignin and a phenolic heteropolymer, has allowed it to make inroads into the high value polymer and natural biomass material industries. Supercritical fluids (SCF) have been shown to be a promising technique for future large-scale biofuel and base-chemicals production, especially for depolymerization production from lignin. This paper reviews the research progress of lignin-depolymerization processes, including effects of process parameters, such as reaction time, temperature, pressure and catalyst, product analysis, and reaction mechanism with different supercritical fluids. The problems of depolymerization with supercritical fluid technology and its development direction are also briefly discussed. Compared with conventional lignin production methods, the SCF technology processes of lignin can produce smaller fragments through breakage of the ether linkages and produce larger fragments through cross linking between the reactive fragments, and the depolymerization lignin processes are typically conducted at mild operating conditions, and the monomeric products have a high economic value because the aromatic products can be readily blended into current transportation fuels or used in chemical industry.