Hydrothermal Liquefaction (HTL) of Kraft Lignin (KL) Recovered from Lignocellulosic Biomass: State of the Art

Abstract

AbstractThe continued use of fossil fuels has led to the depletion of fossil fuels. Also, increasing environmental pollution is driving the need to find alternative sources for fossil fuels. In this context, biomass-derived fuels appear to be a promising method. There are various methods for processing biomass such as pyrolysis, hydrothermal liquefaction, and transesterification. Among these methods, hydrothermal liquefaction (HTL) of biomass seems to be a promising approach. The HTL process is carried out for wet biomass with a moisture content above 50% at high pressure (50–250 bar) and temperature (250–300 °C). The final by-product of the HTL process includes (a) biochar, (b) bio-oil, (c) aqueous crude, and (d) gas. The HTL process is considered to have great potential for the production of fuels and chemicals. However, the conditions vary for different lignocellulosic biomass. These products have several commercial applications. However, several studies related to bio-oil from lignocellulosic biomass have been discussed in the literature. This chapter focuses on HTL of kraft lignin (KL) derived from different lignocellulosic biomass. This chapter presents a discussion on the recovery of KL from different lignocellulosic biomass by alkaline pretreatment. Converting kraft lignin (KL) into different by-products through the HTL process was discussed in detail. The factors that significantly impact the yield of by-products in the HTL process were also discussed in detail. State of the art and challenges encountered in the HTL process for various chemical products have been critically discussed.KeywordsBio-oilFossil fuelHydrothermal liquefactionKraft ligninLignocellulosic biomass