Hydrothermal Liquefaction of Lignocellulosic Biomass

The introduction of a bio-refinery approach in producing bio-chemicals represents a potential opportunity to cover the increased demand for fine chemicals and reduce the societal dependence on fossil sources for petrochemicals. Valorisation of lignocellulosic material for the production of renewable chemicals has attracted much attention as such chemicals could significantly improve the economics of bio-refineries. The present work has investigated the conversion of brewer's spent grain (BSG), a raw material in the form of food industry wastes into value-added chemical and biofuels. BSG represent around 85% of the total by- products generated from the brewing industry and is available in large quantities throughout the year; however its primary application has been limited to animal feed. Despite this, due to its chemical composition, it has value as lignocellulosic rich material. In this thesis, raw BSG has undergone physical and chemical characterisation to determine the composition and selection of appropriate technologies for their utilisation. BSG contains a high moisture content (approx. 75 wt. %). As a consequence, any application towards utilisation of this waste needs to consider the best way to handle their moisture content. Hydrothermal liquefaction (HTL) is the thermochemical conversion of biomass by processing in a hot, pressurised water environment for sufficient time to break down the solid biopolymeric structure to predominantly liquid components. The potential of HTL to break down the lignocellulosic compounds was demonstrated by using both biomass model components (cellulose and lignin) and real biomass, BSG. However, due to the complex composition of real biomass, the product distribution obtained from BSG HTL is significantly different when compared to the biomass model. The most favourable processing condition identified based on both model and real biomass systems were found to be 250 oC, 30 min reaction time and 80 barg. Further investigation on HTL shows, with the addition of methanol, ethanol and 2-propanol in direct liquefaction reaction, the conversion and water-soluble oil (WSO) yield increased significantly compared to the pure water system. The best conversion was obtained by a methanol-water solvent system at 82%, while 2-propanol-water system produces the highest WSO yield at 29%. Moreover, BSG biochar also shows a potential to be used directly as solid fuel without the need for significant modifications.