The integration of low temperature supercritical water gasification with continuous in situ nano-catalyst synthesis for hydrogen generation from biomass wastewater

This work reviews the brown-rot fungal biochemical mechanism involved in the biodegradation of lignified plant cell walls. This mechanism has been acquired as an apparent alternative to the energetically expensive apparatus of lignocellulose breakdown employed by white-rot fungi. The mechanism relies, at least in the incipient stage of decay, on the oxidative cleavage of glycosidic bonds in cellulose and hemicellulose and the oxidative modification and arrangement of lignin upon attack by highly destructive oxygen reactive species such as the hydroxyl radical generated non-enzymatically via Fenton chemistry [Formula: see text]. Modifications in the lignocellulose macrocomponents associated with this non-enzymatic attack are believed to aid in the selective, near-complete removal of polysaccharides by an incomplete cellulase suite and without causing substantial lignin removal. Utilization of this process could provide the key to making the production of biofuel and renewable chemicals from lignocellulose biomass more cost-effective and energy efficient. This review highlights the unique features of the brown-rot fungal non-enzymatic, mediated Fenton reaction mechanism, the modifications to the major plant cell wall macrocomponents, and the implications and opportunities for biomass processing for biofuels and chemicals.

The global energy demand has laid emphasis on the exploration of alternate sources of energy. The global energy demand has laid emphasis on the exploration of alternate sources of energy. With the application of many thermochemical and biochemical technologies, waste biomass can be converted into green fuels. Gasification is one of the most effective thermochemical (biomass-to-gas) technologies that can transform organic substrates into combustible syngas. Supercritical water gasification is an iteration of conventional gasification that uses water as the reaction medium to efficiently decompose biomass to hydrogen-rich syngas. The yields and composition of products from supercritical water gasification largely depend on the process parameters such as temperature, pressure, residence time, and feed concentration, biomass particle size, reactor configurations as well as reaction pathways and catalysis. These factors also determine the gasification efficiency, carbon conversion and heating value of the gas products. This paper reviews different homogeneous and heterogeneous catalysts involved in supercritical water gasification of biomass. Several reaction mechanisms occurring during gasification of biomass in supercritical water have also been illustrated and discussed, and research gaps for future studies have been identified. Overall, this review is an update to the compiled literature and the aspects involved in supercritical water gasification of different biomass feedstocks.