Hydrolysis of Lignocellulosic Biomass in Hot-Compressed Water with Supercritical Carbon Dioxide

Coupled Biohydrogen Production and Bio-Nanocatalysis for Dual Energy from Cellulose: Towards Cellulosic Waste Up-Conversion into Biofuels

Hydrogen, an emergent alternative energy vector to fossil fuels, can be produced sustainably by fermentation of cellulose following hydrolysis. Fermentation feedstock was produced hydrolytically using hot compressed water. The addition of CO2 enhanced hydrolysis by ~26% between 240 and 260 °C with comparable hydrolysis products as obtained under N2 but at a 10 °C lower temperature. Co-production of inhibitory 5-hydromethyl furfural was mitigated via activated carbon sorption, facilitating fermentative biohydrogen production from the hydrolysate by Escherichia coli. Post-fermentation E. coli cells were recycled to biomanufacture supported Pd/Ru nanocatalyst to up-convert liquid-extracted 5-HMF to 2,5-dimethyl furan, a precursor of ‘drop in’ liquid fuel, in a one-pot reaction. This side stream up-valorisation mitigates against the high ‘parasitic’ energy demand of cellulose bioenergy, potentially increasing process viability via the coupled generation of two biofuels. This is discussed with respect to example data obtained via a hydrogen biotechnology with catalytic side stream up-conversion from cellulose feedstock.

Recent advances in lignocellulosic biomass for biofuels and value-added bioproducts - A critical review

Lignocellulosic biomass is a highly renewable, economical, and carbon-neutral feedstock containing sugar-rich moieties that can be processed to produce second-generation biofuels and bio-sourced compounds. However, due to their heterogeneous multi-scale structure, the lignocellulosic materials have major limitations to valorization and exhibit recalcitrance to saccharification or hydrolysis by enzymes. In this context, this review focuses on the latest methods available and state-of-the-art technologies in the pretreatment of lignocellulosic biomass, which aids the disintegration of the complex materials into monomeric units. In addition, this review deals with the genetic engineering techniques to develop advanced strategies for fermentation processes or microbial cell factories to generate desired products in native or modified hosts. Further, it also intends to bridge the gap in developing various economically feasible lignocellulosic products and chemicals using biorefining technologies.

Multistage fractionation of pine bark by liquid and supercritical carbon dioxide

Multistage fractionation of pine bark was performed using subcritical and supercritical CO₂ at increasing pressures and temperatures. In total, seven fractions were collected, which demonstrated different enrichments of families of compounds. In particular, subcritical CO₂ yielded 41% of the total extract in which unsaturated fatty acids represented the most abundant family. The subsequent five supercritical steps increased the recovery of sterol esters, wax esters and resin acids at higher temperatures and pressures, reaching 80% of the total extractable mass. In the last step, using ethanol as a co-solvent, an additional 20% of extract was recovered, which was enriched with phenolics and glycerol. A full characterisation of the extracts was accomplished by high-temperature GC-MS/FID using four internal standards, which were representative of the main classes of compounds contained in the pine bark extract.