Progress in the development of alkali and metal salt catalysed lignocellulosic pretreatment regimes: Potential for bioethanol production.

Lignocellulosic biomass (LCB) is well suited to address present day energy and environmental concerns, since it is abundant, environmentally benign and sustainable. However, the commercial application of LCB has been limited by its recalcitrant structure. To date, several biomass pretreatment systems have been developed to address this major bottleneck but have shown to be toxic and costly. Alkali and metal salt pretreatment regimes have emerged as promising non-toxic and low-cost treatments. This paper examines the progress made in lignocellulosic pretreatment using alkali and metal salts. The reaction mechanism of alkali and metal chloride salts on lignocellulosic biomass degradation are reviewed. The effect of salt pretreatment on lignin removal, hemicellulose solubilization, cellulose crystallinity, and physical structural changes are also presented. In addition, the enzymatic digestibility and inhibitor profile from salt pretreated lignocellulosic biomass are discussed. Furthermore, the challenges and future prospects on lignocellulosic pretreatment and bioethanol production are highlighted.