Production of ethanol by bioconversion of lignocellulosic biomass has attracted much interest in recent years. However, the pretreatment process for increasing the enzymatic digestibility of cellulose has become a key step in commercialized production of cellulosic ethanol. During the last decades, many pretreatment processes have been developed for decreasing the biomass recalcitrance, but only a few of them seem to be promising. From the point of view for integrated utilization of lignocellulosic biomass, organosolv pretreatment provides a pathway for biorefining of biomass. This review presents the progress of organosolv pretreatment of lignocellulosic biomass in recent decades, especially on alcohol, organic acid, organic peracid and acetone pretreatments, and corresponding action mechanisms. Evaluation and prospect of organosolv pretreatment were performed. Finally, some recommendations for future investigation of this pretreatment method were given.

Lignocellulosic biomass is recalcitrant to biodegradation due to the rigid and compact structure of plant cell wall. The recalcitrance of biomass is mainly constructed by its chemical compositions that build a spatial network as a protective bulwark. Generally, the factors affecting the accessibility of biomass cellulose can be divided into direct and indirect factors. The direct factors refer to the accessible surface area, and the indirect factors include biomass structure‐relevant factors (pore size and volume, particle size, and specific surface area), chemical compositions (lignin, hemicelluloses, and acetyl group), and cellulose structure‐relevant factors (cellulose crystallinity and degree of polymerization). Pre‐treatment is actually the process to alter indirect factors and improve direct factors thus enhancing the accessibility of cellulose. In this review, we summarize the effects of chemical compositions and physical structures on the enzymatic digestibility of lignocellulosic biomass. We suggest that future work should be focused on but not limited to the molecular mechanisms of biomass recalcitrance by investigating the microscale and nanoscale features as well as hydrogen bonds network of lignocellulosic biomass. © 2012 Society of Chemical Industry and John Wiley & Sons, Ltd

The research progress on the production of 2,5-furandicarboxylic acid by the oxidation of biomass-derived 5-hydroxymethyl furfural has been reviewed, focusing on the chemical-catalytic routes.

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A number of pre-treatment methods have been developed during the last few decades to overcome biomass recalcitrance. Although the mechanisms of these pre-treatments are different, the fi nal objective is the sameincreasing cellulose accessibility to cellulase enzymes. Generally, pre-treatment is the process to disrupt the compact structure of lignocellulosic biomass and expose cellulose fi bers, which can be achieved by mechanical comminution, chemical modifi cations of biomass compositions, biological degradation, or a combination of these methods.After pre-treatment, the accessible surface area is increased resulting in the enhancement of cellulose digestibility.In this paper, we review the recent progress of the fundamental researches of various biomass pre-treatment processes, especially on how these pre-treatments alter chemical composition and physically change cell wall structure. Understanding these changes would be helpful to further optimize existing pre-treatments, and would aid in developing novel pre-treatment methods.