Selective Breakdown of (Ligno)cellulose in Ionic Liquids

Abstract

(Ligno)cellulose is mainly composed of cellulose, lignin, hemicellulose, and extractives, which represents an abundant carbon-neutral renewable resource. Increasing concerns about global warming and diminishing fossil fuel reserves have stimulated much effort to use (ligno)cellulose as an alternative to petroleum for the production of fuels and chemicals. From a sustainability point of view, shifting society’s dependence away from fossil-based energy resources to renewable alternatives can be regarded as an important contribution towards the establishment of sustainable and “Low Carbon” economy for all nations (Ragauskas et al. 2006; Corma et al. 2007). It is estimated that by 2025, up to 30% of raw materials for the chemical industry will be produced from renewable sources. To achieve this goal, innovative processing technologies, separation and depolymerization processes, as well as catalytic conversion systems are in high demand. In general, it is difficult to dissolve (ligno)cellulose in its native form because of the three-dimensional cross-linked lignin network and strong hydrogen bonds among the polymeric matrix. The inaccessibility of a reliable medium for dissolution of (ligno)cellulose has severely hampered the efficient utilization of lignocellulosic biomass (Kamm 2007). The emerging ionic liquid-based technologies have paved an environment-friendly and homogenous manner to use (ligno)cellulose. Recent reviews have presented the progresses in bio-materials derived from biopolymers with the ionic liquids platform (Zhu et al. 2006; Pinkert et al. 2009), we thus will not cover this area here. The primary focus of this chapter is to provide an up-to-date overview on the selective breakdown of (ligno)cellulose into platform molecules with catalytic strategies in ionic liquids and to address ongoing in-depth understanding of key issues that bridge the carbohydrates chemistry and petroleum chemistry through ionic liquids. In this regard, those studies on the chemistry of monosaccharides in ionic liquids will be mentioned only if it is essential to clarify some issues related to transformation of (ligno)cellulosic materials.