Haibo Xie, Wujun Liu and Zongbao K. Zhao

3.1 Introduction

The impacts of climate change are forcing governments to limit greenhouse gas (GHG) emission through the utilization of sustainable energy, such as solar energy, wind energy, hydrogen energy, etc. Being well recognized as one of the sustainable energy alternatives to petroleum fuels, biofuels are developed from biomass, which are storage of solar energy via photosynthesis by nature. All countries have put the development of biofuels at the top of their agenda on the road to a clean energy system. Traditionally, biofuels were usually produced from corn, sugarcane, and so on. They are recognized as food sources for human and animals. Recently, the overdevelopment of biofuels has simulated concerns about food-based biofuels, and it was regarded as potential threat of food security and strains on natural resources [1]. As the most abundant biomass on the planet, lignocellulose is mainly consisted of cellulose, hemicellulose, and lignin [2]. The utilization of lignocellulosic resources was regarded as one pathway for production of biofuels without occupying plowland and contributing to the greenhouse effect. Additionally, nowadays almost all alternative energy sources have low-energy return on investment (EROI) values, because they require high-energy input [3]. Therefore, the development of energy-efficient conversion technologies is a challenge during the biofuel industrialization process.

Lignocellulosic biomass, primarily being a complex mixture of cellulose, hemicellulose, and lignin, is naturally resistant to breakdown by pests, disease, and weather. This inherent recalcitrance makes the production of monosugars or other valuable chemicals from lignocellulose expensive and inefficient. It is well

H. Xie (H) • W. Liu • Z. K. Zhao

Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, CAS, Dalian 116023, People’s Republic of China e-mail: hbxie@dicp. ac. cn

C. Baskar et al. (eds.), Biomass Conversion,

DOI: 10.1007/978-3-642-28418-2_3, © Springer-Verlag Berlin Heidelberg 2012 recognized that cellulose crystallinity, covalent interactions between lignin and polysaccharides, and robust hydrogen bond in cellulose microfibrils must be broken before cellulose and hemicellulose are converted to sugars efficiently through pretreatment processes [4]. Lignocellulose pretreatment, which involves many physical, chemical, structural, and compositional changes, is considered to be a central unit in an efficient and economic conversion of lignocellulosic biomass into fuels and chemicals. Presently, there are quite a lot of various physical-, chemical — and biological-based pretreatment technologies for lignocellulosic bio­mass available [5]. However, they still suffer from different problems, such as hash conditions, high cost, and low efficiency. Sometimes, an integration of different pretreatment strategies is needed aiming to a more efficient pretreatment.

The full dissolution of cellulose and lignocellulose in ionic liquids (ILs) was accompanied by the destruction of cellulose crystallinity and inter (or inner) hydrogen-bonding network, partially deconstruction of covalent bonds between carbohydrate and lignin, and decrease in the lignin content in cellulose rich products, all of which are beneficial factors for further chemical or biological conversion of carbohydrates into monosugars and chemicals. This chapter aims to provide an up-to-date progress in the understanding of the fundamental sciences and its relation to enzymatic hydrolysis with the ILs-based strategies at this start point of lignocellulose biorefinery.