The Application of Ionic Liquids in Dissolution and Separation of Lignocellulose

Abstract

There are many problems in traditional chemical industry, such as environmental pollution, low production efficiency and high energy consumption. Nowadays, energy and environment become two main bottlenecks in the development of chemical industry. As non-renewable fossil resource, petroleum and coal are still widely used in the modern world. The excessive use of fossil resource will accelerate the deterioration of environment. Therefore, it is necessary to find new kinds of energy for the sustainable development and environmental protection. Biomass is renewable, environmentally friendly and abundant in the natural world. According to the statistics, the total energy produced from photosynthesis is nearly ten times more than that of fossil fuel used in the world every year. However, the utilization rate of biomass energy is less than 1%. Although the preparation of ethanol from glucose and starch has already been employed in industry for a long time, the universal shortage of food restricts the application of this method in the large-scale production of clean energy. Therefore, it is very important to produce green energy and bio-products from lignocellulose which is the most abundant biomass (Pu et al., 2008; Zhu, 2008). Lignocellulose is hard to be dissolved and separated with common solvents due to its complex structure, strong intraand inter-molecular hydrogen bonding. Traditional acid and basic systems used in the lignocellulose industry are environmentally polluted, and can not be recycled (Li et al., 2007). Therefore, development of new efficient solvents is the first step for the transformation and utilization of lignocellulose. As novel green solvents, ionic liquids (ILs) have many attractive properties, including negligible vapor pressure, non-flammability, thermal stability and recyclability, and have been used in organic synthesis, electrochemistry, catalysis, extraction and among others (Qian et al., 2005; Dupont et al., 2002; Scurto et al., 2002; Kubo et al., 2002). In 2002, Rogers and co-workers (Swatloski et al., 2002) found that some hydrophilic ILs are effective solvents for the dissolution of cellulose. The high solubility of cellulose in the ILs attracts great attention of the scientists and engineers in the world. Since then, significant progress 4