Ionic liquids as ‘green solvents’ are becoming ever more important in a wide variety of chemical applications. Certain ionic liquids, based on the imidazolium cation in particular, have been shown to be suitable for solubilising lignocellulosic materials, such as woods, rapid growing grasses and waste agricultural products, which do not interfere with food based crops. For these reasons, from waste or unneeded biomass materials, useful products can be produced, which have fewer ethical and economical issues.
The major difficulty with exploiting lignocellulosic materials is the pre-treatment step, to be able to access the chemical products within biomass. Current methods of pre-treatment to produce biofuels involve concentrated corrosive acids or high temperature and pressure reactors (steam explosion), both of which are environmentally unfriendly. Ionic liquids can be designed to be environmentally friendly, as well as potential biodegradability, depending on the choice of the ions used in synthesis.
This work has successfully shown the use of diethanolammonium chloride, (which is cheap and biodegradable), to pre-treat miscanthus with a 12 times improvement of sugar release compared to 4 times improvement with dilute acid. Similar improvements have been observed with poplar biomass. Lignin removal has been identified as the major benefit in this IL pre-treatment, while hemicellulose removal also played a role. Surface morphology is a factor but cellulose crystallinity was not determined to be a factor with this ionic liquid. A yield of 30% bio-ethanol was achieved with one step saccharification and fermentation but considerable improvements are required for the process to be more efficient.
