Use of Ionic Liquids in the Pretreatment of Forest and Agricultural Residues for the Production of Bioethanol

Pretreatment of lignocellulosic materials is an important step to achieve higher amounts of simple sugars, mono- and disaccharides, for obtaining ethanol as a biofuel, via enzymatic hydrolysis. The study introduces a concept that utilizes ionic liquids (ILs) as solvents in the pretreatment step, before enzymatic saccharification, for both forest residues (Eucalyptus (Eucalyptus globulus Labill.) and Lenga (Nothofagus pumilio (POEPP. EX. ENDL.) KRASSER) and for agricultural residues (wheat and corn). The procedure was evaluated at four different temperatures (80, 121, 150 and 170 °C) for 30 and 60 min, respectively, with 1-ethyl-3-methylimidazolium chloride ([EMIM+][Cl-]). Subsequent enzymatic hydrolysis of these materials was carried out at 47 °C, for 72 h, with commercial cellulases. The results demonstrated that the best experimental conditions found for wheat, corn and Eucalyptus residues were the following: 150 °C, for 60 min, yielding a total of 46, 48 and 30% sugars, respectively; in the case of Lenga residues, the optimum conditions were: 150 °C for 30 min, yielding a total of 40% sugars after saccharification. Temperatures exceeding 170 °C are not recommended for this type of pretreatment with [EMIM+][Cl-], because significant portions of cellulose could be dissolved in this IL. Finally, an analysis of the solid material after ionic liquid pretreatment is required, to determine the changes related to lignin, cellulose and hemicellulose composition.