Rapid dissolution of lignocellulosic biomass in ionic liquids using temperatures above the glass transition of lignin

Rapid dissolution of bagasse and southern yellow pine has been achieved in the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C(2)mim]OAc) by using a dissolution temperature above the glass transition of lignin (ca. 150 degrees C). When 0.5 g of bagasse or pine is added to 10 g of [C(2)mim]OAc, complete dissolution can be obtained in 5-15 min for bagasse at a temperature of 175-195 degrees C, compared to 15-16 h at 110 degrees C, and over 90% of added pine can be dissolved with heating at 175 degrees C for 30 min. Upon regeneration in acetone/water, lignin and carbohydrate can be partially separated as lignin and a cellulose-rich material (CRM, pulp). Compared to published methods with lower temperatures and longer times (e.g., 110 degrees C, 16 h), processing bagasse in [C(2)mim]OAc at 185 degrees C for 10 min results in higher yields of both recovered lignin (31% vs. 26% of the available lignin) and carbohydrate (carbohydrate yield = 66% vs. 63% of the available carbohydrate). In addition, the CRM pulp recovered using the higher temperature method has much lower residual lignin content (6% vs. 20%). Similar results were obtained for pine (lignin content in CRM with higher vs. lower temperature method = 16.1% vs. 23.5%). The IL was recycled and reused although the efficiency decreased and ca. 15% of the IL had degraded after the higher temperature process. These latter results suggest further optimization of the choice of IL and heating conditions might be needed to develop an energy and chemical efficient process.