International Research Fellowship Program: Computer-Aided Molecular Design of Ionic Liquids for the Pretreatment of Cellulose

Weis Derick C, Cookeville TN

Investigators

Abstract

1006204 Weis The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad. This award will support a twenty-four month research fellowship by Dr. Derick Weis to work with Dr. Doug MacFarlane at Monash University in Australia and in the U.S. with Dr. Robin Rogers at the University of Alabama. Cellulose is an abundant, renewable resource available from plants that can be turned into ethanol and help replace fossil fuels. Potential feed stocks for cellulose include waste products like corn stover and sugar cane bagasse, or planting a specific crop of switch grass for harvest. Currently, the cost of cellulosic ethanol is too high for practical consideration. Environmentally friendly solvents, known as ionic liquids, have been identified for a pretreatment step in the production of cellulosic ethanol as a way to reduce the cost by making it easier for enzymes to break down biomass into fermentable sugars. Ionic liquids can be formally defined as salts that melt below 100 oC, and generally consist of a positively charged organic cation with a negatively charged anion. The solvation properties can be fine-tuned for particular applications depending on the cation/anion chosen. In recent years, ionic liquids have received a lot of focus because of the potential to develop environmentally friendly solvents. Some of the favorable characteristics include negligible vapor pressure, non-flammability, and thermal stability. The negligible vapor pressure is an important feature because of the reduced risk of respiratory problems compared to the fumes given off from traditional solvents. There is also a cost savings for industrial applications because it is possible to separate and recycle ionic liquids from other components in the process. Some important properties for developing more effective ionic liquids to be used in a pretreatment step include melting point, viscosity, and cellulose solubility. Both melting point and viscosity are essential because of process operating considerations. For example, the ionic liquid must be present in liquid form at the required temperature. Energy can also be conserved by specifically designing ionic liquids with a low melting point because a significant amount of heat will not be necessary. In a similar manner, ionic liquids with low viscosity will require less energy to pump and transport. A computer-aided molecular design (CAMD) technique is being applied to help identify potentially new ionic liquids with favorable properties for more effective cellulose pretreatment. Applying this approach is much quicker, less expensive and allows for a more comprehensive search for the most suitable candidates. Currently, there are only a limited number of ionic liquids in the literature with cellulose solubility data, and thus, few options exist for the desired application. The CAMD technique helps to select potential ionic liquids for synthesis and testing in the laboratory from the numerous combinations of cation/anion pairs available.