(345d) Biomass Dissolution and Conversion to Transportation Fuels in Ionic Liquids

Lignocellulosic biomass is an attractive feedstock for the production of transportation fuels and it has been estimated that the ratio obtained from this source to the energy consumed for its conversion to liquid fuels can be in excess of 15. However, lignocellulosic biomass is refractory because of its highly ordered structure that involves crystalline cellulose bundles surrounded by hemicellulose that is in turn linked to a coating of lignin. As a result, the initial processing of such biomass has required initial pretreatment with high temperature steam, acid, or base, in order to gain access to the cellulosic components that can be converted to sugars and then fermented to alcohols, such as ethanol or butanol. Recent work, however, has shown that ionic liquids (ILs) are capable of dissolving all of the components of biomass at relatively mild conditions and this discovery has simulated the investigation of biomass processing in such solvents. (1,2) The present studies were undertaken with the aim of identifying the role of IL composition on the solubility of cellulose and lignin, as well as the products derived from these components. A further objective was to investigate the catalyzed hydrolysis of dissolved cellulose to sugars, the conversion of sugars to fuel additives, and the depolymerization of lignin to products. This work has shown that cellulose and lignin solubilities of up to ~ 30 wt% can be achieved but that such solutions are highly viscous. The viscosity can be reduced to modest levels the addition of a cosolvent selected so as to avoid precipitation of the dissolved cellulose or lignin. The catalyzed hydrolysis of dissolved cellulose in ionic liquids was studied using a variety of acidic catalysts. The yields of glucose and cellobiose, were studied as a function of catalyst type, acid loading, reaction temperature, reaction time, and water content. 5-hydroxymethyl furfural, produced by dehydration of glucose, was also detected in low concentration. Metal-catalyzed hydrogenation of glucose yielded sorbitol, whereas hydrogenation of 5-hydroxymethyl furfural led to a spectrum of products that could be used as additives to either gasoline or diesel. Investigation are being conducted to maximize the yield of specific products and to identify the reaction pathways by which products are produced.

1. R.P. Swatloski S. K Spear, J.D. Holbrey and R.D Rogers, J. Am. Chem. Soc., 2002, 124, 4974-4975.

2. T. Welton, Chem. Rev., 1999, 99, 2071-2084; V.I. Parvulescu and C. Hardacre, Chem. Rev., 2007, 107, 2615-2665; M.J. Earle and K.R. Seddon, Pure Appl. Chem.., 2000, 72, 1391-1398.