(710a) Understanding the Mechanisms of Cellulose Dissolution in Ionic Liquids

Heightened interest in energy independence and environmental awareness has accelerated the search for combustible fuel sources which are both renewable and have a low environmental impact. One promising route is the conversion of waste biomass into tailor-made fuels. An important aspect of this process is the low-energy separation of cellulose from the biomass. Ionic liquids (ILs) have been demonstrated capable of dissolving cellulose while being essentially non-volatile, making them strong candidates for "green" processing. However, full exploitation of ILs as a commercially viable processing medium requires better understanding of the dissolution mechanism. However, in spite of extensive research, many parts of this process remain uncertain. Using molecular dynamics simulations, we examine the behavior of cellulose in the ionic liquids [BMIM]Cl, [EMIM][Ac] and [DMIM][DMP] as well as water. All three of these ionic liquids have been observed to dissolve cellulose quite well yet have differently sized anions. We explore these differences and the impacts they have on their interactions with cellulose. First, we examine the dynamics of a single cellulose strand in these ionic liquids, and study the structural and dynamic properties, such as the radius of gyration and the number and lifetime of hydrogen bonds that are formed between the anions and cellulose. Next, we probe the dissolution mechanism of multiple, bound cellulose oligomers of varying lengths, examining interactions at the IL/cellulose interface and the breakup of inter-cellulose hydrogen bonds. We also study the relationship between the anion strength and the hydrogens in hydroxyl groups in determining the relative aggregation of cellulose chains in these different solvent media.