(111b) Recycling of Inexpensive Ionic Liquids for Lignocellulose Fractionation
Lignocellulosic biomass is a composite material comprising cellulose, hemicellulose and lignin and is a target feedstock for the bio-based chemicals and material economy. We have developed low-cost ionic liquids that are alternatives to aqueous or organic solvent deconstruction (aka pretreatment) systems, with distinct processing advantages in the separations, such as excellent separation of cellulose from lignin and recovery of a valuable lignin fraction.
Previous IL-based biomass research has focused on swelling and dissolving the entire lignocellulose with dry ILs. The requirement for costly ionic liquids has resulted in challenges for IL recovery. Water, a major component of biomass, prevents cellulose dissolution, necessitating extensive drying of biomass and the hygroscopic IL, increasing energy costs.
We have overcome this by redesigning the process for lignin dissolution, yielding filterable cellulose, preconditioned for further use, and an IL-lignin solution for precipitation or conversion to high-value chemicals. We use a range of ‘protic’ ILs, the family typically used in IL industrial processes because their simple acid-base chemistry makes them easy and cheap to prepare. Despite the low cost (as low as $1.24 per kg)1 and low environmental impact, solvent recycling is mandatory for this application.2
The results from this study demonstrate that the ILs maintain solvent stability under long-term processing conditions, that they can be recovered and continue to exhibit very good cellulose lignin fractionation after multiple reuses.
1 L.Chen, M. Sharifzadeh, N. Mac Dowell, T.Welton, N.Shah, J.P. Hallett, Green Chemistry, 2014.
2 D. Klein-Marcuschamer, B. A. Simmons and H. W. Blanch, Biofuels, Bioprod. Biorefin., 2011, 5, 562–56.