Ionic liquids (ILs) have proven to be highly tunable ‘designer solvents’ capable of a wide range of exciting chemistries. However, industrial application at large scale is hampered by high solvent cost. This cost is, however, a tunable feature of the solvent itself – provided the ion selection is handled with a careful eye aimed at limiting synthetic complexity. Lowering the solvent cost will increase the attractive opportunities of ILs for bulk processing of lower cost end products – including such applications as biofuels.
One of the key challenges in biorefining is the initial separation or deconstruction of lignocellulosic feedstock into separate components. ILs offer unique advantages in this area, due to their unusual thermochemical properties. However, there are serious concerns about the economic viability of their use due to the very high cost of most ionic liquids (> €50/kg).
We have overcome this by redesigning the IL based deconstruction process to use low-cost, acidic ILs for lignin dissolution rather than cellulose dissolution, yielding filterable cellulose and a dissolved lignin for precipitation or conversion to high-value chemicals. We have found that processability of the cellulose is high and lignin recoveries near quantitative.
We use a range of ‘protic’ ILs, the family typically used in IL industrial processes, because their simple acid-base chemistry results in a simple and cheap synthesis, with a cost (< €1/kg) similar to common organic solvents such as acetone or toluene. This presentation will discuss how ionic liquids can be ‘tuned’ to control cost structure of the final solvent, and what implications this will have for the chemical processes involved. The impact of the solvent on large-scale applications, such as biomass pretreatment, will be discussed, with a focus on performance and process considerations such as how the ILs maintain solvent stability under long-term processing conditions, that they can be recovered and continue to exhibit very good performance after multiple reuses. These properties highlight that the ILs have the flexibility to be useful for a variety of downstream chemical processing techniques, and for use in other applications as well.
References
[1] F.J.V. Gschwend, L.M. Hennequin, A. Brandt-Talbot, F. Bedoya-Lora, G.H. Kelsall, K. Polizzi, P.S. Fennell, J.P. Hallett, Green Chem. 22 (2020) 5032-5041.
[2] H. Baaqel, I. Díaz, V. Tulus, B. Chachuat, G. Guillén-Gosálbez, J.P. Hallett, Green Chem. 22 (2020) 3132-3140.
[3] F.J.V. Gschwend, F. Malaret, S. Shinde, A. Brandt-Talbot, J.P. Hallett, Green Chem. 20 (2018) 3486-3498.
[4] A. Brandt-Talbot, F.J.V. Gschwend, P.S. Fennell, T.M. Lammens, B. Tan, J. Weale, J.P. Hallett, J.P. Green Chem. 19 (2017) 3078-3012.
[5] C.J. Clarke, W.-C. Tu, O. Levers, A. Bröhl, J.P. Hallett, Chem. Rev. 118 (2018) 747-800.
He did his BS degree in Chemical Engineering at the University of Maine (USA) and PhD in Chemical Engineering at the Georgia Institute of Technology (USA) under the direction of Prof Charles Eckert and Prof Charles Liotta. He joined the Department of Chemistry at Imperial College in 2006 as a Marshall-Sherfield Postdoctoral Research Fellow, and later became a Research Lecturer in 2008. He joined the Department of Chemical Engineering at Imperial College London as Senior Lecturer in 2014 and was later promoted to Reader (2016) and Professor (2018). He currently leads a group of 40 researchers with a focus on solvent design for reduced environmental impact in chemical processes. This has included the development of cost-effective designer solvents (ionic liquids) for large-scale applications in renewable energy, most prominently the processing of lignocellulosic biomass. These solvents are lower cost than common organic solvents, and capable of targeted separations in a variety of industrial applications. In 2017 he embarked on the commercialization of his biorefinery research by founding Lixea LTD, the first of seven spin-out companies to commercialize his sustainability research. Lixea built a pilot-scale ionic liquid based biorefinery in 2022. Prof Hallett has co-founded 7 companies in total, all in the field of sustainable technology and 4 of which use ionic liquids as process solvents. He has published more than 150 papers which have been cited more than 26,000 times. He is also co-director of the UK’s national Supergen Bioenergy Hub and formulation lead for the UK’s national Future Vaccine Manufacturing Research Hub.