(193ac) Cellulose Dissolution Mechanisms in Tetrabutylphoshonium Hydroxide—Water Mixtures As Explored By Molecular Dynamics

In previous experiments, the ionic liquid tetrabutylphosphonium hydroxide (TBPH) and water has been shown to dissolve high concentrations of cellulose at room temperature, within a wide range of water concentrations.¹ Tolerance of water is a critical feature of any sustainable manufacturing process, because all cellulosic biomass naturally contains substantial amounts of water. Therefore, the TBPH-water ionic liquid shows promise for reducing the overall energy consumption of the cellulose extraction process. Our molecular dynamic simulations investigate the chemical mechanisms that allow this rapid cellulose dissolution process to occur at room temperature. The TBPH-water mixture appears to have increased molecular diffusion in the range of water concentrations (above 21 wt % water) where cellulose dissolution is maximized. This research explores the extent of the cellulose dissolution, enhanced diffusion effects, as well as the bindingand cleavingproperties of the TBPH-water solution.² We also investigate how the TBPH interacts with the individual cellulose strands, inhibiting the initial reformation of original cellulose bundle structure. Determining the unique chemical mechanisms of the TBPH-water solution enables more efficient cellulose dissolving ionic liquids to be designed in the future.

¹Mitsuru Abe, Yukinobu Fukaya and Hiroyuki Ohno, 2011, Fast and facile dissolution of cellulose with tetrabutylphosphonium hydroxide containing 40 wt% water

²Brooks D. Rabideau, Animesh Agarwal, and Ahmed E. Ismail, 2013, Observed Mechanism for the breakup of small bundles of cellulose 1a and 1b in ionic liquids from molecular dynamic simulations