Cellulose Dissolution and Biomass Pretreatment Using Quaternary Ammonium Ionic Liquids Prepared from H-, G-, and S-Type Lignin-Derived Benzaldehydes and Dimethyl Carbonate

Abstract

The synthesis of novel benzyl alkylammonium ionic liquids (IL) from starting materials derived from grass, softwood, and hardwood lignin was performed using batch reactor systems followed by facile methyl carbonate ion exchange chemistry. Approximately 90% yields of the ILs were achieved over three synthetic steps, and all novel materials were fully characterized by 1H and 13C nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. The structure–activity relationships of the lignin-derived ILs were evaluated for their ability to dissolve microcrystalline cellulose and convert switchgrass to fermentable sugars (glucose and xylose). All ILs tested, including a 1:1:1 mixture of ILs prepared from vanillin, syringaldehyde, and p-anisaldehyde yielded 52–71% of the glucose and 50–71% of the xylose from the total amount of glucan and xylan available in the raw feedstock. These data compared well to the yields obtained from switchgrass pretreatment with the IL, 1-ethyl-3-methyl imidazolium a...