Pyridinium based ionic liquid: A pretreatment solvent and reaction medium for catalytic conversion of cellulose to total reducing sugars (TRS)

In the last decade, the transformation of lignocellulosic biomass into biofuel through a sugar platform has been an active research subject due to depletion of fossil fuel sources. Total reducing sugars (TRS) obtained from lignocellulosic materials are considered intermediates for the preparation of various valuable chemical compounds. In this work, pyridinium based ionic liquids were synthesized and utilized for the dissolution of cellulose and further conversion to TRS in the presence of metal salts as catalysts. The prepared ILs were characterized using 1H NMR and evaluated for the dissolution of cellulose and found that [C4C1Py][Cl] is the best solvent to dissolve it up to 28% at 110 °C. Optical microscopy in conjunction with FTIR, SEM, XRD and TGA analyses were employed to monitor dissolution phenomenon and ascertain structural changes in regenerated cellulose. SEM results showed disrupted flaky construction for regenerated cellulose. The thermal stability decreased for regenerated cellulose as observed by TGA analysis. This desirable change in cellulose after IL pretreatment was utilized to facilitate metal salts based on the catalytic conversion of cellulose to TRS. Among metal salts, CoCl2 was identified as the best one to generate the highest yield of TRS i.e. 78% at 110 °C for 4 h. Various reaction conditions like time, temperature, and catalyst loading were optimized for catalytic conversion. The optimum conditions were observed at 4 h treatment time, 120 °C and 12% catalyst loading.