Enzymatic Hydrolysis of N-Methyl Morpholine N-oxide and Ionic Liquid-treated Cellulose: A Comparative Study

Abstract

The effect of N-methyl morpholine N-oxide (NMMO), 1-ethyl-3-methyl-imidazolium acetate ([Emim]Ac) and 1-ethyl-3-methyl-imidazolium diethyl phosphate ([Emim]DEP) on pretreatment and enzymatic hydrolysis of dissolving pulp was studied. X-ray diffraction measurements of regenerated cellulose from these solvents showed that solvent pretreatment reduces the crystallinity of cellulose. However, crystallinity might not be a major factor affecting the in-situ enzymatic hydrolysis of cellulose in these solvents. Although regenerated cellulose from [Emim]DEP showed the lowest crystallinity index (∼15%), in-situ enzymatic hydrolysis of cellulose dissolved in NMMO showed the highest cellulose conversion (68% compared with 65% for [Emim]Ac and 37% for [Emim]DEP at enzyme loading of 122 FPU/g). Moreover, results showed that enzymes could tolerate up to NMMO concentration of 100 g/l and still yield full conversion of cellulose. Since it is not necessary to remove all of the NMMO, less water will be required for the washing step and thus the process will be more economical. This study thus establishes the effectiveness of NMMO as a pretreatment solvent and the current work will form the basis for developing a continuous process for conversion of biomass to hydrogen, ethanol and other hydrocarbons.