ENZYMATIC BIOPROCESSING OF CELLULOSE IN NMMO

摘要

Enzymatic conversion of cellulose was accomplished by dissolving cellulose in the lyocellsolvent, N-methylmorpholine N-oxide/water (NMMO/H_2O) near monohydrate, followed by gelformation caused by increased water content due to pH adjustment and enzyme addition. Theinitial dissolution and subsequent phase separation upon dilution is similar to the commercialTencel? fiber production in which more than 99% of the solvent is recovered due to theessential lack of vapor pressure for NMMO/H_2O monohydrate. Previous rheological studies bythe presenting author indicate that lignin is not soluble in NMMO/H_2O and can be separated bysimple filtration, whereas cellulose and hemicelluloses are soluble in NMMO/H_2O as well as inthe ionic liquids tested: 1-ethyl-3-methylimidazolium acetate ([Emim]Ac), 1-ethyl-3-methylimidazolium diethyl phosphate ([Emim]DEP), and 1-butyl-3-methylimidizoluim chloride([Bmim]Cl). NMR, MRI and X-ray diffraction were used to characterize the formation of a gelphase for the cellulosic solutions and related diffusion characteristics after dilution with water.High cellulosic loading in the initial solvent (at least 15%w cellulose) and yields of reducingsugars (up to 90% conversion) were accomplished by dissolution in a modified twin screwextruder. Hydrolysis was similar in both a reactor after the extruder and in the extruder whenequipped with recycle. The commercial enzyme mixtures (primarily Accelerase?1000 byGenencor) were more active in NMMO/H_2O than in the three ionic liquids tested or in aqueoussystems with suspended cellulose. Initial reaction rates are much more rapid in the gel statethan in suspension due to the accessibility of the cellulose by the enzymes. Two-way analysis ofvariance of the data (ANOVA) was performed using MATLAB. At the 95% confidence level,conversion of cellulose to sugars after dissolving in NMMO/H_2O were higher at higher celluloseconcentrations, higher at lower pH, and dependent upon the general form of the cellulose (gel,suspended or regenerated). Also at the 95% confidence level, the conversion to sugars washigher in NMMO/H_2O than in the ionic liquids and higher than in cellulose suspended in H_2O,and the initial conversion rate in NMMO/H_2O was also higher than cellulose re-suspended afterpretreatment with NMMO/H_2O. However, at the 95% confidence level, the overall conversion inNMMO/H_2O gels is not significantly different from cellulose re-suspended after pretreatment withNMMO/H_2O. Trend line analysis for R~2 correlation factors using Excel indicated most of the dataindicated a dependence of conversion on the logarithm of time at the 95% confidence levelexcept at 60oc, high enzyme loading and high pH. The preliminary results at 60 oc and HPLCresults imply subsequent reactions could follow hydrolysis in NMMO/H_2O.