Enzymatic Hydrolysis of Pulp Dissolved In N Methyl Morpholine Oxide (NMMO) and Ionic Liquids
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The first step in the conversion process of biomass to biofuels or hydrogen lies in picking an environmentally friendly solvent which is capable of breaking up the crystalline microstructure of cellulose. Once the cellulose is in suspension, enzymes (cellulases) are added to the reactor to hydrolyze the cellulose to simple sugars that are then fermented by bacteria to biofuels. Till date, a number of solvents have been used for dissolving cellulose and for reprecipitating it by the addition of an anti-solvent thus making it a multi-stage process. In this work, it is shown that the number of processing steps can be reduced by directly carrying out the enzymatic hydrolysis in NMMO which is an excellent solvent for dissolving crystalline cellulose. Dissolving pulp of degree of polymerization 1160 is used as the substrate and Accellerase 1000 purchased from Genentech is the cellulase used. The rates of enzymatic hydrolysis and total sugars released are studied as a function of solution conditions – solution pH, temperature and enzyme loading. These studies reveal that the enzymes are active in NMMO and that the rates of hydrolysis of cellulose dissolved in NMMO are comparable to the rates of hydrolysis of regenerated cellulose suspended in aqueous buffer solutions. A comparative study of enzymatic hydrolysis reactions of cellulose dissolved in NMMO and in cellulose dissolved in ionic liquids (Emim Ac and Emim DEP) was also carried out. These studies reveal that processing with NMMO results in a higher rate and yield of sugars when compared with the ionic liquids. It will also be shown that high yields of sugars can be achieved by using a twin screw reactor for processing of high concentrations of the pulp (upto 15% w/w) and by carrying out the reactions in the twin screw reactor itself.