Abstract
This thesis is focused on the enzymatic hydrolysis of cellulose while it is in an N-methylmorpholine- N-Oxide (NMMO)/H20 solution. The reason for using NMMO/H20 solvent is due to the solvent’s utilization in making lyocell fibers, and its ability to pretreat cellulose by breaking down its crystalline structure. This pretreatment leads to an increase in the yield of reducing sugars from the enzymatic hydrolysis. The enzymatic hydrolysis is done in NMMO/H20, so that one step in the pretreatment process, the removal of the pretreated cellulose prior to enzymatic hydrolysis, can be eliminated. This enzymatic hydrolysis was achieved by first dissolving the cellulose in the near monohydrate form of NMMO solution before adding water or 10 % (w/w) acetic acid; together with a diluted cellulase solution. By so doing, the structure of the cellulose substrate is changed, and, the hydrolysis reaction medium is different from the typical 50C and pH 4.8 reaction medium. This reaction medium was investigated at temperatures of 40, 50 and 60C; enzyme loadings of 34.9, 122 and 1445.6 FPU/g; and pH conditions of 5.7 and 7.4. The yield of reducing sugars was lowest at 60C, when compared to other temperatures.
For experiments at 40C and 50C, there was an interaction between the effect of temperature and pH. The 7.4 pH systems seemed to favor temperatures of 40C, while the 5.7 pH systems favored temperatures of 50C. Increases in enzyme loading led to an increase in the yield of reducing sugars; however it was observed that the increase in enzyme loading was not proportional to the increase in reducing sugar yields. For this reason, increases in enzyme loading led to a decrease in sugar yield per enzyme loading. The highest cellulose conversion, 92% conversion, was achieved at a temperature of 40C, enzyme loading of 1445.6 FPU/g and a pH of 7.4.
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