Effective Saccharification and Fermentation of Kraft Pulp to Produce Bioethanol

Abstract

Bioethanol was obtained from softwood bleached kraft pulp (NBKP), an intermediate product from industrial paper processes, by successive or simultaneous saccharification and fermentation. Saccharification of NBKP was performed with several cellulases, revealing that Cellic CTec2 cellulase was the most effective at saccharification and resulted in yield of 76.3% after 72 h. Though X-ray measurements, it was noted that the crystallinity of NBKP decreased after alkali treatment with 9% sodium hydroxide (NaOH) solution for 10 min at ­10̊C. Alkali-treatment also decreased the weight of NBKP by 5 wt%. This was hypothesized to be due to removal of dissolved hemicellulose and lignin. Short time saccharification of alkali-treated NBKP resulted in good yields of glucose production and the yields did not increase with longer saccharification times. Successive saccharification and fermentation of untreated and alkali-treated NBKP were conducted using Cellic CTec2 (at 1:10 ratio by wt with respect to NBKP) for 72 h and then addition of a recombinant yeast (pYBGA 1) to give ethanol in 91.3% and 93.3% yields under the optimum conditions of cellulase and yeast, respectively, based on saccharified glucose. In contrast, simultaneous saccharification and fermentation could not effectively produce ethanol from NBKP, regardless of alkali-treatment; this may because of low efficiency of the saccharification. Using other combinations of cellulases and yeast strains to produce ethanol, it was found that Sucrase C,Meicelase, and Sumizyme C were also effective cellulases for the saccharification of alkali-treated NBKP. Furthermore pYBGA 1 was more effective at fermentation than yeast strain Kyokai No. 7 (K 7). Under optimized conditions for cellulase and recombinant yeast, ethanol yields were 91.3 and 93.3% for untreated and alkali-treated NBKP, respectively; these results show that a combination of Cellic CTec2 and pYBGA 1 was the most effective for the process of successive saccharification and fermentation of NBKP.