Bioethanol Production from Ulva pertusa Kjellman by High-temperature Liquefaction

W. Choi, J. G. Han, C. Lee, C. Song, J. Kim, Y. Seo, S. E. Lee, K. H. Jung, D. H. Kang, S. J. Heo, J. S. Cho and H. Y. Lee

Abstract
This work was investigated to improve hydrolysis yields of macro alga, Ulva pertusa Kjellman by high-temperature liquefaction process (HTLP). We hydrolyzed this alga to produce bioethanol. U. pertusa Kjellman contains approximately w = 32 % glucose, comprising w = 6 % cellulose and 20 % starch, along with w = 5.9 % xylose. Among 32 % of total carbohydrates, ca. 26 % of glucose was hydrolyzed from starch (20 %) and cellulose (6 %), respectively, which tells that a more efficient process might be considered to completely hydrolyze the polymers containing fermentable sugars such as glucose and galctose, etc. Optimal hydrolysis conditions for the high-temperature liquefaction process (HTLP) were determined to be 15 MPa and 150 °C for 15 min, with water as the solvent. We found that the process temperature and time were the most important factors in the operation. Under these conditions, the conversion yields of glucose and xylose were 9.08 and 21.14 %, respectively. After cellulase and amyloglucosidase treatment, 61.1 % glucose (based on w = 32.1 %, dry basis) was converted into glucose without further conversion into xylose. The present process provided 3.1 to 12.6 % higher overall hydrolysis yields from U. pertusa Kjellman than those from other agricultural biomass. The HTLP process generated only about 40 mg L–1 of HMF (5-hydroxymethylfurfural). This concentration was much less than those from other pretreatment processes and resulted in approximately 90 % of the maximum theoretical ethanol yield. In addition, the hydrolysis pattern of U. pertusa Kjellman was much different from those of agricultural biomass materials due to different starch compositions and polymer structures.

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Keywords
bioethanol, U. pertusa Kjellman, High-Temperature Liquefaction Process (HTLP), high converted yield, different sugar compositions