芒草之前處理法對於乙醇發酵產率之影響

Influence of Pretreatment on The Ethanol Fermentation Using Miscanthus Floridulus as The Raw Material

葉人華(Ren-Hua Yeh)

指導教授 ： 李文乾

國立中正大學/工學院/化學工程學系/碩士(2013年)

摘要

芒草中富含高達80%的木質纖維素，經由各種前處理法，可降解成具可消化性纖維素固體原料，以供乙醇固態發酵之用。本研究主要利用(1)鹼處理法、(2)蒸氣爆破法、(3)酸催化蒸氣爆破法、及(4)爆破後雙氧水處理法等四種前處理法，將芒草進行固態降解。根據SEM (scanning electron microscope)電子顯微鏡的分析，利用酸催化蒸氣爆破法，為最有效可將芒草莖桿之纖維束，產生深層碎裂與表面粗糙化。利用四種前處理法，對於芒草內的木質素去除率分別為(1)鹼處理法：74%；(2)蒸氣爆破法：42.5%；(3)酸化蒸氣爆破法：63.2%；(4)爆破後雙氧水處理法：37.6%。在半纖維素去除率方面，分別為(1)鹼處理法：35.5%；(2)蒸氣爆破法：55.9%；(3)酸催化蒸氣爆破法：96%；(4)爆破後雙氧水處理法：82.8%。將降解處理之芒草固體原料，與Ethanol Red™乾酵母(Saccharomyces cereviside)、 纖維素水解酶(Accellerase 1000)混合，並透過SSF (simultaneous saccharification and fermentation)發酵程序，進行乙醇發酵。利用不同降解之芒草固體，在10% WIS (water-insoluble-solids)條件之下，經SSF發酵後，在初始八小時內，乙醇生成素率分別為(1)鹼處理法：1.053 g•L-1•h-1；(2)蒸氣爆破法：0.749 g•L-1•h-1；(3)酸化蒸氣爆破法：0.959 g•L-1•h-1；(4)爆破後雙氧水處理法：1.019 g•L-1•h-1。在24小時發酵後，相對於固體中之理論還原糖而言，其乙醇轉化率分別為：(1)鹼處理法：48.93%；(2)蒸氣爆破法：46.35%；(3)酸化蒸氣爆破法：69.01%；(4)爆破後雙氧水處理法：61.7%。最後經過固液分離後，固體殘留率分別為：(1)鹼處理法：43.6%；(2)蒸氣爆破法：46%；(3)酸催化蒸氣爆破法：41%；(4)爆破後雙氧水處理法：32.5%。本研究結果顯示，利用酸催化蒸氣爆破法可有效降解芒草莖桿，利於纖維素之水解發酵，以取得近7成之酒精產率。然而，芒草經過酸催化蒸氣爆破法後，其固體收率僅為39.7%，相對於鹼處理法之45.6%與蒸氣爆破法的49.8%，仍有改進空間。另外，根據結果來進行推論，利用酸催化蒸氣爆破法使半纖維素的去除率提升，可促進酒精產率的提高。未來將針對不同品種來源之芒草，探討四種前處理法的適用性，以作為工業化生產製程之應用開發。

關鍵字

纖維素 ； 同步糖化與發酵製程 ； 乙醇 ； 芒草 ； 半纖維素 ； 木質素

並列摘要

Miscanthus is a C4 grass and composes of up to 80% cellulose, hemicelluloses, and lignin on dry base. With a proper pretreatment it can be degraded into sugars which are subsequently used for microbial fermentation to produce ethanol. In this study, four pretreatment methods: (1) alkali treatment, (2) steam explosion, (3) acid-catalyzed steam explosion, and (4) Alkaline-Peroxide Delignification, were tested for Miscanthus floridulus. The delignification rates were determined to be 74%, 42.5%, 63.2%, and 37.6% respectively by these four methods. While the hemicelluloses removal rates were respectively 35.5%, 55.9%, 96%, and 82.8%. Residual solids after different pretreatments were undergone simultaneous saccharification and fermentation (SSF) with dried yeast (Ethanol RedTM) and cellulases (Accellerase 1000) to produce ethanol. With 10% water-insoluble-solids (WIS) of alkali-pretreated M. floridulus as the substrate, the SSF led to an ethanol productivity of 1.053 g•L-1•h-1 in first 8 h and an ethanol yield of 48.93% in 72 h. When steam-explored M. floridulus was used, the SSF led to an ethanol productivity of 0.749 g•L-1•h-1 in first 8 h and an ethanol yield of 46.35 % in 72 h. When M. floridulus was pretreated with Alkaline-Peroxide Delignification, results indicate that the Alkaline-Peroxide Delignification, i.e.,incubation with 1% H2O2 after steam explosion, the SSF led to an ethanol productivity of 1.019 g•L-1•h-1 in first 8 h and an ethanol yield of 61.7 % in 72 h. The ethanol productivity and yield were 0.959 g•L-1•h-1 and 69.01%, respectively when M. floridulus was pretreated with acid-catalyzed steam explosion. Results indicate that the acid-catalyzed steam explosion, i.e., incubation with 0.9% H2SO4 prior to steam explosion, could effectively degrade the miscanthus stems and the fermentation of hydrolysate led to nearly 70% of ethanol yield. However, the solid yield from this pretreatment was only 39.7%, relative lower compared with alkali treatment (45.6%) and steam explosion (49.8%).

並列關鍵字

cellulose ； SSF ； ethanol ； miscanthus ； hemicellulose ； lignin

參考文獻

Aiello, C., Ferrer A., and Ledesma A. (1996). "Effect of alkaline treatments at various temperatures on cellulase and biomass production using submerged sugarcane bagasse fermentation with Trichoderma reesei QM 9414. " Bioresource Technology 57:13-18.

Allen, S. G., Schulman, D., Lichwa, J., Antal, M. J., Jennings, E., and Elander, R. (2001). "A comparison of aqueous and dilute-acid single-temperature pretreatment of yellow poplar sawdust. " Industrial and Engineering Chemistry Research 40:2352-2361.

Alfani, F., Gallifuoco, A., Saporosi, A., Spera, A., and Cantarekka, M. (2000). "Comparison of SHF and SSF processes for the bioconversion of steam-exploded wheat straw. " Journal of Industrial Microbiology and Biotechnology 25: 184-192.

Avellar, B. K., and Glasser, W. G. (1998). "Steam-assisted biomass fractionation. I. Process considerations and economic evaluation. "Biomass and Bioenergy 14:205–218.

Bisaria, V. S. and Ghose, T. K. (1981). "Biodegradation of Cellulosic Materials - Substrates, Microorganisms, Enzymes and Products. " Enzyme and Microbial Technology 3:90-104.