以相思樹與藍桉生產纖維酒精之效率與能源分析

Abstract

本研究使用台灣相思樹與藍桉木片進行蒸氣爆碎前處理，後續的酵素水解與發酵實驗。前處理方法為將木片浸泡在1.5%硫酸96小時，再通入190oC蒸氣，持溫10分鐘進行爆碎。再將蒸氣爆碎漿進行96小時酵素水解試驗，材料濃度為2.5克/100毫升，酵素包括cellulase、β-glucosidase以及xylanase等配方組合，添加量比例：2與6毫升酵素/100克絕乾漿，溫度為50oC，pH 5.0。酵素添加量為6毫升酵素/100克絕乾重的蒸氣爆碎漿中，葡萄糖的最大得率為藍桉蒸氣爆碎漿的986.3毫克/每克纖維素，相思樹蒸氣爆碎漿為831.0毫克/每克纖維素。蒸汽爆碎漿中，木醣與木質素的含量與葡萄糖的水解效率成反比。 發酵試驗中，材料以濃度為3克纖維素/100毫升，加入上述酵素，並加入酵母菌Saccharomyces cerevisiae D5A進行同時糖化與發酵試驗，溫度條件為37oC，pH值 4.8，發酵170小時，再利用HPLC分析酒精得率。酒精產量中，相思樹蒸氣爆碎漿轉化率為70.72 克酒精/每公斤絕乾木片，藍桉蒸汽爆碎漿轉化率為測得65.21克酒精/每公斤絕乾木片。 能源分析方面，以相思樹生產一公升酒精需要11.24公斤絕乾木片，並消耗能量80.20百萬焦耳，經過發酵後剩餘的殘渣絕乾重為3.32公斤，以殘渣熱值為每公斤22.88百萬焦耳而言，殘渣部分可產出87.17百萬焦耳。而利用藍桉生產一公升酒精需要12.20公斤絕乾木片，並消耗86.24百萬焦耳。經過發酵後剩餘的殘渣為2.61公斤絕乾重，其熱值為每公斤22.31百萬焦耳，殘渣部分可產出67.38百萬焦耳。根據上述能源分析結果，相思樹為發酵纖維酒精較佳原料。

Steam explosions were conducted to pretreat acacia and eucalypt chips, then further saccharification and fermentation were also conducted. Acidic steam explosion (1.5 % w/v H2SO4) was employed at 190oC for 10 min. For the saccharification of exploded pulps, enzyme formulations with cellulase, β-glucosidase and xylanase activities were applied with two dosages: 2 and 6 percents weights to dried pulps at 50oC, pH 5.0. Optimal hydrolyzed glucose yields were 986.3 mg and 831 mg per gram of pulp alpha cellulose for acidic exploded eucalypt and acacia pulps. It’s also found that the hydrolysis efficiencies were negatively impacted by lignin and xylan contents of pulps. Simultaneous saccharification and fermentation (SSF) were also conducted using Saccharomyces cerevisiae D5A under 37oC and pH 4.8 at shake flask level with 1 % (w/v) yeast extract and 2 % (w/v) peptone. After 170 hours, 70.72 and 65.21 gram of ethanol were produced from acidic exploded acacia and eucalypt chips. The above yields are based on per kilogram of oven dried wood chip. After all the analysis, it was found that 11.24 kg dried acacia wood chip and 80.2 MJ were required to produce 1L ethanol and 3.32 kg dried residue. The dried acacia residue could generate the energy 87.17 MJ, with unit heating value of 22.88 MJ/kg. And it was found that 12.20 kg dried eucalypt wood chip and 86.24 MJ were required to produce 1L ethanol and 2.61 kg dried residue. The dried eucalypt residue could generate the energy 67.38 MJ, with unit heating value of 22.31 MJ/kg. Based on the above energy analysis, acacia was the superior raw material for the fermentation of cellulosic ethanol.