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  • 學位論文

柳杉及相思樹幹材於生質能源利用之特性評估

Bioenergy Application Characteristics of Cryptomeria japonica and Acacia confusa Wood

指導教授 : 葉汀峰

摘要


柳杉(Cryptomeria japonica)及臺灣相思樹(Acacia confusa)為臺灣常見之造林樹種,其抽出成分的生物活性與醫藥應用已有廣泛的研究;然而,在提煉完抽出成分後,剩餘的殘料未能加以利用,實之可惜。為了達到全株利用及提供燃料需求之目標,提煉抽出成分後之殘料可作為生物燃料應用時的來源。因此,為了瞭解柳杉及相思樹之生質能利用障礙,本研究將提煉抽出成分後之心材進行基本化學組成、木質素單體及纖維素結晶度等試驗,以探討木材組成結構是否具有作為生物燃料利用的潛力。結果發現,柳杉之總醣含量較相思樹低,木質素含量則較高。柳杉之木質素主要由Guaiacyl lignin組成,且以縮合木質素為主,相思樹木質素則同時由Syringyl lignin及Guaiacyl lignin組成,非縮合木質素約佔54.4%,S/V比例為2.6。纖維素結晶度指數方面,柳杉的結晶度指數較低,為49.7%,相思樹較高,為59.2%。將無抽出成分的柳杉及相思樹進行稀酸前處理後發現,相思樹具有較佳的糖類釋出效果,經過170oC、20 min前處理後之總糖釋出比例為14.6%,可移除大約65%的Xylose,殘料的Glucose含量為50.2%;然而,在相同條件下,柳杉之總糖釋出比例僅7.4%,殘料的Glucose含量為44.1%。從木質素單體分析及纖維素結晶度指數結果可知,柳杉及相思樹木質素總氧化產物均會隨著稀酸前處理反應溫度及時間的增加而降低,結晶度則大致隨溫度增加而提升。若將柳杉及相思樹經過亞硫酸鹽前處理(Sulfite pretreatment to overcome recalcitrance of lignocellulose,SPORL),則發現柳杉是在8% NaHSO3 + 1% or 2% H2SO4時、相思樹是在4% NaHSO3 + 1% H2SO4時具有較佳的前處理效果,均可以移除75%以上Xylose,H2SO4添加量對柳杉則無呈現明顯差異。而剩餘之殘料,柳杉Glucose的含量比例為46.0–48.8%,相思樹則是51.2–63.3%;雖然SPORL前處理產生的Furfural含量較稀酸前處理高,但5-Methylfurfurl及Phenol則較稀酸前處理低。同樣從木質素單體及纖維素結晶度結果可知,無論經過何種條件,柳杉及相思樹木質素之總氧化產物均大幅降低,結晶度指數也較未前處理時提高。若比較不同前處理的酵素水解效率,柳杉即使經過前處理及研磨10 Cycles後,其酵素水解效果仍舊不佳,在稀酸前處理為170oC、20 min時,即使加上前處理釋出之水解物比例,Glucose及Xylose轉換率為20.6%及76.4%,而SPORL前處理為8% NaHSO3 + 1% H2SO4時,其Glucose及Xylose轉換率也僅為30.8%及66.2%。若換算成理論生質酒精收率,大約只能生產83.6 g/kg的酒精。然而,相思樹在經過SPORL前處理後,總和前處理的水解物釋出比例及酵素水解釋出之Glucose及Xylose,兩者轉換率分別為44.1-51.2%及41.3-85.7%。換算成理論生質酒精收率後,相思樹在經過4% NaHSO3 + 1% H2SO4之前處理及酵素水解後應能生產最多酒精,預計產量為179.9 g/kg。然而,含抽出成分之柳杉及相思樹即使經過SPORL前處理,預期理論生質酒精收率只有68.4 g/kg及125.7 g/kg。因此,綜合上述結果可以得知,無抽出成分的相思樹之生質能利用障礙較低,若經過適當的前處理步驟即可作為生物燃料利用,柳杉若要開發成生物燃料則可能需要依靠其他前處理來改善其生質能利用障礙。

並列摘要


Cryptomeria japonica and Acacia confusa are common afforestation species in Taiwan. The outstanding bioactivity and medical applications of their extractives have been extensively studied. However, after removing extractives, the extractive-free wood residues found not utilize. In order to achieve the goal of whole tree utilization and provide the demand of fuel in the future, extractive-free wood residues can be considered as a candidate for biofuel. Therefore, it’s essential to understand the biomass recalcitrance of these two wood species. In this study, we tested the extractive-free heartwood residues for chemical composition, lignin composition and cellulose crystallinity index to investigate the characteristics whether both wood species have the potential for biofuel utilization. According to the results, we found that the total polysaccharides content of C. japonica was lower than that of A. confusa, but total lignin content was higher. Furthermore, the lignin composition of C. japonica was mainly constituted of Guaiacyl (G) lignin, and that of A. confusa was composed of syringyl (S) lignin and Guaiacyl lignin. The non-condensed lignin of A. confusa was about 54.4% and the S/V was 2.6. The cellulose crystallinity index (CrI) of C. japonica and A. confusa was 49.7% and 59.2%, respectively. After dilute acid (DA) pretreatment, extractive-free A. confusa released more sugar then that of C. japonica. When the DA pretreatment was at 170oC for 20 min, the sugar percentage released from A. confusa was 14.6%, with about 65% xylose removal, DA pretreated wood meals contained 50.2% glucose. However, under the same condition, the sugar percentage released from C. japonica was only 7.4% and its DA pretreated wood meals contained 44.1% glucose. Moreover, C. japonica and A. confusa lignin condensed and cellulose CrI slightly increased after DA pretreatment when the reaction time and temperature increased. We also pretreated C. japonica and A. confusa with sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL). Results showed that C. japonica pretreated with 8% NaHSO3 + 1% or 2% H2SO4 and A. confusa pretreated with 4% NaHSO3 + 1% H2SO4 could remove over 75% xylose. The glucose content of SPORL pretreated wood meals was 46.0–48.8% for C. japonica and 51.2–63.3% for A. confusa, respectively. Although SPORL pretreatment produced higher amount of furfural than DA pretreatment, 5-methylfurfural and phenol extent were lower. From the results of lignin composition and cellulose CrI, the total yield of nitrobenzene oxidation products decreased and cellulose CrI increased after SPORL pretreatment. Comparing the results of different pretreatment and enzymatic hydrolysis efficiencies, C. japonica performed poorly in enzymatic hydrolysis. Glucose and xylose conversion were 20.6% and 76.4% when C. japonica pretreated at 170oC for 20 min, while glucose and xylose conversion were 30.8% and 66.2%, about 83.6 g/kg of theoretical bioethanol yield, when C. japonica pretreated SPORL condition of 8% NaHSO3 + 1% H2SO4. However, the glucose and xylose conversion of A. confusa were 44.1-51.2% and 41.3-85.7% after SPORL pretreatment and enzymatic hydrolysis. If we convert the sugars into theoretical bioethanol yield, A. confusa could produce 179.9 g/kg after 4% NaHSO3 + 1% H2SO4 pretreatment and enzymatic hydrolysis. However, the theoretical bioethanol yield of non-extracted C. japonica and A. confusa were still low after SPORL pretreatment and enzymatic hydrolysis, just 68.4 g/kg and 125.7 g/kg, respectively. Taking all these results together, extractive-free A. confusa was more appropriate for biofuel utilization than C. japonica.

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