以氫氟酸搭配鹼性過氧化氫浸泡前處理法提升稻殼產醣效率之研究

Abstract

木質纖維素(Lignocellulose)是來源豐沛的再生能源，其來源可由農林廢棄物及能源作物取得，而主要成分為纖維素(Cellulose)、半纖維素(Hemicellulose)、木質素(Lignin)及灰分(Ash)。木質纖維素為一種結構堅固複雜的天然高分子複合體，不同於澱粉或糖質原料可直接經由纖維水解酵素醣化後醱酵製成生質酒精，必須透過適當之前處理，去除木質纖維素中束縛纖維素之木質素及半纖維素，令酵素更易對纖維素作用，成功轉換為葡萄糖，以利酵母醱酵為生質酒精。 本研究以稻殼為原料，其為亞洲農業廢棄物最大宗之一，它有豐富的纖維素及半纖維素（分別佔稻殼約36%和22%），成為具有發展生質酒精潛力之廢棄物。本研究先利用氫氟酸於不同濃度下浸泡進行前處理，結果顯示在氫氟酸與二氧化矽莫耳比為14時，其稻殼中之灰分已幾乎被溶出並對木質素影響到達極限，處理後和原始葡萄糖產率開始固定且為最高，較未處理稻殼之產率高約1倍左右。然而，氫氟酸對於稻殼內木質素影響有限，稻殼結構依舊緊密，因此接著使用鹼性過氧化氫作進一步之處理；本研究得知使用4%過氧化氫及16%氫氧化鈉調配出之鹼性過氧化氫處理氫氟酸浸泡過的稻殼，其處理後葡萄糖產率為99%，而木質素去除率為80%，較文獻高約10%，對纖維素束縛最小，而使酵素幾乎能完全水解處理過之稻殼；而原始葡萄糖產率於使用3%過氧化氫及12%氫氧化鈉調配出之鹼性過氧化氫處理氫氟酸浸泡過的稻殼為最佳，約83%。然而若無氫氟酸先行處理，葡萄糖產率及木質素去除率則大幅下降，顯示氫氟酸處理能初步鬆散木質纖維素結構，使後續鹼性過氧化氫處理更易發揮作用，溶解出更多的木質素，更易與酵素進行水解提升葡萄糖產率。

At present, fossil fuels represent the prime energy sources in the world. It is anticipated that these sources of energy will be exhausted in the near future. Moreover, fossil fuel combustion causes the undesirable environmental damages. On the other hand, biofuels are renewable sources which can replace the fossil fuels. Lignocelluloses are abundant renewable biomass and are major components of different wastes from forestry, agriculture, industry and municipalities. However, the close binding of the main components which are cellulose, lignin, hemicellulose and ash in the plant cell wall will restrict the complete utilization of lignocellulosic materials. Therefore, pretreatment is an inevitable process which can alter the crytallinity of lignocelluloses for making lignocelluloses more acceptable to bioprocesses such as enzymatic hydrolysis and yeast fermentation. Rice husk is one of the major agricultural residues produced in Asia. It is a complex lignocellulosic material with cellulose (~36%), hemicellulose (~22%), lignin (~21%) and ash (~11%) as major contents. It has the advantage of a low-cost source for ethanol production. This study addresses on the effect of using hydrofluoric acid (HF) and alkaline H2O2 for the pretreatment of rice husk on the sugars (xylose and glucose) yield by saccharification of enzyme. Compare with raw rice husk, the results indicated that when rice husk was treated by hydrofluoric acid (14 nHF/nSi) with alkaline peroxide (4% H2O2 16% NaOH) pretreatment. Furthermore, the ash can be recovered after HF treatment. In sum, the delignification and sugars conversion rate were increased to 80% and 99%, respectively.