發(fā)布時間：2018-04-03 22:49

  本文選題：纖維素溶劑　切入點：玉米秸稈　出處：《江蘇大學》2017年碩士論文

【摘要】：木質纖維素是地球上儲量最大的可再生資源,利用木質纖維素制備生物乙醇是緩解環(huán)境和能源問題的重要途徑之一。在長期的自然進化過程中,植物細胞壁形成了抵御酶降解及外部微生物的復雜結構。由于底物結構及酶解過程體系的復雜性,傳統(tǒng)預處理方式存在著效率低和能耗高等缺點。與傳統(tǒng)預處理相比,基于纖維素溶劑的木質纖維素預處理方法在預處理條件和預處理效果等方面具有一定的優(yōu)勢。本論文使用纖維素溶劑對玉米秸稈進行預處理,通過對比不同纖維素溶劑的預處理效果,篩選出適用于玉米秸稈的預處理方法,從經(jīng)過高效預處理的玉米秸稈中提取木質素,初步探索預處理對木質素物理化學結構的影響;進一步擴大篩選出的纖維素溶劑的適用范圍,研究其對麥稈的預處理效果,同時分析預處理液固比對預處理效果的影響;對傳統(tǒng)的預處理與酶解糖化工藝進行改良,提出利用預處理與酶解糖化“一鍋法”制備可發(fā)酵糖的方法,探究該方法可行性,并與傳統(tǒng)“分步法”進行對比,分析其優(yōu)越性。本論文的主要研究成果歸納如下:(1)酸性和堿性纖維素溶劑預處理后,玉米秸稈的酶解轉化率都得到了大幅提升。它們都是通過破壞纖維素分子內(nèi)和分子間的氫鍵,從而破壞纖維素的剛性結構,同時去除玉米秸稈中一定量的半纖維素和木質素,降低生物質的頑抗性,提高酶解糖化效果。與85%濃磷酸相比,低溫NaOH/尿素溶液對玉米秸稈預處理效果較好。其中,在酶加載量為15 FPU/g底物的條件下,酶解24 h后,葡聚糖可以完全轉化為葡萄糖。(2)85%濃磷酸預處理后,底物中存在大量的木質素,雖然纖維素結晶度降低較多,但沒有獲得較高的酶解轉化率。研究表明,與纖維素結晶度相比,木質素對玉米秸稈酶解糖化的效果影響較大。通過對木質素的初步探索發(fā)現(xiàn),低溫NaOH/尿素預處理后的木質素“核心”結構沒有被破壞,含有較多的化學活性基團,可能具有較好的化學活性。(3)低溫NaOH/尿素溶液對麥稈同樣具有良好的預處理效果。在酶加載量為15 FPU/g底物條件下,酶解糖化48 h,葡聚糖轉化率可達95%,木聚糖轉化率為84%。不同預處理液固比對麥稈中纖維素結晶度具有一定影響,但對麥稈的化學成分和酶解性能沒有顯著影響,這為高固載量預處理生物質的進一步研究提供了參考。(4)低溫NaOH/尿素預處理與酶解糖化“一鍋法”是可行的。最優(yōu)預處理與酶解糖化條件下,葡聚糖與木聚糖的酶解轉化率均可達到90%以上�！耙诲伔ā笨梢援a(chǎn)生比傳統(tǒng)“分步法”更多的可發(fā)酵糖,其產(chǎn)生的可發(fā)酵糖占原料中總糖的90.24%,明顯高于傳統(tǒng)“分步法”的73.17%。低溫NaOH/尿素預處理液中不含有如糠醛和5-羥甲基糠醛發(fā)酵抑制物,該方法具有廣闊的應用前景。
[Abstract]:Lignocellulose is the largest renewable resource on the earth. Bioethanol using lignocellulose is one of the important ways to alleviate the environmental and energy problems.During long term natural evolution, plant cell walls formed complex structures resistant to enzyme degradation and external microorganisms.Because of the complexity of substrate structure and enzymatic hydrolysis process, the traditional pretreatment method has the disadvantages of low efficiency and high energy consumption.Compared with the traditional pretreatment, the lignocellulose pretreatment method based on cellulose solvent has some advantages in pretreatment conditions and pretreatment effect.In this paper, cellulose solvent was used to pretreat corn straw. By comparing the pretreatment effect of different cellulose solvents, the suitable pretreatment method for corn straw was selected, and the lignin was extracted from the corn straw which was pretreated with high efficiency.The effect of pretreatment on the physicochemical structure of lignin was explored preliminarily, the suitable range of cellulose solvent was expanded, the effect of pretreatment on wheat stalk was studied, and the effect of pretreatment liquid / solid ratio on pretreatment effect was analyzed.The traditional pretreatment and enzymatic saccharification process were improved, and the method of preparing fermentable sugar by pretreatment and enzymatic saccharification "one pot method" was put forward. The feasibility of this method was explored, and compared with the traditional "step by step method", the superiority of the method was analyzed.The main research results of this paper are summarized as follows: 1) after pretreatment with acidic and alkaline cellulose solvents, the conversion rate of enzymatic hydrolysis of corn straw was greatly improved.All of them destroy the rigid structure of cellulose by destroying the hydrogen bond in and between molecules of cellulose. At the same time, they remove a certain amount of hemicellulose and lignin from corn straw, reduce the resistance of biomass, and improve the effect of enzymatic hydrolysis and saccharification.Compared with 85% concentrated phosphoric acid, the pretreatment effect of low temperature NaOH/ urea solution was better than that of 85% concentrated phosphoric acid.Under the condition of enzyme loading of 15 FPU/g substrate and enzymatic hydrolysis for 24 h, dextran could be completely converted into glucose, 2n 85% concentrated phosphoric acid pretreatment, and there was a large amount of lignin in the substrate, although the crystallinity of cellulose decreased more.But no higher enzymatic conversion was obtained.The results showed that lignin had a greater effect on the enzymatic hydrolysis and saccharification of corn straw than cellulose crystallinity.Through the preliminary study of lignin, it was found that the "core" structure of lignin treated with NaOH/ urea at low temperature was not destroyed and contained more chemical active groups.NaOH/ urea solution at low temperature also has good pretreatment effect on wheat straw.The conversion rate of dextran and xylan was 95 and 84 respectively under the condition of enzyme loading of 15 FPU/g substrate and enzymatic hydrolysis and saccharification for 48 h.The crystallinity of cellulose in wheat straw was influenced by different ratio of pretreatment liquid to solid, but had no significant effect on the chemical composition and enzymatic hydrolysis performance of wheat stalk.This provides a reference for the further study of biomass pretreatment with high solid load.) the pretreatment of low temperature NaOH/ urea and enzymatic hydrolysis and saccharification are feasible.The conversion rate of dextran and xylan could reach above 90% under the optimal pretreatment and enzymatic saccharification conditions.The "one-pot method" can produce more fermentable sugar than the traditional "step method". The fermentable sugar accounted for 90.24% of the total sugar in the raw material, which is obviously higher than that of the traditional "step method" 73.17%.Low temperature NaOH/ urea pretreatment solution does not contain such as furfural and 5-hydroxymethylfurfural fermentation inhibitors. This method has a broad application prospect.
【學位授予單位】：江蘇大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TQ352.1;X712

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