木质素在H-LAT预处理中的解构行为及酶解抑制机制研究

Enzyme inhibition of lignin during the process of bioethanol production from lignocellulosic material has been widely recognized. However, the enzyme inhibition of current alkali pretreatment was only associated with lignin removal rate, this was unable to express the changes of composition and structure of residual lignin during pretreatment, and it was unable to reveal the inhibition mechanism caused by composition and structure of lignin. This project is aiming at the effects of pretreatment on lignin structure and inhibition mechanism, and focusing on combined hydrogen peroxide and liquid ammonia treatment (H-LAT). Milled wood lignins isolated from raw materials and pretreatment substrates will be described quantitatively based on the lignin monomer model using spectroscopy, wave spectroscopy, chromatography and other analytical techniques. Based on the changes of properties, composition and structure of lignin, on the one hand, the deconstruction of lignin in H-LAT pretreatment will be interpreted through the study on the effects of pretreatment on lignin structure, on the other hand, the enzymatic inhibition mechanism of lignin will be revealed through the study on the effects of lignin on enzyme activity, enzyme adsorption, hydrolysis rate and enzymatic digestibility. And then to build a relational model between lignin deconstruction and enzymolysis macro results. The results will provide theoretical basis for the control of lignin structure for pretreatment improving the enzymatic hydrolysis of lignocellulose.

木质素在纤维素乙醇制备过程中的酶解抑制作用已得到广泛认可。但是，现行的碱预处理酶解抑制作用仅关联于木质素去除率：①无法表达木质素的基本特征、结构单元及连接键型在预处理中的变化；②无法考察木质素结构单元及连接键型对酶解的抑制机制。本项目拟针对预处理对木质素解构行为及酶解抑制机制的关键科学问题展开研究，以过氧化氢液氨联合预处理（H-LAT）为研究对象，组合运用光谱、波谱、色谱等分析技术定量描述从原材料和预处理底物中提纯的磨木木质素；以其基本特征、结构单元与连接键型的变化为中间载体，一方面研究预处理对木质素结构的影响，解译木质素在预处理中的解构行为，另一方面研究木质素对酶活、酶吸附、酶解速率及酶解率的影响规律，揭示木质素结构单元与连接键型对酶解的抑制机制；进而构建木质素解构行为与酶解率的关联模型，为实现预处理对底物木质素结构的定向调控、提高木质纤维原料的酶解率提供理论依据。

木质素在纤维素乙醇制备过程中的酶解抑制作用已得到广泛认可。但是，现行的碱预处理酶解抑制作用仅关联于木质素去除率：（1）无法表达木质素的基本特征、结构单元及连接键型在预处理中的变化；（2）无法考察木质素结构单元及连接键型对酶解的抑制作用。本项目提取了经AFEX、H2O2及联合预处理H-LAT（H-AFEX）玉米秸秆的磨木木质素，研究木质素在预处理过程中的结构变化及其对酶水解的影响。研究表明：（1）H-LAT预处理后，木质素的分子量降低且分布更均匀；G型木质素在预处理过程中最易通过芳基醚断裂导致去甲氧基化而发生降解；木质素中阿魏酸酯和对香豆酸酯发生氨解反应；然而，树脂醇、对香豆满和苯环结构在预处理中较稳定。（2）AFEX预处理主要作用于木质素中羰基以及酯键的变化；H2O2预处理主要作用于烷基醚键、芳基醚键的断裂。（3）木质素对微晶纤维素酶水解有明显的抑制作用，经H-LAT预处理后，木质素分子量降低，G型木素大量降解，对酶水解的影响大大降低；然而，随着木质素添加量的升高酶水解效率逐渐降低，木质素含量、结构对酶解影响显著。（4）酶解残渣木质素热解需要较高的活化能，热稳定性较高，在制备生物质炭过程中有较高的得率，在制备耐热性环氧树脂和新型阻燃材料上具有较高的应用价值。