残渣木质素分子活化及合成多元共缩聚树脂的机理研究

Lignocellulosic fermentation residue, which predominantly composed of lignin, is the primary byproduct produced from bioethanol production process. It possesses a very complex matrix structure and relatively low reactivity. The structural elucidation and efficient conversion of this byproduct are the key and difficult basic researches of lignocellulosic utilization. The project will focus on the three major difficulties of lignin research, structural elucidation, molecular activation, and value-added conversion. The main industrial lignocellulosic fermentation residues in China will be chosen as raw material. A novel method based on mild alkaline preswollen and in-situ enzymatic hydrolysis will be used to isolate the whole lignin from the lignocellulosic fermentation residue, and the quantification of the molecular structural of the obtained lignin will be achieved by using various quantitative NMR techniques. To improve the reaction activity of lignocellulosic fermentation residue for subsequent utilization, a new activation technique based on alkaline medium will be firstly adopted to create more active sites in lignin fraction. A novel multiple co-condensation resin synthesis technique, in which the activated lignocellulosic fermentation residue used as a partial substitution for phenol, will be developed. Based on isotope-labelled lignin model compounds, which is firstly employed, the synthesis mechanism of the co-condensation resins will be explored at the molecular level through matrix assisted laser desorption ionization time of flight mass spectrometry and other instrumental analysis techniques. By regulating bonding properties of co-condensation resins, the correlation between macromolecular structure and bonding strength will also be explained. The researches conducted in this project will provide valuable theoretical instruction and technical support for the value-added utilization of lignin.

木质纤维发酵残渣是纤维素乙醇生产过程中的主要副产物，其主要成分为木质素，具有分子结构复杂及反应活性低等特性，其结构解译及高效活化转化是木质纤维利用基础研究领域的重点及难点。本项目针对木质素在结构表征、分子活化及高值转化时存在的研究难点，拟选用我国主要工业木质纤维发酵残渣为原料，采用弱碱预润胀结合原位酶水解新技术分离得到原料中全部木质素组分，并利用定量核磁共振等技术，对木质素分子结构进行定量表征研究；率先采用碱性介质高效活化新技术，增加发酵残渣中木质素分子的活性位点，提高其化学反应活性；以活化发酵残渣为原料代替苯酚，创建多元共缩聚树脂合成新技术，并率先采用同位素标记木质素模型物，利用基质辅助激光解析电离飞行时间质谱等技术，在分子水平上阐明其共缩聚机理；通过对共缩聚树脂胶合性能的调控，解译其分子结构与胶合性能之间的关系。本项目的研究将为木质素的高值化利用提供理论指导和技术支撑。

项目以三种我国主要工业木质纤维发酵残渣为原料，采用弱碱预润胀结合原位酶水解新技术分离得到原料中全部木质素组分。利用定量核磁共振等技术对木质素分子结构进行定量表征发现，木质纤维发酵残渣中木质素含量最低仅有37%，且木质素活性位点在0.7 mmol g-1左右，不利于制备共缩聚树脂。采用碱性介质高效活化新技术，将发酵残渣中木质素分子的活性位点数最高提升270%。以活化发酵残渣为原料代替苯酚，创建了多元共缩聚树脂合成新技术。率先采用同位素标记木质素模型物在分子水平上研究其共缩聚机理发现，木质素在碱性介质中酚化改性的反应历程较单一，通过苯酚对位与木质素α位发生亲核取代反应生成结构唯一的酚化改性产物。甲醛作为交联剂可以与苯酚或酚化改性后的木质素发生亲核加成反应，生成一元及多元羟甲基苯酚。在制备树脂的过程中产生了大量的共缩聚键从而形成了稳固的树脂结构。此外，含有碳水化合物的残渣还可以用来替代面粉作为人造板的填料，不仅可以调节胶黏剂的黏度，还可以防止胶黏剂在板材中的过度渗透，从而增强树脂胶黏剂的粘结强度。在木质素与碳水化合物的协同作用下，用发酵残渣基树脂胶黏剂制备的胶合板胶合强度可达1.07 Mpa，且该胶合板的甲醛释放量可以降低94%。本项目为木质素的高值化利用提供了理论指导和技术支撑。