杨木水解液中胶体木素的稳定机理及果胶酶处理改善木素去除选择性的研究

It is believed as an effective process for biorefinery that hemicelluloses are extracted by autohydrolysis prior to wood pulping, and the high value-added utilization of purfied hemicelluloses in the hydrolysates is one of the key processes for biorefinery.However,the stable colloidal lignin particles are formed during the cooling of the extracted hydrolysates due to the condensation of the lignin, which results in the problem of separation and purification of the hemicelluloses in the hydrolysates.In the present work, in order to discover the stable mechanism of the colloidal lignin particals in the hydrolysates,the anonic charge sources of the hydrolysates would be firstly studied, and the effect of the adsoption of the polysaccharides on the colloidal lignin on the stability of the colloidal lignin in the aspen hydrolysates would be aslo studied.The xylanase,mannanase and pectinase would be respectively used to treat the hydrolysates,and the effects of the degradation of the corresponding polysaccharides in the hydrolysate on the stability of the colloidal lignin would be discussed.In addition, the effects of dissolved lignin and other low molecular weight substances in the hydrolysates on the stability of the colloidal lignin would be also discussed.In order to discover the mechanism of the improvement of lignin removal selectivty by treating the hydrolysates with pectinase prior to flocculation with cationic polymers,the effects of pectinase treatment processes of the hydrolysates on the stability of the colloidal lignin and lignin removal selectivity, as well as the interaction mechanism between polygalacturonic acid and cationic polymers would be investigated. The present work would provide the theory evidences for the extraction of polysaccharides by autohydrolysis in the biorefinery.

木材原料制浆前通过自水解提取半纤维素是生物质精炼的一个有效途径，对水解液中的半纤维素分离提纯后高附加值利用是生物质精炼关键技术之一。然而,提取的水解液中的木素在冷却过程中容易发生缩合，并在水解液中形成稳定的木素胶体，导致半纤维素分离纯化困难。为了研究水解液中胶体木素的稳定机理,本项目首先研究杨木水解液中阴电荷的来源，还研究聚糖在胶体木素上的吸附及其对胶体木素稳定性的影响。分别采用聚木糖酶、甘露糖酶和果胶酶处理水解液，研究水解液中相应聚糖的降解对胶体木素稳定性的影响；另外，对水解液中溶解木素和其他低分子物质对胶体木素稳定性的影响也进行了研究。研究水解液果胶酶处理工艺对胶体木素稳定性和木素去除选择性的影响，以及聚半乳糖醛酸与阳离子聚合物的作用机制，揭示水解液果胶酶处理结合阳离子聚合物处理改善木素去除选择性的机理。通过本项目的研究，为以自水解提取聚糖为基础的生物质精炼平台的构建奠定理论基础。

植物纤维原料制浆前通过自水解溶出原料中的半纤维素并经过分离纯化后进行利用，是传统的制浆造纸厂向生物质精炼工厂转换的一个重要途径。在水解液中半纤维素糖分离纯化过程中，木素包括胶体木素和溶解木素的去除对于半纤维素糖的进一步处理和高附加值利用尤为重要。本项目研究了杨木自水解后水解液体系的阴电荷来源以及水解液中胶体木素和溶解木素与阳离子聚合物之间的相互作用及机理。明确了水解液中聚半乳糖醛酸与阳离子聚合物的作用机制，并采用果胶酶处理水解液，探讨了果胶酶预处理结合阳离子聚合物处理改善水解液中木素去除及其选择性的新途径，并明确了其作用机理。另外，还研究了辣根过氧化物酶处理对水解液中木素去除的影响。. 研究结果表明，在杨木自水解液中，聚半乳糖醛酸是阴电荷的一种重要来源，它能够通过电荷稳定机制稳定胶体木素颗粒，降低了阳离子聚合物絮凝去除胶体和溶解木素的效果。在水解液阳离子聚合物处理过程中，溶解木素与阳离子聚合物形成复合电解质胶体，进而发生失稳被除去。果胶酶降解聚半乳糖醛酸可以减少预水解液中的阴电荷，提高阳离子聚合物的作用效果。在较低的阳离子聚合物用量下，改善了胶体和溶解木素的去除效果，并减少了半纤维素聚糖的损失，从而改善了水解液中木素去除选择性。水解液在过氧化氢存在下采用辣根过氧化酶处理后，水解液中木素的平均分子量增加，可以直接导致部分胶体和溶解木素的去除，并且辣根过氧化物酶预处理还能够显著提高后续阳离子聚合物处理和酸处理去除水解液中木素的效果。以上研究对自水解液中半纤维素糖的分离纯化以及后续高附加值利用具有重要意义，并对自水解为基础的生物质利用平台的构建提供了一定的理论基础。

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