稻麦草氧碱制浆黑液降粘除硅作用机理及调控机制的研究

Rice and wheat straw are abundant and low-cost sources of biomass that are widely distributed around the world, which were the main raw material in pulping and paper making industry. However, that the application of them in pulping industry were conditioned by their handicaps such as high silica content which hindered its application on the recovery system. Soda-oxygen pulping is considered as one of the most competitive methods for industrialization of straw pulping. It can reduced the silicon content of black liquor by synergistic effect between oxygen and alkali. In this project, the effect of dissolution, migration and transformation process of silicon on dissolution of lignin and carbohydrate were revealed. Besides, synthetic effect between soda and oxygen on desilicication mechanism of soda-oxygen pulping was also investigated. Based on abovementioned work, both the dissolution and precipitation during the cooking process and the flocculation during the evaporation concentration process were controlled by adjusting the cooking condition. By this kind regulation, the desilicication and viscosity reduction of straw cooking black liquor were achieved, which established a new solution for breaking through the bottleneck of clearing production of straw pulping.

稻麦草秸秆资源量巨大、纤维含量较高、价格低廉且分布广泛，曾是我国主要的制浆造纸原料，但由于制浆黑液硅含量高，使之难以在传统碱回收系统中循环利用，因而制约了秸秆在制浆造纸行业的应用。氧碱制浆是秸秆资源工业化利用的理想方法，通过氧-碱协同作用可以有效减少黑液中的硅含量，从而有利于草类制浆黑液的碱回收利用。本课题通过对稻麦草在氧碱制浆各阶段中木质素及碳水化合物溶出规律的探究，揭示含硅固形物溶出、迁移及转化过程对木质素及碳水化合物溶出的影响规律，阐明氧-碱反应对黑液除硅降粘的协同促进机制。在此基础上，调控含硅固形物在蒸煮过程的溶出和沉积，以及蒸发浓缩过程的絮凝过程，在蒸煮过程有效减少硅含量，构建氧碱制浆过程除硅降粘的调控新方法。本课题将为解决长期困扰草浆清洁化生产的黑液高硅高粘瓶颈问题提供新思路。

针对制浆黑液硅含量高，使之难以在传统碱回收系统中循环利用的问题。本课题通过氧碱制浆黑液降粘除硅作用机理及调控机制的研究，构建氧碱制浆过程除硅降粘的调控新方法。课题取得的主要相关研究成果如下：.(1)探究氧碱制浆中硅、木质素、碳水化合物溶出规律，揭示了氧碱蒸煮过程中黑液除硅降粘的调控机制。研究了不同（pH<10，11<pH<12）蒸煮终点黑液在离心、过滤前后蒸发过程黑液的黏度及热膨胀系数随固形物浓度变化。氧碱制浆黑液的 pH 值接近10时，其硅含量降低至3%，在90oC黏度300Pa∙S情况下，黑液固形物含量明显提升至65%以上。.(2)耦合低温低碱浓浸渍和循环氧碱蒸煮过程，提出了黑液降黏除硅新方法。利用低碱浓7.5%（wt%原料）低温碱浸渍，可有效提取半纤维素。碱浸渍后的残渣收率为56.3%，提取超过60%的半纤维素，同时去除62.8%的木质素。碱浸渍后循环氧碱蒸煮所产生的纸浆得率稳定在40~43%，纸浆的Kappa值低于16，纸浆的白度为55%（%ISO）。碱浸渍有利于降低循环黑液的粘度，黑液含有少量的二氧化硅并且黏度较小，经过5次循环氧碱蒸煮后黏度低于0.1Pa∙S。.(3)改变黑液pH环境跟踪黑液硅-木质素沉淀絮凝过程，揭示了蒸发浓缩过程中的含硅固形物的絮凝沉淀规律。黑液pH值为10时，硅的去除率达58.3%。pH值进一步的降低，大量木质素析出可附着在硅颗粒的表面。当pH值为9.5，反应温度为20℃，木质素二氧化硅复合材料的产量最高，二氧化硅质量百分含量为77.8%，粒径分布较为均匀集中分布在500nm。.(4)解析氧碱蒸煮过程黑液木素及氢解产物结构变化，提出了氧-碱协同作用脱木素机理。在深度氧碱蒸煮过程中，碱木质素的结构和平均分子量发生了显著变化。氧-碱协同作用可以预先氧化木质素单体间C-C键及C-O键的邻近化学基团，降低Cβ-O的键解离能，进一步促进木质素氢解制备高附加值芳香族单体，生物油收率及单体酚的选择性分别增加了33.6%和17.8%。.本课题将为解决长期困扰草浆清洁化生产的黑液高硅高粘瓶颈问题提供新思路，并且对稻麦草秸秆全组分高值化应用提高新的技术方案。