氧及活性氧群对高木质素未漂浆的可及性及诱导传质机制的研究

Currently, oxygen delignification has become the first priority to produce chemical pulps incorporated with alkaline pulping. Previous studies showed that shortening cooking time followed by the extended oxygen delignification will not only maximize pulp yield but also be beneficial to its energy conservation and emission reduction. However, shortening cooking process will result in high level of residual lignin in pulp, which will lead to high level of dissolved lignin in the process liquor during oxygen delignification. Oxygen and activated oxygen radicals (AOs) that initiated by functional groups in lignin and oxygen can participate in the further degradation reactions on dissolved lignin in liquid phase, which has a negative effect on the accessibility of oxygen and AOs to residual lignin in pulp and thus the delignification efficiency. Through analyzing the blocking effect of dissolved lignin on oxygen and AOs, this project will establish the criterion of the accessibility of oxygen and AOs to unbleached pulp, and clarify its main factors on the accessibility and the inducing and enhancing mechanism. This will provide a better understanding of theoretical fundamentals aiming at developing new oxygen delignification technology on high lignin chemical pulp. The success of this project will give the guidance for exploiting the potentials for the present alkaline pulping combined with oxygen delignification process, enhancing the material utilization, energy saving and waste reduction.

氧脱木素是当前结合碱法蒸煮生产化学未漂浆的首选工艺。前期研究表明:若能进一步缩短蒸煮时间进而提前氧脱木素，可进一步提高纸浆得率以及制浆生产的节能减排水平。然而，缩短蒸煮意味着纸浆残余木素含量还很高，导致在氧脱木素段溶液中产生高含量的溶解木素。氧气经溶解木素等物质引发活性氧群将直接在液相中参与降解溶解木素的反应，进而影响到氧和活性氧群对纸浆上残余木素的可及性、降低了纸浆上脱木素反应的效率。本研究的主要内容：考察溶解木素对氧和活性氧群对纸浆传质可及性的影响及其主控因素；以辅助方式进行诱导可及；建立可及性的判据并阐明可及性和诱导传质的机制；新型氧脱木素新工艺的探索。该研究的成功将对高木质素含量纸浆氧脱木素工艺的开发提供理论的依据。这对于木材资源匮乏的我国制浆造纸工业充分挖掘现有碱法蒸煮联合氧脱木素的制浆工艺的潜力、提高制浆生产原材料的利用和节能减排水平，将具有重要的现实意义。

缩短硫酸盐法蒸煮时间，提前进行氧脱木素，是进一步提高纸浆得率较有潜力的突破口。然而，缩短蒸煮时间意味着高木质素含量的纸浆进入氧脱木素工艺，导致过程中脱除的溶解木素含量也高。因此开展氧和活性氧群对高木质素未漂浆的可及性以及旨在诱导强化其在未漂浆中传质而参与纸浆中残余木素的反应的机制研究，对于高木质素未漂浆氧脱木素工艺的有效实施，将具有重要的指导意义。本研究发现在相同的工艺条件下，未漂浆卡伯值越高，氧脱木素过程中纸浆脱木素量越大，脱木素效率更高。利用顶空气相色谱的相平衡技术，检测常压条件下，一定温度及碱浓时溶解木素消耗氧气的情况，首次证明了溶解木素与纸浆残余木素间竞争反应的存在。桉木硫酸法制浆过程废液中碳酸根和甲醇的生成规律进行动力学分析发现，碳酸根的碳源中碳水化合物的比例占约46%，木素约占54%。基于二氧化硅催化过量的硼氢化钠选择性还原羰基的反应，开发了一种顶空气相色谱快速检测木素中羰基含量的方法。该方法不但简单、操作方便，同时与传统检测方法相比，大大提高了检测效率:室温条件下，醛基可在30s内被还原；80oC条件下，酮基可在30min内被还原。综合考虑纸浆卡伯值、成浆情况、得率、黏度及未漂浆在氧脱木素过程中脱木素效率，从而确定桉木高卡伯值制浆段的最优节点为27~30。经过多段不同工艺过程的能耗比较，可以得知：蒸煮段终点卡伯值越低，能耗越高，一方面说明高卡伯值制浆联合氧脱木素过程在能耗方面的优势，另一方面也可说明整个过程的能量消耗主要是集中在硫酸盐法制浆段。至此在本项目的资助下，共发表论文65篇，其中SCI论文48篇，申请专利53项，其中已授权的发明专利6项。