固定化漆酶-固定化Co(salen)组合催化漂白竹浆机理的研究

On the basis of the biological and biomimetic bleaching of pulp, the bleaching process of bamboo pulp was preliminarily researched using the combined catalysis of immobilized laccase-immobilized Co(salen). It was found that there was a temperature range applicable for the two catalysts, and the combination of the two catalysts significantly favored the improving of the pulp strength and brightness showing a significant bleaching selectivity. It is the main process of bleaching pulp to degrade lignin in pulp. It is involved in the catalytic oxidation of lignin by laccase or Co(salen) for the catalytic center, organic peroxy and other free radicals, Cα- and β-O-4 cleavage of lignin, which related to the initiation of peroxidation. This is a basic understanding for the mechanism of lignin oxidation by laccase or Co(salen). However, it is unclear how lignin is degraded by the combined catalysis of immobilized laccase-immobilized Co(salen) in bamboo pulp. Aiming at this purpose in this project, the oxidative degradation of lignin side chains and unit linkages is analyzed using FTIR and NMR, and the catalytic center and free radicals are monitored using the dissolved oxygen analysis as well as UV and ESR. By adding oleic acid in the reaction system or not, the peroxidation effect in lignin degradation is analysed. The mechanism is finally obtained for the catalytic bleaching of bamboo pulp by the combined catalysis, which may solve the scientific problem about the efficient bleaching of the bamboo pulp by the combined catalysis.

对纸浆生物酶和仿酶漂白的研究基础上，初步探讨了固定化漆酶-固定化Co(salen)组合催化漂白竹浆的工艺，发现这两种固定化催化剂有共同最适温度。与单独使用相比，组合催化显著提高竹浆强度和白度，表现出显著漂白选择性。漂白纸浆主要是降解纸浆中木素的过程。对于漆酶或Co(salen)催化氧化木素，反应涉及催化剂活性中心、有机过氧自由基和其他自由基、木素Cα-位和结构单元之间β-O-4连接断裂，其中涉及过氧化反应的启动。这是对漆酶或Co(salen)单独催化氧化木素机理的基本认识。但是关于漆酶和Co(salen)组合催化氧化竹浆中木素的途径还不清楚。本项目围绕这个主题，采用红外和核磁分析木素侧链和单元连接的氧化降解，利用溶解氧分析以及UV和ESR，监测催化剂活性中心和自由基。通过加或不加亚油酸，分析过氧化反应在木素降解中的作用。最终得出组合催化漂白竹浆的机理，解决组合催化能高效漂白竹浆的科学问题。

本项目围绕“漆酶和Co(salen)组合催化氧化竹浆中木素的途径”这个主题，分析木素侧链和结构单元连接的氧化降解，监测活性中心和自由基，分析过氧化反应在木素降解中的作用，最终得出组合催化漂白竹浆的机理，解决组合催化能有效改进竹浆漂白的科学问题。. 漆酶/MCM和Co(salen)/NaY催化漂白竹浆的脱木素选择性分别为5.06、5.53，竹浆白度分别为50.8%ISO和52.4%。再进一步，漆酶/MCM与Co(salen)/NaY组合催化漂白竹浆，脱木素选择性提高至8.29，竹浆白度提高至61.9%ISO。漆酶/MCM与Co(salen)/NaY组合催化漂白竹浆具有明显的协同催化效应，提高了竹浆脱木素的选择性和漂白效果。. 漆酶/MCM与Co(salen)/NaY组合催化增强了竹浆木素侧链和芳香环氧化降解，这导致竹浆木素羰基和羧基含量增加，侧链脂肪族羟基含量减少；增强了木素结构单元连接断裂，导致木素酚羟基增加；促进了木素愈创木基结构和难降解的5-CH2-5'、α-5、β-5、β-β缩合型结构降解。这种催化作用与组合催化促进了LCuO2和LCoO2活性中间态形成有关，并与组合催化促进了过氧自由基和木素酚氧自由基形成有关。在LCuO2和LCoO2活性中间态、过氧自由基和木素酚氧自由基达到最佳含量水平时（活性中间态在420~460nm吸收强度为1.56，ROO•的稳态浓度为2.11×10-8 mol/L，木素酚氧自由基为41.7μM），竹浆木素特别是难降解型结构单元被有效降解，竹浆木素被深度脱除，竹浆脱木素选择性和漂白效率得到有效提高。但是，过度的催化反应易使活性中间态转化为活性较弱的Cu-O-O-Cu和Co-O-O-Co中间体，导致催化能力下降。而且，过度的催化反应易使木素降解反应产生的中间体缩合，导致木素难以被深度降解。