自振空化降解壳聚糖机理及产物调控机制研究

Degradation of chitosan is one of research hotspots in sugar chemistry in recent years. The improvement of degradation efficiency, the control of molecular weight distribution and degree of deacetylation are the keypoints of degrading chitosan to produce oligochitosan, and the choice of degradation method and the knowledge of degradation mechanism are the basis for the optimization and the control of degrading process and product distribution. In this research, the self-resonating cavitation will be used for the degradation of chitosan, and the analysis methods such as three-dimensional particle image velocimetry, gel permeation chromatography and infrared spectroscopy, and the numerical methods such as computational fluid dynamics simulation, cavitation bubble dynamics simulation and calculation of free radicals composition and output based on free energy minimization will be used. Based on the analysis and numerical methods, both free radicals effect and mechanical effect on chitosan degradation, molecular weight distribution of product and molecular structure produced at such operational condition as various specifications of chitosan, various condition of degradation, various types and content of gas, various types and structure of self-resonating cavitation device, and their action mechanism will be systematically studied, and then both association model of dynamics and association model of molecular weight distribution of product will be developed. Based on the study above, the mechanism of product control will be proposed, which will provide theoretical basis for chitosan degradation to produce oligochitosan by using self-resonating cavitation. The studied results will provide important significance for promoting the research of self-resonating cavitation on the field of chitosan and polysaccharide degradation.

壳聚糖降解是糖化学领域近年来的研究热点之一。提高降解效率、有效控制降解产物分子量分布以及脱乙酰度是降解制备低聚壳聚糖的关键，而降解方法的选择及其降解机理的认识是优化和控制降解过程和产物分布的基础。本项目采用自振空化的方法对壳聚糖进行降解，通过三维粒子图像测速仪、凝胶渗透色谱、红外光谱等实验分析手段，以及计算流体动力学模拟、空化泡动力学模拟、基于自由能最小化原理的自由基组成和产量的计算等数值模拟手段，系统研究不同规格的壳聚糖、不同降解条件、不同气体种类及含量、不同类型及结构参数的自振空化器的空化产生的自由基效应、机械效应对壳聚糖的降解作用、产物分子量分布、分子结构等的影响及其作用机理，建立动力学关联模型、产物分子量分布关联模型，并在此基础上提出产物调控机制，为通过自振空化降解壳聚糖的方法制备低聚壳聚糖提供相关理论基础。研究结果对自振空化在壳聚糖乃至多糖降解领域的应用具有重要的价值。

壳聚糖（CS）降解是糖化学领域近年来的研究热点。提高降解效率、有效控制降解产物分子量分布以及脱乙酰度是降解制备低聚壳聚糖的关键。本项目采用自振空化对壳聚糖进行降解，通过实验和数值模拟手段，系统研究不同降解条件、不同结构及参数的自振空化对壳聚糖的降解产物分布及其作用机理，并提出产物调控机制，研究结果表明：. 自振空化对壳聚糖有很好的降解效果，壳聚糖特性黏度下降率及还原糖产量随壳聚糖浓度升高而降低，随温度及入口压力的升高而升高，随pH的增大先升高后开始下降；降解工艺参数影响顺序为：处理时间＞CS浓度＞pH，优化降解条件为：壳聚糖浓度为1.6 g/L、pH 4.4、处理时间172 min，此时CS黏度下降率预测值为93%。壳聚糖降解主要是通过切断糖苷键完成，这种方法没有破坏壳聚糖原有的结构，没有改变壳聚糖的脱乙酰度。 .数值模拟研究表明，入口压力增大，或下游恢复压力增大，空泡膨胀和溃灭加剧，·OH产量增加；CS溶液浓度增大，或液体温度升高，空泡溃灭强度降低，不利于生成·OH；β不变，孔板下游管道直径增大，·OH产量提高；β增加，空泡溃灭强度提高，·OH产量增加，且在 β=0.36时效果最好。当 β>0.36时发生阻塞空化。CS溶液空泡群·OH产量的数值模拟结果验证了上述结论。比较核心区汽含率和速度压力脉动情况，自振型空化装置优于孔板、文丘里管型空化装置，具有更强的空化效应与水力脉冲性能。壳聚糖降解的断裂方式主要为随机断裂和中间断裂，降解机制主要为化学效应和机械效应相结合，且降解始终以化学效应占主导；随机断裂的比例为91~100%，而中间断裂的比例为0%~9%；降解时间延长，壳聚糖中间断裂的比例降低，且机械效应的极限分子量约为40000左右；壳聚糖初始分子量增大，或上游压力增大，中间断裂比例提高。 .以上研究结果为通过自振空化降解壳聚糖制备低聚壳聚糖提供相关理论基础，并对自振空化在壳聚糖乃至多糖降解领域的应用具有重要价值。