半纤维素的红外及热解实验研究.doc

摘要 本文利用红外光谱实验技术研究半纤维素的分子结构。通过分析红外光谱图，得出以下结论：在 897cm－1附近有较强的振动吸收峰，表明糖单元之间以β-糖苷键连接1161~988cm－1之间的谱带是木聚糖的典型吸收峰，这说明半纤维素的成分以木糖为主，结构主要为吡喃环结构。1161cm－1处的弱吸收峰表示有阿拉伯糖基侧链的存在。结合红外光谱实验，整合前人的研究成果，获得简化了的半纤维素二聚体模型物的分子结构。实验结果和现有理论研究表明该结构模型是合理的。采用热重分析法对木聚糖的热解特性进行实验研究。通过 TG 和 DTG 曲线的分析，把木聚糖的热解反应过程分为四个阶段。综合分析热解实验结果发现，30℃/min的升温速率是反应的最佳环境。由分子模拟计算结果，500K 和 700K 分别对应热解实验的第二阶段和第三阶段。低温时半纤维素的热解反应进行得十分剧烈，主要对应半纤维素支链的断裂。随着温度的升高，半纤维素主链发生分解生成各种产物。实验结果和分子模拟的结果能够较好地吻合。 关键词：半纤维素；分子模型；热解；微观反应机理 ABSTRACT The infrared spectrum experiment technology is applied to study the molecular structure of the hemicellulose. We got the following conclusions by analyzing the infrared spectrogram: There is a strong vibration absorption peak around 897 cm-1, which shows that the sugar units is connected by beta - glycosidic bond. The band between 1161~988cm-1is the typical absorption peaks of xylan, which suggests that the main composition of hemicellulose is xylose and its main structure is pyran ring. The weak absorption peak at 1161 cm-1reflects that there are Arab carbohydrate side chains there. We obtained the simplified molecular structure of hemicellulose dimmer model by combining infrared spectrum experiment result with the fruits of other researchers. The experimental results and the existing theoretical model also shows that the model structure is reasonable.Thermogravimetric analysis is used to research the pyrolysis characteristics of xylan.The xylan pyrolysis reaction process is divided into four stages according to the TG and DTG curves. And the pyrolysis experiment result tells hat 30 ℃ / min heating rate is the best reaction circumstance. It is found that 500K and 700K respectively corresponding to the second stage of pyrolysis experiment and the third stage by analyzed the molecular simulation results. Pyrolysis reaction of hemicellulose is severe when the temperature is low, mainly corresponding the rupture of hemicellulose branched chain. The main chain of the hemicellulose decomposed to gene