芝麻秸秆超临界CO₂降解脱除木质素的研究

Delignification of Cotton Stalk and Sesame Straw by CO₂ Supercritical Fluid

摘要: 本文使用超临界CO₂流体萃取技术，对芝麻杆渣中木质素进行萃取脱除实验研究。本文首先通过Van Soest成分分析法，采用4因素3水平的正交实验，对纤维素含量、半纤维素含量、木质素含量和木质素脱除率的影响因素进行了分析，同时用GC-MS对不同条件下的超临界CO₂萃取液成分进行分析。结果表明，温度是影响超临界CO₂脱除木质素的最大因素。在200℃、24 MPa下，用1,4-二氧六环1.5 mL作夹带剂反应60 min，脱木质素率达到80.84%。GC-MS分析表明在总离子流图的流出峰中有甲氧基和乙氧基的支链结构和含氧戊环类结构以及醇、醛、酸、脂和酚类化合物，萃取液受温度的影响很大，低温时(160℃)二氧戊环类物质几乎没有，随着温度升高才相继出现，说明在高温作用下，芝麻秸秆中不仅木质素易于脱除，还会导致纤维素和半纤维素碳水化合物等其他化合物的降解。使用电镜扫描对超临界萃取前后的芝麻杆渣做分析比较，结果表明在超临界处理之后样品表面有许多孔洞和非晶态无定形物质该物质可能是残余木质素或木素碳水化合物复合体。

Abstract: A technology of CO₂ supercritical fluid extraction was adopted to remove the lignin in sesame straw. First, by Van Soest method, the content of lignin and cellulose was evaluated through or-thogonal experiments. The results showed that the temperature is the most important factor on the degradation and removal behavior of lignin. At the temperature of 200˚C, pressures of 20 Mpa, adding 1.5 mL entrainer (1,4-dioxane) for 60 min reaction, delignification rate can reach 80.84%. At the same time using GC-MS of supercritical CO₂ extraction fluid composition was analyzed under different conditions. The temperature rise will also lead to other carbohydrates, the degradation of cellulose and hemicellulose to generate phenolic, dioxolane ring material. Scanning electron microscope (SEM) was used to compare the extraction before and after the supercritical extraction. The results showed that there were many pores and amorphous substance on the surface of the sample after supercritical treatment, which may be the residual lignin or lignin-carbohy- drate complex.