酸性助水溶剂脱除木质素机理分析

系统探讨了酸性助水溶剂对甲苯磺酸(p-toluenesulfonic acid，TSA)和马来酸(maleic acid，MA)分离桉木各组分的工艺过程，并对其中木质素脱除机理进行了研究。通过分析对比两种优化后的工艺发现：(1)两种酸性助水溶剂都可以高效脱除木质素，TSA木质素脱除率为67.94%，MA为65.14%；(2)在相同质量分数下，TSA的木质素脱除率比MA更高；(3)在温和条件下，TSA木质素的β-芳醚键含量比MA的高，随着反应条件的加剧，TSA和MA处理后木质素产品中β-芳醚键含量逐渐减少；(4)两种酸性助水溶剂处理后，纤维素保留率都较高，可保持90%以上；但是半纤维素的降解程度随着反应条件的加剧而增加；(5)酸性助水溶剂质量分数越高，在疏水表面的接触角越小，对木质素的助溶作用越明显，脱除木质素效率越高，溶液中木质素聚集体的粒径越小。综上所述，酸性助水溶剂对木质素的脱除基于润湿溶解、木质素芳醚键断裂、半纤维素降解等的综合作用。相关研究可为后续实现温和条件脱木质素工艺优化及机理提供参考。

Delignification mechanism study of acid hydrotropes

p-Toluenesulfonic acid (TSA) and maleic acid (MA) are important acid hydrotropes for lignocellulose fractionation in recent years. The delignification mechanism of TSA and MA fractionation of eucalyptus wood chips was studied. The results were as follows: (1) Both acid hydrotropes have high delignification efficiency. The delignification rate of TSA was 67.94% and that of MA was 65.14%; (2) The delignification rate of TSA was higher than that of MA at the same hydrotrope concentration; (3) TSA hydrotropic lignin has higher β-aryl ether linkage content than that of MA lignin under mild condition, the β-aryl ether linkage content of acid hydrotrope dissolved lignin was reduced with the increasing fractionation severity; (4) More than 90% cellulose was well retained after fractionation, but the hemicellulose degradation rate increased with the reaction severity; (5) The contact angle decreased with the increasing hydrotrope concentration, so the wetting ability of lignin increased, and delignification rate increased also, the size of lignin aggregate in acid hydrotropes decreased. In conclusion, delignification of hydrotropes is a combined effect of wetting dissolution, aryl-ether linkages cleavage and hemicellulose degradation etc. The research can provide a reference for the process optimization and mechanism of delignification under mild conditions.