关键词: 木质素分级, 碱木质素, 分子量, 多分散性, 膜分级, 分离, 纯化

Abstract:

As a complicated natural phenolic polymer, lignin contains abundant functional groups, including hydroxyl groups, carboxyl groups, double bonds, etc., which has drawn significant research and industrial attention for decades. Technical lignins, especially the alkali lignins, are mainly separated from black liquors after alkali or kraft pulping. As the primary lignin resource, technical lignin plays an essential role in current lignin utilization. On account of the variety of functional groups and interunit linkage types between the structural units, the structures of technical lignins from different sources are quite different. In addition, due to the depolymerization and condensation of lignin during the pulping process, technical lignins show a much higher polydispersity and heterogeneity, which have a profound impact on the stability and uniformity of lignin-based products. To reduce the polydispersity and heterogeneity of lignin, various methods to fractionate lignin into different fractions with specific chemical characteristics and properties by molecular weights are developed. This article summarized the advances of prevailing lignin fractionation methods as well as their influence on the corresponding applications. Furthermore, the current problems and new insights on the development of lignin fractionations were highlighted and discussed.

Key words: lignin fractionation, alkali lignin, molecular weight, polydispersity, membrane fractionation, separation, purification