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

摘要：

木质素是一种结构复杂的天然芳香类聚合物，功能基团丰富，具有良好的开发应用前景。工业碱木质素是当前木质素转化利用的主体，主要源于制浆黑液。由于原料来源、制浆工艺的影响，木质素多分散性高、结构与性能不一，致使相应的木质素基产品的均一性与稳定性较差。通过木质素分级可以获得具有不同分子量或特定化学结构特征的木质素级分，促使各级分的多分散性降低、均一性提高，进而针对特定性能的级分进行改性或者直接利用可进一步提高产品的稳定性。对现行木质素的主要分级方式进行了总结，重点探讨了工业碱木质素的分级方式对其后续利用的影响及存在问题。最后，针对木质素不同级分的特点对木质素未来分级的方向及应用前景提出了展望。

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