Department of Chemistry, Technische Universität München, Lichtenbergstr. 4, 85747 Garching, Germany.
Chemistry. 2011 May 16;17(21):5939-48. doi: 10.1002/chem.201002438. Epub 2011 Apr 6.
The products of base-catalyzed liquid-phase hydrolysis of lignin depend markedly on the operating conditions. By varying temperature, pressure, catalyst concentration, and residence time, the yield of monomers and oligomers from depolymerized lignin can be adjusted. It is shown that monomers of phenolic derivatives are the only primary products of base-catalyzed hydrolysis and that oligomers form as secondary products. Oligomerization and polymerization of these highly reactive products, however, limit the amount of obtainable product oil containing low-molecular-weight phenolic products. Therefore, inhibition of concurrent oligomerization and polymerization reactions during hydrothermal lignin depolymerization is important to enhance product yields. Applying boric acid as a capping agent to suppress addition and condensation reactions of initially formed products is presented as a successful approach in this direction. Combination of base-catalyzed lignin hydrolysis with addition of boric acid protecting agent shifts the product distribution to lower molecular weight compounds and increases product yields beyond 85%.
木质素的碱性催化液相水解产物明显取决于操作条件。通过改变温度、压力、催化剂浓度和停留时间，可以调整从解聚木质素中获得的单体和低聚物的产率。结果表明，酚类衍生物单体是碱性催化水解的唯一初级产物，而低聚物是次级产物。然而，这些高反应性产物的聚合和聚合会限制可得的产油中含有低分子量酚类产物的量。因此，在热木质素解聚过程中抑制同时发生的低聚物化和聚合反应对于提高产物收率很重要。本文提出了一种将硼酸作为封端剂应用于抑制初始形成产物的加成和缩合反应的方法。碱性催化木质素水解与硼酸保护剂的添加相结合，可将产物分布转移到低分子量化合物，产率超过 85%。
