Xiang Q, Lee Y Y
Department of Chemical Engineering, Auburn University, AL 36849-5127, USA.
Appl Biochem Biotechnol. 2000 Spring;84-86:153-62. doi: 10.1385/abab:84-86:1-9:153.
Precipitated hard-wood lignin (PHL) is a major byproduct in the biomass-to-ethanol process. Oxidative cracking of PHL by hydrogen peroxide in aqueous medium was investigated as a means to produce potentially useful chemicals. The cracking reaction takes place at moderate temperatures (80-160 degrees C), giving mono- and dicarboxylic acids as the main products. The yields of these products are in the range of 30-50% of initial lignin. The reaction mechanism and the product distribution are dependent upon the reaction conditions, especially the pH. The reaction under strong alkaline condition proceeds well even at low reaction temperatures (80-90 degrees C). Under acidic conditions, higher temperatures (130-160 degrees C) are required to attain the same degrees of cracking. The reaction patterns of the oxidative cracking reaction involve the cleavage of lignin ring, aryl ether bond, or other linkages within lignin. By using the findings of this investigation and those of previous work, we have illustrated the reaction pathways for degradation of PHL under alkaline and acidic conditions. Aldehydes and aromatic acids are intermediate products in the oxidative degradation of lignin. However, they were produced only in trace amounts owing to rapid degradation induced by hydrogen peroxide.
沉淀 hardwood 木质素（PHL）是生物质制乙醇过程中的主要副产物。研究了在水介质中用过氧化氢对 PHL 进行氧化裂解，以此作为生产潜在有用化学品的一种方法。裂解反应在适中温度（80 - 160℃）下进行，主要产物为一元和二元羧酸。这些产物的产率在初始木质素的 30% - 50%范围内。反应机理和产物分布取决于反应条件，尤其是 pH 值。即使在低反应温度（80 - 90℃）下，强碱性条件下的反应也能顺利进行。在酸性条件下，需要更高温度（130 - 160℃）才能达到相同的裂解程度。氧化裂解反应的反应模式涉及木质素环、芳基醚键或木质素内其他键的断裂。通过利用本研究结果以及先前工作的结果，我们阐述了碱性和酸性条件下 PHL 降解的反应途径。醛类和芳香酸是木质素氧化降解的中间产物。然而，由于过氧化氢引起的快速降解，它们仅以痕量产生。
