Wang Qing, Tian Dong, Hu Jinguang, Shen Fei, Yang Gang, Zhang Yanzong, Deng Shihuai, Zhang Jing, Zeng Yongmei, Hu Yaodong
Institute of Ecological and Environmental Sciences, Sichuan Agricultural University Chengdu Sichuan 611130 P. R. China
Rural Environment Protection Engineering & Technology Centre of Sichuan Province, Sichuan Agricultural University Chengdu Sichuan 611130 P. R. China.
RSC Adv. 2018 Apr 3;8(23):12714-12723. doi: 10.1039/c8ra00764k.
Xylan, de-alkaline lignin and microcrystalline cellulose were employed as representative models of hemicellulose, lignin and cellulose in lignocellulosic biomass. These three model compounds, together with the real-world biomass, wheat straw were pretreated using the newly developed PHP pretreatment (concentrated phosphoric acid plus hydrogen peroxide) to better understand the structural changes of the recovered solid and chemical fractions in the liquid. Results showed that almost all xylan and higher than 70% lignin were removed from wheat straw, and more than 90% cellulose was recovered in the solid fraction. The pretreated model xylan recovered ethanol-precipitation still maintained its original structural features. The degree of polymerization of soluble xylooligosaccharides in liquid was reduced, resulting in the increase of monomeric xylose release. Further xylose oxidization the path of 2-furancarboxylic acid → 2(5)-furanone → acrylic acid → formic acid was mainly responsible for xylan degradation. The chemical structure of de-alkaline lignin was altered significantly by PHP pretreatment. Basic guaiacyl units of lignin were depolymerized, and aromatic rings and side aliphatic chains were partially decomposed. Ring-opening reactions of the aromatics and cleavage of C-O-C linkages were two crucial paths to lignin oxidative degradation. In contrast to lignin, no apparent changes occurred on microcrystalline cellulose. The reason was likely that acid-depolymerization and oxidative degradation of cellulose were greatly prevented by the formed cellulose phosphate.
木聚糖、脱碱木质素和微晶纤维素被用作木质纤维素生物质中半纤维素、木质素和纤维素的代表性模型。这三种模型化合物与实际生物质小麦秸秆一起，采用新开发的PHP预处理方法（浓磷酸加过氧化氢）进行预处理，以更好地了解回收固体和液体中化学组分的结构变化。结果表明，小麦秸秆中几乎所有的木聚糖和70%以上的木质素被去除，90%以上的纤维素保留在固体组分中。经乙醇沉淀回收的预处理模型木聚糖仍保持其原始结构特征。液体中可溶性木寡糖的聚合度降低，导致单体木糖释放量增加。木糖进一步氧化时，2-呋喃羧酸→2(5)-呋喃酮→丙烯酸→甲酸的路径是木聚糖降解的主要原因。PHP预处理显著改变了脱碱木质素的化学结构。木质素的碱性愈创木基单元发生解聚，芳环和侧链脂肪族链部分分解。芳环的开环反应和C-O-C键的断裂是木质素氧化降解的两个关键途径。与木质素不同，微晶纤维素没有明显变化。原因可能是形成的纤维素磷酸酯极大地阻止了纤维素的酸解聚和氧化降解。
