Characterization and Catalytic Transfer Hydrogenolysis of Deep Eutectic Solvent Extracted Sorghum Lignin to Phenolic Compounds
Characterization and Catalytic Transfer Hydrogenolysis of Deep Eutectic Solvent Extracted Sorghum Lignin to Phenolic Compounds
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DOI：
10.1021/acssuschemeng.8b01763
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发表时间：
2018-08-01
影响因子：
8.4
通讯作者：
Shi, Jian
中科院分区：
文献类型：
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作者：
Das, Lalitendu;Li, Mi;Shi, Jian
低共熔溶剂（DES）本质上比许多离子液体（IL）便宜，这是由于前体成本低、合成简单和可回收性提高。同时，DES可以与IL一样有效地从植物材料中溶解木质素。然而，DES中木质素的解聚机理、DES提取木质素（DES-EL）的结构和化学性质以及DES-EL向增值产品的可能增值途径尚不清楚。本研究旨在表征DES（1：2氯化胆碱：乳酸）处理高粱的木质素流，并进一步将提取的木质素升级为酚类化合物。如HSQC、C-13和P-31 NMR分析所揭示的，DES裂解天然木质素中几乎所有的醚键，导致显著的尺寸减小。我们进一步催化升级DES-EL酚类化合物通过催化转移氢解在异丙醇的存在下。在三种测试的催化剂（Ru/C、Pd/C和Pt/C）中，Ru/C被证明在解构DES-EL中是最有效的，油、炭和气体产率分别为36.3wt%、46.4wt%、17.3wt%。油中的主要木质素单体产物是苯酚、4-乙基苯酚、4-乙基-2-甲氧基苯酚、2-甲氧基-4-丙基苯酚和4-羟基-苯丙酸。本研究提供了一个机制的理解，木质素解聚在DES和演示一个可能的途径，催化改质DES-EL低分子量酚类化合物。
Deep eutectic solvent (DES) is intrinsically cheaper than many ionic liquids (ILs) due to low precursor cost, simple synthesis, and improved recyclability. Meanwhile, DES can be as effective as ILs toward dissolving lignin from plant materials. However, the lignin depolymerization mechanism in DES, the structural and chemical properties of DES-extracted lignin (DES-EL), and the possible valorization pathways of DES-EL toward value-added products were not well understood. This study aims to characterize the lignin streams from DES (1:2 choline chloride:lactic acid) treated sorghum and further upgrade the extracted lignin to phenolic compounds. As revealed by HSQC, C-13, and P-31 NMR analysis, DES cleaved nearly all ether linkages in native lignin, resulting in significant size reduction. We further catalytically upgraded DES-EL to phenolic compounds via catalytic transfer hydrogenolysis in the presence of isopropyl alcohol. Among the three tested catalysts (Ru/C, Pd/C, and Pt/C), Ru/C proved the most effective in deconstructing DES-EL, with oil, char, and gas yields of 36.3, 46.4, 17.3 wt %, respectively. Major lignin monomeric products in the oil were phenol, 4-ethylphenol, 4-ethyl-2-methoxyphenol, 2-methoxy4-propylphenol, and 4-hydroxy-benzenepropanoic acid. This study provides a mechanistic understanding of lignin depolymerization in DES and demonstrates a possible way to catalytic upgrading of DES-EL to low molecular weight phenolic compounds.