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Elucidating transfer hydrogenation mechanisms in non-catalytic lignin depolymerization
Green Chemistry ( IF 9.3 ) Pub Date : 2018-07-06 , DOI: 10.1039/c7gc03239k Florent P. Bouxin 1, 2, 3, 4 , Henri Strub 5, 6, 7 , Tanmoy Dutta 1, 2, 3, 4, 8 , Julie Aguilhon 5, 6, 7 , Trevor J. Morgan 4, 9, 10, 11 , Florence Mingardon 4, 12, 13 , Murthy Konda 1, 2, 3, 4 , Seema Singh 1, 2, 3, 4, 8 , Blake Simmons 1, 2, 3, 4 , Anthe George 1, 2, 3, 4, 8
Green Chemistry ( IF 9.3 ) Pub Date : 2018-07-06 , DOI: 10.1039/c7gc03239k Florent P. Bouxin 1, 2, 3, 4 , Henri Strub 5, 6, 7 , Tanmoy Dutta 1, 2, 3, 4, 8 , Julie Aguilhon 5, 6, 7 , Trevor J. Morgan 4, 9, 10, 11 , Florence Mingardon 4, 12, 13 , Murthy Konda 1, 2, 3, 4 , Seema Singh 1, 2, 3, 4, 8 , Blake Simmons 1, 2, 3, 4 , Anthe George 1, 2, 3, 4, 8
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Lignin undergoes catalytic depolymerization in the presence of a variety of transfer hydrogenation agents, however the mechanisms for non-catalytic depolymerization of lignin via transfer hydrogenation are not well understood; this makes process optimization difficult. Herein, for the first time a mechanism for this process is proposed. For the purposes of understanding the mechanisms involved in these non-catalytic lignin depolymerization processes, this study investigates the equilibrium system of formic acid, methyl formate and carbon monoxide, as agents for the depolymerization of lignin, in the presence of either water or methanol as solvents. In the methyl formate/water (at 300 °C) system, 73 wt% oil was produced which contained a significant amount of low molecular weight alkylphenols, with less than 1 wt% char produced. In aqueous media, the results showed that methyl formate maintains an equilibrium with formic acid which is itself in equilibrium with carbon monoxide. It was found that using either formic acid or methyl formate for non-catalytic transfer hydrogenation of lignin can produce high amounts of oil, and can be described as a two-stage mechanism. After 10 min of reaction at 300 °C, around a quarter of the formic acid is consumed via hydride transfer of the formate proton, preventing the condensation of lignin fragments. At the same time, approximately three quarters of the formic acid decomposes to carbon dioxide and carbon monoxide. Once the formic acid is consumed, the carbon monoxide was identified as the precursor to a reactive reductive reagent and was able to activate the proton of the water molecule preventing further condensation of the lignin fragments. It has been previously thought that transfer hydrogenation in lignin using formic acid occurs via the production of molecular hydrogen. Here it is demonstrated that formic acid reacts directly with the lignin, without this hydrogen formation. Therefore the key parameters for efficient transfer hydrogenation of the lignin to maximize bio-oil yield appear to involve controlling the reactions between lignin and formic acid, methyl formate or carbon monoxide under aqueous conditions, thereby reducing the reagent cost and loading while maintaining efficient lignin conversion.
中文翻译：
阐明非催化木质素解聚中的转移加氢机理
木质素在多种转移加氢剂的存在下进行催化解聚，但是木质素通过以下途径进行非催化解聚的机理氢化转移尚未得到很好的理解；这使过程优化变得困难。在此，首次提出了用于该过程的机制。为了理解这些非催化木质素解聚过程的机理，本研究研究了甲酸，甲酸甲酯和一氧化碳作为木质素解聚剂的平衡体系，在水或甲醇存在下进行。溶剂。在甲酸甲酯/水（在300°C下）系统中，生成了73 wt％的油，其中包含大量的低分子量烷基酚，而生成的炭少于1 wt％。在水性介质中，结果表明甲酸甲酯与甲酸保持平衡，而甲酸本身与一氧化碳保持平衡。发现使用甲酸或甲酸甲酯进行木质素的非催化转移氢化可以产生大量的油，并且可以描述为两阶段机理。在300°C下反应10分钟后，大约消耗了四分之一的甲酸通过甲酸酯质子的氢化物转移，防止木质素碎片的凝结。同时，大约四分之三的甲酸分解为二氧化碳和一氧化碳。一旦甲酸被消耗掉，一氧化碳就被确定为反应性还原剂的前体，并且能够激活水分子的质子，从而防止木质素片段进一步缩合。以前曾认为使用甲酸通过木质素转移木质素中的氢化反应是通过分子氢的产生。在此证明了甲酸直接与木质素反应，而没有这种氢的形成。因此，木质素有效转移加氢以最大化生物油产量的关键参数似乎涉及控制木质素与甲酸，甲酸甲酯或一氧化碳在水性条件下的反应，从而降低试剂成本和载量，同时保持有效的木质素转化率。
更新日期：2018-07-30
中文翻译：
阐明非催化木质素解聚中的转移加氢机理
木质素在多种转移加氢剂的存在下进行催化解聚，但是木质素通过以下途径进行非催化解聚的机理氢化转移尚未得到很好的理解；这使过程优化变得困难。在此，首次提出了用于该过程的机制。为了理解这些非催化木质素解聚过程的机理，本研究研究了甲酸，甲酸甲酯和一氧化碳作为木质素解聚剂的平衡体系，在水或甲醇存在下进行。溶剂。在甲酸甲酯/水（在300°C下）系统中，生成了73 wt％的油，其中包含大量的低分子量烷基酚，而生成的炭少于1 wt％。在水性介质中，结果表明甲酸甲酯与甲酸保持平衡，而甲酸本身与一氧化碳保持平衡。发现使用甲酸或甲酸甲酯进行木质素的非催化转移氢化可以产生大量的油，并且可以描述为两阶段机理。在300°C下反应10分钟后，大约消耗了四分之一的甲酸通过甲酸酯质子的氢化物转移，防止木质素碎片的凝结。同时，大约四分之三的甲酸分解为二氧化碳和一氧化碳。一旦甲酸被消耗掉，一氧化碳就被确定为反应性还原剂的前体，并且能够激活水分子的质子，从而防止木质素片段进一步缩合。以前曾认为使用甲酸通过木质素转移木质素中的氢化反应是通过分子氢的产生。在此证明了甲酸直接与木质素反应，而没有这种氢的形成。因此，木质素有效转移加氢以最大化生物油产量的关键参数似乎涉及控制木质素与甲酸，甲酸甲酯或一氧化碳在水性条件下的反应，从而降低试剂成本和载量，同时保持有效的木质素转化率。
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