Humins, (side-)products of the acid-catalysed dehydration of carbohydrates, will be produced in substantial quantities with the development of industrial biorefining processes. Most structural knowledge about such humins is based on synthetic model humins prepared at lab-scale from typical carbohydrate(-derived) compounds. Here, we report the first extensive characterisation study of an industrial humin. The soluble humin was generated from pilot plant-scale methanolic cyclodehydration of D-fructose to 5-methoxymethyl-2-furfural (MMF), as part of the Avantium YXY® process to produce FDCA. Purification of the industrial humin followed by fractionation allowed isolation of a water-insoluble, high molecular weight fraction (WIPIH) and a water-soluble, low-to-middle molecular weight soluble fraction (WES). Characterisation by elemental analysis, thermogravimetry, IR and NMR spectroscopy and size exclusion chromatography provided a detailed picture of the humin structure in both fractions. Aided by a comprehensive NMR spectral library of furanic model compounds, we identified the main furanic building blocks and inter-unit linkages and propose a structure for this industrial humin sample. The WIPIH and WES fractions were found to be composed of furanic rings interconnected by short aliphatic chains containing a wide range of functionalities including alcohols, ethers, carboxylic acids, esters, aldehydes and ketones. The low level of crosslinking and high functional group content of the industrial humin differ from the more extensively studied, (highly over-)condensed synthetic model humins, towards which they can be considered intermediates. The structural and compositional insights into the nature of an actual industrial humin open up a broad spectrum of valorisation opportunities.

中文翻译：

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工业胡敏素及其馏分的分子结构和组成阐明

腐殖质是碳水化合物酸催化脱水的（副）产物，随着工业生物精炼工艺的发展，将大量生产。关于此类腐殖质的大多数结构知识都是基于在实验室规模上由典型的碳水化合物（衍生的）化合物制备的合成模型腐殖质。在这里，我们报告了工业胡敏素的首次广泛表征研究。可溶性胡敏素是通过中试工厂规模的 D-果糖甲醇环脱水生成 5-甲氧基甲基-2-糠醛 (MMF)，作为生产 FDCA 的 Avantium YXY® 工艺的一部分。对工业胡敏素进行纯化，然后进行分馏，可以分离出不溶于水的高分子量级分 (WIPIH) 和水溶性的低至中分子量可溶级分 (WES)。通过元素分析、热重分析、红外和核磁共振光谱以及尺寸排阻色谱进行表征，提供了两种馏分中胡敏素结构的详细图像。借助呋喃模型化合物的综合核磁共振谱库，我们确定了呋喃的主要结构单元和单元间连接，并提出了该工业胡敏素样品的结构。研究发现 WIPIH 和 WES 馏分由通过短脂肪链互连的呋喃环组成，其中含有多种官能团，包括醇、醚、羧酸、酯、醛和酮。工业胡敏素的低交联水平和高官能团含量不同于更广泛研究的（高度过）缩合的合成模型胡敏素，它们可以被视为中间体。对实际工业胡明本质的结构和组成洞察开辟了广泛的增值机会。