Frontier advances in humins research: Exploring key challenges and opportunities in biomass refining

The formation mechanism of humins in the lignocellulosic biomass refining process has long been a topic of great interest and puzzlement. As by-products generated from the condensation and coupling of intermediate fragments during biomass refining, humins have triggered a series of serious negative impacts. They lead to the waste of carbon resources, cause clogging of reactor pipelines, result in catalyst inactivation, and pose heavy obstacles to product separation. Recently, researchers from South China Agricultural University (Jun Xie, Cheng Cai), Dalian Institute of Chemical Physics, Chinese Academy of Sciences (Feng Wang), along with many other prestigious organizations, have carried out a comprehensive and in-depth investigation into the mechanism of humins generation during biomass refining and its resource utilization. The findings have been published in the Chinese Journal of Catalysis (10.1016/S1872-2067(24)60248-2).

The article systematically examines the structure and formation mechanisms of humins derived from cellulose and hemicellulose feedstocks, delving into the intricate process of random condensation among intermediate products such as 5-hydroxymethylfurfural (HMF), furfural (FF), 2,5-dioxo-6-hydroxyhexanal (DHH), and 1,2,4-benzenetriol (BTO). The study particularly highlights that during practical biorefinery processes, the presence of lignin facilitates the formation of a distinct humins variant termed "pseudo-lignin," which significantly complicates downstream separation processes. This comprehensive analysis enhances our understanding of humins formation pathways while emphasizing the practical challenges in biomass conversion systems.

Furthermore, this study provides a comprehensive and in-depth analysis of the influence of multiple factors on humin formation, encompassing feedstock properties, reaction temperature and duration settings, acid/base conditions, as well as the optimization of solvent systems and catalytic agents. Building on these insights, the research emphasizes the pivotal role of designing efficient solvent systems and catalysts in minimizing humins generation, while offering actionable guidance for process optimization in practical production scenarios.

The study further explored the methods of value-added application of humins. Through pyrolysis and catalytic hydrogenation, humins containing furan rings and aliphatic linkers can be depolymerized into platform molecules for fine chemical production. Leveraging its cross-linked structure and carbon-rich nature, humins can be functionalized through oligomer grafting or carbonization to yield high-value materials including polymeric networks, catalytic scaffolds, and engineered carbon composites.

In summary, this research comprehensively explores the humins generation mechanism and influencing factors in lignocellulosic biomass refining, proposes inhibition strategies, and examines its value-added applications. It offers crucial guidance for humins chemistry development, promotes the lignocellulosic biomass refining process toward efficiency, eco-friendliness and cost-effectiveness, boosts industrial sustainability, and provides effective solutions to resource waste and safety issues, serving as a reference for biomass refining studies.

About the Journal

Chinese Journal of Catalysis is co-sponsored by Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and it is currently published by Elsevier group. This monthly journal publishes in English timely contributions of original and rigorously reviewed manuscripts covering all areas of catalysis. The journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives, and Viewpoints of highly scientific values that help understanding and defining of new concepts in both fundamental issues and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top one journals in Applied Chemistry with a current SCI impact factor of 15.7. The Editors-in-Chief are Profs. Can Li and Tao Zhang.

At Elsevier http://www.journals.elsevier.com/chinese-journal-of-catalysis

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