Online Mass Spectrometric Characterization of Oligomeric Products in High-Pressure Liquid-Phase Lignin Depolymerization Reactions

Lignin depolymerization involves complex reactions that occur in heterogeneous environments, leading to the formation of a wide range of products with diverse molecular structures. The complexity of these products arises from the different bond strengths and locations within the lignin polymer, which makes it difficult to fully understand the reaction pathways. Conventional analytical techniques often fall short of providing a clear and comprehensive picture of the reaction mechanism. This highlights the need for more advanced methods that can offer real-time, in situ analysis to probe product evolutions and unravel the detailed mechanisms of lignin depolymerization. Herein, we present a concise perspective of the recent developments in online mass spectrometry, particularly its applications in probing heavy oligomeric products formed during lignindepolymerization. After introducing the current analytical technologies and analytical challenges, we focus on the development of online mass spectrometric method, especially those combined with batch and flow-through reactors, for the real-time characterization of lignin depolymerization products. Several key case studies are highlighted. Finally, we discuss the potential opportunities and remaining challenges in this field.