Lignin Depolymerisation under Continuous-Flow Conditions : Highlights of Recent Developments

Lignin is a poly-aromatic polymer contained in the plant cell wall, and it is considered the most abundant non-carbohydrate polymer on Earth. The aromaticity and richness of its functional groups render lignin an attractive starting biomacromolecule for conversion into a variety of value-added products. The development of successful strategies for lignin valorisation infers the design of effective depolymerisation protocols. Most research on lignin depolymerisation have focused on batch-mode processing, whereas only a few studies have tackled such lignin transformation in continuous reactor systems. In the present paper, we highlight the emerging developments within the concept of continuous lignin processing and the challenges remaining in realising the efficient valorisation of lignin using this technology concept. A special focus is set on the hydrothermal conversion of technical lignin under continuous-flow conditions, together with suggestions for future research