Controlled depolymerization of lignin in an electrochemical membrane reactor

• Continuous electrochemical degradation of lignin to low-molecular-weight compounds.
• In-situ separation of lignin and low-molecular-weight products by nanofiltration.
• Permeate stream free of high-molecular-weight fractions.
• Increase in permeability of the separation by 62% by the electrochemical reaction.
• Increase of the low-molecular-weight products gained by nanofiltration of lignin by 100%.

The electrochemical oxidative cleavage of lignin is a promising approach to valorize lignin's monomeric subunits as bulk and fine chemicals. It is attractive since it does not require toxic solvents or expensive catalysts. However, due to the rather unselective nature of the electrochemical depolymerization, overoxidation of the generated products occurs. In order to prevent the degradation of the aromatic monomeric compounds into acids and CO2, a selective product removal strategy from the reaction environment is necessary. We report the use of an electrochemical membrane reactor for the continuous electrochemical cleavage of lignin integrated with an in-situ nanoporous filtration process. The generated cleavage products are removed through the nanofiltration membrane from the oxidative environment and product degradation is prevented. The reaction/separation unit comprises an unprecedented electrode configuration: electrode rods integrated into a 3D-printed turbulence-promoting mixer minimizing fouling and polarization phenomena at membrane and electrodes.

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