Electrochemical hydrogenation of bioprivileged cis,cis-muconic acid to trans-3-hexenedioic acid: from lab synthesis to bench-scale production and beyond

Abstract

The integration of microbial and electrochemical conversions in hybrid processes broadens the portfolio of products accessible from biomass. For instance, sugars and lignin monomers can be biologically converted to cis,cis-muconic acid (ccMA), a bioprivileged intermediate, and further electrochemically upgraded to trans-3-hexenedioic acid (t3HDA). This novel monounsaturated monomer is gaining increasing attention as it can substitute adipic acid in Nylon 6,6 to introduce desired properties and yield polyamides with performance advantages. The implementation of t3HDA for advanced polymer production is, however, hampered by the low productivities achieved to date, in the order of milligrams per hour per cm². Here, we report on new synergies between microbial and electrochemical conversions and present a simple strategy to enhance the productivity of t3HDA by over 50 times. Specifically, we show that the broth composition has a dramatic role on the subsequent electrochemical step. Broth with neutral pH and high ccMA titer obtained from bacteria was found to enhance the electrochemical hydrogenation while impeding the parasitic hydrogen evolution reaction. As a result, high productivities were achieved under industrially-relevant current densities (200–400 mA cm⁻²). The effect of other parameters that are key for scale up and continuous operation, namely reactor configuration, potentiostatic/galvanostatic operation mode, and cathode material are also discussed. The experimental results served as input parameters for a detailed technoeconomic analysis and the blueprint of a hybrid microbial electrosynthesis process for t3HDA production.