Understanding the electrocatalytic oxidation of propionic acid for the sustainable production of ethylene

The need for the chemical industry to transition to renewable energy sources to achieve industrial decarbonization has propelled the study of alternative production pathways for important chemicals. Thermochemical ethylene production is one of the most significant contributors to greenhouse gas emissions. In this paper, we explore the electrochemical oxidation of propionic acid, a component of aqueous waste from a hydrothermal liquefaction process, as an alternative pathway for ethylene production. We investigate the effect of initial substrate concentration, operating current density, and electrolyte pH on faradaic efficiency towards ethylene and other reaction products. Our results show that a faradaic efficiency of >50% towards ethylene production can be achieved for initial substrate concentrations above 2 M, with an increase in initial concentration leading to an increase in faradaic efficiency towards ethylene. We also demonstrate how the distribution of organic products remained unaffected within the range of current density evaluated (20-95 mA cm⁻²). Finally, our results show how operating at electrolyte pH above the pK_a of propionic acid favors the oxidation of propionic acid over the parasitic oxygen evolution reaction. This study provides valuable insights into the effect of electrolyte composition and electrochemical conditions on the electrocatalytic oxidation of propionic acid and its competition with oxygen evolution in aqueous electrolytes.