Oxidative Activation Mechanism for Glycerol Carbonate Electrosynthesis

Abstract

The electrochemical synthesis of glycerol carbonate from glycerol and potassium carbonate enables utilizing electricity under mild conditions to upgrade the glycerol waste into valuable glycerol carbonate while consuming carbon dioxide. To scale up the reaction for industrial application, understanding the reaction mechanism is essential. Conventional electrochemical reaction with carbon dioxide in acidic and neutral conditions involves carbon dioxide activation by forcing electron into neutral-charged carbon dioxide species. Under the novel alkaline system for high carbon dioxide solubility, the reductive activation is no longer feasible considering the double negatively-charged carbonate ions impose electrostatic repulsion to electron. The separated cell study reveals that products are formed in the order of: mixed cell>anode>cathode. Compared to the reductive reaction proposed in acidic and neutral systems, this suggests that the glycerol carbonate reaction is oxidative in alkaline system, implying that anodic activation of both glycerol and carbon dioxide species is much easier than cathodic activation under alkalinity. Interestingly, synergistic effect of mixing is found to boost product formation, while simple mixing of glycerol and carbonate ions leads to spontaneous formation of novel species that could be precursor to forming glycerol carbonate product. From the results, the novel alkaline electrochemical production of glycerol carbonate from glycerol and carbon dioxide, involves a unique oxidative mechanism different from the conventional system, potentially bypassing the kinetic limit of the conventional system to make the industrial production of glycerol carbonate more economically viable. However, further questions, such as intermediates and bonds involved, remain to complete the puzzle.