Electrosynthesis of Ethylene Glycol Coupled with CO₂ Capture

Ethylene glycol is a $25B/year commodity chemical, used mainly as a precursor to polyethylene terephthalate (PET) and as antifreeze, responsible for the emission of 46 MMt CO₂/year. Its present-day production via thermocatalytic ethylene oxidation leads to a carbon intensity of ~ 1.2 CO₂eq per tonne of ethylene glycol.<br/>Electrochemical systems for ethylene oxidation have, to date, suffered from high voltages. To reduce voltage, we sought to build a membrane electrode assembly (MEA)-based system; but observed that a high pH gradient across the membrane causes hydroxide counter-migration, and – when we measured local pH at the membrane-catalyst interface – we found that this resulted in an unfavorable microenvironment for anodic ethylene oxidation, accounting for low FE in MEA studies.<br/>We sought a cathodic reaction that would serve as a sink for pH-increasing hydroxide. Carbon capture demands a local flux of OH^-, and we pursued therefore this reaction on the cathode.<br/>We report as a result the anodic transformation ethylene-to-EG (94% Faradaic efficiency) coupled with cathodic CO₂ capture (91% carbon capture efficiency with CO₂ concentrations ranging from 1% to 10%). An integrated system, operating at full cell voltage 1.8 V and current density 100 mA cm^-2, captures 0.75 tonnes of CO₂ for every tonne of EG produced. The electrified system requires 12.7 GJ compared to 22.6 GJ/tonEG for thermocatalytic ethylene oxidation. This approach offset the substantial carbon footprint of the fossil fuel-derived ethylene feedstock, leading to an estimated carbon intensity of 0.13 tonCO₂eq/tonEG, compared to the 1.2 tonCO₂eq/tonEG global average for ethylene glycol today.