Various processes have been developed for removing gaseous VOCs such as toluene. Electrochemical removal has been considered as a frontier mainly due to the mechanisms at which it operates at ambient temperature. However, existing electrolysis and catalytic oxidation processes still have weaknesses, such as homogeneous catalysts and gas-liquid mass transfer. Conventional electrolysis and catalytic processes require the mass transfer of gas-phase pollutants to liquid phase electrolytes. It is inefficient from an economic and environmental point of view. Therefore, in this study, we tried to remove toluene by gas-solid electrolysis at room temperature. To this end, an electrode coated with an electron transfer mediator on a metal having a 3D structure was developed and applied. A commercial NiCrFeAl alloy was used as the substrate of the 3D foam electrode, and Ni(CN)42- was coated with the high base condition. After confirmation of mediator presence, the electrode was mounted in the cathodic half-cell for the gas phase electrolysis. A polyvinyl alcohol gel was selected for the solid electrolyte to facilitate the electron transfer process. The electrochemical reduction of gas-phase toluene was carried out by semi-continuous mode. Different experimental parameters (i.e, current densities, feed gas flow rates, and feed concentrations) were investigated on toluene removal. Additionally, the effect of O2 or air gases was performed to achieve and control the intermediate products. In-situ FTIR gas analyzer and ex-situ GC analyses were adopted to monitor toluene concentration and intermediate compounds identification. Also, GC-MS analysis was carried out to confirm the intermediate product. Under given conditions, high removal efficiency was observed for a 1-hour batch electrolysis process. A possible reaction mechanism was derived and discussed at the end.

Electrochemical reduction of gaseous toluene by gas-solid electrolysis system: Application of three-dimension foam electrode with nickel complex mediator

ACS Spring 2022

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