Valorizing the Steel Industry Off-Gases: Proof of Concept and Plantwide Design of an Electrified and Catalyst-Free Reverse Water-Gas-Shift-Based Route to Methanol

Conversion of steel industry off-gases to value-added chemicals enabled by renewable electricity can significantly reduce the environmental burden of the steelmaking process. Herein, we demonstrate that CO₂ reduction by H₂, both contained in steel mill off-gases, to form syngas via the reverse water-gas-shift reaction is effectively performed by nanosecond pulsed discharges at atmospheric pressure. The experimental results suggest the following: (i) An optimum interelectrode distance exists, maximizing CO₂ conversion. (ii) CO₂ conversion at constant SEI follows a nonmonotonic trend with H₂ excess. CO₂ conversion increases with H₂ excess up to H₂:CO₂ = 3:1 upon shifting the chemical equilibrium. At larger H₂:CO₂, both gas cooling, promoted by the high H₂ content, and hindered CO₂ collisions in a highly diluted stream hamper CO₂ conversion. (iii) SEI enhances CO₂ conversion, but the effect decreases with increasing SEI due to equilibrium limitations. A stoichiometric H₂:CO₂ feed ratio in the plasma reactor is recommended for higher energy efficiency. Intensifying MeOH productivity via SEI elevation is not advised as a 2-fold SEI increase results only in 17% higher MeOH throughput.