Can "Electric Flare Stacks" Reduce CO₂ Emissions? A Case Study with Nonthermal Plasma

Gas flare stacks are the current benchmark technology for industrial pollution control. However, their impact on human health and the environment is not negligible. If net zero CO2 emissions are to be achieved, their current significant CO2 impact (400 Mt y(-1) globally, 2022) should be reduced. Herein, a model nonthermal plasma "electric flare stack" consuming 6.6% less energy than an equivalent steam aided methane flare, with significant CO2 emission reductions (between 2.0x and 11.4x lower), when removing isobutylene is demonstrated. Isobutylene streams in air (1.3% v/v) are completely and rapidly consumed (>99% at flow rates up to 125 mL min(-1), 1 atm, RT) by the electrically generated nonthermal plasma in a linear flow reactor. At low powers (<= 50 J L-1 specific input energy), the major degradation products (>95%) are a complex mixture of low-molecular-weight oxygenates, including acetone, isobutylene oxide, and isobutyraldehyde. Only small amounts of CO/CO2 (<5% selectivity) are generated (at 50 J L-1). Complete oxidation of isobutylene to CO2 (>99% selectivity) results when the plasma oxidation is coupled to a heterogeneous catalyst bed. For the optimal V2O5 catalyst, synergistic interactions between the plasma and V2O5 are evident, as positioning the catalyst after the plasma provides optimal reactor performance (two-stage vs single-stage oxidation). Placement of shorter catalyst beds close to the plasma discharge region gives optimal reactor performance.