Proof of Concept for O2 Removal with Multiple LCCF Membranes Accommodated in the Effluent of a CO2 Plasma Torch

The removal of oxygen from the effluent of a CO2 plasma using multiple perovskite La0.6Ca0.4Co0.5Fe0.5 O3-δ hollow fiber membranes is reported. A microwave plasma torch featuring a water-cooled 5 mm nozzle operated at quasi-atmospheric pressure was used. This configuration yielded moderate CO2 conversions (≥20%) and sufficiently large temperatures to thermally activate up to 21 membranes distributed over various rows in the plasma effluent. The CO2 conversion was only slightly affected by the microwave power and remained unchanged, regardless of the number of membranes placed in the effluent. The amount of permeated oxygen increased both with the microwave power and with the number of membranes, since the former yields hotter effluents (>700 °C) and the latter increases the surface area available for permeation. The largest O2 permeation flow was obtained for 21 membranes and a microwave power of 2550 W: ≃42 sccm or ≃4.8% of the available O2. These correspond to the highest performances of such a plasma-membrane reactor thus far. The permeated O2 flow was also affected by the argon flow purging the membranes. Using one membrane, the flow of extracted oxygen decreased for an Ar flow below 250 sccm, while the opposite was observed with 10 membranes, yielding an increase in the oxygen flow from ≃25 to ≃28 sccm upon decreasing the total Ar flow below 2500 sccm. Key aspects that must be tackled for the design and testing of a plasma-membrane prototype that aims to remove O2 beyond 90% are discussed.