CO2 concentration using adsorption and nonthermal plasma desorption

The gas flow rates of hazardous air pollutant emissions are generally large and their concentrations low (in ppm ~ % levels, 1%=10000 ppm). When high flow rate and low concentration exhaust gases are treated directly, energy efficiency becomes low and the size of equipment becomes large resulting in high operating costs. The objective of the present study is to convert exhaust gases with large flow rates and low concentrations into ones with low flow rates and high concentrations by desorbing the gas from an adsorbent by application of an atmospheric plasma within a nonthermal plasma (NTP) reactor. The present paper focuses on the treatment of carbon dioxide (CO₂) by this method. The adsorbent consists of spherical molecular sieve pellets of zeolite having a diameter of approximately 2 mm. Plasma desorption is carried out by applying nanosecond high voltage pulses (peak voltage ~35 kV, pulse frequency = 140-350 Hz, pulse width ~600 ns) to the plasma reactor. The gas flow rate is 4 L/min; the gas concentrations are CO₂ = 2.75%, O₂ = 18%, H₂O = 1%, and N₂ = balance. It is found that CO₂ can be desorbed effectively and more rapidly in a repeated adsorption and NTP desorption process. Peak concentrations are higher (typically 13 %) in the NTP desorption process than in the thermal one at equal electric power. The efficient NTP dissociation of CO₂ to CO, which can be utilized in the production of combustion fuels, is possible.