Effect of Operation Conditions on Low Concentration CO ₂ Adsorption of Zeolite 13X for in-Vehicle Air Quality

In confined spaces, especially a car cabin, CO2 may lead to fatigue, weariness, drowsiness, sleepiness, etc. and limit the ability to concentrate with its concentration. Although ventilation is frequently used to maintain the in-vehicle CO2 concentration as low levels, any other pollutants such as particulate matters are brought in simultaneously. We investigated the feasibility of commercial CO2 adsorbents for an in-vehicle CO2 capture system. Among several commercial adsorbents, low silica zeolites such as 4 A, 5 A and 13X exhibited high CO2 adsorption capacity at 1000 ppm CO2 concentration and zeolite 13X showed superior performance on both CO2 adsorption capacity and adsorption kinetics even under wet conditions. In various operation conditions, relative humidity and column pressure were most effective on the breakthrough time, tb, and tb exceeded 2 h at 40%RH and SV= 3 m3 h−1 kg−1, which corresponds to an operation condition that a human exhalation is treated by 6 kg of adsorbent under the circulation mode. With decreasing the relative humidity at 13%RH, more than 2 h of tb was obtained at 4 m3 h−1 kg−1, corresponding to 4.5 kg of adsorbent required per person. The regeneration efficiency of zeolite 13X was significantly improved under vacuum and an ambient air intake with small flow rate, whereas it was difficult to regenerate only under vacuum without air flow. This study demonstrated that single column CO2 capture system using zeolite 13X enables us to maintain in-vehicle concentrations under 1000 ppm for the average driving time of passenger cars and would realize a simple and small in-vehicle CO2 capture system.