Experimental and kinetic study on the cyclic removal of low concentration CO2 by amine adsorbents in confined spaces.

Amine-based adsorbents show great promise for removing low-concentration CO 2 from environmental control and life support systems (ECLSSs) to ensure crew safety and task execution. In this work, granular silica gel (SG) support was prepared by the extrusion–spheronization (ES) method, and amine-based adsorbent pellets were synthesized by impregnating the SG support with tetraethylenepentamine (TEPA). Dynamic CO 2 circulation removal tests were carried out under simulated confined space conditions in a 100 L chamber to evaluate the low concentration CO 2 removal performance of the adsorbent pellets. The effect of operating parameters on CO 2 removal performance was investigated by orthogonal experiments. CO 2 adsorption capacity and removal efficiency were significantly affected by CO 2 concentration and reaction temperature, while reaction rate was intimately depended on CO 2 concentration and gas flow rate. The maximum CO 2 adsorption capacity (0.55 mmol CO 2 /g), removal efficiency (83.25%) and reaction rate (0.93 mmol CO 2 /min) were achieved under the optimized conditions of 20 °C, 1.25%CO 2 and 2 L/min. A kinetic equation well representing the correlation between reaction rate and CO 2 concentration and gas flow rate was established. The TEPA-SG-ES adsorbent pellets exhibited satisfactory working stability, with CO 2 removal efficiency and adsorption capacity slightly decreased from 83.25% and 0.55 mmol CO 2 /g to 75.45% and 0.53 mmol CO 2 /g in 10 cycles, respectively. The slight decay in CO 2 adsorption performance was associated with the oxidative degradation of amine species in oxygenated atmosphere to form amide, nitrite and imine phases, and the change of amine distribution over the pellets in multiple cycles. Overall, the desired TEPA-SG-ES adsorbent pellets could be nice scavenger candidates for circulating purification of CO 2 in confined spaces. [ABSTRACT FROM AUTHOR]