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

Abstract

Amine-based adsorbents show great promise for removing low-concentration CO2 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 CO2 circulation removal tests were carried out under simulated confined space conditions in a 100 L chamber to evaluate the low concentration CO2 removal performance of the adsorbent pellets. The effect of operating parameters on CO2 removal performance was investigated by orthogonal experiments. CO2 adsorption capacity and removal efficiency were significantly affected by CO2 concentration and reaction temperature, while reaction rate was intimately depended on CO2 concentration and gas flow rate. The maximum CO2 adsorption capacity (0.55 mmol CO2/g), removal efficiency (83.25%) and reaction rate (0.93 mmol CO2/min) were achieved under the optimized conditions of 20 °C, 1.25%CO2 and 2 L/min. A kinetic equation well representing the correlation between reaction rate and CO2 concentration and gas flow rate was established. The TEPA-SG-ES adsorbent pellets exhibited satisfactory working stability, with CO2 removal efficiency and adsorption capacity slightly decreased from 83.25% and 0.55 mmol CO2/g to 75.45% and 0.53 mmol CO2/g in 10 cycles, respectively. The slight decay in CO2 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 CO2 in confined spaces.