Thermogravimetric analysis of kinetic characteristics of K2CO3-impregnated mesoporous silicas in low-concentration CO2

The requirement for self-sustained and long-duration human operations in confined spaces including submarines, spacecrafts, or underground citadels has made ambient removal of low-concentration CO2 a critical technology. Mesoporous silica materials have been regarded as promising carriers to support active components for CO2 sorption. The CO2 sorption kinetic of mesoporous silica-supported adsorbent is an important parameter to be assessed. In this paper, K2CO3-impregnated mesoporous silicas were prepared by impregnating K2CO3 on MCM-41, SBA-15, and silica gel (SG) in ethanol solution, respectively. The CO2 sorption experiments were performed in a simulated confined space atmosphere of 1.0 % CO2, 2.0 % H2O, and 293-333 K using thermogravimetric analysis. The kinetic performances of the sorbents were evaluated by fitting the experimental data to the shrinking core model. K2CO3/SG exhibited the optimum carbonation kinetic performance. The apparent activation energies for chemical reaction-controlled region and internal diffusion-controlled region are 3.95 and 64.87 kJ mol(-1), respectively. To obtain the specific carbonation kinetic mechanism, a double exponential model was used to simulate the carbonation process of K2CO3/SG. The apparent activation energies for H2O diffusion-hydration and CO2 diffusion-carbonation stages are 8.40 and 4.32 kJ mol(-1), respectively. H2O diffusion-hydration is the rate limiting step in the whole carbonation process.