Adsorption Behaviour of Si-MCM-41 for CO2: Effect of Pressure and Temperature on Adsorption

Abstract

Adsorption process is an alternative process for CO₂ removal which could offer solutions to the existing problems associated with absorption process. A suitable adsorbent which has high adsorption capacity and selectivity for CO₂ is required in adsorption process. Highly ordered siliceous mesoporous molecular sieve, Si-MCM-41 which has high surface area and large pore volume is an attractive candidate for use as adsorbent in the adsorption separation. Si-MCM-41 material was synthesized by hydrothermal process at 100 °C for 8 days then dried at 120 °C for 24 hours and finally calcined at 550 °C for 6 hours. Calcined Si-MCM-41 was characterized by XRD, FTIR, HRTEM and N₂ physisorption. All the characterization results confirm that the synthesized material is Si-MCM-41. Adsorption behaviour of Si-MCM-41 for CO₂ was investigated at temperatures between 25 - 100 °C and pressures from 0 - 20 bar using Rubothermgravimetric-densimetric apparatus. Si-MCM-41 showed low adsorption capacity of 27.43 mg-CO₂/g- adsorbent at 1 bar and 25 °C. This low adsorption of CO₂ on Si-MCM-41 could be attributed to the weak interaction between the siliceous material and CO₂. Results show that adsorption of CO₂ increases with increasing pressure and at it reaches to 296.48 mg CO₂/g-adsorbent at 20 bar which can be explained asthe CO₂ molecules are forced into the deep inside the pores of Si-MCM-41 at high pressure. The Si-MCM- 41 material also shows an increased in CO₂ adsorption with increased temperature with 335.77 mg-CO₂/g- adsorbent adsorbed at 50 °C. However, further increase in temperature to 75 °C and 100 °C decreases theadsorption of CO₂ to 295.07 mg-CO₂/g-adsorbent and 269.86 mg-CO₂/g-adsorbent, respectively. This decrease in adsorption is suggested due to weakening of the Van der Waals forces between Si-MCM-41 and CO₂. Overall results show that Si-MCM-41 has high potential to be used as adsorbent for CO₂ removalat pressures up to 20 bar and temperatures up to 75 °C.