CO2 CAPTURE FROM GASES USING ACTIVATED CARBON

Abstract

Research on the CO2 adsorption on activated carbon (AC) adsorbents has gained significant interest due to their low cost, low regeneration energy, and eco-friendly characteristics. The current research was focused on the systematic development of AC using different types of biomass, pyrolysis conditions and activation conditions to prepare adsorbent with tailored textural properties for CO2 separation under simulated flue gas conditions. Impact of MgO impregnation on CO2 adsorption behavior of AC was also studied and an isothermal mass transfer model was developed to model the CO2 adsorption process in a binary mixture on porous carbon. The work was divided into four phases. The first phase of the work was focused on the synthesis of activated carbon using steam, CO2 and potassium hydroxide (KOH) as activating agents and evaluation of the CO2 adsorption performance under a range of temperature and inlet CO2 concentrations (CCO2). The KOH treated activated carbon had the best CO2 adsorption performance of 1.8 mol/kg due to its microporous structure under the optimized experimental conditions of 30 mol% CO2 and 25°C. All prepared activated carbon samples had a better performance at low temperature (~25°C) and/or high CCO2 (~30 mol%). In the second phase, the KOH activation conditions in the first phase was used for the activated carbon preparation using three different types of biomass (forest residue, agricultural residue and animal manure) as precursor and two different pyrolysis processes (fast and slow pyrolysis). The main finding in this phase was that activated carbons have different sensitivity to CO2 separation according to their micro-pore distributions; and total pore volume and surface area are not significant factors for CO2 adsorption on ACs. Overall, the pinewood saw dust derived ACs showed the best adsorption capacity of 78.1 mg/g (at 15 mol% CO2 in N2 and 25°C). In phase 3, the results of impregnating AC with magnesium oxide (MgO) showed that preparation method has a greater impact than metal content on the surface area and porosity of ACs. Moreover, MgO impregnation of AC overcomes the limitation of using not–impregnated AC at moderate temperature and low partial pressure of CO2. In the phase 4, an isothermal mass transfer model for CO2 adsorption in a mixture of CO2/N2 has been developed. The adsorption equilibrium data of CO2 on KOH activated carbon were determined at 273, 298, 323 and 348 K. The simulation of CO2 adsorption in a fixed-bed of activated carbon was performed in Python using a bi-Linear Driving Force (bi-LDF) approximation for isothermal mass transfer. The model was used to reproduce the CO2 adsorption breakthrough curves for CO2/N2 gas mixture and it can be used for designing a fixed-bed adsorption process to separate CO2 and N2 using microporous and mesoporous carbon materials.