Fabrication and kinetic study of spherical MgO agglomerates via water-in-oil method for pre-combustion CO2 capture

Abstract

The granulation of solid sorbents is essential for its practical application to CO2 capture because fine powder causes a pressure drop in a packed bed and uncontrollable blockage in a fluidized bed. In this study, salt-promoted spherical MgO agglomerates with diameters of several hundred micrometers were synthesized via a water-in-oil method and alkali metal salts were simultaneously impregnated. The CO2 capture performance of the spherical MgO agglomerates was compared with that of MgO powder. At 240 min and 300 °C, the MgO agglomerates exhibited a sorption capacity of 45 wt%, whereas the MgO powder showed 65 wt%. To further improve the performance of the MgO agglomerates and analyze the mechanism of CO2 capture, an activation method and a kinetics model were developed. The CO2 activation enhanced the capacity of the MgO agglomerates due to the better dispersion and coating of molten salt over the MgO surface. Consequently, the working capacity became comparable to that of the MgO powder in the mild cyclic test condition. With wet mixture gas for sorption and CO2 regeneration, the MgO agglomerates showed stable working capacity of 23 wt%. The semi-empirical dispersive kinetic model with the characteristic parameters for induction time and accelerated conversion rate was developed for CO2 uptake with respect to induction time, which could describe highly asymmetric sigmoidal-shaped uptake curves. Also, CO2 capture efficiency and energy consumption for the regeneration were investigated. When the ratio of the recycled sorbent flow rate to CO2 flow was 2.5 and the sorbent make-up ratio was 0.027, the regeneration energy of 141 kJ per 1 mol of captured CO2 was required for 0.95 of CO2 capture efficiency under mild cyclic test conditions.