Design of CaO-Based Sorbents for CO2 Separations
Carbon dioxide separation from gas mixtures is critical process in several emerging energy-related industries, including in hydrogen production by means of biomass utilization and exhaust gas clean up. Some studies on this topic suggest using calcium-based sorbents for effective CO2 capture from gases because of a reduced energy penalties and low cost.
However, the use of CaO as a regenerable CO2 sorbent is limited by the rapid decay of the carbonation conversion with the number of carbonation/calcination cycles due to syntering.
In this work, we used template approach and deposition on inert carriers to design the sorbents with appropriate sorption properties and outstanding stability. Three groups of sorbents were synthetized:
1. Pure CaO synthetized by template technique as follows: at first step the template polystyrene particles with definite shape and size were introduced to matrix of calcium hydroxide paste. After that, matrix material solidified and template was deleted.
2. Calcium oxide was supported on yttria porous matrix pellets by means of consecutive impregnations of Y2O3 with CaNO3 water solution, drying and calcinations.
3. In this case, approaches 1 and 2 were combined: firstly, porous yttrium oxide was synthetized using polystyrene template to increase porosity. Than calcium oxide was deposited to Y2O3 as described in 2.
The pore size distribution of prepaid sorbents drastically depends on the quantity and the size of introduced template. The introducing of template significantly increases the rate both of sorbent carbonation and calcination reactions. Thus, the template synthetic technique looks like a direct way to control sorption performance of the sorbents. The supported sorbents exhibited outstanding CO2 adsorption stability over 150 repeated carbonation/ decarbonation cycles. This enhanced stability is due to the segregation effect, which prevented the contact of CaO crystal grains.