Effects of Morphology on the Reaction Kinetics of Calcium Oxide Carbonation
A foundation for the analysis of chemical reactions using thermogravimetric analysis is presented here. Calcium oxide has been shown to be invaluable in steam-methane reform processes due to its ability to pick up and sequester carbon dioxide. Calcium oxide derived from marble, calcium acetate, and electrospun composite nanofibers are carbonated in a thermogravimetric analyzer at various temperatures. Generally, a larger conversion of calcium oxide to calcium carbonate was reached at higher temperatures. For the marble precursor, the conversion increased from 40% at 600ï¿½C to 66% at 800ï¿½C under an atmospheric pressure of 100% CO2. The conversion trends are compared and contrasted between the precursors. A study on the effect of sample age and sample pretreatments was conducted, which showed that sample age slightly affected carbonation kinetics by increasing peak reaction rate of a marble-derived sample from 0.07 mol/min to 0.10 mol/min. Multiple pretreatments seemed to have no effect on conversion nor reaction rates. The electrospun composite nanofibers outperformed the other precursors across all temperatures, reaching complete conversion at 650ï¿½C, while the marble-derived sample only reached 41%, and the calcium acetate-derived sample only reached 84%. By applying the random pore model and the overlapping grain model to these conversion trends, kinetic rate constants and diffusivities can be estimated, providing a quantitative method to compare and contrast sorbent performance, With this method, the marble-derived sample was shown to exhibit poor performance, with a kinetic rate constant of 2.6 x 10-4 cm2/mol/s compared to the nanofiber’s 5.6 x 10-4 cm2/mol/s at 650ï¿½C.