(439e) Kinetic Study and Modeling of the High Temperature CO2 Capture by Na2zro3 Solid Sorbent

The use of high temperature solid CO2 capture in several fossil fuel-based energy production processes is an option to improve the efficiencies of such processes and simultaneously reduce the emission of greenhouse gases to the atmosphere. Recent studies in our laboratory [1] have shown the use of Na2ZrO3 as an alternate synthetic CO2 solid sorbent compared to expensive lithium-base sorbents (Li2ZrO3 and Li4SiO4) [2,3] due to its excellent thermal stability, kinetics and CO2 capture capacity features. The objective of the present work was to establish the CO2 sorption kinetics parameters such as: order of reaction, kinetic rate constant, apparent, intrinsic and diffusional activation energies and rate determining step. Na2ZrO3 was synthesized through the solid state reaction using stoichiometric amounts of a mixture of Na2CO3 and ZrO2 and calcined at 900ºC for four hours in an air-heated box furnace. Afterwards the sample was divided in nine equal portions. Sorption kinetics of prepared samples was evaluated through an electrobalance reactor (TGA) as a function of CO2 mol fraction (0.4, 0.6 and 0.8) and temperature (500, 600 and 700ºC) at a flowrate of 150 sccm. The global rate of the reaction was of first order in CO2 and strongly dependent on temperature. The calculated apparent activation energy was EA = 20.4 kcal/mol. Data analysis used the approximate solution to the shrinking core model for a gas-solid reaction. A two resistance (surface reaction and product layer diffusion) kinetic variation of the model provides good match with the conversion-time data. Modeling results include; an intrinsic activation energy of 23.5 kcal/mol and a product layer diffusional activation energy of 7.7 kcal/mol. The dependence of the reaction coefficients on reaction variables was in general in agreement with theory. Finally, results indicate that the main resistance to the reaction rate is the surface reaction, which is controlling the reaction kinetics (rate determining step) with only a minor contribution of the product layer diffusion resistance towards the end of the reaction.

[1] López Ortiz A., Pérez Rivera N. G., Reyes Rojas A., Lardizábal Gutiérrez D. Sep. Sci. Tec. 39 (2004) 3559.

[2] Nakagawa, K; Ohashi, T. J., J. Electrochem. Soc., 145 (1998) 1344

[3] Kato, M.; Yoshikawa, S.; Essaki, K.; Nakagawa, K. In Toshiba Corporation. INTERMAC, 2001, Japan Electric Measuring Instruments Manufacturers' Association, Joint Technical Conference, Paper ID: SE-3 (1021).