(95b) Study on the Kinetics of Ca-Based CO2 Sorbent of Carbonation and Calcination for Adsorption Enhanced Reforming Process

Abstract Ca-based CO2 adsorbent may have different properties according to the kinds of application in fuel gas release, adsorption enhanced reforming (AER), energy storage and chemical pump system. Ca-based adsorbent applied in AER process needs a rapid adsorption rate and decomposition rate at lower temperature to ensure a synergic action with the methane steam reforming process. The author has systematically studied and find that nano scale Ca-based CO2 sorbent is desirable with the advantages of rapid CO2 reaction rate and high adsorption capacity, lower decomposition temperature and re-useable.

A nano scale CaCO3(70 nm) was used as precursor for CO2 adsorbent. The properties of calcination followed by carbonation was studied by TGA In order to pursue the reaction condition of as a criterion of reaction section and diffusion section, The data simulated with the Avrami-Erofeeve kinetic equationF obtained a good results at the temperature of 500-650°C, CO2 partial pressure of 0.33atm. The simulation results showed that a relative deviation of CO2 adsorption ratio of the reaction section and diffusion section were lower than 3.5% and 0.86% respectively. The activity energy of reaction section of nano scale CaO is 11.9 kJ/mol. The activity energy of diffusion section of nano scale CaO is 106.9 kJ/mol.

Calcination kinetics of CaCO3 using equation of is in coincidence with the experimental data under the temperature of 650-800°C. At the CO2 partical pressure of 0.20 atm and 0.40 atm ,the relative deviation is lower than 7.82% and 5.01% , and the active energy of calcination reaction is 34.72kJ/mol and 113.2kJ/mol respectively.

In a summary, nano Ca-based CO2 sorbent has a lower activity energy for carbonation and followed by calcination. This advantage of nano Ca-based CO2 adsorbent is in consistence with the higher adsorption ratio and reaction rate than the micrometer scale Ca-based adsorbent. The lower decomposition reaction condition under low CO2 partial pressure and easy to be regenerated of nano scale Ca-based CO2 adsorbent are unparalleled. Also the nano Ca-based CO2 sorbent used in the AER process for producing hydrogen has been studied. Good results showed it has an attractive potential to be used in the AER process for producing hydrogen.

Keywords: hydrogen, CO2 sorbent, nano CaCO3, kinetics, adsorption, decomposition