Modeling CO2 adsorption on amine-functionalized mesoporous silica: 1. A semi-empirical equilibrium model

An equilibrium model capable of describing CO2 adsorption isotherms on amine-grafted mesoporous silica using a semi-empirical method was developed. The proposed model is based on the assumption that adsorption of CO2 occurs via two independent mechanisms: (i) chemical adsorption on the amine-functional groups, and (ii) physisorption on the surface of the adsorbent. The CO2 adsorption isotherms on triamine-grafted pore-expanded MCM-41 silica were measured at different temperatures and used to develop the proposed model. The equilibrium model was capable of describing CO2 adsorption over a wide range of pressure, from 0.001 to 20 bar. Furthermore, when applied in a temperature-dependent form, it fitted experimental data at different temperatures between 25 and 55 °C. The adequacy of the model was reflected by the low values of the normalized standard deviations (<8%) obtained at all temperatures. The model was also successfully used to fit experimental CO2 isotherms of a triamine-grafted mesoporous silica with lower amine content and five varieties of monoamine-grafted SBA-15, as well as experimental data for H2S adsorption at 25, 35 and 50 °C. Moreover, the heat of CO2 and H2S adsorption calculated using the temperature-dependent parameters of the proposed model was in excellent agreement with experimental data.