(724d) CO2 Capture On Amine-Functionalized Nanoporous Adsorbents: Modeling Equilibrium, Kinetics and Breakthrough Curves

In the search for efficient alternatives for CO2 capture, novel adsorbents have been produced by incorporating amine functional groups on nanoporous supports. These adsorbents reportedly offer high adsorption capacity, fast rate of adsorption and excellent selectivity toward CO2 while being tolerant to moisture. With the aim of predicting the behavior of fixed bed columns packed with amine-functionalized adsorbents, we developed equilibrium and kinetic models capable of describing CO2 adsorption under various operating conditions [1,2]. A semi-empirical equilibrium model was developed 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. This semi-empirical 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 temperatures between 25 and 55 °C. Moreover, the heat of CO2 adsorption calculated using the temperature-dependent parameters of the proposed model were in excellent agreement with experimental data. To investigate the adsorption kinetics of CO2 on amine-functionalized mesoporous silica, experimental data of CO2 uptake on triamine-grafted mesoporous MCM-41 silica (TRI-PE-MCM-41) as a function of time at temperatures between 25 and 70 °C, were fitted to a series of kinetic models, namely Lagergen's pseudo-first and pseudo-second order and Avrami's kinetic models. The best fit was obtained using Avrami's model, as it provided a fractional reaction order (ca. 1.4), which has been associated with the occurrence of multiple adsorption pathways. Using the aforementioned equilibrium and kinetic models, a series of simulations of CO2 adsorption in a column packed with TRI-PE-MCM-41 was carried out to predict breakthrough curves. The simulation results were compared to experimental data produced at various flow rates of a stream containing 5% CO2 balance nitrogen. In all cases, the predicted breakthrough time and the corresponding CO2 uptake were in close agreement with the experimental data. References: [1] R. Serna-Guerrero, Y. Belmabkhout, A. Sayari, Modeling CO2 adsorption on amine-functionalized mesoporous silica. 1. A semi-empirical equilibrium model. Chem. Eng. J. (2010) doi:10.1016/j.cej.2010.04.024 [2] R. Serna-Guerrero, A. Sayari, Modeling adsorption of CO2 on amine-functionalized mesoporous silica. 2. Kinetics and breakthrough curves. Chem. Eng. J. (2010) doi:10.1016/j.cej.2010.04.042 2