In recent years social awareness and legal requirements have increased the concern about carbon dioxide capture, especially since the establishment of the reduction of their emission and the search for alternatives set by Kyoto's protocol and the IPCC reports.
Traditionally industrial separation of CO2 is performed using aqueous amines. One of the main setback of this process is that it consumes a large amount of energy for the regeneration of the amine. This occurs primarily due to the high heat capacity of water. Therefore in order to avoid the energetic penalty of heating water, a suitable alternative to this process is to use the solid analogue of the amine solution.
Mesoporous silica can be used as a support media of organic molecules, such as amines. They have a well defined porous structure of tunable pore size in the mesoporous range. Their surface silanol groups can react with aminosilanes to form organic-inorganic hybrid materials with high affinity for CO2. These functionalized materials can be used to capture CO2 reversibly using adsorption.
The use of functionalized mesoporous silica adsorbents is one of the most promising mid-term alternatives to achieve a viable alternative for CO2 separation and capture. The effective design of these materials requires a method that can relate the structure of the adsorbent to its performance in the application of interest. An understanding of the physics behind them can be achieved by using molecular simulations. Molecular simulations relate the microscopic behavior of the molecules during the adsorption process to the macroscopic behavior of the system, allowing one to search for the best materials for separating a mixture of gases.
We analyze by means of Grand Canonical Monte Carlo (GCMC) simulations the behavior of CO2 molecules captured on functionalized silicas. We calculate the different adsorption sites and the orientation and distribution of the adsorbed molecules. The understanding of those processes plays a key role on further optimization of the synthesis of these materials. We present our experimental adsorption isotherms and show the potential capabilities of this kind of materials to be used for CO2 capture; these results are compared to the simulated isotherms to validate the models.
This work was partially financed by the Spanish Government under projects CTQ2008-05370/PPQ, NANOSELECT and CENIT SOST-CO2 (CEN-2008-1027), these last two projects belonging to the Programa Ingenio 2010. Additional support from the Catalan Government was also provided (2009SGR-666). S.B. acknowledges a grant from MATGAS 2000 AIE.
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