(456b) Investigation of Aminopolymer Loading on the MCM-36 Crystal for CO2 Capture
Current research on amine impregnated adsorbents for carbon dioxide capture has focused on the attempt to increase amine loading onto the solid support in order to improve overall capture performance. The hope with this method is to drastically improve the selectivity and capture capacity of the material by shifting it from a physical to chemical adsorbent through the introduction of amine sites, which actively attach to entering carbon dioxide in a 2 to 1 amine to CO2 molar ratio. However, this methodology so far has missed an opportunity for further optimization of these materials by the careful control of the diffusion and kinetic changes that occur upon impregnation of the amine molecules into the solid support. In our work, we have investigated these changes by the introduction of a branched polyethyleneimine amino-polymer into the large pores of the MCM-36 support.
MCM-36 was chosen for this work because of the large literature background on the synthesis and characterization of this material, as well as the interest within the carbon dioxide capture community on the potential implementation of this adsorbent for capture applications. MCM-36 was first reported in the literature by Corma et al. from the swelling and pillaring of the MCM-22-Precursor crystal (MCM-22-P). This solid is composed of approximately 2 nm microporous layers of aluminosilicate charge balanced one on top of the other by the presence of hexamethyleneimine cations in the interlayer space. This yields a crystal with the porosity of zeolites and the lamellar structure of clays, allowing for the implementation of clay chemistries to swell and pillar the precursor to form the fully inorganic MCM-36 structure, which is composed of microporous layers bridged by SiO2 pillars, which generate a large pore space between the layers. After synthesis this material can be impregnated with amino-polymers to generate an adsorbent with open CO2 channels within the layers and large pore spaces filled with amines for chemical adsorption of the CO2molecules.
The capture capacity, diffusion of entering molecules, and kinetics of carbon dioxide capture were investigated in this work for various amine loadings on the MCM-36 support to attempt to find a method to further optimize polymer impregnated adsorbents for carbon dioxide capture. We have found that increased amine loading within the material past a critical point can only further decrease the capture performance, suggesting that the optimum loading conditions are at a lower weight percent of loaded amines than that currently suggested in the literature. Furthermore this work has found that the use of 2-D porous sorbents may be ultimately hindered for carbon dioxide capture because of the tradeoff between ease of diffusion and capture kinetics upon amine impregnation, and that a new sort of amine impregnated solid must be developed to overcome these challenges if this carbon dioxide capture method is to ever be implemented in practical applications.