Microporous materials, such as zeolites are promising candidates for the challenges related to the adsorption of CO2. They are typically characterized by a good selectivity and fast kinetics towards CO2 adsorption coupled with quick regeneration of the adsorbent. Understanding the fundamental differences in specific microporous materials is crucial for designing superior adsorbents. This is evidenced by P1 favoring the uptake of H2O gases compared to its polymorph P2, of the same GIS framework. This work aims to highlight the enhanced performance for CO2 adsorption of materials obtained via synthesis design as well as post-synthetic modification. By adjusting the inherent elemental composition of the hydrogel used to obtain the zeolite it was possible to affect the particle size based on the chosen method of agitation leading to particles spanning an order of magnitude difference in size, but comparable elemental composition. The materials were investigated with several techniques, such as helium ion microscopy, N2-physisorption and 27Al MAS NMR suggesting that the state of the active site, Al, is the same in large and small particles. Material of smaller particle size, however, showed superior CO2 uptakes. Additionally, increasing the concentration of active sites, by lowering the Si/Al ratio, further enhanced the CO2 uptake. Using this design matrix, microporous materials of high CO2 adsorption capacity could be obtained. This approach was then further investigated by introducing post-synthetic modifications such as hydrophobization aimed at producing a water-repelling outer particle surface. This modification is facilitated by a tested approach using silane vapors, purging a zeolite bed at 300 °C, enabling the silylation of hydroxyls. Exploiting the small pore openings of SSZ-13, the reactive silane molecules are not able to penetrate the crystal body, hence, mainly silylating the outer surface and inter-crystalline spaces in the aggregated particles. The micropore volume showing no appreciable changes verified this. Designing materials of high CO2 uptake and hydrophobic surfaces is believed to significantly enhance the separation efficiency of zeolites for CO2 from wet streams such as flue gases. Potential applications can be found in the post-combustion capture process of coal factories.

Microporous materials for the effective adsorption and separation of CO2 from flue gases

253rd National Meeting (2017)

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