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Sr 2+ ÀSAPO-34 materials were prepared via solid-state ion exchange (SSIE) to improve their CO 2 adsorptive properties, particularly at low partial pressure, and study the effect of the ion exchange treatments on the structural and textural properties of the materials. In the past, these materials have been prepared with traditional liquid-state ion exchange (LSIE) methods yielding a strontium(II) content of about one cation per unit cell, well below the theoretical maximum and probably due to aqueous phase equilibrium constraints. Characterization of the SSIE materials included coupled thermal gravimetric analyses/Fourier transform infrared spectroscopy (TGA/FT-IR), X-ray diffraction (XRD), energy-dispersive analysis by X-rays (EDAX), surface area, and pure component CO 2 equilibrium adsorption. Coupled TGA/FT-IR studies were used for the selection of the SSIE temperature for both NH 4 + ÀSAPO-34 and as-synthesized Na + ÀSAPO-34 starting materials. In general, the results indicated that temperatures well above the Tammann point are necessary to achieve acceptable strontium(II) loadings via SSIE while minimizing the loss of effective surface area due to pore clogging with unexchanged SrCl 2 . Furthermore, in situ partial detemplation (PD) of the as-synthesized material during SSIE avoided the formation of excess proton (acid) sites and allowed further loading of strontium(II) onto sites suitable for interaction with CO 2 . In order to increase the strontium(II) loading per unit cell, a combined PD/SSIE/LSIE strategy was used to remove some of the remaining tenacious sodium(I) cations remaining after SSIE. This approach resulted in materials with a loading of nearly two strontium cations per unit cell and, as a result, improved the overall CO 2 adsorption performance of the materials in a remarkable fashion.

A Sr 2+ -SAPO-34 bed was assembled to study CO 2 dynamic adsorption under conditions that emulate those found in closed volume and portable applications. Although the surface area was reduced by 7% during pelletization, adsorption capacities estimated from breakthrough curves compared well with static volumetric adsorption data. Modeling of the breakthrough adsorption was achieved using a Linear Driving Force mass transfer rate model, showing good agreement with the experimental data and confirming fast kinetics and efficient use of the bed. Fast kinetics were also evidenced by the length of the unused section of the bed as calculated from a Mass Transfer Zone model. Adsorption capacity degradation was not observed after multiple regeneration cycles. Apparent and equilibrium adsorption isotherm data estimated from the bed and static volumetric experiments at 25 C were compared to that of 5A Zeolite. These showed that Sr 2+ -SAPO-34 is a superior adsorbent for CO 2 removal in the low partial pressure range (<1500 ppm). CO 2 and H 2 O multicomponent adsorption breakthrough curves were also gathered for a CO 2 inlet concentration of 1000 ppm and dew points of −5 and 8 C. The addition of moisture resulted in a decrease in total processed gas volume by 31 and 47%, respectively.

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