CO2 sorption and desorption performance of thermally cycled hollow fiber sorbents

We describe here the CO2 sorption and desorption properties of hollow fiber sorbents—a polymer/zeolite hybrid sorbent that possesses a coated bore that allows for exceedingly fast heat transfer between the heat transfer fluid and the sorbent. The fiber sorbents are intended for use in post-combustion CO2. The fiber sorption properties are tested chromatographically with simulated flue gas in the absence of a heat transfer fluid and are found via in situ thermal measurements to be highly non-isothermal, which results in up to 40% losses in CO2 breakthrough capacities. The thermal front moving through the fiber wall was found to progress approximately 30% faster than the propagating speed of the CO2 sorption front. Upon the addition of a heat transfer fluid (water) in the bores of the fibers, breakthrough CO2 capacities were maintained at all flue gas superficial velocities studied (up to 50 cm/s). The propagation speed of the CO2 front was reduced by 38% by the addition of cooling water in the bores, and the in situ thermal measurements revealed that the fiber sorbents were nearly isothermal during the CO2 sorption step. One of the main conceptual advantages of a fiber sorbent CO2 capture platform is the ability to transfer the released sorption enthalpy to the bore-side cooling water, which can then be later used in a beneficial way. By varying the cooling water velocity, in situ thermal measurements showed that 22,000 J per mol of flowing CO2 could be transferred to the cooling water out of a possible 36,000 J per mol. Finally, plug flow-mode desorption experiments were performed, and a 40.5 mol% CO2 product was obtained. The small scales of the system prohibit sharper thermal fronts, which likely causes unwanted product CO2 and interstitial N2 mixing.

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► Hollow fiber sorbents maintained CO2 breakthrough capacity when coupled with cooling water.
► The fibers remained nearly isothermal during the sorption step due to cooling water.
► Up to 70% of the sorption enthalpy was successfully transferred to the cooling water.
► Using hot water, a 41 mol% CO2 product was generated during the desorption step.