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Effective thermal modulation and storage are important aspects of efforts to improve energy efficiency across all sectors. Phase change materials (PCMs) can act as effective heat reservoirs due to ...

Adsorption of CO2 from post-combustion flue gas is one of the leading candidates for globally impactful carbon capture systems. This work focused on understanding the opportunities and limitations of sub-ambient CO2 capture processes utilizing a multistage separation process. A hybrid process design using a combination of pres- sure-driven separation of CO2 from flue gas (e.g., adsorption- or membrane-based separation) followed by CO2-rich product liquefaction to produce high-purity (>99%) CO2 at pipeline conditions is considered. The operating pressure of the separation unit is a key cost parameter and also an important process variable that regulates the available heat removal necessary to reach the sub-ambient operating conditions. The economic viability of applying pressure swing adsorption (PSA) processes using fiber sorbent contactors with internal heat management was found to be most influenced by the productivity of the adsorption system, with productivities as high as 0.015 molCO2 /kgsorb -1 sec -1 being required to reduce costs of capture below $60/ ton CO2 captured. This analysis was carried out using a simplified two-bed process, and thus there is opportunity for further cost reduction with exploration of more complex cycle designs. Three exemplar fiber sorbents (MIL-101(Cr), UiO-66, and zeo- lite 13X) were considered for application in the sub-ambient process of PSA unit. Among the considered sorbents, zeolite 13X fiber composites were found to perform better at ambient temperatures as compared to sub-ambient. MIL-101(Cr) and UiO- 66 fiber composites had improved purity, recovery, and productivity at colder tem- peratures reducing costs of capture as low as $61/ton CO2. Future economic improvement could be achieved by reducing the required operating pressure of the PSA unit and pushing the Pareto frontier closer to the final pipeline requirement via a combination of PSA cycle design and material selection. KEYWORDS CO2 capture, fiber sorbents, heat management, pressure swing adsorption, sub-ambient process

The synthesis and functionalization of porous organic cages (POCs) for separation have attracted growing interest over the past decade. However, the potential of solid-phase POCs for practical, large-scale separations will require incorporation into appropriate gas-solid or liquid-solid contactors. Contactors with more effective mass transfer properties and lower pressure drops than pelletized systems are preferred. Here, we prepared and characterized fiber sorbents with POCs throughout a cellulose acetate (CA) polymer matrix, which were then deployed in model separations. The POC CC3 was shown to be stable after exposure to spinning solvents, as confirmed by NMR, powder X-ray diffraction, and gas sorption experiments. CC3-CA fibers were spun using the dry-jet wet-quench spinning method. Spun fibers retained the adsorptive properties of CC3 powders, as confirmed by CO2 and N2 physisorption and TGA, reaching upward of 60 wt % adsorbent loading, whereas the pelletized CC3 counterparts suffered significant losses in textural properties. The separation capabilities of the CC3-CA fibers are tested with both simulated postcombustion flue gas and with Xe/Kr mixtures. Fixed bed breakthrough experiments performed on fibers samples show that CC3 embedded in polymeric fibers can effectively perform these proof-of-concept gas separations. The development of fiber sorbents embedded with POCs provides an alternative to traditional pelletization for the incorporation of these materials into adsorptive separation systems.

Adsorption of CO2 from post-combustion flue gas is one of the leading candidates for globally-impactful carbon capture systems. This work highlights opportunities and limitations of sub-ambient CO2 capture processes utilizing a multi-stage separation process. A hybrid process design using a combination of pressure-driven separation of CO2 from flue gas followed by CO2-rich product liquefaction to produce high purity (>99%) CO2 at pipeline conditions is considered. The economic viability of applying pressure swing adsorption (PSA) processes using fiber sorbent contactors with internal heat management were found to be most influenced by the productivity of the adsorption system. Three exemplar fiber sorbents (MIL-101(Cr), UiO-66, and zeolite 13X) were considered for application in the sub-ambient process of PSA unit. MIL-101(Cr) and UiO-66 fiber composites were estimated to have costs of capture as low as $61/tonne CO2.

Microencapsulated phase change materials (μPCM) are combined with the metal-organic framework (MOF) UiO-66 and a cellulose acetate fiber support to introduce thermal modulation into CO2 capture devices operating in subambient conditions. μPCM particles are incorporated into sorbent fibers during the fiber spin dope preparation step and are observed to withstand the spinning and subsequent solvent exchange steps with little to no loss of thermal modulating properties as determined by differential scanning calorimetry (DSC). The spinning of this novel sorbent-μPCM fiber sorbent is the first instance of single step spinning of sorbents with a thermal modulator. It was found that μPCM weight loading as high as 75 wt % was attainable while maintaining spinable fibers. Breakthrough adsorption experiments and subsequent temperature profile analysis were collected to compare CO2 breakthrough capacity and heat release for sorbent systems with and without phase change materials incorporated. In adsorption modules with a diameter of 0.455 cm, where heat dissipation through the module wall dominates the global thermal response of the system, modulated fibers showed a 20-25% increase in breakthrough capacity at short times (CO2 concentration C/C0 = 0.05) as compared to their unmodulated counterparts. Higher breakthrough capacity indicates the phase change material would help manage the heat effects due to the local contact between the μPCM and the MOF. In larger diameter modules (0.7 cm) where wall heat dissipation effects are less dominant than the 0.455 cm diameter modules, fibers with "inactive" μPCM (i.e., 50 °C below their melting point) show larger sorption-induced thermal excursions and as much as 4× lower capacities at low adsorbate leakage as compared to fibers where the phase change material was active. Through the incorporation of phase change material, the sorbent in the system acts more efficiently, thus potentially driving down adsorption system cost.

Recent advances in adsorptive gas separations have focused on the development of porous materials with high operating capacity and selectivity, useful parameters that provide early guidance during the development of new materials. Although this material-focused work is necessary to advance the state of the art in adsorption science and engineering, a substantial problem remains: how to integrate these materials into a fixed bed to efficiently utilize the separation. Structured sorbent contactors can help manage kinetic and engineering factors associated with the separation, including pressure drop, sorption enthalpy effects, and external heat integration (for temperature swing adsorption, or TSA). In this review, we discuss monoliths and fiber sorbents as the two main classes of structured sorbent contactors; recent developments in their manufacture; advantages and disadvantages of each structure relative to each other and to pellet packed beds; recent developments in system modeling; and finally, critical needs in this area of research.