Appropriate selection of adsorbent materials is essential in developing adsorption-based processes such as CO 2 capture. Approximate methods to evaluate material candidates exist using adsorbent evaluation metrics or simplified process models. These approximate methods do not, of course, completely describe the performance of adsorbents in real separation processes. Here, we assess the correlations between approximate predictions and detailed process models of pressure swing adsorption (PSA) at subambient temperatures for postcombustion CO 2 capture using metal−organic frameworks (MOFs). Our results indicate that CO 2 swing capacity and adsorbent performance score are useful in predicting the ranking of materials for this process. These results illustrate the opportunities and challenges in bridging approximate and detailed methods for evaluating adsorbents for cyclic separations processes.

The Ideal Adsorbed Solution Theory (IAST) developed by Myers and Prausnitz and Radke and Prausnitz provides a powerful tool to calculate multicomponent adsorption equilibria based on single component adsorption isotherms. An important aspect of the application of IAST is that it requires the solution of an implicit algebraic system of equations. Analytical solutions can be derived only for few simple single component isotherm models. This work offers a new concept to solve the equations of the IAST for mixtures of N components characterized by nondecreasing single component adsorption isotherm behavior. The approach is based on transforming the algebraic system of IAST equations to a system of ODEs with one specified initial value. This work also provides analytical expressions for the partial derivatives of the predicted adsorption equilibria and increases the efficiency of numerical calculations for fixed-bed adsorber dynamics. The strength of the solution method is illustrated in case studies. Figure 3. Trajectories for the 10 component case of Example 3.(a): Solution orbit. and (b): inset of (a) for the low-pressure region.

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/C 0 = 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.

Adsorption of CO 2 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 CO 2 capture processes utilizing a multistage separation process. A hybrid process design using a combination of pressure-driven separation of CO 2 from flue gas (e.g., adsorption-or membrane-based separation) followed by CO 2 -rich product liquefaction to produce high-purity (>99%) CO 2 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 mol CO 2 /kg sorb À1 sec À1 being required to reduce costs of capture below $60/ ton CO 2 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 zeolite 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 temperatures reducing costs of capture as low as $61/ton CO 2 . 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.

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