(129b) The Development of a Pressure Swing Adsorption Model to Evaluate Metal Organic Frameworks

Metal organic frameworks (MOFs), a diverse class of crystalline materials that are defined by metal ions coordinated to organic ligands, are a promising candidate for CO₂ capture. The advances in this area of reticular chemistry over the last 25 years has lead metal organic frameworks to become a playground for chemists to design unprecedented porous materials that can be used for reversible CO₂ capture. However, identifying MOFs for reversible CO₂ adsorption presents a major challenge because of the number of competing phenomena within a MOF that contribute to effective capture and regeneration within an adsorption column.

In this work we present a pressure swing adsorption model that quantifies the potential of a specific MOF to act as an adsorbent within a packed bed adsorber. The model allows for the user to input experimentally determined values for the adsorption isotherm and effective diffusivity constants of the MOF. This allows for the MOF’s complex microstructure to be translated into a set of macroscopic adsorption and diffusion parameters that determine saturation and desaturation times of a pressure swing adsorber. The model assumes plug flow through an adsorption column filled with M spherical particles of a specific MOF. The packed bed of length L is then divided into i stages of size L/N with M/N identical particles. Diffusion into a porous sphere with appropriate boundary conditions is assumed to be the driving force of CO₂ uptake into the MOF particles.

We implemented this model to predict the behavior of an adsorption column packed with the MOF known as zeolitic imidizolate framework-8 (ZIF-8). Preliminary results for an adsorption column on the length scale needed for installation into a vehicle suggests that approximately 2.5% of all CO₂ input into the system can be adsorbed over the saturation time of the filter. A saturation time on the order of two hours is achieved for a flow rate of 0.144 g CO₂ per hour. These results show that our model offers a route towards evaluating the performance of specific MOF geometries in large scale adsorption processes. Our model presents a unique solution to determine which MOFs are worth investing resources into for further development as a large scale CO₂ capture technology.