(227b) Comparative Performance Evaluation of Structured and Packed Bed Contactors for Solid-Sorbent Direct Air Capture of CO2

Direct air capture (DAC) is a carbon dioxide removal technology that has the potential to remove 1-5 Gigatonnes of CO₂ per year by 2050. Large-scale deployment of adsorption-based DAC is, however, impeded by its high cost that stems from high energy consumption and annualized plant cost. The design of the air-sorbent contactor can influence the productivity and specific energy consumption of DAC processes and help in minimizing the size (capital cost) and operating costs of DAC. Various designs of air-sorbent contactors include packed beds and structured contactors such as monoliths, laminates, and fibers. Structured contactors are expected to provide a significant advantage in air moving costs due to very low pressure drop along the columns but could be limited by a lower sorbent mass per unit volume of contactor when compared with packed bed contactors. A comparative performance evaluation of these contactors at the process scale is less explored and is the focus of this study.

A height equivalent to theoretical plate (HETP) analysis was performed for packed bed and structured contactors. It was found that there exist ranges of geometric parameters in structured contactors (channel density, channel width, adsorbent thickness, etc.) for which the HETP of structured contactors (monoliths and laminates) is lower than that of the packed bed contactor. This implies that mass transfer could be more efficient in structured contactors than in packed bed contactors. Geometric parameters for packed bed (particle diameter) and monolith contactors were selected based on the HETP analysis and used to simulate the DAC process in these contactors. Two DAC-suitable adsorbents viz. amine-functionalized divinyl benzene polymer (Lewatit® VP OC 1065) and 3-aminopropyl-methyl-diethoxysilane (APDES) on alumina were considered in this study. A 4-step temperature vacuum swing adsorption process for DAC in packed bed and monolith contactors was simulated using an in-house model. The impact of the type of contactor and choice of sorbent on key performance indicators of productivity, specific energy consumption, recovery, and product purity gauged from the simulation exercise will be discussed.