Thermal Management of Adsorption-Based Biogas Upgrading Systems via Incorporation of Phase-Change Materials

Abstract

Thermal management of adsorption columns is necessary to maintain their effectiveness while reducing the energy requirements of the overall separation process. In this work, we aimed at investigating the suitability of blending adsorbents with phase-change materials (PCMs) to adjust the thermal profile of a biogas upgrading column. A commercially available PCM (Nextek 28D) in quantities of 10, 20, and 30 wt % was blended with zeolite 13X in two configurations, namely, traditional pellets and 3D-printed monoliths. The use of different structures allows for better analysis of thermal profiles and assessment of the effectiveness of the PCM in a packed bed adsorption column. Due to low thermal stability, PCM was not mixed directly into the pellets and monoliths; rather, it was incorporated into the adsorption column in the form of mixedpellet and stacked-monolith structures. Our results indicated that pelletized and stacked-monolith configurations gave rise to different degrees of heat transfer across the column. The pure 13X bed exhibited a maximum temperature of 35.8 °C at a CO 2 capacity of 2.44 mmol/g 13X . In comparison, while the implementation of 20 wt % PCM resulted in only an average temperature drop of 0.35 °C, the CO 2 adsorption capacity was enhanced by 11.8% per gram of 13X for mixed-pellet bed. On the other hand, the stacked-monolith bed required a minimum 20 wt % PCM to become favorable with an average temperature drop of 4.9 °C for an 8.5% increase in CO 2 uptake, but under identical conditions, the mixed-pellet bed was found to outperform the stacked-monolith counterpart. Additionally, simulation results confirmed that the energy balance shift caused by 185 J/g of PCM can be effective to lower the temperature of the column during the adsorption step, thereby improving the separation efficiency. This work highlights the potential of incorporating phase change materials into adsorption column to regulate temperature during adsorption step and increase equilibrium capacity by maintaining favorable thermodynamic conditions.