Electrical swing adsorption on 3D-printed activated carbon monoliths for CO2 capture from biogas

Abstract

Direct, resistive or Joule heating of the adsorbent allows for the intensification of Thermal Swing Adsorption processes by reducing process cycle time and reducing heat losses. In this work, an electrically conductive activated carbon monolith was 3D-printed using a potassium silicate binder. The monolith was assessed for biogas upgrading, using Joule heating for regeneration of the monolith. The electrification of the 3D-printed monolith resulted in very rapid and homogenous heating, to 150 °C in less than 30 s at a potential of 8 V. Next, the monolith was subjected to cyclic adsorption-desorption experiments for CO2 capture from a synthetic biogas mixture (30 v% CO2 – 70 v% CH4). The main parameters in ESA, namely voltage, electrification time, purge conditions and an additional rinsing step were investigated by determining the impact on the heating, regeneration efficiency and purity. Increasing the voltage from 4 V to 8 V step is preferred for recovery (82–95%) as well as for energy consumption, as it increases the efficiency (27.1–28.4%). It was also found that using the same amount of purge gas, it is preferred to use a higher purge flow rate for a shorter time (100 Nml/min for 15 s) over a lower purge flow rate for a longer time (50 Nml/min for 30 s). This benefits both recovery (87.3% vs 84.0%) and purity (84.5% vs 83.4%). Lastly, the benefit of adding a rinse step to increase the purity was demonstrated, where having a rinse step prior to electrification allowed to augment the total purity from 58% to 81.2%, while the regeneration of the monolith was as efficient.