Investigation of thermal effects and transient reactor profiles in a plasma-sorbent system for simultaneous CO2 capture and conversion

Abstract

CO₂ capture and utilisation (CCU) is a promising solution to mitigate greenhouse gas emissions and has received much attention recently. Usually, CO₂ is captured and utilised in two separate processes. In this work, we focus on integrating both processes in one single unit using a non-thermal plasma reactor packed with zeolite 5 A as the CO₂ sorbent. CO₂ adsorbed by the sorbent can be desorbed and simultaneously activated by applying a plasma over the sorbent bed. In such case, the plasma-sorbent system demonstrated a transient behaviour including the variation of CO₂ concentration, plasma power and reactor temperature. This work aims to understand such behaviour better and to optimise the process by selecting a suitable desorption duration. To study the time-resolved radial temperature profiles and to highlight the effect of in situ CO₂ conversion on CO₂ desorption rate, a 2D phenomenological reactor model was developed. This model predicts heating and desorption behaviour in two different cases: 1) heating from a central heating rod, and 2) heating from the bulk of the sorbent bed with a fixed conversion that is provided as a modelling input. The first case represents temperature swing adsorption (TSA), while the latter represents the heating effect in the case of plasma-assisted desorption. Experiments were also conducted to verify the model and investigate the desorption and conversion of CO₂. The results showed that in situ CO₂ conversion during plasma-assisted desorption increases the desorption rate compared to TSA. Thermal desorption plays an important role in the plasma-induced desorption of CO₂, and a more uniform radial temperature profile can be achieved compared to using a central heating rod. In addition, it was observed that CO₂ conversion stagnates after 4 minutes of plasma exposure. Longer exposure times did not lead to higher CO₂ conversions because the reverse reaction of O₂ and CO to CO₂ competed with the forward reaction. Although plasma-induced desorption has a much higher energy consumption compared to TSA, 14.5 % CO₂ conversion can be achieved during the desorption process, and shorter cycle times can be achieved because of the faster desorption rate.