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

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.