Experimental procedure of CO2 absorption and microwave assisted desorption

https://doi.org/10.1016/j.petlm.2016.11.002

“Four sets of experiments were performed: heating and cooling profiles, comparison of conventional and microwave regeneration, CO₂ absorption isotherms and multiple microwave regeneration cycles. For the heating and cooling profiles, 5 mL samples were separately heated in a water bath and the microwave applicator at an input power of 100 W between room temperature and 70 °C with 100 mL/min N₂ bubbling through. The solution was then left to cool by removing the heat source. The samples used were water, 30 wt% MEA and 30 wt% MEA previously loaded with CO₂ during a 20 min absorption step.

For the regeneration experiments, during the absorption step a binary gas feed of 20% CO₂ and 80% N₂ was bubbled through 5 mL MEA solution at 100 mL/min for 20 min at ambient temperature. A blank absorption run was performed with an empty reactor to allow the absorbed quantity of CO₂ to be calculated. For the desorption step, the CO₂ was stopped and the input N₂ flow rate set to 100 mL/min. The CO₂-rich solution was heated to the desired regeneration temperature (70 °C or 90 °C) and held there for 10 min, followed by 10 min with no heating. The microwave heating was performed at an initial input power of 100 W to reach the desired temperature and then the power manually adjusted at around 40 W for 70 °C and 60 W for 90 °C to maintain a constant temperature. Conventional heating experiments were performed in a water bath at the regeneration temperature. The outlet CO₂ flow rates were determined by taking the CO₂ sensor reading as a percentage of the total mass flow meter reading. The volume of CO₂ absorbed was calculated by integrating the difference between the blank and sample CO₂ outlet flow rates. The amount of CO₂ released by the desorption step was determined by direct integration of the outlet CO₂ flow rate. The steady-state CO₂ loadings could then be ascertained by difference of the absorbed and desorbed quantities.

For the isotherm experiments, the quartz bubbler containing 7 mL of 30 wt% MEA solution was continually heated at 65 °C either in the microwave applicator or in a water bath. Heating continued well past the point at which a steady temperature was achieved (with heat dissipated to the surroundings through the un-lagged quartz vessel in the case of microwave heating). A gas feed of 20% CO₂ and 80% N₂, to provide an inlet CO₂ partial pressure 20 kPa, was bubbled through the solution at 50 mL/min for up to 4 h until a material steady-state was achieved, i.e. the liquid became saturated at the given gas partial pressures. The CO₂ partial pressure was then increased to 29 kPa and the system left for steady-state to re-establish. Due to the continuous bubbling the temperature distribution within the bubbler is expected to be very even. A blank run was also performed without any MEA solution to determine the amount of CO₂ absorbed. Equilibrium CO₂ loadings were confirmed by titration with BaCl₂ according to Refs. [43], [44], [45]. The CO₂ partial pressure was monitored with the CO₂ sensor on the outlet gas stream.”