Absorption of CO₂ into Aqueous Solutions of Methyldiethanolamine and Activated Methyldiethanolamine from a Gas Mixture in a Hollow Fiber Contactor

A membrane gas absorption (MGA) process was evaluated in this work for CO 2 capture from CO 2 /N 2 gas-mixed streams at room temperature. The experimental study of a polypropylene (PP) hollow fiber membrane contactor in combination with the technique of CO 2 absorption into aqueous solutions of activated methyldiethanolamine (MDEA) and MDEA as absorbents was carried out. A laboratory-scale setup, in which the solution with CO 2 loading was able to be hot-regenerated into the solution without CO 2 loading and used circularly, was established in this study. The effects of a variety of operation factors, such as gas and liquid flow rates, membrane pore-wetting, and liquid CO 2 loading, on the separation performance of the membrane contactor were investigated. The absorption performances were compared between activated MDEA and MDEA. A mathematical model was developed to simulate the mass-transfer behavior of the membrane gas−liquid contactor. The experimental results show that the use of a membrane gas−liquid contactor with improved alkanolamines such as activated MDEA can be completely applied to CO 2 capture. Low and steady liquid CO 2 loading was able to be controlled by hot-regeneration. The CO 2 absorption performance of activated MDEA was remarkably better than that of MDEA. The CO 2 removal efficiency could reach more than 99% with activated MDEA. The average overall mass-transfer coefficient with activated MDEA was 2.25 times that with MDEA. The activator piperazine (PZ), even with a small quantity in the activated MDEA, plays a significant role in the improvement of mass transfer in MGA. A comparison of model estimations with experimental results indicates that estimations of the nonwetting mode are divaricated from experimental data. Taking partial-wetting of the membrane into account, the model simulation is validated with experimental data. Partial-wetting can result in significant membrane resistance to mass transfer in MGA.