Selective Absorption of H2S from a Gas Mixture with CO2 by Aqueous N-Methyldiethanolamine in a Rotating Packed Bed
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Abstract
In this work, selective absorption of H2S from a gas mixture with CO2 into N-methyldiethanolamine (MDEA) is investigated experimentally and theoretically in a rotating packed bed (RPB). In the RPB, various rotating speeds, gas flow rates, liquid flow rates, and concentrations of MDEA aqueous solutions were studied by means of the evaluation of removal efficiency, selectivity, and overall volumetric mass transfer coefficient. The reaction−diffusion mass transfer model based on penetration theory for the selective absorption process is developed, accordingly. The results of experiment and model show that the uppermost function of RPB in selective absorption of H2S is to restrain the CO2 removal efficiency but sharply intensify the absorption of H2S. The mass transfer coefficient of CO2 absorption is enhanced in RPB. However, the total amount of CO2 mass transfer virtually is low because of the short gas−liquid contact time, small volume of packing, and large gas−liquid ratio within the RPB, and the CO2 removal efficiency is merely around 9.50%. For the penetration of H2S into liquid film, it is just 2.0 × 10−9 s that H2S needs to be exhausted at 10−8 m into the liquid film. And the lifetime of a liquid film in the RPB is 7 orders of magnitude bigger than this penetration time of H2S. So the reaction and mass transfer of H2S still can be completed even at the very short gas−liquid contact time within the RPB, and a high H2S removal efficiency of around 99.76% also can be achieved. In addition, a quantitative analysis based on the model, which suggests that the existence of CO2 has little effect on the absorption of H2S while the H2S has an apparent negative impact on the absorption of CO2, can be obtained for the selective absorption process. The experimental and model results have been found to be in a good agreement.
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