Absorption of CO₂ from natural gas using different amino acid salt solutions and regeneration using hollow fiber membrane contactors

Natural gas consists primarily of methane but it also contains considerable amounts of contaminating compounds mainly carbon dioxide (CO₂). In the present work, the absorption/Stripping performance of four different amino acid salt (AAS) aqueous solutions was compared with MEA and NaOH solutions by using homemade PVDF hollow fiber gas-liquid membrane contactor modules. Compared to MEA, AAS have enhanced CO₂ absorption/stripping performance. The experimental results show that the absorption performance can be enhanced by increasing liquid flow rate. However, the gas flow rate has negative effect on the removal efficiency although flux increases. Furthermore, it has been observed that AAS shows negligible effect of temperature on absorption performance. To improve the stripping performance, enhanced CO₂ desorption (based on pH-shift) was studied by using asymmetric solutions of AAS. Higher molar ratios of amino acid shows better stripping and reduced absorption performance because lower pH shifts the CO₂ reaction equilibrium towards the release of CO_2. Also it has been observed AAS solutions have lower potential of membrane wetting due to its high surface tension. Further it has been proved AAS solutions have good recyclability.