Simultaneous removal of CO2 and H2S from pressurized CO2–H2S–CH4 gas mixture using hollow fiber membrane contactors

• Published in: Separation and purification technology Vol. 86; pp. 88 - 97
• Main Authors: Marzouk, Sayed A.M., Al-Marzouqi, Mohamed H., Teramoto, Masaaki, Abdullatif, Nadia, Ismail, Zahoor M.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15.02.2012; Elsevier
• Subjects: absorption; Absorption, stripping; Applied sciences; carbon dioxide; Chemical engineering; e-PTFE hollow fiber; Exact sciences and technology; gases; Gas–liquid membrane contactors; Heat and mass transfer. Packings, plates; mass transfer; methane; monitoring; natural gas; PFA hollow fiber; Physical and chemical absorption; Simultaneous removal of CO2 and H2S at high pressures; sodium hydroxide; solvents; streams; Simultaneous removal of CO2 and H2S at high pressures; PFA hollow fiber; Physical and chemical absorption; e-PTFE hollow fiber; Gas–liquid membrane contactors; Gas absorption; Chemisorption; Gas mixture; S at; Carbon dioxide; Distilled water; Hydrogen sulfides; Liquid membrane; Liquid phase; high pressures; Mass transfer; Simultaneous removal of CO; Microporosity; Mass transfer coefficient; Surveillance; and H; Hollow fiber; Gas-liquid membrane contactors; Natural gas
• ISSN: 1383-5866; 1873-3794
• DOI: 10.1016/j.seppur.2011.10.024

► High-pressure simultaneous removal of H2S and CO2 from pressurized gas mixture into absorption solvents was realized. ► Perfluoroalkoxy (PFA) and ePTFE hollow fiber membranes have been used in custom made high pressure modules. ► PFA fibers provided significantly higher fluxes for CO2 and H2S than those obtained with the more common ePTFE fibers. ► Liquid phase mass transfer resistance dominates at low pressures. ► Gas phase mass transfer resistance contributes considerably at high pressures. In the present paper, the simultaneous removal of CO2 and H2S from their pressurized mixture with CH4 (5% CO2–2% H2S–93% CH4) using custom made membrane contactors equipped with micro-porous polymeric hollow fibers is described. Two types of commercial hollow fibers were employed and compared, i.e., expanded poly(tetrafluoroethylene) (ePTFE) and poly(tetrafluoroethylene-co-perfluorinated alkyl vinyl ether) (PFA). The feed gas mixture composition was 2% H2S, 5% CO2 in balance of CH4 to mimic the typical natural gas composition. Distilled water, aqueous sodium hydroxide and amine solutions of different concentrations were tested as absorption liquids to achieve the selective removal of the acid gases from the pressurized gas streams. The effect of pressure on the simultaneous CO2 and H2S absorption rates was investigated by the simultaneous pressurization of the absorption liquid and the feed gas (up to 50bar) and monitoring the residual acid gases in the exit stream. The obtained experimental results indicated that the simultaneous CO2 and H2S fluxes were enhanced by increasing the inlet gas pressure for both physical and chemical absorption solvents. Up to the authors’ best knowledge, this is the first report on (i) the experimental simultaneous removal of CO2 and H2S from pressurized gas streams using HFM contactors and absorption solvents up to 50bar and (ii) the utilization of PFA fibers in custom made high pressure-membrane modules. PFA fibers exhibited impressive higher fluxes (9–10 times) for CO2 and H2S than those obtained with the common ePTFE fibers which could be attributed in part to the associated higher mass transfer coefficient. The anticipated CO2/H2S flux ratio of 2.5 (which matches the ratio of their inlet concentrations in the feed gas) was obtained whenever the co-absorption was unhindered into absorption solvent of sufficient capacity, e.g., 2.0 M NaOH solution. Analysis of the mass transfer coefficients showed that while the overall mass transfer coefficients are determined by the liquid phase mass transfer coefficients at low pressures, gas phase mass transfer resistance contributes considerably to the overall resistance at high pressures.