Journal of Membrane Science 377 (2011) 191–197 Contents lists available at ScienceDirect Journal of Membrane Science jo u rn al hom epa ge: www.elsevier.com/locate/memsci Simultaneous separation of H 2 S and CO 2 from natural gas by hollow fiber membrane contactor using mixture of alkanolamines Mahdi Hedayat, Mohammad Soltanieh ∗ , Seyyed Abbas Mousavi Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, P.O. Box 11365/8639, Islamic Republic of Iran a r t i c l e i n f o Article history: Received 12 February 2011 Received in revised form 22 April 2011 Accepted 24 April 2011 Available online 30 April 2011 Keywords: Hollow fiber membrane contactor Hydrogen sulfide Carbon dioxide Mixed alkanolamines Natural gas sweetening a b s t r a c t In the present work we studied the use of a membrane contactor system for simultaneous absorption of H 2 S and CO 2 from a gas mixture similar to natural gas. MDEA solution and mixtures of MDEA/DEA and MDEA/MEA were used as absorbent liquid. PVDF and PSf hollow fiber membranes were used in the membrane contactor modules. Design of experiments were carried out by Taguchi method in a manner that a systematical investigation of the effect of operational parameters (temperature, pressure, gas and liquid flow rates, absorbent concentration and acid gas content of the feed), in addition to the effect of membrane material and absorbent liquid, was implemented on process performance parameters includ- ing removal efficiencies, overall mass transfer coefficients and H 2 S to CO 2 selectivity. The results indicate that liquid side resistance is negligible in comparison with membrane and gas side resistances. Both membranes were wetted by the liquid, but PSf suffered more. The presence of a dense layer in mem- brane side adjacent to the liquid, changes the influence of operational parameters. It was observed that increasing absorbent concentration had a different effect in the presence or absence of CO 2 . Addition of MEA enhanced the removal efficiencies while DEA had no significant effect. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Many industrial gas streams contain acid gases, e.g., CO 2 and H 2 S. An important example is crude natural gas. These acid gases are impurities which lower the quality of the gas and cause corro- sion problems. In addition, H 2 S is a very toxic agent which must be removed before application of the gas. Removal of acid gases from natural gas is a well-known process in the industry. Usually the gas stream is contacted directly with a liquid solvent stream in a conventional packed bed column. Contacting gas and liquid streams via a microporous membrane is an effective alternative for traditional separation processes. In a membrane absorption system (contactor), the membrane is just a fixed interface (medium) between gas and liquid streams and does not offer any selectivity between the gases. This technology has many advantages over packed columns, e.g., high specific mass transfer area, modularity of the system with easy scale-up and independent control of gas and liquid streams which eliminates operational problems such as flooding and entrainment [1]. Qi and Cussler studied membrane absorption of acid gases for the first time [2,3]. Since then the majority of studies have been done on the removal of CO 2 , particularly from combustion gases ∗ Corresponding author. Tel.: +98 21 6616 5417; fax: +98 21 6602 2853. E-mail address: msoltanieh@sharif.edu (M. Soltanieh). which are the major sources of greenhouse gas emissions [4]. Few experimental studies on simultaneous absorption of H 2 S and CO 2 by membrane contactors have been reported. Kreulen et al. [5] studied selective removal of H 2 S from gas streams containing CO 2 and N 2 . They used MDEA solvent and polypropylene and nylon 66 flat sheet membranes as non-wetted and wetted membranes, respectively. They found that non-wetted membranes decrease the H 2 S selectivity. Wang et al. [6] continued their work by using tailor made poly vinylidene fluoride hollow fiber membrane and sodium carbonate solution. They found that gas to liquid flow ratio and CO 2 concentration have significant effect on removal efficiencies and H 2 S selectivity. Mathematical modeling of simultaneous absorption of CO 2 and H 2 S was carried out in recent years. Keshavarz et al. [7] performed their modeling with DEA as absorbent and investigated wetting and operational parameters. They found that wetting has a great influence on CO 2 removal, comparing with H 2 S. Also, decreasing of DEA concentration mostly decreases the CO 2 removal. Faiz and Al-Marzouqi [8] performed a modeling with MEA as the solvent. They found that low concentration of MEA is efficient in complete removal of H 2 S, but increase of MEA concentration enhances CO 2 removal efficiency. Wetting of micro pores in membrane absorption of CO 2 has been a major field of interest for researchers [9–12]. Kreulen et al. [9] determined mass transfer rates in wetted and non-wetted microporous membranes. They found that the thickness of the wet- ted membranes, reduces mass transfer significantly and thus they 0376-7388/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2011.04.051