A novel separation process for olefin gas purification: Effect of operating parameters on separation performance and process optimization Maryam Takht Ravanchi a,b , Tahereh Kaghazchi a, *, Ali Kargari a , Mansoureh Soleimani a a Department of Chemical Engineering, Center of Excellence for Petrochemical Engineering, Amirkabir University of Technology (Tehran Polytechnic), No. 424, Hafez Ave., PO Box 15875-4413, Tehran, Iran b National Petrochemical Company, Research and Technology Co., No. 12, Sarv Alley, Shirazi South Street, Molla Sadra Ave., PO Box 14358-8471, Tehran, Iran 1. Introduction In the petrochemical industry, olefins such as ethylene and propylene are the most important chemicals used for the production of polyethylene, polypropylene, styrene, ethyl benzene, ethylene dichloride, acrylonitrile, and isopropanol. Various petro- chemical streams contain olefin and other saturated hydrocarbons. These streams typically originate from steam cracking units (ethylene production), catalytic cracking units (motor gasoline production), or the dehydrogenation of paraffins (Agam et al., 2001; Meyers, 1986). An important step in the manufacture of olefins is large-scale separation of the olefin from the correspond- ing paraffin. During the years, different processes have been used for the separation of olefin–paraffin mixtures, such as low-temperature distillation, extractive distillation, physical or chemical adsorption and physical or chemical absorption (Bryan, 2004; Eldridge, 1993). Currently, this separation is carried out by cryogenic distillation, which is highly energy-intensive due to the cryogenic tempera- tures required for the process and low relative volatilities of components. Distillation columns are often up to 300 ft tall and typically contain over 200 trays. With reflux ratios greater than 10, a very high energy input is required for the distillation process. This large capital expense and energy cost have created incentive for extensive research in this area of separations. Nowadays, membrane technologies are becoming more fre- quently used for the separation of wide varying mixtures in the petrochemical-related industries. The range of applications covers the supply of pure or enriched gases such as He, N 2 and O 2 from air, the separation of acid gases such as CO 2 and H 2 S, the separation of H 2 in the petrochemical and chemical industries, the separation of gold and mercury from industrial wastes and the separation of hydrocarbons. An overview of various types of membrane processes can be found in the literature (Baker, 2002, 2004; Kaghazchi et al., 2006; Kargari et al., 2004a, 2006a,b; Mohammadi et al., 2008; Mulder, 1996; Nabieyan et al., 2007; Takht Ravanchi et al., 2009). Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 511–517 ARTICLE INFO Article history: Received 20 June 2008 Received in revised form 17 February 2009 Accepted 18 February 2009 Keywords: Facilitated transport membrane Propylene Propane Silver nitrate Taguchi analysis ANOVA ABSTRACT Separation of propylene–propane mixtures using facilitated transport membrane is potentially a novel separation process for olefin gas purification. The main purpose of this study was to find optimum values of the process parameters using the Taguchi approach. The Taguchi method was selected as the statistical technique since it allows the main effects to be estimated with a minimum number of experimental runs. Moreover, it makes use of fractional factorial and orthogonal arrays to identify the factors and the optimum factor setting for each experimental run. Trans-membrane pressure and carrier concentration were two influential parameters that affect the separation performance of the present membrane system. These control factors in three levels were considered in the Taguchi analysis. L9 orthogonal array has been used to determine the signal-to-noise (S/N) ratio. Analysis of variance (ANOVA) was used to determine the optimum conditions. It indicated that carrier concentration has the most contribution (72%) in the membrane separation of propylene–propane mixture. Moreover, to achieve an optimum operating condition, trans-membrane pressure and carrier concentration should be set at 120 kPa and 20 wt.%, respectively. According to the Taguchi approach, by setting control factors at optimum values a product with 99.801 (vol.%) propylene was obtained. A verification test was also performed to check the optimum condition. Experimental results confirmed optimum values obtained by the Taguchi analysis and showed that at optimum operating conditions, a product with 99.63 (vol.%) propylene was obtained. ß 2009 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +98 21 64543152; fax: +98 21 66405847. E-mail address: Kaghazch@aut.ac.ir (T. Kaghazchi). Contents lists available at ScienceDirect Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice 1876-1070/$ – see front matter ß 2009 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jtice.2009.02.007