Separation and Purification Technology

Transcription

1 Separation and Purification Technology 97 (2012) Contents lists available at SciVerse ScienceDirect Separation and Purification Technology journal homepage: Experimental study of the separation of propane/propylene mixtures by supported ionic liquid membranes containing Ag + RTILs as carrier Marcos Fallanza, Alfredo Ortiz, Daniel Gorri, Inmaculada Ortiz Advanced Separation Processes Research Group, Department of Chemical Engineering and Inorganic Chemistry, University of Cantabria, Santander, Cantabria, Spain article info abstract Article history: Available online 30 January 2012 Keywords: Olefin Silver Ionic liquid Supported liquid membrane Gas separation During the last two decades the use of supported liquid membranes (SLMs) has been widely studied as an attractive alternative in gas separation processes. In this work supported ionic liquid membranes were used for propane/propylene gas mixtures separation using AgBF 4 dissolved in BMImBF 4 as carrier solution. Gas permeation experiments were carried out with pure gases and with a 50:50 C 3 H 8 /C 3 H 6 gas mixtures as feed gas under different operational conditions in order to study the influence of the different variables such as the transmembrane pressure, sweep gas flow rate and silver concentration in the membrane. It was found that under the similar operation conditions the permeability of the gaseous components in mixed gas experiments was about 6.1% lower for propane and 15% higher for propylene than in pure gas experiments. Moreover, it was observed that although the flux of propane was almost not affected by changes in the sweep gas flow rate, the flux of propylene increases reaching asymptotically a maximum value as the sweep gas flow rate was increased. With regard to the concentration of silver cations in the membrane it has no influence on the flux of propane, however the flux of propylene increased following a linear trend when the silver concentration in the membrane was increased from 0 to 1 M. High permeabilities and selectivities up to 20 were obtained, so Ag + SILMs systems are suitable to separate C 3 H 8 /C 3 H 6 gas mixtures since it is possible to obtain a permeate stream with a purity of propylene high enough to be used in most of the applications of propylene. Finally, the performance of the system was tested at longer times and it was observed that although the ionic liquid membranes seems to be stable, the flux of propylene started to decrease after 90 min of operating time because the silver cations began to be reduced to metallic silver. For this reason further research in order to avoid, or at least minimize the reduction of the silver cations is needed. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Light olefins such as ethylene and propylene are important petrochemical building blocks which are further processed to yield a wide range of final products such as cosmetics, textile products, paints, tools or plastics for instance. Light olefins are usually obtained, as a mixture with paraffins, by steam cracking processes, fluidized catalytic cracking or alkane dehydrogenation [1,2]. The separation of these streams is a key issue because it is one of the most difficult and also the most costly separation process in the petrochemical industry. Traditional separation processes like low-temperature distillation, require voluminous equipments Corresponding author. Address: Advanced Separation Processes Research Group, Department of Chemical Engineering and Inorganic Chemistry, University of Cantabria, Avenida de los Castros s/n., Santander, Spain. Tel.: ; fax: address: ortizi@unican.es (I. Ortiz). operating at high pressures or low temperatures and very large reflux ratios due to the very small difference in the relative volatilities between olefins and their corresponding paraffins [1 3]. In recognition of these costs alternative energy-saving separation processes are required. In last years many alternatives has been explored and in particular many attention is paid to reactive absorption of olefins using silver salts because it seems to be a viable and cost-effective process. The separation performance is mostly associated with the ability of olefins to react selective and reversibly with certain metal ions, such as Ag +,byp-complexation formation mechanism [4 6]. During the last two decades the use of supported liquid membranes (SLMs) has been widely studied as alternative separation processes because facilitated transport in supported liquid membranes containing carriers dispersed in a liquid matrix offer advantages over conventional membranes [7,8]. Some of the major benefits of SLMs are that high selectivities and permeabilities, even /$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. doi: /j.seppur

2 84 M. Fallanza et al. / Separation and Purification Technology 97 (2012) Nomenclature A effective membrane area (m 2 ) F gas molar flow rate (mol s 1 ) J molar flux (mol m 2 s 1 ) P m permeability (mol/bar m s) D diffusivity (m 2 s 1 ) S Solubility coefficient (mol/m 3 bar) P pressure (bar) T temperature (K) y gas molar fraction ( ) Greek letters d membrane thickness (m) l viscosity (Pa s) q density (kg m 3 ) Superscripts/subscripts Ag + silver ion N 2 nitrogen C 3 H 4 propane C 3 H 6 propylene at low driving forces, can be obtained and small amount of solvent and carrier are needed. This result critical from an economical point of view and allow the use of a wide range of complexation chemistry that would not be feasible to implement otherwise [9]. Although non-porous gas separation membranes could be also an alternative to carry out the separation of olefin/paraffin gas mixtures, the results summarized by Faiz and Li [10] show that the application of dense polymeric membranes is not attractive for industrial purposes mainly due to the relatively low separation factors obtained. SLMs consist of a solvent containing a carrier immobilized in the pores of a microporous membrane only by capillary forces. For this reason supported liquid membranes allow to operate at moderate transmembrane pressures, always below the breakthrough pressure so that the liquid is not expelled from the membrane pores. Also when using conventional solvents, temperature and pressure must be carefully controlled in order to avoid solvent losses by evaporation. For this reason even though SLMs are considered as an attractive alternative for gas mixtures separation their industrial application is still limited mainly due to these instability issues. Previous studies [11,12] show that silver ions in aqueous systems act as a carrier for the transport of olefins thereby facilitating their permeation though the membrane. These results suggested that supported ionic liquid membranes containing silver ions as carriers could be an attractive alternative to carry out the separation of these mixtures. In this sense the use of ionic liquids is attracting increased attention as solvent to overcome the instability problems because solvent losses by evaporation are avoided due to their negligible vapor pressure. Recently, several works which remark the viability to apply the supported ionic liquid membranes (SILM) for gas separation have been published [13]. Scovazzo et al. [14] determined the pure gas permeabilities and selectivities of N 2,CH 4 and CO 2 and compared their results to those of polymeric membranes in the Robeson plot and concluded that supported ionic liquid membranes were competitive compared to other membrane materials. Neves et al. [15] studied the potential of using supported ionic liquid membranes for CO 2 /N 2 and CO 2 /CH 4 gas separation and the influence of the structure of the ionic liquid used in the performance of the separation process. Gan et al. [16] studied the permeability of H 2,O 2,N 2, CO and CO 2 through SILMs supported on nanofiltration membranes using different ionic liquids with the anion Tf 2 N. They observed that SILMs immobilized on a nanoporous support presented good stability even at operating pressures up to 7 bar, which are relevant to industrial applications. On the other hand, previous works on reactive absorption report the improvements of the solvent potential of the ionic liquid in terms of capacity and selectivity for the olefin/paraffin separation [17 21]. This work provides an experimental study of the performance of supported liquid membranes with BMImBF 4 containing Ag + for the separation of propane/propylene mixtures. Several experiments were carried out in order to study the effect of different operating variables (transmembrane pressure, sweep gas flow rate and silver concentration in the membrane) in the separation process. Furthermore, the stability of the SILMs has been tested by performing medium-term gas permeation experiments of more than 8 h. 2. Experimental 2.1. Materials Propylene and propane gas were purchased from Praxair with a minimum purity of 99.5%. The ionic liquid selected in this work is 1-buthyl-3-methylimidazolium tetrafluoroborate (CAS No ) supplied by Iolitec, with a minimum purity of 99% and residual halide content less than 500 ppm. The silver salt used in this work is silver tetrafluoroborate (CAS No ) of 99% purity purchased from Apollo Scientific Ltd. All chemicals were used as received. The microporous membrane used as polymeric support was a hydrophilic PVDF polymeric membrane supplied by Millipore. The main characteristics of the membrane are shown in Table Preparation of SILMs First of all the reactive solution is prepared dissolving the silver tetrafluoroborate in the BMImBF 4 at room temperature and stirring with a magnet stirrer. Then the polymeric membrane used as support is placed into a flask, which is closed with a septum, and then vacuum is applied for 30 min in order to remove the air inside the pores. Then 2 ml of the reactive solution is injected through the septum with a syringe and the reactive liquid fills the void pores. The system remains under vacuum 90 more minutes to let the reactive solution to impregnate completely the porous support. Finally the excess of liquid is removed from the polymeric surface using a tissue Permeation cell A schematic diagram of the permeation cell is shown in Fig. 1. The upper and lower compartments, with an inner and outer diameter of 90 and 102 mm, respectively were made of stainless steel (AISI 316L). The supported ionic liquid membrane is placed in the lower chamber, over a disk made of porous stainless steel which provides mechanical strength to the membrane. A gasket of synthetic rubber allows to close hermetically both chambers avoiding the leakage of the gas. In the upper chamber there are two ports which correspond with the feed gas inlet and the feed gas outlet. Similarly, in the lower chamber there are also two

3 M. Fallanza et al. / Separation and Purification Technology 97 (2012) Table 1 Characteristics of the microporous membrane used as support. Material PVDF Wettability Hydrophilic Refractive index 1.42 Water flow rate ml/min cm Bubble point at 23 C (bar) P4.8 Maximum operating T( C) 85 Pore size (lm) 0.1 Porosity (%) 70 Thickness (lm) 125 Membrane diameter (mm) 90 In order to check the replicability of the permeation runs several experiments were carried out. Each experiment was performed twice using a new SILM and in all cases the standard deviation between experimental results and the replicates Eq. (1), was lower than 0.04 concluding that there was a good experimental reliability. sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 r ¼ P n i¼1 J C3 H 6 J 0 C 3 H 6 n 1 J C3 H 6 The experimental permeabilities of each gas are calculated according to Eq. (2): ð1þ J i ¼ P m;i DP i d ð2þ Fig. 1. Schematic diagram of the permeation cell. connections which are the sweep gas inlet and the permeate stream outlet Gas permeation experiments Once the supported ionic liquid membrane has been prepared it is placed into the permeation cell. In the start-up of the separation experiments the complete filling of the polymeric support was checked. Vacuum was applied to the permeate side; when the pores were completely filled with the ionic liquid solution, the pressure fell below 1 mbar, if there were any unfilled pore the gas would pass from the feed side to the permeate side and the vacuum of 1 mbar would not be achieved anymore. To begin the gas permeation experiments the flow rate of each gas is adjusted by a mass flow controller and before starting the experiment the composition of the feed stream (which can be a pure gas or a 50:50 mixture of propane and propylene) is analyzed by gas chromatography. The feed stream flows through the upper chamber, while the nitrogen used as sweep gas flows through the permeate side. The pressure of both streams is controlled using two micrometric valves. The flow rate of the permeate stream is measured using a mass flowmeter and at the cell outlet the composition of both, the feed stream and the permeate stream are analyzed by gas chromatography. The analysis was performed in a gas chromatograph HP 6890 equipped with a thermal conductivity detector (TCD) and a column HP Al/S (30 m length, nominal diameter of 0.53 mm). Several experiments were carried out at room temperature (293 K) at different operational conditions in order to analyze the influence of the transmembrane pressure, sweep gas flow rate and silver concentration in the membrane. A schematic diagram of the experimental set-up is shown in Fig. 2. where J i is the flux of the specie i across the membrane, P m,i is the permeability of each gas, DP i difference in the partial pressure of the gas between both sides of the membrane and d is the thickness of the supported ionic liquid membrane (125 lm). 3. Results and discussion 3.1. Determination of permeabilities in SILMs without carrier Gas mixture permeation experiments were carried out in order to measure gas permeabilities and determine the selectivities of the separation of C 3 H 6 /C 3 H 8. The influence of different operational conditions such as the transmembrane pressure, the sweep gas flow rate and the silver concentration in the membrane in the separation of propane/propylene gas mixtures was experimentally analyzed. Finally and in order to increase the knowledge on the separation fundamentals, the results of the permeability of the components of gas mixtures were compared to the experiments performed with pure gases. For both components, a comparison of pure gas and mixed gas permeabilities under the following operation conditions: pressure of the feed gas of 1.2 bar, pressure of the permeate stream of 1 bar and temperature of 293 K was carried out. The results collected in Table 2 show that the permeabilities obtained from the runs with mixed gas feeds differ from the values obtained working with pure gas phases; actually propane permeability is 6.1% lower in the mixed gas whereas propylene permeability is increased by 15%. Those results are in agreement with the differences in gas solubilities previously determined in the absence of the complexing agent that showed a considerably lower equilibrium solubility of propane and at the same time a slightly higher solubility of propylene compared to the values with pure gases [18]. A similar behavior was evidenced by the results obtained by Neves et al. [15] from

4 86 M. Fallanza et al. / Separation and Purification Technology 97 (2012) Fig. 2. Diagram of the experimental setup. 1 Gas bottles, 2 mass flow controllers, 3 two way valves, 4 permeation cell, 5 mass flowmeter, 6 pressure transducer, 7 micrometric valve, 8 three way valves, 9 gas chromatograph. Table 2 Pure and mixed gas permeabilities for 50:50 C 3 H 8 and C 3 H 6 gas mixtures at 293 K in the SILM without silver. Permeability (mol/bar m s) C 3 H 8 C 3 H 6 Pure Mix Pure Mix Pure 100 Pure Mix Pure Mix Pure E E E E gas permeation studies working with CO 2 /CH 4 and CO 2 /N 2 mixtures and supported ionic liquid membranes Mixed gas experiments The separation of propane/propylene gas mixtures though supported ionic liquid membranes is a combination of three processes: absorption, diffusion and desorption which take place in the feed side, in the liquid membrane and in the permeate side, respectively. The transport of both species across the membrane is a process driven by the partial pressure difference between both sides of the membrane. Therefore, the higher the transmembrane pressure, the higher driving force for the separation is obtained. In supported ionic liquid membranes in absence of a carrier, the transport of the gaseous species (propane and propylene) is due to Fickian diffusion. However, when a carrier (Ag + ) is added to the membrane system, propylene permeation is the contribution of two mechanisms: Fickian diffusion and facilitated transport. Based upon facilitated transport mechanism, higher carrier concentration in the membrane will enhance the transport of propylene along the membrane thickness, and as a result the membrane would have a better separation performance. of the sweep gas over 10 mln/min. This is because higher flow rates of the sweep gas remove more efficiently the gas molecules which arrive to the permeate side, allowing to operate with higher driving forces. For this reason a trade-off solution must be found in order to maximize the flux of propylene across the membrane without diluting in excess the permeate stream Effect of the transmembrane pressure The effect of the transmembrane pressure was studied in the range from 0.2 to 1.65 bar. Fig. 4 shows that higher transmembrane pressures result in higher fluxes of both gases due to the higher driving force according to Eq. (2) Effect of the sweep gas flow rate The effect of the sweep gas flow rate in the fluxes of propane and propylene across the membrane was studied in the range from 2 to 15 mln/min. Non linear profiles of the flux of propylene across the membrane with the flow rate of the sweep gas were observed as is depicted in Fig. 3. The flux of propane is almost unaffected by changes in the sweep gas flow rate. However, the flux of propylene increases as the sweep gas flow rate was increased, at a higher rate at low flow rates and achieving asymptotically a maximum value at flow rates Fig. 3. Effect of the sweep gas flow rate in the flux of C 3 H 8 and C 3 H 6 at 293 K, at pressures of the feed and permeate streams of 1.2 and 1.0 bar, respectively and [Ag + ]=1M.

5 M. Fallanza et al. / Separation and Purification Technology 97 (2012) Table 3 Influence of silver concentration on the permeabilities and selectivities at 293 K, pressure of the feed and permeate streams of 1.2 and 1.0 bar, respectively and a flow rate of the sweep gas that allows operation with the maximum driving force. [Ag + ] (M) PC 3 H 8 (mol/bar m 2 s) PC 3 H 6 (mol/bar m 2 s) a i=j E E E E E E E E E E Fig. 4. Effect of the transmembrane pressure in the flux of C 3 H 8 and C 3 H 6 at 293 K, and a [Ag + ] = 0.1 M and a flow rate of the sweep gas of 2 mln/min. where a i=j is the selectivity and P m,i and P m,j are the experimental permeabilities of the species i and j, respectively (see Table 3). The achieved selectivity in the separation process using pure BMImBF 4, with no addition of silver ions, in the supported liquid membrane is However this selectivity is increased to almost 20 when the silver concentration is increased up to 1 M. The permeability of a gas is a contribution of both the solubility and the diffusivity through the membrane Eq. (4). P m;i ¼ S i D i ð4þ where, P m,i is the permeability of each gas and S i and D i are the solubility coefficient and diffusivity of the specie i in the supported ionic liquid membrane. The solubility coefficients were obtained in previous studies by our research group [17], thus after having calculated the experimental permeabilities in this work it is possible to calculate the experimental diffusivities of propane and propylene in the ionic liquid membrane at different concentrations of silver ions (Table 4). The diffusivities of gases in the Ag + BMImBF 4 liquid membrane were also predicted using the correlation proposed by Morgan for imidazolium-based ionic liquids in terms of the gas molar volume and the ionic liquid viscosity [24] Eq. (5). Fig. 5. Effect of the silver concentration in the flux of C 3 H 8 and C 3 H 6 at 293 K, a pressure of the feed and permeate streams of 1.2 and 1.0 bar respectively and a flow rate of the sweep gas which allows to operate with the maximum driving force. At the same time it is worth noticing that increasing the transmembrane pressure the selectivity is not affected. Therefore, it would be interesting to work at the highest possible transmembrane pressure, in order to maximize the flux of propylene, without compromising the stability of the supported ionic liquid membrane Effect of silver ions concentration Many authors have reported previously the enhancement in the permeation flux of olefins across a supported liquid membrane under the presence of silver cations. This is because the silver ions act as carriers facilitating the transport of the olefins from the feed stream to the permeate side [22,23]. Several experiments were carried out at different silver concentrations and results are shown in Fig. 5. Fig. 5 shows that although the flux of propane is no influenced by the addition of silver to the supported liquid membrane ( mol/m 2 s), the flux of propylene is gradually increased from to mol/m 2 s following a linear trend when the silver concentration in the membrane was increased from 0 to 1 mol/l. The mixed gas permeabilities were calculated from the experimental results according to Eq. (2). The selectivity for a given gas pair (a i=j ) is calculated as the ratio of the permeabilities of the gases of interest Eq. (3): a i=j ¼ P m;i P m;j ð3þ D 12 ¼ 2: l 0:660:03 2 V 1:040:03 1 where D 12 is the diffusivity of the gas in the ionic liquid, l 2 is the ionic liquid viscosity and V 1 is the molar volume of the gas. It is also known that the rheological properties of the ionic liquid may change with the concentration of silver salts. This influence previously reported by Ortiz et al. [19] must be considered in the estimation of the diffusivity of both gases using Eq. (5). Fig. 6 shows a comparison between the experimentally determined diffusivities and the diffusivities obtained using Eq. (5). It can be seen that the diffusivities of propane and propylene irrespective to the concentration of silver ions in the membrane are well predicted by Morgan s equation. Moreover, Fig. 6 shows that the diffusivity of propylene in the liquid membrane slightly decreases when adding silver cations. This is in good agreement with previous results published by Teramoto et al. [25] where they reported a decrease in the diffusivity of ethylene in water from to m 2 s 1 when the concentration of silver nitrate was increased from 0 to 4 M. Fig. 7 shows the influence of the silver concentration in the membrane on the composition of the permeate stream without nitrogen. This is because due to the high difference in the normal boiling points between nitrogen (77 K) and propane (231 K) and propylene (226 K), after obtaining a permeate stream mixture of nitrogen, propane and propylene it would be easy to remove the nitrogen from the mixture by only compressing this stream. Then on one hand pure nitrogen ready to be reused as sweep gas would be obtained, and on the other hand a final stream with high purity in propylene could be stored for example as liquefied gas. As depicted in Fig. 7, when the silver concentration in the ð5þ

6 88 M. Fallanza et al. / Separation and Purification Technology 97 (2012) Table 4 Experimental solubility coefficients and diffusivities for C 3 H 8 and C 3 H 6 at 293 K and different silver concentrations. [Ag + ] (M) SC 3 H 8 (mol/ m 3 bar) DC 3 H 8 (m 2 / s) SC 3 H 6 (mol/ m 3 bar) DC 3 H 6 (m 2 / s) E E E E E E E E E E-11 Fig. 8. Evolution of the fluxes of C 3 H 8 and C 3 H 6 across the supported ionic liquid membranes with time at 293 K, a transmembrane pressure of 0.2 bar, a flow rate of the sweep gas 2 mln/min and [Ag + ] = 0.5 M. Fig. 6. Comparison between experimental diffusivities of C 3 H 8 and C 3 H 6 and calculated using Morgan s equation. membrane is 1 M, the purity of the permeate stream is high enough to be used in most applications of propylene Stability of SILMs The durability of the supported ionic liquid membrane was studied by performing medium-term gas permeation experiments working with 50:50 propane/propylene gas mixtures. The liquid membrane showed good stability throughout the experimental period operating with a transmembrane pressure of 0.2 bar. Fig. 8 shows the evolution of the fluxes of propane and propylene across the supported ionic liquid membrane with time. Fig. 8 shows that the supported ionic liquid membrane seems to be stable during the 8 h that lasted the experiment. However for times longer than 90 min it was observed a progressive decay of Fig. 9. Picture of the supported ionic liquid membrane after 8 h operating time at 293 K, a transmembrane pressure of 0.2 bar, a flow rate of the sweep gas of 2 mln/ min and [Ag + ] = 0.5 M. the flux of propylene started that was attributed to a partial reduction of the silver ions that facilitate the transport of propylene across the membrane to metallic silver (reaction 1). Fig. 7. Composition of the permeate stream at different silver concentrations in the membrane at 293 K, a pressure of the feed and permeate streams of 1.2 and 1.0 bar, respectively and a flow rate of the sweep gas which allows to operate with the maximum driving force.

7 M. Fallanza et al. / Separation and Purification Technology 97 (2012) Ag þ light! Ag 0 ðreaction1þ Therefore, further research on membrane stability is needed in order to minimize or prevent, if it is possible, the reduction of silver ions. The macroscopic studies confirmed that after the experiment the ionic liquid solution remains inside the pores of the membrane. Nevertheless the color of the liquid membrane has changed from almost transparent to a brownish color because the reduction of part of the silver ions to metallic silver is taking place. There are also some zones where the reduction reaction was more pronounced and it is possible to observe some gray spots of metallic silver on the surface of the membrane (Fig. 9). 4. Conclusions This work reports the analysis of the performance of the supported ionic liquid ionic membrane (SILMs) technology containing silver ions in the separation of propane/propylene gas mixtures under different operational conditions. The effect of the operational variables such as the transmembrane pressure, sweep gas flow rate and silver concentration on the separation process was also studied. The flux of propane across the membrane does not depend on the carrier concentration; however the flux of propylene increases following a linear trend with the concentration of Ag +. Increasing the flow rate of the sweep gas, the fluxes of both gases are increased because the molecules of gas that arrive at the permeate side were removed more efficiently leading to a higher driving force. Also higher transmembrane pressures result in higher fluxes because the driving force is higher, whereas the stability of the SILM could be compromised. Moreover, Ag + SILMs are suitable to separate propane-propylene gas mixtures to obtain a permeate stream with high purity of propylene which can be used in most applications of propylene. Finally it was observed that although the liquid membrane remained stable after 8 h of operating time, Ag + SILMs loosed efficiency at operating times longer than 90 min, because the silver ions were being reduced to metallic silver. For this reason further research on membrane stability is needed. Specifically, it is crucial to find procedures to avoid or at least minimize the reduction of silver cations. Acknowledgements This research has been funded by the Spanish Ministry of Science and Innovation (Projects CTQ /PPQ and CTM ). Marcos Fallanza also thanks MICINN for the FPI fellowship. References [1] M. Teramoto, S. Shimizu, H. Matsuyama, N. Matsumiya, Ethylene/ethane separation and concentration by hollow fiber facilitated transport membrane module with permeation of silver nitrate solution, Separation and Purification Technology 44 (2005) 19. [2] T.A. Reine, R.B. Eldridge, Absorption equilibrium and kinetics for ethyleneethane separation with a novel solvent, Industrial and Engineering Chemistry Research 44 (2005) [3] D.T. Tsou, M.W. Blachman, J.C. Davis, Silver-facilitated olefin/paraffin separation in a liquid membrane contactor system, Industrial and Engineering Chemistry Research 33 (1994) [4] R.T. Yang, Adsorbents: Fundamentals and Applications, in Anonymous, Wiley- Interscience, 2003 (p. 424). [5] M.R. Antonio, D.T. Tsou, Silver ion coordination in membranes for facilitated olefin transport, Industrial and Engineering Chemistry Research 32 (1993) 273. [6] K. Nymeijer, T. Visser, W. Brilman, M. Wessling, Analysis of the complexation reaction between Ag + and ethylene, Industrial and Engineering Chemistry Research 43 (2004) [7] A. Figoli, Liquid membrane in gas separations, in: V.S. Kislik (Ed.), Liquid Membranes: Principles and Applications in Chemical Separations and Wastewater Treatment, Elsevier Science, Amsterdam, 2009, p [8] R. Noble, J. Way, Liquid Membranes: Theory and Applications, American Chemical Society, Washington, DC, [9] R.D. Noble, C. Koval, Review of facilitated transport membranes, in: Y. Yampolskii, I. Pinnau, B.D. Freeman (Eds.), Materials Science of Membranes for Gas and Vapour Separation, John Wiley & Sons, USA, 2006, p [10] R. Faiz, K. Li, Polymeric membranes for light olefin/paraffin separation, Desalination 287 (2012) 82. [11] A. Ito, S. Duan, Y. Ikenori, A. Ohkawa, Permeation of wet CO 2 /CH 4 mixed gas through a liquid membrane supported on surface of a hydrophobic microporous membrane, Separation and Purification Technology 24 (2001) 235. [12] M. Teramoto, N. Takeguchi, T. Maki, H. Matsuyama, Gas separation by liquid membrane accompanied by permeation of membrane liquid through membrane physical transport, Journal of Membrane Science 24 (1986) 101. [13] P. Scovazzo, Determination of the upper limits, benchmarks, and critical properties for gas separations using stabilized room temperature ionic liquid membranes (SILMs) for the purpose of guiding future research, Journal of Membrane Science 343 (2009) 199. [14] P. Scovazzo, J. Kieft, D.A. Finan, C. Koval, D. DuBois, R. Noble, Gas separations using non-hexafluorophosphate [PF6]- anion supported ionic liquid membranes, Journal of Membrane Science 238 (2004) 57. [15] L.A. Neves, J.G. Crespo, I.M. Coelhoso, Gas permeation studies in supported ionic liquid membranes, Journal of Membrane Science 357 (2010) 160. [16] Q. Gan, Y. Zou, D. Rooney, P. Nancarrow, J. Thompson, L. Liang, et al., Theoretical and experimental correlations of gas dissolution, diffusion, and thermodynamic properties in determination of gas permeability and selectivity in supported ionic liquid membranes, Advances in Colloid and Interface Science 164 (2011) 45. [17] A. Ortiz, A. Ruiz, D. Gorri, I. Ortiz, Room temperature ionic liquid with silver salt as efficient reaction media for propylene/propane separation: Absorption equilibrium, Separation and Purification Technology 63 (2008) 311. [18] A. Ortiz, L.M. Galán Sanchez, D. Gorri, A.B. De Haan, I. Ortiz, Reactive ionic liquid media for the separation of propylene/propane gaseous mixtures, Industrial and Engineering Chemistry Research 49 (2010) [19] A. Ortiz, L.M. Galán, D. Gorri, A.B. De Haan, I. Ortiz, Kinetics of reactive absorption of propylene in RTIL Ag + media, Separation and Purification Technology 73 (2010) 106. [20] A. Ortiz, D. Gorri, A. Irabien, I. Ortiz, Separation of propylene/propane mixtures using Ag + RTIL solutions. Evaluation and comparison of the performance of gas-liquid contactors, Journal of Membrane Science 36 (2010) 130. [21] M. Fallanza, A. Ortiz, D. Gorri, I. Ortiz, Effect of liquid flow on the separation of propylene/propane mixtures witha gas/liquid membrane contactor using Ag + RTIL solutions, Desalination and Water Treatment 27 (2011) 123. [22] S. Duan, A. Ito, A. Ohkawa, Separation of propylene/propane mixture by a supported liquid membrane containing triethylene glycol and a silver salt, Journal of Membrane Science 215 (2003) 53. [23] M. Teramoto, H. Matsuyama, T. Yamashiro, S. Okamoto, Separation of ethylene from ethane by a flowing liquid membrane using silver nitrate as a carrier, Journal of Membrane Science 45 (1989) 115. [24] D. Morgan, L. Ferguson, P. Scovazzo, Diffusivities of gases in room-temperature ionic Liquids: Data and correlations obtained using a lag-time technique, Industrial and Engineering Chemistry Research 44 (2005) [25] M. Teramoto, N. Takeuchi, T. Maki, H. Matsuyama, Ethylene/ethane separation by facilitated transport membrane accompanied by permeation of aqueous silver nitrate solution, Separation and Purification Technology 28 (2002) 117.