Highly permeable ionic liquid/Cu composite membrane for olefin/paraffin separation
Introduction
Facilitated transport has been widely exploited in the membrane field over the last few decades [1], [2], [3], [4], [5], [6], [7]. Facilitated transport results in the rapid transport of some molecules through specific media by both Fickian and carrier-mediated transport [1], [2], [3], [4], [5], [6], [7]. For example, olefin molecules such as propylene and ethylene can be rapidly moved by carriers, e.g., silver ions, while paraffin molecules such as propane and ethane are transferred only by Fickian diffusion. As a result, when silver ions complexed with POZ or PVP to form a polymer electrolyte, the selectivity of propylene/propane reached 56 with a permeance of 11 GPU (1 GPU = 1 × 10−6 cm3 (STP)/(cm2 s cm Hg)) [1], [7]. Recently, facilitated transport has also been applied to CO2 separation membranes. Since it is well known that amine groups can reversibly interact with CO2 molecules, they were used as CO2 carriers for separation membranes [8], [9], [10], [11], [12], [13], [14] For example, the application of an ionic liquid containing amine groups, i.e., 1-butyl--methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, as a membrane resulted in a CO2/CH4 selectivity of 6.1 with a permeance of 1.3 × 10−9 mol s−1 m−2 Pa−1 [8]. Uchytila’s group reported that the application of a poly(vinylidene fluoride-co-hexafluoropropylene) membrane containing 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid for CO2/CH4 separation resulted in a selectivity and CO2 permeability of 11.4 and 1090 × 1016 mol m m−2 s−1 Pa−1, respectively [14]. In addition to these molecules, various ionic liquids with different cations and anions have been used due to their many advantages that include thermal stability and negligible vapor pressure [9], [10], [11], [12], [13].
Very recently, various gas carriers have been reported for olefin and CO2 separation membranes. Kang’s group reported that silver nanoparticles that were positively polarized by electron acceptors such as p-benzoquinone and TCNQ could reversibly interact with propylene molecules [4], [6]; poly(ethylene-co-propylene) (EPR)/Ag nanoparticles/p-benzoquinone and PVP/Ag nanoparticles/TCNQ composite membranes showed propylene/propane selectivities of 11 and 50, respectively [4], [6].
Furthermore, our groups reported that the use of copper nanoparticles that were positively polarized by 1-butyl-3-methylimidazolium tetrafluoroborate () ionic liquid increased the ideal selectivity for CO2/CH4 from 4.8 to 11 with a CO2 permeance of 25 GPU [5]. These results were attributed to the presence of more free ions from the ionic liquid and polarized copper nanoparticles. For olefin separation, silver nanoparticles polarized by ionic liquid showed enhanced separation performance towards olefin/paraffin mixtures [3].
Unfortunately, even though ionic liquid/metal nanocomposite mixtures show excellent separation performance for olefin/paraffin mixtures, their permeance remains too low for practical applications due to their high viscosity. To solve this problem, the ionic liquid was introduced for facilitated olefin transport membrane. Since the free-ion state is dominant for , the free imidazolium ions should easily interacted with the olefin molecules as well as positively polarize the Cu nanoparticles, resulting in enhanced separation performance.
Section snippets
Experimental section
Microsized copper particles (1–5 μm, 99%, Aldrich Chemicals) were introduced into 1-methyl-3-octylimidazolium tetrafluoroborate (, C-TRI). Transmission electron microscopy (TEM) images were obtained using a JEOL JEM-3000 operating at 300 kV. The UV–vis absorption spectrum of the /Cu composite solution was obtained using a Beckman Coulter DU® 730UV/Vis spectrophotometer. Raman spectra were obtained using a Horiba Jobin–Yvon/LabRAM ARAMIS instrument at 785 nm (diode laser). X-ray
Results and discussion
Fig. 1 shows the appearance of the 1/0.002 /Cu composite solution after stirring for 24 h. When the copper metal was incorporated into neat with stirring, the solution went from colorless to deep green after 24 h, indicating that copper nanoparticles were generated in the ionic liquid. The formation of copper nanoparticles is attributed to the strong coordination between the counteranions of and the metal surface, as reported previously [5].
TEM was used to investigate
Conclusions
To prepare a highly permeable membrane for olefin separation, ionic liquid and Cu nanoparticles were utilized for facilitated olefin transport. The ideal selectivity of propylene over propane through neat was 1.4 with a propylene permeance of 8.8 GPU. When copper nanoparticles were generated in , the separation performance was greatly enhanced: The propylene permeance was 18.0 with an ideal selectivity of 2.0. Furthermore, the actual selectivity increased from 1.1 to
Acknowledgement
This work was supported by a 2012 Research Grant from Sangmyung University.
References (15)
- et al.
J. Membr. Sci.
(2001) - et al.
J. Membr. Sci.
(2004) - et al.
Chem. Eng. J
(2011) - et al.
J. Membr. Sci.
(2009) - et al.
J. Membr. Sci.
(2011) - et al.
J. Membr. Sci.
(2012) - et al.
Adv. Mater.
(2000)
Cited by (18)
Ultra-stable copper decorated deep eutectic solvent based supported liquid membranes for olefin/paraffin separation: In-depth study of carrier stability
2022, Journal of Membrane ScienceCitation Excerpt :The carrier is dispersed into the membrane matrix to generate metal ions (Ag+ and Cu+), metal complex ions (CuCl2−), or positively-charged nanoparticles via the interactions with membrane matrix, thus significantly accelerating the transport of olefin molecules. Among them, the positively-charged copper or silver nanoparticles exhibit good stability but low olefin/paraffin selectivity, and special electron acceptors are needed to activate the surface charge of nanoparticles [35,36]. Silver salts possess the best ability to transport olefin molecules, which render the resultant membranes with extremely high olefin/paraffin selectivity.
Double-salt ionic liquid derived facilitated transport membranes for ethylene/ethane separation
2021, Journal of Membrane ScienceCitation Excerpt :Thus, tremendous efforts have been devoted to the development of effective, sustainable, and energy-efficient methods for the olefin purification, among which membrane separation technology has been proposed as a cost-efficient and energy-saving alternative for the efficient olefin/paraffin separations [4,5]. In this scenario, the worldwide researchers have hammered at the construction of high-performance olefin/paraffin separation membranes such as polymers of intrinsic microporosity (PIM) membranes [6,7], carbon molecular sieve (CMS) membranes [8], zeolite membranes [9], organic silicon membranes [10], two-dimensional nanosheet membranes [11,12], metal organic framework (MOF) membranes [13–16], mixed matrix membranes (MMMs) [17,18], polyelectrolyte membranes [19,20], ionic liquid (IL) membranes [21,22], and deep eutectic solvent (DES) membranes [23,24]. Based on separation mechanism, all these membranes can be broadly segregated into two major categories: 1) molecular sieve membranes driven mainly by the difference of molecular size, such as CMS membranes and MOF membranes [25–27]; 2) facilitated transport membranes (FTMs) originated from selective π-complexation interaction between olefin and transition metal ions (Ag+ or Cu+), including polyelectrolyte membranes, IL membranes and DES membranes [28–31].
Membrane engineering for a sustainable production of ethylene
2021, Fuel Processing TechnologyCitation Excerpt :In the case of MOF structures, the unsaturated metal sites can complex the olefins (via π-complexation). Gas-liquid Membrane Contactors, substitutes of conventional columns for absorption processes [123], were recently studied using aqueous AgNO3 solutions to extract ethylene from a gaseous feed stream [124]. In these systems, the membrane does not possess selective properties, but it is an interface between the gas and liquid phases, providing a high specific surface area.
Mixed matrix membranes based on dual-functional MgO nanosheets for olefin/paraffin separation
2017, Journal of Membrane ScienceCitation Excerpt :Separation processes and techniques have been developed, most of which employ cryogenic column distillation, but this process is accompanied by a high capital cost for equipment and energy intensive steps [4–7]. To address the issues of process complexity and energy cost and to expand the applicability of the process, extensive research has been devoted to membrane technology over the past decades [8–12]. Membrane technology offers several advantages, such as a facile fabrication process, low energy cost, and a wide array of applications, and is thus effectively utilized to separate gaseous mixtures such as CO2/H2, CO2/N2, or CO2/CH4.