Membranes olefin transport

Goering RM, Bowman CN, Koval CA, and Noble RD. Mechanisms of olefin transport through facilitated transport membranes. Polym Mater Sci Eng 1997 77 260-261. 

Ryu JH, Lee H, Kim YS, Kang YS, Kim HS. Facilitated olefin transport by reversible olefin coordination to silver ions in a dry cellulose acetate membrane. Chem EurJUXA 7(7) 1525-1529. 

S.W. Kang, J.H. Kim, K. Char, J. Won, Y.S. Kang, Nanocomposite silver polymer electrolytes as facilitated olefin transport membranes. Journal of Membrane Science 2006, 285,102. 

The selectivity of this type of membrane materials is based on a reversible specific interaction of the pi-electrons of olefins with certain metal ions, such as ionic silver, dissolved in the polymer matrix, which results in facilitated olefin transport of the ion-olefin coupling through the membrane. 

Solid PVA-Co2+ composite asymetric membranes have been prepared starting from PVA and two different salts Co(N03)2 and Co(CH3COO)2, respectively, in order to separate cyclohexene/cyclohexan mixtures. A facilitated transport mechanism has been evidenced, due to the capacity of Co2+ ions to coordinate the olefin molecules [82], The authors reported stronger complexation of Co2+ ions with cyclohexene in the case of PVA/ Co(CH3COO)2 mixtures then in the case of PVA/ Co(N03)2 mixtures. It was found that for a concentration ratio of ([Co2+]/[OH]) by 0.75 mol/mol, the permeation flux of PVA membrane containing Co2+ increases 2-3 times and the separation factor increses 50 times compared with pure PVA membrane. 

Steigelmann and Hughes develop olefin/paraffin facilitated transport membrane demonstrate process at the Peinemann demonstrates pilot scale - 1980-1982 dispersed solid Ag + salts can facilitate olefins -1992... 

Significant progress has been made in alleviating the first two physical causes of membrane instability. The magnitude of the long-term chemical stability problem depends on the process. It is a major issue for carriers used to transport oxygen and olefins, but for carriers used to transport carbon dioxide, chemical stability is a lesser problem. 

Concurrently with the work on carbon dioxide and hydrogen sulfide at General Electric, Steigelmann and Hughes [27] and others at Standard Oil were developing facilitated transport membranes for olefin separations. The principal target was the separation of ethylene/ethane and propylene/propane mixtures. Both separations are performed on a massive scale by distillation, but the relative volatilities of the olefins and paraffins are so small that large columns with up to 200 trays are required. In the facilitated transport process, concentrated aqueous silver salt solutions, held in microporous cellulose acetate flat sheets or hollow fibers, were used as the carrier. 

Figure 11.26 Performance of a 37 m2 hollow fiber silver-nitrate-impregnated facilitated transport membrane for the separation of propylene/propane mixtures. The feed pressure was 5-13 atm the permeate was a hexane liquid sweep stream. The vertical dotted lines show when the membrane was regenerated with fresh silver nitrate solution [27]. Reprinted with permission from R.D. Hughes, J.A. Mahoney and E.F. Steigelmann, Olefin Separation by Facilitated Transport Membranes, in Recent Developments in Separation Science, N.N. Li and J.M. Calo (eds) (1986). Copyright CRC Press, Boca Raton, FL...

J.C. Davis, R.J. Valus, R. Eshraghi and A.E. Velikoff, Facilitated Transport Membrane Hybrid Systems for Olefin Purification, Sep. Sci. Technol. 28, 463 (1993). 

A. Morisato, Z. He, I. Pinnau and T.C. Merkel, Transport Properties of PA12-PTMO/ AgBF4 Solid Polymer Electrolyte Membranes for Olefin/Paraffin Separation, Desalination 145, 347 (2002). 

Another type of gas exchange process, developed to the pilot plant stage, is separation of gaseous olefin/paraffin mixtures by absorption of the olefin into silver nitrate solution. This process is related to the separation of olefin/paraffin mixtures by facilitated transport membranes described in Chapter 11. A membrane contactor provides a gas-liquid interface for gas absorption to take place a flow schematic of the process is shown in Figure 13.11 [28,29], The olefin/paraffin gas mixture is circulated on the outside of a hollow fiber membrane contactor, while a 1-5 M silver nitrate solution is circulated countercurrently down the fiber bores. Hydrophilic hollow fiber membranes, which are wetted by the aqueous silver nitrate solution, are used. 

In membrane distillation, two liquids (usually two aqueous solutions) held at different temperatures are mechanically separated by a hydrophobic membrane. Vapors are transported via the membrane from the hot solution to the cold one. The most important (potential) applications of membrane distillation are in water desalination and water decontamination (77-79). Other possible fields of application include recovery of alcohols (e.g., ethanol, 2,3-butanediol) from fermentation broths (80), concentration of oil-water emulsions (81), and removal of water from azeotropic mixtures (82). Membrane (pervaporation) units can also be coupled with conventional distillation columns, for instance, in esterifications or in production of olefins, to split the azeotrope (83,84). 

In addition to the polymer and facilitated transport membranes, novel materials are being proposed and investigated to achieve membranes with economically attractive properties. Carbon molecular sieve (CMS) membranes prepared by pyrolysis of polyimides displayed much better performance for olefin/paraffin separation than the precursor membranes [39, 46, 47]. Results obtained with CMS membranes indicated properties well beyond the upper-bond trade-off curve, as shown in Figure 7.8. Nonetheless, this class of materials is very expensive to fabricate at the present time. An easy, reliable, and more economical way to form asymmetric CMS hollow fibers needs to be addressed from a practical viewpoint. 

Ho, W.S. and Dalrymple, D.C. (1994) Facilitated transport of olefins in Ag + containing polymer membranes./oumal of Membrane Science, 91, 13. 

The opposing reactant contactor mode applies to both equilibrium and irreversible reactions, if the reaction is sufficiently fast compared to transport resistance (diffusion rate of reactants in the membrane). This concept has been demonstrated experimentally for reactions requiring strict stoichiometric feeds, such as the Claus reaction, or for kinetically fast, strongly exothermic heterogeneous reactions, such as partial oxidations. Triphasic (gas/liquid/solid) reactions, which are limited by the diffusion of the volatile reactant (e.g., olefin hydrogenation), can also be improved by using this concept. 

In membrane separation of the olefin/paraffin mixture, the predominant selective separation of the olefin is evident. First, the olefin molecule is smaller in size compared to the respective paraffin. Specifically, C—C distance in paraffins is 0.1534 nm, whereas the C=C distance in olefins is 0.1337 nm. Atoms of carbon in paraffins feature sp hybridization and free rotation around C—C bonds. Atoms of olefins feature sp hybridization. The rigid C=C bond impedes internal rotation in the olefin molecule and makes it flat. It is therefore clear why olefin molecules are smaller in size compared to paraffin and why the diffusion coefficients of olefins in polymers would be higher than those of paraffins. Second, the presence of unsaturated bonds in olefin molecules makes them capable of specific interactions with the membrane matrix. Efforts to take advantage of these capabilities resulted in the development of an important field of research facilitated transport. 

Davis JC, Valus RJ, Eshraghi R, and Vilikoff AE. Facilitated transport membrane hybrid systems for olefin purification. Separation Science and Technology 1993 28(1-3) 463-476. 

Safarik DJ and Eldridge RB. Olefin/paraffin separation by reactive absorption a review. IndEng Chem Res 1998 37 2571-2581. 61. Matsumoto H, Tanioka A, and Kawauchi S. Effect of fixed charge groups and counter ions on the transport phenomena and paraffin and olefin across anhydrous negatively charged membranes. J Colloid Interface Sci 1998 208 310-318. 

R. D. Huges, E. 1. Steigelman, J. A. Mahoney, Olefin separation by facilitated transport membranes, paper presented at the 1981 AIChE Spring National Meeting, Houston, Texas, April 1981, paper Id. 

Huang JF, Luo H, Liang C et al (2008) Advanced hquid membranes based on novel ionic liquids for selective separation of olefin/paraffin via olefin-facilitated transport. Ind Eng Chem Res 47 881-888... 

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