Olefins facilitated transport

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... 

Olefins. Facilitated transport of olefins has also been reported in the literature. LeBlanc et al. (2 ) studied ethylene transport using a silver Ion carrier in an Ion exchange membrane. Hughes et al. (23) presented the results of a bench and pilot scale study of ethylene and propylene transport using a silver ion Immobilized In anisotropic, porous hollow fiber membranes. This work is very significant because it is the first report facilitated transport membranes used on a commercial scale. Teremoto et al. (24) also studied ethylene transport with a silver ion carrier in a supported liquid membrane. They found a selectivity for ethylene over ethane of approximately 1000 when the silver nitrate concentration was 4 mol/ dm. ... 

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... 

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). 

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 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. 

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. 

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. 

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. 

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. 

Ethylene has been separated from ethane by a silver nitrate solution passing countercurrent in a hollow fiber poly-sulfone.165 This separation has also been performed with the silver nitrate solution between two sheets of a polysilox-ane.166 A hydrated silver ion-exchanged Nafion film separated 1,5-hexadiene from 1-hexene with separation factors of 50-80.167 Polyethylene, graft-polymerized with acrylic acid, then converted to its silver salt, favored isobutylene over isobutane by a factor of 10. Olefins, such as ethylene, can be separated from paraffins by electroinduced facilitated transport using a Nafion membrane containing copper ions and platinum.168 A carbon molecular sieve made by pyrolysis of a polyimide, followed by enlargement of the pores with water at 400 C selected propylene over propane with an a-valve greater than 100 at 35°C.169... 

C.A. Koval and T. Spontarelli, Condensed phase facilitated transport of olefins through an ion exchange membrane, J. Am. Chem. Soc., 1988, 110, 293-295. 

R.M. Goering, C.N. Bowman, C.A. Koval, R.D. Noble and D.L. Williamson, Role of ion-exchange membrane morphology and sorption properties in facilitated transport di-olefin/mono-olefin separation, J. Membr. Sci., 1998, 144, 133-143. 

The separation of olefin/paraffin gas mixtures is one of the most energy-intensive processes in the petrochemicals industry, because it is mainly performed by cryogenic distillations. Membrane processes using the concept of facilitated transport have been considered as an intriguing alternative to cryogenic distillation, as they can simultaneously improve both permeability and selectivity. Silver ions incorporated in liquid membranes act as olefin... 

Small-molecule transport other than olefin and molecular oxygen facilitated transport through a metal-polymer complex containing carriers (silver ions and metalloporphyrins, respectively) has also received attention, such as nitrogen transport by a cyclopentadienylmanganese and benzenechromium complex attached to a polymer [50,51], and CO2 and H2S transport based on ion-... 

Liquid-phase olefin separation was performed in perstraction mode at 25°C (Sungpet et al. 2001). For this to occur, it is postulated that simultaneous complex-ation of olefin-silver (I) ion-poly(pyrrole) is a necessary condition. Althongh silver is believed to be able to facilitate the transportation of certain components in this research, the researchers did not explain in detail the conditions or limitations for this facilitated transportation to occur. The researchers did not clearly state whether this facilitated transportation can only be achieved by silver (I) ions and not by any other metal ion with the same charges. Thus, there is room for future investigation on the properties of the different types of incorporated metal ions with the same charges, to facilitate the separation processes. 

Kang, S.W., Char, K. and Kang, Y.S. 2008a. Novel apphcation of partially positively charged silver nanoparticles for facilitated transport in olefin/paraffin separation membranes. 

The chapters in this book by Langsam, Xu et aL, Hirayama et aL, Fritsch, and Maier et al focus on polymer structure modification to improve the performance of gas separation membranes relative to the upper bound tradeoff relations. Mahajan et al, describe characteristics of hybrid inorganic/organic membranes as a route to break the simple rules that result in equations 8 and 9, possibly resulting in materials with properties which are above and beyond the upper bound lines. Koval et al and Eriksen et al, describe facilitated transport membranes. They seek to strongly enhance solubility selectivity for penetrant pairs i,e, olefin/paraffin) where... 

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