Facilitated transport membranes fibers

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...

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. 

Matsumiya N, Teramoto M, Kitada S, Matsuyam H. Evaluation of energy consumption for separation of CO2 in flue gas by hollow fiber facilitated transport membrane module with permeation of amine solution. Sep Purif Technol 2005 46 26-32. 

In bench-scale tests, using hoUow-fiber membrane as support and a carrier concentration of 2 M the ethylene permeance was 4.6 X 10 barrer/cm with an ethylene partial pressure of 65 psia, while the selectivity C2H4/C2H6 was about 240. Same tests were carried out for separation of propylene from propane. The selectivity obtained was greater than 100 but this result was confirmed only at bench scale. In fact, in the large pilot system, the selectivity and flux dechned over some weeks due to loss of solvent and carrier and to the necessity of remove hydrogen from the feed gas to prevent reduction of Ag f carrier. Despite the result, this remains the first study on the use of facilitated transport membrane for gas separations on a pilot scale. 

M. Teramoto, S. Shimizu, H. Matsuyama, N. Matsumiya, Ethylene/ethane separation and concentration by hoUow-fiber facilitated transport membrane module with permeation of silver nitrate solution, Sep. Purif. Technol. 44 (2005) 19-29. 

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. ... 

This paper describes pure N2 permeation and CO2-N2 separation characteristics of ILM-s of pure water and aqueous 302 wt/wt K2CO3 solutions Immobilized in Celgard X-10 hollow fibers. Measurements were carried out over a wide range of applied pressure differences. The CO2 partial pressure difference was varied from about 40 cm Hg to 140 cm Hg while the N2 partial pressure difference was Increased from about 125 cm Hg to 425 cm Hg. The total applied pressure difference was varied between 140 to 550 cm Hg. Facilitated transport membranes of aqueous 3UZ wt/wt K2CO3 solution for the separation of CO2 from were utilized and the separation behaviors... 

Membrane Processes in Separation and Purification published in 1993, contains chapters on pervaporation, facilitated transport membrane processes, membrane gas absorption processes, hollow fiber contactors, membrane reactors, and the preparation and application of inorganic membranes. In addition to an introductory chapter by the editors. Polymeric... 

Facilitated Transport Membranes Separation of Ethene from Ethane with Silver Ion-Exchanged Nafion Hollow Fibers... 

Water-swollen, silver ion-exchanged hollow fibers would be an interesting alternative to porous hollow fibers for which aqueous solutions of Ag can be immobilized. Such fibers should offer a facilitated transport membrane separation system for gaseous olefins with improved stability and performance compared to immobilized liquid membranes (BUM) for two main reasons ... 

In order to develop the liquid membrane techniques, i.e., emulsion Hquid membrane (ELM), supported liquid membrane (SLM), non-dispersive extraction in hollow fiber membrane (HFM), etc., for practical processes, it is necessary to generate data on equilibrium and kinetics of reactive extraction. Furthermore, a prior demonstration of the phenomena of facilitated transport in a simple liquid membrane system, the so-called bulk liquid membrane (BLM), is thought to be effective. Since discovery by Li [28], the liquid membrane technique has been extensively studied for the separation of metal ion, amino acid, and carboxyHc acid, etc., from dilute aqueous solutions [29]. 

Facilitated transport of penicilHn-G in a SLM system using tetrabutyl ammonium hydrogen sulfate and various amines as carriers and dichloromethane, butyl acetate, etc., as the solvents has been reported [57,58]. Tertiary and secondary amines were found to be more efficient carriers in view of their easy accessibility for back extraction, the extraction being faciUtated by co-transport of a proton. The effects of flow rates, carrier concentrations, initial penicilHn-G concentration, and pH of feed and stripping phases on transport rate of penicillin-G was investigated. Under optimized pH conditions, i. e., extraction at pH 6.0-6.5 and re-extraction at pH 7.0, no decomposition of peniciUin-G occurred. The same SLM system has been applied for selective separation of penicilHn-G from a mixture containing phenyl acetic acid with a maximum separation factor of 1.8 under a liquid membrane diffusion controlled mechanism [59]. Tsikas et al. [60] studied the combined extraction of peniciUin-G and enzymatic hydrolysis of 6-aminopenicillanic acid (6-APA) in a hollow fiber carrier (Amberlite LA-2) mediated SLM system. 

There have been several modified systems since the invention of liquid membranes, including a facilitated transport mechanism. One of them is to disperse the receiving solution in an organic membrane phase on one side of a porous hollow fiber.Two plants to treat contaminated groundwater were built and operated based on this revised liquid membrane system. More discussion about this application is given below in the application section. 

Recently, Bao et al. [68] compared the efficiency of facilitated transport of CO2 across a liquid membrane by different carriers (diethanolamine (DEA) and carbonic anhydrase (CA) + bicarbonate (NaHCO3) in a polypropylene HFCLM configuration. The hollow fibers used are made of polypropylene, pore size 0.04 pm. In all the experiments, the measured CO2 permeance and selectivity (CO2/O2) using CA bicarbonate as carrier was higher than in the case of DEA. The separation factor (CO2/O2) using DEA was about 152 which are 65% lower than the selectivity calculated with CA bicarbonate. 

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... 

Noble ( ) extended the one dimensional solution for facilitated transport to obtain an analytical solution for solute flux through a hollow fiber membrane. This result allows for convective transport through the lumen and radial transport through the membrane walls. The solution can also be used with planar geometry and... 

An alternative approach to solving stability problems with ILMs is presented by Bhave and Sirkar (114). Aqueous solutions are immobilized in the pore structure of hydophoblc, polypropylene hollow fibers by a solvent exchange procedure. Gas permeation studies are reported at pressures up to 733 kPa with the high pressure feed both on the shell and lumen sides of the laboratory scale hollow fiber permeator. No deformation of the hollow fibers is observed. Immobilizing a 30 weight % KjCO, solution in the hollow fibers greatly improved the separation factor, a(C02/Na). from 35.78 with pure water to 150.9 by a facilitated transport mechanism. Performance comparisons with commercial COj separation membranes are made. 

Jeong et al. [101] studied the counteractive facilitated transport of Co-Ni mixture by HFSLM. The mass conservation equations were written along with boundary conditions and solved to get the permeation profiles of metal ions. The diffusivity of Co(Il) and Ni(ll) was used from the literature while that of hydrogen ion was calculated by Nemst-Haskell equation. Stokes-Einstein equation was used for calculating the diffusivity of cobalt-carrier complex and nickel-carrier complex. The authors have shown the concentration profiles of cobalt inside the fiber at various flow rates and described that at low flow rate of feed phase, the concentration of cobalt decreases from the center to the feed-membrane interface. 

Tanigaki, M., Shiode, T., Okuttii, S., and Eguchi, W. (1988). Facilitated transport of zinc chloride through hollow fiber supported Uqitid membrane. Part 3. Module operation. Sep. Set Teehnol 23, 1171. 

---