Propane-propylene separation membranes

Separation, CO2/C2 hydrocarbons Separation of mixtures Separation, membrane Separation, membrane, asymmetric Separation, propane/propylene Separation, xylenes SFe-Xe diffusion in BOG, modelling Shape selectivity 11-P-24 25-P-07 25-... 

Benali, M. and Aydin, B. (2010) Ethane/ethylene and propane/propylene separation in hybrid membrane distillation systems Optimization and economic analysis. Separation and Purification Technology, 73 (3), 377-390. 

Figure 13.11 Two-step propane dehydrogenation to propylene with minimum CO2 emissions (1) Combustion chamber (2) post-combustion chamber (3) convective furnace (4) and (5) membrane modules for H2 separation (6) boiler (7) propane/propylene separator (8) H2 compressor.

Ito A and Hwang S. Permeation of propene and propylene through cellulosic polymer membranes. J Appl Polym Sci 1989 38 483 90. Sridhar S and Khan A. Simulation studies for the separation of propylene and propane by ethylcellulose membrane. J Membr Sci 1999 159 209-219. 

Gas separation membrane technologies are extensively used in industry. Typical applications include carbon dioxide separation from various gas streams, production of oxygen enriched air, hydrogen recovery from a variety of refinery and petrochemical streams, olefin separation such as ethylene-ethane or propylene-propane mixtures. However, membrane separation methods often do not allow reaching needed levels of performance and selectivity. Polymeric membrane materials with relatively high selectivities used so far show generally low permeabilities, which is referred to as trade-off or upper bound relationship for specific gas pairs [1]. 

Another very large potential application of membranes in ethylene plants is replacing the C2 and C3 splitters. An example of a possible process design is shown in Fig. 7.15. In this example, a two-step membrane system equipped with propylene-permeable membranes is used to split a 50/50 propylene/propane overhead stream from a depropanizer column into a 90% propylene stream and a 90% propane stream. Both streams could then be sent to distillation units for polishing, but the size of columns required would be much reduced. For this design to be feasible, membranes with an olefin/paraffin selectivity of 5 to 10 are required. Many other designs that combine membranes and distillation columns to achieve good separation are possible [23]. 

Krol, J.J., Boerrigter, M. and Koops, G.H. 2001. Polyimide hollow fiber gas separation membranes Preparation and the suppression of plasticization in propane/propylene environments. 184 275-286. 

Hayashi J, Mizuta H, Yamamoto M, Kusakabe K, Morooka S (1996) Separation of ethane/ ethylene and propane/propylene systems with a carbonized BPDA-pp ODA polyimide membrane. Ind Eng Chem Res 35 (11) 4176-4181... 

Dehydrogenation processes in particular have been studied, with conversions in most cases well beyond thermodynamic equihbrium Ethane to ethylene, propane to propylene, water-gas shirt reaction CO -I- H9O CO9 + H9, ethylbenzene to styrene, cyclohexane to benzene, and others. Some hydrogenations and oxidations also show improvement in yields in the presence of catalytic membranes, although it is not obvious why the yields should be better since no separation is involved hydrogenation of nitrobenzene to aniline, of cyclopentadiene to cyclopentene, of furfural to furfuryl alcohol, and so on oxidation of ethylene to acetaldehyde, of methanol to formaldehyde, and so on. 

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...

The problem with use of polymeric membranes in this application is plasticization, leading to much lower selectivities with gas mixtures than the simple ratio of pure-gas permeabilities would suggest. For this type of separation, a Robeson plot based on the ratio of pure-gas permeabilities has no predictive value. Although membranes with pure-gas propylene/propane selectivities of 20 or more have been reported [43, 44], only a handful of membranes have been able to achieve selectivities of 5 to 10 under realistic operating conditions, and these membranes have low permeances of 10 gpu or less for the fast component (propylene). This may be one of the few gas-separation applications where ceramic or carbon membranes have an industrial future. 

Giannakopoulos IG and Nikolakis V. Separation of propylene/propane mixtures using faujasite membranes. Ind Eng Chem Res 2005 44(l) 226-230. 

M. Asaeda, A. Yamamichi, M. Satoh and M. Kamamura, Preparation of porous silica membranes for separation of propylene/propane gaseous mixtures in Yi Hua Ma (Ed.), Proceedings of the Third International Conference on Inorganic Membranes, July 10-14,1994. Worcester Polytechnic Institute, Worcester, MA, pp. 315-325. 

Catalytically active supported ionic liquid membranes were used for propylene/propane vapor mixture separation. In this case, the ionic Hquid was immobilized in the pores of an asymmetric ceramic support, displaying sufficient permeability, good selectivity, and long-term stabUity [51]. Porous inorganic membranes were also used as a support for chiral-selective liquid membranes. For this purpose, porous tubular ceramic membranes were impregnated with 3-cyclodextrin polymer. Such SLMs were used for separation of enantiomers of racemic pharmaceutical chlorthahdone [52]. 

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. 

Duan et al. [57] reported a very high separation of propylene/propane mixture by a double layer liquid membrane using different solutions of silver salt, AgBF4, or AgNO in triethylene glycol (TEG) as facilitating agent of propylene. The selectivity (a) Cldh/Cdh was 40 for TEG/... 

S. Duan, A. Ito, A. Ohkawa, Separation of propylene/propane mixture by a supported liquid membrane containing triethylene glycol and silver salt, J. Membr. Sci. 215 (2003) 53-60. 

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... 

Further progress is expected from new developments and combinations of processes. Thus, it would be possible to make the disposal of the gaseous (and highly pure) waste gas streams (residual propane content of the propylene feed) cost-effective and a source of electric power by connection to novel, compact, membrane fuel cells. Potential synergisms would also occur in the operating temperature of the cells (medium-temperature cells at 120 °C using the residual exothermic heat of reaction from the oxo reaction), the membrane costs by means of combined developments (e.g., for membrane separations of the catalysts [22]), and also in the development of the zero-emission automobile by the automotive industry. The combination of hydroformylation with fuel cells would further reduce the E-factor - thus approaching a zero-emission chemistry. ... 

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