Organic vapor separation systems

This effluent is cooled to 38°C and enters a flash-decanter vessel at 278 kPa. Three phases leave that vessel. The vapor phase (hydrogen rich) is sent to the vapor separation system. The aqueous phase (mostly water, with some methanol) is sent to the aqueous stream separation system. The organic-rich phase is sent to the organic stream separation system, which you will design. To obtain the composition of the feed to your section, use a simulator with the UNIFAC method to perform a three-phase flash for the above conditions. If the resulting organic liquid stream contains small amounts of hydrogen and water, assume they can be completely removed at no cost before your stream enters your separation section. 

FIGURE 9.3 Dependence of Henry s solubility coefhcient on Van der Waals volume of penetrant molecules for the systems of natural mbber/hydrocarbons. (From Semenova, S.I., Membranes in Russian), 13, 37, 2002 Baker, R.W. and Wijmans, J.G., Membrane separation of organic vapors from gas streams. In Paul D, Yampolskii Yu, Eds., Polymeric Gas Separation Membranes. CRC Press, 1994 353-397 Crank, J. and Park, G., Ed., Diffusion in Polymers. London, Academic Press, 1968.)... 

For other systems separate lines must be used for psychrometric lines. With nearly all mixtures of air and organic vapors the psychrometric lines are steeper than the adiabatic-saturation lines, and the wet-bulb temperature of any mixture other than a saturated one is higher than the adiabatic-saturation temperature. 

D.R. Paul and Yuri P. Yampol skii, Polymeric Gas-separation Membranes, Chapter 8, R.W. Baker and J.G. Wij-MANS, Membrane Separation of Organic Vapors from Gas Systems., CRC Press, 1994, p. 353 397. 

Of the two developing membrane processes Usted in Table 3, gas separation and pervaporation, gas separation is the more developed. At least 20 companies worldwide offer industrial membrane-based gas separation systems for a variety of applications. In gas separation, a mixed gas feed at an elevated pressure is passed across the surface of a membrane that is selectively permeable to one component of the feed. The membrane separation process produces a permeate enriched in the more permeable species and a residue enriched in the less permeable species. Important, well-developed applications are the separation of hydrogen from nitrogen, argon, and methane in ammonia plants the production of nitrogen from air the separation of carbon dioxide from methane in natimal gas operations and the separation and recovery of organic vapors from air streams. Gas separation is an area of considerable current research interest the munber of applications is expected to increase rapidly over the next few years. 

The recovery of organic vapors from waste gas streams using polymeric membranes is a well established process (7). Typically, composite membranes are used for this process. These membranes consist of a diin, selective rubbery layer coated onto a microporous support material. The selectivities of these membranes for organic vapors over nitrogen are typically about 10-100. Currently, commercial vapor separation membrane applications include small systems (10-100 scfin) to recover fluorinated hydrocarbons (Freons) and other high-value solvent vapors from process vent streams to large systems (100-1,000 scfin) for recovery of hydrocarbon vapors in the petrochemical industry (7). 

Design of membrane separation system is a little more complex and to some extent limited in comparison of the other separation processes. In addition to the selection of a given membrane material and module design, all membrane gas separation systems require some type of pre-treatment to get rid of all the particulates, aerosols, oil and organic condensable vapors. The feed gas may be heated or cooled depending on the feed stock and the nature of separation. Theoretically, a membrane will operate at its best if the feed stream consists nothing but the gases which need to be separated. 

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