Novel Developments for High-Purity Oxygen

Porous membrane support Dense, slotted backbone 

FI CU RE 4.29 A schematic illustration of the ion transport membrane (ITM) device developed and patented by Air Products and Chemicals, Inc. The supported membrane wafers are separated by spacer rings and attached to a common product withdrawal tube. (From Armstrong P. A., Stein V.E.E., Bennet D.I., Foster E.P., Ceramic Membrane Development for Oxygen Sypply to Gasification Applications, Air Products and Chemicals, Inc., Allentown, PA, 2002. With permission.) 

Successful separation of alkanes and alkenes has been documented when microporous membranes have been used [79,138]. The physiochemical properties, size, and shape of the molecules will play an important role for the separation, hence critical temperatures and gas molecule configurations should be carefully evaluated for the gases in mixture. On the basis of gas properties and process conditions, the separation may be performed according to selective surface flow or molecular sieving (refer to Section 4.2 on transport). The transport may also be enhanced by having a Ag compound in the membrane. The Ag ion will form a reversible complex with the alkene, and facilitated transport results. Selectivities in the range of 200-300 have been reported for separation of ethene-ethane and propene-propane [138]. Successful separation of alkanes and alkenes will be important for the petrochemical industry. Today the surplus hydrocarbons in the purge gas are usually flared. Membranes which should be suitable for this application are the carbon molecular sieves (see Section 4.3.2) and nanostructured materials (Section 4.3.3). 

FIGURE 4.30 Illustration of a hybrid solution for removal of organic vapor from a gas stream, as documented by Vaconocore. (From Ohlrogge K., Wind J., Behling R.D., Erdoel Kohle Erdgas Petrochemie, 46, 326, 1993. With permission.) 

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