Organic vapor separation

This cost differential can be tolerated only in applications in which polymeric membranes completely fail in the separation [78]. Demanding separation applications, where zeolite membranes could be justified, due to the high temperatures involved or the added value of the components, and have been tested at laboratory scale, are the following separation of isomers (i.e., butane isomers, xylene isomers), organic vapor separations, carbon dioxide from methane, LNG (liquefied natural gas) removal, olefines/paraffins and H2 from mixtures. In most cases, the separation is based on selective diffusion, selective adsorption, pore-blocking effects, molecular sieving, or combinations thereof. The performance or efficiency of a membrane in a mixture is determined by two parameters the separation selectivity and the permeation flux through the membrane. 

Lai ZP, Bonilla G, Diaz I, Nery JG, Sujaoti K, Amat MA, Kokkoli E, Terasaki O, Thompson RW, Tsapatsis M, and Vlachos DG. Microstructural optimization of a zeolite membrane for organic vapor separation. Science 2003 300 456-460. 

The membrane modules, which are commonly used in organic vapor separation, are spiral-wound modules or the envelope-type GKSS GS modules. Gapillary or hollow-fiber modules are only used in small-scale laboratory applications. The spiral-wound module and the envelope module are based on flat-sheet membranes. Spiral-wound modules are compact and cheaper in comparison to installed membrane area, but there are limitations in mass transfer on both sides of the membrane. The packing density - the ratio of installed membrane area over pressure vessel housing volume - of a spiral-wound module varies from approx. 300 to 1000 m /m (Fig. 1.3). 

Basic process data are available from the development of organic vapor separation. The real challenge is the transformation of the available knowledge into high-pressure applications. Several drawbacks such as the compaction of the substructure of composite membranes and the influence of the boundary layer On the membrane selectivity have to be overcome. Pour structure and polymer compositions have to be suited to the high operating pressure in the presence of higher hydrocarbons [22, 23]. 

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