Gases separating with molecular

S. J. Miller, W. J. Koros, D. Q. Vu, Mixed matrix membrane technology enhancing gas separations with polymer/molecular sieve composites. Studies Surf. Sci. Cated., 170, 1590-1596 (2007). 

Linear alkylbenzene sulfonates are produced from the reaction of benzene and secondary monochloroparaffins the latter are obtained by chlorination of n-paraffins. A requirement of this process was the availability of pure n-paraffins, which was made possible by the introduction of molecular sieves. The n-paraffins can be separated with molecular sieves from kerosene or gas oil, since they have a smaller diameter (ca. 4.9 A) than the branched paraffins. 

Effusion separator (or effusion enricher). An interface in which carrier gas is preferentially removed from the gas entering the mass spectrometer by effusive flow (e.g., through a porous tube or through a slit). This flow is usually molecular flow, such that the mean free path is much greater than the largest dimension of a traverse section of the channel. The flow characteristics are determined by collisions of the gas molecules with surfaces flow effects from molecular collisions are insignificant. 

However, ia some cases, the answer is not clear. A variety of factors need to be taken iato consideration before a clear choice emerges. Eor example, UOP s Molex and IsoSiv processes are used to separate normal paraffins from non-normals and aromatics ia feedstocks containing C —C2Q hydrocarbons, and both processes use molecular sieve adsorbents. However, Molex operates ia simulated moving-bed mode ia Hquid phase, and IsoSiv operates ia gas phase, with temperature swiag desorption by a displacement fluid. The foUowiag comparison of UOP s Molex and IsoSiv processes iadicates some of the primary factors that are often used ia decision making ... 

Hatori, H., H. Takagi, and Y. Yamada, Gas separation properties of molecular sieving carbon membranes with nanopore channels, Carbon, 42, 1169-1173, 2004. 

The carbonyl complex [Ag(L9)(C0)] (12), also of quite remarkable stability, is obtained by reaction of [Ag(L9)(C2H4)] (11) with CO in hexane. Nevertheless, the CO can be easily removed by increasing the temperature of the solution or by purging with an inert gas. Hence, such a reversible guest encapsulation within a molecular container might find applications for gas separation and storage. Again, one likely reason for the stability of the complexes is the protection offered by the bulky mesityl substituents that surround the ethylene or CO unit. 

Molecular sieves are synthetic zeolites that can be manufactured with extremely close control of pore size. Therefore, they can be tailored to suit specific applications. In addition to gas drying applications, molecular sieves are used for the separation of gases and vapors on the basis of molecular size and shape. Surface areas range from 350 to 1000 ft2/ft3. 

Considering all we know up to now, the specific properties of zeolites can be summarized as follows. Zeolites are aluminosilicates with defined microporous channels or cages. They have excellent ion-exchange properties and can thus be used as water softeners and to remove heavy metal cations from solutions. Furthermore, zeolites have molecular sieve properties, making them very useful for gas separation and adsorption processes, e.g., they can be used as desiccants or for separation of product gas streams in chemical processes. Protonated zeolites are efficient solid-state acids, which are used in catalysis and metal-impregnated zeolites are useful catalysts as well. 

Kulkarni, S.S., David, H.J., Corbin, D.R., and Patel, A.N. (2003) Gas separation membranes with organosilicone-treated molecular sieve. US Patent 6,508,860. 

These results are not unlike those reported by others, for separation of gases with molecular sieves. For example, when HgS is stripped from natural gas with a Davison 5A molecular sieve, the reaction front is typically 1 to 5 feet at superficial gas velocities of 15 to 30 feet per minute (lO). From this perspective, the operation of a hydride-hydrogen separation system is similar to conventional units. 

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