Hydrogen separation carbon molecular sieve

By far the most fully developed application for carbon molecular sieves is in the separation of small gas molecules. A large number of patents describe claims for materials and processes that include carbon-based sieves. Separations that have been accomplished include oxygen and nitrogen, hydrogen and coke gases, methane and carbon dioxide, methane and xenon, ethylene and ethane, propylene and propane. A number of companies in Europe and the United States have recently offered commercial systems for the separation of nitrogen from air. A review of the use of carbon molecular sieves in separation technology is well beyond the scope of this article and the interested reader is referred to recent reviews and references sited therein (12,18.). ... 

Liu, P.K.T., Carbon Molecular Sieve Membrane as Reactor/Separator for Water-Gas-Shift Reaction, Proceedings of2007 U.S. DOE Hydrogen Annual Merit Review Meeting, Arlington, VA, May 2007. 

Carbon molecular sieves are prepared by the controlled pyrolysis of poly(vinylidene chloride) or sulfonated polymers (Carboxen ). They consist of very small graphite crystallites cross-linked to yield a disordered cavity-aperture structure. Carbon molecular sieves are microporous and of high surface area, 200-1200 m g . They are used primarily for the separation of inorganic gases, C1-C3 hydrocarbons, and for the separation of small polar molecules such as water, formaldehyde, and hydrogen sulfide. Less volatile compounds cannot be desorbed efficiently at acceptable temperatures. 

Briceno, K., lufianelU, A., Montane, D., Garcia-Valls, R., Basile, A. (2012). Carbon molecular sieve membranes supported on non-modified ceramic tubes for hydrogen separation in membrane reactors. International Journal of Hydrogen Energy, 37, 13536—13544. 

Parsley, D., Ciora, R. J., Jr., Flowers, D. L., Laukaitaus, J., Chen, A., Liu, P. K. T., et al. (2014). Field evaluation of carbon molecular sieve membranes for the separation and purification of hydrogen from coal- and biomass-derived syngas. Journal of Membrane Science, 450, 81-92. 

Pan, Z.J., el al.. Pore structure alteration of a carbon molecular sieve for the separation of hydrogen sulfide from methane by adsorption. Adsorpt. Sci Technol.. 10. 193-202 (1994). 

Areas in which further developments are expected are related to the optimization of the solution of air and water pollution, gas purification (removal of oxides of sulfur and nitrogen, of hydrogen sulfide, motor vehicle emissions, etc.), gas separation, mineral industries, regeneration, etc. Many of these areas will require the use of new forms of activated carbon such as cloth, felts, fibers, monoliths, etc., and consequently a search for the appropriate precursor and preparation mode is essential. Other areas in continuous progress will be gas storage, carbon molecular sieves and heterogeneous catalysis, all of them requiring considerable research efforts in the next few years. 

Carboxen 1010 PLOT Carbon molecular sieve separation of hydrogen, nitrogen, CO, methane, carbon dioxide, and C2 and C3 hydrocarbons. 

Adsorption systems employing molecular sieves are available for feed gases having low acid gas concentrations. Another option is based on the use of polymeric, semipermeable membranes which rely on the higher solubiHties and diffusion rates of carbon dioxide and hydrogen sulfide in the polymeric material relative to methane for membrane selectivity and separation of the various constituents. Membrane units have been designed that are effective at small and medium flow rates for the bulk removal of carbon dioxide. 

ZeoHte-based materials are extremely versatile uses include detergent manufacture, ion-exchange resins (ie, water softeners), catalytic appHcations in the petroleum industry, separation processes (ie, molecular sieves), and as an adsorbent for water, carbon dioxide, mercaptans, and hydrogen sulfide. 

Experience in air separation plant operations and other ciyogenic processing plants has shown that local freeze-out of impurities such as carbon dioxide can occur at concentrations well below the solubihty limit. For this reason, the carbon dioxide content of the feed gas sub-jec t to the minimum operating temperature is usually kept below 50 ppm. The amine process and the molecular sieve adsorption process are the most widely used methods for carbon dioxide removal. The amine process involves adsorption of the impurity by a lean aqueous organic amine solution. With sufficient amine recirculation rate, the carbon dioxide in the treated gas can be reduced to less than 25 ppm. Oxygen is removed by a catalytic reaction with hydrogen to form water. 

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