Hydrogen separation zeolite membranes

There are two main separation techniques to extract hydrogen membranes and adsorption. Studies indicate that separation of hydrogen through zeolite membranes is ineffective for FCV applications, since the toluene content in the permeate is too high (>2000 ppm). When toluene was present at high concentrations, the diffusion of hydrogen was hindered due to a strong adsorption of toluene in the membranes. Palladium membranes are... 

Recently, high-quality SOD membranes for water separation have been developed by Khajavi etal. [21, 52]. These zeolite membranes should allow an absolute separation of water from almost any mixture since only very small molecules such as water, hydrogen, helium, and ammonia can theoretically enter through the six-membered window apertures. Water/alcohol separation factors 10 000 have been reported with reasonable water fluxes up to 2.25 kg nr h at 473 K in pervaporation experiments. 

The separation factors are relatively low and consequently the MR is not able to approach full conversion. With a molecular sieve silica (MSS) or a supported palladium film membrane, an (almost) absolute separation can be obtained (Table 10.1). The MSS membranes however, suffer from a flux/selectivity trade-off meaning that a high separation factor is combined with a relative low flux. Pd membranes do not suffer from this trade-off and can combine an absolute separation factor with very high fluxes. A favorable aspect for zeoHte membranes is their thermal and chemical stability. Pd membranes can become unstable due to impurities like CO, H2S, and carbonaceous deposits, and for the MSS membrane, hydrothermal stability is a major concern [62]. But the performance of the currently used zeolite membranes is insufficient to compete with other inorganic membranes, as was also concluded by Caro et al. [63] for the use of zeolite membranes for hydrogen purification. 

S., Fiaty, K., and Dalmon, J.-A. (2000) Experimental smdy and numerical simulation of hydrogen/isobutane permeation and separation using MFI-zeolite membrane reactor. Catal. Today, 56 (1-3), 253-264. 

Bernardo, P., Algieri, C., Barbieri, G. and Drioli, E. (2008) Hydrogen purification from carbon monoxide by means of selective oxidation using zeolite membranes. Separation and Purification Technology, 62, 631—637. 

Cheng Y.S. Performance of alumina, zeolite, palladium, Pd-Ag alloy membranes for hydrogen separation from Towngas mixture. J.Membr.Sci 2002 204 329-340. 

Moron F, Pina MP, Uiriolabeitia E, Menendez M, and Santamaria J. Preparation and characterization of Pd-zeolite composite membranes for hydrogen separation. Desalination 2002 147(1-3) 425M-31. 

Dong J, Lin YS, and Liu W. Multicomponent hydrogen/hydrocarbon separation by MFI-type zeolite membranes. AIChE J 2000 46(10) 1957-1966. 

Nanoporous inorganic ceramic membranes show significant promise for hydrogen separation and purification, primarily due to the high selectivity that is afforded by this class of membranes. Development work has focused on zeolites although... 

The role of zeolite membranes in hydrogen separation and purification has recently been reviewed by Ockwig and Nenoff (2007). They report that more than 14 zeolite structure types have been employed as H2 selective separation... 

The Sandia aluminosilicate zeolite membranes have fluxes on the order of 10-6 mole/mole per meter squared Pascal secont (flux unit) (m Pa sec) and pure gas separations of H2/N2 >61, H2/CO2 >80, H2/ CH4 =7, CH4/CO2 >11. H2 (hydrogen), N2 (diatomic nitrogen),C02 (carbon dioxide), CH4 (methane). 

Hong et al. [29] exploited silylation reactions with proper silane precursors to engineer the pore size of zeolite membrane for hydrogen separation. As a result, H2/CH4 separation selectivity can be increased more than 50% from 35 to 59. 

Welk et al. from Sandia National Laboratories (SNL) (USA) [34] have intensively studied the potential applications of zeolite membranes in reforming streams separation. ZSM-5 zeolite membranes synthesized by them showed excellent performance for hydrogen separation from light gases mixture. It was reported that after a single pass through the ZSM-5 zeolite membrane, the Ha purity was enriched from 76% (simulated reforming stream) to >98%. 

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