Hydrogen separation membranes methods

Thicker, self-supporting, dense metal membranes are known. These are tubular and are usually commercially successful palladium-silver hydrogen separation membranes were of this type.21 Currently, Power and Energy, Inc. also fabricates this type of membrane, although planar membranes are more common due to easier fabrication and a greater variety of fabrication methods. 

Based on the different compositions, structures and configurations, the dense metallic membranes can be prepared using various methods. As described earlier, the dense metallic hydrogen separation membrane can be... 

In addition to the Pd-based membranes, microporous silica membranes for hydrogen permeation [8] can be produced by a special type of chemical vapor deposition [140] named chemical vapor infiltration (CVI) [141], A large amount of studies have been carried out on silica membranes made by CVI for hydrogen separation purposes [8,121], CVI [141] is another form of chemical vapor deposition (CVD) [140] (see Section 3.7.3). CVD involves deposition onto a surface, while CVI implies deposition within a porous material [141], Both methods use almost similar equipment [140] and precursors (see Figure 3.19) however, each one functions using different operation parameters, that is, flow rates, pressures, furnace temperatures, and other parameters. 

S. Van, H. Maeda, K. Kusakabe, and S. Moro-Oka, Thin palladium membrane formed in support pores by metal-oiganic chemical vapor deposition method and application to hydrogen separation, IruL Eng, Chem. Res. Ji 616 (1994). 

The separation of refinery gases is also an item of interest, such as gas streams containing hydrogen. In the main, membrane methods pertain to the separation of noncondensable gases—that is, to gases that are not readily hquefiable except by low temperature or cryogenic means. 

Zakrzewska-Trznadel, G. et al.. Separation of hydrogen and oxygen isotopes by membrane method, Sudia Universitaties Babes-Bolyai, Physica, Special Issue 1, XLVIII, 39, 2003. 

R.S.A. de Lange, J.H.A. Hekkink, K. Keizer and A.J. Burggraff, Microporous sol-gel modified membranes for hydrogen separation. Key Engirt. Mater., 61 62 (1991) 77. R.J.R. Ulhorn, K. Keizer and A.J. Burggraff, Synthesis of ceramic membranes. Part II. Modification of thin alumina films reservoir method. J. Mater. Sci., 17 (1992). 

Z.Y. Li, H. Maeda, K. Kusakabe, S. Morooka, H. Anzai and S. Akiyama, Preparation of palladium-silver alloy membranes for hydrogen separation by the spray pyrolysis method. J. Membr. Sci., 78 (1993) 247. 

In recent years, new concepts to produce hydrogen by methane SR have been proposed to improve the performance in terms of capital costs reducing with respect to the conventional process. In particular, different forms of in situ hydrogen separation, coupled to reaction system, have been studied to improve reactant conversion and/or product selectivity by shifting of thermodynamic positions of reversible reactions towards a more favourable equilibrium of the overall reaction under conventional conditions, even at lower temperatures. Several membrane reactors have been investigated for methane SR in particular based on thin palladium membranes [14]. More recently, the sorption-enhanced steam methane reforming (Se-SMR) has been proposed as innovative method able to separate CO2 in situ by addition of selective sorbents and simultaneously enhance the reforming reaction [15]. 

Gas separation membrane technologies are extensively used in industry. Typical applications include carbon dioxide separation from various gas streams, production of oxygen enriched air, hydrogen recovery from a variety of refinery and petrochemical streams, olefin separation such as ethylene-ethane or propylene-propane mixtures. However, membrane separation methods often do not allow reaching needed levels of performance and selectivity. Polymeric membrane materials with relatively high selectivities used so far show generally low permeabilities, which is referred to as trade-off or upper bound relationship for specific gas pairs [1]. 

Hydrogen is used in a large number of chemical processes, and may be used as a fuel itself or as a reactant in the production of synthetic fuels such as in the Fischer-Tropsch hydrocarbon synthesis process, for example. In applications where hydrogen purification is required, membranes can be used for hydrogen separation. Other hydrogen purification methods include pressure swing adsorption and cryogenic separation. 

It has been shown to be feasible to produce pore-free membranes below 5 p.m in thickness that should consequently be competitive with other methods for hydrogen separation in energy applications. 

Tong J, Suda H, Haraya K, Matsumura Y (2005) A novel method for the preparation of thin dense Pd membrane on macroporous stainless steel tube filter. J Memb Sci 260 10-18 Ryi SK, Park JS, Kim SH, Cho SH, Park JS, Kim DW (2006) Development of a new porous metal support of metallic dense membrane for hydrogen separation. J Memb Sci 279 439-445... 

Membrane integration into the reaction environment ensures a first substantial hydrogen separation step (up to 90% of the hydrogen produced can be removed) as for CO2 separation, because of the higher carbon dioxide partial pressure in the reformer outlet stream, due to the hydrogen removal, physical separation methods could be used to separate CO2 rather than the chemical adsorption in mono-diethanol ammine (MDEA). 

The last section Applied Aspects of Membrane Gas Separation contains three chapters. Brunetti et al. start their contribution with a brief review of membrane materials and membranes used in gas separation and survey the main directions of industrial applications of gas separation (hydrogen recovery, air separation, etc.). In the second part of their chapter they present a new concept for comparison of membrane and other, more traditional, methods for gas separation. Their approach includes a consideration of engineering, economical, environmental and social indicators. Something similar had been written 15 years ago [2] but this analysis is now rather outdated. White (Chapter 15) focuses on a specific but very important problem in industrial gas separation membrane separation of natural gas. The main emphasis is on cellulose acetate based membranes that have the longest history of practical applications. This chapter also contains the results of field tests of these membranes and considers approaches how to reduce the size and cost of industrial membrane systems. The final chapter is an example of detailed engineering... 

Yan S, Maeda H, Knsakabe K and Morooka S (1994), Thin palladinm membrane formed in snpport pores by metal-organic chemical vapor deposition method and application to hydrogen separation , Ind Eng Chem Res, 33, 616-622. 

As to a comparison of membrane gas separation technologies with such methods as pressure swing absorption (PSA) and low-temperature or cryogenic separations, the last-cited chapter in Polymeric Gas Separation Membranes must remain somewhat inconclusive, given the wide range of variables, parameters, and applications. Moreover, for the most part, the separations compared were confined to air and hydrogen-containing systems. 

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