Hydrogen separation palladium-based

The unusual interaction of hydrogen with palladium-based membrane materials opens up the possibility of oxidative hydrogen pump for tritium recovery from breeder blankets. The feasibility for this potential commercial application hinges on the hot-fusion and cold-fusion technology under development [Saracco and Specchia, 1994]. At first, Yoshida et al. [1983] suggested membrane separation of this radioactive isotope of hydrogen followed by its oxidation to form water. Subsequently, Hsu and Bauxbaum [1986] and Drioli et al. [1990] successfully tested the concept of combining the separation and reaction steps into a membrane reactor operation. 

Franz et al. [93] developed a palladium membrane micro reactor for hydrogen separation based on MEMS technology, which incorporated integrated devices for heating and temperature measurement. The reactor consisted of two channels separated by the membrane, which was composed of three layers. Two of them, which were made of silicon nitride introduced by low-pressure chemical vapor deposition (0.3 pm thick) and silicon oxide by temperature treatment (0.2 pm thick), served as perforated supports for the palladium membrane. Both layers were deposited on a silicon wafer and subsequently removed from one side completely... 

Because Pd-based metal membranes, commonly used for hydrogen separation [11] are not resistant towards sulphur, not much research has been performed on the use of such membranes in H2S dehydrogenation reactors. Some success has, however, been reported by Edlund and Pledger [12], They developed a platinum-based layered metal membrane that could resist irreversible attack by H2S at 700°C. At this temperature a conversion of 99.4% was achieved in the membrane reactor. Without hydrogen removal the conversion was only 13%. No permeance data is provided, but platinum-based metal membranes are known for their low hydrogen permeance [14], Johnson-Matthey developed palladium composite membranes with a hydrogen permeance of about 1 10 mol/m sPa [14], but these are most probably not resis-... 

Franz AJ, Schmidt MA, Jensen KF, and Firebaugh S. Integrated palladium-based micromembranes for hydrogen separation and hydrogenation/dehydrogenation reactions. US Patent 6,541,676, Apr 2003. 

When absorption of hydrogen is finished, the separated palladium is filtered and the alcohol distilled until nearly to dryness. The residue is made alkaline and extracted with ether. The ether is distilled and the residue extracted in dilute hydrochloric acid. The portion insoluble in acid is separated by means of ether and the base is precipitated by means of caustic soda lye, extracted and fractionated. At 140° C. at 1 mm. pressure colourless triethoxyphenylethylamine distills. The hydrochloride forms white crystals soluble in water and of melting point 178—179°... 

The first commercial metal membranes for hydrogen separation and purification were made of palladium alloyed with 23-25 wt % silver. These membrane were of the unsupported type and tubular in shape. Nevertheless, the wall thickness was substantial by current standards—typically at least 100- an thick. Advances in drawing thin-walled metal tubes has allowed for palladium-silver tubular membranes to be made with much thinner walls, about 20- an thick. Composite membranes are also usually at least 25-/an thick. REB Research and Consulting (Oak Park, MI) provides tubular composite metal membranes consisting of a palladium coating over a tantalum base metal, although other group 4 or 5 base metals may be used. 

Power + Energy. Hydrogen separation and purification products based on palladium alloy, http // www.purehydrogen.com (accessed November 3, 2005). 

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]. 

B. A. Wilhite, M. A. Schmidt, K. F. Jensen, Palladium-based micromembranes for hydrogen separation Device... 

N. I. Timofeev, F. N. Berseneva, V. M. Makarov, New palladium-based membrane alloys for separation of gas mixtures to generate ultrapure hydrogen, Int.]. Hydrogen Energy 1994, 39(11), 895-898. 

Phair, J.W. and R. Donelson, Developments and design of novel (non-palladium-based) metal membranes for hydrogen separation. Industrial and Engineering Chemistry Research, 2006.45(16) 5657-5674. 

The first scientific study on palladium-based membranes, available in the Elsevier Scopus database [1], where more than 6,000 scientific journals are taken into account, is dated 1955, when Juenker et al. [2] analyzed the use of palladium membranes for hydrogen purification. Today, it is well known that the palladium membranes are, mainly, applied in the field of gas separation and, particularly, in the issue of the hydrogen rich-stream purification [3], As reflected by the data of Fig. 2.1, the scientific interest towards palladium-based membranes is increased... 

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