Purification of hydrogen

While cathode reactions tend to be quite efficient, low concentrations of mercury and oxygen may be objectionable. Sections 9.2.5.1 and 9.2.5.2 deal with their removal. Volatile impurities in the catholyte may also contaminate the hydrogen. This is most likely in diaphragm cells, and Section 7.5.8.5 gave an example in which the removal of ammonia from brine reduced the concentrations of chloramines and other nitrogen compounds in the hydrogen. 

Accept chilled water at a higher temperature, as produced for the purpose of cooling chlonne gas (Section 9.1.3.5 A), and so allow a higher mercury concentration in the next stage of treatment. 

Produce chilled water in the utility section of the plant at the temperature desired for hydrogen chilling, and temper the water to the chlorine system by allowing some of the return to bypass the water chiller (cf. Fig. 9.30). 

Provide local refrigeration to control the temperatures in the hydrogen chiller and scrubber. 

The hydrogen chiller resembles the chlorine coolers in its design. It is mounted vertically, with downward flow of the gas. The bottom head serves as a gas-liquid separator, and the condensate flows on to a receiver. The condensate separates into two phases, and the receiving vessel should be designed for easy removal of the metal. The water will be contaminated with mercury and so must be returned to the process or treated carefully before being discharged (Section 16.5.5.3). 

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In the 1990s and beyond 2000, there has been an explosion of interest in metal/ partially reducible oxide catalysts for low temperature water-gas shift, mainly directed at the production/purification of hydrogen in a fuel processor for fuel cell applications. 

For the purification of hydrogen, and its separation from mixed gases, its interaction with palladium may be used. A large quantity of hydrogen may be absorbed by metallic palladium it is first chemisorbed at the surface of the metal but at... 

Purification of Hydrogen.—Where very pure hydrogen is required it is necessary to employ chemical methods to remove the 3 per cent, of impurity, which may be done by passing the gas through heated soda lime, where the carbon monoxide is absorbed in accordance with the following equation —... 

As with air separation the purification of hydrogen via a PSA process is also a well developed field. The market place is highly competitive and UOP competes with... 

The methanation reaction is a highly exothermic process (AH = —49.2 kcal/ mol). The high reaction heat does not cause problems in the purification of hydrogen for ammonia synthesis since only low amounts of residual CO is involved. In methanation of synthesis gas, however, specially designed reactors, cooling systems and highly diluted reactants must be applied. In adiabatic operation less than 3% of CO is allowed in the feed.214 Temperature control is also important to prevent carbon deposition and catalyst sintering. The mechanism of methanation is believed to follow the same pathway as that of Fischer-Tropsch synthesis. 

Small pieces of pumice stone of a convenient size are soaked in a concentrated solution of nickel nitrate in distilled water, and heated in a basin over a free flame until the nitrate has been converted into the oxide. Alternatively the pumice is impregnated with a paste of its own weight of nickel oxide and distilled water, and dried on a water bath. The nickel oxide is reduced by heating in a current of pure, thoroughly dried hydrogen in a combustion tube. The arrangement of the apparatus and the preparation and purification of hydrogen are the same as for the prepara-... 

H. Palladium. Palladium (mp 1,SS2°C), is soft and ductile but work-hardens. At elevated temperatures, the diffusion of hydrogen through palladium is rapid, which forms the basis of a method for the purification of hydrogen. The best performance is obtained from a palladium-silver alloy containing about 18% silver because, unlike pure Pd, this alloy does not undergo a phase transition in the presence of hydrogen. Palladium is not as inert as platinum and is attacked by sulfuric and nitric acids. 

The applicability of POLYBED is not restricted to steam reforming hydrogen plants. The advantages of high capacity, high recovery and high purity make the concept suitable for economic purification of hydrogen from a variety of process streams. Other applications includes... 

Currently, low-temperature CO oxidation over Au catalysts is practically important in connection with air quality control (CO removal from air) and the purification of hydrogen produced by steam reforming of methanol or hydrocarbons for polymer electrolyte fuel cells (CO removal from H2). Moreover, reaction mechanisms for CO oxidation have been studied most extensively and intensively throughout the history of catalysis research. Many reviews [4,19-28] and highlight articles [12, 29, 30] have been published on CO oxidation over catalysts. This chapter summarizes of the state of art of low temperature CO oxidation in air and in H2 over supported Au NPs. The objective is also to overview of mechanisms of CO oxidation catalyzed by Au. 

This chapter overviews some strategies that have been developed and applied at the academic level, by presenting a case study on the basis of our own experience the search for new catalytic material and processes adapted to the production and purification of hydrogen for feeding PEM fuel cells. 

J.B. Hunter, Silver-Palladium Film for Separation and Purification of Hydrogen, US Patent 2,773,561 (December, 1956). 

Monsanto and Ube (Japan) developed membrane processes for purification of hydrogen gas mixtures. This process is based on the selective diffusion of hydrogen through semi-permeable membranes in the form of hollow fibers. The Monsanto PRISM separator process (owned by Air Products as of 2004) uses a polysulfone fiber whereas Ube uses an aromatic polyimide fiber.46... 

Fig. 1.2. Circuit for the recovery and purification of hydrogen by Jou(e> Thompson expansion.

Table 1.2 lists miscellaneous economic data pertaining to the purification of hydrogen by adsorption, cryogenics and penn tion. 

The other methods that can be employed for add gas separation are those already discussed for the purification of hydrogenated effluents, but applied to the removal of compounds often present in high contents ... 

Tithman, L. M., Oyogenic purification of hydrogen , AICHE Sprite Natkaud Afeoing, Anaheini, Califonua (6/10 June 1982). 

D.R Paul and Y.P. Yampol skii, Polymeric gas separation membranes, CRC Press inc, 1994 L.M. Lehman, Cryogenic Purification of Hydrogen Energy Progress 3 (1983), 7... 

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