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Extraction of Hydrogen from Low Grade Sources

IP.com Disclosure Number: IPCOM000049451D
Original Publication Date: 1982-Jun-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 5 page(s) / 57K

Publishing Venue

IBM

Related People

Gambino, RJ: AUTHOR [+2]

Abstract

There are many low grade sources of hydrogen. The concentration of H(2) in air, for example, is 5 x 10/-7/ atmospheres. Water vapor has an equilibrium dissociation partial pressure of 7.4 x 10/-25/ atmospheres at room temperature and 1.2 x 10/-15/ atmospheres at 500 K. Ammonia gas has an even higher dissociation pressure (3 x 10/-2/ atmospheres) at these temperatures. The dissociation of both these gases is promoted by ultraviolet (UV) excitation (1600 to 1800 Angstroms), e.g., by concentrated sunlight. Certain anaerobic bacteria metabolize waste materials and produce ammonia and/or hydrogen. The most important sources of atmospheric hydrogen are decomposition of organic matter, photolysis of H(2)O and the flux of protons from the sun.

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Extraction of Hydrogen from Low Grade Sources

There are many low grade sources of hydrogen. The concentration of H(2) in air, for example, is 5 x 10/-7/ atmospheres.

Water vapor has an equilibrium dissociation partial pressure of 7.4 x 10/-25/ atmospheres at room temperature and 1.2 x 10/-15/ atmospheres at 500 K. Ammonia gas has an even higher dissociation pressure (3 x 10/-2/ atmospheres) at these temperatures. The dissociation of both these gases is promoted by ultraviolet (UV) excitation (1600 to 1800 Angstroms), e.g., by concentrated sunlight. Certain anaerobic bacteria metabolize waste materials and produce ammonia and/or hydrogen. The most important sources of atmospheric hydrogen are decomposition of organic matter, photolysis of H(2)O and the flux of protons from the sun. In addition, the off gas from many industrial processes contains significant traces of hydrogen.

If this hydrogen could be recovered, it would have a major economic impact. Here, means is provided for hydrogen extraction for some of these low grade sources with hydrogen getters which extract hydrogen from low partial pressure sources. These getter materials circumvent the competing oxidation reactions which interfere with the hydrogen gettering action. These getters are also designed to release the hydrogen at relatively low temperatures so that low grade heat sources, e.g., flat plate solar collectors, or industrial waste heat, can be used to recover the hydrogen gas for use as a fuel.

Some rare earths such as dysprosium incorporate hydrogen when exposed to water vapor at elevated temperatures. The common belief is that this is a metal oxidation reaction where the by product hydrogen remains in the lattice (3H(2) O + 5Dy approaches D(2)O(3) + 3DyH(2)). However, it is not necessary for the oxidation reaction to occur for hydrogen absorption. In our analysis, we plot both the hydrogen source and absorption reactions on the same Van't Hoff plot since the process by which a hydride absorbs hydrogen can be represented by: (see original), where P is the metal/hydride equilibrium pressure (atmospheres); Delta H is the enthalpy of formation of the hydride (cal/mole); Delta S is the entropy of free H(2) (cal/mole); R is the universal gas constant; and T is the equilibrium temperature (degree K). Therefore, for most hydrides we can write the general expression: (see original), where Delta H (cal/mole) for some typical elemental hydrides is La (-50,000), Zr (-39,000), Ti (-30,000).

The hydrogen source reactions can be written in a similar form. Some examples are: Water H(2) O approaches H(2) + 1/20 (ln P=-17,000 1/T + 2.6); Ammonia NH(4) approaches 2H(2) + 1/2N(2) (ln P=-3100 1/T + 6.5); Air ln P=-1
4.5.

The general features of this type of plot are shown in Fig. 1. Above T(c) the hydride can evolve hydrogen, and below it the metal can absorb hydrogen if it is in equilibrium with the plotted source reaction. This type of analysis leads us to the unique conclusion...