Large quantities of H2 are needed in the petroleum and chemical industries. The largest application of H2 is for the processing ("upgrading") of fossil fuels, and in the production of ammonia. The key consumers of H2 in the petrochemical plant include hydrodealkylation, hydrodesulfurization, and hydrocracking. H2 has several other important uses. H2 is used as a hydrogenating agent, particularly in increasing the level of saturation of unsaturated fats and oils (found in items such as margarine), and in the production of methanol. It is similarly the source of hydrogen in the manufacture of hydrochloric acid. H2 is also used as a reducing agent of metallic ores.[83]
Hydrogen is highly soluble in many rare earth and transition metals[84] and is soluble in both nanocrystalline and amorphous metals.[85] Hydrogen solubility in metals is influenced by local distortions or impurities in the crystal lattice.[86] These properties may be useful when hydrogen is purified by passage through hot palladium disks, but the gas's high solubility is a metallurgical problem, contributing to the embrittlement of many metals,[10] complicating the design of pipelines and storage tanks.[11]
Apart from its use as a reactant, H2 has wide applications in physics and engineering. It is used as a shielding gas in welding methods such as atomic hydrogen welding.[87][88] H2 is used as the rotor coolant in electrical generators at power stations, because it has the highest thermal conductivity of any gas. Liquid H2 is used in cryogenic research, including superconductivity studies.[89] Because H2 is lighter than air, having a little more than 1⁄15 of the density of air, it was once widely used as a lifting gas in balloons and airships.[90]
In more recent applications, hydrogen is used pure or mixed with nitrogen (sometimes called forming gas) as a tracer gas for minute leak detection. Applications can be found in the automotive, chemical, power generation, aerospace, and telecommunications industries.[91] Hydrogen is an authorized food additive (E 949) that allows food package leak testing among other anti-oxidizing properties.[92]
Hydrogen's rarer isotopes also each have specific applications. Deuterium (hydrogen-2) is used in nuclear fission applications as a moderator to slow neutrons, and in nuclear fusion reactions.[3] Deuterium compounds have applications in chemistry and biology in studies of reaction isotope effects.[93] Tritium (hydrogen-3), produced in nuclear reactors, is used in the production of hydrogen bombs,[94] as an isotopic label in the biosciences,[53] and as a radiation source in luminous paints.[95]
The triple point temperature of equilibrium hydrogen is a defining fixed point on the ITS-90 temperature scale at 13.8033 kelvins.
الأربعاء نوفمبر 14, 2012 12:23 am
