Hydrogen is produced by the steam reforming of natural gas, the electrolysis of water and the dissociation of ammonia. Hydrogen is also a by-product of petro- leum distillation and chlorine manufacture. The primary method of hydrogen generation is steam reforming of natural gas. Other feedstocks, which are less common, can include ethane, propane, butane, and light and heavy naphtha. The steam reforming process produces syngas, which is a mixture of hydrogen and carbon monoxide. Regardless of the method of production, the product stream is separated into its components. The hydrogen is dried and purified. This gaseous hydrogen is then compressed and cooled to sufficiently low cryogenic temperatures by the use of heat exchangers, along with reciprocating and tube expanders, to form liquid hydrogen.
Liquid hydrogen is used in large volumes in the space program as a primary rocket fuel for combustion with oxygen or fluorine, and as a pro- pellent for nuclear powered rockets and space vehicles. Although used more commonly in the gaseous state, hydrogen is stored and transported as a liquid. Hydrogen is a raw material for innumerable chemical processes ranging from the manufacturing
of high-density polyethylene and polypropylene to the hydrogenation of food-grade oils. In the metallurgical industry, hydrogen is used to reduce metal oxides and prevent oxidation in heat treating certain metals and alloys. Hydrogen is also used by semi- conductor manufacturers.
