Hydrogen (pronounced /?ha?dr?d??n/), is a chemical element represented by the symbol H and an atomic number of 1. At standard temperature and pressure it is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas (H2).

With an atomic mass of 1.00794 g/mol, hydrogen is the lightest element.

Hydrogen is the most abundant of the chemical elements, constituting roughly 75% of the universe's elemental mass. Stars in the main sequence are mainly composed of hydrogen in its plasma state. Elemental hydrogen is relatively rare on Earth, and is industrially produced from hydrocarbons such as methane, after which most elemental hydrogen is used "captively" (meaning locally at the production site), with the largest markets about equally divided between fossil fuel upgrading (e.g., hydrocracking) and ammonia production (mostly for the fertilizer market). Hydrogen may be produced from water using the process of electrolysis, but this process is presently significantly more expensive commercially than hydrogen production from natural gas.

In refineries, hydrogen is produced as a by-product of naphtha reforming, and any supplemental hydrogen is produced from steam reforming of natural gas. The chemical industry also uses hydrogen, mostly to manufacture ammonia and other nitrogen-based fertilizers. Hydrogen for the chemical industry is also produced from steam reforming of natural gas, although some chemical plants use coal gasification (i.e., partial oxidation) to produce hydrogen. In total, about 95 percent of U.S. hydrogen production for supplemental refinery needs and the chemical industry is produced from natural gas using steam reforming technology.

Steam Reforming of Natural Gas

Steam reforming is a catalytic process that involves a reaction between natural gas or other light hydrocarbons and steam. The result is a mixture of hydrogen, carbon monoxide, carbon dioxide, and water that is produced in a series of three reactions:

The first reforming step catalytically reacts methane (the chief chemical constituent of natural gas) to form hydrogen and carbon monoxide in an endothermic (heat-absorbing) reaction.

The carbon monoxide is then "shifted" with steam to form additional hydrogen and carbon dioxide in an exothermic (heat-releasing) reaction.

The carbon dioxide and trace amounts of carbon monoxide are removed using one of several adsorption processes, leaving hydrogen separated for its commercial use.

Current Coal-Based Technology

Today, hydrogen is produced from coal by gasification and the subsequent processing of the resulting synthesis gas. This approach is currently used primarily to produce ammonia for fertilizer. At one plant, the Eastman Chemical Complex in Kingsport, Tennessee, the coal-derived synthesis gas is being converted to methanol for use as an intermediate for chemical production, but it could also be used as a hydrogen carrier for subsequent applications.

In its simplest form, coal gasification works by first reacting coal with oxygen and steam under high pressures and temperatures to form a synthesis gas consisting primarily of carbon monoxide and hydrogen. This synthesis gas is cleaned of virtually all of its impurities and shifted to produce additional hydrogen. The clean gas is sent to a separation system to recover hydrogen.

Cost - The Primary Hurdle

Although natural gas will likely provide the earliest affordable feedstock for hydrogen, today's costs are prohibitively expensive. The cost of producing and delivering hydrogen from a small scale reformer of natural gas for a fuel cell vehicle could be as high as $40 per million BTUs with today's technology. This would make hydrogen about four times as expensive as gasoline at the pump untaxed.

The Energy Department's Office of Fossil Energy, therefore, has begun a new effort to develop new technologies that can dramatically lower the cost of producing hydrogen from coal.