Natural Gas Reforming

Photo of Petroleum Refinery

Although today most hydrogen is produced from natural gas, the Fuel Cell Technologies Office is exploring a variety of ways to produce hydrogen from renewable resources.

Natural gas reforming is an advanced and mature production process that builds upon the existing natural gas pipeline delivery infrastructure. Today, 95% of the hydrogen produced in the United States is made by natural gas reforming in large central plants. This technology is an important pathway for near-term hydrogen production.

How Does It Work?

Natural gas contains methane (CH4) that can be used to produce hydrogen with thermal processes, such as steam-methane reformation and partial oxidation.

Steam-Methane Reforming

Most hydrogen produced today in the United States is made via steam-methane reforming, a mature production process in which high-temperature steam (700°C–1,000°C) is used to produce hydrogen from a methane source, such as natural gas. In steam-methane reforming, methane reacts with steam under 3–25 bar pressure (1 bar = 14.5 psi) in the presence of a catalyst to produce hydrogen, carbon monoxide, and a relatively small amount of carbon dioxide. Steam reforming is endothermic—that is, heat must be supplied to the process for the reaction to proceed.

Subsequently, in what is called the "water-gas shift reaction," the carbon monoxide and steam are reacted using a catalyst to produce carbon dioxide and more hydrogen. In a final process step called "pressure-swing adsorption," carbon dioxide and other impurities are removed from the gas stream, leaving essentially pure hydrogen. Steam reforming can also be used to produce hydrogen from other fuels, such as ethanol, propane, or even gasoline.

Steam-Methane Reforming Reaction
CH4 + H2O (+heat) → CO + 3H2

Water-Gas Shift Reaction
CO + H2O → CO2 + H2 (+small amount of heat)

Partial Oxidation

In partial oxidation, the methane and other hydrocarbons in natural gas react with a limited amount of oxygen (typically from air) that is not enough to completely oxidize the hydrocarbons to carbon dioxide and water. With less than the stoichiometric amount of oxygen available, the reaction products contain primarily hydrogen and carbon monoxide (and nitrogen, if the reaction is carried out with air rather than pure oxygen), and a relatively small amount of carbon dioxide and other compounds. Subsequently, in a water-gas shift reaction, the carbon monoxide reacts with water to form carbon dioxide and more hydrogen.

Partial oxidation is an exothermic process—it gives off heat. The process is, typically, much faster than steam reforming and requires a smaller reactor vessel. As can be seen in chemical reactions of partial oxidation, this process initially produces less hydrogen per unit of the input fuel than is obtained by steam reforming of the same fuel.

Partial Oxidation of Methane Reaction
CH4 + ½O2 → CO + 2H2 (+heat)

Water-Gas Shift Reaction
CO + H2O → CO2 + H2 (+small amount of heat)

Why Is This Technology Being Considered?

Reforming low-cost natural gas to produce hydrogen can provide the commercial hydrogen production capacity needed to support a full fleet of fuel cell electric vehicles (FCEVs). Over the long term, DOE expects that hydrogen production from natural gas will be augmented with production from renewable, nuclear, coal (with carbon capture and storage), and other low-carbon, domestic energy resources.

Greenhouse gas emissions are lower than gasoline-powered internal-combustion engine (ICE) vehicles. Producing hydrogen from natural gas does result in the emission of greenhouse gases, as shown in the chemical reactions above. When compared to ICE vehicles using gasoline, however, FCEVs using hydrogen produced from natural gas reduce greenhouse gas emissions.