Hydrogen production is the family of industrial methods for generating hydrogen. Hydrogen is primarily produced by steam reforming of natural gas. Other major sources include naphtha or oil reforming of refinery or other industrial off-gases, and partial oxidation of coal and other hydrocarbons. A small amount is obtained by water electrolysis and other sources.Steam-methane reforming is a mature production process in which high-temperature steam (700°C–1,000°C) is used to produce hydrogen from natural gas. Methane reacts with steam under 3–25 bar pressure in the presence of a catalyst to produce hydrogen, carbon monoxide, and a relatively small amount of carbon dioxide. For steam reforming to proceed, heat must be supplied to the process. In a separate reactor vessel, 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 coal and oil products.
There are no natural hydrogen deposits, but hydrogen is required for essential chemical processes. Therefore, the production of hydrogen plays a key role in any industrialized society. The hydrogen generation market is expected to be valued at $115.25 billion USD in 2017. Millions of tons of hydrogen were consumed on-site in oil refining, and in the production of ammonia (Haber process) and methanol (reduction of carbon monoxide). Hydrogen is also produced as a by-product of the chlor-alkali process.As of 1999, the majority of hydrogen (∼95%) is produced from fossil fuels by steam reforming or partial oxidation of methane and coal gasification with only a small quantity by other routes such as biomass gasification or electrolysis of water. Around 8GW of electrolysis capacity is installed
worldwide, accounting for around 4% of global hydrogen production. Developing affordable methods for producing hydrogen with less damage to the environment is a goal of the hydrogen economy. Electrolysis of water using electricity produced from fossil fuels emits significant amounts of CO2.