Air gases - principally oxygen, nitrogen and argon, but also in some of the larger plants krypton, xenon or neon - are generally produced to high purity specification in cryogenic (low temperature) plants. The products can be in either gaseous or liquid form. Adsorption technology, by pressure swing or membrane are other technologies used to produce oxygen and nitrogen, generally at slightly lower purities.
These plants are generally sited close to large customers. Nevertheless, the network of transmission pipelines in Europe through which the product is supplied stretches for 5,000 kilometres.
Other gases such as hydrogen and carbon monoxide are manufactured by steam reforming of natural gas or from hydrocarbon feed-stocks, and purified by cryogenic or adsorption technologies. Both are supplied in gaseous form; hydrogen can also be liquefied in a separate cryogenic plant.
Carbon dioxide is manufactured by taking feedstock from the reforming process, from other chemical or combustion processes or from natural wells removing unwanted impurities, and then liquefying it in an industrial refrigeration plant. It can be supplied in gaseous, liquid or solid ("dry ice") forms.
Other industrial gaseses are produced in special installations, and are supplied in pure form or as mixtures with other gases.