Praxair Inc. said it will build a new hydrogen plant in Louisiana after signing a long-term supply contract with a major refinery in the area.

The industrial gas company, a subsidiary of Irish chemical giant Linde plc, said the new plant will start up in 2021 and be one of the largest hydrogen production units in the U.S. 

It is not clear where the plant will be located. Praxair said it will be integrated with the firm's "already extensive Louisiana production network via its Mississippi River Corridor hydrogen pipeline system." 

Hydrogen is used by petroleum refiners to produce transportation fuels and by chemical companies to make some specialty chemicals and intermediates. 

Praxair recently started a new carbon monoxide unit at is Geismar manufacturing site.