Hydrogen: From Gray to Green

Hydrogen is poised to play a significant role in the search for a “clean” and secure energy source, since it offers the advantage of producing no carbon dioxide upon combustion. The process currently used to produce the bulk of the hydrogen, steam methane reforming (SMR), however, does produce carbon dioxide. SMR uses fossil fuels and the resulting hydrogen is called “gray hydrogen.”While work is progressing to make “green hydrogen” from water via electrolysis using renewable energy sources, much focus is also being given to reduce the amount of carbon dioxide resulting from the SMR process, for example by using carbon capture. Hydrogen produced this way is termed “blue” hydrogen. Alternative processes for producing hydrogen are also being studied, such as producing “turquoise hydrogen” via methane pyrolysis.With the increasing activity in the area of hydrogen production, Chemical Engineering set out to cover different aspects of the work in several articles to keep our readers abreast of the latest technological advances in various routes toward greener hydrogen production. The four articles presented here focus on advances in green, gray and turquoise hydrogen production processes.