Production of Hydrogen as a Byproduct

Flydrogen-containing gases (refinery gas) are formed in large quantities as a byproduct in the processing of crude oil in refineries by cyclization and aromatization e.g. by catalytic reforming. 

This hydrogen is, however, mostly used in house. Hydrogen is also produced in other petrochemical and chemical processes (synthesis of olefins, ethyne, styrene, acetone). Coke oven gas contains over 50 volume % of hydrogen, from which it can be isolated. Finally hydrogen occurs as a valuable byproduct in chloralkali-electrolysis (directly with the diaphragm process or indirectly with the amalgam process and hydrochloric acid hydrolysis) see Section 1.7.3.3. The electrolysis processes account for less than 5% of the worldwide production of hydrogen. 

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