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In coking units and visbreaker units, heavy feedstocks are converted to petroleum coke, oil, light hydrocarbons (benzene, naphtha, liquefied petroleum gas), and gas (Chapter 14). Depending on the process, hydrogen is present in a wide range of concentrations. Because petroleum processes need gas for heating purposes, adsorption processes are best suited to recover the hydrogen because they feature a very clean hydrogen product and an offgas suitable as fuel.