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Why does hydrocracking use hydrogen at high pressure?

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Aerial view of an oil refinery complex near New Orleans, Louisiana, with storage tanks, industrial structures, and smoke rising from the facility, surrounded by open land. — petroleum refining Aerial view of an oil refinery near New Orleans.

In petroleum refining, hydrocracking utilizes high pressure—typically ranging from 55 to 170 bars (800 to 2,500 psi)—to facilitate the chemical reaction between hydrogen gas and heavy hydrocarbon molecules.1

The primary purpose of using hydrogen at these elevated pressures is to improve the hydrogen-to-carbon ratio in the cracked molecules. By introducing hydrogen under high pressure, the process can effectively convert heavy gas oils and distillation residues into higher-quality, lighter products such as gasoline, kerosene, and diesel fuel. This high-pressure environment, combined with the use of specific hydrogenation catalysts (such as nickel, tungsten, platinum, or palladium), allows for greater flexibility in product yields and produces high-quality, low-sulfur distillates that often require no further processing.21