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How does hydrotreating remove sulfur and nitrogen compounds from petroleum products?

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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.

Hydrotreating is the primary chemical engineering process used to remove sulfur and nitrogen impurities from petroleum products. The process involves combining the oil with high-purity hydrogen and vaporizing the mixture. This vapor is then passed over a catalyst, typically composed of tungsten, nickel, or a mixture of cobalt and molybdenum oxides on an alumina base.1

The reaction occurs at temperatures ranging from 260 to 425 °C (500 to 800 °F) and pressures between 14 and 70 bars (200 to 1,000 psi). During this process, sulfur compounds are converted into hydrogen sulfide, while nitrogen compounds are converted into ammonia.1

Following the reaction, the hydrogen sulfide is separated from the hydrogen stream by absorption in a solution, such as diethanolamine, which can be regenerated for reuse. The recovered hydrogen sulfide is often used to manufacture high-purity elemental sulfur, while the ammonia is either processed into fertilizers, burned as fuel, or converted into elemental nitrogen and hydrogen. This purification is essential, as nitrogen compounds can poison refinery catalysts and sulfur compounds contribute to engine corrosion and harmful emissions.12