How diesel fuel is made

Diesel is the middle slice of crude oil, boiled off between kerosene and the heavy stuff, then scrubbed of sulfur.

stations: 5
things upstream: 11
raw sources: 6
steps from the ground: 5

The short version

Diesel is the part of crude oil that vaporizes at medium temperatures. It is drawn from the side of a distillation tower, treated with hydrogen to strip out sulfur, and blended with heavier or lighter streams to meet a standard for cold flow and ignition. Some biodiesel or additives may be mixed in.

Desalt and heat the crude

Crude is washed to remove salt and then heated in a furnace until most of it turns to vapor. The hot mixture feeds the base of the tower.

Goes in
Crude oil
Draw the middle cut

In the distillation tower, diesel condenses between kerosene above it and heavier gas oil below it. At normal pressure it boils off between 200 and 350 °C, and its molecules have 9 to 25 carbon atoms.

boils from 200 to 350 °C
Treat it with hydrogen

The cut meets hydrogen over a catalyst in a process called hydrodesulfurization. Sulfur is converted to a gas and removed, which produces ultra-low-sulfur diesel.

Goes in
Hydrogen
Blend to a standard

Blenders adjust the mix of streams, and sometimes biodiesel, to meet limits on cetane number, density, flash point and sulfur. Winter diesel is blended differently from summer diesel so that it keeps flowing in the cold.

Goes in
Biodiesel
Add additives and dispatch

Small doses of additives improve cold flow, lubricity and cleanliness. Tank trucks and pipelines take the finished fuel to depots.

End of the lineDiesel fuel Next it goes into locomotive.

Worth repeating

The diesel engine shown at the 1900 Paris Exposition ran on peanut oil instead of crude oil, with no modifications.
Diesel can also be made without petroleum, from sources such as biodiesel, biomass or natural gas.