ELi5: how do we get gasoline, kerosene, and diesel from the same crude oil?

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I get that there’s some sense of just letting it sit there and heating it up, but I don’t get it.

In: Chemistry

4 Answers

Anonymous 0 Comments

Crude oil is basically a mix out of different substances, that have different chemical characteristics. Crude Oil is not useable for most purposes, but the different pieces are. One of the attributes they are different in is the boiling point, so you can use heat to take them apart. But in the beginning, all of the fuels are mixed together.

Anonymous 0 Comments

They all have different boiling points so by controlling the temperatures inside the large distillation columns (the tall towers you see at refineries) you can separate them. The lighter components will boil off the top as vapor while the heavier ones stay in liquid at the bottom.

Anonymous 0 Comments

Crude oil is a mixture of a ton of different hydrocarbons (long chains of carbon atoms with hydrogens hanging off them). The very short hydrocarbons, methane/ethane/propane/butane, are gasses, and make up natural gas. The rest of them are liquid-ish at room temperature but they all boil at different temperatures. The longer the molecule, the higher the boiling point.

Gasoline, kerosene, and diesel are just different fractions of the crude oil. You heat the crude until most of it turns to gas and the slowly cool it in a big tower called a “distillation column”. The heaviest/longest molecules will condense out first (highest temperature), that’s the super heavy stuff like fuel oil. Diesel and kerosene are lighter and come out next. Gasoline is last and is the lightest/lowest boiling point. The crap left at the bottom that never evaporated is tar.

Anonymous 0 Comments

Crude oil is a mixture of all sorts of hydrocarbons organized in (among other things) chains. Longer chains are thicker, heavier fuels, whereas shorter chains are thinner and lighter fuels. You remove (through distillation, basically the same process as with alcohol but with *lots* of different chemicals being distilled out) different subsets of those hydrocarbon chains to get particular fuels.

Of note, though; kerosene, standard #2 diesel, and jet fuel are all pretty closely related to each other (to the degree that any diesel engine can absolutely run on jet fuel without any modifications, although it might throw a trouble code on your emissions system), and as a result the distillation process is largely the same. The big difference is in refining of the fuel after distillation.