distillate

"What exactly is distillate?

: Distillate is simply the left over parts of crude oil after the more popular fractions have been distilled out! Hence the name.....
: : Basically, you'd take the crude oil and heat it in a still. The different hyrdocarbons in the crude mix will distill out in order of their complexity.
: : Methane (one), Butane (two), Propane (three), etc. All come out in order as gas and are sent to storage facilities at the well sites (usually). The crude oil is a mix of all of the liquid (at normal temperatures) HC chains. If you heat it up, the liquids turn into gas, with the lighter ones boiling off first, followed in succession by the heavier ones. The crude oil in the still will settle out at temperature points, which tells you what fraction is boiling off currently.
: : Now, since you want reasonably pure Gasolene, Kerosene, diesel, etc. you have a point where the liquid in the still is ramping to the next temperature point; you need to dump the output during the ramping into a different container. Once the temp. stabilizes at the next point, you switch the output to the pipes leading to the specific storage tanks (gas, kero, etc.)
: : So, when you're done with this process you have a number of tanks containing specific grades of fuels, and an extra tank containing a mixture of all of the fuels. This extra mixed fuel was referred to as distillate!
: : Now, you wonder where you can get it today? You can't! It hasn't existed since 1943! you see, the oil refining process was forever changed as a result of the Second World War!
: : A process for making a barrel of crude oil into a barrel of gasolene was needed to fuel the war effort. The distillation process was replaced by the cracking process.
: : Cracking involves a catalytic process whereby all of the HC chains in the crude are split in to single HC molecules. Then, these molecules are recombined into the required HC chains necessary to produce a specific fuel (Gasolene, Kerosene, Diesel, etc)."

I think it's a bit more complicated than that, or maybe just a lot of confusion in terms.. First off every fuel we're accustomed to burning is broadly called a distillate - from propane to heating oil.

Also, it all stil starts with distillation of crude, the various types of cracking are used to extract the last bit of every possible fuel, as this diagram shows.

If anyone is interested in a description of the process, Chevron has a decent one on the link below.

• Refining crude oil