In the producing phase what goes differently for diesel and petrol considering that both are produced from crude oil?
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Different ingredients in raw oil have different boiling points. So if you keep the mixture ad specific temperatures you can seperate the stuff based on their boiling points
It’s not that oil is *turned into* one or the other. Raw oil is like a box full of all sorts of rocks, some are tiny sand, some are pea-gravel, some are fist sized chunks of stone.
The producing process filters the rocks by size, the tiny sand would be things like methane, butane, propane; the pea-gravel is a mix of medium sized rocks which we call “petrol” but is mostly a similar sized rock called “octane”. Diesel fuel would be everything bigger than pea-gravel up to the fist sized rocks. If you had a few random massive rocks in the given box, those would be “fuel oil” or “bunker fuel” or even set aside as engine oil (lubricant) vs. a fuel source.
So the single box of “oil” gets broken down into the sub groups, so 1 box of oil might be 1/3 sand, 1/2 pea-gravel, and the remainder is fist sized.
The point being petrol and diesel are themselves composites, not a single sized ‘rock’, that are filtered down out of the larger mixture.
The ratio of petrol to diesel you get out of a single ‘box’ might vary by oil source.
Crude oil is a mixture of different hydrocarbons. All the way from methane to tar. But these have different boiling points. Methane is even a gas at room temperature while tar remain very solid at even high temperatures. So the oil refinery put the crude oil into a distillation column where it is heated to a boil at the bottom and then gradually cooled as it goes up the column. Heavy hydrocarbons will condense near the bottom while light hydrocarbons will get all the way to the top. The condensed hydrocarbons is then collected at different elevations in the column. Diesel will collect lower in the column, then parafin, and the next level up will be petrol.
Look up hydrotreating and you will understand.
Also, we don’t refine for gas or distillate, we refine for petroleum chemicals (petchems) they are literally in EVERYTHING in life, from plastic to medicines.
Don’t get me wrong, gas and disty and Jet and others happen because of refining but def not why we do it.
The replies about different hydrocarbons going to different products are generally correct but also keep in mind that apart form the mentioned physical treatment (distillation, or rectification), the separated crude oil fractions also undergo different stages of chemical treatment, the main of which is reforming. This process leads to increase of aromatics in the product which means higher octane rating. At the last stage, different additives are added to different final products as they are supposed to be used in slightly different circumstances.
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