Our modern economy runs on fossil fuels, and there are many steps between pulling oil out of the ground and having a refined product that can be sold to consumers. Fossil fuel refineries are factories, turning crude oil into the feedstocks for gasoline and plastics. Refineries, because of the large capital investment, have to run nearly continuously.
The first step in refining is to boil the crude oil. Different components of crude oil have different melting and boiling points, and by carefully regulating the temperature, you can have some components boil off while others remain liquid. The process involves moving oil through a pipeline that runs over heat sources that are carefully monitored with the oil flowing at a specific rate.
The vapors from different parts of crude oil are captured in distillation columns, where they're left to condense. The temperature of the boil-off process and the height (and temperature regulation) of the distillation columns allow the components to be separated by weight. Liquid natural gas and gasoline are the lightest, with kerosene and diesel oil about medium weight and lubricating oil and waxes the heaviest. At the end of the process are oil tar and sulfur compounds to be disposed of.
Each of the distillates of oil generally needs some amount of processing before it becomes a commercially usable product. That process is called cracking, and it uses high heat and pressure to break down larger hydrocarbon molecules into smaller ones. The tools that perform the cracking process are called reactors.
One of the primary cracking processes is catalytic cracking, in which very high temperatures, a low-pressure environment and a catalyst are introduced into the stream of distillate. This breaks down molecules that would be too large into smaller gasoline molecules and allows the conversion of heavier distillates into more commercially valuable gasoline.
This is a similar process to catalytic cracking but uses significantly higher pressure vessels, a somewhat lower temperature and introduces hydrogen to the product. This induces the heavier hydrocarbon molecules to split, and it is cheaper in large volumes than catalytic cracking, though the higher pressure vessel increases the upfront capital costs of the unit.
Alkylation is a post-cracking chemical process that turns byproducts of a cracking process into gasoline, extracting more fuel out of the refining process. Other processes include hydrogen forcing, which is used to break sulfur bonds in the oil products and replace them with hydrogen to make them burn cleanly. One of the benefits of hydrogen cracking is that it combines this step with the cracking process. Once all processing is done, the various elements are combined to make commercial gasoline in standardized grades and mixes.
