Final answer:
Fractional distillation is used in oil refineries to separate crude oil into fractions based on hydrocarbon chain length, with lighter fractions condensing at the top and heavier ones at the bottom. Cracking and reforming further process these fractions to meet specific market demands. Finally, treatment ensures the purity of the final products.
Step-by-step explanation:
An oil refinery separates crude oil into different fractions through a process called fractional distillation. By heating crude oil at the base of a fractionating column, various components are vaporized and rise within the column. The components then condense at different levels depending on their boiling points, correlating to their hydrocarbon chain lengths. The lighter compounds with shorter chains, such as propane and butane, condense at the top of the column, while heavier compounds with longer chains, like lubricating oil and tar, are collected at the bottom.Additional processes like cracking and reforming are employed to transform less volatile fractions into more valuable mixtures. Cracking breaks down larger hydrocarbon molecules into smaller ones, thus converting heavy fractions into lighter ones such as gasoline. Reforming, on the other hand, converts straight-chain alkanes into branched-chain alkanes or aromatic hydrocarbons, often using metal catalysts like platinum. These processes help refineries meet the market demand for products like gasoline and jet fuel, which require precise compositions.