9.6 Separating crude oil
Refining is the process of separating crude oil into usable products. These useful products contain a group of hydrocarbon molecules that have similar chain lengths, similar boiling points, and condense over a range of temperatures. These groups of hydrocarbons are called fractions. This means that each useful fraction consists of a combination of different hydrocarbons that boil at a specific temperature. Oil refining takes place in a high- temperature fractionation tower, where the temperature at the top of the tower is colder than at the bottom of the tower (see figure). Crude oil is heated under high pressure in a furnace to a temperature of . The oil is then passed through a distillation column where vapour rises. As the hot vapour move up the tower, it condenses into different fractions according to the boiling point. Compounds with the highest boiling point condense near the bottom, compounds with the lowest boiling point at the top, and non- boiling compounds collect at the bottom (see Figure 9.1). Therefore, crude oil is divided into several fractions. Each fraction has its specific boiling range and composition. How many fractions are obtained?