Which separation technique is routinely applied in the petroleum industry?

Step 1: Analyze the question The question asks which separation technique is routinely used in the petroleum (crude oil) industry.

Step 2: The concept Crude oil is a mixture of many hydrocarbons, each with a different boiling point. To separate them, refineries use fractional distillation. This technique separates liquids whose boiling points are close to one another, using a fractionating column.

Step 3: How it works

1. Crude oil is heated in a furnace until it vaporizes.
2. The vapor enters the fractionating column, which is hotter at the bottom and cooler at the top.
3. As the vapors rise, each hydrocarbon condenses at the level where the temperature matches its boiling point.
4. The fractions are collected at different levels: • Top (lowest boiling point): refinery gas, petrol (gasoline) • Middle: kerosene, diesel (gas oil) • Bottom (highest boiling point): lubricating oil, fuel oil, bitumen

Step 4: Evaluate the options

• A. Chromatography: used for separating small amounts of dissolved substances such as dyes and pigments. It is not used for bulk refining.
• B. Distillation: this is simple distillation, which separates a liquid from a dissolved solid or from liquids with widely different boiling points. It is not precise enough for crude oil.
• C. Evaporation: used to recover a dissolved solid from a solution, as in salt production.
• D. Fractional crystallization: separates solids by differences in solubility.
• E. Fractional distillation: separates crude oil into its fractions, so this is correct.

Note on option B: Fractional distillation is a type of distillation, so B is not completely wrong. But the question asks for the technique used in the petroleum industry, and the specific answer is fractional distillation.

Exam tip: Remember the link "Petroleum → Fractional distillation," and also "Liquid air → Fractional distillation" and "Ethanol from fermented liquid → Fractional distillation." Whenever a mixture of liquids has close boiling points, think fractional distillation.