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Difficulty: HardIndustrial Applications of Separation Methods

In a petroleum refinery's fractionating tower, crude oil is separated into different fractions based on boiling points. Considering four fractions—gasoline (boiling range 40∘C−170∘C40^\circ\text{C} - 170^\circ\text{C}), kerosene (boiling range 170∘C−250∘C170^\circ\text{C} - 250^\circ\text{C}), gas oil (boiling range 250∘C−350∘C250^\circ\text{C} - 350^\circ\text{C}), and lubricating oil (boiling range >350∘C> 350^\circ\text{C})—which of the following correctly lists these fractions in order of their collection from the bottom to the top of the fractionating column?

  1. Lubricating oil, gas oil, kerosene, gasolineAnswer
  2. B
    Gasoline, kerosene, gas oil, lubricating oil
  3. C
    Gasoline, gas oil, kerosene, lubricating oil
  4. D
    Lubricating oil, kerosene, gas oil, gasoline

Answer

Lubricating oil, gas oil, kerosene, gasoline
In industrial petroleum refining, the fractionating tower operates on a temperature gradient where the bottom is hottest and the top is coolest. Hydrocarbons with high boiling points (like lubricating oil) condense near the bottom where temperatures remain high. Hydrocarbons with progressively lower boiling points (gas oil, kerosene, gasoline) rise higher in the column before reaching their condensation temperatures. Thus, the order from bottom to top is lubricating oil, gas oil, kerosene, gasoline.

Step-by-Step Solution

1
Analyze the temperature gradient in an industrial fractionating column
The bottom of the column is kept at the highest temperature, while the top of the column is the coolest.
Vapors rise through the column and condense when the surrounding temperature drops to their respective boiling points.
2
Correlate fraction boiling points with condensation height
Higher boiling fractions condense lower in the column (near the bottom), whereas lower boiling fractions remain gaseous longer and condense higher up (near the top).
Substances with high boiling points require higher temperatures to remain in the vapor phase.
3
Arrange the given fractions from highest boiling point to lowest boiling point
Lubricating oil (>350∘C> 350^\circ\text{C}) →\rightarrow Gas oil (250∘C−350∘C250^\circ\text{C} - 350^\circ\text{C}) →\rightarrow Kerosene (170∘C−250∘C170^\circ\text{C} - 250^\circ\text{C}) →\rightarrow Gasoline (40∘C−170∘C40^\circ\text{C} - 170^\circ\text{C}).
This sequence matches bottom-to-top collection in the fractionating tower.

Key Concept

Industrial Fractional Distillation of Petroleum
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Topics

Industrial Applications of Separation Methods