Question

simple and fractional distillation
2. briefly explain the principle of fractional distillation and show how this technique has been applied in refining oil

Answer 1

Distillation is a widely used method for separating mixtures based on differences in the conditions required to change the phase of components of the mixture. To separate a mixture of liquids, the liquid can be heated to force components, which have different boiling points, into the gas phase.

Simple Distillation
Simple distillation may be used when the boiling points of two liquids are significantly different from each other or to separate liquids from solids or nonvolatile components. In simple distillation, a mixture is heated to change the most volatile component from a liquid into vapor. The vapor rises and passes into a condenser. Usually, the condenser is cooled (e.g., by running cold water around it) to promote condensation of the vapor, which is collected.

Fractional Distillation
Fractional distillation is a process by which components in a chemical mixture are separated into different parts (called fractions) according to their different boiling points. Fractional distillation is used to purify chemicals and also to separate mixtures to obtain their components.It's used as a lab technique and in industry, where the process has vast commercial significance.The chemical and petroleum industry rely on fractional distillation.

How Fractional Distillation Works
Vapors from a boiling solution are passed along a tall column, called a fractionating column. The column is packed with plastic or glass beads to improve the separation by providing more surface area for condensation and evaporation. The temperature of the column gradually decreases along its length. Components with a higher boiling point condense on the column and return to the solution; components with a lower boiling point (more volatile) pass through the column and are collected near the top. Theoretically, having more beads or plates improves the separation, but adding plates also increases the time and energy required to complete a distillation.

Difference between the fraction, fractional distillation

	Simple Distillation	Fractional Distillation
Uses	Used for separating relatively pure liquids that have large boiling point differences. Also useful for separating liquids from solid impurities.	Used to isolate components of complex mixtures with small boiling point differences.
Advantages	faster requires less energy input simpler, less expensive equipment	results in better separation of liquids better at purifying liquids containing many different components
Disadvantages	only useful for relatively pure liquids requires a large boiling point difference between components doesn't separate fractions as cleanly	slower requires more energy more complicated and expensive set-up

The oil refining process: fractional distillation
Crude oil (also called petroleum) is a mixture of different hydrocarbons. Many useful products can be made from
these hydrocarbons. But first the useful ones must be extracted from the crude oil and separated from one another.
How is this done?
The different hydrocarbon components of crude oil are called fractions. The fractions are separated from one another
using a process called fractional distillation. This process is based on the principle that different substances boil at
different temperatures. For example, crude oil contains kerosene and naphtha, which are useful fractions (naphtha
is made into petrol for cars, and kerosene is made into jet fuel). When you evaporate the mixture of kerosene and
naphtha, and then cool it, the kerosene condenses at a higher temperature than the naphtha. As the mixture cools,
the kerosene condenses first, and the naphtha condenses later.
This is how fractional distillation works. The main equipment is a tall cylinder called a fractionator (or fractional
distillation column). Inside this column there are many trays, or horizontal plates, all located at different heights.
Each tray collects a different fraction when it cools to its own boiling point and condenses.
The crude oil is heated to at least 350°C, which makes most of the oil evaporate. The fluid then enters the column.
As the vapour moves up through the fractionator, each fraction cools and condenses at a different temperature. As
each fraction condenses, the liquid is collected in the trays. Substances with higher boiling points condense on the
lower trays in the column. Substances with lower boiling points condense on the higher trays.
The trays have valves, which allow the vapour to bubble through the liquid in the tray. This helps the vapour to cool
and condense more quickly. The liquid from each tray then flows out of the column.

Answer 2

Fractional Distillation: Principle & Application in Oil Refining

1. Principle of Fractional Distillation

Fractional distillation separates a mixture of liquids based on their boiling points (BPs) using a fractionating column. Key steps:

• The mixture is heated, and vapors rise into the column.

• The column contains trays/plates where vapors condense and re-evaporate repeatedly.

• Compounds with lower BPs (more volatile) rise higher, while higher BP components condense lower down.

• Each fraction (group of similar BP compounds) is collected separately.

Why better than simple distillation?

• Simple distillation only separates liquids with large BP differences (e.g., water vs. ethanol).

• Fractional distillation refines complex mixtures (e.g., crude oil) with close BPs.

• 
  

---

2. Application in Oil Refining

Crude oil is a mix of hydrocarbons (chains of C and H) with varying BPs. Fractional distillation in a refinery tower splits it into useful fractions:

Fraction	Carbon Atoms	Boiling Range (°C)	Uses
Gases	C1–C4	< 30	LPG, propane, butane
Gasoline	C5–C10	30–200	Fuel for cars
Kerosene	C10–C16	200–300	Jet fuel, heating oil
Diesel	C15–C20	250–350	Trucks, generators
Lubricating Oil	C20–C50	300–500	Engine oil, grease
Residue	>C50	>500	Asphalt, tar

Process Summary:

1. Crude oil is heated to ~400°C, vaporizing most components.

2. Vapors enter the fractionating column, cooling as they rise.

3. Each fraction condenses at its BP level and is piped out.