Extraction of various substances by partial distillation in an oil refinery

In an oil refinery, fractional distillation is the primary method used to separate crude oil into its various components (fractions). This process relies on the differences in boiling points of the hydrocarbons present in the crude oil. Each fraction contains a mixture of hydrocarbons that have similar boiling points.

Process of Fractional Distillation in an Oil Refinery

1. Heating: Crude oil is heated in a furnace to a high temperature (around 350-400°C). This causes the crude oil to partially vaporize.
2. Entering the Distillation Column: The heated mixture is then fed into a distillation column, which is a tall, vertical column filled with trays or packing material.
3. Separation by Boiling Points: As the vapor rises through the column, the temperature decreases. Components with higher boiling points condense at lower levels in the column, while those with lower boiling points continue to rise.
4. Collection of Fractions: Different fractions are collected at various heights of the column. Each fraction contains hydrocarbons with similar boiling points.

Main Fractions Obtained from Crude Oil

1. Refinery Gas: Collected at the top of the column, this fraction contains methane, ethane, propane, and butane. It is used as fuel gas and feedstock for petrochemical processes.
2. Gasoline (Petrol): Collected just below the refinery gases, gasoline is used as fuel for internal combustion engines.
3. Naphtha: This fraction is used as a feedstock for the production of chemicals and plastics.
4. Kerosene: Used as jet fuel and in domestic heating.
5. Diesel Oil: Used as fuel for diesel engines and heating oil.
6. Lubricating Oil: Used for lubricants and as a base for various industrial products.
7. Fuel Oil: Used in ships and industrial heating.
8. Residuum (Residue): The heavy fraction collected at the bottom, used for asphalt, tar, and as feedstock for further processing.

Detailed Illustration of a Fractional Distillation Column

+---------------------------+
|          Refinery         |
|            Gas            |
|  (Methane, Ethane, etc.)  |
|                           |
|          Gasoline         |
|  (Petrol for engines)     |
|                           |
|          Naphtha          |
|  (Petrochemical feedstock)|
|                           |
|         Kerosene          |
|  (Jet fuel, heating)      |
|                           |
|        Diesel Oil         |
|  (Diesel engines, heating)|
|                           |
|      Lubricating Oil      |
|  (Lubricants, industrial) |
|                           |
|         Fuel Oil          |
|  (Ships, industrial)      |
|                           |
|         Residuum          |
|  (Asphalt, tar)           |
+---------------------------+

Steps in the Distillation Column

1. Crude Oil Heating: Crude oil is pre-heated in a furnace.
2. Entry into Column: The heated crude oil enters the distillation column.
3. Vapor Ascent: As the vapor rises, it cools and the components with higher boiling points condense on trays or packing material.
4. Fraction Collection: Different fractions are drawn off at various heights where they condense.

Additional Processes

In addition to fractional distillation, refineries use other processes to further refine and convert fractions into more valuable products:

1. Cracking: Breaking down larger molecules into smaller ones (e.g., converting heavy oil into gasoline and diesel).
2. Reforming: Rearranging molecular structures to improve the quality of gasoline.
3. Hydrotreating: Removing sulfur and other contaminants to produce cleaner fuels.

Summary

Fractional distillation in an oil refinery is a sophisticated process that efficiently separates crude oil into various useful components based on their boiling points. Each fraction has distinct applications, from fuels to petrochemical feedstocks, making this process essential in the petroleum industry.