11.1 Fossil Fuel

• Fossil fuels are the remains of plants and animals from ancient times, found underground. These include coals, natural gases, and petroleum. The remains of these organisms have been discovered as fossils, buried deep under the ground. Fossil fuels are formed from ancient plants, animals, and aquatic organisms (like phytoplankton and zooplankton) that lived hundreds of millions of years ago.

• Formation Process:

• In ancient times, the Earth had forests, marshy lands, and seas filled with aquatic plants and animals. These organisms, including tiny fungi (phytoplankton) and small water creatures (zooplankton), were buried due to natural disasters.

• Over time, as they became deeper under the ground, pressure and temperature increased. In the absence of air, these remains decayed and underwent chemical changes, gradually forming fossil fuels.

• Coals formed from large plants, and petroleum formed from smaller organisms like phytoplankton, zooplankton, and dead animals. As the process continued, petroleum transformed into natural gas.

• Some areas have both petroleum and natural gas, like the Haripur Gas Field in Bangladesh. The primary elements of fossil fuels are carbon and carbon compounds.

11.1.1 Natural Gas

• The composition of natural gas varies based on its natural source.

• The main component is Methane (80%), followed by Ethane (7%), Propane (6%), Butane and Isobutene (4%), and Pentane (3%).

• In Bangladesh, the natural gas discovered contains 95-99% Methane.

11.1.2 Constituents of Petroleum and their Separation

• Petroleum is typically found deep underground, around 5000 feet or more, often accompanied by natural gas. The natural gas exerts pressure on petroleum, helping it rise when a well is dug.

• The petroleum extracted from the well is called Crude Oil, which is opaque and may have a foul odor due to sulfur compounds. Crude oil is a mixture of various hydrocarbons and isn’t directly usable.

Separation of Crude Oil:

• Crude oil is separated through a process called Fractional Distillation, which separates it based on different boiling points. This method uses a column with sections for condensation of vapor.

• Fractional Distillation works by vaporizing the crude oil through heating, where it moves up the column. Components of the liquid, based on their boiling points, separate into different sections. The higher the section in the column, the lower the temperature.

Components of Crude Oil from Fractional Distillation:

1. Petroleum Gas:

• Boiling Point: 0°C to 20°C.

• Carbon Range: 1 to 4 carbons in the molecule.

• Uses: Converted to Liquefied Petroleum Gas (LPG) by applying pressure. Used for heating, cooking, and other applications.

2. Petrol (Gasoline):

• Boiling Point: 21°C to 70°C.

• Carbon Range: 5 to 10 carbons in the molecule.

• Uses: Fuel for vehicle engines.

3. Naphtha:

• Boiling Point: 71°C to 120°C.

• Carbon Range: 7 to 14 carbons in the molecule.

• Uses: Fuel and a base for producing chemicals in the petrochemical industry.

4. Kerosene:

• Boiling Point: 121°C to 170°C.

• Carbon Range: 10 to 16 carbons in the molecule.

• Uses: Fuel for jet engines.

5. Diesel:

• Boiling Point: 171°C to 270°C.

• Carbon Range: 17 to 20 carbons in the molecule.

• Uses: Fuel for vehicles, lubricant, and solvent.

6. Paraffin Wax:

• Boiling Point: 271°C to 340°C.

• Carbon Range: 20 to 30 carbons in the molecule.

• Uses: Used in producing toiletries and Vaseline.

7. Pitch:

• Boiling Point: Above 340°C.

• Carbon Range: More than 30 carbons in the molecule.

• Uses: Used in road construction.