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Petrochemical: Petroleum, LPG & CNG | Chemistry Class 11 - NEET PDF Download

Petroleum

It is a dark coloured oily liquid with an offensive odour, found at various depths in many regions below the earth’s surface. It is also called rock oil, mineral oil or crude oil. It is covered by an atmosphere of a gaseous mixture known as natural gas.

It contains mainly alkanes, cycloalkanes, aromatic hydrocarbons, sulphur, nitrogen and oxygen compounds.

When subjected to fractional distillation, it gives different fractions at different temperatures.

Petrochemical: Petroleum, LPG & CNG | Chemistry Class 11 - NEET
Petrochemical: Petroleum, LPG & CNG | Chemistry Class 11 - NEET
Petrochemical: Petroleum, LPG & CNG | Chemistry Class 11 - NEET
Petrochemical: Petroleum, LPG & CNG | Chemistry Class 11 - NEET
Petrochemical: Petroleum, LPG & CNG | Chemistry Class 11 - NEET


LPG (Liquified Petroleum gas):

It is a mixture of butane and isobutane with a small amount of propane. A strong foul smelling substance, called ethyl mercaptan (C2H5SH) is added to LPG cylinders, to help in the detection of gas leakage.

CNG (Compressed Natural Gas):

It consists mainly of methane (95%), which is a relatively unreactive hydrocarbon and makes its nearly complete combustion possible.

Artificial Methods for Manufacturing Petrol:

From higher alkanes, petrol or gasoline is obtained by cracking or pyrolysis.

From coal, petrol can be synthesised by following two processes :

(i) Bergius process:

Petrochemical: Petroleum, LPG & CNG | Chemistry Class 11 - NEET

(ii) Fischer- Tropsch process:

Petrochemical: Petroleum, LPG & CNG | Chemistry Class 11 - NEET

The best catalyst for this process is a mixture of CO, thoria, magnesia and kieselguhr.

The overall yield in this process is slightly higher than Bergius process.

Octane Number:

The quality of petrol is expressed in terms of octane number which is defined as the percentage of iso-octane by volume in a mixture of iso-octane and n-heptane which has the same antiknock properties as the fuel under test.

The octane number is 100 for iso-octane (2, 2, 4-trimethylpentane)

Natural gas has octane number 130.

TEL (tetraethyl lead) is used as antiknocking compound.

Octane number is increased by isomerisation, alkylation or aromatization.


Cetane Number:

Quality of diesel oils is measured in terms of cetane number which is defined as the percentage of cetane (hexadecane) by volume in a mixture of cetane and a-methyl naphthalene which has the same ignition property as fuel oil under similar experimental conditions.

It is 100 for cetane and 0 for α – methyl naphthalene.

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FAQs on Petrochemical: Petroleum, LPG & CNG - Chemistry Class 11 - NEET

1. What is the difference between petroleum, LPG, and CNG?
Ans. Petroleum, also known as crude oil, is a naturally occurring liquid found beneath the Earth's surface and is a major source of various fuels and petrochemicals. Liquefied Petroleum Gas (LPG) is a flammable hydrocarbon gas that is derived from petroleum and primarily used as fuel for heating and cooking. Compressed Natural Gas (CNG), on the other hand, is a natural gas that is compressed to a higher pressure and used as a fuel for vehicles.
2. How is petroleum refined into different products?
Ans. Petroleum refining involves a complex process called fractional distillation, where crude oil is heated and separated into various components based on their boiling points. These components include gasoline, diesel, jet fuel, heating oil, and other petrochemicals. Each component is further processed through additional refining processes to obtain the desired products.
3. What are the main uses of LPG?
Ans. LPG has a wide range of uses. It is commonly used as a fuel for cooking and heating in residential, commercial, and industrial settings. LPG is also used as a propellant in aerosol products, a refrigerant, and as an alternative fuel for vehicles. Additionally, LPG is utilized in the production of petrochemicals and as a feedstock for various chemical processes.
4. How does CNG compare to gasoline as a fuel for vehicles?
Ans. CNG is considered a cleaner fuel compared to gasoline as it emits lower levels of pollutants such as carbon monoxide, nitrogen oxides, and particulate matter. It also has a higher octane rating, which can result in improved engine performance. However, CNG requires specialized vehicles and refueling infrastructure, limiting its widespread adoption compared to gasoline.
5. What are the environmental benefits of utilizing LPG and CNG?
Ans. The use of LPG and CNG as fuels can lead to several environmental benefits. Both fuels produce fewer greenhouse gas emissions compared to traditional fuels like gasoline and diesel, contributing to lower levels of air pollution and reduced carbon footprint. Furthermore, the combustion of LPG and CNG produces fewer harmful pollutants, such as sulfur dioxide and particulate matter, resulting in improved air quality.
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