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CNG and LPG are two important gaseous fuels. Liquified Petroleum Gas is the abbreviation of LPG whereas CNG stands for Compressed Natural Gas.
- CNG is mainly methane compressed at a pressure of 200 to 248 bars.
- LPG is a combination of propane and butane liquefied at 15 °C and a pressure of 1.7 - 7.5 bar.
- CNG is cheaper and cleaner, but LPG has a higher calorific value.
- Natural Gas Distribution is easier over long distances via pipelines.
- LPG, on the other hand, is highly flammable as it is much heavier than air.
Read More: NCERT Solutions for class 11 Chemistry Hydrocarbons
Key Terms: CNG, LPG, Natural Gas, Greenhouse Effect, Calorific Value, Hydrocarbons, Chlorofluorocarbons, Fossil Fuels
What is CNG?
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CNG is generally a compressed form of pure methane gas. It is used to produce clean fuel without creating any pollution and it is almost clean to the atmosphere. Hence, Compressed Natural Gas is also called “clean fuel”. CNG is kept in hard containers at a pressure of around 20-25 MPa, which are in a cylinder or spherical shape.
- It burns quickly and is less pollutive, i.e. it creates a very less amount of greenhouse Effect compared to Fossil Fuel.
- Carbon emission produced by CNG is very small.
- As CNG is not toxic, it does not harm groundwater.
- Vehicles running on CNG fuels generate very less noise when compared to gasoline and other fuels such as diesel vehicles, thus reducing Noise Pollution.
- CNG is inflammable and does not possess a big risk for fire hazards.
Compressed Natural Gas
What is LPG?
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LPG is abbreviated as Liquefied Petroleum Gas.
- LPG is made up of light gaseous hydrocarbons like propane, butane, and some other light petroleum products.
- It is further transformed into a liquid by applying very high pressure.
- LPG production is done during oil refining.
- This gas is filled in cylindrical cylinders at very high pressure. Then it is transported, and stored, in an easy and safe manner.
Liquefied Petroleum Gas
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Difference Between CNG and LPG
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Here are the key differences between CNG and LPG:
| Parameters | Compressed Natural Gas (CNG) | Liquified Petroleum Gas (LPG) | |
|---|---|---|---|
| Fuel Components | The main component present in CNG is methane. | The main components present in LPG are propane and butane. | |
| Uses | Its main usage is as a fuel and is also used as an alternative for fuel in automobiles. | It can be used in heating and cooking in homes, and industrial and agricultural uses. | |
| Cost | It is less costly. | It is expensive comparatively. | |
| Calorific Value | CNG has a very low calorific value. | LPG has a higher calorific value, thus it burns at a much higher rate comparatively. | |
| Greenhouse Effect | Compressed natural gas has a very little greenhouse effect. | This fuel produces Carbon Dioxide which is a greenhouse gas, however, it is much cleaner as compared to gasoline. | |
| Sources | CNG is procured from oil wells, methane wells, coal wells, and other natural gas wells. | Its primary source is the extraction procedure of natural gas from the reservoir. | |
Advantages of CNG and LPG
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Important advantages of CNG and LPG are listed below:
- Gasoline-powered vehicles and CNG-powered automobiles are safe and most efficient.
- CNG is the cheapest, cleanest, and least harmful fuel gas for the environment.
- CNG is lighter than air, it is dissipated fastly and proportionately in the atmospheric air.
- Deposition of residual fumes and substances on the equipment is low resulting in a decrease in the maintenance price of the equipment and machinery.
- Chlorofluorocarbons have been replaced by LPG within various machinery such as refrigerators, thus freeing the Earth from chlorofluorocarbons which are the main reason for ozone depletion.
- Decentralized electricity can be produced from LPG in various areas by combining heat and power technologies (CHP).
Disadvantages of CNG and LPG
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Some notable disadvantages of CNG and LPG are listed below:
- The presence of methane gas burns quickly in air and has low ignition temperature so it imposes a risk of catching fire when the nozzle of the container is left open or any issue of leakage.
- CNG is accepted as a clean gas, but due to its volatile nature, it has not been useful as a cooking gas as it has a high ignition temperature (540°C) and a small range of ignition of 5 to 15%.
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Things to Remember
- LPG stands for Liquified Petroleum Gas whereas CNG stands for Compressed Natural Gas.
- CNG is primarily made up of Methane, while LPG is made up of propane.
- CNG is primarily used as an alternative fuel in automobiles.
- LPG is used for heating and cooking in homes and also has industrial and agricultural uses.
- CNG is relatively safe while LPG is highly flammable.
Previous Years’ Questions
- Which of the following alkane cannot be made in good yield… (NEET - 2020)
- The reagent 'X' used for the following reaction is… (KCET - 2018)
- In the following skew conformation of ethane… (JEE Main - 2019)
- Which of the following compounds is not aromatic… (JEE Main - 2019)
- Which among the following conformations is the most stable… (JKCET - 2019)
- Which of the following reactions is used for producing… (JKCET - 2019)
- With respect to the conformers of ethane, which of the… (NEET - 2017)
- target="_blank"The correct statement(s) for the following addition reactions… (JEE Advanced - 2017)
- In pyrrole, the electron density is maximum on… (NEET - 2016)
- Which of the following is aromatic compounds… (AMUEEE - 2016)
Sample Questions
Ques. What are the advantages of using CNG and LPG as fuels? (3 Marks)
Ans. The advantages of using Compressed Natural Gas (CNG) and Liquified Petroleum Gas (LPG) as fuels are as follows:
- They are easily transported and stored (by cylinders or pipelines).
- They are abundantly available.
- They are cost-efficient.
- They are very clean gases as they do not produce any smoke when burnt.
- They produce a huge amount of heat energy when burnt as compared to other fuels such as kerosene, coal, etc
Ques. State the benefits of CNG. (3 Marks)
Ans. The important benefits of CNG are as follows:
- Lower Maintenance Costs: As it does not contain benzene and lead, it helps in improving the durability of spark plugs.
- Economical: The cost of running automobiles on CNG is much less than the cost of running them on other types of fuel, like diesel and petrol.
- Less Pollution: It is great for the environment, as it does not contain elements such as lead and sulfur, which causes environmental pollution.
Ques. Which fuel is better CNG or LPG? (1 Mark)
Ans. CNG is better than LPG in terms of mileage, but its conversion expense is more than that of LPG. when we consider the performance, then LPG affects the engine performance at a minimum rate while CNG will deplete the power of the engine by 10%.
Ques. The main component of CNG is
(A) Butane
(B) Methane
(C) Hydrogen
(D) Coal Gas (2 Marks)
Ans. (B) Methane
Methane is the first member of the alkanes family. Methane is the primary component of CNG. CNG is a fuel that does not harm the environment therefore it is used in vehicles in place of petrol and diesel vehicles. It is stored at high temperatures.
Ques. L.P.G is liquefied petroleum gas which is a compound of butane and propane and used as:
(A) Cooking Fuel
(B) Motor Fuel
(C) Refrigeration
(D) All of these (2 Marks)
Ans. (D) All of these
Explanation: LPG is used in Gas-motor fuel, pyrolysis and cracking, and gas processes. It is also used in daily activities such as domestic consumption like heating and cooking, and refrigeration.
Ques. What is the physical state of Liquified Petroleum Gas when used as a fuel? (2 Marks)
Ans. Liquefied petroleum gas is stored in various containers such as tans and cylinders. It is stored in liquid vapor at an equilibrium state. For instance, LPG cylinders at home are supplied in a liquid LPG state. When an amount of open air is supplied, it generally turns back to gas form, which is then used as fuel in a gaseous state.
Ques. How is LPG produced? (3 Marks)
Ans. LPG is produced while oil refining or is collected during the natural gas production procedure. If you leave LPG, gas is emitted. In order to move the gas, LPG is to be kept under moderate pressure to form a liquid. It can then be processed for storing and transportation using LPG cylinders.
It is a flammable gas generally used in residential heating, cooking, and hot water systems. It is also used as a fuel in cars and also in industrial, agricultural, and manufacturing contexts. It is also useful as an engine fuel and in backup generators. Unlike other fuels like diesel, LPG can be kept in containers almost indefinitely without degradation.
Ques. How is CNG produced? Where is it used? (3 Marks)
Ans. Compressed natural gas is very eco-friendly and also a financial replacement for fuels such as petrol and diesel. It is obtained by compressing a gas, mostly methane (CH4), to a percentage less than 1% of its original volume i.e., the volume possessed by it at standard atmospheric pressure.
The uses of CNG are
- Motor Vehicles: A motor vehicle could be transformed into a dual fuel engine in a way that it can make use of both CNG with the cylinder and various fuels such as petrol or diesel to proceed. The price of CNG is almost half of that of petrol.
- Locomotives: Many locomotives work on CNG. Generally, CNG locomotives are converted from diesel-electric locomotives to make use of CNG as a generator in place of diesel to create electricity. CNG engines produce a higher fuel efficiency than diesel engines as they fire selectively when it is in need of power.
- Natural Gas Transport: Natural gas can be moved to distances by using seaway and CNG carrier ships, mainly when there is a lack of LNG or pipeline infrastructure.
Ques. What is the calorific value of CNG?
(A) 35 to 40 MJ/m3
(B) 350 to 400 MJ/m3
(C) 60 to 80 MJ/m3
(D) 65 to 70 MJ/m3 (1 Mark)
Ans. (A) 35 to 40 MJ/m3
Ques. Any substance that undergoes combustion is called:
(A) Fuel
(B) Combustible substance
(C) Both 1 and 2
(D) None of these (2 Marks)
Ans. (C) Both 1 and 2
Explanation: A substance is said to be combustible if it can burn in the presence of air. Fuel is a combustible substance that produces useful energy when undergoes combustion. There is a chemical change during combustion. Heat is produced when the substance reacts with oxygen.
Ques. Which of the following is not true for LPG?
(A) LPG is not cost-effective fuel when compared to CNG.
(B) The calorific value of LPG is 35 to 40 MJ/m3.
(C) Propane and butane are the constituent gasses in LPG.
(D) LPG is primarily produced during the extraction of natural gas. (1 Mark)
Ans. (B) The calorific value of LPG is 35 to 40 MJ/m3.
Explanation: Compared to CNG, LPG has a higher calorific value of 90 to 95 MJ/m3. 35 to 40 MJ/m3 is the calorific value of CNG.
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