What Is Liquefied Petroleum Gas Definition Composition and Applications
Liquefied petroleum gas (LPG), which is also known as LP gas, is any of multiple liquid mixtures of the volatile hydrocarbons propane, propene, butane, and butene. It was used from the early 1860s as a portable fuel source, and the production and consumption of this gas for both industrial and domestic use have expanded ever since. A typical commercial mixture can also contain ethylene and ethane, and a volatile mercaptan as well, which is an odorant added as a safety precaution.
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About LPG
Liquefied petroleum gas - LPG is recovered from the “wet” natural gas (the gas with the compounds of condensable heavy petroleum) by absorption. The recovered product has a low boiling point and should be distilled to remove the lighter fractions, and then it is treated to remove carbon dioxide, hydrogen sulfide, and water. The resultant product can be transported by pipeline and by building seagoing tankers, especially. Transportation by rail, barge, and truck has also developed, specifically in the United States.
LPG reaches the domestic consumers in cylinders at relatively low pressures. The largest part of the LPG, which is produced, can be used in the central heating systems, and the next largest one as a raw material for chemical plants. Commonly, LPG can be used as fuel for gas cooktops and ovens, gas barbecue grills, portable heaters, and gas fireplaces. LPG water heaters are common in Europe. It is also used as backup generators and engine fuel. Unlike diesel, LPG is stored nearly indefinitely without any degradation.
Global Production
In 2015, the Global LPG production reached over 292 million metric tons per year, while global LPG consumption rose to around 284 mn t per year. 62% of the LPG is extracted from the natural gas, where the rest can be produced by the petrochemical refineries from crude oil. 44% of global consumption is present in the domestic sector. The leading producer and exporter of LPG are the USA.
Security of Supply
Due to the oil-refining and natural gas industry, Europe is considered as almost self-sufficient in LPG. The security of supply in Europe is further safeguarded by:
a wide range of sources, which are both inside and outside of Europe;
a flexible supply chain through rail, road, and water with a number of routes and entry points into Europe
As per 2010–12 estimates, the proven world reserves of the natural gas, from which the major amount of LPG is derived, stand at 300 trillion cubic meters (which is 10,600 trillion cubic feet). Added to the LPG, which is derived from the cracking crude oil, these amounts subject to a major energy source which is untapped virtually and has massive potential. The production continues to grow at an average rate of 2.2%, annually, and virtually assuring that there is no demand outstripping supply risk in the foreseeable future.
Comparison with Natural Gas
LPG-based SNG can be used in the emergency backup systems for several industrial, public, and military installations and several other utilities use LPG peak shaving plants in times of high demand to make up shortages in the natural gas, which is supplied to their distributed systems. LPG-SNG installations can also be used during the initial gas system introductions when the distribution infrastructure present in the place before gas supplies are connected. Developing Indian and China markets (among others) use LPG-SNG systems to build up the customer bases before expanding the existing natural gas systems.
Natural gas or the LPG-based SNG with localised storage and the piping distribution network to the households for catering to every cluster of 5000 domestic consumers is planned under the first phase of the city gas network system. This would eliminate the last mile of LPG cylinders road transport, which is a cause of safety and traffic hurdles in the Indian cities. However, these localised natural gas networks are operating successfully in Japan with the feasibility to get connected to a wider network in both cities and villages.
Environmental Effects
Let us discuss the Environmental effects of LPG.
Commercially available Liquid Petroleum Gas (LPG), is currently derived primarily from fossil fuels. Also, LPG burning releases carbon dioxide, which is a greenhouse gas. The reaction also forms some carbon monoxide. However, LPG does release less CO2 per unit of energy compared to oil or coal, but more than the natural gas. It emits 81% of the CO2 per kWh formed by oil, 70% to that of coal, and less than 50% of that, emitted by the coal-generated electricity distributed through the grid. Being a mix of butane and propane, LPG emits less amount of carbon per joule compared to the butane, but more carbon per joule compared to propane.
LPG also burns more cleanly compared to the higher molecular weight hydrocarbons, since it releases fewer particulates.
FAQs on Liquefied Petroleum Gas LPG Composition Properties and Uses
1. What is Liquefied Petroleum Gas (LPG)?
Liquefied Petroleum Gas (LPG) is a flammable hydrocarbon fuel mainly composed of propane (C3H8) and butane (C4H10) that is stored as a liquid under moderate pressure.
LPG is obtained during petroleum refining and natural gas processing. It exists as a gas at room temperature but is easily liquefied under pressure, making it convenient for storage and transport in cylinders.
2. What is the chemical composition of LPG?
The chemical composition of LPG mainly includes propane (C3H8) and butane (C4H10), with small amounts of other hydrocarbons.
Its composition may vary depending on source and climate:
- Propane-rich LPG – preferred in colder regions due to lower boiling point.
- Butane-rich LPG – used in warmer climates.
- Trace components may include propene or butene.
3. Why is LPG stored as a liquid under pressure?
LPG is stored as a liquid under pressure because liquefaction greatly reduces its volume, making storage and transportation efficient.
Key points:
- At atmospheric pressure, LPG exists as a gas.
- Under moderate pressure, it converts to a liquid.
- Liquid LPG occupies about 1/250th of its gaseous volume.
When the cylinder valve is opened, pressure decreases and the liquid vaporizes to form a combustible gas.
4. What is the balanced chemical equation for the combustion of LPG?
The balanced combustion equation of propane, a major component of LPG, is C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g).
For butane, another major component, the balanced equation is:
2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(g)
These are examples of complete combustion reactions producing carbon dioxide and water.
5. Why does LPG burn with a blue flame?
LPG burns with a blue flame because it undergoes complete combustion in sufficient oxygen, producing mainly carbon dioxide and water.
A blue flame indicates:
- Efficient mixing with air.
- Minimal soot formation.
- High temperature and clean burning.
If oxygen supply is limited, incomplete combustion may occur, forming carbon monoxide (CO) and a yellow, sooty flame.
6. What happens during incomplete combustion of LPG?
During incomplete combustion, LPG reacts with insufficient oxygen to produce carbon monoxide (CO) and sometimes carbon (soot) instead of carbon dioxide.
For example, incomplete combustion of propane can be represented as:
2C3H8(g) + 7O2(g) → 6CO(g) + 8H2O(g)
Carbon monoxide is a toxic gas, so proper air supply is essential when using LPG for cooking or heating.
7. What is the difference between LPG and natural gas?
The main difference between LPG and natural gas is that LPG contains propane and butane, while natural gas mainly consists of methane (CH4).
Key differences:
- Composition: LPG (C3H8, C4H10) vs methane (CH4).
- Storage: LPG is stored as a liquid under pressure; natural gas is stored as compressed gas.
- Calorific value: LPG generally has a higher energy content per unit volume.
8. Why is LPG considered a cleaner fuel?
LPG is considered a cleaner fuel because it burns efficiently to produce mainly CO2 and H2O with very little soot or sulfur compounds.
Reasons include:
- High hydrogen-to-carbon ratio.
- Low sulfur content.
- Minimal particulate matter formation.
Compared to coal or wood, LPG combustion causes less air pollution and fewer harmful emissions.
9. Why is a strong smell added to LPG?
A strong-smelling compound called ethanethiol (C2H5SH) is added to LPG to detect gas leaks easily.
Pure LPG is colorless and odorless, so ethanethiol is added as an odorant because:
- It has a strong, unpleasant smell.
- It helps detect leaks at very low concentrations.
- It improves safety in homes and industries.
10. What are the main uses of Liquefied Petroleum Gas in daily life?
Liquefied Petroleum Gas (LPG) is mainly used as a domestic, industrial, and automotive fuel due to its high calorific value and clean combustion.
Common uses include:
- Cooking fuel in household gas cylinders.
- Heating in homes and industries.
- Autogas for vehicles.
- Fuel for metal cutting and welding.
Its efficient energy release comes from exothermic combustion reactions of propane and butane.
