Liquefied petroleum gas

Liquefied petroleum gas, commonly known as LPG, is a flammable fuel gas. It consists of a mixture of hydrocarbon gases. The primary components are propane, n-butane, and isobutane. It may also contain small amounts of propylene, butylene, or isobutylene. LPG is a vital energy source used for heating, cooking, and powering vehicles. It also serves as a refrigerant and an aerosol propellant. Because it can replace chlorofluorocarbons, it helps reduce damage to the ozone layer.

LPG is produced through the refining of petroleum or "wet" natural gas. It is almost entirely derived from fossil fuel sources. The gas is extracted from petroleum or natural gas streams as they emerge from the ground. To store this gas efficiently, it must be turned into a liquid. This is done by using high pressure inside steel vessels. At normal temperatures and pressures, LPG evaporates very quickly. However, inside a pressurized tank, the gas becomes a liquid.

Storage requires careful management of pressure and volume. A typical LPG reservoir is filled to only 85% of its capacity. This remaining space, called ullage, allows for the thermal expansion of the liquid. If the liquid expands too much due to heat, it could cause safety issues. The density of the liquid and the vapor varies with temperature and pressure. For example, the vapor pressure of pure butane is about 2.4 bar at 20°C. For pure propane, it is about 8.4 bar at 20°C.

LPG is sold in different varieties depending on the region and season. Most common mixes include both propane and butane. In the northern hemisphere, mixes contain more propane during the winter. In the summer, the mixes contain more butane. In the United States, two main grades are sold: commercial propane and HD-5. The HD-5 specification limits propylene to 5% and is used for autogas. To ensure safety, a strong odorant called ethanethiol is added. This allows people to detect leaks easily by smell.

History shows that LPG has been used for over a century. Walter O. Snelling first produced LPG in 1910. The first commercial products appeared in 1912. Today, LPG provides about 3% of all energy consumed globally. It is a relatively clean fuel because it burns without soot. It also produces very little sulfur emission. While it does not pollute ground or water, it can cause air pollution.

LPG has many specific applications across the globe. In India, the domestic sector consumed 28.5 million metric tons in 2023–24. In 2016, India had 215 million domestic connections. In Brazil, LPG is the most common cooking fuel in urban areas. In the United Kingdom, about 200,000 households use it for heating. When used in engines, it is often called autogas. Propane is the third most widely used motor fuel in the world. As of 2013, over 24.9 million vehicles used propane gas.

Using LPG as a motor fuel offers several technical advantages. It has a high octane rating between 102 and 108 RON. It is also non-toxic, non-corrosive, and free of tetraethyllead. However, it has a lower energy density per liter than petrol. This means vehicles may consume more fuel by volume. Additionally, LPG provides less lubrication for engine cylinders. This can lead to more valve wear if engines are not modified.

LPG also plays a role in modern chemical and maritime industries. It is a feedstock used to synthesize olefins like ethylene and propylene. In the maritime industry, BW LPG retrofitted a Very Large Gas Carrier with LPG propulsion. This technology helps the industry meet stricter emission standards. LPG can also be used in combined heat and power (CHP) technologies. This allows for the simultaneous generation of electricity and useful heat.