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What Is LPG Gas? Propane, Butane, and More

what is LPG gas

What is LPG gas? Liquefied petroleum gas (LPG) is primarily composed of propane (C3H8), alongside a mix of other hydrocarbons such as propylene, butane, and butylene, although propane is the predominant component. At room temperature and pressure, the elements that make up LPG are in gas form. Vehicles that run on propane are known to experience less carbon accumulation than those powered by gasoline or diesel.

LPG is generated as a secondary product from two main processes: the treatment of natural gas and the refining of crude oil. During the extraction of natural gas, it’s not just methane that’s obtained, but also lighter hydrocarbons. These are then separated out in a processing facility, yielding products like ethane, propane, and butane, as well as heavier hydrocarbons. Similarly, the refining of crude oil produces propane and butane among other gases as a side effect of the chemical processes designed to alter or break down molecules to create more valuable petroleum products.

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What is LPG gas?

All chemicals that make up the category LPG are hydrocarbons: They are exclusively composed of hydrogen and carbon atoms. What differentiates the various gasses is how many hydrogen and carbon atoms they have, and the types of chemical bonds, such as having double bonds versus only single bonds. Here’s a closer look at the chemical structures of liquefied petroleum gasses:

Propane chemical structure

The chemical formula for propane is C3H8. This means it has 3 carbon atoms and 8 hydrogen atoms. Every chemical bond in propane is a single bond. In terms of chemical groups, propane is made up of 2 methyl groups — CH3 — and 1 methylene group — CH2. The ball-and-stick model of a propane molecule is featured below.


When propane burns, it produces carbon dioxide, water, and heat. However, if not enough oxygen is present when propane is burned, it produces carbon monoxide and carbon (typically in the form of soot), in addition to the carbon dioxide and water. The reason you don’t “see” the water when propane is burned is because it comes off as water vapor.

Butane chemical structure

Butane is another type of liquefied petroleum gas. Sometimes called n-butane, the chemical formula for butane is C4H10. Like propane, butane possesses 2 methyl groups — CH3. It also contains 2 methylene — CH2 — groups, as opposed to propane’s 1 methylene group. The ball-and-stick model of a propane molecule is featured below.

butane chemical formula

Butane is sometimes called n-butane because it is normal butane. There’s another form of butane called isobutane, or i-butane. This has the same chemical formula as butane — C4H10 — but the atoms are arranged differently. When a chemical has the same formula but takes on a different structure, it’s called an isomer. Hence, isobutane is an isomer of normal butane.

Isobutane chemical structure

Now we turn to the isomer of normal butane: Isobutane. Like n-butane, i-butane is composed of 4 carbon atoms and 10 hydrogen atoms. However, they are arranged differently and so the chemical formula for isobutane is written as HC(CH3)3. The ball-and-stick model of a propane molecule is featured below.

isobutane chemical formula

Isobutane is used in various ways that consumers might not be away of, such as propellant in aerosol spray cans and as a component in blended fuels for camping. Isobutane is often used in the production of various petroleum-based products. It’s also very popular as a refrigerant, due to its superior environmentally-friendly character compared to old chlorofluorocarbons.

Propene chemical structure

Propene, also referred to as propylene, is an unsaturated organic compound and has the chemical formula CH3CH=CH2. Unsaturated means that the compound is not composed solely of single bonds; propene has one double bond between 2 carbon atoms. A compound is called saturated when it is composed of only single bonds. The ball-and-stick model of a propane molecule is featured below.

propene chemical formula

Propene is mainly produced in a process called steam cracking. By steam cracking propane, a mixture of various hydrocarbons can be produced, including propene, ethylene, methane, hydrogen gas, and other related compounds. Unlike propane, butane, and isobutane, propene is not really used in fuels that the average consumer uses. Propene is used as the raw material in several petrochemical products, with polypropylene manufactures consuming approximately two-thirds of global production; polypropylene is a very useful compound, utilized for the production of packaging, containers, films, fibers, and caps and closures. Propene is also used as an alternative fuel in brazing, heating metal in order to bend it, and welding and cutting.

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How LPG gas is made

The process of turning these gases into a liquid form involves a combination of compression and cooling, exploiting the physical properties of these hydrocarbons. At atmospheric pressure, these gases exist in a gaseous state at room temperature. However, under increased pressure or decreased temperature, they transition into a liquid, which significantly reduces their volume, making it more economical to store and transport. This principle is fundamental to the production of LPG, allowing for the efficient handling of these gases.

The first step in the liquefaction process is compression, where the gaseous hydrocarbons are compressed using high-pressure pumps. This compression increases the pressure, which raises the temperature of the gas due to the gas laws governing pressure, volume, and temperature relationships (Boyle’s and Charles’s laws). Following compression, the gas is cooled in a heat exchanger, a process that removes the heat generated during compression. The cooling phase is critical; it reduces the gas’s temperature to a point where it condenses into liquid at the applied pressure. The exact pressure and temperature conditions required for liquefaction vary depending on the composition of the gas mixture but typically involve pressures ranging from a few to several hundred pounds per square inch (psi) and cooling to temperatures well below ambient.

After liquefaction, the LPG is stored in pressurized vessels or tanks designed to maintain the high pressure necessary to keep the gas in liquid form at ambient temperatures. These storage solutions are crucial for the safe handling, transportation, and use of LPG. When LPG is needed as a gas, for instance, when used as fuel for cooking or heating, it is released from the tank through a regulator that reduces the pressure. This drop in pressure causes the liquid to revert to its gaseous state, exploiting the same physical properties in reverse. This process of liquefaction and vaporization allows LPG to be an efficient, portable, and clean-burning fuel source, widely used across various applications from household to industrial settings.

How do I know if I have LPG or natural gas?

Determining whether you have LPG (Liquefied Petroleum Gas) or natural gas supplying your home or appliance involves a few key indicators:

Source and storage

The most straightforward indicator is the source and storage method. LPG is typically supplied in tanks or bottles that are refilled or exchanged when empty. These tanks can be situated outside your home or in a designated area for gas storage. In contrast, natural gas is supplied through a network of underground pipelines directly to your home or appliance. If you have a tank or cylinder that gets refilled, you’re likely using LPG. If your supply comes without any visible storage tank and is continuous, it’s probably natural gas.

Supply pressure and equipment

Natural gas and LPG appliances require different pressure levels to operate correctly. Natural gas typically operates at a lower pressure than LPG. Many appliances are specifically designed for one type of gas and are equipped with regulators or jets calibrated for the appropriate pressure. Checking the documentation or labels on your gas appliances can indicate which gas they’re intended for. If you’ve moved into a home with existing appliances, look for any stickers or marks indicating “LPG” or “Natural Gas.” If modifications have been made for a specific gas type, it might also be documented on the appliance.

Billing and service

Your utility bills and service contracts can also provide a clue. If you receive regular bills from a gas utility company for gas usage, it’s likely natural gas, as the service is metered and continuous. On the other hand, if you arrange for gas delivery or tank exchange through a supplier, it indicates LPG usage. Additionally, in many regions, the supplier or utility company’s name and contact information are on the bill or tank, which can offer insights into the type of gas supplied.

If you’re still unsure, contacting a licensed gasfitter or your gas supply company can provide a definitive answer. They can inspect your setup, identify the gas type, and ensure your appliances are correctly configured and safe to use. Get quotes from up to 5 propane dealers in your area today to get the best pricing on propane delivery.

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