Why the gas in your barbecue bottle changes with the seasons
The propane and butane sold as LPG is not one fixed recipe. Suppliers in the northern hemisphere add more propane in winter and more butane in summer, because the two boil at very different temperatures. That blend now fuels grills, cooking stoves, off-grid homes and nearly 25 million vehicles.
Liquefied petroleum gas comes from refining crude oil or from separating wet natural gas as it leaves the ground. The chemist Walter Snelling first made it in 1910, and it went on sale two years later. It boils below room temperature, so it is kept liquid under pressure in steel cylinders, filled only to around 80 to 85 percent to leave room for expansion. The liquid is roughly 250 times denser than its vapour. Pure gas has no smell, so a pungent compound, ethanethiol, is added to reveal leaks.
Unlike natural gas, the vapour is heavier than air. Escaping LPG creeps along floors and pools in basements, where it can either explode on meeting a spark or push out the oxygen people need to breathe. Kilogram for kilogram it holds more energy than petrol, 46.1 megajoules against 43.5, but it is much less dense, so a litre carries less and cars burn more of it.
As autogas it has powered spark-ignition engines in some countries since the 1940s, and propane ranks as the world's third most used motor fuel. It burns without soot, has an octane rating of 102 to 108, and is often lightly taxed, though some European governments claw that back with higher annual car taxes. Engines need modification, since the gas lubricates valves less than petrol. In 2020 the shipping firm BW LPG converted a very large gas carrier to run on its own cargo.
Cooking is the biggest everyday use. Indian homes burned nearly 28.5 million tonnes in 2023-24, and by 2016 the country had 215 million domestic connections. In Brazil it is the standard urban cooking fuel outside Rio and São Paulo, with poor families receiving a dedicated grant to buy it since 2001. A propane and isobutane blend also replaces ozone-damaging refrigerants.
Source: Liquefied petroleum gas
