Propane is not a synonym for Liquefied Petroleum Gas (LPG); rather, propane is a specific type of gas that falls under the broader category of LPG. This distinction is often a source of confusion because in some regions, like the United States and Canada, the commercial product sold as LPG is nearly pure propane. In other parts of the world, including many European and Asian countries, the fuel referred to as LPG is sold as a mixture that contains both propane and butane. Understanding the relationship between these terms requires looking at the composition of the fuel and the properties of its individual components.
Defining Liquefied Petroleum Gas
Liquefied Petroleum Gas, or LP gas, is the general term for a flammable mixture of hydrocarbon gases that can be easily liquefied through pressurization. These gases are extracted during natural gas processing and crude oil refining. The primary components that make up the LPG family are propane, normal-butane, and isobutane.
Commercial LPG is typically a blend of these three- and four-carbon hydrocarbons, and the exact ratio of propane to butane can vary significantly. For instance, the mixture is often adjusted seasonally to optimize performance in colder or warmer weather.
Propane’s Unique Chemical Properties
Propane (C₃H₈) possesses specific chemical characteristics that make it distinct from its fellow LPG components, especially butane (C₄H₁₀). The most important difference is its remarkably low boiling point, which is the temperature at which the liquid fuel turns into a usable gas. Propane’s boiling point is approximately -42°C (-44°F).
This low boiling point means that even in freezing conditions, the liquid propane inside a storage tank will continue to vaporize into a gas to fuel appliances. Butane, by contrast, has a much higher boiling point of about -0.4°C (31°F). Once the ambient temperature drops below this threshold, butane remains a liquid and cannot generate the necessary gas pressure to flow to a burner. Propane’s ability to function reliably in sub-freezing weather is why it is often the preferred fuel for year-round outdoor storage and whole-home heating systems.
Practical Differences in Usage and Storage
The chemical variations between propane and butane-heavy LPG mixtures lead to substantial differences in real-world application and storage requirements. Because of propane’s low boiling point, it must be stored in tanks built to withstand a higher internal pressure than those used for butane. This results in the sturdier, thicker-walled tanks typically seen outside homes and commercial buildings.
Regional fuel standards dictate the composition of commercial LPG, directly impacting where each type of gas is primarily used. For instance, in regions with consistently cold winters, the commercial LPG sold is mandated to be nearly pure propane to ensure reliability. Conversely, butane-rich mixtures are more common in warmer climates and for indoor applications, such as small portable heaters or camping stoves, where temperature is not a limiting factor. Butane’s lower storage pressure also allows it to be kept in smaller, lighter canisters, making it ideal for highly portable uses.