22.09.2015 12:09

The refrigerant gas R600a - or methylpropane

All About the Refrigerant Gas R600a

The refrigerant gas isobutane is also known as methylpropane and more commonly as R600a. Its molecular formula is C4H10 and it is the simplest alkane (saturated hydrocarbon) to have a tertiary carbon (three carbon atoms around a central carbon atom) structure.

The compound has a molar mass of 58.12g mol-1 and presents as a colourless and odourless gas. It has a boiling point of -13C to -9C and at standard temperature and pressure has a density of 2.51 mg mL. Its high heat capacity makes it an ideal coolant.


Since global concerns about the depletion of the ozone layer arose, isobutane has replaced the damaging freon gases in refrigeration systems and freezers and as the propellant gas in aerosol spray cans. The compound has been in widespread use in fridges since 1993. When used as a refrigerant, it is called R600a, otherwise it is usually called isobutane. Isobutane is also used in some portable camping stoves, usually as part of an 80:20 mixture with propane.

R600a has almost no ozone depletion potential and a very low Global Warming Potential - just 3.3 times the GWP of carbon dioxide. Some safety concerns about isobutane surfaced in 2009 when a number of domestic refrigerators in the United Kingdom caught fire as a result of the gas leaking into the chill cabinet and being ignited by electrical sparks. These concerns were eventually dismissed in the light of there being more than 300 million R600a-cooled refrigerators in use worldwide.

Other Uses

When mixed with argon, isobutane is used in Geiger counters as part of the filler gas mixture. The gas is also used as a component in calibration gas mixtures in the petrochemical industry. It is used to detect environmental gas emissions, trace impurities in the products of the oil and gas industry and also as a reagent gas in ionisation mass sprectrometry.

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