LPG Structure – Chemical Formula of LPG Gas – LPG Gas Chemical Formula
LPG structure – Propane molecule
LPG is comprised primarily of propane and butane, whilst natural gas is mostly methane. LPG is generally a mixture of predominantly propane (C3H8) and/or butane (C4H10), with smaller amounts of other NGL hydrocarbons including ethane, isobutane and pentanes. LPG physical structure is as both a liquid, when under pressure, and as a gas.
LPG structure (propane structure) is as a three carbon molecule with the chemical formula of LPG gas – propane as C3H8. That’s 3 carbon atoms and 8 hydrogen atoms making one molecule of propane.
LPG structure (butane structure) is a four carbon molecule with the formula C4H10, with 4 carbon atoms and 10 hydrogen atoms making one molecule of butane.
These are also chemical formulae (formulas) of LPG gas. The illustrations shows models of the LPG structure of a propane molecule and the LPG structure of a butane molecule.
There are a number of LPG gas chemical formulas (formulae). Ethane chemical formula is C2H6. Propane chemical formula is C3H8. Butane and Isobutane both have the same chemical formula C4H10, as isobutane is an isomer of butane. Pentane (n-pentane) chemical formula is C5H12 but is only a gas over 36.1°C. Heavier hydrocarbons (pentanes plus) are liquids or waxy solids.
LPG structure – butane molecule
Propane Boiling Point – LPG Boiling Point
Propane boiling point is -42°C or -44°F at atmospheric pressure, the point at which liquid propane vaporises into gaseous propane. Propane stays liquid above the propane boiling point because it is under pressure in a gas cylinder. In contrast, natural gas – methane – has a boiling point of -161.5°C (-258.7°F) at atmospheric pressure.
Water boils at 100°C or 212°F, becoming a gas (steam). In comparison, LPG boils at -42°C or -44°F, becoming gas vapour. LPG stays liquid because it is under pressure in a gas cylinder.
As a liquid, LPG looks a lot like water. It is colourless and odourless in its natural state.
Butane Boiling Point
Butane boiling point is -0.4°C at 1 atm pressure. Above -0.4°C, at 1 atm, it becomes gas vapour. Butane stays liquid because it is under pressure in a gas cylinder.
As a liquid, it looks a lot like water. It is colourless and odourless in its natural state.
Liquid Propane Temperature – LPG Gas Temperature When Liquid
Liquid propane temperature (LPG gas temperature) must be below -42°C or -44°F, unless it is under pressure. Propane would be liquid in an open container in -43°C or -45°F or lower ambient temperature. Liquid propane can be warmer when contained under pressure in a gas cylinder.
LPG Gas Temperature: Flame, Boiling Point, Melting/Freezing Point – Liquid Propane TemperatureLPG Gas Temperature – Flame Temperature
LPG gas temperature includes LPG gas flame temperature, LPG gas boiling temperature, LPG gas ignition temperature, LPG gas auto ignition temperature, LPG gas flash point temperature and LPG gas freezing temperature.
LPG gas temperature, both propane and/or butane, have adiabatic flame temperature about 1967°C (3573ºF), when burned in air.
LPG gas temperature for liquid propane boiling, when it turns to LPG gas, is -42°C or -44°F.
LPG gas temperature flash point is -104°C or -156°F
LPG gas temperature for ignition in air is 470°C – 550°C (878°F – 1020°F)
LPG gas temperature also affects gas pressure, as pressure rises with temperature.
LPG gas temperature for melting/freezing is at -188°C or -306.4°F (liquid propane freezing)
So, liquid propane temperature for freezing is a much lower temperature than water, which freezes at 0ºC.
LPG is composed of liquid or gas (vapour), depending on pressure and LPG gas temperature. The LPG boiling point is the liquid propane temperature at boiling and becomes vapour (gas).
LPG – liquefied petroleum gas – temperature also affects the gas cylinder pressure.
LPG Liquefaction – LPG-Propane Dew Point
The LPG-propane dew point is the temperature at which gas changes into its liquid state, which is more accurately called liquefaction. The conversion of LPG vapour to LPG liquid is called liquefaction, and depends on temperature and pressure of the vapour. The higher the temperature of the vapour, the higher the pressure needed to convert the vapour to liquid.
For Propane vapour at 20°C must be pressurised to about 836 kPa to see it liquefy, and at 50°C, about 1713 kPa pressure is required. The lower the temperature, the easier it is to liquefy the vapour.
For n-Butane vapour at 20°C must be pressurised to about 115 kPa to see it liquefy, and at 50°C, about 510 kPa pressure is required.
For mixtures of Propane and Butane, the liquefaction conditions also depend on the composition of the mix, as well as the temperature and pressure of the vapours.
LPG Specific Heat Capacity
LPG energy content is approximately 25MJ per litre. One gallon of propane has the LPG energy content of 91,547 BTU (60°F). 25MJ also converts to 6.9kWh.
Commercial & Domestic LPG Composition: Which Gas is Present in LPG?
The commercial and domestic LPG composition includes propane, butane and mixtures of these gases. LPG – Liquefied Petroleum Gas – describes flammable hydrocarbon gases.
LPG, liquefied through pressurisation, comes from natural gas processing and oil refining.
In different countries, the commercial and domestic LPG composition can be propane, butane or propane-butane blends.
In Australia, LPG is just propane.
The vapour density of propane is 1.882 kg/m³ at 0°C (32°F). The density of propane liquid is 0.493 g/cm³ at 25 °C (77 °F) or 4.24 pounds per US gallon. Propane expands at 1.5% for every 5.56°C (10°F).
LPG at 1 atm of pressure and 20°C is a gas which is about 1.55 (propane) to 2.08 (butane) times heavier than air. LPG is liquefied under modest pressure of 1,220 kPa (177 psi) at 37.8°C (100°F). LPG liquid propane density is slightly less than 50% that of water at 25°C and almost 60% at -40°C.
LPG density of propane liquid is lighter than water, at about ½ that of water. LPG density of butane liquid is lighter than water, at about 60% that of water.
Liquid propane density is 495 kg/m³ at 25°C.
Density of Liquid Propane at Different Temperatures
The density of liquid propane at different temperatures is inversely proportional to the change in temperature. As the temperature increases, the density of liquid propane decreases. The industry uses correction factors to make sure that honest value of energy content is delivered.
Density of Liquid Propane at Different Temperatures
State Temperature Pressure Density
°C °F ATM psia kg/m³ lbm/ft³
Liquid -188 -306 1 14.5 733 45.8
Liquid -173 -280 1 14.5 718 44.8
Liquid -153 -244 1 14.5 698 43.6
Liquid -133 -208 1 14.5 678 42.3
Liquid -113 -172 1 14.5 657 41.0
Liquid -93 -136 1 14.5 637 39.8
Liquid -73 -100 1 14.5 615 38.4
Liquid -53 -64 1 14.5 593 37.0
Liquid -42 -44 1 14.5 581 36.3
Numbers have been rounded. Copyright © 2019 Elgas Ltd