LPG Composition – Chemical Composition of LPG Gas

Chemical Composition of LPG – LPG Composition

LPG composition, the gas in gas bottles, is propane, butane, isobutane and gas mixtures of the three gases. In some countries, like Australia and the USA, the chemical composition of LPG is limited to propane. In other countries, like NZ and many in Europe, it is a propane-butane blend.  

These are the common alternative where there are no gas mains.

The most common gas supplied and used in homes is natural gas (methane) via gas mains, although the energy content can vary from country to country.

CNG and even Biogas are also used in some places. The deciding factor is the local supply situation.

Cooking Gas LPG – Gas Cook Top

Cooking gas in LPG gas bottles is primarily used as cooking fuel. The popularity of cooking with gas on a gas cook top makes cooking gas in gas bottles a necessity in areas without natural gas mains. LPG vs natural gas for cooking is virtually identical.

Cooking Gas Composition

Cooking gas contains either natural gas (methane) or LPG. If it is LPG, the LPG composition of cooking gas contains either propane, butane or a mixture of the two. If the cooking gas is CNG or Biogas, the main constituent is still methane.

Cooking Gas Cylinder

A cooking gas cylinder can be a 9kg, 45kg or a 14.2kg domestic cooking gas cylinder.

Cooking gas cylinder sizes are contingent upon the usage, the requisite volume of gas and the location of the gas cylinder installation.

For those who use LPG for cooking only, an Australian cooking gas cylinder is typically a single 45kg LPG gas cylinder that lasts for a year or more. 45kg gas bottle have a cylinder capacity of 88 litres.

The standard cooking gas cylinder weight in India (fuel tank weight) has a gas cylinder weight of contents of 14.2kg ± 150 grams. Domestic cooking gas cylinder weight (fuel tank weight) is about 29.5kg for a full 14.2kg cooking gas cylinder. The empty cooking gas cylinder weight is a tare weight (empty gas cylinder weight) of approximately 15.3kg.

BBQ gas bottle sizes come in 4kg & 9kg gas bottle dimensions, cylinder capacity & gas bottle sizes (propane gas bottle sizes).

Small LPG gas bottles are portable, as used in camping.

LPG gas bottles include a main gas valve for controlling the release of the gas.

The Pressure Relief Valve (PRV) is a safety device incorporated into the main gas valve on the LPG gas bottles.

If the pressure of the gas inside the LPG gas bottle increases, as the result of a fire or other heat source, the pressure relief valve releases some of the gas to relieve the pressure.

The various gas bottles sizes and cylinder capacity contain liquid and gas, as LPG – Liquefied Petroleum Gas – liquefies under pressure.

An LPG gas bottle is considered low pressure versus high pressure gas bottle sizes, as used with CNG.

Compressed natural gas storage is the storage of gaseous methane at the high pressure of 20 – 25 MPa (200 bar to 250 bar) in special CNG gas cylinders.

CNG – compressed natural gas storage cylinders have a tare weight approximately 3x heavier than comparable capacity LPG cylinders.

Wobbe Index

The Wobbe Index is used to compare the combustion energy output of different fuel gases. Not all natural gas has the same Wobbe Index.

Wobbe Index of Natural Gas & LPG

Home Gas Bottles – What Uses Gas in the Home

Home gas is very popular regardless of whether it is natural gas or LPG. Natural gas (methane) it the type of gas used in homes most frequently. In areas where natural gas is unavailable, LPG, CNG or Biogas are used.

Natural gas is delivered via pipelines whilst LPG and CNG are delivered in cylinders or tanks.

Biogas is frequently produced on-site.

Of the four types of gas used in homes, chemical composition of LPG has a highest energy content at 93.2MJ/m³ vs natural gas (methane) at 38.7MJ/m³.

CNG and Biogas are also methane, although biogas typically has a lower percentage of methane.

LPG Composition in Gas Bottles – Gas is Used in Gas Bottles

The gas used in gas bottles is typically LPG – liquefied petroleum gas – which is either propane or butane, flammable hydrocarbons used as fuel for home heating, cooking, hot water, cars and other vehicles.

LPG composition used in home gas bottles is either propane, butane or a mixture of the two.

The other type of gas used in homes comes from natural gas (mains gas) or CNG (compressed natural gas), both of which are methane.

Propane, butane and natural gas are all hydrocarbon gases.

Propane and butane fall under the broad label of “LPG”, as liquefied petroleum gases and also referred to as natural gas liquids – NGL.

CNG – Compressed Natural Gas – is methane.

CNG supply is also a possibility, but rare for practical and economic reasons.

Biogas, with methane as the primary constituent, has the same limitations.

Kind-Type of Gas is Used in Homes in Your Country or Area

Assuming that the kind-type of gas is used in homes is LPG, LPG composition can be propane, butane or a mixture of the two.

The relative availability and economics of the different kind-type of gas is used in homes drive the differences.

For example, the chemical composition of LPG supplied in both the USA and Australia is pure propane.

Some countries, like New Zealand, provide a propane/butane blend.

In certain countries, like England, you can buy either propane or butane.

Difference between CNG and Propane-LPG – LPG Energy Content

The big difference between CNG and propane is in volumetric energy density.

Propane energy content is almost 3x the energy density with 25MJ/L for LPG-propane versus only 9MJ/L for CNG (methane).

In other words, for comparable capacity cylinders, the LPG energy content means LPG cylinders will last more than twice as long.

Another major difference between CNG and propane is that CNG storage pressures can be more than 10x that of LPG.

For example, LPG pressure is less than 2 MPa whilst CNG is 20 – 25 MPa.

This much higher pressure requires a much heavier and more expensive cylinder or tank.

It also means it is impractical to make them large enough to offset the energy density deficit.

This is due to the size and weight required.

CNG vs LPG for Gas Used in Gas Bottles

LPG is more cost effective and commercially viable than CNG.

Due to the greater LPG energy content, a CNG cylinder would need replacement more than twice as often.

This means the inconvenience of checking the CNG cylinders and placing orders much more often.

The homeowner would also have to absorb extra freight costs.

This would result from the extra deliveries and added weight.

For example, an empty 45kg LPG cylinder only weighs approximately 35kg.

An empty CNG cylinder, with comparable volume capacity, is about 108kg.

So, when comparing empty cylinders, a CNG cylinder is 3x the weight.

This also makes it impossible to increase the cylinder size to hold an equal amount of energy.

The cylinder would be too large and too heavy to transport for exchange purposes.

Higher cylinder rental is also likely, as the heavier CNG cylinders cost more.

Finally, the equipment to fill the CNG cylinders is expensive – much more than LPG.

The supplier would need to offset these higher costs in the cost of the gas.

It is the energy density and pressure that affect the comparable convenience and affordability of use.

Weather and Seasonal Effects on the Gas Used in Gas Bottles

Weather, or more specifically temperature, can affect the LPG composition used in gas bottles.

Propane works better as the gas is used in gas bottles in cold climates.

Propane will continue to vaporise – turn to gas – even in low temperatures.

Propane’s biggest advantage is a lower boiling temperature, at -42°C vs -0.4°C for butane.

So, propane will continue to vaporise at temperatures well below 0°C.

With butane, when it drops below freezing, you end up with no gas.

Some countries, like Italy, vary the chemical composition of LPG by season.

In NZ, they even vary the mix by latitudes, as well as by season.

For example, New Zealand’s North Island and South Islands may receive different mixtures.

The colder regions get a different LPG composition of propane, vs butane, in winter.

Needless to say, propane is the preferred choice for cold weather climates.

The Name Game

The names for the gases are dependent upon what country you are in.

In Australia, we call it LPG but it is propane.

In New Zealand, LPG is almost always a propane and butane mix.

In the USA, they don’t use the term LPG often.  They just call it “Propane”.

In some countries, like England, you buy propane or butane by name.

In other countries, they call it “GPL” or “GLP” instead of “LPG”.

This is because the acronyms comes from different languages and syntax.

For example, in French it is “gaz de pétrole liquéfié” or in Spanish it is “gas licuado de petróleo”.

Final Thoughts

For many people, the kind or type of gas used in homes or LPG composition used in gas bottles is indistinguishable and never poses an issue.

However, for others the various gases provide the flexibility for use in diverse conditions.

Either way, LPG is the most common gas used in gas bottles.