LPG Compound: Chemical Composition of LPG – Cooking Gas LPG

LPG Compound: Chemical Composition of LPG – Cooking Gas LPG

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

The LPG in gas bottles is rarely just butane.

These are the common alternative for cooking gas LPG where there are no gas mains.

The most common gas supplied as household gas 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 as household gas in some places. The deciding factor is the local supply situation.

Cooking Gas LPG – Household Gas

For cooking gas LPG in gas bottles, the LPG compound is primarily used as household gas.

Cooking gas LPG and natural gas for household gas are virtually identical in use.

The popularity of cooking with gas on a gas cook top makes LPG in gas bottles a necessity in areas without natural gas mains. 

LPG Composition

LPG composition contains either propane, butane or a mix of the two.

If the gas is CNG or Biogas, the main constituent is methane.

Cooking Gas LPG Cylinder

Cooking gas LPG cylinder can be a 9kg, 14.2kg, or a 45kg gas bottle.

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

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

The standard cooking gas LPG cylinder weight in India (fuel tank weight) has a gas cylinder weight of contents of 14.2kg ± 150 grams. Domestic cooking gas LPG 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.

Cooking gas LPG cylinders also come in BBQ gas bottle sizes of 4kg & 9kg.

Small cooking gas bottles are portable, as used in cooking gas for camping.

LPG – 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 cooking gas LPG cylinder (see image).

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.

LPG in 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 – LPG gas cylinders.

Wobbe Index

The Wobbe Index is used to compare the combustion energy output of different fuel gases, such as natural gas and cooking gas LPG. Note that, as with the LPG compound, not all natural gas has the same Wobbe Index.

Wobbe Index of LPG Compound (cooking gas LPG) and Natural Gas

Household Gas Bottles – What Uses Gas in the Home

Household gas is very popular regardless of whether it is natural gas or an LPG compound.

Natural gas (methane) is the household gas used in homes most frequently.

In areas where natural gas is unavailable, Household, CNG or Biogas are used.

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

Biogas is frequently produced on-site.

Of the four types of household gas, the chemical composition of the LPG compound 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 Compound in Gas Bottles

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

LPG compound used as cooking gas LPG is also either propane, butane or a mixture of the two.

The other types 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 but different kinds of gas..

Propane and butane types of gas 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.

Types of Household Gas Used in Your Country or Area

Assuming that the household gas is cooking gas LPG in gas bottles, the LPG compound can be propane, butane or a mixture of the two.

The relative availability and economics of the different kinds of gas used as household gas drive the differences.

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

Some countries, like New Zealand, the LPG compound provided is a propane/butane blend.

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

GPL Gas or GLP Gas (Gas GLP)

GPL gas or GLP gas (Gas GLP) is what LPG is called in some other countries.

GPL gas or GLP gas are also acronyms, as in France it is called ‘gaz de petrole liquefie’ (GPL), in Italy it is ‘gas di petrolio liquefatto’ (GPL), and in Spain it is “gas licuado de petróleo” (GLP).

Having heard “GPL gas” pronounced in both French and Italian, it sounds much better than LPG – LPG gas.

They just have different syntax, with the word ‘gas’ or ‘gaz’ coming first.

The name may change but the LPG compound remains the same.

As with LPG gas, GPL gas is also a redundant acronym, with the word gas repeated in word and acronym. (Think ATM machine)

LPG Gasul

LPG gasul is the term they us in the Philippines for LPG.

‘Gasul’ is the Tagalog (Filipino) word for propane.

Different Kinds of Gas: CNG and Propane-LPG – LPG Energy Content

The big difference between CNG and propane (LPG) 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). See chart.

A different LPG compound, with butane or a propane-butane mix, would have a slightly different energy content.

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

The exact duration is dependent upon the LPG compound used.

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

For example, the pressure of LPG in gas bottles 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 in Gas Bottles for Household Gas

LPG in gas bottles is more cost effective and commercially viable than CNG as household gas, regardless of which LPG compound is compared.

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

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 household gas deliveries and added weight.

For example, an empty 45kg cooking gas LPG bottle 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 – LPG gas.

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 influence the LPG compound used in gas bottles.

Propane works better than the other types of LPG 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 LPG compound of the different kinds of gas by season.

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

For example, in New Zealand’s North Island and South Islands, the LPG compound may vary with different kinds of gas mixtures.

The colder regions get the different type of gas composition of propane vs butane, in winter.

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

The Name Game for LPG – Cooking Gas LPG

The names for the different types of LPG – cooking gas LPG are dependent upon what country you are in.

In Australia, we call it “LPG” or “LPG gas” 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, they sell two types of gas, buying propane or butane by name.

‘Household gas’ and ‘home gas’ are also used for domestic applications.

As previously mentioned, in other countries, they call it “GPL gas” or “GLP gas” instead of “LPG gas”.

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 types of cooking gas LPG, natural gas or LPG composition used as LPG 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 – LPG gas is the most common gas used in gas bottles.