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How is Propane Fuel Made?

Satyajeet Vispute
Propane plays an important role as an energy source. It has several domestic and industrial applications. We find out what it is, and how it can be extracted from various sources.

Did You Know?

Propane gas is odorless and colorless. It is also highly flammable. Therefore an external odorant is added to it for easy detection in case of a leak.
When a liquid boils, natural tendency is to assume it very hot. However, there is one liquid which boils at temperatures much below freezing point of water. But that's not all that is amazing about it. This liquid which boils at freezing subzero temperatures, also produces a gas that burns! Bewildering isn't it? This unusual liquid is known as propane.
Propane is one of the many by-products obtained from petroleum. But being a by-product doesn't mean that it's a waste product. It finds a lot of use in everyday life. As of 2014, 6.2 million American households use propane as their primary heating fuel.
Propane is a useful handyman in many homes. It cooks food in our kitchens, heats water in bathrooms and warms our house in cold. In farms, it allows the farmer to generate electricity, warm his chicks and fuel his tractors. Propane is used in industries to power the forklift truck. It is used to heat treat different metals and other industrial uses.
Clearly, propane is an important source of energy. In the further sections, we shall look at what this bizarre yet highly useful fuel is, and how is it made.

What Elements is Propane Made Of

Propane is an alkane comprising a linear chain of 3 carbon atoms. Its molecular formula is C3H8. It belongs to the group of liquefied petroleum gases which includes butane, propylene, butadiene, butylene, isobutylene, and its mixtures.
Propane is a gas at room temperatures, but becomes a liquid under high pressure or low temperatures. It has a molecular weight of 44.1 g/mol and has a boiling point temperature of -43.6ºF at 1 atm.

How is Propane Made

Propane is a naturally occurring gas which gets created with several other hydrocarbons as crude oil, gasoline, and butane, from decomposition of organic matter beneath the Earth's surface over a long time. It is found as a mixture in natural gas and oil reserves and has to be processed to be separated. There are two ways to extract propane.
Both methods begin with the digging of oil wells to pump out the oil that is present underground. The oil and gas mixture that is pumped out of the oil well is collected into a gas trap. The crude oil in the mixture being heavier, sinks to the bottom of the trap and is pumped out for further refinement.
The 'wet' gas from the mixture rises to the top of the trap from where it is piped out for processing. Propane is extracted from both these natural sources as discussed ahead.

From Natural Gas

The natural gas used by consumers is very different from the 'wet' gas that comes out of the wells. It is almost purely methane, while that present in the wells comprises several different constituents, such as methane, hydrocarbons, moisture, hydrogen sulfide, helium, nitrogen and other compounds, that make it impure.
For the purpose of purification, natural gas is processed, and it is during this processing that propane is obtained from it as a by-product.
Natural gas processing involves separating all the different hydrocarbons and fluids from the raw gas in order to obtain pure pipeline quality dry gas. Propane is extracted from these fluid components as a by-product. To separate propane, hydrocarbons are fractionated by passing the raw natural gas through an oil.
The oil which is used has an affinity for hydrocarbons and readily absorbs them. The hydrocarbons from the hydrocarbon-rich oil are later separated on being adsorbed by surface-active agents or through the process of refrigeration. Natural gas typically consists of nearly 90% methane and 5% propane. Yet, half the propane used in U.S. comes from natural gas.

From Oil

During the process of refining crude oil, liquefied petroleum gases are produced at various stages. The liquefied petroleum gases have two major components―propane and butane―which together constitute a total of 1% to 4% of processed crude oil.
To separate propane, crude oil is made to undergo the process of fractional distillation. Heavier hydrocarbons in the oil sink to the bottom, and lighter ones, including propane, are easily extracted from uppermost layer of the mixture. The quantity of propane obtained by the oil extraction is usually variable depending on particular type of oil refinery.
Propane burns much more cleanly as compared to other fuels such as gasoline, kerosene etc. It releases much fewer harmful emissions including greenhouse gases, and is therefore, a much better alternative fuel especially for powering vehicles. But propane reserves are only as extensive as those of oil and natural gas.
With tremendous increase in the demands for fossil fuels in past few decades, it is quite likely that natural stores of propane, along with all other fossil fuels, will run out in the near future. In response, scientists have begun investigating alternative sources of energy. In many laboratories across the world, fuels are being artificially produced.
Propane has been chosen as the best candidate for being artificially created, thanks to its lower emissions and ease of transport. These are the two artificial means of production of propane that are currently being researched.

From Biomass

Many renewable sources including vegetable oil and biomass, such as sugarcane, switchgrass, etc., are being considered for synthesizing propane. Scientists have successfully been able to demonstrate the production of propane from these sources in laboratories; however, the procedures being used currently aren't very cost-effective.
A lot of research is being done in order to find an economical way of producing propane from these sources.

From Bacteria (E. coli)

Recently, a team of scientists from London have successfully demonstrated that they can obtain propane from glucose by using a genetically engineered version of bacterium E. coli. The team was able to modify the process of fatty acid synthesis in this bacterium by introducing group of enzymes into it that resulted in conversion of fatty acids to propane.

How is Liquid Propane Made from Propane Gas

Propane gas when liquefied, compresses to nearly 270 times its volume as a gas. This makes it possible to transport a large amount of propane making liquefaction of propane of great commercial importance. Propane gas is liquefied using high pressure or by freezing it to very low temperatures.
Propane needs to be carefully isolated from the mixture of petrochemicals. If these impurities are allowed to remain, propane won't liquefy properly. Appropriate temperatures and pressures are critical for optimum liquefaction. For this, standards and specifications have been established by the liquefied gas industry.
Commercially useful propane cannot have more than 0.0017 ounces (0.05 ml) of residual matter and must have a maximum vapor pressure of 200 psig at 100º F. Other than this, commercial propane also needs to adhere to the standards for corrosiveness, volatility, moisture, etc.
Thus, propane is derived using different processes from its natural sources such as natural gas and oil. Research is also being carried out for producing it artificially. Propane as a fuel can act as an almost clean source of energy. Produced artificially and in a renewable manner, it may even help solve our energy crisis in the coming years.