Hydrocarbons - Definition, classes and chain lengths

A hydrocarbon is any chemical compound that is made of just carbon atoms and hydrogen atoms. They are obtained from crude oil by fractional distillation and can be classified in different groups. The four general classes of hydrocarbons are alkanes, alkenes, alkynes and aromatics. The first two groups are the most commonly known as they are used to obtain regular petrol or natural gas and in the production of plastic respectively.

Crude oil is a mixture of hydrocarbons with different carbon chain lengths. The length of these chains will have an effect in the ways how hydrocarbons can be obtained. Smaller hydrocarbons have a low boiling point and are quite volatile, making them ideal for ignition and they are not as useful. In order to obtain shorter chains, long hydrocarbon chains need to be cracked.

Cracking methods

There are two different methods to obtain shorter hydrocarbon chains:

Through thermal cracking. Hydrocarbon thermal cracking involves using high temperatures and low pressure. Here, long hydrocarbon chains are heated to temperatures up to 750 degrees Celsius and 70 atmospheres.

Catalytic cracking. This method is widely used by industries and it involves heating hydrocarbons at a low temperature, usually of 500 degrees Celsius and are passed over a zeolitic catalyst. This catalyst breaks the long chains and it provides a useful hydrocarbon chain.

Transporting short-chain hydrocarbons

As explained above, cracking methods allow for shorter hydrocarbons to be formed. Once these shorter chains have been obtained, due to their volatility, they need to be pressurised regularly, specially if the end product is natural gas. Compressors play an essential role in keeping this hydrocarbons pressurised as they will be transported from compressor stations to other locations.

A compressor stations is, therefore, a site where natural gas or hydrocarbons with very short chains are pressurised and transported. In order to do so, there must be compressor stations every 40 to 100 miles of distance. This will vary depending on terrain and the of wells in the vicinity. There are several types of compressors such as centrifugal compressors, reciprocating compressors, or diaphragm compressors.

The energy used to move a compressor is obtained from two sources:

- natural gas

- electric power

When the source is natural gas, it is the pipeline itself that provides it to the compressor. When it is electric power, this usually is provided by a nearby and highly reliable source. Moreover, this type of source may still require an air permit.

Further information at www.secop.com