Fuels - Part VI

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Natural gas : Natural gas is obtained along with petroleum from oil wells. It contains mainly methane (CH4) and has some quantities of ethane (C2H6) and propane (C3H8). The formation of natural gas is always along with the formation of petroleum deep within the earth’s crust. When there is a search for an oil well, if natural gas is struck, there is a strong possibility of having an oil well close to the site.  

Uses of natural gas :  

  • Natural gas is used as fuel in industries. It is also used as domestic fuel where piped gas is made available from the wells to the homes.

  • Natural gas is used as a source for obtaining hydrogen. Hydrogen is needed by industries as a reducing agent. Hydrogen is also used to make ammonia and ammonium fertilizers. Methane is heated strongly so that it decomposes into its component gases : carbon and hydrogen.

  • Carbon obtained from the decomposition of natural gas is used in tyre industries.  

Advantages of using natural gas :
1. Natural gas burns easily without any smoke. Hence it is very useful as a domestic fuel.
2. Natural gas has a very high calorific value (55 kJ/g) which is good for heating.
3. It causes no pollution or produces no poisonous gases.
4. Natural gas can be supplied directly through pipes from the oil wells. This eliminates the need for storage and transport of the gases in cylinders.

Disadvantages of using natural gas :
1. Natural gas is highly flammable and many precautions have to be taken before using it.
2. Pipelines to deliver the gas from the well to the site of use are very expensive. The pipelines need to be laid underground and checked for leakage, pilferage, etc. Thus the maintenance cost of the pipelines becomes very expensive.  

Synthetic petroleum : Artificial or synthetic petrol is obtained from coal and not from oil wells. A scientist called Bergius developed this process in Germany in 1913. Artificial petrol is used in countries that have large demand for petrol but do not have adequate oil wells themselves.

Preparation of synthetic petrol :
There are mainly three steps for obtaining synthetic petrol.
1. Hydrogen is made to react with large unsaturated hydrocarbons in coal, so that saturated hydrocarbons are formed.
2. Catalytic cracking process is done on the big saturated hydrocarbons to obtain small unsaturated as well as saturated hydrocarbons.
3. Hydrogen is made to react with small unsaturated hydrocarbons in the second step to produce liquid saturated hydrocarbons, which are closely like petroleum.

The reaction below shows how coal is converted into petroleum.  

Coal is mixed with heavy oil and is heated to a temperature of 450°C. The pressure is kept at about 250 atmospheres. The catalyst used is an organic derivative of tin. The synthetic petroleum obtained has to be subjected again to fractional distillation. The fractions are petrol, middle oil and heavy oil. The middle oil is again subjected to hydrogenation in step 1. The heavy oil is again reused with coal powder and the process from step 1 is restarted.

Synthetic natural gas : Methane produced artificially is called synthetic natural gas. The raw material here is again coal. Finely powdered coal is heated in hydrogen under pressure. A catalyst is also used. Complex hydrocarbons present in coal react with hydrogen to form methane. Other reaction products are also obtained, but they are not gaseous.  

 

 

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