Fortunately, almost every country has built up its natural petroleum sources during few decades. However, the supply of motor fuel petrol or gasoline from all sources put together falls far short of the actual needs of a developing country. Therefore, the production of petrol by the synthetic method is engaging the attention of our organic chemists. The 'synthetic petrol' has been produced in Germany from coal, lignite, and other carbonaceous material. The chief methods used for preparing petrol from coal are:
- Fischer - Tropsch Process ( Reduction of Carbon monoxide )
This method was developed in 1923 by two German chemists, Franz Fischer and Hans Tropsch. Carbon monoxide needed in this process is made by passing steam over red-hot 'coke'. The water gas thus obtained is mixed with hydrogen and passed at a pressure of 5-10 atmospheres into a chamber containing a 'cobalt catalyst ' at 200-degree celsius. The product is a mixture consisting mainly of liquid hydrocarbons.
nCO + ( 2n+1 ) H2 reaction Alkane + nH2O
Reactants Products
The ' artificial petroleum ' so obtained is separated by fractional distillation, similar to the one used in Bergius process. The various fractions separated are petrol, kerosene oil, lubricating oil, diesel oil and paraffin wax.
In this method, finely powdered coal and a suitable catalyst is made into a paste with Heavy Oil produced in the process. The coal paste is then preheated and pumped to the converter. Here, the paste is heated to 450 degree Celsius and hydrogen bubbled through it at 250 atm pressure. The coal, which is really a mixture of high molecular complex organic compounds deficient in hydrogen, and elementary carbon, combines with hydrogen to form higher saturated compounds. These as a resulted of cracking and simultaneously hydrogenation yield a mixture of alkanes. Thus the vapours leaving the converter upon condensation yield ' Synthetic Petroleum ' or Crude Oil.This crude oil upon fractional distillation produces:
(1) Petrol; (2) Middle Oil; and (3) Heavy Oil. The Middle oil fraction is again hydrogenated in the vapour phase in contact with a solid catalyst to give more petrol. Actually, the second process yields four times the petrol obtained by the primary hydrogenation of coal.
The heavy oil obtained in the process is recirculated for making fresh coal paste. One ton of soft coal treated as above yields 140 gallons of petrol. The Bergius Process is at present the most promising of all methods so far invented for the production of synthetic motor fuel.
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