Cracking:
Cracking is the breaking up of longer hydrocarbon molecules into smaller ones at high temperature and pressure and in the presence of the catalysts.
Types of Cracking:
Thermal cracking: Thermal cracking involves heating heavy oil or large hydrocarbons e.g. diesel oil, kerosene at high pressure to give low molecular mass hydrocarbon.
\( \scriptsize \underset{Kerosense}{C_{11}H_{24}} \overset{thermal \; cracking}{\normalsize\rightarrow} \scriptsize \underset{Petrol}{C_8H_{18}} \; + \; \underset{Propane}{C_3H_6} \)
Catalytic cracking: Catalytic cracking involves the use of catalyst such as SiO2-Al2O3, natural clay, etc. to break down large hydrocarbons into smaller molecular mass hydrocarbons.
\( \scriptsize C_{18}H_{36} \rightarrow \underset{Hexane}{C_6H_{14}} \; + \; \underset{Petrol}{C_8H_{18}} \; + \; \underset{Ethene}{2C_2H_4} \)
Cracking increases the yield of petrol.
Reforming:
Reforming is the conversion of straight-chain hydrocarbons using catalyst into branch chain isomer, cycloalkanes, and benzenes. The purpose of reforming is to obtain a higher grade of petrol from a lower grade of petrol i.e. improve the quality of petrol.
Reforming Techniques:
Reforming techniques involve: isomerization, cyclization and aromatization
Differences between Cracking and Reforming:
| Cracking | Reforming |
| – Improves the quantity of petrol | – Improves the quality of petrol |
| – Breaks large factions of hydrocarbons into smaller ones | – Rearranges the fractions |
| – Involves high temperature, high pressure and the use of catalyst | – Does not involve high temperature and pressure. It only uses catalyst |
Importance of Cracking:
i. It increases the yield of petrol
ii. It produces petrochemicals such as ethene, propene etc. which are the major raw materials in chemical industry.
Importance of Reforming:
i. To produce high quality petrol
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