As I wrote about the composition of petroleum here and here, oil is not a homogeneous compound, but is a mixture of various types of hydrocarbon compounds with their respective differences in character, both physical and chemical properties.
Petroleum processing itself consists of two main types of processes, namely Primary Process and Secondary Processes. Some people define the Primary Process as physical processes, while the secondary process is a chemical process. It was understandable because the primary process is usually a component or fraction of petroleum are separated based on one of the nature of physics, namely the boiling point. While the process of separation by Secondary work based on the chemical properties of chemicals, such as cracking or splitting or conversion, where the activities occurring in the process of changing the chemical structure of petroleum.
