Lets discuss Processing / Refining :

Refining use to be a low cost operation until the OPEC (Organization of Petroleum Exporting Countries) raised the price. Refining involves two major branches one is Separation and the other is Conversion process. In the past, refineries use to separate petroleum into saleable components using distillation. After the separation these crude products were Chemically treated Or Heat treated. This was done so that it could improve the quality of crude product. At some point in history the demand for gasoline exceeded the supply of gasoline and therefore a new way was found to generate more gasoline from the amount available at the supply. Refinery started using a method in which the application of heat and pressure to Heavier unwanted fractions caused the large molecules in these fractions to convert into smaller ones, this occurred once the substance reached the boiling range of gasoline. This process was carried out in a pressure still and is now known as cracking. So basically, Cracking / Pyrolysis is a process which involves the breakdown of large hydrocarbons molecule into smaller molecules by heat or catalytic action, referred to as Thermal Cracking or Catalytic Cracking. This is one of the most important processes for the production of gasoline. Cracking produces a Superior gasoline because more olefins and branched chain hydrocarbons are present in the product produced by cracking compared to the original run gasoline. The cracking process improved even more when an active catalyst was added during the cracking process, this is now known as Catalytic cracking. There are other chemical conversion processes other than Cracking but these processes are carried out on a large but lesser scale, these include alkylation, isomerization, hydrogenation, polymerization, reforming and dehydrogenation. Refineries were originally batch units with cylindrical under fired shell still which were operating as topping units. These units were continuously pumping oil through to heaters known as pipe stills or tube stills. After which the constituents were separated in a continuous fractionating columns. These continuous fractionating columns were responsible for separating many fractions between gas and asphalt. This process is now universally practiced. The conversion process is meant to optimize yields, from the primary separation process, into more saleable and profitable products. Usually this applies to maximum yields of gasoline. It is possible to convert all the crude into gasoline since this above mention method is mostly carried out to produce gasoline. But it would be a very expensive process.