crude oil - origin of bitumen part 2

The first step in petroleum refinery is rectification. Since the boiling points of the compounds of petroleum lie close to each another, differential distillation is employed for the primary separation. 

The refinery involves one or more distillation towers, depending on the desired products. The classification into atmospheric towers and vacuum towers is according to the predominant pressure inside the operating tower. Atmospheric towers operate under "normal" pressure and vacuum towers operate at lower pressure (1333 to 13332 Pa), induced by vacuum pumps or steam ejectors and require different tower geometries. Due to lower pressure and temperature under 425 °C thermal cracking of components is avoided.

During these treatments of separation no chemical changes occur, it is based on the physical properties of petroleum. Further processing of bitumen involves chemical changes and are thermal cracking, catalytic cracking, visbreaking, coking and hydroprocessing.

The vacuum residue has not always the desired properties and so it is post processed. To receive “harder” bitumen (decreasing needle penetration value, change in temperature-viscosity property) the bitumen can be oxidized with air. There are two grades of oxidised bitumen: semi-blown and blown bitumen. The blowing column is about 70% filled with 230 to 260 °C hot vacuum residue. The air is introduced at the bottom and occasionally for more intense mixing baffles or agitation systems are installed. To control the temperature of the generally exothermic reaction water can be sprayed from the top or injected laterally.

Further the vacuum residue can be deasphalted. With solvent (alkane) the asphaltene fraction is removed from bitumen.

For the final product bitumen is blended with itself or other compounds resulting in modified bitumen. The compounds for modified bitumen are for example emulsifier (for production of emulsion), petroleum distillates, polymers, sulphur or waxes. The final product is stored in heated tanks at a temperature of about 185 °C. To avoid oxidation (oxidative hardening) the tanks are pressurise with nitrogen. The delivery too is done by tank lorries at temperature 185 °C ±5 °C.