Production: Bitumen is produced from selected crude oils through a process of fractional distillation. The crude oil is heated to temperatures of between 300 and 350 degrees Celsius and fed into a distillation column allowing the lightest fractions of the crude to separate, through vaporization, from the heavier fractions, which remain liquid.
The higher boiling point fractions are then drawn-off via a heat exchanger and enter a vacuum distillation column. This process produces a "short residue" that is used to manufacture several grades of bitumen. The pressure and temperature conditions within the vacuum process will determine the hardness of the short residue, and as such the grade of bitumen produced.
The short residue may be further modified by 'air blowing' in which air is passed through the residue at temperatures of 250 - 300 degrees Celsius.
Shown opposite are the typical Penetration or Paving Grades of bitumen. Additional processing provides other grades of bitumen products such as
- Oxidised bitumens - produced by more vigorous air blowing; they are more 'rubber like' and less temperature susceptible than the paving grades.
- Hard Grade bitumens - harder paving grades.
Cutback bitumens - blends of penetration bitumens with solvent such as kerosene.
Emulsions - stabilised suspensions of bitumen in water.
Polymer Modified Bitumens - mixtures of selected bitumens with polymers such as thermoplastics or elastomers.