Of the wide variety of crude oils commercially available, only a limited number are considered suitable for producing bitumen of the required quality, in commercial quantities. In general, these are heavy crude oils with high sulfur content. In modern, integrated refineries it is common practice to blend multiple crude oils to produce consistent quality high grade bitumen that meets precise engineering specifications.
Bitumen Production Overview | Delayed Coking Process Overview
Residues from the distillation of meticulously selected crude oils provide the base materials for bitumen production. Bitumen refining separates the lighter fractions from the residues. Several manufacturing methods are used to produce specification bitumen depending on the crude source and processing capabilities available. Often a combination of processes is selected. The most common refining process is straight reduction from crude or a crude blend, using atmospheric and vacuum distillation. Atmospheric distillation is used to separate lighter petrochemical and fuel fractions from the non-boiling component at the bottom, known as an atmospheric residue.
The lighter fractions, such as gas oil and fuel oils are fed to other refinery units. The atmospheric residue is retained for bitumen. To remove the last traces of the lighter fractions and avoid heat transformation of the molecules, the atmospheric residue is introduced into a vacuum distillation unit, here the pressure reduction lowers boiling temperatures and unwanted thermal cracking of the molecules can be avoided.
Specific solvents can also be used to separate the lubricant and bitumen components of crude, without damaging their chemical structure. According to the solvent used – propane or butane – different categories of bitumen can be obtained. Along with finely controlled variations in the vacuum distillation process, these processes permit the production of bitumen with varying levels of penetration. This property and the softening point are the two fundamental defining characteristics of bitumen produced to engineering specifications. Further key physical properties are sensitivity to temperature and ageing, cohesion and elasticity, all of which are measured by precise tests.