In order to produce synthetic crude oil, upgrading extra heavy oil and bitumen involves three main objectives. These are as follows:
- Convert high molecular weight residues into distillates, which are compounds with a boiling point below 525°C
- Increase the hydrogen to carbon ratio of the distillate by increasing the hydrogen content and/or reducing the carbon content
- Reduce the amount of impurities such as sulphur, nitrogen and metals in order to meet standards of quality required by refineries. These processes can be separated into two stages of processing: primary and secondary upgrading
Primary upgrading — as the name suggests — is the first stage of processing extra heavy oil and bitumen in order create a distillate. This process is typically done at high temperatures and pressures, which are needed to break or "crack" carbon–carbon bonds and may also involve the initial stages of adding hydrogen to the residue. This is accomplished through 2 families of technologies:
- carbon rejection
- hydrogen addition
Secondary upgrading focuses on the removal of sulphur, nitrogen, metals, as well as napthanic ring opening through hydrotreating or hydrogenation of the distillate. These processes are typically less severe in their operating conditions (i.e. lower pressure and temperature) and utilize chemical and/or biological catalysts to achieve the objectives.