Corrosive elements

Renewable feedstock is seen by many as the way forward to achieve a sustainable source of aviation fuel and diesel.
The renewable feedstock can be based on a wide variety of raw materials, such as animal fat, used cooking oil, vegetable oil, or pyrolysis oils from waste plastics or car tyres. Depending on the feedstock, processing can include a pretreatment step, but it is always followed by hydrotreating to remove sulphur, nitrogen, oxygen and the possible presence of chlorides from the hydrocarbons. After processing the renewable feedstock, the remaining product is a fuel that is chemically identical to that based on fossil feedstock.
Processing
While hydrotreating is a standard process also used for fossil-based feedstock, there are important differences that put high demands on the corrosion resistance of the materials used in piping and heat exchangers.
Compared to traditional fossil feedstock, renewable feedstock is lower in sulphur and nitrogen while being richer in oxygen. Depending on the source of the renewable feedstock, the chloride content can also be higher.
The effluent from the hydrotreating unit will, therefore, contain...