- Crude oil often contains water, inorganic salts, suspended solids, and water-soluble trace metals.
- Step 0 in the refining process is to remove these contaminants so as to reduce corrosion, plugging, and fouling of equipment and to prevent poisoning catalysts in processing units.
- The two most typical methods of crude-oil desalting are chemical and electrostatic separation, and both use hot water as the extraction agent.
- In chemical desalting, water and chemical surfactant (demulsifiers) are added to the crude, which is heated so that salts and other impurities dissolve or attach to the water, then held in a tank to settle out.
- Electrical desalting is the application of high-voltage electrostatic charges to concentrate suspended water globules in the bottom of the settling tank. Surfactants are added only when the crude has a large amount of suspended solids.
- A third (and rare) process filters hot crude using diatomaceous earth.