refining

Any process that purifies or converts something into a more useful form. Metals usually need refining after they have been extracted from their ores by such processes as smelting. Petroleum, or crude oil, needs refining before it can be used; the process involves fractional distillation, the separation of the substance into separate components or ‘fractions’.

Electrolytic metal-refining methods use the principle of electrolysis to obtain pure metals. When refining petroleum, or crude oil, further refinery processes after fractionation convert the heavier fractions into more useful lighter products. The most important of these processes is cracking; others include polymerization, hydrogenation, and reforming.