ABSTRACT
The basic raw material for refineries is petroleum or crude oil, even though in some areas synthetic crude oils from other sources (Gilsonite, tar sands, etc.) and natural gas liquids are included in the refinery feedstocks. The chemical compositions of crude oils are surprisingly uniform even though their physical characteristics vary widely. The elementary composition of crude oil usually falls within the following ranges. Element Percent by weight Carbon 84-87
In the United States, crude oils are classified as paraffin base, naphthene base, asphalt base, or mixed base. There are some crude oils in the Far East which have up to 80% aromatic content, and these are known as aromatic-base oils. The U.S. Bureau of Mines [1, 2] has developed a system which classifies the crude according to two key fractions obtained in distillation: No. 1 from 482 to 527°F (250 to 275°C) at atmospheric pressure and No. 2 from 527 to 572°F (275 to 300°C) at 40 mmHg pressure. The gravity of these two fractions is used to classify crude oils into types as shown below. Key fractions, •API No. 1 No. 2 Paraffin 40 30
The paraffinic and asphailic classifications in common use are based on the prop-erties of the residuum left from nondestructive distillation and are more descrip-tive to the refiner because they convey the nature of the products to be expected and the processing necessary.
