Petroleum processing and refining

Petroleum processing and refining

The separation of petroleum into fractions and the treating of these fractions to yield marketable products. Petroleum is a mixture of gaseous, liquid, and solid hydrocarbon compounds that occurs in sedimentary rock deposits throughout the world. In the crude state, petroleum has little value but, when refined, it provides liquid fuels (gasoline, diesel fuel, aviation fuel), solvents, heating oil, lubricants, and the distillation residuum asphalt, which is used for highway surfaces and roofing materials. See also: Petroleum; Petroleum products

Crude petroleum (oil) is a mixture of compounds with different boiling temperatures that can be separated into a variety of fractions (Table 1). Since there is a wide variation in the composition of crude petroleum, the proportions in which the different fractions occur vary with origin. Some crude oils have higher proportions of lower-boiling components, while others have higher proportions of residuum (asphaltic components).

Petroleum processing and refining involves a series of steps by which the original crude oil is converted into products with desired qualities in the amounts dictated by the market. In fact, a refinery is essentially a group of manufacturing plants that vary in number with the variety of products in the mix. Refinery processes must be selected and products manufactured to give a balanced operation; that is, crude oil must be converted into products according to the demand for each. For example, the manufacture of products from the lower-boiling portion of petroleum automatically produces a certain amount of higher-boiling components. If the latter cannot be sold as, say, heavy fuel oil, these products will accumulate until refinery storage facilities are full. To prevent such a situation, the refinery must be flexible and able to change operations as needed. This usually means more processes, such as thermal processes to change excess heavy fuel oil into gasoline with coke as the residual product, or vacuum distillation processes to separate heavy oil into lubricating oil stocks and asphalt.

Early refineries (70 years ago) were predominantly distillation units with, perhaps, ancillary units to remove objectionable odors from the various product streams. The refinery of today (Fig. 1), the result of major evolutionary trends, is a highly complex operation. Most of the evolutionary adjustments to refineries have occurred since 1940. In the petroleum industry, as in many other industries, supply and demand are key factors in efficient and economic operation. Innovation is also key.

Fig. 1 Schematic of a petroleum refinery showing the various units. (After J. G. Speight, ed., The Chemistry and Technology of Petroleum, 3d ed., Marcel Dekker, New York, 1999)