petroleum refining

Distillation of kerosene and naphtha

The refining of crude petroleum owes its origin to the successful drilling of the first oil wells in Ontario, Canada, in 1858 and in Titusville, Pennsylvania, U.S., in 1859. Prior to that time, petroleum was available only in very small quantities from natural seepage of subsurface oil in various areas throughout the world. However, such limited availability restricted the uses for petroleum to medicinal and specialty purposes. With the discovery of “rock oil” in northwestern Pennsylvania, crude oil became available in sufficient quantity to inspire the development of larger-scale processing systems. The earliest refineries employed simple distillation units, or “stills,” to separate the various constituents of petroleum by heating the crude oil mixture in a vessel and condensing the resultant vapours into liquid fractions. Initially the primary product was kerosene, which proved to be a more abundant, cleaner-burning lamp oil of more consistent quality than whale oil or animal fat.

The lowest-boiling raw product from the still was “straight run” naphtha, a forerunner of unfinished gasoline (petrol). Its initial commercial application was primarily as a solvent. Higher-boiling materials were found to be effective as lubricants and fuel oils, but they were largely novelties at first.

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The perfection of oil-drilling techniques quickly spread to Russia, and by 1890 refineries there were producing large quantities of kerosene and fuel oils. The development of the internal-combustion engine in the later years of the 19th century created a small market for crude naphtha. But the development of the automobile at the turn of the century sharply increased the demand for quality gasoline, and this finally provided a home for the petroleum fractions that were too volatile to be included in kerosene. As demand for automotive fuel rose, methods for continuous distillation of crude oil were developed.

Conversion to light fuels

After 1910 the demand for automotive fuel began to outstrip the market requirements for kerosene, and refiners were pressed to develop new technologies to increase gasoline yields. The earliest process, called thermal cracking, consisted of heating heavier oils (for which there was a low market requirement) in pressurized reactors and thereby cracking, or splitting, their large molecules into the smaller ones that form the lighter, more valuable fractions such as gasoline, kerosene, and light industrial fuels. Gasoline manufactured by the cracking process performed better in automobile engines than gasoline derived from straight distillation of crude petroleum. The development of more powerful airplane engines in the late 1930s gave rise to a need to increase the combustion characteristics of gasoline and spurred the development of lead-based fuel additives to improve engine performance.

During the 1930s and World War II, sophisticated refining processes involving the use of catalysts led to further improvements in the quality of transportation fuels and further increased their supply. These improved processes—including catalytic cracking of heavy oils, alkylation, polymerization, and isomerization—enabled the petroleum industry to meet the demands of high-performance combat aircraft and, after the war, to supply increasing quantities of transportation fuels.

The 1950s and ’60s brought a large-scale demand for jet fuel and high-quality lubricating oils. The continuing increase in demand for petroleum products also heightened the need to process a wider variety of crude oils into high-quality products. Catalytic reforming of naphtha replaced the earlier thermal reforming process and became the leading process for upgrading fuel qualities to meet the needs of higher-compression engines. Hydrocracking, a catalytic cracking process conducted in the presence of hydrogen, was developed to be a versatile manufacturing process for increasing the yields of either gasoline or jet fuels.

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Environmental concerns

By 1970 the petroleum-refining industry had become well established throughout the world. Delivery of crude oil to be refined into petroleum products had reached almost 2.3 billion tons per year (40 million barrels per day), with major concentrations of refineries in most developed countries. As the world became aware of the impact of industrial pollution on the environment, however, the petroleum-refining industry was a primary focus for change. Refiners added hydrotreating units to extract sulfur compounds from their products and began to generate large quantities of elemental sulfur. Effluent water and atmospheric emission of hydrocarbons and combustion products also became a focus of increased technical attention. In addition, many refined products came under scrutiny. Beginning in the mid-1970s, petroleum refiners in the United States and then around the world were required to develop techniques for manufacturing high-quality gasoline without employing lead additives, and beginning in the 1990s they were required to take on substantial investments in the complete reformulation of transportation fuels in order to minimize environmental emissions. From an industry that at one time produced a single product (kerosene) and disposed of unwanted by-product materials in any manner possible, petroleum refining has become one of the world’s most stringently regulated manufacturing industries, expending a major portion of its resources on reducing its impact on the environment as it processes some 4.6 billion tons of crude oil per year (roughly 80 million barrels per day).

Hydrocarbon chemistry

Petroleum crude oils are complex mixtures of hydrocarbons, chemical compounds composed only of carbon (C) and hydrogen (H).