Petroleum

Introduction

Petroleum, also called crude oil, is a naturally occurring complex liquid mixture of hydrocarbons plus 1-6% oxygen-, sulfur-, and nitrogen-containing compounds. It is usually found beneath the surface of the earth in deep reservoirs, although petroleum does seep out at the earth's surface in a few locations. The physical properties and composition of crude oil vary from one location to another.

Petroleum is refined, that is separated into different products based on boiling point ranges, to produce useful components, such as gasoline, kerosene, and diesel fuel. It is a fossil fuel, which means it is a nonrenewable resource. The burning of petroleum products by humans releases greenhouse gases, particularly carbon dioxide, into the atmosphere.

Historical Background and Scientific Foundations

Petroleum is called a fossil fuel because it is created by the transformation of the remains of plants and animals that lived million of years ago. During what geologists call the Cretaceous Period, about 140 million years ago, great quantities of plankton lived in an ancient sea. They died and sank to the bottom where they accumulated and were buried. After a very long time, they were transformed into the oil fields of the Middle East. The

Middle East is considered to have the largest oil reserves on Earth, estimated at 700 billion barrels in 2004 by the Oil and Gas Journal, an industry trade publication.

All of the world's oil reserves have similar histories. Countries that produce large amounts of crude oil include Saudi Arabia, Iran, Iraq, and Kuwait in the Middle East. Africa, Algeria, Libya, and Nigeria are leading petroleum producers. Other large producers include Indonesia, the former Soviet Union, Mexico, and Venezuela.

Petroleum contains three general groups of hydro-carbon compounds identified by chemists as paraffins, aromatics, and naphthalenes. The amount of each type varies from one oil reserve to another, although most petroleum sources have more paraffins and naphthalenes than aromatics. The sulfur in crude oil is undesirable and has to be removed during the refining process so that the final products are less polluting.

Since the first petroleum refinery opened in 1861 to produce kerosene by simple distillation, petroleum refining processes have undergone many changes. Kerosene was burned in lamps for light. With the invention of electric light and internal combustion engines for automobiles and other transportation applications, petroleum was no longer refined principally for kerosene. Instead gasoline and diesel fuel were produced by newer refining processes. Current refineries principally use a process called catalytic cracking, which takes large hydrocarbons in petroleum and breaks them into smaller ones, using a catalyst to speed up the chemical reaction. After various hydrocarbons are cracked into smaller hydrocarbons, the products go through another fractional distillation column to separate them.

Impacts and Issues

The major refinery products today are gasoline for internal combustion engines; kerosene for jet fuel, cooking and heating, and blending with diesel fuel; liquefied petroleum gas (LPG) for heating; diesel fuel for both transportation and heating applications; and other petrochemicals for the manufacture of products like plastics and for solvents and lubricants. The different products are all mixtures of hydrocarbons and each has a specific boiling point range.

All the petroleum products used in major applications are burned in some way. It is this burning of fossil fuels that produces carbon dioxide, and this carbon dioxide is accumulating in the atmosphere, contributing to global warming. In the United States, automobiles produce an estimated 1.5 billion tons of carbon dioxide annually.

Ice core samples taken from the Antarctic show carbon dioxide levels were consistently 280 ppm (parts per million) in the atmosphere for the past 420,000 years until the mid-1800s, when they started to rise. In 2007, the atmospheric concentration of carbon dioxide exceeded 360 ppm. The excess carbon dioxide in the atmosphere acts like a blanket to keep the warmth from solar radiation near the surface of Earth, making it a major contributor to climate change.

WORDS TO KNOW

AROMATIC: In organic chemistry, a compound whose molecular structure includes some variation of the benzene ring.

CATALYTIC CRACKING: Chemical process in which large organic molecules are broken into smaller molecules with the help of a catalyst, a substance that speeds up a chemical reaction without being changed by it. Used in oil refining; proposed (but not yet commercially viable) for the production of biofuels such as ethanol and biodiesel.

DISTILLATION: The process of separating liquids from solids or from other liquids with different boiling points by a method of evaporation and condensation, so that each component in a mixture can be collected separately in its pure form.

HYDROCARBON: A chemical containing only carbon and hydrogen. Hydrocarbons are of prime economic importance because they encompass the constituents of the major fossil fuels, petroleum and natural gas, as well as plastics, waxes, and oils. In urban pollution, these components—along with NO_x and sunlight—contribute to the formation of tropospheric ozone.

ICE CORE: A cylindrical section of ice removed from a glacier or an ice sheet in order to study climate patterns of the past. By performing chemical analyses on the air trapped in the ice, scientists can estimate the percentage of carbon dioxide and other trace gases in the atmosphere at that time.

INTERNAL COMBUSTION ENGINE: An engine in which the chemical reaction that supplies energy to the engine takes place within the walls of the engine (usually a cylinder) itself.

NAPHTHALENE: White aromatic hydrocarbon having chemical formula C₁₀H₈ and a chemical structure of two benzene rings linked to form a figure 8. Household mothballs are made of naphthalene, which is also used in some industrial chemical processes.

PARAFFIN: Any member of a class of molecules having the formula C_nH_2n+. Methane, with n = 1, is the simplest paraffin, CH₄.

IN CONTEXT: HIGHER OIL PRICES

“The higher the market prices of fossil fuels, the more low-carbon alternatives will be competitive, although price volatility will be a disincentive for investors. Higher priced conventional oil resources, on the other hand, may be replaced by high carbon alternatives such as from oil sands, oil shales, heavy oils, and synthetic fuels from coal and gas, leading to increasing GHG [greenhouse gas] emissions, unless production plants are equipped with CCS [CO₂ capture and storage].”

SOURCE: Metz, B., et al., eds. Climate Change 2007: Mitigation of Climate Change. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change New York: Cambridge University Press. 2007.

See Also Atmospheric Pollution; Biofuel Impacts; Hydrocarbons; Petroleum: Economic Uses and Dependency.

BIBLIOGRAPHY

Web Sites

“Geological Time Capsule, Part II.” Digital Library for Earth System Education. <http://egov.oregon.gov/DSL/SSNERR/docs/EFS/ EFS22geo2.pdf> (accessed September 11, 2007).

“Global Warming Basics.” Natural Resources Defense Council. <http://www.nrdc.org/globalWarming/ f101.asp> (accessed September 11, 2007).

“Oil: A Life Cycle Analysis of Its Health and Environmental Impacts.” Harvard University Center for Health and the Global Environment. <http://chge.med.harvard.edu/publications/documents/oilfullreport.pdf> (accessed September 11, 2007).

“OSHA Technical Manual, Section IV, Chapter 2: Petroleum Refining Processes.” U.S. Department of Labor. Occupational Safety & Health Administration. <http://www.osha.gov/dts/osta/otm/otm_iv/otm_iv_2.html> (accessed September 11, 2007).

Miriam C. Nagel