ASK A SCIENTIST
Question: How is gasoline made? What chemicals are in it? Why is it explosive?
What great questions! Gasoline is one of the products derived from distilling and refining petroleum, or crude oil. Petroleum is formed when decaying organic matter, primarily algae and zooplankton, is trapped underneath sedimentary rock under intense heat and pressure. This can be a process that takes several thousand to several million years. This raw material is pumped up from the ground, like water from a well, and sent to an oil refinery for processing.
Crude oil is a complex mixture of hundreds of different hydrocarbons, molecules consisting entirely of hydrogen and carbon atoms. Each hydrocarbon has different chemical and physical properties due to its length and the configuration of its atoms. The boiling points of hydrocarbons generally increase with size, so a chemical containing one carbon atom will have a lower boiling temperature than a chemical containing 10 caron atoms. Oil refineries are able to separate the compounds present in crude petroleum by exploiting the difference in boiling point through a process called fractional distillation.
Liquid crude oil is first heated until it vaporizes, just as water turns to steam when boiled on the stove. This gas, containing the many hydrocarbons is then passed into the bottom of a tall distillation tower. As the vapor rises in the tower, its temperature decreases; when the temperature falls below the boiling point of a specific compound in the mixure, that compound will condense out of the mixture and back into a liquid. By collecting the liquid at various heights in the tower, the refinery is able to separate the petroleum into more useful "fractions." While there is no precise recipe for gasoline, hydrocarbons that have between 5 carbon atoms and 11 carbon atoms are blended with additives to help clean, lubricate and boost the performance of your engine.
Gasoline is explosive because it has a lot of energy stored in each molecule, and it is able to give off flammable vapors at low temperatures. Gasoline is only combustible when it mixes with air in its gaseous state, and there must be a specific amount in the air-fuel mixture. If the mixture contains less than 1.4% gasoline, or greater than 7.6% gasoline, it wil not burn.
It's important to note that refined petroleum is not just used for fuel. One 42 gallon barrel of oil yields approximately 19.5 gallons of gasoline. The rest (over half), once refined from crude oil, can be further chemically transformed into a myriad of other organic compounds - the precursors to products we use every day. The health and beauty industry uses these materials to produce products including soap, toothpaste, lip balm, and nail polish. In addition, candle wax, toilet seats, DVDs, footballs, dentures and viola strings, all have material origins in crude oil.
Ask a Scientist appears Thursdays. Questions are answered by faculty at Binghamton University. Teachers in the greater Binghamton area who wish to participate in the program are asked to write to Ask A Scientist, c/o Binghamton University, Office of Communications and Marketing, PO Box 6000, Binghamton, NY 13902-6000 or e-mail email@example.com. Check out the Ask a Scientist Web site at askascientist.binghamton.edu. To submit a question, download the submission form(.pdf, 460kb).