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Working Knowledge: Oil Refineries—Carbon Hooch

Heating oil, gasoline, jet fuel, kerosene and plastics. These products and more are derived from crude oil in one big fuming silo, siphoned off and fine-tuned through a bewildering maze of pipes.


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Crude oil contains hundreds of different hydrocarbons. Yet U.S. refineries convert half of all crude into gasoline--a blend of fuel stocks, particularly 2,2,4-trimethylpentane (eight carbon atoms chained together) and heptane (seven carbon atoms). The more complex the chain, the more the molecule can be compressed before it ignites spontaneously, allowing an engine to operate at a higher compression ratio--greater power output. The test mixture by which a gasoline's octane rating is judged combines 2,2,4-trimethylpentane and heptane (87 to 13 percent for "87 octane").

Refiners have tried additives over time to boost octane rating. Tetraethyl lead worked in "leaded" gasoline but was phased out because it spoiled catalytic converters. Producers switched to methyl tertiary butyl ether (MTBE), but it has been implicated in contaminating groundwater, and state governments are banning it. An alternative increasingly being used is ethanol, which has an octane rating of 108 or 110; gasoline with 10 percent ethanol is marketed as gas-o-hol.

Mark Fischetti has been a senior editor at Scientific American for 17 years and has covered sustainability issues, including climate, weather, environment, energy, food, water, biodiversity, population, and more. He assigns and edits feature articles, commentaries and news by journalists and scientists and also writes in those formats. He edits History, the magazine's department looking at science advances throughout time. He was founding managing editor of two spinoff magazines: Scientific American Mind and Scientific American Earth 3.0. His 2001 freelance article for the magazine, "Drowning New Orleans," predicted the widespread disaster that a storm like Hurricane Katrina would impose on the city. His video What Happens to Your Body after You Die?, has more than 12 million views on YouTube. Fischetti has written freelance articles for the New York Times, Sports Illustrated, Smithsonian, Technology Review, Fast Company, and many others. He co-authored the book Weaving the Web with Tim Berners-Lee, inventor of the World Wide Web, which tells the real story of how the Web was created. He also co-authored The New Killer Diseases with microbiologist Elinor Levy. Fischetti is a former managing editor of IEEE Spectrum Magazine and of Family Business Magazine. He has a physics degree and has twice served as the Attaway Fellow in Civic Culture at Centenary College of Louisiana, which awarded him an honorary doctorate. In 2021 he received the American Geophysical Union's Robert C. Cowen Award for Sustained Achievement in Science Journalism, which celebrates a career of outstanding reporting on the Earth and space sciences. He has appeared on NBC's Meet the Press, CNN, the History Channel, NPR News and many news radio stations. Follow Fischetti on X (formerly Twitter) @markfischetti

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Scientific American Magazine Vol 294 Issue 6This article was originally published with the title “Carbon Hooch” in Scientific American Magazine Vol. 294 No. 6 (), p. 0