Oct 23, 2026 04:26 PM
https://www.acsh.org/news/2026/10/22/why...stry-50367
EXCERPTS: Diesel used to be cheaper than gasoline. Not anymore. Both fuels come from the same crude oil, so why the big price difference? Economics plays a role, but chemistry deserves much of the blame. Especially the surprisingly difficult and expensive business of getting rid of stinky sulfur.
[...] Crude oil contains sulfur, sometimes several percent by weight. But we're not talking about little chunks of yellow sulfur floating around in the oil. Much of it is chemically incorporated into organic molecules, appropriately called organosulfur compounds. Why does this matter? When sulfur-containing fuels burn, they produce sulfur dioxide (SO₂), which contributes to air pollution, acid rain, and the formation of fine particulate matter.
To reduce these emissions, the EPA progressively tightened sulfur limits in diesel fuel. Beginning in 2006, the United States began transitioning to ultra-low-sulfur diesel (ULSD), which contains no more than 15 parts per million (ppm) sulfur. That's an extraordinarily low concentration, especially considering that some crude oils contain 30,000–50,000 ppm sulfur. Getting down to 15 ppm requires some serious chemistry, none of which you will be especially eager to read about. (MORE - details)
EXCERPTS: Diesel used to be cheaper than gasoline. Not anymore. Both fuels come from the same crude oil, so why the big price difference? Economics plays a role, but chemistry deserves much of the blame. Especially the surprisingly difficult and expensive business of getting rid of stinky sulfur.
[...] Crude oil contains sulfur, sometimes several percent by weight. But we're not talking about little chunks of yellow sulfur floating around in the oil. Much of it is chemically incorporated into organic molecules, appropriately called organosulfur compounds. Why does this matter? When sulfur-containing fuels burn, they produce sulfur dioxide (SO₂), which contributes to air pollution, acid rain, and the formation of fine particulate matter.
To reduce these emissions, the EPA progressively tightened sulfur limits in diesel fuel. Beginning in 2006, the United States began transitioning to ultra-low-sulfur diesel (ULSD), which contains no more than 15 parts per million (ppm) sulfur. That's an extraordinarily low concentration, especially considering that some crude oils contain 30,000–50,000 ppm sulfur. Getting down to 15 ppm requires some serious chemistry, none of which you will be especially eager to read about. (MORE - details)