Web Date: August 12, 2011
Detecting Crude Oil In Water
On a tiny island at Scotland’s northeast tip, workers at the Flotta Oil Terminal process crude oil carried by pipelines from North Sea oil fields and then pump the oil into tankers for distribution across the globe. Now researchers have shown that a type of mass spectrometry could help workers at Flotta and other oil processing facilities to detect seawater that’s contaminated with low levels of oil (Anal. Chem., DOI: 10.1021/ac2008042).
Oil pumped from undersea wells contains seawater. At the Flotta Oil Terminal and other facilities, workers extract oil from the water until the oil-in-water concentration drops to a low, government-regulated level. They then discharge the resulting water back to the sea. Even with government regulations, an estimated 2.1 million barrels of oil per day worldwide enter the sea with the released water, says Stephen Taylor, an electrical engineer at the University of Liverpool, in the U.K.
Facilities currently rely on methods such as ultraviolet fluorescence and infrared spectroscopy for oil-in-water monitoring. Taylor and his colleagues thought that mass spectrometry could enhance existing detection techniques by measuring oil levels more accurately and at lower concentrations, while also providing information about the type of oil present. Knowing the type of crude oil present in water could help oil terminal workers pinpoint problems with the oil extraction process.
The team tested the ability of membrane inlet mass spectrometry (MIMS) to detect and analyze crude oil in seawater. MIMS relies on a membrane to block water and other polar molecules in a sample from entering the mass spectrometer, while allowing hydrophobic compounds such as oil to pass through for detection.
Although MIMS isn’t a new technique, researchers haven’t tested it extensively in field trials. “It’s one thing to use MIMS on a beaker full of oily water in the lab, but quite another to do it in the harsh environment of the North Sea,” Taylor says. He and his colleagues wanted to see if a portable MIMS system could handle the non-standard temperature, salinity, and particulate concentration of the water at Flotta.
For their field tests, the researchers mixed crude oil with seawater from the Flotta facility at known oil concentrations. The team measured concentrations of crude oil as low as 15 mg/L, which is half the legal discharge limit in the U.K. Also, the technique could differentiate between two types of North Sea crude oil, API 35 and API 36, based on differences in hydrocarbon composition. MIMS effectively detected oil at a range of water temperatures and oil droplet sizes.
Now Taylor is working on improvements to the MIMS system that will enhance its sensitivity and ease of use. He plans to eventually couple the portable MIMS instrument with existing oil-in-water monitors to complement, rather than replace, their abilities.
“Very few groups have ventured far from the lab with mass spectrometry,” says Guido F. Verbeck, a chemist at the University of North Texas. “Taylor’s instrument is one that breaks this mold and applies mass spectrometry directly to field analysis.” He adds that in addition to monitoring oil in water at processing facilities, the portable MIMS system might prove useful for early detection of spills at wellhead sites.
The story was updated on July 15, 2011, to correct the measured oil concentration units.
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