June 4, 1998 Nanotech Device Promises Wide Applications
A new, inexpensive filter efficiently removes sulfur and other impurities from crude oil and serves as a miniature refinery to upgrade the crude, a University of Southern California researcher reports.
"In preliminary tests, our filter removes as much as 60% of the sulfur in a single pass," says Teh Fu Yen, Ph.D., a professor of environmental and civil engineering at the USC School of Engineering. Dr. Yen is developing the device with funding from Klinair Environmental Technologies, of Dublin, Ireland.
To make the filter, a mixture of two metals is heated to nearly 1,000 degrees Fahrenheit and sprayed through a nozzle. Emerging as a fine crystalline powder, this "intermetallic" substance is bonded to an inert substrate, such as carbon fiber.
The coated substrate is then packed into a hollow glass cylinder -- creating a large interior surface. The greater the surface, the higher the efficiency of the filter.
Crystals occur in an infinite variety of shapes. Yen can control the shape of the crystals by using certain chemicals. To remove sulfur, he treats the intermetallic powder to produce a crystalline structure containing small pits that match the size and shape of sulfur molecules.
"The crystalline structure can sort out the bad without affecting the good," says Yen. "Analogous methods of nanotechology might also be used to remove nitrogen compounds, metals and other impurities. South America, China, Canada and certain republics of the former Soviet Union have large reserves of crude that are heavily contaminated with sulfur, metals and other impurities. Intermetallic filters could purify such oils both efficiently and economically."
By altering the crystalline structure, variants of the intermetallic filter might also be used to treat sewage and purify wastewater, Yen suggests.
Yen says his sulfur-removing filter works best when the crude is mixed in an emulsion of water. In nature, petroleum is often found in that very sort of emulsion; and sometimes drillers create such emulsions by pumping water or steam into petroleum deposits to force out the crude.
Because of the polarity of oil molecules in a water emulsion, the petroleum's sulfur molecules tend to hide within clusters of hydrocarbon molecules called micelles, Yen explains. When sodium and calcium surfactants are added, he says, the emulsion changes polarity and the sulfur molecules move to the surface of the micelles, where they are exposed to the intermetallic filter.
When Yen first tested the filter, it not only removed the sulfur but also absorbed the surfactants. The device soon stopped working. But Yen found that running an electrical current through the filter and the oil and water emulsion forces the surfactants to stay in solution, thus preserving the desired polarity and allowing the filter to continue removing sulfur.
Periodically, the electrical current may be reversed to dislodge the accumulated impurities, which are removed. The filter can then be used again and again.
By fine-tuning several parameters, such impurities as oxygen compounds, nitrogen compounds and organometallic compounds can also be extracted from crude.
In its natural, unprocessed state, crude oil is a mixture of hydrocarbon compounds, and the mixture is found in thousands of variations. After the crude's volatile compounds have been taken off, three main parts remain. The thickest, heaviest and most viscous compounds are classified as asphaltene. Next come the resins. Last are the lighter compounds, known as gas oils.
In addition to removing impurities, Yen's filter serves as a miniature refinery. When crude passes through it, some of the asphaltene can be "cracked" and upgraded into resin. "We can reduce the asphaltene content by about 20%," says Yen.
By changing the electrical current, the filter also can do the reverse and turn some of the resin into asphaltene. "This application could improve the specifications of roofing and paving asphalt by increasing the asphaltene content," says Yen.
With further research, he predicts, we can someday use intermetallic filters to do much of the processing that petroleum refineries now perform. "We will no longer need high temperatures and pressures, just an array of inexpensive intermetallic filters to process the oil," he says. "The process -- and its products -- will be far more environmentally friendly."
Sulfur in petroleum pollutes the air when oil products burn. Sulfur in gasoline poisons the catalyst in catalytic converters and causes them to stop working. Refineries can remove the sulfur by heating the petroleum to 700 degrees Fahrenheit at 70 times atmospheric pressure, but that process is too expensive to be widely used today.
Yen has been studying the basic science of petroleum components for decades. Assisting him in the intermetallic filter research are environmental engineering graduate students Steve Lu, Iris Yang and Harry Mei.
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