Researchers make clean diesel fuel from chip fat

Oil that has been used to fry potatoes can be converted into an environmentally friendly diesel fuel faster and less expensively than current processes while producing an even higher grade fuel, say researchers at the the U.S. Department of Energy Idaho National Engineering and Environmental Laboratory.

The process of converting vegetable oils or animal fats to diesel fuel is nothing new. Biodiesel fuel has been produced and tested for years as an alternative to petroleum based diesel fuel, or “petrodiesel.”

Using biodiesel in place of petrodiesel offers some distinct advantages. First, the biodiesel is much more environmentally friendly. It burns cleaner and more completely, meaning less pollution. Pollutants include hydrocarbons, sulfur, carbon monoxide and particulates, which are responsible for the thick black exhaust clouds that foul the air behind some diesel-powered vehicles.

Biodiesel is also free of aromatic compounds, the substances that give fuel its “cetane” rating (diesel’s equivalent of gasoline’s more familiar octane rating). However, these compounds include toxic chemicals like benzene and toluene and are carcinogenic. Biodiesel actually has a better cetane rating than petrodiesel without using aromatics.

Particulates and aromatic compounds lead to the familiar, caustic odor of burned petrodiesel fuel. Biodiesel has a different, yet probably more familiar odour when it burns. It smells like fried chicken.

In fact, it smells so much like fried chicken that when the US National Park Service considered using biodiesel fuel for tour buses in the parks, it worried that bears would chase the vehicles in the mistaken perception they were chasing finger-licking-good meals on wheels.

“We told the park service that bears don’t often eat at Kentucky Fried Chicken,” researcher Bob Fox laughs while explaining how the service’s fears were allayed. Yellowstone National Park later began experimenting with biodiesel in its “Truck in the Park.”

A major benefit for the national parks and many other users of biodiesel is that the fuel is rapidly biodegradable, unlike petroleum based fuels. In case of an accidental spill, any damage would be reversible and make a minimal impact.

Improving the process

The current method of producing biodiesel is very time consuming. It is not a continuous process but, is made in batches that take two or three days to complete.

First, a liquid base is added to a mixture of used oil and an alcohol, such as ethanol. This base causes the chemical reaction that forms biodiesel and glycerol. After several hours the reaction is complete and then biodiesel, glycerol and unreacted compounds must sit for several more hours to promote compound separation.

More time is needed to allow residue alcohol to evaporate, and then acid is added to neutralize the base added earlier. Finally, the remaining acid is rinsed away, creating three gallons of wastewater for every one gallon of biodiesel fuel.

Working in the Idaho National Engineering and Environmental Laboratory’s Research Center labs, Fox and Ginosar have developed a new method that produces a higher grade biodiesel with less waste at a lower cost.

Their technology eliminates the need for a base liquid, which thus eliminates the need for acid to neutralize the base and water to rinse away the acid. The process is continuous, without all the steps and the unnecessary wastewater.

Fox and Ginosar accomplished this by developing a system using a catalyst fixed in the solution. The solvent is constantly recycled, in the processing solution, leaving it out of the finished product. The result is a better separation of biodiesel and glycerol, and a cleaner, higher grade of both substances.

Current separation methods result in a low-grade glycerol, which is worthless. On the other hand, the high quality glycerol produced by the new process is very valuable. Conservative estimates place high-grade glycerol at close to $10 per gallon.

Fox and Ginosar believe sales of the glycerol could pay for the entire process, making the price of their biodiesel around the same price as regular petrodiesel. Biodiesel made by the old process is priced considerably higher than petrodiesel.

Markets and funding

Much of Fox and Ginosar’s research was done with used french fry oil donated by the J.R. Simplot Co. For Simplot and other food processors, the large volumes of used vegetable oils is a real liability. Transporting the oil to landfills or “yellow oil” markets is expensive, so the prospect of turning a waste product into fuel to power its large trucking fleet is appealing.

Fox and Ginosar envision a time when waste oil-to-biodiesel conversion plants are connected to food processing plants everywhere, giving processors an environmentally sound source of fuel.

The two have secured a provisional patent for the technology, but lack funding to refine the process and complete the project.

Contact: Teri Ehresman

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