Wake Up and Smell the Coffee Biodiesel

Diesel-powered vehicles could emit the aroma of fresh-brewed coffee, thanks to the research being conducted at the University of Nevada-Reno.
By Susanne Retka Schill | February 10, 2009
The cup of java that fuels many people in the morning could soon fuel trucks too, in the form of coffee biodiesel.

The project at the University of Nevada-Reno came about rather serendipitously, when engineering professor Mano Misra, who is known as a prodigious coffee drinker, picked up a cup of forgotten coffee. Noticing the sheen from the oil floating on top of the cold coffee, it occurred to him that coffee oil could be a biodiesel feedstock. "Coffee is the most used beverage in the world," he says. "Last year the world drank 15 billion pounds of coffee." In mid-2007, he set a couple of students to work on the project. Jason Strull and Narasimharao Kondamudi began conducting experiments to find out how much oil coffee grounds hold and whether that oil could be used to make a high-quality biodiesel. The research became part of an award winning business plan and was the topic of a paper published in November by the Journal of Agricultural and Food Chemistry. It didn't take long for details about the research to hit the newspapers and the blogosphere.

The New York Times' treatment of the story is one of Strull's favorites. The headline read "Diesel, Made Simply From Coffee Grounds (Ah, the Exhaust Aroma)." The article started out saying the new research touches on two of American's great obsessions-coffee and cars. Other writers had fun with the recycling theme writing: "The next time you drink your morning coffee, think of the money you could make by recycling. Car fumes that smell like coffee, breathing coffee biodiesel." And, "Why make your car smell like french fries when it could loft the sweet aroma of coffee?" Another favorite: "Move the focus of energy from the Persian Gulf to the back alleys of your neighborhood coffee shop."

MG - monoglyceride, DG - diglyceride, TG - triglyceride, TAN - total acid number.

Actually, the concept of making biodiesel from coffee is not new. For several years, Brazilians have been extracting oil from defective and surplus coffee beans to produce biodiesel. At the University of Nevada, the researchers are focusing on spent coffee grounds, collected from the local Starbucks. The Starbucks outlets in Reno participate in the company's Grounds for Your Garden program, where customers are encouraged to recycle waste coffee grounds for their gardens, Strull says. The students recycled the grounds into their research project instead.

Biodiesel Performance
The research determined that coffee grounds yield from 11 percent to 20 percent oil, depending on the variety of beans, with an average yield of 15 percent oil. The resulting biodiesel has an unusually high oxidative stability, but that's offset by high sulfur levels. Kondamudi says they use hexane extraction in the laboratory and process the oil into biodiesel using standard transesterification. The biodiesel is quite stable and can sit for more than a month in the laboratory without any observable physical changes, even though many of the antioxidants are extracted in the water used to brew the coffee-only 10 percent remains in the grounds. The chart on page 58 shows the ASTM analysis of a sample of biodiesel that sat in the laboratory for several weeks, Kondamudi says. The coffee oil has a free fatty acid content of 4 percent to 6 percent, and contains 60 percent unsaturated fats. The resulting coffee biodiesel meets ASTM standards and has a cloud point of 11 degrees Celsius (52 degrees Fahrenheit).

Researchers solved the sulfur problem by developing a method to remove excess sulfur from the coffee biodiesel, thereby meeting ASTM standards. Because coffee trees grow in volcanic soils high in sulfur content, pure coffee contains from 50 parts per million (ppm) to more than 300 ppm, depending on the growing region, variety and type of roast, Strull says. While sulfur, which provides the aroma and taste coffee is known for, comes out in the brewing process, too much sulfur stays in the grounds for an acceptable biodiesel in markets where emissions are regulated. In Brazil, the standards are not as stringent as in the United States or Europe, Strull adds. The research team has developed a process that can reduce sulfur in biodiesel from 70 ppm to 3 ppm. They hope to publish a paper on that research soon.

Business plans
It's not unusual for graduate students to have their papers published, but it's rare to get the kind of publicity the Nevada research received when news of the journal article spread.

The students also received $5,000 when the business plan they developed around the research won the Nevada Lieutenant Governor's Award for the business plan that best employs clean, renewable or efficient energy technologies and services.

In their business plan, the engineering students estimated that if the waste coffee grounds from all of Starbucks' market in the U.S. were collected and the oil converted to biodiesel, it would amount to 2.9 million gallons of biodiesel annually. If waste grounds from all world coffee production were used, 208 million gallons of biodiesel could be produced annually. The students also evaluated the potential for using the grounds remaining after oil extraction for fuel pellets. They found that 1 pound of pellets contains an energy value of approximately 8,700 British thermal units. They estimate that if all the leftover grounds from Starbucks in the U.S. were used that could generate 89,000 tons of fuel pellets annually, while world production could yield 6.4 million tons per year. Using early 2008 market prices, the students figured Starbucks could make $13 million annually from biodiesel and $20 million from the fuel pellets. Worldwide, that could amount to $935 million from biodiesel and $1.4 billion from the pellets. Those figures were calculated using biodiesel at $4.50 per gallon and fuel pellets at $225 per ton. Strull says the numbers are overstated because the students assumed that all of the waste grounds would be used, which is unattainable, and the values were calculated more than a year ago when prices were high. "Coffee biodiesel doesn't have the potential to replace a huge amount of diesel because of the limited amount available," Strull admits. "What it can do is make people wonder-if we can make biodiesel out of coffee grounds, what else can they use to make biodiesel?"

While they continue their research in the laboratory on other waste streams with extractable oil content, the students and their faculty advisor, Misra, have turned their business plan into a company called Bio-Grounds LLC. The entrepreneurs have applied for a patent on the process and are doing due diligence now on several companies proposing to partner with them in developing the company. The first step will be to build a pilot plant at the Starbucks roasting and distribution plant in Minden, Nev., and to further and confirm the research begun at the University of Nevada. Among the issues they will address is whether the unusually good oxidative stability of coffee biodiesel make it a premium oil to blend with other feedstocks in the place of additives, Misra says. The researchers also want to double-check their cost estimate of $1 to $1.50 per gallon for the coffee oil. They also are looking at alternative oil extraction methods, preferring to avoid the permitting issues that accompany commercial-scale solvent extraction. While mechanical extraction would reduce oil yields, the result would be a "greener" final product, Misra says. Another issue they are working on is the logistical challenge of cost-effectively collecting the coffee grounds. "Starbucks has 11,000 stores around the country," Misra says. Other potential sources are roasting plants and fast food chains.

In the meantime, the entire Department of Material Science and Engineering at the University of Nevada can tell when the students are working on the coffee biodiesel project in the laboratory. Not only does the extracted oil smell like coffee, but the biodiesel also smells like coffee and when it's burned-the exhaust smells like coffee. Ah-the aroma.

Susanne Retka Schill is a Biodiesel Magazine staff writer. Reach her at [email protected] or (701) 738-4922.
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