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Waste Coffee Grounds as Biodiesel Feedstock; Potential for 340M Gallons Per Year of Coffee Biodiesel

11 December 2008

Coffeebiodiesel
GC analysis of the coffee grounds-derived biodiesel showing the different methyl esters of fatty acids present. The presence of various methyl esters in coffee biodiesel obtained by MS is shown in the inset table (spectra not shown). Click to enlarge. Credit: ACS

Waste coffee grounds can provide a cheap, abundant, and environmentally friendly source of biodiesel fuel, according to a study by researchers at the University of Nevada-Reno. According to the USDA, world coffee production is 16.34 billion pounds per year; the scientists estimated that spent coffee grounds can potentially add 340 million gallons of biodiesel to the world’s fuel supply. A paper on the work was published online in the ACS Journal of Agricultural and Food Chemistry.

Spent coffee grounds contain between 11-20 wt.% oil. The process developed by Mano Misra, Susanta Mohapatra, and Narasimharao Kondamudi for extracting that oil for subsequent transesterification yields 10-15% oil depending on the coffee species (Arabica or Robusta).

As an additional advantage, the biodiesel derived from coffee oil possesses better stability than biodiesel from other sources due to its high antioxidant content (which hinders the rancimat process). The solid waste remaining after oil extraction can be utilized as compost,  as a feedstock to produce ethanol, and as fuel pellets.

For their study, the team collected Starbucks’s (Reno, Nevada) “grounds for your garden” spent coffee grounds. They dried the grounds in an over overnight at 50° C to remove moisture (mostly 50-60 wt%) and then refluxed them with low-boiling organic solvents such as n-hexane, ether, and dichloromethane to extract the oil from the coffee particles. The oil was separated from the solvents using a rotary evaporator, and the solvents were reused in the next batch of extraction.

More polar solvents extracted greater amounts of FFA and, in turn, more crude oil yields (13.4% hexane, 14.6% diethyl ether, and 15.2% dichloromethane), which caused a decrease in pH. Hexane extraction resulted in a more neutral pH (6.8) of the extracted crude oil, and was selected as a suitable solvent for the oil extraction process.

Free fatty acids (FFAs) present in the crude oil were separated by converting them into soap by mixing a basic solution with the extracted oil. Soap was removed from the pure oil by centrifuging the mixture.

GC-MS and HPLC analyses indicated that the coffee biodiesel consisted of both saturated (51.4%) and unsaturated (48.6%) esters. ASTM analysis confirmed that this biodiesel can be used industrially as an alternative to diesel. This can add approximately 340 million gallons of biodiesel to the world’s fuel supply.

—Kondamudi et al. 2008

The reserachers plan to develop a small pilot plant to produce and test the experimental fuel within the next six to eight months.

Resources

  • Narasimharao Kondamudi, Susanta K. Mohapatra, and Mano Misra (2008) Spent Coffee Grounds as a Versatile Source of Green Energy. J. Agric. Food Chem., Article ASAP doi: 10.1021/jf802487s

December 11, 2008 in Biodiesel | Permalink | Comments (20) | TrackBack (0)

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Comments

Beg's the question as to whether it'll smell like coffee when you run it? I remember reading about someone who converted peppermint oil to biodiesel and the car smelled like a candy cane when ran...

You're kidding me right? Coffee grounds? Stupid. Electric cars is where it's gonna be as soon as EEStor deploys its technology all over the world. Diesel and gasoline will still be in demand for transportation (aviation, trucking) for a while after that. CANDU reactors will be able to provide baseload electicity, and space elevators being worked on by the Japanese will be able to bring the radioactive waste into space where it can then be sent to the sun for final disposal. ...ejj...

I'd love to know the cold-flow properties of this stuff. The fact that it has some saturated oils means (I think) that it will get too thick at colder temperatures. Perhaps it would work in the south, but not in the Northeast. Nonetheless, this sounds like it could be promising.

There's a synergy here; all those yuppies jumping into their cars each morning just to go to the local Starbucks can now gas up their cars while they're juicing up themselves. lol

With all the sources of fatty acids we're now using to make BioDiesel (and now with spent coffee supplying more fatty acids), we're going to need a lot of methanol to perform the esterification process. So I imagine we'll be seeing a lot of big ships on the high seas carrying methanol.

Biomass to fuel is usually a bad idea, but any organic material that might wind up in a landfill under present circumstances should be made into a gas, a liquid fuel or burned to produce steam for electricity. Much gas from decomposition in landfills goes with energy loss directly into the air where the methane is a more potent greenhouse gas than CO2.

Organic landfills are becomming much more rare in Europe because of new laws. Coffee grounds wind up in many landfills. Orange peelings also excited much interest for their oil.

Another option is to form charcoal out of waste biomass to be used in the soil for improving the growth of plants. There are newer techniques for efficient creating charcoal.

There are non-methanol processes for biodiesel.

..HG..

lol There's still someone fooled by EEstore..

Local hardware stores here in Vancouver are selling low-smoke firelogs compressed from waste coffee grounds, from some S. America instant coffee factory.

It does smell like coffee when it burns.

If this can be done on a small scale local business groups could do it easy. There are many small coffee shops around here, very easy to go daily to each one if it yielded enough return. If it does not then this is pointless.

Inventing a different recycling infrastructure just to recycle coffee grounds sounds at least somewhat silly.
Just mix all your organic waste together and transform it to fuel using coskata's technology or algae or just make a combination of syngas and agrichar.
that would be much, much more efficient than extracting the 10-20% fatty (unsuitable) acids.

@Alain:

Right you are. The Coskata process easily handles municipal organic waste. Every municipality could be making their own liquid fuels by building this type treatment facility.

It would be more efficient to use the coffee oils directly than to go through the Coskata process; it would also provide a liquid-fuel byproduct even if the solids were used for firing boilers.  If the stream is big enough to be worth diverting, do it; it's nowhere near a panacea, but it certainly doesn't hurt.

Coming to Starbucks: Java High Octane Blend $7 per cup.

Question: if waste coffee grounds = X amount of energy potential, what do unsteeped coffee grounds equal? And would the arabica roasted bean have great e-density than say a green bean?

The whole bean (pulp and pit) yields around 40 gal EtOH per u.s. ton in addition to the oil and other co-products.

Electric cars? Who wants coal-burning cars as a solution?

Fuel your day, fuel your car. I think we Office Coffee distributors can play a big part in the collection of used grounds.

Why do people question converting waste to economically viable products? It might not be a complete solution nor the most prettiest but dam it its going to be one of the solutions implemented, next to increasing efficiency its going to be big.

If you can't make the conversion at a competitive price, you don't have a viable product.

That said, 340M gallons isn't much compared to US diesel consumption of ~40 billion gallons, but it's nothing to sneeze at either.  If the oils can be recovered from grounds and converted at a reasonable cost (in both money and energy), instant coffee plants could have themselves a very useful co-product.  Recovering grounds from homes or even restaurants is probably not worthwhile.

A by product like coffee grounds may be fine, as long as we don't affect the food supply chain like ethanol seems to do. BTW, I am not sure we are putting enough effort into finding a solution. If the price of fuel dropped and the price of alternative energy went up, we would have had a solution by now.

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