Saturday, March 24, 2007

Orange peels to ethanol

It seems like every time you turn around, there’s a promising new replacement for corn ethanol. Switchgrass, earwax, whatever. But this one got me thinking about how regional sources of ethanol make the most sense. Crop material like corn stalks and prairie grasses for the Midwest, and orange peels in the sunnier climes.

In fact, the Florida orange juice industry could provide up to 60 million gallons of cellulosic ethanol for the state, made from 5 million tons of citrus peel waste. This isn't even a juice drop in the bucket compared to the amount of fuel the U.S. consumes, but it could be a good start for a regional ethanol market. The process, according to Bill Widmer with the USDA-ARS Citrus and Subtropical Products Laboratory, goes something like this:

"...we can break apart the complex carbohydrates and liquefy the citrus waste. Basically what we end up with is a four to five percent fermented stream -- or citrus beer. I use that term 'beer' loosely. You definitely would not want to drink that stuff."

Some companies are full steam ahead: Citrus Energy LLC and Southeast Biofuels are building biorefineries near existing facilities or will co-locate at the citrus processing facility itself. The citrus waste doesn't cost anything, and there are hardly any transportation costs.

Currently, citrus waste from orange juice processing is dried into pulp pellets and fed to cattle. The drying process emits toxins that companies have to contain with expensive equipment. But those emissions are negated in the citrus-to-ethanol conversion process because no drying takes place, and the by-products can be marketed at an additional profit (like limonene, a ingredient of commercial cleaners). According to Widmer, about 1/2 pound of peel oil is produced for every gallon of ethanol.

There will still be some hurdles, of course. After the limonene removal there's still about one-third of a solid left, and the short-term solution is to dry it and make it into cattle feed. Widmer hopes that with more research, material from the residue could be turned into another profitable industrial product, like building-material additives for concrete.

Widmer believes the technology to make ethanol from citrus peel waste will be economically viable for companies in the next 1-3 years. Countries like Spain are also exploring this technology.

Photo credit: Soybean design

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