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Converting Orange Peels into Cellulosic Ethanol

Producing approximately 5 million tons of citrus peel waste annually, the Florida orange juice industry has the potential to provide up to 60 million gallons of cellulosic ethanol for Sunshine State residents, according to Bill Widmer, a research chemist with the USDA-ARS Citrus and Subtropical Products Laboratory in Winter Haven.

Although 60 million gallons of cellulosic ethanol per year would not even come close to satisfying U.S. fuel demand, this hasn't stopped companies from seeing the economic and environmental benefits the technology would offer consumers on a regional scale. "Really, the citrus waste conversion to ethanol, would be a local biomass source in Florida," said Widmer, noting that amount could meet a local demand for oxygenating fuel additives in central Florida as well as generating additional revenue for citrus growers. The citrus waste, a pectin, cellulose and soluble sugar rich mixture of peel, segment membranes and seeds is available at no cost and in large volumes with potentially no transportation costs since companies like Florida-based Citrus Energy LLC, and newly incorporated Southeast Biofuels, plan to build biorefineries in the local vicinity or co-locate at the citrus processing facility itself. "I think what you're going to see over the next fifteen years is wood plants in Georgia and Alabama; citrus plants in Florida; and corn plants in the Midwest," said Tom Endres, senior vice-president of operations at Xethanol Corporation. Xethanol, which formed a joint venture with Renewable Spirits last year to create Southeast Biofuels, plans to build a pilot plant this year with the potential to produce up to 50,000 gallons of ethanol from the citrus waste. "We're optimistic that we're going to build a pilot plant and we're hopeful that the results and analysis are going to be economically viable to scale it up to a commercial operation," said Endres, adding that construction on the pilot plant will begin in the second or third quarter of this year. Citrus Energy LLC, which plans to build a four million gallon per year ethanol biorefinery in Florida, notes the citrus waste to ethanol technology is able to take advantage of a feedstock where the primary costs of growing, harvesting and collection are supported by the existing product stream. "Companies don't have to buy the citrus waste," said Widmer. "Corn is over four dollars a bushel. Two years ago it was about two dollars a bushel. Corn costs are going up." Currently, citrus waste from orange juice processing companies is dried into citrus pulp pellets and fed to cattle with little or no return on investment. In addition, during the drying process toxins are released requiring citrus processing companies to install costly equipment to ensure that organic emissions do not escape into the atmosphere. However, those emissions are negated in the citrus-to-ethanol conversion process since no drying takes place, and the by-products, such as limonene (a valuable ingredients in commercial cleaning products) can be marketed at an additional profit. Approximately half a pound of peel oil is produced for every gallon of ethanol produced, said Widmer. "Where the process stands right now is 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," said Widmer. Fermentation of the sugars is done using traditional brewers yeast and the resulting 'beer' has the ethanol separated and converted to fuel grade ethanol using a distillation and dehydration process. However, Widmer notes there are still minor hurdles left to overcome in the laboratory with the citrus to ethanol conversion process. "After stripping the alcohol we still end up with a residue that we need to get rid of -- about one-third of the solid is still there and the short term solution right now is to dry that, and produce cattle feed from it," said Widmer. But with more research, material from the residue left after limonene removal and ethanol production could be turned into other profitable industrial products, such as building-material additives for concrete, said Widmer. "Will they be producing at a profit by next processing season? I don't know," said Widmer, commenting on the likelihood of the technology being economically viable for companies in the next one to three years. "We haven't demonstrated everything from a raw peel to two-hundred proof alcohol -- and stripping that ethanol out of the beer stream -- I don't think it's a major hurdle, I think it's a minor one. But it's one that we do have to demonstrate."

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