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Hybrid Process Boosts Yield Of Biomass Ethanol

A process that uses two separate streams to convert biomass to ethanol is much more efficient than either stream operating separately, Tim Eggeman told delegates at the Agricultural Biotechnology International Conference held recently at Saskatoon.

“We use a combination of a biochemical and thermochemical process — a hybrid approach. We bring in biomass — wood, stover, wheat straw, sugar cane or whatever — and produce a sugar stream and a residue stream. The sugar stream we send through fermentation,” says Eggeman, chief technology officer and founder of ZeaChem Inc. at Lakewood, Colorado.

“The initial fermentation process produces acetic acid, which doesn’t lose any carbon dioxide. The next product is ethyl acetate, which is then converted to ethanol. On the residue side, a thermochemical process converts the residue to ethanol through a different pathway.”

Eggeman says the three traditional biomass production systems –biochemical, thermochemical and syngas –each have a maximum theoretical production of about 112 gallons of ethanol per bone-dry ton (BDT) of biomass.

His hybrid system has a theoretical yield of about 156 gallons/BDT and a realistic yield, with mature technology, of around 135 gallons/BDT. That’s about 50 per cent higher than what you can get using only one technology.

“Yield drives economics and yield drives our environmental footprint. The dominant operating cost for biorefiners is feedstock. If I can get 50 per cent more product per ton of wood, I’m decreasing the main cost and building a better margin with better profitability,” he says.

The company was founded in 2002. In 2006 it raised $6 million to prove its technology on a laboratory scale, then raised another $34 million in 2008 to build a demonstration plant.

ZeaChem’s product line includes: acetic acid, which is a $3 billion/year market in the U.S.; ethyl acetate, which is a $0.2 billion/year solvent market; and ethanol, which is a $20 billion/ year fuel market.


“Our technology is feedstock neutral, in that we can run just about any feedstock. But you do have to pick a feedstock and design around that. For our first plant, we’ve decided to work with GreenWood Resources and have them supply us with hybrid poplar,” he says.

“GreenWood has commercial operations in the U.S., Chile, China and Europe. Today they have about 35,000 acres under management in the Pacific Northwest and we’re located next to one of their hybrid poplar farms.”

Part of GreenWood’s operation includes 12-year poplar rotations, where a straight tree is harvested for timber and the land is replanted.

“We’ve been working on an “Energy Farm regime,” where we plant, let it grow for three years, cut it and then it grows back on its own, you let it grow for another three years and cut it again. We can do that four or five cycles before we have to replant and start over again,” says Eggeman.

ZeaChem uses a forage harvester- type system to chop and transport the chipped poplar material to the processing plant.

“As a company, we’ve finished our lab work, we’ve built some small pilot units, we’ve scaled up the ferment from two litres to a 3,500-gallon fermenter and we feel we’ve dealt with the scale-up issues successfully,” he says.

“The initial biorefinery is under construction near Boardman, Oregon, next to 28,000 acres of GreenWood hybrid poplar. We are using residuals off that farm to supply our integrated biorefinery. The plant will produce 250,000 gallons per year of ethanol and ethyl acetate.”


Eggeman says there have been long discussions around the food versus fuel issue with ethanol, so he produced some visual aids to illustrate land productivity, or miles per acre per year — how far can you drive on ethanol produced from an acre of land each year on a sustainable basis (see Figure 1).

With corn ethanol, at 150 bu./ acre per year and 2.7 gallons per bushel, at a rating of 14 m.p.g., that works out to 5,670 miles/ acre/year.

For first generation cellulosics, at 7.5 BDT/ac/yr and 90 gallons/ BDT at 14 m.p.g., that provides 9,450 miles/acre/year — a 60 per cent improvement over baseline corn.

Advanced cellulosics like the ZeaChem system, at 15 BDT/ acre/yr, 135 gal/BDT and 14 m.p.g., provides 28,350 miles/ acre/yr. — a five-times improvement over corn.

“In that case, you could take five acres used for corn ethanol, replace them with one acre of biomass, then use the other four corn acres for something else,” says Eggeman. “And if auto efficiencies move from 14 to 25 miles/gallon of ethanol, that gives you 50,000 miles/acre/year, which is a 10-times improvement over corn.”

He says right now, corn ethanol is responsible for five to seven per cent of the fuel ethanol pool.

“I’m saying that without bringing in any additional land, if I was to implement this technology today, I could produce 50 to 70 per cent of our light-duty transportation fuel. So when you hear all the stuff about food versus fuel, you have to understand that technologies coming down the pipeline are going to hit a lot of these issues and make them go away,” says Eggeman.

He adds that greenhouse gas emissions from ethanol compared to gasoline have significant reductions, with corn ethanol producing 21 to 24 per cent less GHG than gasoline; cellulosic ethanol from stover producing 86 to 89 per cent less GHG; and, the ZeaChem Energy Farm system ethanol producing 94 to 98 per cent less GHG than gasoline.

BillStrautmanisafreelancewriterbased nearSaskatoon

The more efficient the process of converting biomass to ethanol, the fewer acres pulled out of food production. Eggeman uses a miles per acre per year measure to determine efficiency of different ethanol processes.





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