Cob chic: as cellulosic biofuels arrive, the humble corn cob reigneth anew

September 23, 2013 |

macarthurAfter achieving celebrity via Gen. Douglas MacArthur, Huck Finn and Frosty the Snowman, the corn cob has been languishing of late. 

No more, as cobs appear poised to emerge as a biofuels feedstock rockstar.

In days gone by, no one living on the land wasted anything if they could find a use for it. That’s one of the reasons that corn cobs were used just about anything — pipes, pot scrubbers, for corn cob jelly, as bird feeders, firestarters, paint rollers, dolls. There are even some enterprising corn cob wines — which of course, tells you something about the opportunities to find sugars in there and ferment them to make ethanol.

In that newsvein, good news arrived from Iowa State last week — that up to one ton of corn stover per acre can be safely removed from the field — creating the potential for some 8 billion gallons of ethanol if you could somehow master all the logistics and have a cellulosic ethanol plant conveniently at hand for every corn field. It’s great news for POET and those working with corn stover — and, in general, for fans of advanced, cellulosic biofuels.


But for some reason cobs have become all but forgotten in the mix. Why is that?

Why indeed, asks the team at FarmMax, which has developed a single-pass system for cob collection.

“At 180 bushels per acre, there would be approximately a ton of cobs. They say take a ton. So take the cobs for Pete’s sake!” says FarmMax’s Beth Stukenholtz.

“We will be in the field in October, harvesting corn and cobs all at once, on our farms. We’re farmers, ag engineers, we get it, no agenda, no fancy research budget that’s corporately supported. Just us, our land and our machines. We’re keeping our stover (less the cobs), because it’s not just about cost to replace the nutrients, it’s also about the organic matter that keeps soil from becoming compacted and increases it’s ability to hold moisture. Big picture stuff.”

There’s some reason to be more selective in our enthusiasm about stover, in fact — when we look at the data.

Cobs vs other forms of cellulosic corn residue

A recent master’s thesis at Iowa State by Keith Webster points out some of the difficulties — which don’t relate as much to the sustainability of corn stover as much as the economics.

Looking at the agroeconomics of a single-pass stover harvest system, Webster wrote: “The corresponding harvest rates for 2010 for the 6 row collection [was] 1.1 tons per acre with productivity reduction levels of 45% [compared to a normal combine harvest]. At these harvest rates and productivity reductions the total cost for stover harvest was determined to be $30.39 per ton and $30.22 per acre for each scenario respectively.” he also found that “the cost per acre indicated that as more stover was harvested the cost increased.”

Yikes. $30.39 per ton for harvest — that’s tough if you are looking for $50 feedstock.

Need more data? Webster’s thesis is here.

Cob developments in Mexico

For that reason, it’s welcome news that researchers at the Iberoamerican University (IBERO) in Mexico City are looking to consolidate a pilot biorefinery that will use the waste of various fruits, vegetables, flowers and plants produced in urban and rural areas — as well as cobs — and to transform them into fuels and high value products.

Lorena Pedraza Segura, researcher at the Department of Engineering and Chemical Sciences, explained that the proposed biorefinery has its origins in two previous investigations, one oriented towards the production of ethanol from cobs . And the second one, based on various studies that allowed researchers at Ibero to obtain this fuel from the organic waste generated at Central de Abasto (biggest Latin-American supply center for vegetable and animal products) in Mexico City.

Subsequently, Pedraza Segura shifted the focus of the research to raise the construction of a biorefinery. This could be installed in the areas surrounding the Central de Abasto or near disposal centers in Jalisco or Sinaloa, major corn production areas in Mexico.

The Ibero specialist said there are great expectations regarding the manufacture of high value products from Central de Abasto’s organic waste and cob, due to several aspects. “Waste” not apt for human consumption would be used for this purpose, this residue are composed by lignocellulosic material, ie having a composition of three polymeric layers: cellulose, hemicelluloses and lignin.

“Particularly the cob is one of the most effective waste material used  to produce ethanol due to the amount of sugar it contains and because it is easier to treat, since it is very consistent,” said the researcher. He added that in the case of waste from the Central de Abasto, the raw material for bioethanol is changing due to seasonality of each product.

Pedraza Segura concluded that the pilot biorefinery would be equipped to a semi-industrial level. This would allow to perform diverse experiments with more trustworthy results than those observed at laboratories; besides, it would permit the generation of human resources specialized in the manufacturing of products derived from lignocellulosic material.

Cobs in the cellulosic supply chain

You’ll see cobs featured among the feedstocks at the POET-DSM cellulosic ethanol pmabnt known as Project LIBERTY, scheduled to open next year in Emmetsburg, Iowa.

The plant will use corn cobs, leaves, husks, and stalk, and annually produce 20 million gallons of cellulosic ethanol, with an ultimate capacity of 25 million gallons. The facility’s biomass receiving and grinding building will process a daily average of 770 tons of biomass.

After that, we’ll see cobs in the mix at the DuPont Industrial Biosciences first commercial facility in Nevada, Iowa.

The bottom line

Cobs are cool — they are cost-effective to remove using systems available today — according to FarmMax. The economics look good. Corn cob biofuels may not quite replace the corn cob pipe and corn cob jelly in the popular imagination — at least as long as kids are still singing “Frosty the Snowman” — but it’s a cool feedstock for hot companies looking for sustainable, affordable, reliable, available feedstocks and harvesting technologies.

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