Best summary of Cellulose Ethanol —DOE’s 2006 Annual Energy Outlook
The underutilization of crop residue has driven decades of research into ethanol production from cellulose; however, several obstacles continue to prevent commercialization of the process, including how to accelerate the hydrolysis reaction that breaks down cellulose fibers and what to do with the lignin byproduct. Research on acid hydrolysis and enzymatic hydrolysis is ongoing. The favored proposal for dealing with the lignin is to use it as a fuel for CHP plants, which could provide both thermal energy and electricity for cellulose ethanol plants, as well as electricity for the grid; however, CHP plants are expensive.

Inside the first cellulose-ethonal plant

Currently, Canada’s Iogen Corporation is trying to commercialize an enzymatic hydrolysis technology for ethanol production. The company estimates that a plant with ethanol capacity of 50 million gallons per year and lignin-fired CHP will cost about $300 million to build. By comparison, a corn ethanol plant with a capacity of 50 million gallons per year could be built for about $65 million, and the owners would not bear the risk associated with a new technology. Co-location of cellulose ethanol plants with existing coal-fired electric power plants could reduce the capital cost of the ethanol plants but would also limit siting possibilities.

 

The sugar in cellulosic biomass is locked up in cellulose, which contains normal C6 sugar, and hemicellulose, which contains Xylose (C5) sugar. Since normal yeast can’t ferment Xylose, Celunol has acquired genetically engineered E. coli bacteria which can turn almost all of it into ethanol.

The diagram explained. First the hemicellulose in the biomass is broken into Xylose sugar (gray bar). Then the Xylose is separated from the remaining cellulose (blue bar). The Xylose is fermented with E. coli (top yellow), and the cellulose is broken down into normal glucose (red) which is fermented the normal way (bottom yellow). Finally all the ethanol is distilled (the water and lignin byproducts removed). The lignin is burned in the the still’s boilers.

MONTREAL — Iogen Corp., a Canadian firm at the forefront of efforts to turn agricultural waste into ethanol, has become the first supplier of such biofuel to the commercial fuel market.

The moderate initial shipment marks a milestone in the development of so-called cellulose ethanol, made from farm refuse such as wheat straw and corn stalks, instead of the corn or other grains used for the ethanol now commonly blended with gasoline. Turning farm waste into fuel for automobiles has long been an alluring, but technically tricky, prospect.

Iogen officials have said they hope to begin work on a full-scale commercial plant next year, but significant hurdles remain.

Iogen is ahead of other firms seeking to commercialize ethanol from farm waste, said John Ashworth, an official of the Department of Energy’s National Renewable Energy Laboratory in Golden, Colo., which has a pilot plant where companies test cellulose-ethanol concepts. Iogen’s much-larger plant in Ottawa is the only demonstration plant for the technology, he said.

The plant, which has an annual production capacity of 260,000 gallons, began about two weeks ago to turn wheat straw into ethanol that meets Canadian fuel specifications, according to people familiar with the situation. Petro-Canada will take delivery today of Iogen’s initial 1,300 gallon shipment.

Proponents of cellulose ethanol argue that it has great potential to help reduce greenhouse-gas emissions, since the feedstock is readily available as a byproduct of farm crops. But wheat straw or corn stalks must be broken down into sugars that can be fermented, making the production process for cellulose ethanol more complex and costly than for conventional ethanol. Iogen and others have been developing techniques to reduce those costs.

Within the next year or so, Iogen hopes to begin construction of the full-scale plant, which would cost around US$250 million, and have annual production capacity of about 52 million gallons. But company officials have acknowledged that the risks involved in scaling up production will make it difficult to secure conventional financing for the project.

Fortune Magazine, 23 August 2004
Nicholas Varchaver

One biomass fuel offers tremendous promise, though it will take time to put into wide-scale use, is cellulosic ethanol— which shouldn’t be confused with corn-based alcohol best known for the size of its subsidies. Cellulosic ethanol is made from switchgrass, poplar trees, and straw. And it yields more energy than the corn version, says Carnegie Mellon University economist Lester Lave.

One group of supporters, the Energy Future Coalition, a bipartisan group that includes ex-Senator Wirth and Republican former White House counsel Boyden Gray, has put forth its own modest proposal. The World Trade Organization has issued rulings against farm subsidies for cotton and sugar. If the rulings stand, the US will need to either end the subsidies or pay billions in fines. As Wirth puts it, “No politician I know wants to take something away from a lot of constituents.” He proposes shifting subsidies from cotton and sugar to switchgrass and trees. It would cost the government nothing, but would provide benefits for consumers, farmers, and even the environment (grass and trees take a lesser toll on land than cotton). Even without the subsidy swap, a $500- million-a-year investment in ethanol could pay off bigtime, allowing for gas spiked with 20% cellulosic ethanol within 20 years. All of a sudden–if you assume that hybrids and other measures hold the line on usage–you can actually reduce gasoline consumption by that same 20%.

Reality check: Like most alternative fuels, cellulosic ethanol is expensive (though subsidies will reduce the cost), and significant production remains at least five years away. As of now only one plant–run by a company called Iogen in Canada (with the support of Shell)–is producing it. Moreover, as economist Lave acknowledges, many tens of millions of acres would be required to grow the biomass. Still, it is promising enough that it earned the endorsement of a Pentagon-commissioned study last year, which looked at how the US can prepare for a post-oil world. 

Instead of using the starch from the corn kernel, using cellulose will increase the amount of ethanol from a crop because more of the plant will be used. This also avoids the consumption of food crops for industrial applications.

Starch-based ethanol has limited benefits in terms of oil displacement and greenhouse gas emissions, due to the substantial fossil fuel inputs required to grow grain and convert it to alcohol.

The benefits of cellulose conversion are dramatically larger; indeed, a conventional internal combustion engine operating on cellulosic ethanol produces fewer greenhouse gas emissions on a life-cycle basis than a fuel cell operating on hydrogen derived from fossil fuels.