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University of Wisconsin Team Develops High-Yielding Chemical Hydrolysis Process to Release Sugars from Biomass for Cellulosic Fuels and Chemicals

A University of Wisconsin-Madison research team has developed a chemical process for the hydrolysis of biomass into sugars for subsequent processing into fuels and chemicals that delivers sugar yields approaching those of enzymatic hydrolysis. In an open-access paper published in the 9 March issue of the Proceedings of the National Academy of Sciences, they report that the process leads to a nearly 90% yield of glucose from cellulose and 70-80% yield of sugars from untreated corn stover.

Dr. Ronald Raines, a UW-Madison professor of biochemistry and chemistry, and graduate student Joseph Binder say that the new process generates easily recovered sugars that are “superb feedstocks” for microbial growth and biocatalytic ethanol production.

To release the sugars locked into the cellulose polymers in biomass, producers use both physical and chemical methods, with physical chemical pretreatment processes followed by enzymatic hydrolysis being the most common, note Raines and Binder. While the proper combination of pretreatment and enzymes for a given feedstock delivers high yields of sugars from hemicellulose and cellulose components, the hosts of both pretreatment and enzymes are high—up to one-third of the cost of cellulosic ethanol production—and the rate of hydrolysis can be low.

Although concentrated acids can also be used with high conversion rates, the hazards of handling concentrated acids and the complexities of recycling them have limited the adoption of this technology, they say.

Raines’ chemical approach relies on a chloride ionic liquid-containing catalytic acid to dissolve the long chains of sugars in biomass and break them up into individual molecules of glucose and xylose. Over the course of the reaction, they add water to the mixture to prevent unwanted byproducts from forming. After two rounds of such treatment, a sample of corn stover gave up about 70% of its glucose and 79% of its xylose, a 75% sugar yield overall. From there, the researchers used ion-exclusion chromatography to separate the sugars from the reaction mixture, as well as the ionic liquid, for reuse.

By balancing cellulose solubility and reactivity with water, we produce sugars from lignocellulosic biomass in yields that are severalfold greater than those achieved previously in ionic liquids and approach those of enzymatic hydrolysis. Furthermore, the hydrolysate products are readily converted into ethanol by microorganisms. Together, these steps comprise an integrated process for chemical hydrolysis of biomass for biofuel production.

...In comparison to extant enzymatic and chemical processes to biomass hydrolysis, ours has several attractive features. Like concentrated acid processes, it uses inexpensive chemical catalysts rather than enzymes and avoids an independent pretreatment step. Working in concert, [EMIM]Cl and HCl produce high sugar yields in hours at just 105 °C, whereas enzymatic hydrolysis can take days and many pretreatment methods require temperatures of 160–200 °C. Also, lignocellulose solubilization by the ionic liquid allows processing at high concentrations, which can be a problem in enzymatic hydrolysis.

On the other hand, our process improves on typical acid hydrolysis methods by avoiding the use of hazardous concentrated acid. Using catalytic amounts of dilute acid removes the complexity and danger of recycling large volumes of concentrated acid. The ionic liquid used in its place is likely to be far easier to handle. Despite this difference, our process is similar to commercial processes using concentrated acid hydrolysis and consequently can exploit proven engineering and equipment for facile scale-up, particularly for separations and recycling.

—Binder and Raines

Raines and Binder subsequently used ethanologenic microbes to ferment the sugars they collected into ethanol. All told, says Raines, using this integrated process, they were able to convert half of the sugars available in plant biomass into liquid fuel.

To make it work at the industrial scale, however, a number of hurdles will need to be overcome, the authors note, including:

  • Highly viscous biomass-ionic-liquid mixtures might require special handling, and larger scale fermentation of hydrolysate sugars might reveal the presence of inhibitors not detected in our demonstration experiments.

  • The sugar concentration resulting from stover hydrolysis (about 1%) is too low for practical fermentation and is decreased even further during the chromatographic separation, leading to water-evaporation costs. Methods allowing a higher starting biomass loading and strategies to concentrate rather than dilute the sugars during separation from the ionic liquid would overcome this problem.

  • Separations and ionic-liquid recycling could pose additional challenges to commercialization.

Raines’ project was supported by the Great Lakes Bioenergy Research Center, a US Department of Energy bioenergy research center located at UW-Madison, as well as a National Science Foundation Graduate Research Fellowship awarded to Binder.

Resources

  • Joseph B. Binder and Ronald T. Raines (2010) Fermentable sugars by chemical hydrolysis of biomass. PNAS vol. 107 no. 10 4516-4521 doi: 10.1073/pnas.0912073107

Comments

Henry Gibson

It must always be remmebered that there is not enough land in the US or other parts of the world to produce enough biomass to replace even one forth of the energy provided now by petroleum and coal.

The total process now used for producing ethanol from corn yields 123 units of fuel for every 100 units of fossil fuel input according to US government figures. Others say that there is a net loss. But even with the best estimates the net CO2 production of humans would be lowered by not producing ethanol from corn or cellulose, but just use 23 additional units of fossil fuel and grow large trees on all available land, and never harvest the trees for fuel.

The prodcution of methanol or ethanol from synthesis gas made from biomass seems to be the most efficient and cheapest way of producing liquid fuels from any carbon containing source including corn. Such factories can also use coal and should be preferred since a shortage of cheap biomass will not stop fuel production. These factories can also use hydrogen from any source to make liquid fuel if CO2 is recycled to them.

Nuclear energy, can replace all coal burning generators and the coal can be used to make gasoline and diesel and jet fuel. Pebble bed and other reactors can be made and installed in months once factory production starts. With only one major reactor failure in 60 years of nuclear power and less than a hundred clearly tracable deaths, nuclear power is one of the safest human activities and sources of energy.

The energy from nuclear reactors can also be used to manufacture liquid fuels from recycled CO2. The uranium or thorium cost of nuclear energy is low enough so that there is an infinite supply of fission energy for humans until the Sun explodes a few billion years from now. It may also be easier to develop a method of causing fission of lead, bismuth and other heavy atoms easier and cheaper than it will be to cause fusion of hydrogen. Lead has 75 percent of the energy of fission that uranium and thorium do. Carlo Rubbia invented a way to do fission that does not even require uranium but could use thorium alone, and it can also use the small but massive energy containing supplies of lower U235 containing uranium and used light water fuel. It certainly can use all tranuranics, including plutonium that many people worry excessively about how they can be stored for millions of years. They do not have to be stored, they can be used and destroyed just as uranium is destroyed in nuclear reactors. It is very rarely mentioned that the gamma rays from nuclear reactions can even cause the destruction of the radio activity of fission products. This is only interesting, but not necessary because methods are well known to prevent any substantial increased danger to humans from fission products. Under all circumstances regarding nuclear energy, it must be learned and remembered that all live animals, including humans have always had built in radioactivity and atre exposed to other, mostly unavoidable, natural radioactivity from space and the earth. Obviously, live things have mechanisms built into them to repair small amounts of damage including radioactive damage because radioactive potassium and carbon is built into every live thing. The invention of fusion and fission reactors did not change us from being nuclear virgins to beings corrupted with radiation by nuclear scientists. We always contained radioactivity. More additional radioactive exposure to the human race was done by the engineers and scientists who built airplanes and TV tubes and coal fired furnaces and boilers than was done by nuclear scientists. If you are worried about radiation, ban the sale of cigarettes first and then ground all the airplanes. Then force all the people in Denver to move to New York City or other coastal area or better yet to the shores of the dead sea. ..HG..

HealthyBreeze

@Henry,

Per NanoSolar's website, http://nanosolar.com/company/blog/going-all-electric, using land for solar power for BEV is approximately 50x more land-efficient than the most efficient biofuel production from oil seeds, corn or wheat. We can assume that algae would be several times more land-efficient than traditional land crops, but still nowhere near as land-efficient as solar. Solar has the added advantage that it can be on rooftops, above parking lots, on the fringes of communities, or out in the desert where crops won't grow.

Nuclear power plants tend to cost ~$5 billion a piece, and take a dozen years to finish. Sure, they have their place, but I think we could get to 30% of energy from solar power faster than we could add 30% from nuclear power.

JMartin

@Henry,

You may be correct, but we need not rely on one source of energy nor should we ignore the excess biomass already produced on tillable land.

Ben

@Henry,

Your numbers have nothing to do with cellulosic ethanol.

fred schumacher

As a retired farmer, I have to ask, is everybody missing the bleeding obvious here?

When you eat corn, wheat, rice, any food with starches or sugars, what does your body turn all that food into? It turns it into glucose, your body's fuel at the cellular level.

This process produces glucose from cellulose at high efficiency. Glucose is glucose, whether it comes from a corn cob, a raspberry, a slice of bread, a potato, or a perennial grass stalk.

In trials at the University of Illinois, Urbana-Champaign, plantings of Miscantheus giganteus, a sterile perennial natural hybrid, produces four times as much biomass from fully senescent leafless stalks as field corn, but without any fertilizer, cultivation, or irrigation input.

Since a senescent grass stalk is composed of about three-fourths cellulose and one-fourth lignin, a natural resin that is frequently used as boiler fuel, a low input perennial grass plant could produce three times as much food as high input corn.

However, since glucose is 100% digestible and is readily absorbed by the body, calorie intake could be reduced by 25% with no loss of energy to the body. For a good discussion of energy demand of digestion, read Chapter 3 "The Energy Theory of Cooking" in Catching Fire: How Cooking Made Us Human by Richard Wrangham.

If primary calorie input were to come from perennial grasses, total energy input and acreage required for food production could be drastically reduced. The next step would be to begin research on extracting crude proteins directly from perennial legumes, such as alfalfa.

SJC

We seem to be able to feed most of the world population at this time, but as fossil fuel energy sources are in greater demand and diminishing supply, that seems to be the priority. Without energy we are back to square one.

HarveyD

Fred:

Excellent idea for many of us.

I presume that food industries could quickly come out with multicolor biscuits made from perennial grass stalk extracts. Vitamins and other essential ingredients could be added to fill the needs of growing children, adults and elders.

Wonder how long it would take for the current 50% with over-weight problems to reduce to normal weight if fed with those biscuits?

That alone (weight reduction) could cut health care cost by up to 50% and more in USA and eliminate the national deficits within about 20 years.

Of course, all surpluses could be used as feed stock for animals. Imagine sharing your meals with the house pets.

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