Boost to biohydrogen: high yield production from starch by synthetic enzymes
In what is a breakthrough for the hydrogen economy, scientists from Virginia Tech, Oak Ridge National Laboratory (ORNL), and the University of Georgia announce they have developed a biohydrogen production technique that tackles most of the problems traditionally associated with the production, storage and distribution of hydrogen. Their concept implies we may soon be filling our tanks with dry starch, the powdery stuff sold in grocery stores. Synthetic enzymes will do the rest.
This development gives new hope to the hydrogen economy. As part of what can be called the larger 'carbohydrate economy' the gas will be produced efficiently from starch and sugar-rich biomass instead of expensive and dirty alternatives like coal and natural gas. The new biohydrogen production method is also more efficient and cost-competitive than making the gas from water, which is based on using expensive electricity obtained from nuclear, wind or solar to power the electrolysis process.
According to experts, for hydrogen to penetrate the market for transportation, advances are needed in four areas: production, storage, distribution, and fuel cells. Most industrial hydrogen currently comes from natural gas, which has become expensive and contributes to climate change. Storing and moving the gas, whatever its source, is costly and cumbersome, and even dangerous. And there is little infrastructure for refueling a vehicle.
Synthetic enzymes
The researchers have now come up with a bioconversion process that overcomes these barriers (diagram, click to enlarge). Using synthetic biology approaches, Zhang and colleagues Barbara R. Evans and Jonathan R. Mielenz of ORNL, and Robert C. Hopkins and Michael W.W. Adams of the University of Georgia, are using a combination of 13 enzymes never found together in nature to completely convert polysaccharides (C6H10O5) and water into hydrogen when and where that form of energy is needed. This “synthetic enzymatic pathway” research appears in the May 23 issue of the open access journal Public Library of Science ONE.
Polysaccharides like starch and cellulose are used by plants for energy storage and building blocks and are very stable until exposed to enzymes. Just add enzymes to a mixture of starch and water and “the enzymes use the energy in the starch to break up water into only carbon dioxide and hydrogen,” says Y.H. Percival Zhang, assistant professor of biological systems engineering at Virginia Tech.
Starch in our tanks
A membrane bleeds off the carbon dioxide and the hydrogen is used by the fuel cell to create electricity. Water, a product of that fuel cell process, will be recycled for the starch-water reactor. Laboratory tests confirm that it all takes place at low temperature - about 86 degrees F - and atmospheric pressure.
The vision is for the ingredients to be mixed in the fuel tank of your car, for instance. A car with an approximately 12-gallon tank could hold 27 kilograms (kg) of starch, which is the equivalent of 4 kg of hydrogen. The range would be more than 300 miles, Zhang estimates. One kg of starch will produce the same energy output as 1.12 kg (0.38 gallons) of gasoline.
Since hydrogen is gaseous, hydrogen storage is the largest obstacle to large-scale use of hydrogen fuel. The American Department of Energy’s long-term goal for hydrogen storage was 12 mass percent, or 0.12 kg of hydrogen per one kg of container or storage material, but such technology is not available, said Zhang. Using polysaccharides as the hydrogen storage carrier, the research team achieved hydrogen storage capacity as high as 14.8 mass percent, they report in the PLOS article:
bioenergy :: biofuels :: energy :: sustainability :: biohydrogen :: polysaccharides :: starch :: sugar :: biomass :: synthetic enzymes :: synthetic biology :: carbohydrate economy ::
The idea began as a theory. The research was based on Zhang’s previous work pertaining to cellulosic ethanol production and the ORNL and University of Georgia researchers’ work with enzymatic hydrogen production. UGA Distinguished Professor Adams is co-author of the first enzymatic hydrogen paper in Nature Biotechnology in 1996. The researchers were certain they could put the processes together in one pot. They tested the theory using Oak Ridge’s hydrogen detectors and documented that hydrogen is produced as they predicted.
Mielenz, who heads the Bioconversion Group in ORNL's Biosciences Division, attributed the successful research to a unique collaborative working relationship between scientists, lab divisions, and universities.
"Pairing our biomass conversion capabilities with facilities for studying renewable hydrogen production in the lab's Chemical Sciences Division was a key to this project," Mielenz said. "This also shows the value of partnerships with universities such as Virginia Tech and the University of Georgia."
It is a new process that aims to release hydrogen from water and carbohydrate by using multiple enzymes as a catalyst, Zhang said. “In nature, most hydrogen is produced from anaerobic fermentation. But hydrogen, along with acetic acid, is a co-product and the hydrogen yield is pretty low--only four molecules per molecule of glucose. In our process, hydrogen is the main product and hydrogen yields are three-times higher, and the likely production costs are low--about $1 per pound of hydrogen.
Over the years, many substances have been proposed as “hydrogen carriers,” such as methanol, ethanol, hydrocarbons, or ammonia - all of which require special storage and distribution. Also, the thermochemical reforming systems require high temperatures and are complicated and bulky. Starch, on the other hand, can be distributed by grocery stores, Zhang points out.
“So it is environmentally friendly, energy efficient, requires no special infrastructure, and is extremely safe. We have killed three birds with one stone,” he said. “We have hydrogen production with a mild reaction and low cost. We have hydrogen storage and transport in the form of starch or syrups. And no special infrastructure is needed.”
“The next R&D step will be to increase reaction rates and reduce enzyme costs,” Zhang said. “We envision that in the future we will drive vehicles powered by carbohydrate, or energy stored in solid carbohydrate form, with hydrogen production from carbohydrate and water, and electricity production via hydrogen-fuel cells.
“What is more important, the energy conversion efficiency from the sugar-hydrogen-fuel cell system is extremely high--greater than three times higher than a sugar-ethanol-internal combustion engine,” Zhang said. “It means that if about 30 percent of transportation fuel can be replaced by ethanol from biomass as the DOE proposed, the same amount of biomass will be sufficient to provide 100 percent of vehicle transportation fuel through this technology.”
In addition, the use of carbohydrates from biomass as transportation fuels will produce zero net carbon dioxide emissions and bring benefits to national energy security and the economy, Zhang said.
Interest to the South
The 'carbohydrate economy' is set to benefit those countries that can readily supply large quantities of industrial starch, sugar and cellulose. The developing world is a world leader in this respect and has a tremendous potential to grow.
If it ever becomes feasible to apply the technique developed by the researchers - just putting a starch and water solution in your tank - the main fuel will have to be processed starch. Theoretically it will be possible to extract the sugars from cellulose, but this would require additional processing steps.
Countries with the largest production potential for industrial starch can all be found in the tropics and the subtropics, where crops such as cassava, maize, sago and sweet potatoes grow that yield high quantities of the product (see our previous text, titled "Sweet potatoes and the carbohydrate economy").
Image: potato starch - soon powering our cars?
More information:
Zhang YP, Evans BR, Mielenz JR, Hopkins RC, Adams MW, High-Yield Hydrogen Production from Starch and Water by a Synthetic Enzymatic Pathway. PLoS ONE 2(5): e456, 2007, doi:10.1371/journal.pone.0000456
Article continues
This development gives new hope to the hydrogen economy. As part of what can be called the larger 'carbohydrate economy' the gas will be produced efficiently from starch and sugar-rich biomass instead of expensive and dirty alternatives like coal and natural gas. The new biohydrogen production method is also more efficient and cost-competitive than making the gas from water, which is based on using expensive electricity obtained from nuclear, wind or solar to power the electrolysis process.
According to experts, for hydrogen to penetrate the market for transportation, advances are needed in four areas: production, storage, distribution, and fuel cells. Most industrial hydrogen currently comes from natural gas, which has become expensive and contributes to climate change. Storing and moving the gas, whatever its source, is costly and cumbersome, and even dangerous. And there is little infrastructure for refueling a vehicle.
Synthetic enzymes
The researchers have now come up with a bioconversion process that overcomes these barriers (diagram, click to enlarge). Using synthetic biology approaches, Zhang and colleagues Barbara R. Evans and Jonathan R. Mielenz of ORNL, and Robert C. Hopkins and Michael W.W. Adams of the University of Georgia, are using a combination of 13 enzymes never found together in nature to completely convert polysaccharides (C6H10O5) and water into hydrogen when and where that form of energy is needed. This “synthetic enzymatic pathway” research appears in the May 23 issue of the open access journal Public Library of Science ONE.
Polysaccharides like starch and cellulose are used by plants for energy storage and building blocks and are very stable until exposed to enzymes. Just add enzymes to a mixture of starch and water and “the enzymes use the energy in the starch to break up water into only carbon dioxide and hydrogen,” says Y.H. Percival Zhang, assistant professor of biological systems engineering at Virginia Tech.
Starch in our tanks
A membrane bleeds off the carbon dioxide and the hydrogen is used by the fuel cell to create electricity. Water, a product of that fuel cell process, will be recycled for the starch-water reactor. Laboratory tests confirm that it all takes place at low temperature - about 86 degrees F - and atmospheric pressure.
The vision is for the ingredients to be mixed in the fuel tank of your car, for instance. A car with an approximately 12-gallon tank could hold 27 kilograms (kg) of starch, which is the equivalent of 4 kg of hydrogen. The range would be more than 300 miles, Zhang estimates. One kg of starch will produce the same energy output as 1.12 kg (0.38 gallons) of gasoline.
Since hydrogen is gaseous, hydrogen storage is the largest obstacle to large-scale use of hydrogen fuel. The American Department of Energy’s long-term goal for hydrogen storage was 12 mass percent, or 0.12 kg of hydrogen per one kg of container or storage material, but such technology is not available, said Zhang. Using polysaccharides as the hydrogen storage carrier, the research team achieved hydrogen storage capacity as high as 14.8 mass percent, they report in the PLOS article:
bioenergy :: biofuels :: energy :: sustainability :: biohydrogen :: polysaccharides :: starch :: sugar :: biomass :: synthetic enzymes :: synthetic biology :: carbohydrate economy ::
The idea began as a theory. The research was based on Zhang’s previous work pertaining to cellulosic ethanol production and the ORNL and University of Georgia researchers’ work with enzymatic hydrogen production. UGA Distinguished Professor Adams is co-author of the first enzymatic hydrogen paper in Nature Biotechnology in 1996. The researchers were certain they could put the processes together in one pot. They tested the theory using Oak Ridge’s hydrogen detectors and documented that hydrogen is produced as they predicted.
Mielenz, who heads the Bioconversion Group in ORNL's Biosciences Division, attributed the successful research to a unique collaborative working relationship between scientists, lab divisions, and universities.
"Pairing our biomass conversion capabilities with facilities for studying renewable hydrogen production in the lab's Chemical Sciences Division was a key to this project," Mielenz said. "This also shows the value of partnerships with universities such as Virginia Tech and the University of Georgia."
It is a new process that aims to release hydrogen from water and carbohydrate by using multiple enzymes as a catalyst, Zhang said. “In nature, most hydrogen is produced from anaerobic fermentation. But hydrogen, along with acetic acid, is a co-product and the hydrogen yield is pretty low--only four molecules per molecule of glucose. In our process, hydrogen is the main product and hydrogen yields are three-times higher, and the likely production costs are low--about $1 per pound of hydrogen.
Over the years, many substances have been proposed as “hydrogen carriers,” such as methanol, ethanol, hydrocarbons, or ammonia - all of which require special storage and distribution. Also, the thermochemical reforming systems require high temperatures and are complicated and bulky. Starch, on the other hand, can be distributed by grocery stores, Zhang points out.
“So it is environmentally friendly, energy efficient, requires no special infrastructure, and is extremely safe. We have killed three birds with one stone,” he said. “We have hydrogen production with a mild reaction and low cost. We have hydrogen storage and transport in the form of starch or syrups. And no special infrastructure is needed.”
“The next R&D step will be to increase reaction rates and reduce enzyme costs,” Zhang said. “We envision that in the future we will drive vehicles powered by carbohydrate, or energy stored in solid carbohydrate form, with hydrogen production from carbohydrate and water, and electricity production via hydrogen-fuel cells.
“What is more important, the energy conversion efficiency from the sugar-hydrogen-fuel cell system is extremely high--greater than three times higher than a sugar-ethanol-internal combustion engine,” Zhang said. “It means that if about 30 percent of transportation fuel can be replaced by ethanol from biomass as the DOE proposed, the same amount of biomass will be sufficient to provide 100 percent of vehicle transportation fuel through this technology.”
In addition, the use of carbohydrates from biomass as transportation fuels will produce zero net carbon dioxide emissions and bring benefits to national energy security and the economy, Zhang said.
Interest to the South
The 'carbohydrate economy' is set to benefit those countries that can readily supply large quantities of industrial starch, sugar and cellulose. The developing world is a world leader in this respect and has a tremendous potential to grow.
If it ever becomes feasible to apply the technique developed by the researchers - just putting a starch and water solution in your tank - the main fuel will have to be processed starch. Theoretically it will be possible to extract the sugars from cellulose, but this would require additional processing steps.
Countries with the largest production potential for industrial starch can all be found in the tropics and the subtropics, where crops such as cassava, maize, sago and sweet potatoes grow that yield high quantities of the product (see our previous text, titled "Sweet potatoes and the carbohydrate economy").
Image: potato starch - soon powering our cars?
More information:
Zhang YP, Evans BR, Mielenz JR, Hopkins RC, Adams MW, High-Yield Hydrogen Production from Starch and Water by a Synthetic Enzymatic Pathway. PLoS ONE 2(5): e456, 2007, doi:10.1371/journal.pone.0000456
Article continues
Wednesday, May 23, 2007
Engineers to burn manure as fuel to power an ethanol plant
Engineers from the Texas Cooperative Extension have understood this and are now working with feedyard owners to help them look at the manure produced by their animals as a valuable biofuel that will be used to power an ethanol plant. Besides ethanol, the refinery will produce a byproduct known as distillers' dried grain, which is a prime feed for the cattle that produce the manure. If collected and treated well, the manure has a heating value almost similar to that of Texas lignite coal. The main difference is that the first fuel source has a low carbon dioxide footprint, whereas coal is extremely climate destructive.
Dr. Brent Auvermann, the expert developing the manure combustion process, recently hosted a seminar titled "Producing High-Value Manure for BioFuels and Fertilizer", in Hereford, where Panda Energy International will use the biomass in its ethanol facility. The meeting outlined work by Texas Agricultural Experiment Station researchers to determine best management practices for scraping manure from the feed pens.
"We're doing something that has never been done before," says Arles Graham, Panda Energy International's general manager for the Hereford plant, who spoke at the event. "We're using your manure as an energy source," he told feedyard owners. "It's a very complex process."
After starting up the plant with natural gas as the boiler fuel, Panda Energy will eventually use manure as a fuel source when producing ethanol for an E10 fuel blend, Graham said. The plant will initially process corn for ethanol, although the company is looking at alternative sources of starch to make the ethanol, and it will produce distiller's grains as a by-product. "But manure is our future," Graham said, estimating each plant will use 1,500 tons a day. Jim Adams, Panda Energy vice president-fuels, said the plant will begin asking yards in June to sign up for a percentage of their manure.
The past winter was a wake-up call, Adams said. Sometimes when the weather is too wet, manure can't be harvested from the pens. Manure will be used by this fall, so they have to start stockpiling now to ensure a steady supply. Adams said the plant will use manure on a six-day basis, requiring 70 to 80 truckloads per day. Panda's contractor will collect from the pens when they are dry enough, but will need to pull from stockpiles when pen surfaces are too wet.
Manure quality key
Quality is the biggest issue, Auvermann said. The manure needs to burn at a minimum rate of 2,758 British thermal units per pound of manure. That number changes according to the amount of pollutants – moisture and dirt – included when the pen is scraped:
bioenergy :: biofuels :: energy :: sustainability :: climate change :: fossil fuels :: biomass :: ethanol :: manure :: combustion ::
If all the water and contaminants were removed from the manure, the highest quality would be 8,500 Btu, "but we can't do that, because we can't take the ash out completely," he said.
Manure from soil-surfaced pens may not always meet the minimum heating value on an as-received basis, Auvermann said. Feedyard operators will have to take some steps to improve it. The timeliness of collection and depth of scraping will be key to keeping dirt content below 60 percent and moisture content below 20 percent, he said. "Paving the pens with a crushed ash or a fly-ash material (from coal-fired power plants) will end up returning to you in the form of heating value – big time," Auvermann said.
Partially composted manure from paved pens can have a heating value almost equivalent to that generated by burning Texas lignite coal, he said.
Feedyard owners should consider the process as "harvesting manure" rather than cleaning pens, Auvermann said. The ultimate goal is to have a hard, smooth, well-drained corral surface. Implementing good practices will pay at the bottom line, he said. Conscientious manure harvesting can result in higher fuel and fertilizer values, reduced feed requirements for cattle, improved pen drainage, and reduced odor, dust and flies.
Image 1: Dr. Brent Auvermann, Texas Cooperative Extension engineering specialist, advises feedyard operators to pay close attention to blade depth when harvesting manure from corral surfaces as a boiler fuel source. (Texas Cooperative Extension photo by Sharon Preece).
Image 2: Cleaning manure from feed pens is a common practice, but one that will have to be done more carefully in the future if the harvested product is to be used as a fuel source, according to Dr. Brent Auvermann, Texas Cooperative Extension engineering specialist. (Texas Cooperative Extension photo by Sharon Preece).
More information:
AgNews, Texas A&M University: Cleaner Manure Burns Hotter in Ethanol Processing - May 23, 2007.
Article continues
posted by Biopact team at 10:54 PM 0 comments links to this post