August 09, 2008
Cellulose Biofuels Conversion For Diesel?
We hear a lot about the bright prospects for cellulosic ethanol. But a group at UC Davis thinks they've found a cheap way to turn cellulose into furan-based organic liquids.
Mark Mascal and Edward B. Nikitin at the University of California, Davis (USA) have now developed an interesting new method for the direct conversion of cellulose into furan-based biofuels. As they report in the journal Angewandte Chemie, their simple, inexpensive process delivers furanic compounds in yields never achieved before.
Atmospheric carbon dioxide is viewed as the ultimate carbon source of the future. It is most efficiently "harvested" by plants via photosynthesis. Currently, biofuel producers primarily use starch, which is broken down to form sugars that are then fermented to give ethanol. Cellulose is however the most common form of photosynthetically fixed carbon. The problem is that the degradation of cellulose into its individual sugar components, which could then be fermented, is a slow and expensive process. "Another problem is that the carbon economy of glucose fermentation is poor," explains Mascal, "for every 10 g of ethanol produced, you also release 9.6 g CO2."
Could we avoid the breakdown of cellulose and fermentation? Mascal and Nikitin demonstrate that we can indeed. They have developed a simple process for the conversion of cellulose directly into "furanics", which are furan-based organic liquids. Furans are molecules whose basic unit is an aromatic ring made of one oxygen and four carbon atoms. The main product the researchers obtain under the conditions they have been developing is 5-chloromethylfurfural (CMF).
One of the compounds produced by this process might work in diesel fuel blends.
CMF and ethanol can be combined to give ethoxymethylfufural (EMF), and CMF reacts with hydrogen to give 5-methylfurfural. Both of these compounds are suitable as fuels. EMF has previously been investigated and found to be of interest in mixtures with diesel by Avantium Technologies, a spin-off of Shell.
"Our method appears to be the most efficient conversion of cellulose into simple, hydrophobic, organic compounds described to date," says Mascal. "It also surpasses the carbon yields of glucose and sucrose fermentation. Furanics could be established as both the automotive energy source and chemical starting material of the future."
If this works then it could shift the biomass advantage against ethanol. That would make government ethanol fuel mandates in the United States even dumber than they already are.
Liquid fuels are, of course, convenient, but is it somehow escaping everybody's notice that you can burn cellulose, straight up, as a powder? IC engines running off powdered solid fuel are already a proven technology, with the chief consideration merely being that the fuel not produce an abrasive ash. Granted, not as convenient as liquid fuels, but considerably more efficient.
Cellulosic fuels could also easily be burnt to power industrial boilers that are used for everything from electrical generation to heating. Perhaps instead of thinking of them as substitutes for petroleum we should be considering them as substitutes for coal. There is also the old fashioned standby of heating houses in northern climates with high efficient wood or pellet burning stoves. This way you dodge almost all the conversion costs used to turn solids into liquids. Of course you still need to deal with transportation and storage issues around moving light bulky products around the countryside.
Powdered fuels are, of course, a good government grant project, but it is somehow escaping somebody's notice that there are large numbers of very intelligent engineers and venture capitalists who would be bringing powdered fuel IC engines to market if it were really so simple? IC engines running off liquid fuel are really already a proven technology, with the chief consideration merely being that the fuel not produce pollutants and CO2 and not cost too much. Granted, not as explosive as transporting and pumping powdered fuels, but considerably better understood.
Disclaimer: This was intentionally written as satire and not intended to offend. The purpose is to suggest that running an engine technology in an insular setting (i.e. absent regulatory, supply, packaging, cost, warranty, market, etc. considerations) does not a proven technology make.
I don't want to repeat my previous analysis here.
But I stand by my conclusion: "Personally, I am very concerned that using land to produce fuel will lead to soil depletion and to food shortages in the poorer countries. It is a bad, perhaps even immoral trade-off.
The only biological sources of carbon that I would consider using for the production of fuel are garbage dumps and sewerage systems."
Directly burning cellulose in power plants, is a perfect way of recycling nature's carbon dioxide, and this kind of combustion is tantamount to solar energy converted to electricity and mechanical energy. With genetic engineering we will soon derive plants that grow very fast in the desert and swamps. For instance, there are already well known hybrid poplar trees that grow an astounding 8 feet per year, but if we could enhance these trees to grow in deserts at an even faster rate, then we will have a perfect energy source.
How have the timber and hay industries avoided soil depletion over the last four centuries in America? Can it be applied to our future cellulose industry?
It should be obvious that the oil production rates of algae are so superior to the cellulose sources that it makes little sense to pursue other crops as fuel source except incidental to harvest(and then only after nutrients have receded to the soil via the roots). Unfortunately, there are a lot of charlatans in high profile oil-from-algae start-ups. Since my proposed O-Prize doesn't appear to be receiving any funding there are very few reliable reality tests for those start-ups other than their ultimate delivery of product to the pump.
I'm cynical enough about the capital market failures resulting from subsidizing property rights that I doubt seriously there will be a shake-out in time to avert disaster -- which is why I've relocated to Iowa and am looking at burnable non-food biomass that is relatively immune to export.
"How have the timber and hay industries avoided soil depletion over the last four centuries in America? Can it be applied to our future cellulose industry?"
I do not know if the timber industry has really avoided soil depletion, because when the American wood is shipped to Japan, the minerals absorbed by the tree end up leaving the country. But in the case of trees used for combustion, as long as the ash from the burned trees (or any plants harvested as fuel) is returned back to the fields where these are being grown, there will NOT be any soil depletion because this ash contains all the minerals absorbed from the soil. Moreover, the ash from well burned plants and trees is very light and compact, and therefore it is easy to transport back to the fields even over long distances because its weight and volume would be only a very small fraction of the original mass.
Thus once we have a good battery to store electricity for cars, then we will be able to use biomass directly to burn in power plants.
One important point to emphasize is that biofuels are achieving two goals: harvesting CO2 from the atmosphere, and harvesting energy from sunlight. These goals are not entirely the same. It may well become the case that augmenting biofuel production with non-biomass energy (for example, hydrogen or thermal energy derived from another source) would increase the fuel yield per acre of farmed land.
farmcentre.com has a great article on solid fuel gassifiers burning agricultural and forestry waste at: http://www.farmcentre.com/News/TodaysStory/Article.aspx?id=fe507028-50d8-4021-b639-153b4e5b22fe
An innovative technology from Germany, the HERLT Gasifier, eliminates some of these problems and improves energy performance.
“The units can be used in any agricultural applications that require heat. They can be used for hydronic heating, provide heat for low pressure steam applications, produce hot air to dry grain, or power a multi-blade vapor turbine to generate electricity,
Agricultural biomass, such as straw bales, whole wood logs, or other baled energy crops like willow or switchgrass is fed into the first gasification chamber where the heat is 400 degrees Celsius. At this temperature, the biomass releases CO (carbon monoxide), H2 (hydrogen) and CH4 (methane) combustible gases.The gas is channeled to a second, post-combustion chamber where the internal combustion produces clean, hot gas at a temperature in excess of 1000 degrees Celsius. An appropriate heat exchanger captures the heat for use in various applications.
Emissions tests, conducted by TÜV Nord on gasifiers fueled with whole straw bales, yield average emission levels in the range of 50 mg/Nm3 CO; 300 mg/Mm3 NO2 (Nitrogen dioxide) and 20-120 mg/Mm3 fine particles. These results are better than current government regulations.
The flue gas emission temperatures are under 200 degrees Celsius. The heat radiation losses of the larger boiler are about 2.5%. This results in a boiler efficiency of 85%.
Straw contains about 5% of ash; wood has less than 1%. Ash is removed from the gasification chamber through the discharge doors.
The consumption of five whole, round straw bales per day provides 1,300 MBTU (one million British thermal units) per hour of thermal heat or approximately 30,000 MBTU per day.
Various sizes of HERLT Gasifiers are available, ranging from 85 to 2500 kilowatts (kW), equivalent to 300,000 to 8 million BTU per hour. A 500 kW unit provides the thermal heat requirements for a 3000 square metre chicken broiler farm operation complete with adjacent living quarters and warehouses. A 500 kW unit costs in the range of $230,000. Setting capital costs aside, cost of energy generation is roughly 2.5 cents per kWh
Paul F. Dietz,
I can imagine energy from solar or nuclear power used to generate hydrogen to further reduce CHO molecules produced by agriculture. Why not turn ethanol into a pure hydrocarbon in order to make it a higher mpg fuel? Once photovoltaics become cheap enough using PV electric to reduce (and by that I mean donate hydrogens) biomass seems an obvious thing to do.
I wonder if solid fuel gasifiers would work well with the biomass left over from algae once the liquid hydrocarbons are extracted/
I feel obligated to point out that the energy density of fast growing conifers/and some deciduous species results in very little net positive energy gains after the energy costs of harvest, processing, and transport. Sustainable forest/soil management of conifer forests requires significant energy resources to execute and maintain. The minority of harvested timber comes from well managed "sustainable" forests. The problem we're running up against is that there is no free energy. We have become energy drunk, and the hangover is about to start. As a race our net energy usage will have to fall significantly in order to be within the capacity of our sustainable renewables. "True happiness comes not in the accumulation of more; but in developing the capacity to enjoy less." Technology as powerful as it is, and can become, is only a tool. Society as a whole must understand the problem, before they can (or be willing) to apply the correct tool/s. A hazy truth of the situation, perpetuated by a myriad of interests, is slowing the advancement of the human race. Not a lack of ingenuity or technology.