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16
The Base For Perfume Makes a Great Base for Fuel
March 16, 2012 | 2 Comments
Research presses on for better plant oils to make fuels. The U.S. Department of Energy’s Joint BioEnergy Institute (JBEI) has engineered E.Coli bacteria to produce significantly more of the compound methyl ketone from glucose.
Methyl ketones are a class of chemical compounds we’re most familiar with in fragrance and flavoring products and might provide the clean, green and renewable fuel for transport use. They were discovered more than a century ago in the aromatic evergreen plant known as rue. Since then they’ve been found to be common in tomatoes and other plants, as well as insects and microorganisms. Today they are used to provide scents in essential oils and flavoring in cheese and other dairy products.
The driver is advanced synthetic biofuels, liquid transportation fuels derived from the cellulosic biomass of perennial grasses and other non-food plants, as well as from agricultural waste. The idea is seen as a potential replacement for gasoline, diesel and jet fuels. Equally touted is the synthesis of these fuels through microbes that digest the biomass and convert its sugars into fuel molecules.
At JBEI, researchers are focusing on developing advanced biofuels that can be used in today’s engines and distribution infrastructures. In previous research, lead researcher Harry Beller and his colleagues engineered E. coli with special enzymes to synthesize from fatty acids long-chain alkene hydrocarbons that can be turned into diesel fuel. Fatty acids are the energy-rich molecules in bacterial and plant cells that have been dubbed nature’s petroleum.
Beller-and-Goh-Webvers. Click image for the largest view.
Harry Beller is a JBEI microbiologist who directs the Biofuels Pathways department for JBEI’s Fuels Synthesis Division, and also is a senior scientist with the Earth Sciences Division of Lawrence Berkeley National Laboratory. He is the corresponding author with co-authors of a paper describing this work titled “Engineering of Bacterial Methyl Ketone Synthesis for Biofuels,” which was published in the journal Applied and Environmental Microbiology.
In the research test series the E.Coli production of methyl ketone yielded high cetane numbers, which is a diesel fuel rating comparable to the octane number for gasoline – making them strong candidates for the production of advanced biofuels.
Beller explains, “Our findings add to the list of naturally occurring chemical compounds that could serve as biofuels, which means more flexibility and options for the biofuels industry. We’re especially encouraged by our finding that it is possible to increase the methyl ketone titer production of E. coli more than 4,000-fold with a relatively small number of genetic modifications.” That’s OK, but the press release isn’t saying what the base line is for the 4,000 fold improvement, but does point out native E. coli make virtually undetectable quantities of methyl ketones, Beller and his colleagues were able to overcome this deficiency using the same tools of synthetic biology they used to engineer high fatty acid-producing E.coli.
The JBEI team is focusing on developing advanced biofuels that can be used in today’s engines and distribution infrastructures. In previous research, Beller and his colleagues engineered E. coli with special enzymes to synthesize from fatty acids long-chain alkene hydrocarbons that can be turned into diesel fuel. Fatty acids are the energy-rich molecules in bacterial and plant cells that have been dubbed nature’s petroleum.
Beller sets up the background saying, “In the earlier studies, we noticed that bacteria engineered to produce unnaturally high levels of fatty acids also produced some methyl ketones. When we tested the cetane numbers of these ketones and saw that they were quite favorable, we were prompted to look more closely at developing methyl ketones as biofuels.”
On the technology Beller said, “For methyl ketone production, we made two major modifications to E. coli. First we modified specific steps in beta-oxidation, the metabolic pathway that E. coli uses to break down fatty acids, and then we increased the expression of a native E. coli protein called FadM. These two modifications combined to greatly enhance the production of methyl ketones.”
The team tested two methyl ketones for cetane numbers, undecanone and tridecanone. The cetane number is a measure of ignition delay during compression ignition; a higher number indicates a shorter ignition delay period and is more favorable than a lower number. In the United States, diesel fuel must have a minimum cetane number of 40. The cetane number for undecanone was 56.6. The number for a 50/50 mix of undecanone and tridecanone was 58.4. Despite this impressive performance, there was a concern that both these methyl ketones have a relatively high melting point, which is a disadvantage for cold-temperature fuel properties.
Beller picks up the issue with, “We were able to mitigate the melting point problem in our best producing strains of E.coli by increasing the percentage of monounsaturated methyl ketones, which have much lower melting points than their saturated homologs,”
Next up for the team is a focus on increasing production and optimizing fuel properties of the methyl ketones by modulating their composition with respect to chain length and degree of unsaturation.
“Since these methyl ketones are fatty acid-derived compounds, we hope that advances that we make in enhancing their microbial production will have relevance to other fatty acid-derived biofuels as well,” Beller said.
It’s a long way to get to a “fill her up” order. But methyl ketones are very close to fuel quality needing only a bit of processing – the compounds are very close to petroleum from plants. With those high cetane numbers, it’s pretty good stuff.
Methyl ketone could have a bright future. Still to work out are the extraction, getting from starches cellulose and other sugars to glucose is a challenge. Still these could likely be gene modification solutions.
This early its hard to project, but the properties of methyl ketone are very attractive for compression ignition internal combustion engines – the diesel. If the methyl ketones can mix happily with petroleum diesel and biodiesel perhaps the biobased fuels can finally make major contributions to the alternative mix.
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Ketones, aldehydes and alcohols are good fuels, even if they have lower calorific value due to the oxygen atoms carried. They generally burn more completely leaving less carbon particles in the combustion products.
the crux of bio-fuel production remains
1. Use of agricultural and forest wastes with economical collection.
2. production of biomass without sacrificing food and other cash crops.
3. Conversion of the bio-mass to alcohols, aldehydes and ketones.
This is a good progress in the last item.
You just never can underestimate the power of human creativity!