Butanol
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Butanol or butyl alcohol (sometimes also called biobutanol when produced biologically), is an alcohol with a 4 carbon structure and the molecular formula of C4H10O. It is primarily used as a solvent, as an intermediate in chemical synthesis, and as a fuel. There are four isomeric structures for butanol.
Isomers
The unmodified term butanol usually refers to the straight chain isomer with the alcohol functional group at the terminal carbon, which is also known as n-butanol or 1-butanol. The straight chain isomer with the alcohol at an internal carbon is sec-butanol or 2-butanol. The branched isomer with the alcohol at a terminal carbon is isobutanol, and the branched isomer with the alcohol at the internal carbon is tert-butanol.
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| n-Butanol | sec-Butanol | Isobutanol | tert-Butanol |
Butanol isomers, due to their different structures, have somewhat different melting and boiling points. All are moderately miscible in water, less so than ethanol, and more so than the higher (longer carbon chain) alcohols. Like most alcohols, butanol is toxic.
Uses
Butanol sees use as a solvent for a wide variety of chemical and textile processes, as a paint thinner, as well as a component of hydraulic and brake fluids. It is also used as a base for perfumes, but on its own has a highly alcoholic aroma. Butanol also found use as a biofuelProduction
Since the 1950s, most butanol in the United States is produced commercially from fossil fuels.Butanol can also be produced by fermentation of biomass.
It has also been proposed that butanol be synthesized from ethanol through electrolysis.[[Citing sources citation needed]]
C2H5OH + C2H5OH --> C4H9OH + H2 + 1/2 O2
Butanol as fuel
Butanol may be used as a biofuel in an internal combustion engine engineered for use with butanol or gasoline blended with ethanol. It has several properties that are more similar to gasoline than ethanol and has been demonstrated to work in some vehicles designed for use with gasoline without any modification.[butanol.com]
| Fuel | Energy density | Air-fuel ratio | Specific energy | Heat of vaporization |
| Gasoline | 32 MJ/l | 14.6 | 2.9 MJ/kg air | 0.36 MJ/kg |
| Butanol | 29.2 MJ/l | 11.2 | 3.2 MJ/kg air | 0.43 MJ/kg |
| Ethanol | 19.6 MJ/l | 9.0 | 3.0 MJ/kg air | 0.92 MJ/kg |
| Methanol | 16 MJ/l | 6.5 | 3.1 MJ/kg air | 1.2 MJ/kg |
Energy content
Butanol is reported to yield 36 MJ/kg (15,500 BTU/lb) when burned. This can be expressed volumetrically as 29.2 MJ/l (104,800 BTU/US gal). Switching a petrol engine over to butanol would in theory result in a fuel consumption penalty of about 10%.Octane rating
The octane rating of butanol is significantly higher than that of gasoline.A fuel with a higher octane rating is less prone to knocking and the control system of any modern car engine can take advantage of this by adjusting the ignition timing. This will improve energy efficiency, leading to a better mileage than the comparisons of energy content between butanol and gasoline would indicate. By increasing the compression ratio, further gains in milage, power and torque can be achieved.
Air-fuel ratio
Alcohol fuels like, butanol and ethanol, are partially oxidized fuels and therefore need run at richer mixtures than gasoline. Standard gasoline engines in cars can adjust the air-fuel ratio to accommodate variations in the fuel, but only within certain limits depending on model. If the limit is exceeded, by running the engine on pure butanol or a gasoline blend with a high percentage of butanol, the engine will run lean, something which can damage it. Compared to ethanol, butanol can be mixed in higher ratios with gasoline for use in existing cars without the need for retrofit as the air-fuel ratio and energy content is closer to that of gasoline. [ext.colostate.edu][USA today]Specific energy
Alcohol fuels have less energy per unit weight and unit volume than gasoline but at the same time require richer mixtures. To make it possible to compare the net energy released per cycle a measure called the fuels specific energy is sometimes used. It is defined as the energy released per air fuel ratio. The net energy released per cycle is higher for butanol than ethanol or methanol and about 10% higher than for gasoline.Heat of vaporization
The fuel in an engine has to be vaporized before it will burn. Insufficient vaporization is a known problem with alcohol fuels during cold starts in cold weather. As the latent heat of vaporization of butanol is less than half of that of ethanol, an engine running on butanol should be easier to start in cold weather than one running on ethanol or methanol.[ext.colostate.edu]Production of biofuel
Butanol can also be produced by fermentation of biomass with the bacterium Clostridium acetobutylicum, also known as the Weizmann organism, as it was Chaim Weizmann who first used this bacteria for the production of acetone from starch (with the main use of acetone being the making of Cordite) in 1916. The butanol was a by-product of this fermentation (twice as much butanol was produced). The process also creates a recoverable amount of H2 and a number of other by-products: acetic, lactic and propionic acids, acetone, isopropanol and ethanol.DuPont, British Petroleum, and British Sugar Corporation intend to convert a bioethanol plant in the United Kingdom to produce biobutanol. The first phase of the venture will consist of using existing technology to convert sugar beets into 30,000 tons, or 9 million gallons, of biobutanol annually.[USA today][prnewswire/dupont]
The difference from ethanol production is primarily in the fermentation of the feedstock - producing butanol rather than ethanol like primary fermentation product and minor changes in distillation. The feedstocks are the same as for ethanol - energy crops such as sugar beets, sugar cane, corn grain, wheat and cassava as well as agricultural byproducts such as straw and corn stalks.According to DuPont, existing bioethanol plants can cost-effectively be retrofitted to biobutanol production.[Dupont Fact Sheet on Biobutanol]
Environmental Energy, inc. claims to have developed a two-stage fermentation process for butanol (U.S. Patent 5753474) that delivers a 100% increase in butanol yield from this process over single fermentation and about 42 % more energy in the form of butanol and hydrogen than conventional fermentation of ethanol for a given amount of feedstock. According to the company a bushel of corn (maize) produces 2.5 US gallons of butanol, a volume of butanol comparable to the volume of ethanol produced from a bushel of corn in the traditional fermentative process.
In this processes, biomass feedstock is first fed to the bacteria Clostridium tyrobutyricum, where a large percentage is converted into butyric acid and hydrogen. In the second process, the butyric acid is fed to the bacteria Clostridium acetobutylicum, where it is converted into butanol. This fermentation produces fewer byproducts, namely hydrogen, butyric acid and carbon dioxide.
Distribution
Biobutanol is more tolerant to water contamination and less corrosive than ethanol and therefore, unlike ethanol, suitable for distribution through existing pipelines for gasoline. In blends with diesel or gasoline, butanol is less likely to separate from this fuel than ethanol if the fuel is contaminated with water. There is also a vapor pressure co-blend synergy with butanol and gasoline containing ethanol, which facilitates ethanol blending. This facilitates storage and distribution of blended fuels.[Dupont Fact Sheet Biobutanol] [ext.colostate.edu][USAtoday]See also
- Agricultural byproduct
- Associated British Foods plc and its subsidiary British Sugar Corporation.
- Bioalcohol
- Biofuel
- Biodiesel
- Biohydrogen
- Catalyst
- Destillation
- Emission standards
- Energy crop
- Fermentation facility
- List of vegetable oils section on oils used as biofuel
- Solvent
External links
- [BP DuPont Biofuels]
- [BP and Dupont Biobutanol]
- [Dupont, BP join to produce biofuels].
- [Biobutanol Fact Sheet] (PDF)
- [Environmental Energy Inc's Butanol Webpage: butanol.com]
- [Green Car Congress: Boosting Biomass-to...Butanol?]
- [Butanol 3D view and pdb-file]
- [Acetone-butanol fermertantion revisited].
References
- Continuous two-stage ABE-frementation using Clostridium beijerinckii NRLL B592 operating with a growth rate in the first stage vessel close to its maximal value, J Mol Microbiol Biotechnol. 2000 Jan;2(1):101-5.
See also
External links
- For a full list of external links to MSDSs, spectroscopic data, commercial chemicals suppliers etc. for this compound, see [Chemical sources].
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