Butanol fuel

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Butanol, a C-4 hydrocarbon is a promising bio-derived fuel, which shares many properties with gasoline. Butanol flat structure.png
Butanol, a C-4 hydrocarbon is a promising bio-derived fuel, which shares many properties with gasoline.

Butanol may be used as a fuel in an internal combustion engine. It is more similar to gasoline than it is to ethanol. A C4-hydrocarbon, butanol is a drop-in fuel and thus works in vehicles designed for use with gasoline without modification. [1] Both n-butanol and isobutanol have been studied as possible fuels. Both can be produced from biomass (as "biobutanol" [2] [3] [4] ) as well as from fossil fuels (as "petrobutanol" [5] ). The chemical properties.depend on the isomer (n-butanol or isobutanol), not on the production method.


Although intriguing in many ways, butanol fuel is rarely economically competitive.

Genetically modified bacteria

This method of production offers a way to produce liquid fuels from sustainable sources. [6]

Fermentation however remains inefficient. Yields are low and separation is very expensive. Obtaining higher yields of butanol involves manipulation of the metabolic networks using metabolic engineering and genetic engineering. [7] [8]

Escherichia coli

Escherichia coli , or E. coli, is a Gram-negative, rod-shaped bacterium. E. coli is the microorganism most likely to move on to commercial production of isobutanol. [9] In its engineered form E. coli produces the highest yields of isobutanol of any microorganism.[ citation needed ] Methods such as elementary mode analysis have been used to improve the metabolic efficiency of E. coli so that larger quantities of isobutanol may be produced. [10] E. coli is an ideal isobutanol bio-synthesizer for several reasons:

The primary drawback of E. coli is that it is susceptible to bacteriophages when being grown. This susceptibility could potentially shut down entire bioreactors. [9] Furthermore, the native reaction pathway for isobutanol in E. coli functions optimally at a limited concentration of isobutanol in the cell. To minimize the sensitivity of E. coli in high concentrations, mutants of the enzymes involved in synthesis can be generated by random mutagenesis. By chance, some mutants may prove to be more tolerant of isobutanol which will enhance the overall yield of the synthesis. [12]


n-Butanol can be produced by fermentation of biomass by the A.B.E. process using Clostridium acetobutylicum , Clostridium beijerinckii . C. acetobutylicum was once used for the production of acetone from starch. The butanol was a by-product of fermentation (twice as much butanol was produced). The feedstocks for biobutanol the same as those for ethanol: energy crops such as sugar beets, sugar cane, corn grain, wheat and cassava, prospective non-food energy crops such as switchgrass and even guayule in North America, as well as agricultural byproducts such as bagasse, straw and corn stalks. [13] According to DuPont, existing bioethanol plants can cost-effectively be retrofitted to biobutanol production. [14] Additionally, butanol production from biomass and agricultural byproducts could be more efficient (i.e. unit engine motive power delivered per unit solar energy consumed) than ethanol or methanol production. [15]

A strain of Clostridium can convert nearly any form of cellulose into butanol even in the presence of oxygen. [16]

A strain of Clostridium cellulolyticum, a native cellulose-degrading microbe, affords isobutanol directly from cellulose. [17]

A combination of succinate and ethanol can be fermented to produce butyrate (a precursor to butanol fuel) by utilizing the metabolic pathways present in Clostridium kluyveri . Succinate is an intermediate of the TCA cycle, which metabolizes glucose. Anaerobic bacteria such as Clostridium acetobutylicum and Clostridium saccharobutylicum also contain these pathways. Succinate is first activated and then reduced by a two-step reaction to give 4-hydroxybutyrate, which is then metabolized further to crotonyl-coenzyme A (CoA) . Crotonyl-CoA is then converted to butyrate. The genes corresponding to these butanol production pathways from Clostridium were cloned to E. coli. [18]


Cyanobacteria are a phylum of photosynthetic bacteria. [19] Cyanobacteria are suited for isobutanol biosynthesis when genetically engineered to produce isobutanol and its corresponding aldehydes. [20] Isobutanol producing species of cyanobacteria offer several advantages as biofuel synthesizers:

The primary drawbacks of cyanobacteria are:

Cyanobacteria can be re-engineered to increase their butanol production, showing the importance of ATP and cofactor driving forces as a design principle in pathway engineering. Many organisms have the capacity to produce butanol utilizing an acetyl-CoA dependent pathway. The main problem with this pathway is the first reaction involving the condensation of two acetyl-CoA molecules to acetoacetyl-CoA. This reaction is thermodynamically unfavorable due to the positive Gibbs free energy associated with it (dG = 6.8 kcal/mol). [24] [25]

Bacillus subtilis

Bacillus subtilis is a gram-positive rod-shaped bacteria. Bacillus subtilis offers many of the same advantages and disadvantages of E. coli, but it is less prominently used and does not produce isobutanol in quantities as large as E. coli. [9] Similar to E. coli, Bacillus subtilis is capable of producing isobutanol from lignocellulose, and is easily manipulated by common genetic techniques. [9] Elementary mode analysis has also been used to improve the isobutanol-synthesis metabolic pathway used by Bacillus subtilis, leading to higher yields of isobutanol being produced. [26]

Saccharomyces cerevisiae

Saccharomyces cerevisiae , or S. cerevisiae, is a species of yeast. S. cerevisiae naturally produces isobutanol in small quantities via its valine biosynthetic pathway. [27] S. cerevisiae is an ideal candidate for isobutanol biofuel production for several reasons:

Overexpression of the enzymes in the valine biosynthetic pathway of S. cerevisiae has been used to improve isobutanol yields. [27] [28] [29] S. cerevisiae, however, has proved difficult to work with because of its inherent biology:

Ralstonia eutropha

Ralstonia eutropha is a gram-negative soil bacterium of the betaproteobacteria class. Ralstonia eutropha is capable of converting electrical energy into isobutanol. This conversion is completed in several steps:


High cost of raw material is considered as one of the main obstacles to commercial production of butanols. Using inexpensive and abundant feedstocks, e.g., corn stover, can enhance the process economic viability. [30]

Metabolic engineering can be used to allow an organism to use a cheaper substrate such as glycerol instead of glucose. Because fermentation processes require glucose derived from foods, butanol production can negatively impact food supply (see food vs fuel debate). Glycerol is a good alternative source for butanol production. While glucose sources are valuable and limited, glycerol is abundant and has a low market price because it is a waste product of biodiesel production. Butanol production from glycerol is economically viable using metabolic pathways that exist in Clostridium pasteurianum bacterium. [31]

Improving efficiency

A process called cloud point separation could allow the recovery of butanol with high efficiency. [32]

Producers and distribution

DuPont and BP plan to make biobutanol the first product of their joint effort to develop, produce, and market next-generation biofuels. [33] In Europe the Swiss company Butalco [34] is developing genetically modified yeasts for the production of biobutanol from cellulosic materials. Gourmet Butanol, a United States-based company, is developing a process that utilizes fungi to convert organic waste into biobutanol. [35] [36] Celtic Renewables makes biobutanol from waste that results from the production of whisky, and low-grade potatoes.

Properties of common fuels


Isobutanol is a second-generation biofuel with several qualities that resolve issues presented by ethanol. [9]

Isobutanol's properties make it an attractive biofuel:


Butanol better tolerates water contamination and is less corrosive than ethanol and more suitable for distribution through existing pipelines for gasoline. [14] In blends with diesel or gasoline, butanol is less likely to separate from this fuel than ethanol if the fuel is contaminated with water. [14] 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. [14] [40] [41]

Fuel Energy
Heat of
Gasoline and biogasoline 32 MJ/L14.72.9 MJ/kg air0.36 MJ/kg  91–99  81–89  87-95
Butanol fuel29.2 MJ/L11.13.6 MJ/kg air0.43 MJ/kg  96  78  87
Anhydrous Ethanol fuel 19.6 MJ/L  9.03.0 MJ/kg air0.92 MJ/kg107  89
Methanol fuel 16 MJ/L  6.43.1 MJ/kg air1.2 MJ/kg10692

The octane rating of n-butanol is similar to that of gasoline but lower than that of ethanol and methanol. n-Butanol has a RON (Research Octane number) of 96 and a MON (Motor octane number) of 78 (with a resulting "(R+M)/2 pump octane number" of 87, as used in North America) while t-butanol has octane ratings of 105 RON and 89 MON. [43] t-Butanol is used as an additive in gasoline but cannot be used as a fuel in its pure form because its relatively high melting point of 25.5 °C (79 °F) causes it to gel and solidify near room temperature. On the other hand, isobutanol has a lower melting point than n-butanol and favorable RON of 113 and MON of 94, and is thus much better suited to high fraction gasoline blends, blends with n-butanol, or as a standalone fuel. [44]

A fuel with a higher octane rating is less prone to knocking (extremely rapid and spontaneous combustion by compression) 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 fuel economy than the comparisons of energy content different fuels indicate. By increasing the compression ratio, further gains in fuel economy, power and torque can be achieved. Conversely, a fuel with lower octane rating is more prone to knocking and will lower efficiency. Knocking can also cause engine damage. Engines designed to run on 87 octane will not have any additional power/fuel economy from being operated with higher octane fuel.

Butanol characteristics: air-fuel ratio, specific energy, viscosity, specific heat

Alcohol fuels, including butanol and ethanol, are partially oxidized and therefore need to 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 ethanol or a gasoline blend with a high percentage of ethanol, the engine will run lean, something which can critically damage components. 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 are closer to that of gasoline. [40] [41]

Alcohol fuels have less energy per unit weight and unit volume than gasoline. 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. [45]

at 20 °C
Butanol3.64 cSt
Diesel>3 cSt
Ethanol1.52 cSt
Water1.0 cSt
Methanol0.64 cSt
Gasoline0.4–0.8 cSt

The viscosity of alcohols increase with longer carbon chains. For this reason, butanol is used as an alternative to shorter alcohols when a more viscous solvent is desired. The kinematic viscosity of butanol is several times higher than that of gasoline and about as viscous as high quality diesel fuel. [46]

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 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. [40]

Butanol fuel mixtures

Standards for the blending of ethanol and methanol in gasoline exist in many countries, including the EU, the US, and Brazil. Approximate equivalent butanol blends can be calculated from the relations between the stoichiometric fuel-air ratio of butanol, ethanol and gasoline. Common ethanol fuel mixtures for fuel sold as gasoline currently range from 5% to 10%. It is estimated that around 9.5 gigaliter (Gl) of gasoline can be saved and about 64.6 Gl of butanol-gasoline blend 16% (Bu16) can potentially be produced from corn residues in the US, which is equivalent to 11.8% of total domestic gasoline consumption. [30]

Consumer acceptance may be limited due to the potentially offensive banana-like smell of n-butanol. [47] Plans are underway to market a fuel that is 85% Ethanol and 15% Butanol (E85B), so existing E85 internal combustion engines can run on a 100% renewable fuel that could be made without using any fossil fuels. Because its longer hydrocarbon chain causes it to be fairly non-polar, it is more similar to gasoline than it is to ethanol. Butanol has been demonstrated to work in vehicles designed for use with gasoline without modification.

Butanol in vehicles

Currently no production vehicle is known to be approved by the manufacturer for use with 100% butanol. As of early 2009, only a few vehicles are approved for even using E85 fuel (i.e. 85% ethanol + 15% gasoline) in the USA. However, in Brazil all vehicle manufacturers (Fiat, Ford, VW, GM, Toyota, Honda, Peugeot, Citroen and others) produce "flex-fuel" vehicles that can run on 100% Gasoline and or any mix of ethanol and gasoline up to 85% ethanol (E85). These flex fuel cars represent 90% of the sales of personal vehicles in Brazil, in 2009. BP and Dupont, engaged in a joint venture to produce and promote butanol fuel, claim [48] that "biobutanol can be blended up to 10%v/v in European gasoline and 11.5%v/v in US gasoline". [49] [50] In the 2009 Petit Le Mans race, the No. 16 Lola B09/86 - Mazda MZR-R of Dyson Racing ran on a mixture of biobutanol and ethanol developed by team technology partner BP.

See also

Related Research Articles

Butanol (also called butyl alcohol) is a four-carbon alcohol with a formula of C4H9OH, which occurs in five isomeric structures (four structural isomers), from a straight-chain primary alcohol to a branched-chain tertiary alcohol; all are a butyl or isobutyl group linked to a hydroxyl group (sometimes represented as BuOH, n-BuOH, i-BuOH, and t-BuOH). These are n-butanol, 2 stereoisomers of sec-butanol, isobutanol and tert-butanol. Butanol is primarily used as a solvent and as an intermediate in chemical synthesis, and may be used as a fuel. Biologically produced butanol is called biobutanol, which may be n-butanol or isobutanol.

Biofuel Type of biological fuel produced from biomass from which energy is derived

Biofuel is fuel that is produced through contemporary processes from biomass, rather than by the very slow geological processes involved in the formation of fossil fuels, such as oil. Since biomass technically can be used as a fuel directly, some people use the terms biomass and biofuel interchangeably. More often than not, however, the word biomass simply denotes the biological raw material the fuel is made of, or some form of thermally/chemically altered solid end product, like torrefied pellets or briquettes.

Ethanol fuel One type of biofuel

Ethanol fuel is ethyl alcohol, the same type of alcohol found in alcoholic beverages, used as fuel. It is most often used as a motor fuel, mainly as a biofuel additive for gasoline. The first production car running entirely on ethanol was the Fiat 147, introduced in 1978 in Brazil by Fiat. Ethanol is commonly made from biomass such as corn or sugarcane. World ethanol production for transport fuel tripled between 2000 and 2007 from 17×109 liters (4.5×109 U.S. gal; 3.7×109 imp gal) to more than 52×109 liters (1.4×1010 U.S. gal; 1.1×1010 imp gal). From 2007 to 2008, the share of ethanol in global gasoline type fuel use increased from 3.7% to 5.4%. In 2011 worldwide ethanol fuel production reached 8.46×1010 liters (2.23×1010 U.S. gal; 1.86×1010 imp gal) with the United States of America and Brazil being the top producers, accounting for 62.2% and 25% of global production, respectively. US ethanol production reached 57.54×109 liters (1.520×1010 U.S. gal; 1.266×1010 imp gal) in 2017–04.

Liquid fuel

Liquid fuels are combustible or energy-generating molecules that can be harnessed to create mechanical energy, usually producing kinetic energy; they also must take the shape of their container. It is the fumes of liquid fuels that are flammable instead of the fluid. Most liquid fuels in widespread use are derived from fossil fuels; however, there are several types, such as hydrogen fuel, ethanol, and biodiesel, which are also categorized as a liquid fuel. Many liquid fuels play a primary role in transportation and the economy.

Methanol fuel is an alternative [biofuel] for internal combustion and other engines, either in combination with gasoline or independently. Methanol (CH3OH) is less expensive to produce sustainably than ethanol fuel, although it is generally more toxic and has lower energy density. For optimizing engine performance and fuel availability, however, a blend of ethanol, methanol and petroleum is likely to be preferable to using any of these alone. Methanol (a methyl group linked to a hydroxyl group) may be made from hydrocarbon or renewable resources, in particular natural gas and biomass respectively. It can also be synthesized from CO2 (carbon dioxide) and hydrogen. Methanol fuel is currently used by racing cars in many countries but has not seen widespread use otherwise.

Ethanol, an alcohol fuel, is an important fuel for the operation of internal combustion engines that are used in cars, trucks, and other kinds of machinery.

Cellulosic ethanol is ethanol produced from cellulose rather than from the plant's seeds or fruit. It can be produced from grasses, wood, algae, or other plants. It is generally discussed for use as a biofuel. The carbon dioxide that plants absorb as they grow offsets some of the carbon dioxide emitted when ethanol made from them is burned, so cellulosic ethanol fuel has the potential to have a lower carbon footprint than fossil fuels.


E85 is an abbreviation typically referring to an ethanol fuel blend of 85% ethanol fuel and 15% gasoline or other hydrocarbon by volume.

<i>Clostridium acetobutylicum</i> Species of bacterium

Clostridium acetobutylicum, ATCC 824, is a commercially valuable bacterium sometimes called the "Weizmann Organism", after Jewish-Russian-born Chaim Weizmann. A senior lecturer at the University of Manchester, England, he used them in 1916 as a bio-chemical tool to produce at the same time, jointly, acetone, ethanol, and n-butanol from starch. The method has been described since as the ABE process,, yielding 3 parts of acetone, 6 of n-butanol, and 1 of ethanol. Acetone was used in the important wartime task of casting cordite. The alcohols were used to produce vehicle fuels and synthetic rubber.

The word metagenics uses the prefix meta and the suffix gen. Literally, it means "the creation of something which creates". In the context of biotechnology, metagenics is the practice of engineering organisms to create a specific enzyme, protein, or other biochemicals from simpler starting materials. The genetic engineering of E. coli with the specific task of producing human insulin from starting amino acids is an example. E. coli has also been engineered to digest plant biomass and use it to produce hydrocarbons in order to synthesize biofuels. The applications of metagenics on E. coli also include higher alcohols, fatty-acid based chemicals and terpenes.

Isobutanol Chemical compound

Isobutanol (IUPAC nomenclature: 2-methylpropan-1-ol) is an organic compound with the formula (CH3)2CHCH2OH (sometimes represented as i-BuOH). This colorless, flammable liquid with a characteristic smell is mainly used as a solvent either directly or as its esters. Its isomers, the other butanols, include n-butanol, 2-butanol, and tert-butanol, all of which are important industrially.

Alcohol fuel

Various alcohols are used as fuel for internal combustion engines. The first four aliphatic alcohols are of interest as fuels because they can be synthesized chemically or biologically, and they have characteristics which allow them to be used in internal combustion engines. The general chemical formula for alcohol fuel is CnH2n+1OH.

1-Butanol Chemical compound

1-Butanol (IUPAC: Butan-1-ol) also known as n-Butanol is a primary alcohol with the chemical formula C4H9OH and a linear structure. Isomers of 1-Butanol are isobutanol, 2-butanol, and tert-butanol. The unmodified term butanol usually refers to the straight chain isomer.

The United States produces mainly biodiesel and ethanol fuel, which uses corn as the main feedstock. The US is the world's largest producer of ethanol, having produced nearly 16 billion gallons in 2017 alone. The United States, together with Brazil accounted for 85 percent of all ethanol production, with total world production of 27.05 billion gallons. Biodiesel is commercially available in most oilseed-producing states. As of 2005, it was somewhat more expensive than fossil diesel, though it is still commonly produced in relatively small quantities.

Acetone–butanol–ethanol fermentation Chemical process

Acetone–butanol–ethanol (ABE) fermentation is a process that uses bacterial fermentation to produce acetone, n-Butanol, and ethanol from carbohydrates such as starch and glucose. It was developed by chemist Chaim Weizmann and was the primary process used to produce acetone, which was needed to make cordite, a substance essential for the British war industry during World War I.

Second-generation biofuels, also known as advanced biofuels, are fuels that can be manufactured from various types of non-food biomass. Biomass in this context means plant materials and animal waste used especially as a source of fuel.

The Philippines Biofuels Act 2006 requires oil companies to use biofuels in all "liquid fuels for motors and engines sold in the Philippines." All gasoline sold in the country must contain at least 5 percent ethanol by February 2009, and by 2011, the mandated blend can go up to 10 percent. The new law is expected to bring a number of benefits to the country:

"Commercial production of ethanol from sugarcane, cassava or sorghum will help the island nation diversify its fuel portfolio and help to ensure its energy security. It could also generate employment, particularly in rural regions, as investors put up biofuel crop plantations and processing plants. Also, the shift to these plant-based fuels for transportation will help reduce pollution."

Biogasoline or biopetrol is a type of gasoline produced from biomass such as algae. Like traditionally produced gasoline, it is made up of hydrocarbons with 6 (hexane) to 12 (dodecane) carbon atoms per molecule and can be used in internal-combustion engines. Biogasoline is chemically different from biobutanol and bioethanol, as these are alcohols, not hydrocarbons.

Gevo U.S. chemical company

Gevo, Inc. is a renewable chemicals and advanced biofuels company headquartered in unincorporated Douglas County, Colorado in the Denver-Aurora metropolitan area. Gevo is focused on sustainability, using the business model based on the Circular Economy to incorporate renewable energy from a range of sources, de-fossilization of its processes, regenerative agriculture, sequestration of carbon in the soil, systemwide efficiency, and conservation of resources to enhance all of its products. The company develops bio-based alternatives to petroleum-based products using a combination of biotechnology and classical chemistry. Gevo uses the GREET model from Argonne National Laboratory as a basis for its measure of sustainability with the goal of producing high-protein animal feed, corn-oil products, energy-dense liquid hydrocarbons, from every kernel of corn. Gevo is focused on converting sustainably grown raw materials, specifically no. 2 dent corn, into high-value protein and isobutanol, the primary building block for its renewable hydrocarbons, including sustainable aviation fuel, renewable gasoline, and renewable diesel. Gevo believes these fuels can be directly integrated on a “drop in” basis into existing fuel and chemical products. Gevo's investors include Burrill & Company, Khosla Ventures, Lanxess, Osage University Partners, Total, and Virgin Green Fund, among others.

Cofactor engineering

Cofactor engineering, a subset of metabolic engineering, is defined as the manipulation of the use of cofactors in an organism’s metabolic pathways. In cofactor engineering, the concentrations of cofactors are changed in order to maximize or minimize metabolic fluxes. This type of engineering can be used to optimize the production of a metabolite product or to increase the efficiency of a metabolic network. The use of engineering single celled organisms to create lucrative chemicals from cheap raw materials is growing, and cofactor engineering can play a crucial role in maximizing production. The field has gained more popularity in the past decade and has several practical applications in chemical manufacturing, bioengineering and pharmaceutical industries.


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