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220px, Butanol, a C-4 hydrocarbon is a promising bio-derived fuel, which shares many properties with gasoline.
Butanol Butanol (also called butyl alcohol) is a four-carbon alcohol with a formula of C4 H9 O H, which occurs in five isomeric structures (four structural isomers), from a straight-chain primary alcohol to a branched-chain tertiary alcohol; all are a bu ...
may be used as a
fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy b ...
in an
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...
. It is more similar to
gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic c ...
than it is to
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...
. A C4-hydrocarbon, butanol is a
drop-in fuel Biofuel is a fuel that is produced over a short time span from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels, such as oil. According to the United States Energy Information Administration (EIA ...
and thus works in vehicles designed for use with gasoline without modification. Both ''n''-butanol and isobutanol have been studied as possible fuels. Both can be produced from
biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bio ...
(as "biobutanol" ) as well as from
fossil fuel A fossil fuel is a hydrocarbon-containing material formed naturally in the Earth's crust from the remains of dead plants and animals that is extracted and burned as a fuel. The main fossil fuels are coal, oil, and natural gas. Fossil fuels ma ...
s (as "petrobutanol"). The chemical properties depend on the
isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. Is ...
(''n''-butanol or isobutanol), not on the production method. Although intriguing in many ways, butanol fuel is rarely economically competitive.


Genetically modified organisms

Obtaining higher yields of butanol involves manipulation of the metabolic networks using
metabolic engineering Metabolic engineering is the practice of optimizing genetic and regulatory processes within cells to increase the cell's production of a certain substance. These processes are chemical networks that use a series of biochemical reactions and enzym ...
and
genetic engineering Genetic engineering, also called genetic modification or genetic manipulation, is the modification and manipulation of an organism's genes using technology. It is a set of technologies used to change the genetic makeup of cells, including ...
. While significant progress has been made
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food p ...
pathways for producing butanol remain inefficient. Titer and yields are low and separation is very expensive. As such, microbial production of butanol is not cost-competitive relative to petroleum-derived butanol. Although unproven commercially, combining electrochemical and microbial production methods may offer a way to produce butanol from sustainable sources.


''Escherichia coli''

''
Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...
'', or ''E. coli'', is a
Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...
,
rod-shaped A bacillus (), also called a bacilliform bacterium or often just a rod (when the context makes the sense clear), is a rod-shaped bacterium or archaeon. Bacilli are found in many different taxonomic groups of bacteria. However, the name '' Baci ...
bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
. ''E. coli'' is the microorganism most likely to move on to commercial production of isobutanol. In its engineered form ''E. coli'' produces the highest yields of isobutanol of any microorganism. 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. ''E. coli'' is an ideal isobutanol bio-synthesizer for several reasons: * ''E. coli'' is an organism for which several tools of genetic manipulation exist, and it is an organism for which an extensive body of scientific literature exists. This wealth of knowledge allows ''E. coli'' to be easily modified by scientists. * ''E. coli'' has the capacity to use
lignocellulose Lignocellulose refers to plant dry matter (biomass), so called lignocellulosic biomass. It is the most abundantly available raw material on the Earth for the production of biofuels. It is composed of two kinds of carbohydrate polymers, cellulose a ...
(waste plant matter left over from agriculture) in the synthesis of isobutanol. The use of lignocellulose prevents ''E. coli'' from using plant matter meant for human consumption, and prevents any food-fuel price relationship which would occur from the biosynthesis of isobutanol by ''E. coli''. * Genetic modification has been used to broaden the scope of lignocellulose which can be used by ''E. coli''. This has made ''E. coli'' a useful and diverse isobutanol bio-synthesizer. The primary drawback of ''E. coli'' is that it is susceptible to
bacteriophages A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bacterio ...
when being grown. This susceptibility could potentially shut down entire bioreactors. 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
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
s involved in synthesis can be generated by random
mutagenesis Mutagenesis () is a process by which the genetic information of an organism is changed by the production of a mutation. It may occur spontaneously in nature, or as a result of exposure to mutagens. It can also be achieved experimentally using lab ...
. By chance, some mutants may prove to be more tolerant of isobutanol which will enhance the overall yield of the synthesis.


''Clostridia''

''n''-Butanol can be produced by
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food p ...
of biomass by the
A.B.E. process Abe or ABE may refer to: People and fictional characters * Shinzo Abe (1954–2022), former Prime Minister of Japan * Abe (given name), a list of people and fictional characters with the given name or nickname * Abe (surname), a list of people an ...
using ''
Clostridium acetobutylicum ''Clostridium acetobutylicum'', ATCC 824, is a commercially valuable bacterium sometimes called the "Weizmann Organism", after Jewish Russian-born biochemist Chaim Weizmann. A senior lecturer at the University of Manchester, England, he used th ...
'', ''
Clostridium beijerinckii ''Clostridium beijerinckii'' is a gram positive, rod shaped, motile bacterium of the genus ''Clostridium''. It has been isolated from feces and soil. Produces oval to subterminal spores. it is named after Martinus Beijerinck who is a Dutch bacte ...
''. ''C. acetobutylicum'' was once used for the production of
acetone Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscibl ...
from
starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human die ...
. 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 crop Energy crops are low-cost and low-maintenance crops grown solely for energy production by combustion (not for food). The crops are processed into solid, liquid or gaseous fuels, such as pellets, bioethanol or biogas. The fuels are burned to ...
s such as
sugar beet A sugar beet is a plant whose root contains a high concentration of sucrose and which is grown commercially for sugar production. In plant breeding, it is known as the Altissima cultivar group of the common beet ('' Beta vulgaris''). Together ...
s,
sugar cane Sugarcane or sugar cane is a species of (often hybrid) tall, perennial grass (in the genus '' Saccharum'', tribe Andropogoneae) that is used for sugar production. The plants are 2–6 m (6–20 ft) tall with stout, jointed, fibrous stalk ...
,
corn Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The ...
grain A grain is a small, hard, dry fruit ( caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legum ...
,
wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
and
cassava ''Manihot esculenta'', commonly called cassava (), manioc, or yuca (among numerous regional names), is a woody shrub of the spurge family, Euphorbiaceae, native to South America. Although a perennial plant, cassava is extensively cultivated ...
, prospective non-food energy crops such as
switchgrass ''Panicum virgatum'', commonly known as switchgrass, is a perennial warm season bunchgrass native to North America, where it occurs naturally from 55°N latitude in Canada southwards into the United States and Mexico. Switchgrass is one of the ...
and even guayule in North America, as well as
agricultural byproduct Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people ...
s such as
bagasse Bagasse ( ) is the dry pulpy fibrous material that remains after crushing sugarcane or sorghum stalks to extract their juice. It is used as a biofuel for the production of heat, energy, and electricity, and in the manufacture of pulp and building ...
,
straw Straw is an agricultural byproduct consisting of the dry stalks of cereal plants after the grain and chaff have been removed. It makes up about half of the yield of cereal crops such as barley, oats, rice, rye and wheat. It has a number ...
and
corn Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The ...
stalks. According to
DuPont DuPont de Nemours, Inc., commonly shortened to DuPont, is an American multinational chemical company first formed in 1802 by French-American chemist and industrialist Éleuthère Irénée du Pont de Nemours. The company played a major role in ...
, existing bioethanol plants can cost-effectively be retrofitted to biobutanol production.BP DuPont Fact Sheet Biobutanol
(PDF).
Additionally, butanol production from
biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bio ...
and agricultural byproducts could be more efficient (i.e. unit engine motive power delivered per unit solar energy consumed) than
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...
or
methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is ...
production. A strain of ''Clostridium'' can convert nearly any form of
cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wa ...
into butanol even in the presence of oxygen. A strain of ''Clostridium cellulolyticum'', a native cellulose-degrading microbe, affords isobutanol directly from cellulose. A combination of
succinate Succinic acid () is a dicarboxylic acid with the chemical formula (CH2)2(CO2H)2. The name derives from Latin ''succinum'', meaning amber. In living organisms, succinic acid takes the form of an anion, succinate, which has multiple biological ro ...
and ethanol can be fermented to produce
butyrate The conjugate acids are in :Carboxylic acids. {{Commons category, Carboxylate ions, Carboxylate anions Carbon compounds Oxyanions ...
(a precursor to butanol fuel) by utilizing the metabolic pathways present in ''
Clostridium kluyveri ''Clostridium kluyveri'' (CLOKL) is an anaerobic, motile, gram-positive bacterium In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteri ...
''. Succinate is an intermediate of the
TCA cycle The citric acid cycle (CAC)—also known as the Krebs cycle or the TCA cycle (tricarboxylic acid cycle)—is a series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and prote ...
, which metabolizes glucose.
Anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...
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''.


Cyanobacteria

Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...
are a
phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature ...
of
photosynthetic Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
bacteria.
Cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...
Cyanobacteria are suited for isobutanol biosynthesis when genetically engineered to produce isobutanol and its corresponding
aldehydes In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...
. Isobutanol producing species of cyanobacteria offer several advantages as biofuel synthesizers: * Cyanobacteria grow faster than plants and also absorb sunlight more efficiently than plants. This means they can be replenished at a faster rate than the plant matter used for other biofuel biosynthesizers. * Cyanobacteria can be grown on non-arable land (land not used for farming). This prevents competition between food sources and fuel sources. * The supplements necessary for the growth of Cyanobacteria are CO2, H2O, and sunlight. This presents two advantages: ** Because CO2 is derived from the atmosphere, Cyanobacteria do not need plant matter to synthesize isobutanol (in other organisms which synthesize isobutanol, plant matter is the source of the carbon necessary to synthetically assemble isobutanol). Since plant matter is not used by this method of isobutanol production, the necessity to source plant matter from food sources and create a food-fuel price relationship is avoided. ** Because CO2 is absorbed from the atmosphere by Cyanobacteria, the possibility of
bioremediation Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi, and plants), living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluent ...
(in the form of Cyanobacteria removing excess CO2 from the atmosphere) exists. The primary drawbacks of cyanobacteria are: * Cyanobacteria are sensitive to environmental conditions when being grown. Cyanobacteria suffer greatly from sunlight of inappropriate
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tr ...
and intensity, CO2 of inappropriate concentration, or H2O of inappropriate
salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...
though a wealth of cyanobacteria are able to grow in brackish and marine waters. These factors are generally hard to control, and present a major obstacle in cyanobacterial production of isobutanol. * Cyanobacteria
bioreactors A bioreactor refers to any manufactured device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical reaction, chemical process is carried out which involves organisms or biochemistry, ...
require high energy to operate. Cultures require constant mixing, and the harvesting of biosynthetic products is energy intensive. This reduces the efficiency of isobutanol production via Cyanobacteria. 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 Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for ...
dependent pathway. The main problem with this pathway is the first reaction involving the condensation of two acetyl-CoA molecules to
acetoacetyl-CoA Acetoacetyl CoA is the precursor of HMG-CoA in the mevalonate pathway, which is essential for cholesterol biosynthesis. It also takes a similar role in the ketone bodies synthesis (ketogenesis) pathway of the liver. In the ketone bodies digestion ...
. This reaction is thermodynamically unfavorable due to the positive
Gibbs free energy In thermodynamics, the Gibbs free energy (or Gibbs energy; symbol G) is a thermodynamic potential that can be used to calculate the maximum amount of work that may be performed by a thermodynamically closed system at constant temperature an ...
associated with it (dG = 6.8 kcal/mol).


''Bacillus subtilis''

''
Bacillus subtilis ''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacillus ...
'' is a
gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bact ...
rod-shaped bacteria. ''
Bacillus subtilis ''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacillus ...
'' 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''. Similar to ''E. coli'', ''Bacillus subtilis'' is capable of producing isobutanol from lignocellulose, and is easily manipulated by common genetic techniques. Elementary mode analysis has also been used to improve the isobutanol-synthesis
metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell. The reactants, products, and intermediates of an enzymatic reaction are known as metabolites, which are modified by a sequence of chemical ...
used by ''Bacillus subtilis'', leading to higher yields of isobutanol being produced.


''Saccharomyces cerevisiae''

''
Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have b ...
'', or ''S. cerevisiae'', is a species of
yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...
. ''S. cerevisiae'' naturally produces isobutanol in small quantities via its
valine Valine (symbol Val or V) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α- amino group (which is in the protonated −NH3+ form under biological conditions), an α- carboxylic acid group (which is in the deprotona ...
biosynthetic pathway. ''S. cerevisiae'' is an ideal candidate for isobutanol biofuel production for several reasons: * ''S. cerevisiae'' can be grown at low pH levels, helping prevent contamination during growth in industrial bioreactors. * ''S. cerevisiae'' cannot be affected by bacteriophages because it is a
eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacter ...
. *Extensive scientific knowledge about ''S. cerevisiae'' and its biology already exists. Overexpression of the enzymes in the valine biosynthetic pathway of ''S. cerevisiae'' has been used to improve isobutanol yields. ''S. cerevisiae'', however, has proved difficult to work with because of its inherent biology: * As a eukaryote, ''S. cerevisiae''is genetically more complex than ''E. coli'' or ''B. subtilis'', and is harder to genetically manipulate as a result. * ''S. cerevisiae'' has the natural ability to produce ethanol. This natural ability can "overpower" and consequently inhibit isobutanol production by ''S. cerevisiae''. * ''S. cerevisiae'' cannot use five carbon sugars to produce isobutanol. The inability to use five-carbon sugars restricts ''S. cerevisiae'' from using lignocellulose, and means ''S. cerevisiae'' must use plant matter intended for human consumption to produce isobutanol. This results in an unfavorable food/fuel price relationship when isobutanol is produced by ''S. cerevisiae''.


''Ralstonia eutropha''

'' Ralstonia eutropha'' is a
gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...
soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...
bacterium of the
betaproteobacteria Betaproteobacteria are a class of Gram-negative bacteria, and one of the eight classes of the phylum Pseudomonadota (synonym Proteobacteria). The ''Betaproteobacteria'' are a class comprising over 75 genera and 400 species of bacteria. Togeth ...
class. ''Ralstonia eutropha'' is capable of converting electrical energy into isobutanol. This conversion is completed in several steps: * Anodes are placed in a mixture of H2O and CO2. * An electric current is run through the anodes, and through an
electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outc ...
process H2O and CO2 are combined to synthesize
formic acid Formic acid (), systematically named methanoic acid, is the simplest carboxylic acid, and has the chemical formula HCOOH and structure . It is an important intermediate in chemical synthesis and occurs naturally, most notably in some ants. Est ...
. * A
culture Culture () is an umbrella term which encompasses the social behavior, institutions, and norms found in human societies, as well as the knowledge, beliefs, arts, laws, customs, capabilities, and habits of the individuals in these groups ...
of ''Ralstonia eutropha'' (composed of a strain tolerant to electricity) is kept within the H2O and CO2 mixture. * The culture of ''Ralstonia eutropha'' then converts formic acid from the mixture into isobutanol. * The biosynthesized isobutanol is then separated from the mixture, and can be used as a biofuel.


Feedstocks

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 Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn ( North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. T ...
, can enhance the process economic viability.
Metabolic engineering Metabolic engineering is the practice of optimizing genetic and regulatory processes within cells to increase the cell's production of a certain substance. These processes are chemical networks that use a series of biochemical reactions and enzym ...
can be used to allow an
organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fu ...
to use a cheaper substrate such as
glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
instead of
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
. Because
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food p ...
processes require
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
derived from foods, butanol production can negatively impact food supply (see
food vs fuel Food versus fuel is the dilemma regarding the risk of diverting farmland or crops for biofuels production to the detriment of the food supply. The biofuel and food price debate involves wide-ranging views, and is a long-standing, controversial ...
debate).
Glycerol Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
is a good alternative source for
butanol Butanol (also called butyl alcohol) is a four-carbon alcohol with a formula of C4 H9 O H, which occurs in five isomeric structures (four structural isomers), from a straight-chain primary alcohol to a branched-chain tertiary alcohol; all are a bu ...
production. While
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
sources are valuable and limited, glycerol is abundant and has a low market price because it is a waste product of
biodiesel Biodiesel is a form of diesel fuel derived from plants or animals and consisting of long-chain fatty acid esters. It is typically made by chemically reacting lipids such as animal fat ( tallow), soybean oil, or some other vegetable oi ...
production. Butanol production from glycerol is economically viable using metabolic pathways that exist in ''
Clostridium pasteurianum ''Clostridium pasteurianum'' (previously known as ''Clostridium pastorianum'') is a bacterium discovered in 1890 by the Russian microbiologist Sergei Winogradsky. It was the first free living (non-symbiotic) micro-organism discovered that could ...
'' bacterium.


Improving efficiency

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


Producers and distribution

DuPont DuPont de Nemours, Inc., commonly shortened to DuPont, is an American multinational chemical company first formed in 1802 by French-American chemist and industrialist Éleuthère Irénée du Pont de Nemours. The company played a major role in ...
and BP plan to make biobutanol the first product of their joint effort to develop, produce, and market next-generation biofuels. In Europe the Swiss company Butalco 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. Celtic Renewables makes biobutanol from waste that results from the production of
whisky Whisky or whiskey is a type of distilled alcoholic beverage made from fermented grain mash. Various grains (which may be malted) are used for different varieties, including barley, corn, rye, and wheat. Whisky is typically aged in wooden ca ...
, and low-grade
potato The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern Uni ...
es.


Properties of common fuels


Isobutanol

Isobutanol is a second-generation biofuel with several qualities that resolve issues presented by ethanol. Isobutanol's properties make it an attractive biofuel: *relatively high
energy density In physics, energy density is the amount of energy stored in a given system or region of space per unit volume. It is sometimes confused with energy per unit mass which is properly called specific energy or . Often only the ''useful'' or extrac ...
, 98% of that of gasoline. *does not readily absorb water from air, preventing the
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
of engines and pipelines. *can be mixed at any proportion with gasoline, meaning the fuel can "drop into" the existing petroleum infrastructure as a replacement fuel or major additive. *can be produced from plant matter not connected to food supplies, preventing a fuel-price/food-price relationship. *assuming that it is produced from residual lignocellulosic feedstocks, blending isobutanol with gasoline may reduce GHG emissions considerably.


n-Butanol

Butanol better tolerates water contamination and is less corrosive than ethanol and more suitable for distribution through existing pipelines for gasoline. In blends with
diesel Diesel may refer to: * Diesel engine, an internal combustion engine where ignition is caused by compression * Diesel fuel, a liquid fuel used in diesel engines * Diesel locomotive, a railway locomotive in which the prime mover is a diesel engi ...
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 Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed pha ...
co-blend synergy with butanol and gasoline containing ethanol, which facilitates ethanol blending. This facilitates storage and distribution of blended fuels. The
octane rating An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without detonating. The higher the octane number, the more compression the fuel can withstand before detonatin ...
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 An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without detonating. The higher the octane number, the more compression the fuel can withstand before detonatin ...
) of 96 and a MON (
Motor octane number An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without detonating. The higher the octane number, the more compression the fuel can withstand before detonat ...
) 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.
t-Butanol ''tert''-Butyl alcohol is the simplest tertiary alcohol, with a formula of (CH3)3COH (sometimes represented as ''t''-BuOH). Its isomers are 1-butanol, isobutanol, and butan-2-ol. ''tert''-Butyl alcohol is a colorless solid, which melts near ...
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. 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. 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. 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. 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.


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 Stoichiometry refers to the relationship between the quantities of reactants and products before, during, and following chemical reactions. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equ ...
fuel-air ratio of butanol, ethanol and gasoline.
Common ethanol fuel mixtures Several common ethanol fuel mixtures are in use around the world. The use of pure hydrous or anhydrous ethanol in internal combustion engines (ICEs) is only possible if the engines are designed or modified for that purpose, and used only in auto ...
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. Consumer acceptance may be limited due to the potentially offensive
banana A banana is an elongated, edible fruit – botanically a berry – produced by several kinds of large herbaceous flowering plants in the genus ''Musa''. In some countries, bananas used for cooking may be called "plantains", disting ...
-like smell of n-butanol. 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 Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates *Polar climate, the cli ...
, 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 that "biobutanol can be blended up to 10%v/v in European gasoline and 11.5%v/v in US gasoline". In the
2009 Petit Le Mans The 2009 Petit Le Mans powered by Mazda6 was the twelfth running of the Petit Le Mans and the ninth round of the 2009 American Le Mans Series season. It took place at the Road Atlanta circuit in Braselton, Georgia, on September 26, 2009. Originall ...
race, the No. 16 Lola B09/86 - Mazda MZR-R of
Dyson Racing Dyson Racing is a professional sports car racing team based in Poughkeepsie, New York in the United States. Founded by Rob Dyson in 1974, the team competed successfully in North American sports car racing series, including the IMSA GT Championsh ...
ran on a mixture of biobutanol and ethanol developed by team technology partner BP.


See also

* Alcohol to jet fuel * Air-fuel ratio * Bioalcohol *
Biofuel Biofuel is a fuel that is produced over a short time span from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels, such as oil. According to the United States Energy Information Administration ...
*
Biodiesel Biodiesel is a form of diesel fuel derived from plants or animals and consisting of long-chain fatty acid esters. It is typically made by chemically reacting lipids such as animal fat ( tallow), soybean oil, or some other vegetable oi ...
*
Biohydrogen Biohydrogen is H2 that is produced biologically. Interest is high in this technology because H2 is a clean fuel and can be readily produced from certain kinds of biomass. Many challenges characterize this technology, including those intrinsic to ...
*
Bioconversion of biomass to mixed alcohol fuels The bioconversion of biomass to mixed alcohol fuels can be accomplished using the MixAlco process. Through bioconversion of biomass to a mixed alcohol fuel, more energy from the biomass will end up as liquid fuels than in converting biomass to etha ...
*
Butanol Butanol (also called butyl alcohol) is a four-carbon alcohol with a formula of C4 H9 O H, which occurs in five isomeric structures (four structural isomers), from a straight-chain primary alcohol to a branched-chain tertiary alcohol; all are a bu ...
*
Catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
*
Dimethyl ether Dimethyl ether (DME; also known as methoxymethane) is the organic compound with the formula CH3OCH3, (sometimes ambiguously simplified to C2H6O as it is an isomer of ethanol). The simplest ether, it is a colorless gas that is a useful precursor ...
*
Distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the he ...
*
Emission standards Emission standards are the legal requirements governing air pollutants released into the atmosphere. Emission standards set quantitative limits on the permissible amount of specific air pollutants that may be released from specific sources over ...
*
Energy crop Energy crops are low-cost and low-maintenance crops grown solely for energy production by combustion (not for food). The crops are processed into solid, liquid or gaseous fuels, such as pellets, bioethanol or biogas. The fuels are burned to ...
*
Ethanol fuel 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 t ...
*
Fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food p ...
facility *
Formic acid Formic acid (), systematically named methanoic acid, is the simplest carboxylic acid, and has the chemical formula HCOOH and structure . It is an important intermediate in chemical synthesis and occurs naturally, most notably in some ants. Est ...
: can be used as an intermediary to produce isobutanol from using microbesIntegrated Electromicrobial Conversion of CO2 to Higher Alcohols
/ref> * Gevo Biofuels * List of vegetable oils used for biofuel


References


External links


Biobutanol
(
EERE The Office of Energy Efficiency and Renewable Energy (EERE) is an office within the United States Department of Energy. Formed from other energy agencies after the 1973 energy crisis, EERE is led by the Assistant Secretary of Energy Efficiency and ...
).
Biobutanol research news
from Green Car Congress
Butanol 3D view and pdb-file
{{DEFAULTSORT:Butanol Fuel Alcohol fuels