Ethanol, also called
ethyl
alcohol,
pure alcohol,
grain
alcohol, or
drinking alcohol, is a
volatile,
flammable, colorless liquid. It is a
psychoactive drug, best known as the type
of
alcohol found in
alcoholic beverages and in modern
thermometers. Ethanol is one of the
oldest
recreational drugs. In
common usage, it is often referred to simply as
alcohol or
spirits.
Ethanol is a straight-chain alcohol, and its
molecular formula is
C
2H
5OH. Its
empirical formula is
C2H
6O. An
alternative notation is CH
3–CH
2–OH, which
indicates that the carbon of a methyl group (CH
3–) is
attached to the carbon of a methylene group (–CH
2–),
which is attached to the oxygen of a
hydroxyl
group . It is a constitutional
isomer of
dimethyl ether. Ethanol is often
abbreviated as
EtOH, using the common organic
chemistry notation of representing the ethyl group
(C
2H
5) with
Et.
The
fermentation of sugar into
ethanol is one of the earliest
organic
reactions employed by humanity. The intoxicating effects of
ethanol consumption have been known since ancient times. In modern
times, ethanol intended for industrial use is also produced from
by-products of petroleum refining.
Ethanol has widespread use as a solvent of substances intended for
human contact or consumption, including scents, flavorings,
colorings, and medicines. In chemistry, it is both an essential
solvent and a feedstock for the synthesis of other products. It has
a long history as a fuel for heat and light, and more recently as a
fuel for
internal combustion
engines.
History

Ethanol being used as fuel for a
burner
Ethanol has been used by humans since prehistory as the
intoxicating ingredient of
alcoholic
beverages. Dried residues on 9,000-year-old pottery found in
China imply that alcoholic beverages were used even among
Neolithic people. Its isolation as a relatively
pure compound was first achieved by the Persian
alchemist,
Muhammad ibn Zakarīya
Rāzi (Rhazes, 865–925).
Two other chemists who contributed to the development of
distillation techniques were
Geber (Jabir ibn Hayyan) and
Al-Kindi (Alkindus). Writings attributed to Geber
(721–815) mention the flammable vapors of boiled wine. Al-Kindi
(801–873) unambiguously described the distillation of wine.
In 1796, Johann Tobias Lowitz obtained pure ethanol by filtering
distilled ethanol through
activated
charcoal.
Antoine Lavoisier described
ethanol as a compound of carbon, hydrogen, and oxygen, and in 1808
Nicolas-Théodore de
Saussure determined ethanol’s chemical formula. Fifty years
later,
Archibald Scott Couper
published the structural formula of ethanol, which placed ethanol
among the first compounds whose chemical structure had been
determined.
Ethanol was first prepared synthetically in 1826 through the
independent efforts of Henry Hennel in Great Britain and S.G.
Sérullas inFrance. In 1828,
Michael
Faraday prepared ethanol by
acid-catalyzed hydration of
ethylene, a process similar to that which is used
today for industrial ethanol synthesis.
Ethanol was used as lamp fuel in the United States as early as
1840, but a tax levied on industrial alcohol during the
Civil War made this use uneconomical.
This tax was repealed in 1906, and from 1908 onward
Ford Model T automobiles could be adapted to
run on ethanol. With the advent of
Prohibition in 1920 though, sellers of ethanol
fuel were accused of being allied with
moonshiners, and ethanol fuel again fell into
disuse until late in the 20th century.
Physical properties

Ethanol burning with its spectrum
depicted
Ethanol is a volatile, colorless liquid that has a strong
characteristic odor. It burns with a smokeless blue flame that is
not always visible in normal light.
The physical properties of ethanol stem primarily from the presence
of its
hydroxyl group and the shortness of
its carbon chain. Ethanol’s hydroxyl group is able to participate
in hydrogen bonding, rendering it more viscous and less volatile
than less polar organic compounds of similar molecular
weight.
Ethanol is a versatile solvent,
miscible
with water and with many organic solvents, including
acetic acid,
acetone,
benzene,
carbon tetrachloride,
chloroform,
diethyl
ether,
ethylene glycol,
glycerol,
nitromethane,
pyridine, and
toluene. It is also miscible with light aliphatic
hydrocarbons, such as
pentane and
hexane, and with aliphatic chlorides such as
trichloroethane and
tetrachloroethylene.
Ethanol’s miscibility with water contrasts with that of
longer-chain alcohols (five or more carbon atoms), whose water
miscibility decreases sharply as the number of carbons increases.
The miscibility of ethanol with
alkanes is
limited to alkanes up to
undecane, mixtures
with
dodecane and higher alkanes show a
miscibility gap below a certain temperature (about 13 °C for
dodecane). The miscibility gap tends to get wider with higher
alkanes and the temperature for complete miscibility
increases.
Ethanol-water mixtures have less volume than the sum of their
individual components at the given fractions. Mixing equal volumes
of ethanol and water results in only 1.92 volumes of mixture.
Mixing ethanol and water is
exothermic.
At 298 K up to 777 J/mol are set free.
Mixtures of ethanol and water form an
azeotrope at about 89 mole-% ethanol and 11 mole-%
water or a mixture of about 96 volume percent ethanol and 4% water
at normal pressure and
T = 351 K. This
azeotropic composition is strongly temperature- and
pressure-dependent and vanishes at temperatures below
303 K.
Image:Excess_Volume_Mixture_of_Ethanol_and_Water.png|Excess volume
of the mixture of ethanol and water (volume
contraction)Image:Mixing_Enthalpy_Mixture_of_Ethanol_and_Water.png|Heat
of mixing of the mixture of ethanol and
waterImage:Vapor-Liquid_Equilibrium_Mixture_of_Ethanol_and_Water.png|Vapor-liquid
equilibrium of the mixture of ethanol and water (including
azeotrope)Image:Liquid-Liquid Equilibrium
(Miscibility Gap) Mixture of Ethanol and Dodecane.png|Miscibility
gap in the mixture of dodecane and ethanol

Hydrogen bonding in solid ethanol at
−186 °C
Hydrogen bonding causes pure ethanol to be
hygroscopic to the extent that it readily
absorbs water from the air. The polar nature of the hydroxyl group
causes ethanol to dissolve many ionic compounds, notably
sodium and
potassium hydroxides,
magnesium chloride,
calcium chloride,
ammonium chloride,
ammonium bromide, and
sodium bromide.
Sodium and
potassium chlorides are slightly soluble
in ethanol. Because the ethanol molecule also has a nonpolar end,
it will also dissolve nonpolar substances, including most
essential oils and numerous flavoring,
coloring, and medicinal agents.
The addition of even a few percent of ethanol to water sharply
reduces the
surface tension of
water. This property partially explains the “
tears of wine” phenomenon. When wine is
swirled in a glass, ethanol evaporates quickly from the thin film
of wine on the wall of the glass. As the wine’s ethanol content
decreases, its surface tension increases and the thin film “beads
up” and runs down the glass in channels rather than as a smooth
sheet.
Mixtures of ethanol and water that contain more than about 50%
ethanol are
flammable and easily ignited.
An alcohol stove has been developed in India which runs on 50%
ethanol/water mixture.
Alcoholic
proof is a widely used measure of how much ethanol (i.e.,
alcohol) such a mixture contains. In the 18th century, proof was
determined by adding a liquor (such as
rum) to
gunpowder. If the gunpowder still just exploded, that was
considered to be “100 degrees proof” that it was “good” liquor —
hence it was called “100 degrees proof”.
Ethanol-water solutions that contain less than 50% ethanol may also
be flammable if the solution is first heated. Some cooking methods
call for
wine to be added to a hot pan, causing
it to flash boil into a vapor, which is then ignited to burn off
excess alcohol.
Ethanol is slightly more refractive than water, having a
refractive index of 1.36242 (at
λ=589.3 nm and 18.35 °C).
Chemical properties
Ethanol is classified as a primary alcohol, meaning that the carbon
to which its hydroxyl group is attached has at least two hydrogen
atoms attached to it as well. Many of the reactions of ethanol
occur at its
hydroxyl group.
Ester formation
In the presence of acid catalysts, ethanol reacts with
carboxylic acids to produce ethyl
esters and water:
- RCOOH +
HOCH2CH3 → RCOOCH2CH3 + H2O
This reaction, which is conducted on large scale industrially,
requires the removal of the water from the reaction mixture as it
is formed. Esters react in the presence of an acid or base to give
back the alcohol and carboxylic acid. This reaction is known as
saponification because it is used in
the preparation of soap. Ethanol can also form esters with
inorganic acids.
Diethyl sulfate and
triethyl phosphate are prepared
by treating ethanol with sulfur trioxide and
phosphorus pentoxide respectively.
Diethyl sulfate is a useful
ethylating agent in
organic
synthesis.
Ethyl nitrite, prepared
from the reaction of ethanol with
sodium
nitrite and sulfuric acid, was formerly a widely-used
diuretic.
Dehydration
Strong acid desiccants cause the dehydration of ethanol dehydration
to form
diethyl ether, although under
certain conditions ethylene is the product. Millions of kilograms
of diethyl ether are produced annually using sulfuric acid
catalyst:
- 2 CH3CH2OH →
CH3CH2OCH2CH3 +
H2O (on 120'C)
Combustion
Complete
combustion of ethanol forms
carbon dioxide and
water:
- C2H5OH + 3 O2 → 2
CO2 + 3 H2O(l);(ΔHr = −1409
kJ/mol) specific heat = 2.44 kJ/(kg·K)
Acid-base chemistry
Ethanol is a neutral molecule and the
pH of a
solution of ethanol in water is nearly 7.00. Ethanol can be
quantitatively converted to its
conjugate
base, the
ethoxide ion
(CH
3CH
2O
−), by reaction with an
alkali metal such as
sodium:
- 2 CH3CH2OH + 2 Na → 2
CH3CH2ONa + H2
or a very strong base such as
sodium
hydride:
- CH3CH2OH + NaH →
CH3CH2ONa + H2
The acidity of water and ethanol are nearly the same, as indicated
by their
Acid dissociation
constants of 10
-15.7 and 10
-16. Thus,
sodium ethoxide and
sodium
hydroxide exist in an equilbrium that is closely balanced:
- CH3CH2OH + NaOH
CH3CH2ONa + H2O
Halogenation
Ethanol is not used industrially as a precursor to ethyl halides,
but the reactions are illustrative. Ethanol reacts with
hydrogen halides to produce
ethyl halides such as
ethyl chloride and
ethyl bromide:
- CH3CH2OH + HCl → CH3CH2Cl +
H2O
These reactions require a catalyst such as
zinc chloride.HBr requires
refluxing with a
sulfuric
acid catalyst. Ethyl halides can, in principle, also be
produced by treating ethanol with more specialized
halogenating agents, such as
thionyl chloride or
phosphorus tribromide.
- CH3CH2OH + SOCl2 →
CH3CH2Cl + SO2 + HCl
Upon treament with halogens in the presence of base, ethanol gives
the corresponding
haloform
(CHX
3, where X = Cl, Br, I). This conversion is called
the
haloform reaction."An
intermediate in the reaction with chlorine is the
aldehyde called
chloral:
- 4 Cl2 + CH3CH2OH →
CCl3CHO + 5 HCl
Oxidation
Ethanol can be oxidized to
acetaldehyde
and further oxidized to
acetic acid,
depending on the reagents and conditions. This oxidation is of no
importance industrially, but in the human body, these oxidation
reactions are catalyzed by the
enzyme
liver alcohol
dehydrogenase. The oxidation product of ethanol, acetic acid,
is a nutrient for humans, being a precursor to
acetyl CoA, where the acetyl group can be spent
as energy or used for biosynthesis.
Industrial uses
As a fuel
The largest single use of ethanol is as a motor
fuel and
fuel additive.
Brazil
has the
largest national fuel ethanol industry. Gasoline sold in
Brazil contains at least 25%
anhydrous
ethanol. Hydrous ethanol (about 95% ethanol and 5% water) can be
used as fuel in more than 90% of new cars sold in the country.
Brazilian ethanol production is praised for the high
carbon sequestration capabilities of
the
sugar cane plantations, thus making it a real option to
combat
climate change.
Henry Ford designed the first
mass-produced automobile, the famed Model T Ford, to run on pure
anhydrous (ethanol) alcohol - he said it was "the fuel of the
future". Today, however, 100% pure ethanol is not approved as a
motor vehicle fuel in the U.S. Added to gasoline, ethanol reduces
volatile organic compound and hydrocarbon emissions, carcinogenic
benzene and butadiene emissions, and particulate matter emissions
from gasoline combustion.
Ethanol combustion in an internal combustion engine yields many of
the products of incomplete combustion produced by gasoline and
significantly larger amounts of
formaldehyde and related species such as
acetaldehyde. This leads to a significantly larger photochemical
reactivity that generates much more ground level
ozone. These data have been assembled into The Clean
Fuels Report comparison of fuel emissions and show that ethanol
exhaust generates 2.14 times as much ozone as does gasoline
exhaust. When this is added into the custom "Localised Pollution
Index (LPI)" of The Clean Fuels Report the local pollution, i.e.
that which contributes to smog, is 1.7 on a scale where gasoline is
1.0 and higher numbers signify greater pollution. This issue has
been formalized by the
California Air Resources
Board in 2008 by recognizing control standards for
formaldehydes as an emissions control group much like the
conventional
NOx and Reactive Organic Gases
(ROGs).
Before
electronic fuel
injection (EFI) and computerized engine management, the lower
energy content of ethanol required engine
carburetors to be
rejetted to permit a
larger volume of fuel to mix with the intake air. EFI is able to
actively compensate for varying fuel energy densities by
monitoring the oxygen content of exhaust
gases. However, a standard EFI gasoline engine can typically only
tolerate up to 10% ethanol and 90% gasoline. Higher ethanol ratios
require either larger-volume
fuel
injectors or an increase in
fuel rail
pressure to deliver the greater liquid volume needed to equal the
energy content of pure gasoline.
World production of ethanol in 2006 was , with 69% of the world
supply coming from Brazil and the United States. More than 20% of
Brazilian cars are able to use 100% ethanol as fuel, which includes
ethanol-only engines and
flex-fuel engines. Flex-fuel engines
in Brazil are able to work with all ethanol, all gasoline or any
mixture of both. In the US flex-fuel vehicles can run on 0% to 85%
ethanol (15% gasoline) since higher ethanol blends are not yet
allowed. Brazil supports this population of ethanol-burning
automobiles with large national infrastructure that produces
ethanol from domestically grown
sugar
cane.
Sugar cane not only has a
greater concentration of sucrose than corn (by about 30%), but is
also much easier to extract. The
bagasse
generated by the process is not wasted, but is used in power plants
as a surprisingly efficient fuel to produce electricity.
The United States fuel ethanol industry is based largely on
corn. According to the Renewable Fuels
Association, as of October 30, 2007, 131 grain ethanol
bio-refineries in the United States have the capacity to produce
7.0 billion US gallons (26 GL) of ethanol per year. An additional
72 construction projects underway (in the U.S.) can add 6.4 billion
gallons of new capacity in the next 18 months. Over time, it is
believed that a material portion of the ~150 billion gallon per
year market for gasoline will begin to be replaced with fuel
ethanol.
The U.S. federal government gives ethanol producers a
51-cent-per-gallon tax credit and mandates that their fuel be
blended into the nation's gasoline supplies. The
Energy Policy Act of 2005 requires
that 4 billion gallons of "renewable fuel" be used in 2006 and this
requirement will grow to a yearly production of 7.5 billion gallons
by 2012. In the United States, ethanol is most commonly blended
with gasoline as a 10% ethanol blend nicknamed "gasohol". This
blend is widely sold throughout the U.S.
Midwest, and in cities required by the
1990 Clean Air Act to oxygenate their
gasoline during the winter. Ethanol and
isobutene are also the feedstocks for
ethyl tert-butyl ether (ETBE), an
oxygenated antiknock additive. The use of ethanol makes ETBE
partially a biofuel, but also more expensive than the similar
additive
methyl tert-butyl
ether (MTBE), made from methanol and isobutene.
One problem with ethanol is that because it is easily miscible with
water, it cannot be efficiently shipped through modern pipelines,
like liquid hydrocarbons, over long distances.
Ethanol is also used as a cooking and lighting fuel. In India,
ethanol stoves and lanterns have been developed that can run on 50%
by weight ethanol/water mixture. This mixture (hooch or illicit
liquor) is easy to distill, safer to handle and use than 100%
ethanol, can be produced by small local producers, and uses less
energy in its production..
Sri Lankan
automobile manufacturer
Micro Cars Ltd manufactured a car
running on ethanol discharged by local sugar
factories in 2009..
Food versus fuel debate
It is disputed whether
corn ethanol as
an automotive fuel results in a net energy gain or loss. As
reported in "The Energy Balance of Corn Ethanol: an Update," the
energy returned on energy invested (
EROEI) for
ethanol made from corn in the U.S. is 1.34 (it yields 34% more
energy than it takes to produce it). Input energy includes natural
gas based fertilizers, farm equipment, transformation from corn or
other materials, and transportation. However, other researchers
report that the production of ethanol consumes more energy than it
yields. In comparison, sugar cane ethanol EROEI is at around 8 (it
yields 8 joules for each joule used to produce it). Recent research
suggests that cellulosic crops such as
switchgrass provide a much better net energy
production than corn, producing over five times as much energy as
the total used to produce the crop and convert it to fuel. If this
research is confirmed, cellulosic crops will most likely displace
corn as the main fuel crop for producing bioethanol.
Michael Grunwald reports that one person could be fed for 1 year
"on the corn needed to fill an ethanol-fueled SUV". He further
reports that though "hyped as an eco-friendly fuel, ethanol
increases global warming, destroys forests and inflates food
prices." Environmentalists, livestock farmers, and opponents of
subsidies say that increased ethanol production won't meet energy
goals and may damage the environment, while at the same time
causing worldwide food prices to soar. Some of the controversial
subsidies in the past have included more than $10 billion to
Archer-Daniels-Midland since
1980. Critics also speculate that as ethanol is more widely used,
changing irrigation practices could greatly increase pressure on
water resources. In October 2007, 28 environmental groups decried
the Renewable Fuels Standard (RFS), a legislative effort intended
to increase ethanol production, and said that the measure will
"lead to substantial environmental damage and a system of biofuels
production that will not benefit family farmers...will not promote
sustainable agriculture and will not mitigate global climate
change."
Recent articles have also blamed subsidized ethanol production for
the nearly 200% increase in milk prices since 2004, since the price
of fuel has driven up the costs to cultivate, grow, harvest, ship,
refine, bring to market, etc., all commodities including, but not
limited to, milk, although that is disputed by some. Articles also
blame the presence of speculators, and the recent growing interest
in the commodities market by investors who have been scared away
from a falling stock market.
Ethanol production uses the starch portion of corn, but the
leftover protein can be used to create a high-nutrient, low-cost
animal feed.
In 2007 the United Nations' independent expert on the right to
food, called for a five-year moratorium on biofuel production from
food crops, to allow time for development of non-food sources. He
called recent increases in food costs because of fuel production,
such as the quadrupling of world corn price in one year, a growing
"catastrophe" for the poor. In February 2007,
riots occurred in
Mexico because of the skyrocketing price of tortillas. Ethanol has
been credited as the reason for this increase in food prices. The
demand for corn has had a rippling effect on many corn-based
products, like tortillas. The effects of ethanol and the increasing
cost of food have also been felt in Pakistan, Indonesia, and
Egypt.
Oil has historically had a much higher
EROEI
than corn produced ethanol, according to some . However, oil must
be refined into gasoline before it can be used for automobile fuel.
Refining, as well as exploration and drilling, consumes energy. The
difference between the energy in the fuel (output energy) and the
energy needed to produce it (input energy) is often expressed as a
percent of the input energy and called net energy gain (or loss).
Several studies released in 2002 estimated that the net energy gain
for
corn ethanol is between 21 and 34
percent. The net energy loss for
MTBE is about
33 percent. When added to gasoline, ethanol can replace MTBE as an
anti-knock agent without poisoning drinking water as MTBE does. In
Brazil, where the broadest and longest ethanol producing experiment
took place, improvements in agricultural practices and ethanol
production improvements led to an increase in ethanol net energy
gain from 300% to over 800% in recent years. It must be noted that
Brazil produces ethanol more efficiently because its primary input
is the sugar from sugar cane rather than starches from corn.
Consuming known oil reserves is increasing oil exploration and
drilling energy consumption, which is reducing
oil
EROEI (and
energy balance)
further.
Opponents claim that corn ethanol production does not result in a
net energy gain or that the consequences of large scale ethanol
production to the food industry and environment offset any
potential gains from ethanol. It has been estimated that "if every
bushel of U.S.
corn,
wheat,
rice and
soybean were used to produce ethanol, it would only
cover about 4% of
U.S. energy needs on a
net basis." Many of the issues raised could likely be fixed by
techniques now in development that produce ethanol from
agricultural waste, such as paper waste, switchgrass, and
other materials, but EIA Forecasts Significant
Shortfall in Cellulosic Biofuel Production Compared to Target Set
by Renewable Fuel Standard.
Proponents cite the potential gains to the U.S. economy both from
domestic fuel production and increased demand for corn. Optimistic
calculations project that the United States is capable of producing
enough ethanol to completely replace gasoline consumption. In
comparison, Brazil's ethanol consumption today covers more than 50%
of all energy used by vehicles in that country.
In the United States, preferential regulatory and tax treatment of
ethanol automotive fuels introduces complexities beyond its energy
economics alone. North American automakers have in 2006 and 2007
promoted a blend of 85% ethanol and 15% gasoline, marketed as
E85, and their
flex-fuel vehicles,
e.g.
GM's "Live Green, Go Yellow"
campaign. The apparent motivation is the nature of U.S.
Corporate Average Fuel Economy standards, which give an
effective 54% fuel efficiency bonus to vehicles capable of running
on 85% alcohol blends over vehicles not adapted to run on 85%
alcohol blends. In addition to this auto manufacturer-driven
impetus for 85% alcohol blends, the
United States
Environmental Protection Agency had authority to mandate that
minimum proportions of oxygenates be added to automotive gasoline
on regional and seasonal bases from 1992 until 2006 in an attempt
to reduce air pollution, in particular
ground-level ozone and
smog.
In the United States, incidents of methyl
tert(iary)-butyl ether (MTBE) groundwater
contamination have been recorded in the majority of the 50 states,
and the State of California
's ban on the use of MTBE as a gasoline additive has
further driven the more widespread use of ethanol as the most
common fuel oxygenate.
A February 7, 2008
Associated Press
article stated, "The widespread use of ethanol from corn could
result in nearly twice the greenhouse gas emissions as the gasoline
it would replace because of expected land-use changes, researchers
concluded Thursday. The study challenges the rush to biofuels as a
response to global warming." The article does not take into account
that even when grown in an industrial, soil-depleting manner, corn
still sequesters carbon through its unharvested root and stalk
tissues, which form soils, while gasoline production does not have
a carbon-sequestration component in its production cycle.
One acre of land can yield about 7,110 pounds of corn (
kg/ha), which can be processed into 328 US gallons of ethanol
( l/ha). That is about 26.1 pounds of corn per US gallon (
kg/l).
Much overlooked in most discussions about ethanol from corn are the
by-products from the production of ethanol. In general, the waste
product from corn distillation is DDGS,
distillers grains, a protein-rich food.
The vast majority of corn produced in the US and the world goes to
feed not people, but livestock, which in turn feed people. The main
result of feeding corn to a ruminant is excessive flatulence
(production of methane gas, being a greenhouse gas), but the same
animals can readily digest DDGS. Seen in this light, all corn
destined for livestock feeding should probably be distilled to
harvest the ethanol fuel potential while simultaneously making the
feed more nutritious to the livestock and avoiding unnecessary
methane pollution. Wherever corn is used to feed livestock, farmers
can take advantage of this process to make a profit on both food
and fuel from the same bushel of corn.
However, there are supporters of the switch to ethanol fuel. A
federal government sponsored study found a gallon of ethanol makes
almost twice as much energy as it consumes, while it also has the
potential to cut greenhouse gases by 54% if cars ran on ethanol,
rather than gasoline.
Ethanol fuel cells
Ethanol may be used as a fuel to power
Direct-ethanol fuel cells (
DEFC) in order to produce
electricity and the by-products of water and
carbon dioxide.
Platinum is commonly used as an
anode in such fuel cells in order to achieve a
power density that is comparable to
competing technologies. Until recently the high price of platinum
has been cost prohibitive. A company called
Acta Nanotech
has created platinum free
nanostructured anodes
using more common and therefore less expensive metals.
A vehicle using a
DEFC and non-platinum
nanostructured anodes was used in the Shell Eco-Marathon 2007 by a team from Offenburg
Germany which achieved an efficiency of 2716
kilometers per liter (6388
miles per gallon).
Rocket fuel
Ethanol was commonly used as fuel in early
bipropellant rocket
vehicles, in conjunction with an
oxidizer
such as liquid oxygen. The German
V-2 rocket of
World War II, credited with beginning
the space age, used ethanol, mixed with 25% of water to reduce the
combustion chamber temperature. The V-2's design team helped
develop U.S. rockets following World War II, including the
ethanol-fueled
Redstone rocket,
which launched the first U.S. satellite. Alcohols fell into general
disuse as more efficient rocket fuels were developed.
Alcoholic beverages
Ethanol is the principal psychoactive constituent in
alcoholic beverages, with
depressant effects on the
central nervous system. It has a
complex mode of action and affects multiple systems in the brain;
most notably ethanol acts as an agonist to the
GABA receptors. Similar psychoactives include
those which also interact with
GABA
receptors, such as
gamma-hydroxybutyric acid (GHB).
Ethanol is metabolized by the body as an energy-providing
carbohydrate nutrient, as it metabolizes into
acetyl CoA, an intermediate common with
glucose metabolism, that can be used for energy in
the
citric acid cycle or for
biosynthesis.
Alcoholic beverages vary considerably in their ethanol content and
in the foodstuffs from which they are produced. Most alcoholic
beverages can be broadly classified as
fermented beverages, beverages made by
the action of yeast on sugary foodstuffs, or as
distilled beverages, beverages whose
preparation involves concentrating the ethanol in fermented
beverages by
distillation. The ethanol
content of a beverage is usually measured in terms of the volume
fraction of ethanol in the beverage, expressed either as a
percentage or in
alcoholic proof
units.
Fermented beverages can be broadly classified by the foodstuff from
which they are fermented.
Beers are made from
cereal grains or other
starchy materials,
wines and
ciders from
fruit
juices, and
meads from
honey. Cultures around the world have made fermented
beverages from numerous other foodstuffs, and local and national
names for various fermented beverages abound.
Distilled beverages are made by distilling fermented beverages.
Broad categories of distilled beverages include
whiskeys, distilled from fermented cereal grains;
brandies, distilled from fermented fruit
juices, and
rum, distilled from fermented
molasses or
sugarcane juice.
Vodka and
similar
neutral grain spirits
can be distilled from any fermented material (grain or
potatoes are most common); these spirits are so
thoroughly distilled that no tastes from the particular starting
material remain. Numerous other spirits and liqueurs are prepared
by infusing flavors from
fruits,
herbs, and
spices into distilled
spirits. A traditional example is
gin, which is
created by infusing
juniper berries into a
neutral grain alcohol.
In a few beverages, ethanol is concentrated by means other than
distillation.
Applejack is
traditionally made by
freeze
distillation, by which water is frozen out of fermented
apple cider, leaving a more ethanol-rich
liquid behind.
Ice beer (also known by the
German term
Eisbier or more
specifically as
Eisbock) is also
freeze-distilled, with
beer as the base
beverage.
Fortified wines are
prepared by adding brandy or some other distilled spirit to
partially-fermented wine. This kills the yeast and conserves some
of the
sugar in grape juice; such beverages
are not only more ethanol-rich, but are often sweeter than other
wines.
Alcoholic beverages are sometimes used in cooking, not only for
their inherent flavors, but also because the alcohol dissolves
hydrophobic flavor compounds which water cannot.
Just as industrial ethanol is used as feedstock for the production
of industrial acetic acid, alcoholic beverages are made into
culinary/household
vinegar.
Feedstock
Ethanol is an important industrial ingredient and has widespread
use as a base chemical for other organic compounds. These include
ethyl
halides, ethyl
esters, diethyl ether, acetic acid, ethyl
amines and to a lesser extent
butadiene.
Antiseptic use
Ethanol is used in medical wipes and in most common antibacterial
hand sanitizer gels at a
concentration of about 62% (
percentage by
volume, not weight) as an
antiseptic.
Ethanol kills organisms by denaturing their
proteins and dissolving their
lipids and is effective against most
bacteria and
fungi, and many
viruses (including
SARS
[1204]), but is ineffective against bacterial
spores.
Antidote use
Ethanol can be used as an antidote for poisoning by other, more
toxic alcohols, in particular methanol and
ethylene glycol. Ethanol
competes with other alcohols for the
alcohol dehydrogenase enzyme,
preventing metabolism into toxic
aldehyde
and
carboxylic acid derivatives, and
it reduces the glycols' tendency to
crystallize in the
kidneys (which is one of its more serious toxic
effects).
Other uses
- Ethanol is easily miscible in water and is a good solvent. Ethanol is less polar than water and is
used in perfumes, paints and tinctures.
- Ethanol is also used in design and sketch art markers, such as
Copic, and Tria.
- Ethanol is also found in certain kinds of deodorants.
Use in history
Before the development of modern medicines, ethanol was used for a
variety of medical purposes. It has been known to be used as a
truth drug (as hinted at by the maxim
"in vino veritas"), as
medicine for
depression and as an
anesthetic.
Drug effects
Pure ethanol will irritate the skin and eyes. Nausea,
vomiting and intoxication are symptoms of
ingestion. Long term use can result in serious liver
damage.Atmospheric concentrations above one in a thousand are above
the European Union
Occupational exposure
limits.
Short-term
BAC (mg/dL) |
BAC
(% v/v) |
Symptoms |
50 |
0.05% |
Euphoria, talkativeness, relaxation |
100 |
0.1 % |
Central nervous system depression, nausea, possible vomiting,
impaired motor and sensory function, impaired cognition |
>140 |
>0.14% |
Decreased blood flow to brain |
300 |
0.3% |
Stupefaction, possible unconsciousness |
400 |
0.4% |
Possible death |
>550 |
>0.55% |
Death |
Effects on the central nervous system
Ethanol is a central nervous system depressant and has significant
psychoactive effects in sublethal doses; for specifics, see
effects
of alcohol on the body by dose. Based on its abilities to
change the
human consciousness,
ethanol is considered a
psychoactive
drug. Death from ethyl alcohol consumption is
possible when blood alcohol level reaches 0.4%. A blood level of
0.5% or more is commonly fatal. Levels of even less than 0.1% can
cause
intoxication, with
unconsciousness often occurring at 0.3–0.4%.
The amount of ethanol in the body is typically quantified by
blood alcohol content (BAC),
the
milligrams of ethanol per 100
milliliters of blood. The table at right
summarizes the symptoms of ethanol consumption. Small doses of
ethanol generally produce euphoria and relaxation; people
experiencing these symptoms tend to become talkative and less
inhibited, and may exhibit poor judgment. At higher dosages (BAC
> 100 mg/dl), ethanol acts as a
central nervous system depressant, producing at progressively higher
dosages, impaired sensory and motor function, slowed cognition,
stupefaction, unconsciousness, and possible death.
More specifically, ethanol acts in the central nervous system by
binding to the
GABA-A receptor, increasing
the effects of the inhibitory
neurotransmitter GABA
(ie. it is a
positive
allosteric modulator).
Prolonged heavy consumption of alcohol can cause significant
permanent damage to the brain and other organs. See
Alcohol consumption and
health.
In America, about half of the deaths in car accidents occur in
alcohol-related crashes. There is no completely-safe level of
alcohol for driving; the risk of a fatal
car accident rises with the level of alcohol in
the driver's blood. However, most
drunk
driving laws governing the acceptable levels in the blood while
driving or operating heavy machinery set typical upper limits of
blood alcohol content (BAC)
between 0.05% and 0.08%.
Discontinuing consumption of alcohol after several years of heavy
drinking can also be fatal. Alcohol withdrawal can cause anxiety,
autonomic dysfunction, seizures and hallucinations.
Delirium tremens is a condition that
requires people with a long history of heavy drinking to undertake
an
alcohol detoxification
regimen.
Effects on metabolism
Ethanol within the human body is converted into acetaldehyde by
alcohol dehydrogenase and then
into
acetic acid by
acetaldehyde dehydrogenase. The
product of the first step of this breakdown, acetaldehyde, is more
toxic than ethanol. Acetaldehyde is linked to most of the clinical
effects of alcohol. It has been shown to increase the risk of
developing cirrhosis of the liver, multiple forms of cancer, and
alcoholism.
Drug interactions
Ethanol can intensify the sedation caused by other
central nervous system depressant drugs such as
barbiturates,
benzodiazepines,
opioids, and
phenothiazines
Magnitude of effects
Some individuals have less-effective forms of one or both of the
metabolizing enzymes, and can experience more-severe symptoms from
ethanol consumption than others. Conversely, those who have
acquired
alcohol tolerance have a
greater quantity of these enzymes, and metabolize ethanol more
rapidly.
Long-term
Birth defects
Ethanol is classified as a
teratogen. See
fetal alcohol syndrome.
Other effects
Frequent drinking of alcoholic beverages has been shown to be a
major contributing factor in cases of elevated blood levels of
triglycerides.
Ethanol is not a
carcinogen. However, the
first metabolic product of ethanol,
acetaldehyde, is toxic,
mutagenic, and carcinogenic.
Production

94% denatured ethanol sold in a bottle
for household use
Ethanol is produced both as a
petrochemical, through the hydration of
ethylene, and biologically, by
fermenting sugars with
yeast. Which process is more economical is dependent
upon the prevailing prices of petroleum and of grain feed
stocks.
Ethylene hydration
Ethanol for use as an industrial feedstock or solvent (sometimes
referred to as synthetic ethanol) is often made from
petrochemical feed stocks, primarily by the
acid-
catalyzed
hydration of ethylene, represented by the
chemical equation
- C2H4(g) +
H2O(g) →
CH3CH2OH(l).
The catalyst is most commonly
phosphoric
acid,
adsorbed onto a porous support
such as
diatomaceous earth or
charcoal. This catalyst was first used for
large-scale ethanol production by the
Shell Oil Company in 1947. The reaction is
carried out with an excess of high pressure steam at 300 °C. In the
U.S., this process was used on an industrial scale by
Union Carbide Corporation and
others; but now only
LyondellBasell
uses it commercially.
In an older process, first practiced on the industrial scale in
1930 by Union Carbide, but now almost entirely obsolete, ethylene
was hydrated indirectly by reacting it with concentrated sulfuric
acid to produce
ethyl sulfate, which
was then undergo
hydrolysis to yield
ethanol and regenerate the sulfuric acid:
- C2H4 + H2SO4 →
CH3CH2SO4H
- CH3CH2SO4H +
H2O → CH3CH2OH +
H2SO4
Fermentation
Ethanol for use in
alcoholic
beverages, and the vast majority of ethanol for use as fuel, is
produced by fermentation. When certain species of
yeast (e.g.,
Saccharomyces cerevisiae)
metabolize sugar they produce ethanol and carbon
dioxide. The chemical equation below summarizes the conversion:
- C6H12O6
→ 2 CH3CH2OH + 2 CO2.
The process of culturing yeast under conditions to produce alcohol
is called fermentation. Ethanol's toxicity to yeast limits the
ethanol concentration obtainable by brewing. The most
ethanol-tolerant strains of yeast can survive up to approximately
15% ethanol by volume.
In order to produce ethanol from starchy materials such as
cereal grains, the
starch
must first be converted into sugars. In brewing
beer, this has traditionally been accomplished by
allowing the grain to germinate, or
malt, which
produces the
enzyme,
amylase. When the malted grain is
mashed, the amylase converts the remaining starches
into sugars. For fuel ethanol, the hydrolysis of starch into
glucose can be accomplished more rapidly by treatment with dilute
sulfuric acid,
fungally produced amylase, or
some combination of the two.
Cellulosic ethanol
Sugars for
ethanol fermentation
can be obtained from
cellulose. Until
recently, however, the cost of the
cellulase enzymes capable of hydrolyzing cellulose
has been prohibitive. The Canadian firm
Iogen brought the first cellulose-based ethanol
plant on-stream in 2004. Its primary consumer so far has been the
Canadian government, which, along with the
United States Department of
Energy, has invested heavily in the commercialization of
cellulosic ethanol. Deployment of this technology could turn a
number of cellulose-containing agricultural by-products, such as
corncobs,
straw, and
sawdust, into renewable energy resources.
Other enzyme companies are developing genetically engineered fungi
that produce large volumes of cellulase, xylanase, and
hemicellulase enzymes. These would convert agricultural residues
such as
corn stover, wheat straw, and
sugar cane bagasse and energy crops such as
switchgrass into fermentable sugars.
Cellulose-bearing materials typically also contain other
polysaccharides, including
hemicellulose. When undergoing hydrolysis,
hemicellulose decomposes into mostly five-carbon sugars such as
xylose.
S. cerevisiae, the yeast
most commonly used for ethanol production, cannot metabolize
xylose. Other yeasts and bacteria are under investigation to
ferment xylose and other
pentoses into
ethanol.
On January 14, 2008,
General Motors
announced a partnership with Coskata, Inc. The goal is to produce
cellulosic ethanol cheaply, with an eventual goal of US$1 per U.S.
gallon ($0.30/L) for the fuel. The partnership plans to begin
producing the fuel in large quantity by the end of 2008. In June
2009, this goal is still ahead of the firm. By 2011 a full-scale
plant will come on line, capable of producing 50 to 100 million
gallons of ethanol a year (200–400
ML/
a).
Prospective technologies
The
anaerobic bacterium
Clostridium ljungdahlii,
discovered in commercial chicken wastes, can produce ethanol from
single-carbon sources including
synthesis
gas, a mixture of
carbon
monoxide and
hydrogen that can be
generated from the partial
combustion of
either
fossil fuels or
biomass.
Use of these bacteria to produce ethanol from
synthesis gas has progressed to the pilot plant stage at the BRI
Energy facility in Fayetteville
, Arkansas
.. The
BRI technology has been purchased by INEOS.
Another prospective technology is the closed-loop ethanol plant.
Ethanol produced from corn has a number of critics who suggest that
it is primarily just recycled fossil fuels because of the energy
required to grow the grain and convert it into ethanol. There is
also the issue of competition with use of corn for food production.
However, the closed-loop ethanol plant attempts to address this
criticism. In a closed-loop plant, renewable energy for
distillation comes from
fermented
manure, produced from cattle that have been fed the
DDSG by-products from grain ethanol
production. The concentrated compost nutrients from manure are then
used to fertilize the soil and grow the next crop of grain to start
the cycle again. Such a process is expected to lower the fossil
fuel consumption used during conversion to ethanol by 75%.
Though in an early stage of research, there is some development of
alternative production methods that use feed stocks such as
municipal waste or recycled products, rice hulls, sugarcane
bagasse, small diameter trees, wood chips, and switchgrass.
Testing
Breweries and
biofuel plants employ two
methods for measuring ethanol concentration. Infrared ethanol
sensors measure the vibrational frequency of dissolved ethanol
using the CH band at 2900 cm
−1. This method uses a
relatively inexpensive solid state sensor that compares the CH band
with a reference band to calculate the ethanol content. The
calculation makes use of the
Beer-Lambert law. Alternatively, by
measuring the density of the starting material and the density of
the product, using a
hydrometer, the
change in specific gravity during fermentation indicates the
alcohol content. This inexpensive and indirect method has a long
history in the beer brewing industry.
Purification
Ethylene hydration or brewing produces an ethanol–water mixture.
For most industrial and fuel uses, the ethanol must be purified.
Fractional distillation can
concentrate ethanol to 95.6% by volume (89.5 mole%). This mixture
is an
azeotrope with a boiling point of
78.1 °C, and cannot be further purified by distillation.
Common methods for obtaining absolute ethanol include desiccation
using adsorbents such as starch, corn grits, or
zeolites, which adsorb water preferentially, as well
as
azeotropic distillation
and
extractive distillation.
Most ethanol fuel refineries use an adsorbent or zeolite to
desiccate the ethanol stream.
In another method to obtain absolute alcohol, a small quantity of
benzene is added to
rectified spirit and the mixture is then
distilled. Absolute alcohol is obtained in the third fraction,
which distills over at 78.3 °C (351.4 K). Because a small amount of
the benzene used remains in the solution, absolute alcohol produced
by this method is not suitable for consumption, as benzene is
carcinogenic.
There is also an absolute alcohol production process by
desiccation using
glycerol. Alcohol produced by this method is known
as spectroscopic alcohol—so called because the absence of benzene
makes it suitable as a solvent in
spectroscopy.
Grades of ethanol
Denatured alcohol
Pure ethanol and alcoholic beverages are heavily taxed, but ethanol
has many uses that do not involve consumption by humans. To relieve
the tax burden on these uses, most jurisdictions waive the tax when
an agent has been added to the ethanol to render it unfit to drink.
These include
bittering agents such as
denatonium benzoate and toxins
such as methanol,
naphtha, and
pyridine. Products of this kind are called
denatured alcohol.
Absolute ethanol
Absolute or anhydrous alcohol refers to ethanol with a low water
content. There are various grades with maximum water contents
ranging from 1% to ppm levels. Absolute alcohol is not intended for
human consumption. It may contain trace amounts of toxic benzene if
azeotropic distillation is
used to remove water. Absolute ethanol is used as a solvent for
laboratory and industrial applications, where water will react with
other chemicals, and as fuel alcohol.
Pure ethanol is classed as 200
proof
in the USA, equivalent to 175 degrees proof in the UK system.
Wine spirits
Wine spirits are about 188
proof.
The impurities are different from those in 190 proof laboratory
ethanol.
References
- Alcohol in the Encyclopædia
Britannica Eleventh Edition
- Merck Index of Chemicals and Drugs, 9th ed.;
monographs 6575 through 6669
- Chakrabartty, in Trahanovsky, Oxidation in Organic
Chemistry, pp 343-370, Academic Press, New York,
1978
- Appendix B, Transportation Energy Data Book from the
Center for Transportation
Analysis of the Oak Ridge National
Laboratory
- Calculated from heats of formation. Does not correspond exactly
to the figure for MJ/l divided by density.
- Reel, M. (August 19, 2006) "Brazil's Road to Energy Independence",
Washington Post.
- California Air Resources Board, Definition of a Low Emission
Motor Vehicle in Compliance with the Mandates of Health and Safety
Code Section 39037.05, second release, October 1989
- A.Lowi& W.P.L.Carter; A Method for Evaluating the
Atmospheric Ozone Impact of Actual Vehicle emissions, S.A.E.
Technical Paper, Warrendale, PA; March 1990
- T.T.M. Jones, The Clean Fuels Report: A Quantitative Comparison Of Motor
Fuels, Related Pollution and Technologies (2008)
- W. Horn and F. Krupp. Earth: The Sequel: The Race to Reinvent
Energy and Stop Global Warming. 2006, 85
- Dual purpose lantern run on ethanol
- Ethanol Powered Car, Youtube
- The Clean Energy Scam, TIME, April 7,
2008, pages 40–41.
- The Politics of Ethanol Outshine its Costs
- Fuel, Food Demand Raise Corn, Soybean
Prices
- Mexicans stage tortilla protest , BBC News,
February 7, 2007.
- Offenburg students test world's first ethanol
powered fuel cell vehicle Acta.
- Willkommen
beim Projekt "Schluckspecht" der Hochschule Offenburg .
- Braeunig, Robert A. "Rocket
Propellants." (Website). Rocket & Space Technology, 2006.
Retrieved on 2007-08-23.
- "A Brief History of Rocketry." NASA Historical
Archive, via science.ksc.nasa.gov.
- Safety data for ethyl alcohol
- Mills, G.A.; Ecklund, E.E. "
- Lodgsdon, J.E. (1994). p. 817
- Badger, P.C. " Ethanol From Cellulose: A General Review." p. 17–21.
In: J. Janick and A. Whipkey (eds.), Trends in new crops and new
uses. ASHS Press, 2002, Alexandria, VA. Retrieved on September 2,
2007.
- Rapier, R. (June 26, 2006) "E3 Biofuels: Responsible Ethanol" R-Squared
Energy Blog
- Great Britain (2005). The
Denatured Alcohol Regulations 2005. Statutory Instrument
2005 No. 1524.
See also
Further reading
External links