iii. Production Processes
vi. Disadvantages and Concerns
vii. Comparison of Bioethanol and Biodiesel
What is Bioethanol ?
Bioethanol is an alcohol made by fermentation, mostly
from carbohydrates produced in sugar or starch crops
such as corn or sugarcane. Cellulosic biomass, derived
from non-food sources such as trees and grasses, is also
being developed as a feedstock for ethanol production
• Colorless and clear liquid
• Used to substitute petrol fuel for road transport vehicles
• One of the widely used alternative automotive fuel in the
world (Brazil & U.S.A are the largest ethanol producers)
• Much more environmentally friendly
• Lower toxicity level
• The principle fuel used as a petrol substitute is
• Bioethanol fuel is mainly produced by the sugar or
cellulose fermentation process
• Bioethanol is an alternative to gasoline for flexi fuel
vehicles.Ethanol is a high octane fuel and has replaced
lead as an octane enhancer in petrol.
• Wheat/Grains/Corn/Sugar-cane can be used to produce
ethanol. (Basically, any plants that composed largely of sugars)
• Bioethanol is mainly produced in three ways.
• Sugar ethanol
• starch sugar ethanol
• cellulose and hemicellulose ethanol
Bioethanol Production Processes
•Concentrated Acid Hydrolysis
•Dilute Acid Hydrolysis
•Wet milling process
•Dry milling process
•Fractional Distillation Process
Chemical reaction 1
The fructose and glucose sugars react with zymase to
produce ethanol and carbon dioxide.
Chemical reaction 2
Fermentation process requires 3 days to complete and is
carried out at a temperature of between 250°C and 300°C.
Conversion of starch to sugar and then
sugar to ethanol
Temperature - 32˚C and 35˚C
pH - 5.2.
Ethanol is produced at 10-15% concentration and the solution is distilled to produce
ethanol at higher concentrations
Eg:- 2) Sugar cane
Simplest of all the processes
• Fermentation conditions are similar to the above
Ethanol can be produced from a variety of feedstocks such as sugar
cane, bagasse, sugar beet, grass, potatoes, fruit, molasses corn,
stover, wheat, straw, other biomass, as well as many types of
cellulose waste and harvestings
Agricultural feedstocks are considered renewable because they
get energy from the sun using photosynthesis
Cornfield in South
Sugar cane harvest
The top fiveethanol producerstill 2010
Brazil - 16500 billion liters
The United States -16270 billion liters
China - 2000 billion liters
The European Union - 950 billion liters
India - 300 billion liters
• transport fuel to replace gasoline
• fuel for power generation by thermal combustion
• fuel for fuel cells by thermochemical reaction
• fuel in cogeneration systems
• feedstock in the chemicals industry
• Exhaust gases of ethanol are cleaner due to
• Ethanol-blended fuels such as E85 (85% ethanol
and 15% gasoline) reduce up to 37.1% of GHGs.
• Output of energy during the production is more
than the input.
• Any plant containing sugar/ starch can be use for
production of bioethanol .
• Carbon neutral i.e. CO2 released in bioethanol
production process = one the crops previously
absorbed during photosynthesis.
• Decrease in ozone formation
• Renewable energy resource
• Energy security
• Reduces the amount of high-octane
• Fuel spills are more easily biodegraded or
diluted to non toxic concentrations.
Disadvantages and Concerns
• A large amount of arable land is required to grow crops, natural
habitats would be destroyed
• Food vs. Fuel debate
• due to the lucrative prices of bioethanol some farmers may
sacrifice food crops for biofuel production which will increase
food prices around the world
• Carbon emissions (controversial)
• During production of bioethanol, huge amount of carbon dioxide
• Emission of GHGs from production of bioethanol is comparable
to the emissions of internal-combustion engines
Disadvantages and Concerns
• Not as efficient as petroleum
• energy content of the petrol is much higher than
• its energy content is 70% of that of petrol
• Engines made for working on Bioethanol cannot be used for
petrol or diesel
• Due to high octane number of bioethanol, they can be
burned in the engines with much higher compression
• Used of phosphorous and nitrogen in the production
• negative effect on the environment
• Cold start difficulties
• pure ethanol is difficult to vaporise
Disadvantages and Concerns
• ethanol is hygroscopic, it absorbs water from the air and thus has
high corrosion aggressiveness
• Can only be transported by auto transport or railroad
• Many older cars unequipped to handle even 10%
• Negatively affect electric fuel pumps by increasing
internal wear and undesirable spark generation
Comparisonof Bioethanoland Biodiesel
Process Dry-mill method: yeast, sugars and starch
are fermented. From starch, it is
fermented into sugar, afterwards it is
fermented again into alcohol.
Transesterification: methyl esters and
glycerin which are not good for engines,
are left behind.
Both reduce greenhouse gas emissions as biofuels are primarily derived from crops
which absorb carbon dioxide.
Compatibility ethanol has to be blended with fossil fuel
like gasoline, hence only compatible with
selected gasoline powered automobiles.
Able to run in any diesel generated
Costs Cheaper More expensive
420 gallons of ethanol can be generated
60 gallons of biodiesel per acre soybeans
cost of soybean oil would significantly
increase if biodiesel production is
increased as well.
Energy provides 93% more net energy per gallon produces only 25% more net energy.
12% less greenhouse gas emission than
the production and combustion of
41% less compared to conventional
• Employment for locals
• Brazilian sugarcane industry poor record in
respecting worker’s rights.
• Expansion in sugar cane cultivation may increase
• increased the wealth of the sugar and alcohol
sector’s industries, the poor to deal with negative
• For bioethanol to become more sustainable to replace
petrol, production process has to be more efficient
• Reducing cost of conversion
• Increasing yields
• Increase the diversity of crop used
• As microbes are use to convert glucose into sugar which
is ferment in bioethanol
• Microbiology and biotechnology will be helpful in the genetic
Philippidis, G. P., and Smith, T, K, 1995, Limiting factors in the
and fermentation process for conversion of cellulosic biomass to
fuel ethanol, Appl. Biochem.
DEMiRBA AYHAN “Bioethanol from Cellulosic
Selcuk University, Konya, Turkey