Bioethanol:
Production process, Feedstocks, Fuel Properties, Application,
Advantages and Disadvantages
Anisur RAHMAN, (Dr.Ag.Sc.)
Associate Professor
Department of Farm Power and Machinery
Bangladesh Agricultural University
Mymensingh-2202, Bangladesh
What is bioethanol ? 2/20
• Colourless 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 bioethanol producers)
• Much more environmentally friendly
• Lower toxicity level
Bioethanol Production 3/20
• Wheat/Grains/Corn/Sugarcane can be used to
produce ethanol.
Main method : Sugar fermentation
Technical fow chart of bioethanol production from
4/20
corn
Fig. Technical fowchart of bioethanol
production
Bioethanol Production 5/20
Concentrated Acid Hydrolysis
~77% of sulfuric acid is added to the dried biomass
to a 10% moisture content.
Acid to be added in the ratio of 1/25 acid :1
biomass under 50°C.
Dilute the acid to ~30% with water and reheat the
mixture at 100°C for an hour.
Gel will be produced and pressed to discharge the
acid sugar mixture.
Separate the acid & sugar mixture by using a
chromatographic column.
Bioethanol Production 6/20
Dilute acid hydrolysis
oldest, simplest yet efcient method
hydrolyse the bio-mass to sucrose
hemi-cellulose undergo hydrolysis with the addition
of 7% of sulfuric acid under the temperature 190ºC.
to generate the more resistant cellulose portion,
4% of sulfuric acid is added at the temperature of
215ºC
Bioethanol Production 7/20
Wet milling process
Corn kernel is soaked in warm water
Proteins broken down
Starch present in the corn is released (thus, softening
the kernel for the milling process)
Microorganisms, fbre and starch products are produced.
In the distillation process, bioethanol is produced.
Dry milling process
Clean and break down the corn kernel into fne particles
Sugar solution is produced when the powder mixture
(corn germ/starch and fbre) is broken down into sucrose
by dilute acid or enzymes.
Yeast is added to ferment the cooled mixture into
Bioethanol Production 8/20
Sugar fermentation
Hydrolysis process breaks down the biomass cellulosic
portion into sugar solutions which will then be fermented into
bioethanol.
Yeast is added and heated to the solution.
Invertase acts as a catalyst and convert the sucrose sugars
Invertase
into glucose and fructose. (both C6H12O6).
catalyst
C12H22O11 + H2O C6H12O6 + C6H12O6
Sucrose Water Fructose Glucose
The fructose and glucose sugars react with zymase to
Zymase
produce bioethanol and carbon dioxide.
catalyst
C6H12O6 2C2H5OH + 2CO2
Fructose/ Glucose Bioethanol
Fermentation process requires 3 days to complete and is
Bioethanol Production 9/20
Fractional Distillation Process
After the sugar fermentation process, the bioethanol still
does contain a signifcant quantity of water which have
to be removed.
In the distillation process, both the water and bioethanol
mixture are boiled.
Ethanol has a lower boiling point than water, therefore
bioethanol will be converted into the vapour state, then
— frst condensed and separated from water.
Properties of Bioethanol fuel 10/20
Properties Gasoline Bioethanol
Molecular weight [kg/kmol] 111 46
Density [kg/l] 0.75 0.80-0.82
Lower Calorifc alue [MJ/kg] 41.3 26.4
Octane number 97 109
Cetane number 8 11
Boiling temperature [ºC] 30-190 78
• Energy content
—has much lower energy content than gasoline
—about two-third of the energy content of gasoline on a
volume base.
— ery low for ethanol, indicates a slow evaporation
Feedstocks 11/20
• Sugar is required to produce ethanol by fermentation
—Plant materials (grain, stems and leaves) are composed
mainly of sugars
—almost any plants can serve as feedstock for ethanol
manufacture
Choice of raw material depends on several factors
—ease of processing of the various plants available
—prevailing conditions of climate
Crop used for
—landscape and soil composition Bioethanol production
Brazil Sugarcane
—sugar content Europe Wheat
USA Corn
Feedstocks 12/20
• R&D activities on using lignocellulosic (woody materials)
as feedstock
—Lignocellulosic biomass is more abundant and less
expensive than food crops
—higher net energy balance
—accrue up to 90% in greenhouse gas savings, much
higher than the frst generation of biofuel
—However, more difcult to convert to sugars due to their
relatively inaccessible molecular structure
Application 13/20
• Transport fuel to replace gasoline
• Fuel for power generation by thermal combustion
• Blending of bioethanol with a small proportion of a
volatile fuel such as gasoline -> more cost efective
Advantages 14/20
Exhaust gases of bioethanol are much cleaner
—it burns more cleanly as a result of more complete
combustion
Greenhouse gases reduce
—bioethanol-blended fuels reduce up to 37.1% of GHGs
Positive energy balance, depending on the type of raw
stock
—output of energy during the production is more than the
input
Any plant can be use for production of bioethanol
Advantages 15/20
Renewable energy resource
—result of conversion of the sun's energy into usable
energy
Photosynthesis -> feedstock's grow -> processed into
bioethanol
Energy security
—esp. Countries that do not have access to crude oil
resources
—grow crops for energy use and gain some economic
freedom
Disadvantages 16/20
Biodiversity
—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 sacrifce food crops for biofuel production
Carbon emissions (controversial)
—During production of bioethanol, huge amount of carbon
dioxide is released
Disadvantages 17/20
Not as efcient as petroleum
—energy content of the petrol is much higher than
bioethanol 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
ratio
References 18/20
• Guo, M., Song, W., & Buhain, J. (2015). Bioenergy and biofuels:
History, status, and perspective. Renewable and Sustainable
Energy Reviews, 42, 712–725.
• Nigam, P. S., & Singh, A. (2011). Production of liquid biofuels
from renewable resources. Progress in Energy and Combustion
Science, 37(1), 52–68.
• Bioethanol (https://www.slideshare.net/AdrianShazmi/bioethanol,
accessed on 11.09.2018)
• Website…
Next class 19/20
• Details process about Biodiesel
Questions?
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