Bio alcohol

BIO-ALCOHOL
Dr. Ajay Singh Lodhi
Assistant Professor
College of Agriculture, Balaghat
Jawahar Lal Krishi Vishwa Vidyalaya, Jabalpur (M.P.)

Bio-Alcohol
 Ethyl alcohol, known as alcohol and technically termed
ethanol is a colourless and flammable liquid with a
chemical formula C2H5OH.
 It is the alcoholic product of fermenting the sugars in
natural raw materials with yeast. The natural raw
materials include vegetable matter, growing crops, farm
waste, waste organic products (straw and saw dust),
molasses, wastes of paper and pulp industries etc.
 From this annually renewed store of raw materials,
ethanol can be readily produced in quantities sufficient
to meet the world demand. It thus has attributes of
renewal in nature.

ALCOHOL AS AUTOMOBILE FUEL
Ethanol offers certain advantages if used as an
automobile engine fuel:
 It is an antiknock fuel and has the ability to stand very
high compression ratios.
 It is a high octane, water-free alcohol. Octane rating is
defined as the fuel’s ability to resist engine knock.
 Ethanol is both a fuel and an octane enhancer.
 It is an ideal replacement for lead.
 It has a high latent heat of vaporisation. This property
can be utilised to achieve lower charge temperature
during induction for higher charge density. Hence,
higher volumetric efficiency is obtained.
 It tends to produce less carbon deposits than normal
petrol and the deposits are softer and easier to remove.

 Its lower calorific value, higher viscosity, greater surface
tension and hygroscopic nature are some of the
difficulties in its use as a complete fuel in present day
combustion engines.
 It can, however, be mixed with other fuel or fuel
mixtures so as to impart to the resulting blend some of
its important properties namely higher compression
operation without knock, cleaner combustion and cooler
engine operation.
 Ethanol has the potential as the alternative fuel to solve
the problems of limited source of fossil fuels.
 Ethanol is most commonly used as a 10 percent blend
with petrol known as gasohol that can be burned in
unmodified automotive engines.

UNSUITABILITY OF ETHANOL IN DIESEL ENGINES
 Diesel engines operate on an entirely different combustion
principle in comparison to spark ignition engines. It relies on
the fuel to self ignite from an increased pressure and
temperature of the compression cycle.
 Diesel fuel has a high cetane rating. It also has a low octane
rating. The converse is true for ethanol, which is the major
problem in the use of ethanol in diesel engines.
 Ethanol can be burned in diesel engines, but because it
resists self ignition, it can have accompanying knock and
engine stresses that may be unacceptable due to noise and
lower engine life.
 Cetane-enhancer additives are available but expensive and
of questionable performance. Also, phase separation of diesel
and ethanol is more pronounced than with petrol blends,
which limits its performance during cold weather. Hence,
ethanol is not suitable to use as a fuel in diesel engine
systems.

FEEDSTOCKS FOR ETHANOL PRODUCTION
 Ethanol can be produced by the fermentation of any
feedstock that contains sugar or starches. It can be
produced from cellulose materials that can be converted
into fermentable sugar.
 These three groups of biomass are as follows:
(i) sugars (sugar beets, sugarcane, sweet sorghum, fruits);
(ii) starches (small grains such as corn and wheat,
potatoes, cassava); and
(iii) cellulose (wood, solid waste, agricultural residues).

 Sugar crops contain monosaccharide forms of sugar such
as glucose. This can readily be fermented into alcohol by
yeast with no intermediate processing.
 Starch crops contain sugar units that are tied together
in long chains. Yeast cannot use these disaccharide
forms of sugar until the starch chains are converted into
individual six-carbon groups such as glucose or fructose.
 This conversion process can be done fairly simply by the
use of cooking in a dilute acid solution or reacting the
starch with thermophilic (heat tolerant) enzymes.
 Cellulose crops contain chemicals called polysaccharides.
These chains must be broken down to release the sugar.
Breaking the chemical bonds of cellulose is more
complicated than breaking down starch to simple sugar.
The conversion is typically done physically (milling or
heat treatment) or chemically (basic or acid reactions).

ETHANOL PRODUCTION PROCESS
Ethanol production proceeds as follows:
(i) formation of a fermentable sugar solution;
(ii) fermentation of the sugar solution to ethanol; and
(iii) separation of ethanol from other process ingredients.

THE ETHANOL PRODUCTION PROCESS IS
OUTLINED AS FOLLOWS:
1. Milling: Feedstock is first passed through hammer
mills and then it is ground into a fine powder.
2. Sterilisation: If distressed or damaged crop are used,
sterilisation facilities are included to avoid biological
contamination.
3. Cooking: Enzymes (alpha-amylase) and water are
added to form a mash that is cooked for about 30 min.
Heat is applied at this stage to enable liquefaction.
4. Cooling: The mash from the cooker is cooled. The
secondary enzyme (glucoamylase) is added to convert the
liquefied mash to fermentable sugars (dextrose).
5. Fermentation: Yeast is added to the mash to ferment
the sugars to ethanol and carbon dioxide. Mash ferments
for about 2 days, during which the sugar is converted to
alcohol.

6. Distillation:
❑ The fermented mash, now called ‘‘beer’’ contains about
10% alcohol as well as the nonfermentable solids.
❑ Initially the mass is introduced into the first-stage
distillation column that is regulated to maintain a
temperature just a little higher than the boiling point of
ethanol. Alcohol vaporises and ascends out of the
column. Liquid water mixed with residual grain and
yeast (distilliers grain) flows down and out.
❑ The vaporised alcohol (now about 50 percent) is passed
through a second distillation column. It concentrates the
alcohol content to 95 percent (e.g. 190 proof).
❑ Proof is a measure of ethanol content. One percent
ethanol content equals 2 proofs.

7. Dehydration:
 Since the alcohol from the second-stage column contains
5% water, which is unusual for commercial gasohol, it
must be totally dehydrated.
 Benzene and petrol are common additives in a further
process to separate the residual water and produce
anhydrous ethanol (100 percent or 200 proof alcohol).
8. Denaturing:
 Ethanol that will be used for fuel is then denatured with
a small amount (2–5%) of some product, like petrol, to
make it unfit for human consumption.
9. Fuel:
 The denatured anhydrous alcohol is transported to the
gasohol market. It is blended with nonleaded petrol at
the ratio of 10 percent ethanol to 90 percent petrol.

10. Coproducts:
 Two primary coproducts of ethanol production are
distillers grain and carbon dioxide. Both of which have
market value.
 Distiller grain consists of the protein value of corn,
yeast, fibre and water discharge from the first-stage
distillation column. The distillers grain has a high
protein content of about 27 percent. Therefore, it makes
an excellent animal feedstock supplement. It is
competitive with soybean meal, which is about 44
percent protein.
 Carbon dioxide (CO2) that evolves from the fermentation
process can be used in grain storage silos to retard
spoilage.

Bio alcohol

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