Page 213 - Biofuels Refining and Performance

196 Chapter Seven

Malt process. Malt is prepared by germination of barley grains to pro-
duce required enzymes. The grain is ground and steam cooked at
100–150 C to break the cell wall of starch. For every 25 kg of grain, 100 L
of water is added. Then the formed mass is cooled to 60–70 C and taken
to large vessels where malt is added within 2 h and 60–70% of the stock
is converted into maltose. Converted mash is cooled to a fermenting
temperature of 20–25 C. pH is adjusted and fermentation is affected,
producing ethanol.
Acid hydrolysis. This process involves treatment with concentrated
sulfuric or hydrochloric acid at pH 2–3 and 10–20 kg pressure in an auto-
clave to make sugar and then conversion of sugar to alcohol by yeast.

Cellulose material.
Wood. Cellulose from wood is hydrolyzed into simple sugars by using
diluted acid at a high temperature or concentrated acid at a low tem-
perature. Similarly, cellulosic agricultural waste and straws can be used
in place of wood.
Sulfite waste liquor from paper manufacture. Waste liquor contains 2–3.5%
of sugar, out of which 65% is fermentable into alcohol. Before fermen-
tation, all acids in the liquor are removed by adding calcium. Then fer-
mentation is carried out by special yeasts. Generally, 1% of liquor is
converted into alcohol.
Hydrocarbon gases.
Hydration of ethylene. Conversion of ethylene to ethyl alcohol can be
carried out with high yield by first treating ethylene with H SO , forming
4
2
ethyl hydrogen sulphate and diethyl sulfate, as given by the following
reactions:
C H HSO → (C H ) SO 4
2
2
5
4
5 2
2C H H SO → (C H ) SO 4
5 2
2
4
2
2
4
These products, ethyl sulfuric acid and diethyl sulfate, when treated
with water give ethanol as per the following reactions:
C H HSO H O → C H OH H SO 4
2
2
2
5
2
4
5
(C H ) SO 2H O → 2C H OH H SO 4
2
5 2
4
2
5
2
2
Direct hydration. Ethanol is also formed as per the following chemical
reaction:
C H H O → C H OH
2
2
4
2
5
This type of conversion is very small as the reaction is exothermic; it is
not a suitable method for mass production. The corn is first ground, then