LECTURE 7
SPECIFC PROJECT
ETHANOL DISTILLERY
Uses of ethanol
Fuel
Social drink
Industrial solvent (printing ink)
Medicinal uses (antibacterial)
PROCESS
Micro-organisms (yeasts) convert monosaccharides C6H12 O6 to ethanol
Sugar-rich solution inoculated with yeast
Fermentation – produces ethanol
Ethanol separated from solution (beer)
Purification – distillation
Disposal of waste stream
water CO2 heat
Mash preparation Fermentation Distillation alcohol
Molasses Nutrients yeast effluent
Process details
SG (20°C) = 0.789 BP = 78.4 °C
Infinite solubility in water Flammable
C6H12 O6 → 2 C2H5OH + 2 CO2
ΔH = -130 kJ (exo or endo-thermic ?)
Calculate max theoretical yield
Practical yield: 42 – 46 % fermentable sugars
Inversion of sucrose to glucose & fructose
C12H22 O11 + H2 O → 2 C6H12 O6
Molasses composition
(variable)
% (mass) component
14-18 water
50-55 fermentable sugars (sucrose, glucose, fructose, others)
16-20 ash (K, Ca, Mg, Fe, Na, SO4, Cl, PO4, Si, etc)
12-16 other organic constituents
Mashing operation
Dilute molasses with water
Add small amounts nutrients [(NH4)2 SO4, H2SO4 (pH adjustment),
H3PO4]
Mash characteristics: Concentration: 18-22 ° Brix (dissolved
solids)
pH: 5.5 – 5.8, total sugars 10 – 12 g / 100 ml mash
nitrogen : 2.25 g / 100 ml mash, H3PO4 : 0.6 g / 100 ml
mash
Approx. 5 kg dry yeast per 1000 L of mash
Fermentation
Batch process
Liquor after fermentation called “BEER”
Fermentation time: 40 – 72 h
Alcohol concentration (by volume) after complete
fermentation: 7 – 11%
[OH]
9%
Fermentation
complete
T* = fermentation time
T* Time (h)
Factors affecting
fermentation efficiency
Conc. Of sugars in molasses and mash
Sufficient nutrients (KNP)
Temp of fermentation (35 – 38 ° C)
Conc of yeast cells in beer tanks
Conc of alcohol in beer
pH
Inhibitory components (Cu, Cd, other heavy metals)
Fermentation time
Energy requirements
Steam heating for distillation
Power for pumping (mash, beer, final product – storage),
cooling water during exothermic fermentation
Steam requirements: 200 – 300 kg steam / 100 L product
Called slops, vinasse or stillage
7 – 10 % solids
Has fertilizer value : 1.5 % K2O, 0.2 % P2O5, 1 % N
CO2 - dry ice
Fertiliser (liquid or solid)
CALCULATIONS
1. To produce 140 kL per day (i.e. 24 h) of potable
alcohol (96.4%) calculate the fermenter capacity
required assuming the following:
Fermentation time = 52 hours, beer alcohol
concentration = 9.1 % (by volume), only 80% of the
fermenter volume is utilized for actual
fermentation. Recovery of alcohol from the beer is
95%. (4228 m3)
2. Calculate the volume of dilution water and mass
of molasses (in ton) required to prepare 600 m3 of
mash with a fermentable sugar content of 11g/ 100
ml of mash using molasses for which the total
fermentable sugar content is 53.1 %. Assume the SG
of molasses is 1.88. (533.9 m3)
CALCULATIONS (contd)
3. 9.3 tons of molasses are used for the preparation of mash for
a fermenter. The sugars content (by mass) was analysed to be
48.6%, 12.4% being monosaccharide (C6H12 O6) and the
remainder (36.2 %) being sucrose (C12H22 O11 ). Before being
available for fermentation to ethanol (C2H5OH ) , the sucrose
must be inverted to monosaccharide by hydrolysis [C12H22 O11 +
H2 O → 2 C6H12 O6]. If the volume of 94% ethanol recovered
from this batch was 2810 L (SG of 94% ethanol = 0.802),
calculate the overall efficiency of conversion of sugars to
ethanol [overall efficiency = (actual yield)/(theoretical yield) *
100] . Molar masses: C =12, H =1, O = 16.
4. Calculate the volume of CO2 released to the atmosphere from
260 ton of mash containing 15% (m/m) fermentable sugars (C6H12
O6) if the air temperature is 26°C and the fermentation
efficiency (utilization of sugars in the conversion to ethanol) is
86%. [1kmol CO2 at STP has volume of 22.4 m3. Atmospheric
pressure = 1.013 bar.].
