Page 215 - Biofuels Refining and Performance

198 Chapter Seven

It is estimated that 1000 10 ha planted with such trees can pro-
3
vide 10% of Sweden’s electricity. Also in Sweden, work has been carried
out on the common reed, and the estimated yield is 10 ton/(yr
ha),
which is equal to 4.5 tons of oil. Sweden has plans to have 100 10 3
ha of reeds. Brazil’s program of ethanol from sugarcane and manioc may
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employ 200 10 people and save $1600 million each year in foreign
exchange.

7.3 Distillation of Alcohol
If a mixture of water and alcohol is boiled, the percentage of alcohol to
water is greater in vapor than in liquid. Therefore, by repeated distil-
lation and condensation, the alcoholic strength of the distillate can be
increased until it contains 97.6% alcohol. There are different methods
of distillation, but they are not discussed here, as ethanol production is
our prime concern.

7.4 Properties of Ethanol and Methanol
Both ethanol and methanol, as listed in Table 7.3, have high knock
resistance (as the octane numbers are 89 and 92, against 85 for gaso-
line), wide ignition limit, high latent heat of vaporization, and nearly

TABLE 7.3 Important Alcohol Properties
Gasoline Ethyl Methyl
Sr no. Property C 8 H 18 isooctane alcohol alcohol
1. Molecular weight (g) 114.2 46 32
2. Boiling point at 1 bar ( C) 43–170 78 66
3. Freezing point ( C) 107.4 117.2 161.8
4. Specific gravity (150 C) 0.72–0.75 0.79 0.79
5. Latent heat (kJ/kg) 400 900 1110
6. Viscosity (centipoise) 0.503 0.60 0.596
7. Stoichiometric A:F (ratio) 14.6 9 6.45
8. Mixture heating value (kJ/kg) 2930 2970 3070
(for stoicmixture)
9. Ignition limits (A/F) 8–19 3.5–17 2.15–2.8
10. Self-ignition temperature 335 557 574
11. Octane number
a. Research 80–90 111 112
b. Motor 85 92 91
12. Cetane number 15 8 3
13. Lower CV (kJ/kg) 44,100 26,880 19,740
14. Vapor pressure at 38 G (bar) 0.48–1 0.17 0.313
15. Flame speed (m/sec) 0.43 –– 0.76
16. Autoignition temperature ( C) 222 –– 467