Page 235 - Biofuels Refining and Performance

218 Chapter Seven

vaporized mixture and also burns uniformly. One major drawback of
methanol is that it creates vapor locks because of the higher vaporiza-
tion rate. Properties of ethanol and methanol as compared with petrol
are listed in Table 7.3.

7.10 Ecosystem Impacts Using
Alcohol Fuels
7.10.1 Aquatic system impacts
The biological consequences of alcohol spills or leaks into marine water
are sensitive to many factors such as scale and duration of the spill, tidal
patterns, water currents, flow rate, temperature, and available oxygen.
Marine life can tolerate low concentrations of alcohol.
In general, methanol and ethanol are significantly less toxic than
gasoline or crude oil. Because alcohols are miscible, volatile, and degrad-
able, they are dispersed readily, and diluted and neutralized in aquatic
environments. The aquatic environment recovers more rapidly and com-
pletely from an alcohol spill than from a gasoline or crude oil spill of the
same volume.

7.10.2 Terrestrial system impacts
The direct exposure of soils to methanol spills results in immediate
damage of surface vegetation. The miscibility, volatility, and degrad-
ability of alcohols reduce the alcohol residence time in soil and mini-
mizes the environmental impact. Fungal and bacterial populations, which
are important agents of nutrient cycling, exhibit 80–90% recovery with
3 weeks of exposure. Total recovery of the site occurs within a period of
weeks or months. In comparison, recovery of biodegradation by crude
oil and petroleum products takes months or years.

7.10.3 Occupational health impacts
Occupational heath risks associated with using alcohol fuels are lower
than those associated with conventional fuels. The relative toxicity of
alcohol fuels depends on the means of exposure, inhalation, and inges-
tion. Gasoline poses a greater occupational health risk than either
methanol or ethanol as carcinogens in gasoline can be readily absorbed
by the skin or inhaled.

7.10.4 Occupational safety impacts
Two major safety hazards of all fuels are fire and explosion, which can
occur because of improper fuel storage, spills, or vehicle accidents. The
properties of alcohols and gasoline that pertain to fire and explosion