
ALGA (Photo credit: La maldición de Sísifo)
Algae, the green stuff suspended in and floating on the surface of over-fertilized (polluted) water, AKA scum, is supposed to save America’s dependence on foreign crude oil. The President has said so. He stated that “up to 17% of the oil we import for transportation” could be replaced with this fuel [1].
The Chemistry
To begin with, a mass of algae is not the same as a container of crude oil. Algae are small plant-like organisms living in water. Like all plants, they use the energy of sunlight to convert carbon dioxide (CO2, i.e., one carbon and two oxygen atoms per molecule) to plant matter. In chemical terms, crude oil is a pure hydrocarbon of the approximate composition CH2 (i.e., one carbon and two hydrogen atoms per molecule). The composition of algae is more like CH2O, sort of half way in between CO2 and CH2. Because of the remaining oxygen atom in the plant matter (CH2O), its energy content is substantially lower than that of a pure hydrocarbon. You might say that it is already half burnt (the end product of which, of course, is CO2).