Watts Up With That?

Guest post by John Goetz

I keep an active watch of the news for progress being made in the areas of renewable and alternative energy sources. One area that has caught my eye is algal fuel (biofuel produced by algae). One company that has been in the news lately is Sapphire Energy, which claims to be able to produce ASTM compliant 91-octane biogasoline. Sapphire Energy says their technology “requires only sunlight, CO₂ and non-potable water – and can be produced at massive scale on non-arable land”.

I am not trying to pick on any one solution or Sapphire Energy in particular. I simply wondered how massive a scale of CO2 and non-arable land is needed to make a noticeable dent in our gasoline demand.

First, how much CO2 do we need? The IPCC guidelines for calculating emissions require that an oxidation factor of 0.99 be applied to gasoline’s carbon content to account for a small portion of the fuel that is not oxidized into CO2. To calculate the CO2 emissions from a gallon of fuel, the carbon emissions are multiplied by the ratio of the molecular weight of CO2 to the molecular weight of carbon, or 44/12. Thus, the IPCC says the CO2 emissions from a gallon of gasoline = 2,421 grams x 0.99 x (44/12) = 8,788 grams = 8.8 kg/gallon = 19.4 pounds/gallon.

Now let’s assume Sapphire Energy simply reverses the process and consumes the CO2 to produce gasoline. In other words, we take 19.4 pounds of CO2 out of the atmosphere for every gallon of gasoline we produce. This seems like is a nice “carbon neutral” process.

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