In response to an article about ethanol on the popular Motley Fool website, NCGA’s director of biofuels, Pam Keck, Ph.D., provided this comment. The website has not chosen to publish it, so we are offering it here:
I applaud Mr. Funk’s approach to using a real-world example of calculating and comparing the BTU values of gasoline vs. ethanol. There are several, critical elements (no chemistry pun intended) that should also be noted. If the object were to use a real-world example in the classroom, it would be worth including more of the story as it relates to a comparison of ethanol and gasoline. Otherwise, the students will come away from the exercise with the mistaken belief that a BTU calculation provides sufficient data to make an informed decision.
First, the CO2 calculation is misleading. The calculations described only ‘count’ the CO2 emissions from the tailpipe. This is a very small portion of the entire CO2 lifecycle analysis that is done when comparing ethanol from corn and gasoline from petroleum. The EPA, when determining CO2 emissions, considers various models and calculations: production of fertilizers, application of fertilizer to the field, collection and transportation of the corn, and conversion of cornstarch to ethanol. The same system analysis is also done for gasoline production from petroleum. [By the way, corn to ethanol conversion has to account for indirect greenhouse gas impacts (for example, through land use changes), while petroleum production to gasoline doesn’t have to account for indirect impacts.] Even with this large discrepancy, corn starch ethanol is considered to have a 20% reduction in GHG emissions compared to gasoline from petroleum by the EPA. Many published peer-reviewed papers show that the reduction is closer to 50%.
Second, while the kJ/gallon values are in the ballpark range and the assumption that less mileage is obtained from flex-fuel vehicles (FFV), many FFV owners report that after using a tank or two of E85, that their mileage penalty is much less than what the BTU differences would indicate. Some think it might be due to the higher heat of vaporization for ethanol, leading to a cooling effect in the engine. Plus, as has been published in peer-reviewed articles, automobile manufacturers have shown that at higher blends of ethanol, engines can be optimized to not have a penalty loss due to ethanols’ high-octane value and its higher heat of vaporization.
Third, production of ethanol from corn is a renewable process. Gasoline production from petroleum is not renewable; there is a limited supply of petroleum and one day all of the economically extractable petroleum will be gone.
Lastly, and maybe most importantly, chemistry students who are capable of determining BTU content of various fuels will be equally capable of understanding that real-world issues are often very complicated. There are real environmental and societal costs associated with continued use of gasoline, including higher CO2 emissions and pollution, and these costs should be considered when choosing between gasoline and ethanol.