The Chemistry of Biodiesel
If your vehicle runs on diesel fuel, then a recent experiment conducted by 14 members of the Class of 2016 could save you a few trips to the gas station and reduce your carbon footprint too.
The first-year students made their own batch of biodiesel from a vat of used vegetable oil — 10 gallons of expended French fry oil from Proctor Dining Hall — and converted it into fuel that will power a diesel engine.
How difficult is the conversion process? How does the energy output of biodiesel compare with that of petroleum-based diesel fuel? What is the cost savings, if any? How does biodiesel compare with conventional diesel fuel in terms of greenhouse gas emissions?
The students in chemistry professor Jeff Byers’ first-year seminar called Smart Energy Choices pondered all of these questions and more, but first they had to get their hands a little oily too.
For a week on either side of the Thanksgiving break, the aroma of French fries filled Lab 459 in McCardell Bicentennial Hall while Byers and his students converted the used canola oil into biodiesel.
It was a multi-step process, with more than its share of glitches along the way, as the students made their biodiesel through transesterification, which is the chemical reaction that occurs when an ester, or carbon compound, is converted into another ester through the introduction of an alcohol and acid or base catalyst. (The students’ ester was the veggie oil and their alcohol was methanol.)
Byers, who is the Philip Battell and Sarah Stewart Professor of Chemistry and Biochemistry, has taught the seminar before, but he offered it this year with the addition of a weekly lab component to a) ensure that it was writing intensive, and b) give the first-year students a solid foundation in the scientific method. One of the few first-year seminars at Middlebury with a required lab, Byers recommended that students have a year of high-school chemistry and a year of high-school physics before enrolling in Smart Energy Choices.
The professor used research funds from his endowed chair to purchase a 40-gallon “All American Biodiesel” processor. Made in Missouri, the apparatus consists of two large mixing tanks, two electric pumps, a fuel filter, brass valves, and about 15 feet of PVC pipe. Not sleek or high-tech like most of the equipment found in a chemistry lab, the processor looks more like something your eccentric neighbor might assemble in his garage.
Because the experiment involved numerous steps, including filtration and titration (and unclogging sludge build-up in the lines), the class used a shared online document from Google Docs to record, review, and analyze the processes involved. And only toward the end of the experiment, when the class attempted to draw off its first sample of biodiesel to test its energy output, did the entire group come together around the processor.
Then, using a standard bomb calorimeter, the students measured how much heat was generated by the biofuel, and with this data they compared the energy output of biodiesel with that of other combustible fuels.
As Byers explains it, the smartest energy choices are the ones that have the highest ratio of hydrogen to carbon:
“When you define ‘smart energy choices’ within the confines of still having to burn stuff for energy – accepting the fact that the smartest energy choices are the ones in which you don’t have to burn anything at all, like wind or solar – then the fuels that offer the highest ratio of hydrogen to carbon, and with least amount of oxygen in the molecules, are the fuels that will generate the most energy per CO2 emission.
“That has been our standard in this course. High energy is good. High CO2 is bad. So what you are looking for is the ratio between the two.”
So is biodiesel a smart energy choice? “Absolutely,” said Amari Simpson ’16, from Chicago, who would like to carry the experiment one step further. “We have diesel trucks and vans at the College right now, and I would like to know what the feasibility would be of using the All American Biodiesel processor to create our own biodiesel from vegetable oil to use in those engines.”
Simpson continued: “We would need to know the actual cost of making our own biodiesel, and calculate the environmental impact of using it” – studies show that biodiesel is cleaner than conventional diesel fuel – “so I think the College should give it a try.”
Middlebury students have long been a driving force for the environmental movement at the College. A student-driven initiative led to the construction of the biomass heating plant; a recent Winter Term class modified a tractor engine to operate on hydrogen; students have experimented with biodiesel from algae; and in 2003 and 2004 students drove across the U.S. in a school bus powered by veggie oil. So as Middlebury approaches 2016, the year when it has pledged to be a carbon-neutral campus, some members of the “carbon-neutral class” (as the first-year group has been called) are now thinking about ways to get there.