Filed by Erika Engelhaupt
If you don’t know your biodiesel from your bioassay, this blog’s for you.
To bone up on the basic chemistry behind biodiesel, I turned to one of the pros in our tour group: William (Rusty) Sutterlin (shown, right), chief executive officer of Renewable Alternatives, based in Columbia, Mo. As we toured the Biocapital biodiesel refinery in Charqueada today, Sutterlin was always handy with a clear explanation of what was happening inside the tangle of pipes and tanks. So after the tour, I snagged him and sat down for a crash course in methyl esters and a peek inside his company, which turns a by-product from biodiesel production into nontoxic antifreeze, or propylene glycol.
In the beginning, all biodiesel starts with an oil or a fat. Almost anything from used French fry vegetable oil to pork fat will work. The key is that oils (liquid) and fats (solid) store lots of energy, and biofuels are all about getting that energy back out to power vehicles down the highway.
Oils and fats share a basic structure, with a glycerin backbone supporting fatty acid chains. It looks something like this:
The carbon atoms running down the left-hand side form the glycerin backbone, and the bits hanging on are the fatty acids, where the R represents a long hydrocarbon chain.
In biodiesel production, methanol solvent and a catalyst—usually sodium methoxide (NaOCH3)—are added to the oil or fat. The ensuing reaction is called a transesterification, because one kind of ester (a molecule with an oxygen bridging two carbons and a double-bonded oxygen) is turned into another ester. In this case, the glycerin backbone peels away from the fatty acids like the skin off fried chicken. Methyl groups (CH3) from the catalyst replace each of the glycerin carbon atoms, leaving you with three methyl esters:
Each methyl ester is a biodiesel molecule. It’s as simple as that. The glycerin left behind settles out and can be used for consumer products like moisturizers or made into something else (more on that in a moment).
There are a few complications in the real world, of course. For one thing, if you use fairly “dirty” oils or fats to start with (say, 10-week-old grease from a McDonald’s fryer), you’ll have a lot of free fatty acids floating around. These fatty acids will undergo an acid-base reaction with the sodium methoxide, producing methanol and a fatty acid salt, better known as a soap. That soap then has to be separated out of the diesel (and no, you can’t just drive a French fry-powered bubble-mobile).
Companies around the world are working to make biodiesel from fats and oils that otherwise would be waste products, and even the glycerin produced as a by-product doesn’t have to go to waste. Sutterlin wraps up our biodiesel lesson with the latest news from his company, which is doing just that.
Sutterlin started Renewable Alternatives in 2003 to make phase-change materials: compounds that have basic chemical properties that are handy for storing heat. For example, a coffee cup that keeps your coffee at the perfect temperature will be out soon. Sutterlin and his collaborators at the University of Missouri noticed that with the biodiesel boom, a lot of glycerin was coming onto the market. A glut of refined glycerin caused prices for the commodity to crash from $1.10 per lb to 30 cents per lb.
Sutterlin recognized a cheap resource immediately and looked for a way to turn glycerin into a useful product. Sutterlin’s group realized that stripping one hydroxyl group (-OH) from glycerin would yield propylene glycol, and the team set out to improve on the existing conversion process.
Renewable Alternatives licensed the process to U.K.-based Senergy, and that company is building a plant that will start producing propylene glycol by the end of the year. Besides antifreeze, propylene glycol is used in many products such as cosmetics and lubricants.
The test’s on Friday. Class over!