Biodiesel Chemistry 101


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!


8 Responses to Biodiesel Chemistry 101

  1. Monte Magill says:

    Great article! Thanks so much.

  2. Mark S. says:

    thank you for the chemistry- there isn’t much of it easily accessed on the web!

  3. Great Site to get help with chemistry!…

    calculate the solubility product constant for cupric hydroxide from half-cell potential…

  4. Donna says:

    Excellent post Very informative. A little technical perhaps. Can I add something about biodiesel for the rest of us? 😉

    Biodiesel refers to a non-petroleum-based diesel fuel consisting of short chain alkyl (methyl or ethyl) esters, made by transesterification of vegetable oil, which can be used (alone, or blended with conventional petrodiesel) in unmodified diesel-engine vehicles. Biodiesel is distinguished from the straight vegetable oil (SVO) (aka “waste vegetable oil”, “WVO”, “used vegetable oil”, “UVO”, “unwashed biodiesel”, “pure plant oil”, “PPO”) used (alone, or blended) as fuels in some converted diesel vehicles. “Biodiesel” is standardized as mono-alkyl ester and other kinds of diesel-grade fuels of biological origin are not included.

    Blends of biodiesel and conventional hydrocarbon-based diesel are products most commonly distributed for use in the retail diesel fuel marketplace. Much of the world uses a system known as the “B” factor to state the amount of biodiesel in any fuel mix: fuel containing 20% biodiesel is labeled B20, while pure biodiesel is referred to as B100. It is common to see B99, since 1% petrodiesel is sufficiently toxic to retard mold. Blends of 20 percent biodiesel with 80 percent petroleum diesel (B20) can generally be used in unmodified diesel engines. Biodiesel can also be used in its pure form (B100), but may require certain engine modifications to avoid maintenance and performance problems. Blending B100 with petro diesel may be accomplished by:

    * Mixing in tanks at manufacturing point prior to delivery to tanker truck
    * Splash mixing in the tanker truck (adding specific percentages of Biodiesel and Petro Diesel)
    * In-line mixing, two components arrive at tanker truck simultaneously.

    On August 31, 1937, G. Chavanne of the University of Brussels (Belgium) was granted a patent for a ‘Procedure for the transformation of vegetable oils for their uses as fuels’ (fr. ‘Procédé de Transformation d’Huiles Végétales en Vue de Leur Utilisation comme Carburants’) Belgian Patent 422,877. This patent described the alcoholysis (often referred to as transesterification) of vegetable oils using ethanol (and mentions methanol) in order to separate the fatty acids from the glycerol by replacing the glycerol with short linear alcohols. This appears to be the first account of the production of what is known as ‘biodiesel’ today.

    Hope this will help…

  5. Dr. Haddad says:

    Dear Sir/Madam:
    I really appreciate your valuable information. I am highly interested in the biodiesel process and its future development.

    Would you please send me your valuable data/information regularly?

    I wish you all the best.

    Dr. Haddad

  6. Shlomi says:

    Do you know if Castor oil can be a feadstock for Biodiesel?
    Can you send me a name of 1 refinery that actualy use castor oil on commercial base?


  7. Mike Cusack says:

    The chemistry involved is well explained here.

    Have found this a good learn…


  8. Very cool, I build biodiesel processors which turn waste vegetable oil into biodiesel. It is really amazing how simple the process is, as well as saving the customer $2-3 per gallon at the pumps. Algae biodiesel looks even more promising. I have been getting quite a large # of visitors from Brazil due to having my site in a few languages. Feel free to check it out.

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