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Biofuels Part I: Biodiesel Basics

Biofuels Part I: Biodiesel Basics

Some of my readers may be aware that in addition to writing Common Science for, I have occasionally been filling in for D.G. Martin on Who’s Talking. If you are not familiar with Who’s Talking, it’s on AM 1360 WCHL every Tuesday through Friday evening at 6:15 PM with a rebroadcast at 10:00 pm. You can also download episodes here. So check it out.

Last Friday I interviewed, Lyle Estill, founder of Piedmont Biofuels in Pittsboro. Piedmont Biofuels has been making biodiesel since 2002, first in small-scale co-op and then in a large-scale manufacturing plant.   Lyle got his start making biodiesel after deep frying a turkey and wanting to find a way to recycle the used cooking oil.  Piedmont also provides the anchor for an eco-industrial park in Pittsboro which is a nationally known sustainability project. You can listen to the show by following this link. As a companion to my interview with Lyle, this week’s Common Science begins a multi-part series on biofuels.
The first topic I am going to address is biodiesel. But first some background on the diesel engine. In both diesel and gasoline engines, a small amount of fuel is sprayed into a cylinder. Then the engine pushes a piston up into the cylinder to compress the fuel causing it to heat up. In a diesel engine you use fuels with flash points low enough such that the heat from the compression is sufficient to ignite them. Gasoline has a higher flash point than diesel fuels making it necessary to include a spark plug to ignite the compressed fuel.  The diesel or gasoline then explodes within the cylinder pushing the piston back down, which moves the driveshaft and turns the wheels of the vehicle.
Otto Diesel invited the diesel engine in 1893 in Germany, initially using peanut oil for fuel.  As we will discuss below, many vegetable oils can be used as diesel fuel, but they become too thick to use in cold weather. In the early 1900s it was discovered that a fraction of crude petroleum oil could be used in a diesel engine. Petroleum diesel is cheaper to obtain than vegetable oil and does not become too thick to use during cold winter days. Thus petroleum diesel has been the primary fuel for diesel engines ever since. 
Before I proceed to an explanation of how to make biodiesel, allow me a short chemistry lesson. On the left hand side of the graphic at the top of the page is the generic formula for a triglyceride. Triglyceride is the chemical name for fats and oils. The “R” in the formula is the symbol for a hydrocarbon chain. Different types of hydrocarbon chains result in different types of triglycerides. If the triglyceride is low enough in molecular weight to be a liquid at room temperature we call it an oil. If the molecular weight is higher, such that at room temperature it is a solid, we call it a fat. But chemically speaking fats and oils are the same. In the discussion below just remember that vegetable oil and triglyceride are synonyms.
Biodiesel begins its journey to your fuel tank as carbon dioxide. Chlorophyll containing plants capture the carbon dioxide and turn it into glucose some of which is further converted into triglycerides. 
Biodiesel is produced by reacting triglycerides with methanol to break them into four pieces as also shown in the graphic at the top of the page. The three fatty esters are the biodiesel and the glycerin is a byproduct which has a variety of non-fuel uses. Breaking vegetable oil into smaller pieces, the fatty esters, prevents it from becoming too thick to use on cold winter days.
When you burn biofuels in your engine you return approximately the same amount of carbon dioxide to the air that the plants removed to make the triglycerides. Petroleum-based fuels take carbon which has been sequestered underground for millennia and return it to the air, creating a net increase in carbon dioxide, which results in increased absorption of infrared radiation and, thus, higher global temperatures. 
I need to go on a short tangent here which will be important for upcoming parts of this series. When I started this blog, I had not intended to touch on evolution quite so frequently as I have.   First Governor Rick Perry cast some aspersions on Mr. Darwin that I needed to address in “It’s a Theory That’s Out There”. Then I did the series on the flu which required dealing with evolutionary biology (Part I, Part II, Part III, Part IV). Next I was inspired to write about the evolutionary implications of the striking similarity of chlorophyll and hemoglobin, in “Your Mother the Plant”. Well, your mother the plant also developed and passed on to almost every living thing the ability to covert glucose to triglycerides (fats and oils) as energy storage for use in lean times.   So when your next big holiday meal results in increased triglyceride storage around your waist, you know who to blame.  The fact that nearly all of “life” makes similar oils and fats will figure prominently in upcoming columns.
I covered a number of topics in this background piece, which I hope give you some perspective on biofuels and inspire curiosity about the rest of the series. The key items to which I will be referring back include:
  • nearly all living things make triglycerides (oils and fats) as a way to store energy,
  • biodiesel is made from triglycerides which have been broken into smaller pieces, and
  • burning biofuels does not result in a net increase of carbon dioxide in the air.
At first blush, biofuels seem almost perfect. But, alas, biofuels have several key draw backs and limitations. Check out upcoming segments in this series to learn how biofuels can cause food riots and why there will never be five billion cars running on biofuels.
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