Note: Updated June 3, 2010 with new information.

Biodiesel is one of those things that everyone has heard about, but about which many supposed facts and assumptions are wrong.  Myths and legends are popping up around the word “biodiesel” as the public’s awareness of it grows.  Most commercial drivers know that you can get biodiesel at a lot of truck stops nationally now and some companies allow or even promote their drivers to fuel with it.  Any driver who has fueled with it knows that, at the pump, it basically looks like diesel fuel.

So what, exactly, is biodiesel?

Biodiesel is biologically-based diesel fuel.  Instead of being made from petroleum, the diesel is made from biological organisms – usually plants.  The fuel labeled Biodiesel at the pump is probably not pure biodiesel, but is instead a mixture of biodiesel and petroleum-based diesel.

Most diesel engines cannot run on pure biodiesel without some modification, so the fuel at the pump will be labeled “B20″ or something similar.  B20 is 20% biologically-based, 80% petroleum-based diesel and additives.  B100 is pure (100%) biologically-based diesel.

What It’s Made From and How

Biodiesel is most often made from vegetable oils (lipids), but can also be made from animal fats (tallow).  Vegetable oils used are typically from soybeans, rapeseed, or other commonly-grown vegetables with a high oil content.  Other sources include algae, waste animal fats (chicken, pork, etc.), and even waste vegetable oils from cookeries and restaurants.

These oils will be put through a transestrification process, usually with alcohol and heat.  Vegetable oils and animal fats contain long fatty acid chains which must be broken and reformed.  Mixing with an alcohol (typically methyl, which is inexpensive) and then heated either directly, by microwave, or other means, the acid chains will be made into an ester, the type of which depends on the alcohol used.  Methyl produces Fatty Acid Methyl Ester (FAME).

Byproducts of the process include some free fatty acids which will often be converted to soaps for easy extraction and then re-esterified through an acid catalyst to become more biodiesel.  Other byproducts include crude glycerol, which can be sold for other industrial or fuel-making uses.  Purified glycerol is a base for propylene glycol and for epoxy resins.

The biodiesel produced is then ready for use in diesel combustion engines and can either be used straight or mixed with alcohols or petroleum diesel to form mixed biodiesel.

Yields Per Acre in Gallons by Source Stock

A hot mode of contention in the making of biodiesel is the amount of energy required to plant, grow, harvest, and process the base stocks used to make the fuel.  As with ethanol, biodiesel can be more energy intensive per gallon of output than it’s worth and can actually become more polluting than petroleum diesel fuel.  Unlike ethanol, however, biodiesel does not have as intensive a production process, so it is not as often an energy loser.

The following are common feedstocks for biodiesel bases and are the more common ones used on a large scale today.

• Palm: 508 gallons/acre
• Peanut: 90 gallons/acre
• Soy: 59.2-98.6 gallons/acre (depending on type grown)
• Sunflower: 82 gallons/acre
• Hemp: 26 gallons/acre

The burgeoning source for biodiesel is algae, whose production numbers vary widely by source.  Whatever number is correct, the range is far larger than most other stock sources for biodiesel production, ranging from 300 gallons/acre all the way up to 3,000.  Since algae can be grown in areas where food crops are normally not produced and because of its shorter growth period and faster renewal, as well as its relatively easy genetic manipulation properties, it is generally considered a better source for bio-fuels than most others.  Algae is, however, not yet in large-scale production for bio-fuel use, though several companies around the world are getting close.

Other considerations are the fuel used per acre to grow and harvest the crop.  The average farmer uses about 9 gallons of fuel per acre per crop yield (season).  Some crops require much less, such as algae and hemp.

Then the processing method to extract the oil must be considered, with algae, soybeans, and sunflowers coming out on top (in that order) while others are much more difficult to process (hemp chief amongst those).

Then, of course, regional and transportation issues come into play.  While one crop may produce more fuel per acre, if that fuel must be transported thousands of miles, then the game quickly becomes zero-sum.

The Future of Biodiesel

Biologically-based fuels will likely be around for some time to come and will play a role in our efforts to reduce our dependence on petroleum.  Biodiesel, like most biologically-based fuels, has the advantage of being able to be regionally-produced.

Unlike petroleum-based fuels, for which the oil must often be shipped vast distances and then processed at semi-regional plants into fuels, bio-fuels can be produced (grown) in the same area they will be used as fuels.  The soybeans grown in Indiana for fuel can be processed and put into the tanks of Indiana vehicles while the palms grown in southern California can be processed and put into California’s fuel tanks.  This eliminates much of the transportation network and energy use associated with petroleum-based fuels, thus eliminating much of the emissions they cause as well.

More and more research is being put into bio-fuels like biodiesel and commercial enterprises are getting into the game heavily.  Like any relatively new technology, it has its ups and downs, but as diesel engines get more efficient and biodiesel gets more prevalent, the two will work together to reduce emissions and, more importantly, dependence on foreign oil importation.

Related posts:

1. Hino Trucks Approves B20 Biodiesel