 |
|
| |
Biodiesel is defined as the mono-alkyl esters of fatty acids derived from vegetable oils or animal fats. We'll talk more about what that means later. In simple terms, biodiesel is the product you get when a vegetable oil or animal fat is chemically reacted with an alcohol to produce a new compound that is known as a fatty acid alkyl ester. A catalyst such as sodium or potassium hydroxide is required. Glycerol is produced as a byproduct. The approximate proportions of the reaction are:
100 lbs of oil + 10 lbs of methanol  100 lbs of biodiesel + 10 lbs of glycerol
Soybean oil and methanol are the most popular feedstocks in the United States. Soybeans are a major U.S. crop and government subsidies are available to make the fuel economically attractive to consumers who need or want to use a nonpetroleum-based fuel. Biodiesel from soybeans is sometimes called soydiesel, methyl soyate, or soy methyl esters (SME). In Europe, most biodiesel is made from rapeseed oil and methanol and it is known as rapeseed methyl esters (RME). The University of Idaho has done considerable work with rapeseed esters using ethanol, which produces rapeseed ethyl esters (REE).
Biodiesel can also be made from other feed stocks:
- Other vegetable oils such as corn oil, canola (an edible variety of rapeseed) oil, cottonseed oil, mustard oil, palm oil, etc.
- Restaurant waste oils such as frying oils
- Animal fats such as beef tallow or pork lard
- Trap grease (from restaurant grease traps), float grease (from waste water treatment plants), etc.
Using the rough guideline that a pound of oil or fat will give a pound of biodiesel, we can use the total production of fats and oils in the United States to estimate the impact of biodiesel on total diesel consumption. The table below shows the annual production figures for vegetable oils and animal fats.
Table 1. Total Annual Production of US Fats and Oils.
[from Pearl, G.G., "Animal Fat Potential for Bioenergy Use," Bioenergy 2002, The Tenth Biennial Bioenergy Conference, Boise, ID, Sept. 22-26, 2002.]
|
Vegetable Oil Production (Billion pounds/yr)
|
| Soybean
|
18.340
|
| Peanuts
|
0.220
|
| Sunflower
|
1.000
|
| Cottonseed
|
1.010
|
| Corn
|
2.420
|
| Others
|
0.669
|
| Total Veg. Oil |
23.659 |
| Animal Fats (Billion pounds/yr)
|
| Edible Tallow
|
1.625
|
| Inedible tallow
|
3.859
|
| Lard & Grease
|
1.306
|
| Yellow Grease
|
2.633
|
| Poultry Fat
|
2.215
|
| Total Animal Fat |
11.638
|
As can be seen, in the United States, soybean oil dominates the vegetable oil market comprising over 75% of the total vegetable oil volume. Animal fats total almost 50% of the of the vegetable oil market. The combined vegetable oil and animal fat production of 35.3 billion pounds per year. At about 7.6 pounds per gallon of oil, this production would equal 4.64 billion gallons of biodiesel. Table 2, shown below, provides the total consumption of on-highway diesel fuel from 1996 to 2000.
Table 2. Sales of On-highway diesel fuel: [Energy Information Administration,
www.eia.doe.gov]
|
On-highway Diesel (billion gallons)
|
| 1996
|
26.96
|
| 1997
|
28.61
|
| 1998
|
30.15
|
| 1999
|
32.06
|
| 2000 |
33.13 |
It is obvious that biodiesel is not going to completely replace petroleum-based diesel fuel in the near future. If all of the vegetable oil and animal fat were used to produce biodiesel, we could only replace about 15% of the current demand for on-highway diesel fuel. So, why bother with biodiesel?
There are five primary reasons for encouraging the development of biodiesel in the United States.
1. It provides a market for excess production of vegetable oils and animal fats. There is increasing demand around the world for soybean meal to provide the protein for human and animal consumption. If new markets are not found for the soybean oil, then the price will be low and farmers will have even more difficulty producing a profit. The animal by-products industry also has a problem with more supply than the current market can absorb. This is compounded by the potential for even greater restrictions on the use of animal fats in animal feeds because of concerns about the spread of
BSE (Bovine
Spongiform Encephalopathy - Mad Cow Disease).
2. It decreases the country's dependence on imported petroleum. Obviously, this reason should not be overemphasized since the percentage of the country's fuel supply that can be replaced with biodiesel will be small. However, petroleum markets tend to be sensitive to small fluctuations in supply so an additional source of fuel can have a surprising impact on keeping fuel prices stable.
3. Biodiesel is renewable and contributes less to global warming than fossil
fuels due to its closed carbon cycle. Because the primary feedstock for biodiesel is a biologically-based oil or fat, which can be grown season after season, biodiesel is renewable. And, since
most of the carbon in the fuel was originally removed from the air by plants, there is
very little net increase in carbon dioxide levels. However, some fossil carbon is contained in the
methanol used to make methyl esters, and some fossil fuel is used during the production
process. A life cycle study on biodiesl use in an urban bus conducted by the National Renewable
Energy Laboratory [1] found that CO2 emissions were reduced by 79% for pure biodiesel
compared with petroleum diesel fuel. Again, this reason should not be overemphasized because biodiesel does not have the potential to make a major impact on the total carbon dioxide production.
4. The exhaust emissions from biodiesel are lower than with regular diesel fuel. Biodiesel provides substantial reductions in carbon monoxide, unburned hydrocarbons, and particulate emissions from diesel engines. While the carbon monoxide and unburned hydrocarbons from diesels are already very low compared with gasoline engines, biodiesel reduces them further. Particulate emissions, especially the black soot portion, are greatly reduced with biodiesel. Unfortunately, most emissions tests have shown a slight
increase in oxides of nitrogen (NOx) emissions with biodiesel. This increase in NOx can be eliminated with a small adjustment to the engine's injection timing while still retaining a particulate decrease.
5. Biodiesel has excellent lubricating properties. Even when added to regular diesel fuel in an amount equal to 1-2%, it can convert fuel with poor lubricating properties, such as modern ultra-low-sulfur diesel fuel, into an acceptable fuel.
Reference: Sheehan, J., V. Camobreco, J.
Duffield, M. Graboski, and H. Shapouri, Life
Cycle Inventory of Biodiesel and Petroleum
Diesel for Use in an Urban Bus," Report from the
National Renewable Energy Laboratory for the
U.S. Department of Energy's Office of Fuels
Development and for the U.S. Department of
Agriculture's Office of Energy, NREL/SR-580-24089,
May 1998.
These five reasons are the primary reasons for the growth in interest in biodiesel.
- Blends of biodiesel and diesel fuel: Biodiesel is often mixed with petroleum-based diesel fuel. When 20% biodiesel is blended with 80% diesel fuel, this blend is known as B20. Some people mistakenly believe this blend is biodiesel.
- Raw oils: Raw oils can cause durability problems when used in engines.
For more information on using raw oils in engine,
|
|
|