Biodiesel Basics
by Nestor U. Soriano, Jr.What is Biodiesel?
The American Society of Testing and Materials (ASTM) defines biodiesel as "a fuel comprised of mono-alkyl esters of long chain fatty acids derived from vegetable oils oranimal fats, designated B100." Biodiesel is an environmentally friendly alternative to petroleum based diesel fuel. While biodiesel can be used directly in diesel engines without modifications, it is normally blended with petroleum- based diesel fuel (biodiesel blends) to avoid some operational problems associated with the use of neat (100%) biodiesel.How is Biodiesel Made?
Biodiesel is typically produced through a process called transesterification. It involves reacting the vegetable oil or animal fat with an alcohol, normally methanol, in the presence of a catalyst to give the monoalkyl esters of long chain fatty acids and glycerol as by product. Because the glycerol moiety is liberated from the triglyceride molecules through transesterification, biodiesel exhibits viscosity that is about ten times lower than the original vegetable oil or animal fat.
The transesterification process
What are the Benefits of Using Biodiesel?
- Environmental Benefits:
- Reduced emissions: The emissions from neat biodiesel contains 67% less total unburned hydrocarbons, 48% less carbon monoxide, and 47% less particulate matter than conventional diesel.
- Renewability: The biodiesel’s life cycle yields 3.2 units of fuel product per unit of fossil energy consumed as opposed to only 0.83 units for conventional diesel fuel.
- Non-Toxic: Studies conducted by the USDA confirm that biodiesel is ten times less toxic than table salt.
- Biodegradable: The USDA also confirms that biodiesel biologicallydegrades in the environment as fast as dextrose(a form of sugar).
- Operational Benefits:
- Longer Engine Life: Even biodiesel levels as low as 1% can provide up to a 65% increase in the lubricity in distillate fuels, leading to lower wear and tear on engine parts.
- Higher Cetane Number: Biodiesel shows similar fuel consumption, horsepower, torque, and haulage rates as conventional diesel fuel.
- Economic Benefits:
- Promotes domestic agriculture: If the projected 498 million gallons of biodiesel production from 2006 to 2015 is realized, soybean prices will increase nearly 10% by 2015.
- Less Dependence on Imported Oil: The growing biodiesel industry will spare the US from importing 242 million barrels of crude oil between 2006 and 2015, equivalent to $13.6 billion of oil imports.
Biodiesel Production in the United States
There are presently 148 companies that have invested millions of dollars into the development of biodiesel manufacturing plants and are actively marketing biodiesel. The annual production capacity from these plants is 1.39 billion gallons per year.Ninety-six companies have reported that their plants are currently under construction and are scheduled to be completed within the next 18 months. An additional five plants are expanding their existing operations. Their combined capacity, if realized, would result in another 1.89 billion gallons per year of biodiesel production.
Feedstock for Biodiesel Production
The fuel properties of biodiesel vary depending on the vegetable oil starting material. The fatty acid composition of the starting vegetable oil dictates the fuel properties of biodiesel. The most common feeds tocks for biodiesel production include soybean oil in the US, rapeseed oil and sunflower seed oil in Europe, and palm oil and coconut oil in Southeast Asia. While the presence of unsaturation (carbon-carbon double bonds) in biodiesel molecules improves its low-temperature properties, unsaturation also makes biodiesel more susceptible to oxidative degradation. Hence, the presence of saturated components in biodiesel is also desirable to achieved certain level of oxidative stability.Typical fatty acid profile of different vegetable oil commonly used for biodiesel production:
| Oil | Saturated | Mono unsat. | Poly Unsat. |
|||||
| C10:0 | C12:0 | C14:0 | C16:0 | C18:0 | C18:1 | C18:2 | C18:3 | |
| Soybean | 11 | 4 | 24 | 54 | 7 | |||
| Sunflower | 7 | 5 | 19 | 68 | 1 | |||
| Rapeseed | 3 | 1 | 64 | 22 | 8 | |||
| Palm | 1 | 45 | 4 | 40 | 10 | |||
| Coconut | 6 | 47 | 18 | 9 | 3 | 6 | 2 | |
| Beef tallow | 3 | 24 | 19 | 43 | 3 | 1 | ||