What is Biodiesel?

Biodiesel is a renewable and environmentally friendly alternative to traditional diesel fuel, typically derived from renewable resources such as vegetable oils, animal fats, or recycled cooking oils. It is produced through a chemical process called transesterification, where these feedstocks are reacted with an alcohol (usually methanol or ethanol) and a catalyst to break down their complex molecules into biodiesel and glycerin.

Biodiesel can be blended with conventional diesel fuel in varying ratios, such as B20 (20% biodiesel and 80% diesel) or B100 (pure biodiesel). It has several advantages, including reduced greenhouse gas emissions, as it typically emits fewer pollutants and particulates than conventional diesel. It’s biodegradable, non-toxic, and can be used in existing diesel engines without major modifications.

However, the production of biodiesel can sometimes compete with food production if it’s made from edible oils, which can lead to ethical and sustainability concerns. Additionally, its performance may vary depending on factors like feedstock type and the production process. Nonetheless, biodiesel remains a significant step towards reducing the environmental impact of transportation fuels and achieving greater energy sustainability.

How is biodiesel produced?

Feedstock Preparation

The first step involves obtaining and preparing the feedstock, which can be vegetable oils (e.g., soybean oil, canola oil, palm oil), animal fats (e.g., tallow, lard), or used cooking oils. These materials need to be filtered to remove impurities and moisture, which can interfere with the transesterification reaction.

Pre-Treatment

Some feedstocks might require pre-treatment to remove additional impurities, such as water, free fatty acids, and residual contaminants. This step ensures that the feedstock is suitable for the transesterification process.

Transesterification Reaction

In this step, the feedstock is mixed with an alcohol (methanol or ethanol) and a catalyst (usually sodium or potassium hydroxide) to initiate the transesterification reaction. The catalyst helps break down the triglyceride molecules in the fat or oil into fatty acid methyl or ethyl esters (the biodiesel) and glycerin.

The chemical reaction can be represented as follows for a vegetable oil (such as soybean oil) with methanol:

Triglyceride + Methanol → Biodiesel + Glycerin

Separation

After the transesterification reaction is complete, the mixture is allowed to settle. The glycerin, which is denser, separates and sinks to the bottom, while the lighter biodiesel floats on top. The glycerin can be further processed for other uses.

Washing & Neutralization

The biodiesel is then washed to remove any residual impurities, such as soap, catalyst, and excess alcohol. This step helps improve the quality and stability of the biodiesel.

Drying

The washed biodiesel is dried to remove any remaining water content. Water can cause issues during storage and combustion.

Quality Control

The final biodiesel product undergoes quality testing to ensure it meets industry standards and specifications. This includes checking for properties such as viscosity, density, flash point, and other characteristics.

Blending

Biodiesel can be blended with regular diesel fuel in various ratios, such as B20 (20% biodiesel and 80% diesel) or B100 (pure biodiesel). Blending biodiesel with conventional diesel allows for easier use in existing diesel engines.

How is biodiesel used?

Biodiesel can be blended and used in many different concentrations. The most common are:

B100

Pure Biodiesel

B100 (Pure Biodiesel)

B100 and other high-level biodiesel blends are less common than B20 and lower blends due to a lack of regulatory incentives and pricing. B100 can be used in some engines built since 1994 with biodiesel-compatible material for certain parts, such as hoses and gaskets. B100 has a solvent effect, and it can clean a vehicle’s fuel system and release deposits accumulated from petroleum diesel use. The release of these deposits may initially clog filters and require frequent filter replacement in the first few tanks of high-level blends.

B20

20% Biodiesel, 80% Petroleum Diesel

B20 (20% Biodiesel, 80% Petroleum Diesel)

B20 is the most common biodiesel blend in the United States. B20 is popular because it represents a good balance of cost, emissions, cold-weather performance, materials compatibility, and ability to act as a solvent. Most biodiesel users purchase B20 or lower blends from their normal fuel distributors or from biodiesel marketers. Regulated fleets that use biodiesel blends of 20% (B20) or higher qualify for biodiesel fuel use credits under the Energy Policy Act of 1992.

B5

5% Biodiesel, 95% Petroleum Diesel

B5 (5% Biodiesel, 95% Petroleum Diesel)

Low-level biodiesel blends, such as B5 are ASTM approved for safe operation in any compression-ignition engine designed to be operated on petroleum diesel. This can include light-duty and heavy-duty diesel cars and trucks, tractors, boats, and electrical generators.

B2

2% Biodiesel, 98% Petroleum Diesel

B2 (2% Biodiesel, 98% Petroleum Diesel)

Blends like B2 and B5 are popular fuels in the trucking industry because biodiesel has excellent lubricating properties, so usage of the blends can benefit engine performance.

Biodiesel's Benefits

Biodiesel growth boosts the U.S. economy by creating jobs and reducing our dependence on global oil markets and vulnerability to price spikes. There are currently about 200 biodiesel plants across the country – from Washington state to Iowa to North Carolina – with registered capacity to produce some 3 billion gallons of fuel. The industry is supporting more than 62,000 jobs, generating billions of dollars in GDP, household income, and tax revenues. The industry’s economic impact is poised to grow significantly with increased production. The initiative supports jobs in various sectors, from manufacturing to transportation, agriculture, and service.

The EPA has recognized biodiesel’s environmental benefits by classifying it as an Advanced Biofuel, making biodiesel the only commercial-scale U.S. fuel produced nationwide to meet the agency’s advanced criteria. According to the EPA, biodiesel reduces greenhouse gas emissions by at least 57 percent and up to 86 percent compared to petroleum diesel – making it one of the most practical and cost-effective ways to address climate change immediately. In addition, biodiesel sharply reduces major tailpipe pollutants from petroleum diesel, particularly from older diesel vehicles. This is important because the EPA has consistently cited diesel exhaust – primarily from older trucks, buses, and other vehicles – as one of the nation’s most dangerous pollutants.

Biodiesel's Emissions Reductions

IndicatorData
Particulate Matter (PM)12% Reduction with B20, 48% Reduction with B100
Carbon Monoxide (CO)12% Reduction with B20, 48% Reduction with B100
Carbon Dioxide (CO2)16% Reduction with B20, 78% Reduction with B100 (Life-Cycle Reduction)
Hydrocarbons (VOCs)20% Reduction with B20, 68% Reduction with B100
Sulfur Dioxide (SOx)20% Reduction with B20, 100% Reduction with B100

Biodiesel In Action

Tennessee Fleets Using Biodiesel

Averitt Express
City of Crossville
City of Sevierville
Eastman Chemical Company
Knoxville Utilities Board
Metropolitan Government of Nashville & Davidson County
National Park Service (Great Smoky Mountains NP)
Performance Food Group
Sullens Transportation
Tennessee Department of Transportation

Different Blends Used by Tennessee Fleets

B5, B20, and B99

Best Resources for Learning More

Alternative Fuels Data Center (US Dept. of Energy)

Iowa Renewable Fuels Association

The National Biodiesel Board