National Alternative Fuels Training Consortium (NAFTC)

How is biodiesel produced?


Courtesy of Courtesy of National Alternative Fuels Training Consortium (NAFTC)

This article is the first in a series that will take a close look at alternative fuels production and source materials. Over the next several months, we will cover natural gas, propane, ethanol, hydrogen, and fuel cells.

This month, we will focus on biodiesel.

Methods for creating fuels from renewable biomass feedstocks have been used since the 1800s. Vegetable oils were used in diesel engines until the 1920s. At that time diesel engines were redesigned to use a low grade of petroleum that was much like heating oil- used today. A political and economic struggle between petroleum-based fuels and fuels created from biomass ensued. At the end of the struggle, petroleum products became the main fuel supply for the United States, while biofuels were forced into obscurity.

Early diesel engine. Source: NAFTC.

As the price of petroleum-based products rises in the United States, alternative fuels, such as biodiesel are being looked at with renewed interest.

+Note: Neither the Engine Manufacturers Association nor the National Renewable Energy Laboratory recommends the use of raw vegetable oil in modern diesel engines. +

Let’s take a look at some of the ways that biodiesel producers create the fuels for today’s vehicles.


Bio diesel is produced from the process called transesterification. During this process the triglycerides are separated from the glycerin molecules and combined with alcohol in the presence of the catalyst. The alcohol commonly used is methanol, while the catalyst is sodium hydroxide. To accomplish the process, plant oils are heated to a given temperature and then the alcohol and the catalyst are added. At this point the combined materials are mixed for a time and then allowed to settle. When the product settles, three layers develop. The top layer will become biodiesel. The middle layer will contain a soap compound, and the bottom layer will be glycerin. The bottom layer is drained off and the biodiesel is washed to remove any impurities and then dried to remove any remaining water. The middle layer is sometimes used in the cosmetics industry.

Algae Biodiesel Production

Algae can produce up to 300 times more oil per acre than conventional crops such as grapeseed, palms, soybeans or jetropha. Algae has a short harvesting cycle of only one to 10 days allowing it to permit several harvests in a short time. Algae can also be grown on land that is not suitable for other established crops; for instance arid land, land with excessively saline soil, and in drought stricken land. This minimizes the issue of taking away acres of land from cultivation of food crops.
There are three ways that algae can be grown: open pond method, covered pond method, and vertical enclosed method.
The open pond method is when water circulated around a shallow trench arrangement using paddlewheels to expose as much algae as possible to sunlight. Nutrients and carbon dioxide are constantly fed into this system, and algae containing water is harvested for biodiesel production.

Open pond method. Source: NREL.

Using a covered pond method the pond is enclosed within a greenhouse that offers greater productivity and safety. Contamination by wild algae is limited allowing a wider range of algae species to be grown. The amount of carbon dioxide can be increased and monitored safely.

The vertical enclosed method occurs where the algae is fully grown in a managed environment limited through connected vertical plastic sleeves with precise carbon dioxide and nutrient levels. Because there is little danger of contamination, specialized algae, producing lipids tailored to create a particular type of fuels, can be grown successfully. (For example fuels suited for plane use.)

Waste Vegetable Oil

While straight vegetable oil, waste vegetable oil, or synthetic fuels are not considered biodiesel and thus not suitable for engine use, residential or commercial waste vegetable oil are recyclable and suitable for biodiesel. Today there are many cities that set up recycling programs where waste oil can be collected and reused. Cooking oil, such as vegetable, corn, peanut, sunflower, canola, olive, soybean, flaxseed, or any edible cooking oil can be recycled and made into biodiesel.
Some states, like Georgia, have a curbside recycling company that hands out buckets to participants to fill up with unwanted oil and on a scheduled day the company comes to pick up the buckets. People who throw unwanted oil down drains and sewers are costing states thousands of dollars in cleanups and repairs to the sewer systems. By recycling the used oil it reduces landfill disposal, cleans up the sewer systems, and makes a usable alternative fuel – biodiesel.

Many biodiesel companies are happy to haul away oil used in restaurants or other food business industries. Haul away companies can even supply waste cooking oil bins for the supplier to use. Often the haul away is free of charge, and they may even pay the supplier for the donation. Participation in commercial oil recycling creates opportunities to earn money, cut waste, help the economy, and reduce air pollution.

Much of the wasted oil ends up in landfills, while some is used in the soap and cosmetics industry. Waste cooking oil could meet only a small percentage of total U.S. diesel demand. Yet by converting this waste into a low cost resource, it reduces the environmental degradation and cost of disposal in landfills.

Animal Fats

Different types of animal fats can be used to produce biodiesel. The most common types are tallow, lard, grease, and fish oil. Each product takes a special process that breaks it down, separates fats and turns them into biodiesel.

Tallow is a form of animal fat that is processed from marrow beef or other bovine facts. Tallow also has the ability to burn cleaner because of the higher cetane number. Yet there are some disadvantages of using tallow in biodiesel. One is that it tends to crystallize at much higher temperatures than biodiesel made from plants. Thus biodiesel made from tallow is not good to use in colder temperatures.

Lard can be used in production of biodiesel, yet some modifications are needed since lard solidifies at room temperature. A winterizing additive needs to be part of the production process. The winterizing additive makes winter-biodiesel and keeps the fuel from becoming thick and clumping in the engines. Biodiesel made from lard could be used in warmer climate areas because it will avoid thickening.

Brown Grease

Brown grease is grease collected from sewer systems, which are often contaminated with water, trash, wasted food, and other unwanted materials. Since the rise in feed stock prices, biodiesel producers are looking for lower-cost alternatives such as brown grease.

Anything flushed into the sewer system can contain brown grease. After the brown grease collection, it is run through a process that removes unwanted materials and then made into biodiesel.

Fish oil

Fish oil can be used to make clean burning biodiesel. There are some complications with using biodiesel made from fish oil. First it has a higher viscosity so it does not flow well in fuel systems. Secondly, straight and refined fish oils do not burn as cleanly as biodiesel. This is from impurities and will cause carbon buildup on fuel injectors and inside other parts of the engine. Lastly, there is yet to be any tax incentives in place that encourage the use of fish oil biodiesel as an alternative fuel for vehicles.

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