Image Credit: Mut Hardman/Shutterstock.com
Biodiesel is a form of alternative transportation fuel manufactured from renewable sources such as new or used animal fats and vegetable oils. Biodiesel burns cleaner than traditional petroleum-based diesel fuel. Pure biodiesel and biodiesel blended with petroleum diesel can be used to fuel diesel vehicles and engines.
Biodiesel is composed of long-chain mono alkyl esters, fatty acid methyl esters, or fatty acid alkyl esters. It is biodegradable, nontoxic and yet has physical properties similar to petroleum diesel.
Biodiesel can be produced from new as well as used animal fats and vegetable oils. Animal fats and vegetable oils are chemically reacted with an alcohol such as methanol and consequently, a chemical compound called fatty acid methyl ester is produced.
A variety of esterification technologies can be used to produce biodiesel. Animal fats and vegetable oils are filtered and preprocessed to eliminate contaminants and water. Using special pretreatment technologies, any free fatty acids can be destroyed or transformed into biodiesel. The pretreated animal fats and vegetable oils are then mixed with an alcohol such as methanol and a catalyst such as sodium hydroxide. Triglycerides or the oil molecules are broken apart and reformed into glycerin and methyl esters. Glycerin and methyl esters are then separated and purified.
Known as “green solvents”, fatty acid methyl esters are environmentally friendly as they produce low volatile organic compounds (VOCs), are non-toxic to humans and are furthermore, biodegradable.
Schematic of biodiesel production path. Image Credit: Dept. of Energy
B5, B20 and B100 - Biodiesel Blends
B5 (up to 5% biodiesel) and B20, (a blend containing 6% to 20% biodiesel with the remaining petroleum diesel) are the most common blend of biodiesel available in the United States.
All diesel fuel in the U.S is permitted to contain up to 5% biofuel and still be within ASTM (American Society for Testing and Materials) legislation as safe to use in any compression-ignition engine operating on petroleum diesel. It is theoretically classified as standard diesel.
Engine modification is generally not required when using B20 and it can be used in nearly all diesel equipment. B20 is also compatible with most storage and distribution equipment. Likewise, for engines that contain selective catalytic reduction (SCR) systems, there is no difference in air quality whether the engine is running on biodiesel or petroleum diesel.
Pure biodiesel or B100 can be used in some engines manufactured after 1994 with parts such as hoses and gaskets produced from biodiesel-compatible materials. The use of pure biodiesel may be more suitable for professional fleets with a maintenance department.
However, higher-level biodiesel blends are less common as engine and equipment modification to the vehicle is usually required. Advice on the effects of running a vehicle on B100 is highly recommended, as particular contributory factors like wear on filters and hoses and because biodiesel can gel in cold weather, need to be considered.
Environmental Impact of Biodiesel
Biodiesel can be produced domestically. Using biodiesel increases energy security and decreases our reliance on foreign oil. Biodiesel is also nontoxic and causes less damage when spilled or released to the environment. Using biodiesel in conventional diesel engines dramatically decreases the amount of greenhouse gas emitted into the atmosphere. This is because the amount of carbon dioxide released during combustion is offset by the amount of carbon dioxide sequestered during the growth of the feedstock.
The number of pollutants such as particulate matter, polycyclic aromatic hydrocarbons, carbon monoxide, nitrated polycyclic aromatic hydrocarbons, and unburned hydrocarbons is also substantially reduced when biodiesel is used in conventional diesel engines.
However, there are alternative environmental arguments to consider. For instance, in some parts of the world, large areas of natural vegetation, forests, and farmland have been cleared and burned as farmers in countries like South America and Southeast Asia are incentivized to grow crops for biodiesel rather than food. Therefore, the negative environmental effects of this may be greater than any potential benefits.
Biofuels made from palm oil, rapeseed, and other food crops are destroying forests, pushing people off their land, and could fuel the next spike in food prices.
Marc-Olivier Herman, Campaigner, Oxfam.
As demand for crops to produce fuel increases, more fertilizer, and local water resources are used which can also have a significant effect on the environment. In turn, increased transportation of raw materials to produce the fuel may in some cases lead to greater greenhouse gas emissions.
Of all biodiesel, palm oil has the highest greenhouse gas emissions and in 2016/17, 51 percent of the palm oil used in Europe was pumped through the tanks of cars and trucks.
This article was updated on 24th February, 2020.