Biodiesel is a vegetable oil or animal fat-based diesel fuel consisting of long-chain alkyl esters. It is typically formed by the chemical reaction of lipids with alcohol that produce fatty acid esters.
It can be used in any blend with petroleum diesel fuel. Like petroleum diesel, it is used to fuel compression-ignition engines that operate on petroleum diesel. There has always been debate as to whether Biodiesel has significant environmental benefits in terms of reduced emissions, greater energy independence, decreased global warming impacts and a positive impact on agriculture. It seems that whether it is or not very much depends on where it comes from.
Biodiesel is low in sulfur but has a much higher cetane rating than other lower sulfur diesel fuels. The addition of Biodiesel reduces wear in fuel systems and increases the service life of the fuel injection equipment. However, variations in energy density of biodiesel depend more on the feedstock used.
Biodiesel Production Technologies
Biodiesel can be produced from waste oils, animal fats, or vegetable oil. Phospholipids and water from the feedstock used in biodiesel production are first removed as they cause the triglycerides to hydrolyze during the transesterification process.
The cleaned feedstock sample is titrated with a standardized base solution to determine the concentration of free fatty acids present in the vegetable oil sample. These acids are then esterified into biodiesel through three basic routes that include base-catalyzed transesterification of the oil, direct acid-catalyzed transesterification of the oil, and conversion of the oil to its fatty acids and then to biodiesel.
However, base-catalyzed transesterification is the most economical process that requires only low temperatures and pressures and produces a 98 % conversion yield.
If the feedstock has high acid content, acid-catalyzed transesterification can be used to react with fatty acids with alcohol to produce biodiesel and glycerin. Other methods such as ultrasonic reactors, supercritical reactors, and fixed-bed reactors that are used remove the need for chemical catalysts.
Now, the excess alcohol is removed through distillation or flash evaporation process. The glycerin by-product includes unused catalyst and soaps that are neutralized with an acid. In more sophisticated operations, glycerin can be distilled to high purity. After separating biodiesel from glycerin, the biodiesel is purified using warm water to remove residual catalyst or soaps, dried, and stored. The finished biodiesel is then analyzed before its use as a commercial fuel.
Biodiesel produced from waste and vegetable oils. Image Credit: Photos.com
Benefits of Biodiesel
Although recent studies have challenged the claim that biodiesel is carbon neutral, it is biodegradable, meaning it can decompose because of natural agents such as bacteria. Biodiesel degrades at a rate four times faster than conventional diesel fuel. Consequently, any cleanup would be easier.
Additionally, it reduces a country’s dependence on imported oil thereby increasing energy security. It also contributes to the lubricity of an engine and acts as a solvent loosening deposits or other junk present in the engine that could clog. As pure biodiesel does not leave any deposits, it results in increased engine life.
Biodiesel has several other key benefits that include the following:
- It is environmentally friendly if produced from waste oils or no food feedstock
- It is safer than conventional diesel
- It is non-toxic
- It has a higher flashpoint than conventional diesel.
The following are some of the major applications of biodiesel:
Vehicles – Biodiesel can be used to fuel on-road vehicles and also for off-road construction, farm machinery, and mining. It can also be used in hybrid electric vehicles.
Agriculture adjuvants - Biodiesel is used as a carrier for fertilizer and pesticides in agricultural sprays as it is biodegradable and non-toxic.
Boiler fuel – With the rising natural gas prices, biodiesel can be used as an alternative with minor modifications required for the burner train.
Lubricating agents/additives - Natural biodiesel can be used as a lubricity agent/enhancer in marine applications where contamination of water with petroleum lubricity agents can create problems. It can also be used as a lubricity additive due to its low sulfur level.
Fuel additive – It can be used as a diesel fuel additive to maintain the pumps, injectors, and other combustion components clean.
Power generation - Biodiesel generators provide essential standby power during the times of power shortage. Also, the increased lubricity of biodiesel generators has the potential to reduce engine deterioration.
Environmental Impacts of Biodiesel
Carbon dioxide is one of the major greenhouse gases. Although the burning of biodiesel produces carbon dioxide emissions similar to that of ordinary fossil fuels, the plant feedstock used for its production absorbs carbon dioxide from the atmosphere when it grows. Though there can be unintended consequences of turning over food-producing land to planting suitable for biodiesel.
It was estimated that biodiesel produced from used cooking oil or other waste fat reduces CO2 emissions by as much as 85 %. Moreover, biodiesel can reduce the direct emission of particulates, solid combustion products from vehicles with particulate filters by as much as 20 % when compared to low-sulfur diesel.
From the fuel vs food debate, algae have emerged as a promising feedstock for future biofuels due to its high energy content, energy yield per acre, fast growth, and ability to grow in water of varying quality. Algae’s theoretical potential is remarkable. According to the U.S. Department of Energy (DOE), algae may be able to produce 100 times more oil per acre than soybeans or any other terrestrial oil-producing crop. Because of its high energy content, oil from algae can be refined into biodiesel, green gasoline, jet fuel, or ethanol. Lastly, algae need only water, sunlight, and CO2 to grow. And, it grows rapidly.
This article was updated on 24th February, 2020.