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.
Biodiesel has been found to have significant environmental benefits in terms of reduced emissions, greater energy independence, decreased global warming impacts and a positive impact on agriculture.
It is low in sulfur, and has rapid biodegradability and high lubricity. Under specific conditions, used vegetable oils can be recycled as feedstock for producing biodiesel. This can in turn reduce the loss of used oils in the environment.
Biodiesel has much higher cetane rating than other lower sulfur diesel fuels. Biodiesel addition reduces wear of fuel system and increases the service life of the fuel injection equipment. However, variations in energy density of biodiesel are more dependent 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 is first removed as their presence causes the triglycerides to hydrolyze during 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 feedstock has high acid content, acid-catalyzed transesterification can be used to react fatty acids with alcohol to produce biodiesel and glycerin.
Other methods such as ultrasonic reactors, supercritical reactors and fixed-bed reactors are used forgo the use of chemical catalysts.
Once the product is obtained, 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 is 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 using sophisticated analytical equipment prior to the use as a commercial fuel.
Image Credit: Photos.com - Biodiesel produced from waste and vegetable oils.
Benefits of Biodiesel
Biodiesel has a number of beneficial properties. The main benefit of biodiesel is that it is 'carbon neutral'.
This effect occurs due to the fact that the oil crop absorbs the CO2 released during fuel combustion for its growth. Another feature of biodiesel is that it is biodegradable, which means it can decompose as the result of natural agents such as bacteria. Biodiesel degrades at a rate four times faster than conventional diesel fuel. As a result, the cleanup would be easier.
It also reduces the country’s dependence on imported oil thereby increasing energy security. It also contributes to the lubricity of an engine.
It acts as a solvent and loosens deposits or other junk present in the engine that could possibly 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 environment-friendly
- It is safer than conventional diesel
- It is non-toxic
- It has 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 for natural 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 stand-by power during the times of power shortage. In addition, 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 burning of biodiesel produces carbon dioxide emissions similar to that of ordinary fossil fuels, the plant feedstock used for the production absorbs carbon dioxide from the atmosphere when it grows.
It was estimated that biodiesel produced from used cooking oil or other waste fat could reduce 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.
As biodiesel becomes more widely used, it is necessary to consider the effects of biodiesel on water quality and aquatic ecosystems. However, research examining the biodegradability of biodiesel suggested that this fuel is readily biodegradable, and has a relatively high biodegradation rate in water.
In addition, the presence of biodiesel rather increases the rate of diesel biodegradation through co-metabolism.