Diesel is a fuel derived from crude oil extracted from the earth through drilling and pumping. The limited availability of petroleum reserves and resources, which are hydrocarbon deposits at subsurface geologic formations, has increased the need for renewable energy resources.1 Biodiesel is an alternative fuel similar to conventional or ‘fossil’ fuel.2 Although biodiesel production costs significantly more than fossil diesel, the latest technological advancements and government policies have reduced the cost price, which has invariably increased the applicability in the commercial market.
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What is Biodiesel and How Does it Differ From Petrodiesel?
Biofuel is defined as the monoalkyl esters of animal fats or vegetable oils.3 It is derived from biomass and is considered a 100% renewable resource. Although biodiesel is mainly produced from rapeseed, soybean, and palm oils, it has recently been produced from waste vegetable oil obtained from industrial food producers (e.g., Birdseye) and restaurants. The process through which these oils are converted to biodiesels is transesterification.4
Biodiesel differs structurally and chemically from petrodiesel. These differences lead to their variable physical properties. For example, biodiesel has greater lubricity than petrodiesel. The former contains no sulfur, which is essential because it produces less pollution upon combustion. The higher oxygen content of biodiesel also ensures lower pollution emissions.5
Why is Biodiesel a Highly Desirable Alternative Fuel?
The higher heating values (HHV) of biodiesels (39–41 MJ/kg) are comparable to their counterparts, i.e., coal (32–37 MJ/kg), petrodiesel (43 MJ/kg), gasoline (46 MJ/kg), and petroleum (42 MJ/kg).6 This makes biodiesel a potential alternative fuel in commercial markets worldwide.
Diesel emissions adversely affect human health, the global climate, and the environment.7 Exposure to diesel exhaust leads to many adverse health conditions, including asthma and other respiratory illnesses.
Biodiesel is regarded as better than petroleum diesel and gasoline because of its eco-friendly nature. For instance, biodiesel combustion entails lower greenhouse gas emissions, which can significantly help combat the rapid climate-changing crisis.8 Furthermore, it emits 10% less particulate matter and 11% less carbon monoxide than diesel.
Biodiesel is associated with a greater reduction in carbon footprint because the plants grown to produce the biomass used in the fuel are biodegradable and non-toxic.
It must also be noted that compared to petrodiesel, biodiesel is safer to transport, store, and clean in case of a spill due to its lower combustion point. Biodiesel provides greater lubricity, reducing engine parts' wear and significantly increasing the overall engine life. A study revealed that adding 1% biodiesel to petrodiesel improves lubricity considerably.
The Challenges and Strategies in Biodiesel Production and Use
The increased price of biodiesel over petrodiesel has been attributed to the high feedstock price, which accounts for approximately 80% of the total operating cost.
Scientists are currently focusing on expanding feedstock options and improving the sustainability of biodiesel as a viable energy source.9 Conventionally, soybean and rapeseed oil have been used as biodiesel feedstocks, which have recently been expanded to algae, non-food crops like jatropha and camelina, and waste cooking oil.
Several productional modifications and government policies have helped reduce biofuel application. For instance, biodiesel has been exempted from the oil tax. The agricultural sector has heavily subsidized the cultivation of non-food crops that could be used as feedstock.
The use of advanced catalysts (e.g., heterogeneous catalysts, solid acid catalysts, and enzyme catalysts,) in converting vegetable oils or animal fats into biodiesel via the transesterification process has proved to be beneficial in terms of improved reaction rates, biodiesel quality, and reduced energy consumption.
Besides the production cost, another challenge of biodiesel use is its tendency to thicken or become gel-like at low temperatures. It gets oxidized easily to form a semisolid gel-like mass. Therefore, for biodiesel storage, it is imperative to use semi-sealed, dry, and light-tight containers.
Scientists are also addressing the issue linked to variable biodiesel quality. The quality mainly varies during large-scale production, when controlling all parameters becomes challenging. A poor-quality biodiesel could adversely impact engine performance.
Applications of Biodiesels
The European Union (EU) produces 85% of biodiesel produced worldwide. In 2020, the EU produced approximately 20 billion liters of biofuel, which included 15 billion liters of biodiesel and 5 billion liters of bioethanol. The US and Germany are among the largest biodiesel consumers.10
Biodiesels can be used for many purposes, including energy generation, transportation, lubrication, heat production, and cooking. They are injected into fuel cells to produce electricity.11 This technique is ideal for producing power in backup systems that prevent the generation of smog, ozone, and sulfur emissions. In the UK, biofuel generates power for more than 350,000 homes.
Biodiesels are used in their pure form or blended and in many different concentrations.12 For instance, soybean biodiesel improved yield by 4.56 energy units for each unit of fossil energy consumed. Many car manufacturers, such as Volkswagen, have been dedicated to increasing the biodiesel compatibility of their vehicles.
Several biodiesel blends are available, including B5, which contains 5% biodiesel, and B20, which comprises 6% to 20% biodiesel. B100 is the purest biodiesel and is used as a blend sock. However, due to a lack of regulatory incentives and pricing, B100 is rarely used as a transportation fuel. All biodiesel blends enhance gas turbine performance while lowering carbon monoxide, carbon dioxide, nitrogen oxide, and hydrocarbons emissions under various operating conditions.
Japanese shipping major Mitsui O.S.K. Lines (MOL) has supported the production of a hydrogen and biofuel hybrid passenger ship named Hanaria. This ship was created at the Hongawara Ship Yard and has recently started service in Kitakyushu.
Hanaria can select propulsion energy from lithium-ion batteries, fuel cells, and biodiesel fuel. The company predicted that its ship could reduce greenhouse gas emissions by 53%-100% compared to conventional fossil-fueled vessels of the same class.
References and Further Reading
- Satter A, Iqbal G M. Conventional and unconventional petroleum reserves – definitions and world outlook. Reservoir Engineering. 2016; 427-438. https://doi.org/10.1016/B978-0-12-800219-3.00023-1
- Deora PS. et al. Biofuels: An alternative to conventional fuel and energy source. Materials Today: Proceedings. 2022; 48, 1178-1184. https://doi.org/10.1016/j.matpr.2021.08.227
- Rashid U. et al. Moringa oleifera oil: a possible source of biodiesel. Bioresour Technol. 2008;99(17):8175-8179. https://doi.org/10.1016/j.biortech.2008.03.066
- Sajjad N. et al. Biodiesel Production from Alkali-Catalyzed Transesterification of Tamarindus indica Seed Oil and Optimization of Process Conditions. Molecules. 2022;27(10):3230. https://doi.org/10.3390/molecules27103230
- Simbi I. et al., Chemical and quality performance of biodiesel and petrol blends. Energy Conversion and Management: X. 2022; 15, 100256. https://doi.org/10.1016/j.ecmx.2022.100256
- Zuorro A, García-Martínez JB, Barajas-Solano AF. The Application of Catalytic Processes on the Production of Algae-Based Biofuels: A Review. Catalysts. 2021; 11(1):22. https://doi.org/10.3390/catal11010022
- Steiner S. et al. Diesel exhaust: current knowledge of adverse effects and underlying cellular mechanisms. Arch Toxicol. 2016;90(7):1541-1553. https://doi.org/10.1007%2Fs00204-016-1736-5
- Jeswani HK, Chilvers A, Azapagic A. Environmental sustainability of biofuels: a review. Proc Math Phys Eng Sci. 2020;476(2243):20200351. https://doi.org/10.1098/rspa.2020.0351
- Rathore D. et al. Bioengineering to Accelerate Biodiesel Production for a Sustainable Biorefinery. Bioengineering (Basel). 2022;9(11):618. https://doi.org/10.3390/bioengineering9110618
- Ruth L. Bio or bust? The economic and ecological cost of biofuels. EMBO Rep. 2008;9(2):130-133. https://doi.org/10.1038%2Fsj.embor.2008.6
- Demirbas A. Importance of biodiesel as transportation fuel. Energy Policy. 2007; 35(9), 4661-4670. https://doi.org/10.1016/j.enpol.2007.04.003
- Bünger J. et al. Potential hazards associated with combustion of bio-derived versus petroleum-derived diesel fuel. Crit Rev Toxicol. 2012;42(9):732-750. https://doi.org/10.3109%2F10408444.2012.710194
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