Since the beginning of the 21st century, environmental pollution caused by the extensive use of fossil fuels has become a major challenge worldwide. Against the backdrop of global low-carbon emission reduction, biodiesel, with its many excellent properties such as renewability, is emerging as the new favorite in the international fuel industry.
What is Biodiesel?
Biodiesel refers to fatty acid methyl esters or ethyl esters formed by the esterification of vegetable oils (e.g., palm oil, rapeseed oil, soybean oil, cottonseed oil, etc.), animal fats (e.g., fish oil, lard, beef tallow, mutton tallow, etc.), waste oils and fats, or microbial oils with methanol or ethanol.
Known as green diesel, it is a typical green energy source. It boasts excellent environmental performance, good engine start-up performance, superior fuel properties, wide-ranging raw material sources and renewability. Its performance is very similar to that of conventional diesel, making it a high-quality alternative to fossil fuels.
First-generation biodiesel (BD) is produced from crude vegetable oils extracted from soybeans, rapeseeds, oil palms or sunflowers, as well as animal fats. It can be blended with diesel in small proportions and is industrially known as fatty acid methyl ester.
Second-generation biodiesel (RD), or renewable diesel, is made from waste oils and fats or animal fats. Its chemical composition is close to that of fossil diesel, featuring high calorific value and excellent quality. It can be blended with diesel in any ratio and can be directly added for use without modifying engines or components.
Currently, it has evolved to the third generation, which uses microbial oils as the raw material for synthesis.
Advantages of Biodiesel
Compared with traditional petroleum, It has low sulfur content, resulting in reduced emissions of sulfur dioxide and sulfide waste gas. It also has a biodegradability rate of up to 98%, with a hydrolysis rate twice that of conventional diesel. This can significantly reduce environmental pollution in the event of vehicle accidents and oil spills, demonstrating outstanding environmental friendliness.
Compared with fossil diesel, it has the following advantages:
1、Excellent Ignition Performance
The key indicator of diesel fuel, the cetane number, is relatively high for biodiesel – greater than 45 (fossil diesel has a cetane number of 45), giving it better anti-knock performance than fossil diesel.
2、More Complete Combustion
Biodiesel has a lower oxygen content than fossil diesel, averaging around 11%. It requires less oxygen during combustion, resulting in better combustion and ignition performance compared to fossil diesel.
3、Wide Applicability
In addition to being an alternative fuel for diesel engines in buses, trucks and other vehicles, it can also serve as a replacement fuel for non-road diesel engines used in marine transportation, water-borne power equipment, geological and mining machinery, and fuel-fired power plants.
4、High Compatibility
It can be directly added to diesel engines without any modifications. There is no need for additional refueling equipment, special storage and transportation facilities, or technical training for personnel – unlike many other alternative fuels that require engine modifications.
5、Safe and Reliable
It has a higher flash point than fossil diesel, making it less flammable and more conducive to safe storage and transportation.
6、Energy-Saving and Consumption-Reducing
As a fuel in its own right, blending biodiesel with fossil diesel in certain proportions can lower fuel consumption and improve engine power.
7、Good Climate Adaptability
Free of paraffin, biodiesel has excellent low-temperature fluidity, making it suitable for use in a wide range of regions.
8、Multi-functional
It can be used not only as a fuel but also as an additive to enhance combustion efficiency, thus serving a dual purpose.
9、Protects Power Equipment
Biodiesel has a slightly higher kinematic viscosity than diesel fuel. Without affecting fuel atomization, it can easily form an oil film on the inner walls of engine cylinders, improving the lubrication of moving parts and reducing wear and tear.
Microbial Production of Biodiesel
As a new type of renewable energy, it can be produced through various methods, including direct blending, mixing, microemulsification, high-temperature pyrolysis, transesterification, acid or base catalysis, bioenzymatic processes, engineered microalgae technology, and supercritical fluid technology.
Producing microbial oils via microbial fermentation not only provides cheaper and more widely available raw materials for biodiesel production but also leverages the advantages of microorganisms, such as rapid cell proliferation, short production cycles, abundant and low-cost raw materials for growth.
Moreover, some oleaginous microorganisms can convert pentose into oils – a feature particularly suitable for utilizing the hydrolyzed sugar solution derived from lignocellulosic renewable biomass resources. Therefore, the production of biodiesel using microbial oils will play an important role in the future biodiesel industry.
Known oleaginous microorganisms include bacteria, yeasts, molds, and microalgae, among which yeasts and molds are the most widely used.
1、Yeasts
Currently, the main oleaginous yeasts include Rhodotorula glutinis, Pichia caribbica, and Candida spp. Cultivating these yeasts on media containing various carbon and nitrogen sources yields oil-rich biomass. The oil content of yeasts ranges from 17% to 45%, with Candida spp. having the highest oil yield of up to 44.3%. These yeasts are highly adaptable to the environment, easy to cultivate, fast-reproducing, and widely applied.
2、Molds
Common oleaginous molds used for oil production include Penicillium pinophilum, Penicillium spp., Paecilomyces lilacinus, and Trichoderma spp. These filamentous fungi have high oil content, and their fatty acid composition is similar to that of vegetable oils, making them highly promising raw materials for biodiesel production. The oil content of molds typically ranges from 17% to 27%, with Penicillium pinophilum achieving the highest yield of 26.4%.
3、Microalgae
Major oleaginous microalgae include Chlorella spp., Scenedesmus quadricauda, and Scenedesmus obliquus.Chlorella cells are ellipsoidal or spherical, unicellular, and green in color.
Scenedesmus quadricauda consists of two or four ellipsoidal cells with four flagella on both sides, forming a symmetrical and green structure.
Scenedesmus obliquus has spindle-shaped cells arranged in a staggered, grid-like pattern, presenting a green appearance. Colonies are composed of 4–8 spindle-shaped cells, with the free surfaces of the two end cells being concave.
Thanks to their unique physiological advantages – such as short growth cycles, high photosynthetic efficiency, high oil productivity, CO2 fixation capacity, and the ability to thrive on wastewater – microalgae are widely regarded as the optimal raw material for biodiesel production in recent years.
Conclusion
With the continuous development of modern biotechnology and synthetic biology, research on energy microbial oils, guided by the concepts of biorefining and green chemistry, will continuously improve the overall technical and economic efficiency of the production process, ultimately providing reliable technologies for biodiesel manufacturing.
About Ferbio
Ferbio has extensive experience in the manufacturing of various types of bioreactors and pressure vessels. We boast a team of experts specializing in bioreaction, fermentation processes, mechanical manufacturing, and automated control. Our scientific research and technological capabilities are at the leading domestic level and world-class standard, delivering products that offer you comfort, reliability, and peace of mind.