Types of Biofuels
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This page provides a brief overview of how different biofuels can be made from species of algae. To learn about the uses of each biofuel and how they vary from their fossil fuel alternative, have a look at the pop out table by clicking the link opposite:
Biodiesel
This type of biofuel is one of the most commonly mentioned types. It is a natural and renewable fuel alternative which can be used in its pure form or as a blend with regular diesel, without any modification to car engines.
Once the algae have been grown and harvested, the oil is extracted. The resulting product is a vegetable oil often referred to as 'green crude', similar to crude oil. The oil is then transformed through a process known as transesterification. During this process, the oil is mixed with an alcohol catalyst. The lipids in the oil, react with the alcohol to form pure biodiesel and a sugary alcohol compound - glycerol. The glycerol can also be sold as a valuable by-product.
To learn more about the process of transesterification, please follow this link:
Photo courtesy of CarMag blog
Bioethanol
Outside of Europe, bioethanol is the most commonly used biofuel. It can be used as petrol substitute however requires a modified engine if used as a mixture with over 15% bioethanol.
Once grown, algal biomass consists of three main components: lipids, carbohydrates and proteins. Unlike biodiesel, which utilises the lipids in the algal oil, bioethanol is made from left over carbohydrates. Once the lipids are removed and the algal biomass remains, the carbohydrates are converted into the useful sugars that make up bioethanol by a process known as fermentation.
Specific strains, which have a higher content of carbohydrates, may be grown specifically for bioethanol production. Biodiesel and bioethanol may also be produced from the same algae using their different components to yield different fuels.
Biohydrogen
Hydrogen (H2) is seen as a potential future fuel due to its high energy content and zero emissions. However, at present there is very little free hydrogen gas. It is therefore said to be an energy carrier, like electricity, and not a resource. The production of hydrogen normally carries high energy costs however biological methods have been shown to have significantly lower energy requirements in a closed photobioreactor.
Algal species are capable of directly producing biohydrogen through biochemical processes that occur in certain conditions. When algae is grown in conditions where there is no oxygen (anaerobic conditions), enzymes in their cells can split water molecules, releasing H2 gas. Currently hydrogen production from this method is not commercialy viable, however genetic modification of these processess have been shown to increase yields of hydrogen, providing potential for future biohydrogen production.
Photo courtesy of Oilgae.com
Biomethane
When burnt in a gas turbine or steam boiler, methane can be used for electricity generation as well as heating and cooking. It has a high energy content and lower CO2 emissions.
Methane can be produced from the biomass from algae in a closed bioreactor in a process known as anaerobic digestion.