3 Generations of Biofuels
Biofuels are defined as energy derived from biomass via processes such as combustion, gasification or fermentation (Demirbas 2007). Energy is then obtained in the form of liquid or gas fuels.
Biofuels can be divided into 3 generations of which the main differences will be their sources and how they are “manufactured”.
1st generation biofuels are obtained from starchy / or oilseed crops. Starchy crops grown includes sugarcane which accounts for around 65% of all bioethanol production like the PROALCOHOL project of Brazil. Other crops include barley, sorghum and rye. Conversion of these crops into biofuels can be done via the process of fermentation.
Oilseed crops include sunflower, rape seed, soybeans, palm and jatropha. The products from these crops can be converted into methyl esters or more commonly known as biodiesel via the process of transesterification.
This generation of biofuels is however limited by the availability of suitable land for growing these crops.
Other solutions that have been undertaken to solve this problem include the usage of other crop types like jatropha that can survive in poorer land and do not require much management, processing methods to convert cellulose into sugars for conversion into bioethanol.
Two advantages of being able to convert cellulose into sugars for bioethanol production is that plants with high cellulose content can generally survive on poorer land quality and that plant parts that cannot be consumed can be used.
2nd generation biofuels are derived from lignocellulosic materials as feedstock which include dedicated biofuel crops like perennial glasses like switchgrass, trees like poplar and willow and agricultural waste and residue (Pin Koh and Ghazoul 2008). This crops are suitable for lands not suitable for agriculture therefore there is a potential enhancement to biodiversity (Tilman et al 2006).
The cellulosic material derived from these crops can be broken down using methods like biochemical and thermochemical conversion. Biochemical conversion involves the breaking down of the plants’ hemicelluloses and cellulose content into sugar molecules and subsequently fermented to give bioethanol. The processes utilised to break down the cellulosic materials involved enzymatic breakdown or acid hydrolysis.
Thermochemical processes like the Fischer-Tropsch process where gasification of the biomass and subsequent liquefaction are being developed. The Fischer-Tropsch process represents the most efficient technology in 2nd generation biofuel production due to its more efficient energy usage among the other technologies.
This is represented by its capability in a more complete reduction of carbon to give liquid fuel. However this technology is currently not in use because of the high costs required to build and maintain the processing plants and refineries. Fossil fuels are also often required to initiate the gasification process therefore it might not be feasible after all.
For 3rd generation biofuels, the primary focus is on the improvement of feedstock. Some traits that are being analysed are the identification of the genome that control the production of oil or “oiliness” of the crop, development of tress with lower lignin content for cheaper and easier processing. Alternative sources for fuel production are also mooted of which include the usage of algae.
Usage of algae will provide the advantage of an aquatic feedstock that can be cultivated for producing triglycerides for producing biodiesel using similar technology as the 2nd generation biodiesels. The requirement for land will also eliminated and with it the potential for competition with agricultural land.
1. Demirbas A. Importance of biodiesel as transportation fuel. Energy Policy 35(9):4661-4670 (2007)
2. Koh LP and Ghazoul J. Biofuels, biodiversity, and people: understanding the conflicts and finding opportunities. Biological Conservation 141:2450-2460 (2008)
3. Tilman D, Reich PB and Knops JM. Biodiversity and ecosystem stability in a decade-long grassland experiment. Nature Letters 441:629-632 (2006)
4. Smith J. Biofuels and the globalisation of risk: The biggest change in North-South relationships since colonialism. 170pp. Zed Books (2010)
(Last Updated 26th April 2014)