It is very easy to discuss biofuel as a relatively homogenous group of largely compatible fuels, in part because the end product is designed to be as compatible with existing engines as possible.
Whilst the stated target is to be compatible with any car made after 1999, Bentley developed a drop-in biofuel that was compatible with essentially any car made in the 20th century, even one made in 1920, highlighting the huge potential biofuel has for fields that cannot go electric.
However, biofuels are often very different, in terms of raw materials, production and storage needs, which often require pressure relief valves compatible with the fermentation process.
Typically, they can be grouped by generations, which chronicle a transition away from biofuels derived from food sources towards more sustainable, hypothetical sources of fuel.
To understand why, it is important to explain what biofuel generations are, and perhaps more importantly, what they are not.
What Are Biofuel Generations?
Biofuels are often characterised in terms of generations, which relate to the different types of feedstock and technologies used to process and produce fuel.
Generally, earlier generations rely heavily on plants (particularly food crops) to produce fuel, whilst later generations rely on increasingly synthetic and lab-grown means.
It should be noted that generations are not necessarily linear; some fourth-generation fuels existed alongside first-generation fuels.
As well as this, not all later generations of biofuel are necessarily more environmentally friendly than others; some early e-fuels required so much power that came from fossil fuels that it could be worse for the environment than simply using petrol.
First Generation – Food Crops
The earliest, simplest and most cost-effective in terms of yield relied on food crops and one of two main processes to produce either bioethanol or biodiesel.
Bioethanol was produced through a process of fermentation, which created an alcoholic substance from the sugars that could be burned as a fuel.
It is a process not dissimilar to the process used to produce many alcoholic spirits, with the resulting ethanol blended with additives to make it more suitable for use in engines before it is added to existing petrol supplies in specific blend ratios.
By contrast, biodiesel is produced through fats and oils, which in the case of first-generation biodiesel would primarily consist of vegetable oil.
This oil undergoes a process known as transesterification, which produces a less viscous mixture that can be used for fuel alongside glycerine as a side product. It then has additives added before being blended into conventional diesel mixes.
Biofuels are typically easier to make and require less energy to produce than fossil fuels, but the huge problem is just how reliant they are on food crops or arable land that could otherwise be used to produce food crops.
This can potentially cause food security issues, as well as deforestation and the destruction of natural peatland to clear land for palm oil and sugarcane, which can have long-term climate implications.
Second Generation – Inedible Biomass
Much of the research into biofuels at this point is focused on developing processes that allow waste byproducts and inedible plants to be used to produce biofuel instead.
Because of how broad the remit is, the technologies used to produce said biofuels can vary dramatically, from using similar transesterification processes to convert waste fats and oils into fuel, to more elaborate enzyme-based systems to break down the cellulose walls that make plants so strong.
In other cases still, feedstock is heated to produce oils or gases that are cooled to produce fuels.
They avoid the food security issues directly caused by first-generation biofuels, but the increased challenge to process them makes them more expensive, whilst not always fixing the issues with land use.
Third Generation – Aquatic Biomass
At one point, third-generation algae and seaweed-based biofuels were seen as the future of fuel, and it is not difficult to see why.
Algae grows significantly faster than plants grown on land, is high in lipids perfectly suited for processing into oil and thus fuel, whilst not competing with crops for land.
However, the nutrient and especially the water needs have cooled a lot of the enthusiasm surrounding third-generation biofuels, with high production costs causing many major investors to pull funding.
Fourth Generation – Synthetic High-Yield Biofuels
The fourth generation of biofuels is complex and somewhat contentious, given that so many fuels that are grouped in this category are not biological fuels as such.
There are generally two main types of fourth-generation biofuels: fuels produced from genetically modified sources, and outright synthetic electrofuels.
The former involves the use of algae, yeast or bacterial cultures designed to produce fuel directly from photosynthetic processes, whilst the latter typically manually combines captured carbon dioxide with hydrogen to create hydrocarbons, the building blocks of fuels.
The positives of the process are that it can be used to make drop-in fuels that can be used without the need for blending, but they are often highly energy-intensive to produce.
