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Liquid Biofuels

Liquid Biofuels            

Fossil fuels, such as oil, natural gas, gasoline, diesel fuel and coal, come from organic matter that degraded and transformed over millions of years under high pressure and high temperature. As such, they are considered as a finite, depletable resource; hence the term “non-renewable” to qualify them.

Liquid biofuels are designed to be used as alternatives to some of these non-renewable fossil fuels.

Biofuels are renewable transportation fuels made from recently living organic materials called “biomass”, such as agricultural crops, forest residue, algae, plant material and animal waste. The two most common types of biofuels in use today are bioethanol and biodiesel. (Sources : and

The video below illustrates the production processs of liquid biofuels.

Types/Generations of Biofuels

As they unfolded, biofuel’s research and development have led to three different generations of biofuel. Each generation has a unique feedstock and its own potential benefits, drawbacks and its own technology progress. (source:

First generation Biofuels

Referred to as conventional biofuels, first generation biofuels are made from sugar, starch, corn, soy, sugar cane or vegetable oil. These biofuels are made through fermentation or chemical processes that convert the oils, sugars, and starches in the biomass into liquid fuels (source:

First generation biofuels are produced through well-understood and well-established technologies and processes, like fermentation, distillation and trans-esterification that have been used for hundreds of years.

The main downside of 1st generation biofuels is that they are made out of biomass that is food source. Consequently, their production interferes with the food supply chain which is considered problematic when there is not enough food for all.

The table below gives information about some 1st generation biofuels (sources: & Biogas is also included in this table.


Biofuel made from the fermentation of plant starches and sugars. It is used as a blending agent with gasoline to reduce GHG emissions.


Biofuel made from vegetable oils (soybean, palm, canola, rapeseed) and animal fats via a process called transesterification. It is used as a replacement of petroleum diesel in various diesel engines or as a blending agent.


Biofuel produced by the breakdown of organic matter such as food scraps and animal waste. It is used as vehicle fuel and for heating and electricity generation purposes.

The following figure shows how 1st generation Biofuels are made (source: refuelingthefuture.yolasite).

Second generation Biofuels

Referred to as next generation biofuels, Second-generation biofuels are made from non-food biomass, such as perennial grass, wood, organic waste, food waste and fast-growing trees. The technologies used to produce this type of biofuels are more complex. They are less mature and less well established compared to those for first-generation biofuels. The processses often involve converting fibrous non-edible material called “cellulose” into fuel. These technologies include thermochemical and biochemical conversion processes (source:

The main downside of the 2nd generation biofuels is that despite being produced from non-food biomass, they still compete with the food production over land use.

The following figure shows how 2nd generation biofuels are made (source: refuelingthefuture.yolasite).

The table below shows some information about 2nd generation biofuels.

Cellulosic ethanol

This 2nd generation bioethanol is called cellulosic ethanol. It is produced by fermenting the sugar molecules of cellulose. It is made out of vegetation that is unsuitable for human consumption such as wood, grass or none edible plant parts.


This 2nd generation biodiesel is called HVO (Hydrotreated Vegetable Oil), and is based on advanced raw materials such as residues and waste.


This 2nd generation biofuel is produced from biogas that is derived from organic matter such as human waste/sewage, food waste, distillery waste or agricultural materials. It is made using biogas upgrader that removes carbon dioxide from biogas. 

Third generation Biofuels

Third generation biofuels are made out of specially engineered crops, mainly algae as the energy source. These algae are grown and harvested to extract oil within them. This oil can then be converted into biodiesel through a process similar to the one used to produce 1st generation biofuels. The oil can be also refined into other fuels, which in turn can be used as replacements to petroleum-based fuels through genetic manipulations. This gives great potential to this category of biofuels (source:

The following figure shows the main steps of 3rd generation biofuels making (source:

Main processing steps of 3rd generation biofuels production

Because they do not compete with food sources, third generation biofuels are considered to be the best biosource fuel alternative. Because their production avoids the disadvantages of first and second generation biofuels, they can be considered as a better energy source, and more “renewable”.

Algae are also advantageous because they can grow using sewage, wastewater, and saltwater. However, the technologies used for producing third generation biofuels are still immature and not as well developed as 1st generation biofuels (source:

Different types of fuels can be derived from algae (source:, such as: Biodiesel, Butanol, Gasoline, Methane, Ethanol,Vegetable Oil and Jet Fuel.

The following figure (source: shows the global production levels of biofuels in 2019.

: Global production levels of biofuels in 2019 (logarithmic scale), based on data in REN21, GSR, 2020
Contribution of Biofuels to decarbonization

The current use of petroleum fuels for the transportation sector threatens energy security, affects environment, and weakens the economy. Thus, developing technologies to produce and use biofuels represents a promising alternative for transportation fuel solutions that can positively impact these issues. It will help achieve energy transition goals, facing climate change issues and reducing GHG emissions (source:

The following figure shows the forecasted contribution of biofuels in the transport sector by 2030 in the International Energy Agency 2°C scenario (source:

Role of biofuels in transport – IEA 2DS Scenario

The figure below shows the cumulative reduction of some biofuels and other alternatives.

Cumulative CO2 Reductions (million tons). Source: California Energy Commission, Low Carbon Fuel Standard Dashboard

Different senarios about the contribution of biofuels in the climate change policy have been established by various institutions, but the current rates of deployment as represented by the IEA’s forecasts from now to 2024, indicate that in fact the growth in bioenergy in the transport sector is likely to be around half of that projected even in the NPS scenario, emphasizing the need for an urgent effort to step up policy efforts in the biofuels sector (source:

According to an Energy Strategy Reviews article about advanced biofuels in decarbonizing Europian transport by 2030, the ongoing policy mechanisms did set up goals and monitoring frameworks for low carbon fuels and improved car engine performance but have not yet been adequate to facilitate the market uptake of advanced biofuels. In order for the 2030 targets to be achieved, their efficient market roll-out must be immediate.