What is Biodiesel?

Throughout history, the search for sources of energy has been one of humanity’s priorities. Being expected to run out in the mid-term, petroleum is becoming increasingly expensive and complicated to obtain. Also, its indiscriminate use results in greenhouse gas emissions (CO2, CH4,…) which are responsible, according to the broadest scientific consensus, for the planet’s global warming. For these reasons, in recent years, the search has begun focusing on finding clean, sustainable and environmentally balanced energies.

One of the most important sources of energy for replacing petroleum are biofuels, which owe their name to their biological origin. Of all alternative biofuels, biodiesel stands out as an environmentally friendly energy source, accessible for all countries, and capable of enabling growth opportunities for developing countries.

Biodiesel, in its purest form, can be used as replacement for mineral diesel within the EU, subject to compliance with quality standard EN 14214: Fatty Acid Methyl Esters (FAME) for Diesel Engines – Requirements and test methods. However, it is most commonly used blended with mineral diesel in a specific proportion, up to the 7% allowed by European diesel quality standard EN 590.

The basic raw materials of biodiesel are vegetable oils and animal fat, which main components are triglycerides. Chemically, they are fatty acid esters with glycerine. To obtain biodiesel, oils and fats are subject to a TRANSESTERIFICATION reaction, with an alcohol – usually methanol – in the presence of a catalyst, normally a base.

The diagram below summarizes the TRANSESTERIFICATION reaction, where R represents the fatty acid chains, which are not modified during the transesterification process, and which define, basically, the biodiesel’s properties.

Biodiesel production can be based on a broad variety of raw materials, such as vegetable oil, animal fat, waste oil and, in the future, oils produced by algae. Each raw material is processed differently, and has different quality specifications.

Biodiesel can be blended with petroleum diesel in any proportion. These blends are more frequently used than pure biodiesel, and are designated using the acronym BX, where X is the % of biodiesel added to the petroleum diesel.

The production process follows a two-step approach: Pretreatment and transesterification. During the pretreatment stage, the oil is subject to chemical-physical processes in order to eliminate the components which are detrimental to the transesterification reaction, and to guarantee the final quality of the biodiesel. Thus, it is subject to a degumming process, a bleaching process and, finally, a deodorization process. During the transesterification stage, the chemical reaction between the triglycerides and the methanol takes place. The by-product of this reaction is glycerine. The diagram below illustrates the production process.