What is biodiesel?

A natural automotive fuel

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The use of biofuels has increased steadily in recent years, due to their importance in reducing the transportation and energy transition carbon footprint. They are of particular interest in sectors that are difficult to decarbonize, such as road freight transport and the maritime and aviation sectors. According to the European Environment Agency, the two most important plant-based fuels today are bioethanol and biodiesel.

What is biodiesel?

Biodiesel is a natural fuel. Its use makes it possible to reduce greenhouse gas emissions, as it is produced from organic matter (mainly vegetable oils or animal fats).

At present, its main use is as a renewable fuel for automobiles to replace mineral-based diesel. Biodiesel can be blended with mineral diesel by up to 7%. It can also be used for domestic heating, in specific biodiesel boilers. It is obtained through a chemical process where the oil reacts with an alcohol when a catalyst is present.

Depending on the amount of biodiesel in a fuel's composition, a nomenclature is used using the letter B and a number, indicating the proportion of biodiesel in the blend with diesel obtained from oil. So, there can be anything from B2 (containing 2% biodiesel) to B100, which would be pure biofuel.

Types of biodiesel

Biodiesel can be classified in various ways, depending on the raw material it is made from or the percentage of biofuel it contains. For example, depending on the raw material, the following types can be distinguished:

Biodiesel produced from vegetable oils

It is made from oil extracted from oleaginous plants such as rapeseed, sunflower, palm, soybean, and marine plants, such as algae. It is one of the most widespread methods of production, and raw materials are already being cultivated to produce biodiesel.

Biodiesel produced from animal fats

It is also possible to produce biodiesel from animal fats, by extracting and processing the lipids. In Spain, pork, bovine, or poultry fats are usually used.

Biodiesel extracted from used cooking oils

This is the most affordable option and the one that most promotes the circular economy and recycling, as it consists of using used cooking oil in homes, the catering businesses, or the agri-food industry.

Biodiesel uses

The energy contained in biodiesel is so great that it can be put to many different uses, and most importantly, all in a satisfactory way. Some of the most noteworthy are the following:

Fuel for diesel engines and diesel vehicles
For heating systems
Electric generator
As an industrial solvent
As a lubricant, thanks to its sulfur reduction
Fuel for domestic kitchens

Advantages of biodiesel

The worldwide biodiesel boom can be explained by the fact that it's a clean and affordable fuel. Numerous studies have shown that its CO₂, SO₂, or CO emissions, among others, are lower than other fuels. In fact, institutions such as the U.S. EPA (Environmental Protection Agency) estimate that the CO₂ reduction ranges between 57% and 86%. This makes it a very interesting alternative, but that’s not its only advantage:

It is a fuel that comes from vegetable raw materials. The species used to generate it can be recultivated and, in the case of biodiesel produced from used oils, it allows waste to be given a new life, boosting the circular economy.
It can be used in most diesel engines without the need for any major mechanical modifications.
It does not contain sulfur, and therefore does not emit this greenhouse gas during combustion.
It can be produced locally, without the need to depend on imports.
It facilitates the use of soil with crops destined for its production, which in turn reduces erosion and deforestation.

Repsol and biodiesel

At Repsol, we have been incorporating renewable fuels into our automotive fuels for over two decades. Now, with the circular economy as one of the strategic pillars to accelerating the energy transition and achieving our goal of becoming a net zero emissions company by 2050, we will produce renewable fuels from various types of waste (such as used cooking oils and waste from the agri-food industry). By doing so, we give this waste a second life and transform it into high value-added products.

First renewable fuels plant in Cartagena, Spain

We have already commissioned the first renewable fuels plant in Spain, located in Cartagena (Murcia), within the Cartagena Industrial Complex.

In this project, we have invested 250 million euros, with the aim of producing 250,000 tonnes per year, which can even be used in transport that is difficult to decarbonize (such as airplanes, ships, or trucks) and will enable a reduction of 900,000 tonnes of CO₂ per year by reducing net CO₂emissions by 90% compared to the mineral fuel it replaces.

In the words of Antonio Brufau, our Repsol chairman, "with this project, Cartagena will cement its role as a supply center for essential products for the present and for the future, serving as an example of Repsol's commitment to sustainable mobility."

The facilities began operating in the first half of 2024. Their start-up is part of Repsol's transformation plan to decarbonize mobility.

The new plant, according to Antonio Mestre, director of Repsol’s Cartagena refinery, "is a tangible example of circular economy that will allow us to offer sustainable mobility solutions to all sectors of society, and a hugely important step in the transformation of the industrial complex as a multi-energy hub." It will also contribute to the Fit for 55 target, which sets the use of sustainable aviation fuels at 63% by 2050.