In this blog post, we’ll examine how biodiesel differs from conventional petroleum fuels and explore its potential and limitations as an alternative energy source capable of addressing the issues of high oil prices and global warming.
Petroleum is deeply intertwined with modern life. It is not only used as fuel for engines in cars and airplanes but also utilized in various forms in most everyday products, such as clothing, plastics, and dyes. While it is used in so many fields that it is difficult to imagine a society without petroleum today, it also has clear limitations. First, its reserves are finite; second, its use emits greenhouse gases, accelerating global warming. For these reasons, the development of energy sources to replace petroleum is one of the key research topics in chemical engineering, and biodiesel is a prime example.
Biodiesel is a fuel produced from biomass, such as vegetable oils or used cooking oil. The advantages of biodiesel as an alternative energy source are easier to understand when compared to conventional diesel. Crude oil is separated into various petroleum products—such as LPG, gasoline, and diesel—through a series of processes. In contrast, the raw materials for biodiesel—such as vegetable oils or used cooking oil—are renewable resources. Therefore, it reduces dependence on crude oil supply and is regarded as a more sustainable energy resource than fossil fuels.
Biodiesel can be considered an eco-friendly fuel for two main reasons. The first reason is that it has a relatively minor impact on the carbon cycle. Carbon in nature circulates continuously. It exists in the air as carbon dioxide, dissolves in the ocean, or is stored as organic matter through plant photosynthesis. This organic matter moves up the food chain and is released back into the atmosphere through the respiration of plants and animals. Some of it remains buried in geological strata for long periods, eventually becoming fossil fuels such as oil or coal.
The problem is that when humans extract and burn these fossil fuels on a massive scale, they release carbon that had been stored underground for a long time into the atmosphere over a short period. This causes atmospheric carbon dioxide concentrations to rise and exacerbates global warming. In contrast, since biodiesel is produced by re-releasing the carbon absorbed by recently grown plants, it is regarded as a fuel that can reduce carbon emissions compared to fossil fuels. However, the actual greenhouse gas reduction effect may vary depending on the entire life cycle, including raw material production, transportation, and manufacturing processes (Life Cycle Assessment).
The second reason is that biodiesel and petroleum diesel have different molecular structures. Petroleum diesel is a mixture obtained from the distillation of crude oil that falls within a specific boiling point range. Therefore, it contains hydrocarbons with various molecular structures. Some have a linear structure, while others have a cyclic molecular structure.
In contrast, biodiesel is produced from vegetable oils or animal fats through a transesterification reaction using methanol and a catalyst, resulting in molecules in the form of fatty acid methyl esters (FAME). These molecules have a linear structure and contain oxygen atoms.
These differences in molecular structure also affect the fuel combustion process inside the engine. Generally, hydrocarbons with ring structures tend to have a higher carbon-to-hydrogen ratio than those with linear structures, making them more prone to incomplete combustion. While complete combustion produces carbon dioxide and water, incomplete combustion results in the emission of carbon monoxide, fine carbon particles, and hydrocarbons. These fine carbon particles are commonly referred to as “soot” and are known to cause air pollution and health problems.
Since diesel fuel may contain these components, black smoke can be emitted under certain conditions. In fact, you can often see large trucks emitting black exhaust fumes when driving uphill; this is a byproduct of the incomplete combustion process. In contrast, biodiesel has relatively high combustion efficiency due to the characteristics of its molecular structure, which contains oxygen, and is generally known to help reduce emissions of soot and fine particulate matter.
While biodiesel is gaining attention as an alternative that can address the dual problems of high oil prices and environmental pollution, there are still challenges to be overcome. The first is the issue of raw materials. The large-scale use of food crops as raw materials for biodiesel can drive up food prices and create the so-called “food versus fuel” dilemma, where food and fuel compete for the same resources. Given that regions around the world still suffer from food shortages, this has also raised ethical concerns.
Second, the carbon-neutral effect is not consistent across all situations. While biodiesel can reduce greenhouse gas emissions compared to fossil fuels, carbon emissions may actually increase if forests are cleared or land is developed to create large-scale farmland. Furthermore, when the energy consumed during the cultivation, harvesting, transportation, and manufacturing of raw materials is taken into account, the actual environmental benefits can vary depending on the production method.
The third issue is economic viability. Securing raw materials and the manufacturing process for biodiesel are more complex than those for fossil fuels, and the costs of collecting and transporting raw materials are also relatively high. Although production technology has advanced significantly in recent years, reducing costs compared to the past, there remains a limitation in that economic viability is still influenced by raw material prices and international market conditions.
Due to these issues, biodiesel did not spread as quickly as expected in its early stages. However, with technological advancements, its scope of application is steadily expanding. Research is actively underway to utilize a variety of feedstocks—including not only conventional vegetable oils but also used cooking oil, animal fats, and microalgae—and manufacturing processes are also being continuously improved. In particular, biodiesel produced from used cooking oil is being actively utilized in many countries around the world, as it offers the dual benefits of resource recycling and greenhouse gas reduction.
Furthermore, driven by carbon neutrality policies and mandatory blended fuel programs in various countries, the biodiesel industry continues to grow. As next-generation biofuel technologies advance rapidly, research is actively underway to address the limitations of conventional biodiesel.
Biodiesel is not a perfect energy source that solves all problems at once. However, it is significant in that it is one of the practical alternatives available to reduce dependence on fossil fuels and cut greenhouse gas emissions. Going forward, if efforts to diversify feedstocks, advance production technologies, improve economic viability, and establish a sustainable supply system are carried out in tandem, biodiesel is expected to play an even more important role in the transition to eco-friendly energy.
