Green Diesel

Green diesel, also known as renewable diesel or hydrotreated vegetable oil (HVO), is an advanced biofuel produced from renewable biological sources such as vegetable oils, animal fats, or waste cooking oil. It serves as a sustainable alternative to conventional petroleum diesel and plays an increasingly important role in the transition towards cleaner, low-carbon energy systems. Unlike traditional biodiesel, green diesel has chemical properties almost identical to fossil diesel, allowing it to be used directly in existing diesel engines without modification.

Background and Development

The emergence of green diesel is linked to growing global concerns about climate change, fossil fuel depletion, and environmental pollution. As governments and industries sought renewable alternatives to petroleum fuels, research in the late twentieth and early twenty-first centuries focused on developing advanced biofuels with superior performance and compatibility.
Traditional biodiesel, produced through a process called transesterification, had limitations such as poor cold-flow properties and compatibility issues with modern engines. Green diesel, developed later through hydrotreatment technology, overcame these shortcomings, providing a drop-in fuel solution. Countries such as Finland, the United States, and Singapore pioneered large-scale production through companies like Neste, Renewable Energy Group, and TotalEnergies.

Production Process

Green diesel is produced through a process known as hydrotreatment or hydrogenation, which involves reacting natural fats or oils with hydrogen at high temperature and pressure in the presence of a catalyst.
The key stages include:

1. Feedstock Preparation: Renewable sources such as palm oil, soybean oil, canola oil, animal fats, or used cooking oil are filtered and pre-treated to remove impurities.
2. Hydrotreating: The feedstock is subjected to hydrogen in a reactor. Oxygen atoms are removed as water, resulting in hydrocarbons similar to those found in fossil diesel.
3. Isomerisation: The hydrocarbon molecules are rearranged to improve cold-flow properties, ensuring better performance in cold climates.
4. Fractionation: The final fuel is refined and separated into desired distillates, producing high-quality green diesel suitable for transportation and industrial use.

The resulting product is chemically similar to petroleum diesel (a paraffinic hydrocarbon) and meets the same fuel standards such as EN 15940 in Europe and ASTM D975 in the United States.

Characteristics and Composition

Green diesel consists mainly of straight-chain and branched paraffins with negligible oxygen, sulphur, and aromatic compounds. Its chemical structure ensures clean combustion, high energy content, and long storage stability.
Key characteristics include:

• High Cetane Number: Typically between 70 and 90, which ensures efficient ignition and smoother engine performance.
• Low Emissions: Produces lower levels of particulate matter (PM), carbon monoxide (CO), and hydrocarbons (HC) compared with fossil diesel.
• Excellent Storage Stability: Does not absorb water or degrade easily, unlike conventional biodiesel.
• Compatibility: Can be blended in any proportion or used as a 100% replacement (known as HVO100) without engine modification.

Feedstocks Used

Green diesel can be produced from a wide range of renewable sources, including:

• Vegetable Oils: Palm, soybean, sunflower, and rapeseed oils.
• Animal Fats: Tallow, lard, or fish oil.
• Waste Oils: Used cooking oils and industrial greases.
• Algal Oils: Experimental feedstocks derived from microalgae cultivation.

The choice of feedstock depends on local availability, cost, and sustainability considerations. Increasingly, attention is shifting towards second-generation feedstocks that do not compete with food production.

Advantages of Green Diesel

• Environmental Benefits: Produces up to 90% less greenhouse gas (GHG) emissions compared with fossil diesel over its life cycle.
• Full Engine Compatibility: Can be used in existing diesel engines, pipelines, and distribution systems without blending limitations.
• Improved Performance: Offers superior combustion efficiency and lower noise levels due to its high cetane number.
• Lower Pollutant Emissions: Significantly reduces sulphur oxides (SOx), nitrogen oxides (NOx), and soot.
• Non-toxic and Biodegradable: Poses minimal risk of environmental contamination.

Disadvantages and Challenges

• Feedstock Supply Constraints: Limited availability of sustainable feedstocks can restrict production capacity.
• High Production Costs: Hydrogenation and catalytic processes require advanced technology and infrastructure, making production expensive compared with fossil fuels.
• Land Use Concerns: Large-scale cultivation of oil crops for fuel can lead to deforestation and biodiversity loss if not managed sustainably.
• Policy Dependence: The viability of green diesel often relies on government subsidies, carbon credits, and renewable energy mandates.

Applications

Green diesel has diverse applications across sectors due to its compatibility with existing diesel systems.

• Transportation: Used in heavy vehicles, buses, and fleets, often as HVO100 or blended with fossil diesel.
• Aviation (as Sustainable Aviation Fuel – SAF): Can be refined further to produce jet fuel components.
• Marine Industry: Used as a cleaner alternative for shipping, reducing maritime pollution.
• Power Generation: Employed in diesel generators for remote or off-grid electricity supply.

Countries such as Sweden, Finland, and the Netherlands have adopted green diesel extensively in public transportation and logistics due to strict environmental standards.

Global Scenario and Policy Framework

The production and use of green diesel are supported by environmental and renewable energy policies worldwide. The European Union’s Renewable Energy Directive (RED II) and the United States Renewable Fuel Standard (RFS) both classify renewable diesel as an advanced biofuel.
Major producers include:

• Neste (Finland): World’s largest producer of renewable diesel.
• Renewable Energy Group (USA): Significant supplier for North American markets.
• ENI (Italy) and TotalEnergies (France): European refiners investing heavily in bio-refineries.

Emerging economies such as India, Brazil, and Indonesia are exploring renewable diesel to enhance energy security and reduce emissions. India, for instance, has launched programmes to promote the use of used cooking oil (UCO) for biodiesel and green diesel production.

Environmental and Economic Impact

Green diesel contributes to achieving global carbon neutrality targets and supports the Sustainable Development Goals (SDGs), particularly SDG 7 (Affordable and Clean Energy) and SDG 13 (Climate Action). It helps reduce dependency on fossil fuels, enhances rural income through feedstock production, and stimulates green innovation.
Economically, while initial investment and production costs remain high, long-term adoption of green diesel can lower operational costs through carbon savings and reduced maintenance expenses due to cleaner combustion.

Future Prospects

With increasing emphasis on decarbonisation, green diesel is expected to play a vital role in the future energy mix. Technological innovations such as algae-based feedstock, co-processing of renewable oils in petroleum refineries, and carbon capture integration are likely to enhance its sustainability and cost-effectiveness.