What is Biodiesel? Biodiesel is a renewable, biodegradable, and clean-burning alternative to petroleum-based diesel, made from natural oils and fats. It can be used in diesel engines with little or no modifications.

Composition and Chemical Structure

• Chemically, biodiesel consists of fatty acid methyl esters (FAME).
• Produced through transesterification of fats and oils (like vegetable oils, animal fats, or used cooking oil) with an alcohol (usually methanol) in the presence of a catalyst (typically sodium or potassium hydroxide).

General Reaction: Triglyceride (oil) + Methanol → Glycerol + Biodiesel (FAME)

Sources of Biodiesel

Vegetable Oils

• Soybean oil
• Rapeseed oil (canola)
• Palm oil
• Sunflower oil
• Jatropha oil (especially in India)
• Cottonseed oil

Animal Fats

• Tallow (beef fat)
• Lard (pork fat)
• Chicken fat
• Fish oil

Waste Oils

• Used cooking oil (UCO)
• Restaurant grease

Algal Oil

• Still in R&D and commercialization stage
• High oil yield per acre

Production Process: Transesterification

Transesterification is the main chemical process used to convert triglycerides (fats/oils) into fatty acid methyl esters (FAME)—the chemical name for biodiesel.

1. Pre-treatment; Before the actual reaction, raw feedstock (oil/fat) must be cleaned.

➤ Why it’s needed:

• Used cooking oil, animal fats, or low-quality vegetable oils often contain free fatty acids (FFA), water, and solids.
• Water causes soap formation, reducing biodiesel yield.
• FFA reacts with the catalyst and creates soap instead of biodiesel.

➤ Techniques:

• Filtration to remove food particles, debris, or other impurities.
• Heating and settling to remove water content.
• Acid esterification if FFA levels are high (>2%), converting FFAs into esters before main transesterification.

2. Reaction (Transesterification); This is the core chemical process.

➤ Chemical Reaction: Triglyceride (oil) + Methanol + Catalyst → Glycerol + Methyl Esters (Biodiesel)

➤ Requirements:

• Alcohol: Typically methanol (cheaper and more reactive).
• Catalyst: Strong base like NaOH or KOH.
• Temperature: Around 60°C.
• Reaction Time: 1 to 2 hours.
• Molar Ratio: Commonly 6:1 methanol to oil (excess methanol improves conversion).

➤ Process Types:

• Batch Processing (for small-scale production)
• Continuous Processing (for industrial scale)

3. Separation; After reaction completion, two layers naturally form due to differences in density:

➤ Layers:

• Top Layer: Biodiesel (lighter)
• Bottom Layer: Glycerol (denser, by-product)

➤ Time:

• Takes a few hours for full settling
• Sometimes centrifuges are used for faster separation

➤ Glycerol Recovery:

• Glycerol contains unused methanol, catalyst, soap, and water.
• Can be purified and used in pharmaceuticals, cosmetics, or biogas production.

4. Purification; The crude biodiesel contains contaminants that must be removed.

➤ Contaminants:

• Residual catalyst
• Unreacted methanol
• Soap and free glycerin

➤ Washing:

• Water Washing: Water is sprayed or bubbled through biodiesel to wash away impurities.
• Dry Washing: Uses ion-exchange resins or magnesium silicate for a waterless method (used industrially).

➤ Drying:

• Ensures final biodiesel is free from moisture, which can damage engines.
• Vacuum drying or heating under low pressure.

5. Quality Testing; Ensures biodiesel meets required fuel standards for safety, performance, and compatibility.

➤ Common Standards:

• ASTM D6751 (USA)
• EN 14214 (Europe)

➤ Parameters Tested:

• Viscosity
• Flash point
• Cetane number
• Cloud point & pour point (cold flow properties)
• Sulfur content
• Glycerin content (total & free)
• Water and sediment
• Acid number (measure of FFA)

🔁 Optional Step: Methanol Recovery

• Excess methanol is used in the process and can be recovered by distillation and reused.
• Important for cost reduction and environmental safety.

Summary Chart

Properties of Biodiesel (vs Diesel)

Blending of Biodiesel

• B100 – 100% biodiesel
• B20 – 20% biodiesel, 80% diesel (common in transport)
• B5 – 5% biodiesel (used widely without engine modification)
• B2, B10 – Other blends depending on region/policy

Advantages of Biodiesel

Renewable and sustainable
Reduces greenhouse gas emissions
Reduces dependency on fossil fuels
Lower emissions of particulate matter, CO, SOx
Biodegradable and non-toxic
Higher lubricity increases engine life
Compatible with existing diesel engines (up to B20 or higher)

Disadvantages of Biodiesel

Slightly lower energy content (about 8–10% less than diesel)
Cold flow issues (gel at low temperatures)
Higher NOx emissions compared to diesel
May degrade rubber components in old engines
Higher production cost (currently)
Competes with food crops (if made from edible oils)

Biodiesel vs Petroleum Diesel

Environmental Impact

• Carbon neutral (plants absorb CO₂ during growth)
• Low particulate matter emission
• Biodegradable in water and soil
• Helps reduce urban air pollution

Applications of Biodiesel

• Transport Sector: Cars, trucks, buses (B20 common)
• Railways: Indian Railways uses B10/B20 in some trains
• Power Generation: Backup diesel generators
• Agriculture: Tractors and other diesel-operated machinery
• Marine Industry: Boats and ships

Biodiesel in India

• India promotes non-edible oil crops like Jatropha and Pongamia for biodiesel.
• National Bio-Energy Mission and Biodiesel Purchase Policy
• National Policy on Biofuels (2018) aims for:
  • 20% blending of biodiesel in diesel by 2030
  • Support for advanced biofuels and waste to energy

Global Scenario

• USA, Brazil, EU, Argentina: Leading biodiesel producers
• Europe: Uses rapeseed oil
• USA: Uses soybean oil and animal fat
• Indonesia & Malaysia: Palm oil biodiesel

Future of Biodiesel

• Research in algae-based biodiesel
• Development of second-generation and third-generation biofuels
• Use of waste resources to improve sustainability
• Integration into circular bio-economy