ch5

Chapter 05: Biofuels

5.1 Introduction to Biofuels

  • Definition: Biofuels are fuels derived from biological carbon fixation, including biomass conversion, solid biomass, liquid fuels, and various biogases.

  • Increasing Attention: Driven by rising oil prices and the need for greater energy security.

  • Environmental Concerns: The European Environment Agency states biofuels do not significantly mitigate global warming.

  • Bioethanol:

    • Produced through fermentation from carbohydrates in crops like corn and sugarcane.

    • Used in vehicles as a fuel or gasoline additive.

    • Cellulosic biomass offers a non-food source for ethanol production, but current designs do not ferment lignin.

  • Biodiesel:

    • Derived from vegetable oils and animal fats.

    • Functions as a vehicle fuel or diesel additive to reduce emissions.

  • Production Statistics (2010):

    • Global biofuel production reached 105 billion liters, providing 2.7% of transportation fuels, mainly ethanol and biodiesel.

    • The US and Brazil account for 90% of global ethanol production.

    • The EU is the largest biodiesel producer, making up 53% of the total.

    • By 2011, 31 countries had biofuel blending mandates at national levels.

    • Potential for biofuels to meet 25% of transportation fuel demand by 2050.

5.1.1 Transportation Fuels

  • Liquid Requirements: Most transportation fuels are liquids for high energy density.

  • Internal Combustion Engines: Offer cost-effective power density; require clean-burning fuels to minimize pollution.

  • Advantages of Liquid Fuels:

    • Easier to pump and mechanize for handling.

    • More efficient burning capabilities compared to solids.

5.1.2 First-generation Biofuels

1. Bioalcohols

  • Produced by fermentation using microorganisms and enzymes from sugars/starches and cellulose.

  • Biobutanol: Considered a substitute for gasoline, usable in gasoline engines.

  • Ethanol Usage: Produced from various sources (corn, sugar cane, etc.) and often used in blends with gasoline (up to 15%).

  • Energy Density: Ethanol has lower energy density than gasoline but offers a higher octane rating, improving engine efficiency.

2. Biodiesel

  • Common in Europe, produced from oils or fats via transesterification.

  • Chemical Composition: Mainly fatty acid methyl (or ethyl) esters (FAMES).

  • Feedstocks: Include various vegetable oils, animal fats, and algae.

  • Environmental Impact: B100 biodiesel has lower emissions; not as efficient as petroleum alternatives.

  • Engine Compatibility: Compatible with diesel engines, sometimes requiring minimal adjustments.

3. Green Diesel

  • Made via hydrocracking biological feedstocks into diesel-equivalent hydrocarbons.

  • Compatible with existing infrastructures; competitive pricing remains a challenge.

4. Vegetable Oil

  • Unmodified oils are not standard fuels, but lower-quality oils are repurposed.

  • Conversion: Must be heated to improve atomization and combustion efficiency.

  • Hydrogenated oils can form stable diesel substitutes, overcoming some biodiesel issues.

5. Bioethers

  • These cultivate cleaner engine performance and enhance octane rating while reducing harmful emissions.

6. Biogas

  • Produced through anaerobic digestion, using organic waste or energy crops.

  • The byproduct can be utilized as fertilizer.

7. Syngas

  • A mixture created from partial combustion of biomass, allowing more efficient energy extraction compared to direct combustion.

8. Solid Biofuels

  • Include wood, agricultural waste, and similar materials.

  • Processing: Raw biomass is densified for better transport and usability.

5.1.3 What Is Biodiesel?

  • Alternative fuel similar to fossil diesel, convertible from oils and fats through transesterification.

  • Potential Feedstocks: Includes rapeseed, palm, soybean, and waste cooking oils, with rapeseed being prominent in the UK.