Organic Chemistry - Crude Oil

This section explores fossil fuels like natural gas and crude oil as non-renewable energy sources, the process of fractional distillation to separate crude oil, biofuels as renewable alternatives, and the environmental sustainability comparison between biofuels and fossil fuels.

1. Natural Gas and Crude Oil as Non-renewable Energy Sources
  • 🔹 Natural Gas:
    • 🔹 Main Component:

      🔹 Methane (CH₄).

    • 🔹 Source:

      🔹 Underground reservoirs, often found alongside crude oil.

    • 🔹 Uses:

      🔹 Electricity generation, cooking, heating.

  • 🔹 Crude Oil:
    • 🔹 Composition:

      🔹 Complex mixture of hydrocarbons (mainly alkanes).

    • 🔹 Formation:

      🔹 From decomposition of marine organisms under heat and pressure over millions of years.

    • 🔹 Non-renewable:

      🔹 Depleted faster than they form.

  • 🔹 Issues:
    • 🔹 Finite supply and risk of depletion.
    • 🔹 Combustion releases CO₂, contributing to global warming.
    • 🔹 Extraction and transport can cause environmental damage (e.g., oil spills).
2. Separation of Crude Oil by Fractional Distillation
  • 🔹 Principle:

    🔹 Separation by differences in boiling points of hydrocarbons.

  • 🔹 Process:
    • 🔹 Heat crude oil until it vaporises.
    • 🔹 Vapours rise in fractionating column (temperature decreases upwards).
    • 🔹 Hydrocarbons condense at different heights depending on boiling point.
  • 🔹 Fractions and Uses:
    • 🔹 Refinery gas: LPG for cooking/heating.
    • 🔹 Petrol: Fuel for cars.
    • 🔹 Naphtha: Feedstock for petrochemicals.
    • 🔹 Kerosene: Aircraft fuel.
    • 🔹 Diesel oil: Fuel for buses/lorries.
    • 🔹 Lubricating oil & waxes: Lubricants, polishes.
    • 🔹 Bitumen: Road surfacing.
  • 🔹 Trends:
    • 🔹 Smaller molecules → lower boiling point → collected higher.
    • 🔹 Larger molecules → higher boiling point → collected lower.
3. Biofuels as Renewable Alternatives
  • 🔹 Definition:

    🔹 Fuels from biological sources that can be replenished.

  • 🔹 Example - Bioethanol:
    • 🔹 Production:

      🔹 Fermentation of sugar (sugarcane/corn) using yeast.

    • 🔹 Usage:

      🔹 Blended with petrol to reduce fossil fuel use.

  • 🔹 Other Biofuels:
    • 🔹 Biodiesel from vegetable oils.
    • 🔹 Biogas from anaerobic digestion of waste.
  • 🔹 Renewable:

    🔹 Plants for fuel can be grown annually.

4. Environmental Sustainability of Biofuels vs Fossil Fuels
  • 🔹 Biofuels:
    • 🔹 Advantages:
      • 🔹 Considered carbon-neutral (CO₂ released ≈ CO₂ absorbed).
      • 🔹 Lower net greenhouse gas emissions.
      • 🔹 Reduce dependence on non-renewables.
    • 🔹 Concerns:
      • 🔹 Deforestation and biodiversity loss from large-scale farming.
      • 🔹 Competition with food production can raise prices.
  • 🔹 Fossil Fuels:
    • 🔹 Drawbacks:
      • 🔹 Release CO₂ without reabsorption → net increase in atmospheric CO₂.
      • 🔹 Risk of spills, methane leaks during extraction/transport.
  • 🔹 Conclusion:

    🔹 Biofuels are more sustainable if produced without harming ecosystems or food supply.

  • 🔹 Complete combustion of methane: CH₄ + 2O₂ → CO₂ + 2H₂O
  • 🔹 Complete combustion of octane (petrol): 2C₈H₁₈ + 25O₂ → 16CO₂ + 18H₂O
  • 🔹 Fermentation to produce bioethanol: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
  • 🔹 Anaerobic digestion to produce biogas (methane): C₆H₁₂O₆ → 3CO₂ + 3CH₄
  • 🔹 Thermal cracking (alkane → smaller alkanes + alkenes): C₁₀H₂₂ → C₅H₁₂ + C₅H₁₀
  • 🔹 Catalytic cracking (petroleum fraction → alkanes + alkenes): C₁₂H₂₆ → C₈H₁₈ + C₄H₈
  • 🔹 Incomplete combustion of methane (produces CO): 2CH₄ + 3O₂ → 2CO + 4H₂O

  • ⚠️ All biofuels are automatically environmentally friendly.
  • ⚠️ Fossil fuels are abundant and will not run out soon.
  • ⚠️ Fractional distillation chemically changes hydrocarbons.
  • ⚠️ Burning biofuels does not produce any CO₂.

  • 👉 Remember that fractional distillation is based on physical properties (boiling point).
  • 👉 Be able to recall fractions, their positions in the column, and their uses.
  • 👉 Clearly state why fossil fuels are non-renewable.
  • 👉 For biofuels, balance environmental benefits against possible drawbacks in answers.
  • 👉 Use trends in boiling point and molecular size to predict where a fraction condenses.

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