Fossil Fuels: Our Primary Energy Source
🛢️ What are Fossil Fuels?
- Energy-rich substances from decomposed organisms
- Formed over millions of years under heat & pressure
- Main types: Coal, Petroleum (Crude Oil), Natural Gas
- Provide ~80% of world’s energy
⛏️ Formation of Petroleum & Natural Gas
- Time: Millions of years
- Conditions: Absence of air, high pressure, heat
- Result: Dark brown viscous liquid (crude oil)
- Natural Gas: Accumulates above petroleum deposits
🔬 Extraction & Refining
Drilling wells
Natural gas released first
Oil pumped out
Refining in fractionating tower
22.1.2 Refining of Petroleum
🏭 Fractional Distillation Process
- Crude oil heated to 400°C in furnace
- Vapors rise in fractionating tower
- Condense at different levels based on boiling points
- Compounds with highest BP condense first (bottom)
- Compounds with lowest BP condense last (top)
📊 Petroleum Fractions (Table 22.1)
| Fraction | Carbon Atoms | Boiling Point (°C) | Important Uses |
|---|---|---|---|
| LPG | 1-4 | Below 20 | Cylinder gas for cooking |
| Petrol | 5-10 | 35-70 | Fuel for motor vehicles |
| Naphtha | 8-12 | 70-120 | Chemical feedstock |
| Kerosene | 10-16 | 170-250 | Jet fuel, heating, lighting |
| Diesel | 14-20 | 270-340 | Fuel for buses, trucks |
| Lubricating Oil | 20-50 | 350-500 | Lubricants, waxes |
| Fuel Oil | 50-70 | 500-600 | Power stations, ships |
| Bitumen | 70+ | 500+ | Roads, roofing |
22.3.1 Nuclear Energy
⚛️ Nuclear Fission
Fission Reaction
²³⁵U + ¹n → ¹⁴¹Ba + ³n + ⁸⁹Kr + Energy
- Process: Heavy nucleus splits into smaller nuclei
- Trigger: Neutron absorption
- Energy Source: Mass defect converted to energy (E=mc²)
- Fuel: Uranium-235, Plutonium-239
☢️ Nuclear Fusion
Fusion Reaction
²H + ²H → ³He + ¹n + Energy
³H + ²H → ⁴He + ¹H + Energy
- Process: Light nuclei combine to form heavier nucleus
- Conditions: Extremely high temperature & pressure
- Energy: More energy than fission
- By-product: Non-toxic helium (no radioactive waste)
📈 Importance of Nuclear Energy
- Produces large electricity without CO₂ emissions
- Less atmospheric pollution than thermal plants
- Small fuel amount → electricity for extended periods
- Specific energy: Uranium-235 = 3.9 million MJ/kg
22.2 Petrochemicals
🧪 What are Petrochemicals?
- Organic compounds derived from petroleum/natural gas
- Examples: Ethylene, Propylene, Benzene, Toluene, Methanol
- Raw materials for chemical industry
🏭 Petrochemical Products
- Plastics & Synthetic rubbers
- Fibers (polyester, nylon)
- Dyes, Paints, Adhesives
- Pesticides, Detergents
- Medical devices, Electronics
⚙️ Block Processes in Petrochemical Technology
450-750°C, 70 atm
Zeolite catalyst
CH₄ + H₂O → CO + H₂
22.3.3 Solar Energy
☀️ Why Solar Energy?
- Reduces greenhouse gas emissions
- Renewable & inexhaustible
- Decreases fossil fuel dependence
- Low environmental impact
⚡ Conversion Technologies
• Sunlight → Heat
• Used for heating
• Receiver heats liquid
• Sunlight → Electricity
• Semiconductors
• DC → AC via inverter
📊 Advantages & Disadvantages
| Energy Resource | Advantages | Disadvantages |
|---|---|---|
| Fossil Fuels | Reliable | Pollution, finite |
| Nuclear Power | Reliable, high energy | Radioactive waste |
| Solar Cells | Clean, renewable | Intermittent, high setup cost |
| Wind Turbines | Clean, cheap to run | Intermittent, setup cost |
| Hydroelectric | Clean, reliable | Drought affects output |
Complete Solutions: MCQs & Short Questions
Multiple Choice Questions:
1. Which is a petrochemical product?
Answer: (c) Rubber
Explanation: Xylene and toluene are basic petrochemicals, but rubber is a product made from petrochemicals.
2. Which has highest specific energy density?
Answer: (c) Uranium
Explanation: Uranium-235 has 3.9 million MJ/kg, while gasoline has only 46 MJ/kg.
3. J/L is unit of:
Answer: (a) Energy density
Explanation: Energy per unit volume = Energy density (J/m³ or J/L).
4. Petrol fraction carbon atoms:
Answer: (b) 5-10
Explanation: From Table 22.1, petrol contains hydrocarbons with 5-10 carbon atoms.
5. Which is not a petrochemical?
Answer: (c) Plastic
Explanation: Plastic is made from petrochemicals but is not itself a basic petrochemical compound.
Short Answer Questions:
(i) Differentiate energy density and specific energy density
Answer:
• Energy per unit volume
• Unit: J/m³ or J/L
• Measures stored energy in given space
• Energy per unit mass
• Unit: J/kg or MJ/kg
• Measures energy released when burned
(ii) Define and give examples of petrochemicals
Answer: Organic compounds from petroleum/natural gas.
Examples: Ethylene, Propylene, Butadiene, Methanol, Benzene, Toluene, Xylene
Products: Plastics, rubbers, synthetic fibers, dyes, adhesives
(iii) List differences between fission and fusion
Answer:
| Nuclear Fission | Nuclear Fusion |
|---|---|
| Heavy nucleus splits | Light nuclei combine |
| Produces radioactive waste | No long-lived radioactive waste |
| Used in power plants | Occurs in stars (sun) |
| Less energy released | More energy released |
| Neutron-induced | Requires extreme temperature |
(iv) List advantages of solar energy
Answer:
- Renewable & inexhaustible resource
- Low environmental impact
- Reduces greenhouse gas emissions
- Decreases fossil fuel dependence
- Long lifespan (25+ years)
- Low maintenance requirements
- Distributed generation possible
(v) What is catalytic cracking of petroleum?
Answer: Process using catalyst (zeolites) to break large hydrocarbons into smaller molecules.
Purpose: Produce high-octane gasoline
Example: C₇H₁₆ → C₅H₁₂ + CH₂=CH₂
Conditions: Lower temperature than thermal cracking
Concept Assessment Questions:
3. Why is solar energy so important?
Answer: Solar energy is crucial because:
- Reduces carbon emissions and fights climate change
- Provides sustainable energy without depleting resources
- Decreases dependence on finite fossil fuels
- Promotes energy independence and security
- Creates jobs in renewable energy sector
- Can be deployed anywhere with sunlight
4. How is solar energy converted into electricity?
Answer: Through photovoltaic (PV) cells:
Sunlight hits solar panel
Photons excite electrons
Creates electric field
DC current generated
Final Step: Inverter converts DC to AC for use
6. What are block building processes in petrochemical technology?
Answer: Three main processes:
• High temperature (450-750°C)
• High pressure (70 atm)
• Breaks large → small hydrocarbons
• Uses zeolite catalyst
• Produces high-octane fuel
• Lower temperature than thermal
• CH₄ + H₂O → CO + H₂ (700-1000°C)
• Produces synthesis gas
• Used to make methanol
7. How is petroleum refined?
Answer: By fractional distillation:
Heat crude oil to 400°C
Vapors rise in tower
Condense at different levels
Separate fractions
Principle: Different hydrocarbons condense at different temperatures based on boiling points
8. Debate role of solar energy in addressing global warming
Answer: Solar energy plays crucial role:
Positive Role:
- Reduces CO₂ emissions from power generation
- Decreases dependence on fossil fuels
- Promotes clean energy transition
- Mitigates climate change impacts
- Supports sustainable development goals
Challenges:
- Intermittency requires storage solutions
- High initial investment
- Land use for large-scale installations
- Manufacturing has environmental impact
Conclusion: Essential part of climate solution but needs complementary technologies