In-Depth Notes on Petrochemicals and Polymers

Formation of Crude Oil

• Millions of years ago, marine life accumulated on the sea floor after dying.
• Over time, layers of sand and mud (sediments) built up on top.
• Shells and skeletons formed limestone.
• Heat and pressure transformed soft tissues into crude oil over millions of years.

Characteristics of Crude Oil

• Crude oil is a mixture of hydrocarbons, which are compounds made up of carbon and hydrogen only.
• It is classified as a finite, non-renewable resource. Once depleted, it cannot be replaced for millions of years.
• Viscous: This term refers to crude oil's thick and sticky nature, meaning it does not flow easily.

Trends in Physical Properties of Hydrocarbons

• Increasing Carbon Counts: As the number of carbon atoms in hydrocarbons increases:
  • Physical properties such as boiling and melting points change.
  • Intermolecular forces grow stronger, requiring more energy (higher boiling points).
  • Hydrocarbons become darker, more viscous (flow less easily), and less volatile.

Separation of Crude Oil

• Crude oil must be refined to be useful. This is done in an oil refinery using fractional distillation, which separates the oil into fractions based on boiling points.
• Fractional Distillation Process:
  1. Crude oil is heated until it vaporizes.
  2. The vapor rises in a fractionating column, which is cooler at the top and hotter at the bottom.
  3. Different hydrocarbons condense back into liquids at specific temperatures.
  4. Fractions are collected:
  • Examples of Fractions:
    • Refinery Gas (bp < 25°C): Small hydrocarbons (1-3 carbon atoms).
    • Gasoline (bp 60-180°C): 5-10 carbon atoms.
    • Kerosene (bp 180-220°C).
    • Diesel (bp 220-300°C).
    • Fuel Oil (bp 300-350°C).
    • Bitumen (bp > 350°C).

Environmental Impact of Burning Fossil Fuels

• Fossil fuel combustion releases greenhouse gases like CO$_2$, contributing to global warming.
• Acid Rain: Formed when sulfur dioxide and nitrogen oxides react with atmospheric water, leading to sulfuric and nitric acids which lower rain pH below 5.6.
• Emissions from burning fuels include carbon monoxide, which poses health hazards by binding with hemoglobin in the blood, reducing oxygen transport (hypoxia).

Uses of Hydrocarbon Fractions

• Refinery Gases: Used as Liquefied Petroleum Gas (LPG) for cooking.
• Gasoline: Fuel for cars.
• Kerosene: Used as a jet fuel and in heating.
• Diesel: Fuel for various vehicles, can be converted into other chemicals.
• Fuel Oil: For ships and industrial applications.
• Bitumen: Used in road construction.

Cracking Process

• Cracking breaks down long-chain hydrocarbons into shorter, more useful alkanes and alkenes (like ethene and propene).
• Types of Cracking:
  • Catalytic Cracking: uses heat (600-700 °C) and a catalyst (Silicon and Aluminum oxides).
  • Thermal Cracking: involves very high temperatures without a catalyst.

Polymerization

• Polymers: Large molecules made of repeating units (monomers).
• Addition Polymerization: Characterized by the addition of monomers with C=C bonds, resulting in polymers like polythene and PVC.
• Condensation Polymerization: Forms polymers by joining monomers with the loss of small molecules (like water).

Types of Polymers

• Low-Density Polyethene (LDPE): Flexible, used in bags and containers.
• High-Density Polyethene (HDPE): Rigid, used in containers and pipes.
• Polyvinyl Chloride (PVC): Strong and flexible, used in pipes and insulation.
• Polytetrafluoroethene (Teflon): Non-stick coatings, resistant to chemicals.

Advantages and Disadvantages of Plastics

• Advantages:
  • Easily molded, inexpensive, durable, resist corrosion, and are lightweight.
• Disadvantages:
  • Inert towards environmental degradation, non-biodegradable, and can emit toxic fumes when burned.

Disposal Methods for Plastics

• Landfill: Long-lasting impact as plastics take hundreds of years to decompose.
• Incineration: Generates energy but releases CO$_2$ and toxic gases.
• Recycling: Reduces waste but can lower plastic strength over time due to contamination.