CLASS NOTE: PETROLEUM AND PETROCHEMICALS REFINING

Subject: Chemistry Class: Senior Secondary 1 (SS 1) Topic: Petroleum and Petrochemicals Refining: Fractional Distillation and Beyond Curriculum Alignment: Nigerian NERDC Curriculum

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1. COMPREHENSIVE CORE CONCEPTS

A. The Nature and Origin of Petroleum

Petroleum, derived from the Latin words Petra (rock) and Oleum (oil), is a naturally occurring, complex mixture of hundreds of different compounds. Chemically, these compounds are primarily Hydrocarbons—molecules consisting exclusively of Hydrogen and Carbon atoms. In its raw form, extracted directly from the earth, it is known as Crude Oil.

The Organic Theory of Origin: Most scientists agree that petroleum formed from the remains of tiny marine organisms (plankton and algae) and plants that lived millions of years ago. When these organisms died, they sank to the ocean floor and were buried under layers of silt and mud. Over millions of years, these layers became sedimentary rock. The combination of immense pressure from the layers above and high temperature from the Earth’s interior, in the absence of oxygen, chemically transformed the organic matter into liquid oil and natural gas. Because this process takes millions of years, petroleum is classified as a non-renewable energy source.

B. The Refining Process: Fractional Distillation

Crude oil is a dark, viscous (thick) liquid that is virtually useless in its raw state. To make it useful, it must be "refined." The primary process in a refinery is Fractional Distillation.

The Underlying Principle: Fractional distillation relies on the fact that different hydrocarbons within the crude oil mixture have different boiling points.

• Small molecules (with 1 to 4 carbon atoms) have low boiling points and are gases at room temperature.
• Medium molecules (5 to 20 carbon atoms) have moderate boiling points and are liquids.
• Large molecules (20+ carbon atoms) have very high boiling points and are thick liquids or solids.

How the Fractionating Tower Works:

1. Vaporization: Crude oil is heated to about 400°C in a furnace until it turns into a hot vapor.
2. The Column: The vapor is pumped into the bottom of a tall fractionating column. This tower is engineered to have a temperature gradient: it is very hot at the bottom and gradually becomes cooler toward the top.
3. Fractionation (Condensation): As the hot vapor rises through the column, the different molecules begin to cool. When a specific hydrocarbon reaches a height where the temperature is just below its boiling point, it condenses (turns back into a liquid).
4. Collection: These liquids are caught on "bubble trays" and piped out as "fractions." Each fraction contains a group of hydrocarbons with similar boiling points and properties.

C. Major Petroleum Fractions and Their Uses

In a typical Nigerian refinery (like those in Port Harcourt, Warri, or Kaduna), the following fractions are separated:

D. Increasing Yield: Cracking and Reforming

The natural composition of crude oil often yields more "heavy" fractions (like diesel and heavy oil) and less "light" fractions (like petrol) than the market demands. To solve this, chemists use two main processes:

1. Cracking: This is the process of breaking down large, heavy hydrocarbon molecules into smaller, more useful ones.

   • Thermal Cracking: Uses high temperatures and pressure.
   • Catalytic Cracking: Uses a catalyst (a substance that speeds up a reaction without being consumed). This is more efficient and produces high-quality petrol.
   • Equation Example: $C_{18}H_{38} (\text{Heavy Oil}) \rightarrow C_8H_{18} (\text{Petrol}) + C_{10}H_{20} (\text{Other products})$.

2. Reforming: This process uses heat and catalysts to "reshape" straight-chain hydrocarbons into branched-chain or cyclic hydrocarbons. This is done to improve the Octane Rating of fuel, preventing "knocking" in car engines.

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2. REAL-WORLD EXAMPLES & SCENARIOS

• Scenario 1: The Kitchen Connection (LPG) When you open the valve on a gas cylinder at home, you hear a "hissing" sound. This is the Petroleum Gas fraction. It is compressed into a liquid for storage (Liquefied Petroleum Gas), but as soon as the pressure is released, it turns back into gas for cooking. It is preferred over firewood because it is cleaner and does not produce soot.
• Scenario 2: The Infrastructure Connection (Bitumen) Notice the black, sticky substance used by construction workers to pave roads like the Lagos-Ibadan Expressway. That is Bitumen, the "bottom of the barrel" fraction. Because it is thick and does not evaporate easily, it acts as a perfect glue for gravel.
• Scenario 3: The Beauty and Health Connection Petroleum jelly (commonly known by the brand name Vaseline) is a purified form of Lubricating Oil. It is a byproduct of the refining process that has been treated to remove odors and colors, making it safe for human skin to lock in moisture.

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3. PROJECT-BASED LEARNING: "MODEL THE TOWER"

Objective: Build a 3D visual model of a fractionating column to visualize the separation of hydrocarbons.

Materials:

• A clear 1.5-liter empty plastic bottle.
• Cardboard or circular pieces of plastic.
• Markers and labels.
• Small household items (a toy car, a piece of candle, a small piece of "tar" or black cloth).

Step-by-Step Instructions:

1. Preparation: Cut the top of the bottle off carefully.
2. The Trays: Cut 4-5 circles from the cardboard that fit tightly inside the bottle. Punch a few small holes in each circle to represent the "bubble caps" that allow vapor to pass through.
3. Assembly: Insert the trays at different heights.
4. Labeling: Use a marker to write the temperature at each level. (Bottom: 400°C, Middle: 200°C, Top: 20°C).
5. The Fractions: Tape a toy car at the Petrol level, a small bottle of oil at the Lubricant level, and a piece of candle wax at the paraffin level.
6. The Entrance: Draw an arrow at the bottom and label it "Crude Oil Vapor In."

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4. HOME PRACTICE ACTIVITIES

Activity 1: The Petroleum Audit

Objective: Identify the influence of petrochemicals in your immediate environment.

• Task: List 10 items in your house. Use the internet or a textbook to determine if they are made from petrochemicals.
• Format: Create a table: Item Name | Use | Likely Source (e.g., Plastic/Synthetic Fiber).
• Outcome: Students will realize that items like their school bag (polyester), toothbrush (nylon), and plastic containers are all petroleum-based.

Activity 2: The Viscosity Race (Kitchen Science)

Objective: Understand the physical property of "thickness" (viscosity) which relates to carbon chain length.

• Materials: Three spoons, Water, Vegetable Oil, and Honey or thick Liquid Soap.
• Procedure: Tilt a plate and pour a drop of each at the same time. Time how long it takes to reach the bottom.
• Conclusion: Explain that in a refinery, the "slow" liquids are the heavy fractions at the bottom of the tower, while the "fast" liquids represent the lighter fractions like petrol.

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5. LIFE SKILLS & CAREER CONNECTION

The Economic Reality: Nigeria is one of the world's largest producers of crude oil. However, because many of our refineries are not operating at full capacity, we often export crude oil and import refined petrol. Understanding this process empowers you to engage in national conversations about industrialization and energy security.

Career Paths:

1. Chemical Engineer: You could design the next generation of refineries that are more efficient and less polluting.
2. Environmental Scientist: You would work on "remediation"—cleaning up oil spills in areas like the Niger Delta and protecting local ecosystems.
3. Petrochemical Researcher: You could work on turning oil into new types of biodegradable plastics to reduce pollution.

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6. ASSESSMENT THROUGH APPLICATION

1. The Port Harcourt Refinery Manager Challenge: You are the manager of a refinery. The market is demanding more Petrol for "Keke-napeps," but you have a surplus of heavy Diesel.

   • Question: What process will you use to convert the surplus Diesel into Petrol? Explain the chemistry of what happens to the molecules.

2. Environmental Critical Thinking: "Gas Flaring" is common in Nigerian oil fields.

   • Question: Based on what you know about the fractions, which fraction is being wasted during flaring, and what are two ways this gas could be used to help the community instead?

3. Identification Quiz:

   • An airplane is refueling at the Murtala Muhammed Airport. Which fraction is it most likely using?
   • If a hydrocarbon has 25 carbon atoms, at what part of the fractionating tower (Top, Middle, or Bottom) would you expect to find it? Why?

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7. STUDENT REFLECTION QUESTIONS

• If petroleum is non-renewable and takes millions of years to form, what will happen to the Nigerian economy when our oil wells run dry?
• How does your daily life change if the price of the "Petrol" fraction increases?
• Can you think of any material in your classroom that did not come from petroleum or a petrochemical? (Think about wood, metal, or stone).

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Teacher’s Final Word: Chemistry is the key that unlocks the value of "Black Gold." Without the refinery, petroleum is just a mess in the ground; with Chemistry, it is the energy that moves the nation.