Industrial Chemistry 1, Chapter 3: Ethylene

Industrial Chemistry 1, Chapter 3: Chemicals Based on Ethylene

• Ethylene is a hydrocarbon with the chemical formula C₂H₄.
• Ethylene is a colorless, flammable gas with a sweet, musky odor in its pure form.
• Ethylene has a simple structure and high reactivity.
• Ethylene is relatively inexpensive.
• Ethylene produces fewer by-products during reactions with other compounds compared to other olefins.
• Ethylene is a raw material for various chemicals and polymers, such as ethanol and polyethylene.
• It is easily produced from any hydrocarbon source through steam cracking.
• Molecular weight of ethylene is 28.05 g/mol.
• Density of ethylene gas is 1.178 kg/m³ at 15 °C.
• Melting point of ethylene is -169.2 °C or 104.0 K.
• Boiling point of ethylene is -103.7 °C or 169.5 K.

Major Chemicals and Polymers from Ethylene

• Ethylene can be converted into various chemicals and polymers through various chemical reactions.
• A diagram illustrates these transformations, showing different reactions for different chemicals.

Ethylene Oxide

• Ethylene oxide is a key product derived from ethylene.
• It is a precursor for many important chemicals, including ethylene glycol, ethanolamines, and polyesters.
• Ethylene oxide is produced through the controlled oxidation of ethylene, using either oxygen or air over a silver catalyst.
• The reaction is exothermic, and heat control is important.
• The reaction occurs at 200–300°C, with a short residence time (one second).
• The chemical equation for the production of ethylene oxide is: CH₂=CH₂ + ½O₂ → CH₂-CH₂ (Ethylene oxide) (ΔH = –147 kJ/mol)

Acetaldehyde

• Acetaldehyde is another important chemical derived from ethylene.
• Acetaldehyde is a colorless liquid with a pungent odor.
• It has no direct use except for the synthesis of other compounds. It's a raw material used in the production of acetic acid.
• Acetaldehyde can be produced by several methods:
• Old technique: Oxidation or chromium-activated copper catalyzed dehydrogenation of ethanol, typically at temperatures of 500°C (oxidation) or 250°C (dehydrogenation).
• New technique (Wacker process): Oxidation of ethylene using a homogeneous catalyst (Palladium(II) chloride, copper(II) chloride) at 130°C.
• The overall reaction for acetaldehyde production from ethylene is exothermic: CH₂=CH₂ + ½O₂ → CH₃CHO (Acetaldehyde) (ΔH = –218.6 kJ/mol)

Acetaldehyde Production (Wacker Process)

• The Wacker process uses an aqueous system of palladium(II) chloride and copper(II) chloride.
• Palladium(II) ions (Pd²⁺) are reduced to palladium metal (Pd°), and ethylene is oxidized to acetaldehyde.
• Palladium metal (Pd°) is re-oxidized by action of copper(II) ions, which are reduced to copper(I) ions.
• The reduced copper(I) ions are re-oxidized to copper(II) ions by reaction with oxygen and HCl.

Acetaldehyde Production (Process Details)

• Acetaldehyde production can occur in a single- or two-stage process.
• Single-stage: Ethylene, oxygen, and recycled gas are fed into a vertical reactor with catalyst solution; heat control by boiling water, at approximately 130°C and 3 atmospheres.
• Two-stage: Higher pressure (approximately 8 atmospheres) , to ensure higher ethylene conversion, with a reaction temperature of approximately 130°C.
• Acetaldehyde yield is typically 95%.

Conclusion: Ethylene's Importance

• Ethylene is a crucial raw material for various chemicals and polymers.
• It is often referred to as the "king of petrochemicals" due to its importance in the chemical industry.
• Continuous improvements in ethylene manufacturing are essential to increase the production of other petrochemicals derived from it.