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 has a simple structure, is highly reactive, and is relatively inexpensive.
• In its pure form, ethylene is a colorless, flammable gas with a sweet, musky odor.
• Ethylene is a raw material for various chemicals and polymers, including ethanol and polyethylene.
• Ethylene is easily produced from any hydrocarbon source using steam-cracking.
• Ethylene's molecular weight is 28.05 g/mol.
• The density of ethylene gas is 1.178 kg/m³ at 15°C.
• At standard conditions, ethylene's melting point is -169.2°C (104.0 K) and its boiling point is -103.7°C (169.5 K).

Major Chemicals and Polymers Produced from Ethylene

• Ethylene is a precursor for many important commercial chemicals including ethylene glycol, ethanolamines, and polyesters.
• Key chemical reactions include hydrolysis, oxidation/carbonylation, and Wacker catalyst-based reactions. These produce various products like ethanol, acrylic acid, vinyl acetate, acetaldehyde, acetic acid, ethylene oxide, ethoxylates, polyethylene, polystyrenes, vinyl chloride, propionaldehyde, and n-propanol.

Ethylene Oxide: Introduction and Production

• Ethylene oxide is a key product derived from ethylene, with widespread use as a precursor for other chemicals and polymers.
• The production process involves the controlled oxidation of ethylene using a silver catalyst (with either oxygen or air).
• The oxidation of ethylene to ethylene oxide is an exothermic reaction with a ΔH value of -147 kJ/mol.
• The reaction between ethylene and oxygen yields carbon dioxide and water with ΔH value of -1,421 kJ/mol.

Acetaldehyde: Introduction and Production

• Acetaldehyde is a colorless liquid with a pungent odor.
• Acetaldehyde’s primary use is in the synthesis of other compounds, and not for direct use. It is a raw material to produce acetic acid.
• Two methods are used to create acetaldehyde: old technique (using silver-catalyzed oxidation or chromium activated copper) and the new technique (using a homogeneous catalyst like Wacker catalyst and reaction temperature of 130 °C). The old method utilizes oxidation of ethanol while the newer technique employs ethylene.
• The acetaldehyde production is via redox reactions and is exothermic, with ΔH = -218.6 kJ/mol.
• The Wacker process for acetaldehyde production uses an aqueous solution of palladium(II) chloride and copper(II) chloride as a catalyst system.
• Pd²⁺ ions are reduced to Pd metal during the reaction, while ethylene gets oxidized into acetaldehyde. Pd° is re-oxidized by Cu(II) ions, which are reduced to Cu(I) ions and recycled; the overall reaction being exothermic.
• Acetaldehyde production can happen either in a single or two-stage process.
• The yield of acetaldehyde from either process is approximately 95%.
• By-products include acetic acid, ethyl chloride, chloroacetaldehyde, and carbon dioxide.

Conclusion

• Ethylene is a crucial raw material for various chemicals and polymers.
• Ethylene is often referred to as the "king of petrochemicals" due to its wide-ranging importance.
• Constant improvements are desired in ethylene production to bolster production of other petrochemicals to enhance the industry's commercial viability.