by Propylene, also known as methylethylene, is a widely used petrochemical produced primarily from petroleum refineries and natural gas processing plants. As one of the most important organic chemicals in industrial production, propylene forms the basis for many everyday plastics, fibers, and industrial products.
Chemical Properties and Production
Propylene is an alkene hydrocarbon with the formula C3H6. It is a colorless gas that is highly flammable and slightly less dense than air. Propylene has double bond chemical reactivity that allows it to undergo addition polymerization reactions to produce plastics and resins.
The majority of propylene is produced as a coproduct in petroleum refineries during the cracking and steam pyrolysis of petroleum fuels to produce gasoline and other motor fuels. In this process, crude oil derivatives like naphtha are heated and cracked to produce lighter hydrocarbon gases including propane, propylene, and ethylene. Alternative processes for propylene production extract natural gas liquids or use steam cracking of liquid petroleum gas feeds. Global propylene production capacity exceeds 120 million tons annually.
Uses in Plastics and Fibers
Polypropylene – As the largest volume use of propylene, it accounts for over 20 million tons of annual demand. Polypropylene is a tough, lightweight thermoplastic that is injection molded for diverse applications from consumer packaging to automotive parts. Its heat and chemical resistance make it a versatile commodity plastic.
Polypropylene fibers – Fibers spun from polypropylene are strong, durable andretain their shape well. They are fabricated into textiles for geotextiles, diapers, medical garments and carpetface fibers.
Acrylonitrile butadiene styrene (ABS) – The tough, impact-resistant terpolymer ABS contains a 28% aromatic fraction derived from propylene. It is widely shaped as durable housings for appliances, electronics devices and automotive interior trim components.
Polystyrene – General purpose polystyrene is an amorphous polymer produced from approximately 25% propylene content. Its uses span foam cups, food packaging, and insulation boards. High impact polystyrene contains up to 8% polybutadiene rubber for enhanced toughness.
Propylene oxide – An important intermediate chemical, Propylene oxide is hydrated to produce propylene glycol as an automotive antifreeze and aircraft de-icing fluid additive. It also forms polyols applied in polyurethane flexible and rigid foams.
Oxo alcohols – Foremost is n-propyl alcohol used in coatings, cleaning solvents, and plasticizers. Other oxo alcohols help synthesize resins, plasticizers and surfactants.
Roles in Fuel and Chemical Production
Cumene process – In this reaction, benzene undergoes alkylation with propylene over an acid catalyst to produce cumene, the precursor to phenol and acetone production. Major applications are epoxy, polycarbonate and phenolic resins.
Tert-butanol – Made by hydroformylation of propylene followed by hydrogenation, tert-butanol is primarily used as a higher octane gasoline component. It also serves specialty roles as a paint thinner, froth flotation agent and pharmaceutical intermediate.
Acrylic acid and esters – Propylene provides the starting propene unit for catalytic oxidation to acrylic acid, a monomer for water-soluble resins and superabsorbent polymers. Esters like ethyl and butyl acrylate supply adhesive resins and specialty coatings.
Propylene also finds other valuable derivative uses such as:
– Cumene hydroperoxide – Used to initiate polymerizations in unsaturated polyester and acrylic resins manufacturing.
– Isopropyl alcohol – A high purity rubbing alcohol and solvent originally distilled from propylene.
– Propylene glycol ethers – Valuable solvents and industrial cleaning agents produced by reacting propylene oxide.
– Propylene dichloride – A specialty solvent in paints, adhesives and electronic chemical vapor deposition processes.
With its versatile chemical properties and economical production routes, propylene stands poised to continue meeting expanding needs for commodity plastics, fibers and derivatives well into the future. Prospects also exist to increase propylene yields through ongoing refining technology enhancements and new sources such as shale gas processing or bio-based production. Barring unforeseen disruptions in oil and gas resources, propylene will remain one of the top petrochemicals for plastics and industrial applications globally.
