What is propylene and what is it used for in the plastics industry?

Propylene, also known as propene, is one of the most important compounds in the modern petrochemical industry. It is a colorless and flammable gas that acts as an essential raw material for the manufacture of a wide range of plastics, fibers, solvents, and intermediate chemical products, especially in the production of industrial-use thermoplastics. In this article, we explain what propylene is, how it is obtained, what it is used for, and why its role is key in the production of polypropylene and other industrial derivatives.

What is propylene or propene (PP)

Propylene is an unsaturated hydrocarbon from the alkene family, with the chemical formula C₃H₆. It is similar to ethylene, but with an additional carbon molecule. This compound is mainly obtained as a by-product of petroleum cracking and natural gas processing. Under normal conditions, it appears as a light gas, with a slight petroleum-like odor, which liquefies easily under pressure.

Basic properties of propylene

Propylene is highly flammable, with a boiling point of -47.7 °C and a density of 1.8 kg/m³. Although it is a gas, it can be transported in liquid form through compression. Its molecular structure allows it to participate in polymerization, oxidation, and alkylation reactions, making it a versatile compound in the synthesis of plastic materials.

Propene and propylene: are they the same?

Yes. Propene and propylene are different names for the same chemical compound. “Propene” is the name according to IUPAC nomenclature, while “propylene” is the term most commonly used in industry. Both refer to the same gas used as a basis for manufacturing plastic products by extrusion, such as polypropylene and propylene copolymer.

How propylene is obtained

Propylene is mainly produced as a by-product in petroleum refining and natural gas cracking processes. The two most common industrial routes are:

1. Thermal or steam cracking

In this process, long hydrocarbon molecules are broken down by heat. When natural gas or naphtha is subjected to temperatures above 800 °C, light compounds such as ethylene and propylene are released. This method accounts for more than 60% of global production.

2. Propane dehydrogenation

Catalytic dehydrogenation converts propane (C₃H₈) into propylene (C₃H₆) by removing hydrogen. It is a cleaner and more energy-efficient process, widely used in modern plants that seek to reduce emissions and depend less on petroleum.

It can also be obtained from secondary processes such as catalytic reforming or alkylation, although on a smaller scale.

What propylene is used for (PP)

Propylene is one of the pillars of the chemical and plastics industry. It is used to manufacture plastic resins, industrial solvents, synthetic fibers, and high value-added products. It is the second most widely used compound in the world, behind only ethylene.

Main applications of propylene

More than 60% of the world’s propylene is used to manufacture polypropylene, a versatile polymer used in packaging, textiles, automotive components, and medical devices. The rest is used in the synthesis of other compounds such as propylene oxide, acrylonitrile, or isopropyl alcohol.

Examples of industrial use

• Manufacture of polypropylene: base material for packaging, films, caps, molded parts, and automotive components.
• Production of propylene oxide: used in polyurethane foams, solvents, and coatings.
• Production of acrylonitrile: raw material for synthetic fibers, ABS plastics, and technical textiles.
• Isopropanol (isopropyl alcohol): industrial solvent and disinfectant.
• Polyols and synthetic glycerin: derivatives used in cosmetics and pharmaceuticals.

What is polypropylene and how is it related to propylene

Polypropylene (PP) is the polymer resulting from the polymerization of propylene. It belongs to the family of polyolefins within semi-crystalline thermoplastics. It is lightweight and resistant, and shares many of the properties described when discussing the characteristics of plastics. It can be transformed through processes carried out with a plastic injection molding machine, as well as by extrusion or blow molding. PP combines low density, high rigidity, and excellent chemical resistance, making it one of the most widely used materials globally.

Most common uses of polypropylene

Polypropylene material is present in countless everyday and industrial products:

• Food packaging and bottle caps.
• Plastic films and sheets for packaging.
• Fibers for carpets, ropes, and nonwoven fabrics.
• Technical parts in the automotive sector.
• Pipes, valves, and industrial components.

Thanks to its thermal resistance, PP can be sterilized, which is why it is also used in syringes, medical packaging, and laboratory systems. In these environments, the control of properties such as purity, thermal stability, or melt flow index is essential, and is usually supported by laboratory equipment for testing, material validation, and quality control. In many cases, polypropylene is processed using industrial plastic extruders or pelletizing equipment that converts the molten material into pellets.

Propylene oxide: an essential derivative

Propylene oxide is a chemical derivative of propylene obtained through controlled oxidation. It is a volatile, colorless liquid that serves as a base for the production of polyurethane foams, detergents, solvents, and antifreeze products. It is obtained from the reaction of propylene with peroxides or molecular oxygen, with the help of metal catalysts.

Uses of propylene oxide

• Production of polyols for flexible and rigid foams.
• Production of glycols and surfactants.
• Manufacture of epoxy resins and elastomers.
• As an intermediate in cosmetics and pharmaceuticals.

Differences between propylene and polypropylene

Although they are closely related, propylene and polypropylene are not the same. The first is a gas (monomer) that acts as a raw material, while the second is the result of its polymerization. In other words, propylene is chemically transformed through catalysts until it forms long molecular chains of solid PP.

Advantages of propylene as a raw material

• High availability: it is easily obtained as a by-product of petroleum.
• Chemical versatility: it can be transformed into a wide range of useful compounds.
• Energy efficiency: its polymerization requires less energy than other monomers.
• Compatibility with recycled materials: ideal for plastic recycling and pelletizing processes.

Importance of propylene in the circular economy

In today’s sustainability context, recycled propylene is gaining importance. Through pyrolysis or depolymerization processes, polypropylene waste can be converted back into light gases rich in propylene, closing the material cycle. This approach drives the circular economy and reduces dependence on virgin petroleum.

The development of industrial machinery such as motors and gearmotors, speed drives, and industrial fans also helps optimize recycled plastic transformation processes.

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