Propylene CAS 115-07-1

What is Propylene?

Propylene is a three-carbon olefin with a double bond and a methyl group, formula C₃H₆. At normal temperature it is a colourless, flammable gas with a faint petroleum-like odour, and it is easily liquefied under moderate pressure.

It is the second-largest petrochemical by volume after ethylene. Its asymmetric structure matters: the methyl group makes it more reactive in some additions, and it gives polypropylene a stereochemistry that ethylene cannot, which is what lets polypropylene be made rigid, heat-resistant and fibre-forming.

Propylene is supplied in grades set by purity. Polymer grade, at or above 99.5%, is made for polypropylene catalysts. Chemical grade at about 92 to 95% serves oxidation and addition chemistry that tolerates propane. Refinery grade at 50 to 70% is a by-product stream, usually upgraded before sale.

Commercially, propylene is sold both from steam crackers and from refinery FCC units, and increasingly from on-purpose routes such as propane dehydrogenation. Because it liquefies readily, merchant trade by tank, rail and ship is more practical than for ethylene.

Why propylene specifically

• Polypropylene stereochemistry. Isotactic polypropylene crystallises, giving a rigid, heat-resistant, low-density plastic that is difficult to replicate with another monomer.
• Easy to store and ship. It liquefies at about 10 bar at ambient temperature, so it moves as a pressurised liquid in tanks, rail cars and ships.
• Many oxidation routes. Propylene oxide, acrylic acid, acrylonitrile and acrolein all start from it, and each leads to a large downstream chain.
• Several supply routes. Steam crackers, FCC, propane dehydrogenation, methanol-to-olefins and metathesis all produce it, which gives buyers some supply flexibility.

How Propylene is Manufactured

Propylene comes from several processes. The route determines the by-product slate and how much purification the stream needs before it reaches polymer grade.

• Steam cracking. Naphtha, LPG or gas oil is cracked at high temperature, giving ethylene plus propylene in a ratio set by the feedstock. Heavier feeds make more propylene.
• Refinery FCC. Fluid catalytic cracking of gas oil produces a propane-propylene stream. Zeolite additives such as ZSM-5 raise the propylene yield.
• Propane dehydrogenation (PDH). Propane is dehydrogenated over a catalyst to propylene and hydrogen, giving a high-purity on-purpose supply.
• Methanol-to-olefins and metathesis. MTO converts methanol to ethylene and propylene. Metathesis combines ethylene and 2-butene to make propylene.
• Purification. Propylene is separated from propane in a long, energy-intensive C3 splitter, since the boiling points are only a few degrees apart.
• Guard beds and polishing. Adsorbents remove sulphur, arsine, phosphine, COS, water and oxygenates to the levels polymer-grade catalysts require.

Typical Commercial Specification

Figures below are representative of polymer-grade propylene, with chemical grade shown for comparison. Tell us your process and catalyst type and we will advise on the grade and trace limits you should specify.

Physical & Chemical Properties

Behaviour in the process

Propylene behaves as a liquefiable flammable gas that is heavier than air, and that shapes how it is stored, handled and detected:

• Liquefied by moderate pressure. With a critical temperature of 92.4 °C and vapour pressure of about 10 bar at 20 °C, it is stored as a pressurised liquid and pumped as a liquid.
• Heavier than air. Escaped gas collects in low points, drains and trenches rather than dispersing upward, so detectors and ventilation belong low.
• Reactive double bond. It polymerises, oxidises and adds halogens, water and acids. Stereoregular polymerisation to polypropylene needs a catalyst system.
• Cold from flashing liquid. A liquid release flashes and chills sharply, with a large expansion in volume that creates both cold burns and a sizeable flammable cloud.
• Catalyst sensitivity. As with ethylene, trace poisons matter far more to a polypropylene reactor than the bulk purity figure.

Polymer Grade vs Chemical Grade and Related Olefins

Propylene is bought by grade, and the grade decides which downstream plants can use it without further purification.

Stated plainly: polymer grade is a purity and poison specification, chemical grade is the economic choice where propane is inert, and refinery grade is an intermediate stream. Propylene itself has no direct substitute in polypropylene, though some chemicals can be made from other routes.

Industries We Supply Propylene To

The same liquid goes to a polypropylene plant, an acrylonitrile unit and a cumene works. What changes is the purity and the poison limits each process requires.

Where Propylene is Used

Propylene is bought overwhelmingly to make polypropylene, with a large chemical chain behind it. These are the end uses our customers buy it for.

In polypropylene manufacture

Propylene is polymerised with a Ziegler-Natta or metallocene catalyst in a slurry, bulk or gas-phase reactor, with ethylene or butene added for copolymers and hydrogen used to control molecular weight. The catalyst system controls isotacticity, and so crystallinity, stiffness and melting point. Poisons in the monomer reduce productivity and can change the polymer's tacticity.

In propylene oxide manufacture

Propylene is epoxidised either through the chlorohydrin route or through hydroperoxide co-product routes, or by newer HPPO processes using hydrogen peroxide. The choice of route sets the by-products and the feed requirements, and some routes are sensitive to propane and other C3 impurities.

The propane problem

This deserves its own section because propane is the main impurity in propylene and the two are separated only with difficulty. Propane is inert in most chemical uses but wastes reactor volume in polymerisation, so polymer grade specifies it low. Understanding what propane your process can tolerate is the commercial key to buying the right grade.

Quality Control & Testing

Every lot is released against a batch-specific Certificate of Analysis based on gas chromatography, with trace impurities reported to the limits you specify.

• Propylene and propane content — by gas chromatography, the primary grade measure.
• Ethylene and C4 components — checked against polymer-grade limits.
• Carbon monoxide, carbon dioxide and COS — the catalyst poisons, reported in ppm and ppb.
• Arsine and phosphine — trace analysis, particularly for refinery-derived material.
• Total sulphur — by sulphur chemiluminescence or equivalent.
• Water and oxygen — measured to ppm levels, relevant to catalyst activity and corrosion.
• Methanol and other oxygenates — particularly relevant for MTO-derived streams.

Common Process Problems & Likely Causes

When propylene causes trouble, it is usually trace poisons, a propane-content shortfall or a handling problem. This table is the shortcut our technical desk works through before anyone opens a complaint file.

Packaging, Storage & Shipping

• Standard packing. ISO tank containers, road tankers and rail cars for pressurised liquid propylene, with cylinders for small quantities.
• Pressure control. Held as a liquid at around 10 bar at ambient temperature, in tanks rated for the highest expected vapour pressure with relief devices.
• Storage. Outdoors or in well-ventilated, fire-resistant areas, away from heat and ignition sources, in bunded and earthed tanks.
• Low-point awareness. Because the vapour is heavier than air, avoid pits, trenches and basements near storage and use low-level gas detection.
• Segregation. Keep from oxidisers, halogens and strong acids.
• Electrical and ignition control. Earth and bond transfer lines, use flameproof equipment and control static in loading operations.
• Shelf life. Stable in sound, leak-free containers. Re-check purity after long storage, particularly water and oxygen.
• Transport classification. UN 1077 propylene, Class 2.1 flammable gas.

Hazards & Safe Handling

Propylene is an extremely flammable liquefied gas and a simple asphyxiant with mild anaesthetic effects at high concentration. Fire, pressure and cold from flashing liquid are the real hazards.

• Fire and explosion. Flammable range about 2.0 to 11.1% in air. Control ignition sources, fit gas detection and earth all equipment.
• Heavy vapour. Gas pools at low points and can travel to ignition sources some distance away. Ventilate low spaces and monitor.
• Pressure hazard. Tanks and cylinders can rupture in fire or if overfilled. Use pressure relief and protect from heat.
• Asphyxiation. High concentrations in enclosed spaces displace oxygen. Ventilate and monitor before entry.
• Cold burns. Liquid releases flash and freeze skin on contact. Use insulated gloves and a face shield.
• PPE. Flame-resistant clothing, safety glasses, cold-protective gloves and portable gas detection.
• Leak response. Isolate the source if safe to do so, evacuate, ventilate and exclude ignition sources until the area is confirmed gas-free.
• Environment. Readily lost to air and not significantly bioaccumulative. Vent only through approved flare or recovery systems.

Regulatory & Compliance Notes

Propylene is a widely traded commodity with well-established regulatory handling. Because obligations differ by territory and use, the notes below are orientation rather than legal advice — confirm your own position with your regulatory adviser.

• REACH and chemical inventories. Propylene is registered under EU REACH and listed on major inventories, with the supplier's role confirmed in the quotation.
• GHS classification. Flammable gas (Category 1), gas under pressure. The SDS carries the full hazard statements.
• Dangerous goods transport. UN 1077, Class 2.1. ADR, IMDG, IATA and DOT requirements apply to tank design, labelling and routing.
• Process safety. Storage and use fall under major-hazard and flammable-liquid rules in many jurisdictions, including zoning and hazardous area classification.
• Occupational limits. Exposure limits vary by country; confirm local limits and set detection and ventilation accordingly.
• Quality agreements. Polymer producers commonly expect documented specification, test methods and change control. Tell us what your agreement requires.

We Supply Propylene Worldwide

Chelora Chemicals is a supplier and export partner, not a single-plant trader. We ship Propylene from India and from partner sources to customers across Asia, Europe, the Middle East, Africa, and North and South America, handling the export documentation, dangerous-goods paperwork and freight so the material arrives ready to use.

• Incoterms. EXW, FOB, CIF, CFR and DAP quoted to suit your purchasing terms and freight arrangements.
• Ports. Regular shipments through Nhava Sheva (JNPT) and Mundra, with other ports arranged where the dangerous-goods rules and routing allow.
• Documentation. Commercial invoice, packing list, certificate of origin, COA, SDS and the dangerous-goods declaration issued as a complete set.
• Flexible volumes. From cylinder quantities through ISO tanks up to repeat bulk loads on a supply contract.
• Supply continuity. Because we are independent of any one producer, a plant turnaround or a shipping disruption at one source does not have to become your stock-out.

Buying Propylene from Chelora

We are an independent sourcing and supply partner. For propylene that means settling three things at enquiry: the grade and poison limits, the propane tolerance of your process, and the dangerous-goods route to your site — because for this product the logistics are as much a part of the specification as the purity.

• Documentation on every lot. Batch-specific COA with propylene content and trace impurities, plus SDS and dangerous-goods paperwork.
• Analysis before commitment. Representative analysis shared ahead of a commercial order so your lab can qualify the material.
• Quantities. From cylinders through to full ISO tank and bulk loads on contract supply.
• Grade range. Polymer grade, chemical grade and refinery grade, with tighter limits on arsine, phosphine or CO where your catalyst needs them.
• Inspection. Independent third-party inspection available at loading when the contract requires it.
• Related olefins. Ethylene, 1-butene, isobutylene and 1,3-butadiene alongside propylene from one supplier.

How ordering works

• Send the enquiry. Product, grade or purity, quantity, destination port and the Incoterm you buy on. If you have a spec sheet, attach it — it saves a round trip.
• We quote. Price, lead time, packing format and a sample COA, normally within one working day.
• Qualify the supply. For first orders or critical applications, we share the analysis and handling documentation so your technical and safety teams can sign off before you commit.
• Confirm the order. Proforma invoice issued; payment terms agreed against the volume and the relationship.
• Allocation and QC. Material allocated and released against a batch-specific COA, with an independent inspection where the contract calls for it.
• Ship and document. Filled, labelled and loaded with the full export and dangerous-goods document set, and tracked through to arrival.

Related Olefins & Petrochemical Feedstocks

Buyers of propylene often source other olefins alongside it — polypropylene and polyethylene plants typically buy ethylene or butene comonomers on the same programme. Consolidating them cuts freight cost and gives you a single point of contact for documentation.