Propylene, also called propene, a colourless, flammable, gaseous hydrocarbon, C3H6, obtained from petroleum; large quantities of propylene are used in the manufacture of resins, fibres, and elastomers, and numerous other chemical products.
As for its physical properties, it is a gas at room temperature, is soluble in hydrocarbon solvents, it is flammable, combustible, and has a low flash point, and also has a faint butane-like odor. The melting point of propylene is −169.4 °C [−301.4 °F], and its boiling point is −47 °C [−53.8 °F].
Propylene is second only to ethylene as an important raw material for producing other organic chemicals and, like ethylene, it has virtually no use “as-is”. Rather, it is used either alone (as in the production of polypropylene) or after reaction with other chemicals (as in the production of acrylonitrile, propylene oxide and oxo alcohols) for a large variety of industrial products. Propylene is commercially generated as a coproduct, either in an olefins plant or a crude oil refinery’s fluid catalytic cracking (FCC) unit, or produced in an on purpose reaction (for example, in a propane dehydrogenation, metathesis or methanol-to-olefins plant).
After ethylene, the second largest volume product from an ethylene plant is typically propylene. In fact, the production of propylene from such a plant is so important that the name “olefins plant” is often applied to this kind of manufacturing facility. Except where ethane is used as the feedstock, propylene is typically produced at levels ranging from 40 to 60 percent of the ethylene produced. In an olefins plant, propylene is generated by the same pyrolysis and purification process as ethylene.
Propylene was invented in 1950 by Fontana and is characterized by disorderly structure with an elevated molecular weight. The first commercial FCC unit was built by The M.W. Kellogg Company in Standard Oil of New Jersey’s Baton Rouge, Louisiana refinery and commissioned in May 1942.
Between 1942 and 1944 Kellogg built 22 of 34 FCC units constructed throughout the U.S, and the FCC process quickly became a major contributor to worldwide propylene and butylene production.
The global propylene capacity for 2016 is projected at over 127 MMT while the demand is pegged at around 102 MMT for 2016.
BASF SE, China National Petroleum Corp. (CNPC), Eni SpA, Enterprise Products Partners L.P., Exxon Mobil Corp., Formosa Plastics Group (FPG), Ineos Group Ltd., LyondellBasell Industries AF S.C.A., Reliance Industries Ltd., Royal Dutch Shell PLC, Saudi Basic Industries Corp. (SABIC), Sinopec Corp., The Dow Chemical Company, Total S.A., Valero Energy Corp. are some of the leading producers of Propylene. In India, the propylene capacities is projected to be 4.7 MMT for 2016-17 and expected to increase to around 4.8 MMT in 2017-18.
Global propylene demand is dominated by polypropylene production for automotive and mechanical parts, containers, fibers and films. Other important propylene consumption segments include acrylonitrile (used in acrylic fibers and ABS polymers), propylene oxide (used in propylene glycol antifreeze and polyurethanes), oxo-alcohols (used in coatings and plasticizers), cumene/phenol (used in polycarbonates and phenolic resins), acrylic acid (used in coatings, adhesives, and super absorbent polymers) and oxo chemicals (used in surface coatings and plasticizers).
Polypropylene is expected to remain the largest propylene derivative, and over the last five years, it has grown at annual rate of 3.8%. Higher growth rates are due to its low cost and versatility among the polyolefin industry. Propylene prices are expected to remain lower than the 2014 price range for the next five years which in turn will make polypropylene more cost advantage than the other polymers. Polypropylene growth rate over the next five years is expected to remain below the fast pace of expansion typically associated with polypropylene in the past.
A rapidly evolving consumer base in Asia (mainly China and India) continues to drive demand growth for propylene based derivatives. Growth of propylene derivative demand in India is also being fueled by consumers moving into the middle class.
There are several major licensors of conventional commercial olefin technologies, including: Lummus Technology, KBR, Linde, Technip, and the Shaw Group. In addition to the traditional pyrolysis and recovery technologies, new routes to ethylene and propylene production are being developed.
In a crude oil refinery, propylene is a coproduct of FCC units producing useful lighter products from atmospheric and vacuum gas oils. An FCC unit transforms these heavy oils into motor gasoline, fuel oils and significant quantities of olefins, especially butylenes and propylene. In areas where the refinery olefins supply is plentiful and there is a need for a high octane motor gasoline blend stock, the propylene and butylenes are often used to manufacture motor gasoline alkylate.
Although the propylene yielded from olefins plants and FCC units is typically considered a coproduct in the process to produce the more important primary products of ethylene and motor gasoline, propylene is also increasingly commercially produced on purpose.
Propylene production in refineries:
In a crude oil refinery, propylene is a coproduct of FCC units producing useful lighter products from atmospheric and vacuum gas oils. An FCC unit transforms these heavy oils into motor gasoline, fuel oils and significant quantities of olefins, especially butylenes and propylene.The main purpose of refinery is to produce motor gasoline and various grades of fule oils by separating crude oil into useful high value fractions and converting the other fractions into high value components by various specialized processes.
Propylene production in refineries
Catalytic dehydrogenation of propane produces propylene. This process is attractive when the local propane supply is abundant and steady, with a stable price structure relative to propylene. Two predominant propane dehydrogenation technologies are available, the UOP Oleflex process and the Lummus Catofin process.
Metathesis – the catalytic disproportionation of ethylene and butene – is an alternative method for the on purpose generation of propylene. This process enables propylene production from other olefinic products generated in an FCC unit or olefin plant.
Another potential propylene production technology, Methanol-to-propylene (MTP), is a catalytic conversion process developed by Lurgi. It is much like MTO process (as in ethylene section), but the products are propylene, gasoline, fuel gas and LPG rather than short chain olefins.