Propylene - Wikipedia

Steam cracking

edit Main article: Steam cracking

The dominant technology for producing propylene is steam cracking, using propane as the feedstock. Cracking propane yields a mixture of ethylene, propylene, methane, hydrogen gas, and other related compounds. The yield of propylene is about 15%. The other principal feedstock is naphtha, especially in the Middle East and Asia.[7] Propylene can be separated by fractional distillation from the hydrocarbon mixtures obtained from cracking and other refining processes; refinery-grade propene is about 50 to 70%.[8] In the United States, shale gas is a major source of propane.

Olefin conversion technology

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In the Phillips triolefin or olefin conversion technology, propylene is interconverted with ethylene and 2-butenes. Rhenium and molybdenum catalysts are used:[9]

CH 2 = CH 2 + CH 3 CH = CHCH 3 → Re, Mo catalyst 2 CH 2 = CHCH 3 {\displaystyle {\ce {CH2=CH2{}+CH3CH=CHCH3->[][{\text{Re, Mo}} \atop {\text{catalyst}}]2CH2=CHCH3}}}  

The technology is founded on an olefin metathesis reaction discovered at Phillips Petroleum Company.[10][11] Propylene yields of about 90 wt% are achieved.

Main article: Syngas to gasoline plus

Related is the Methanol-to-Olefins/Methanol-to-Propene process. It converts synthesis gas (syngas) to methanol, and then converts the methanol to ethylene and/or propene. The process produces water as a by-product. Synthesis gas is produced from the reformation of natural gas or by the steam-induced reformation of petroleum products such as naphtha, or by gasification of coal or natural gas.

Fluid catalytic cracking

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High severity fluid catalytic cracking (FCC) uses traditional FCC technology under severe conditions (higher catalyst-to-oil ratios, higher steam injection rates, higher temperatures, etc.) in order to maximize the amount of propene and other light products. A high severity FCC unit is usually fed with gas oils (paraffins) and residues, and produces about 20–25% (by mass) of propene on feedstock together with greater volumes of motor gasoline and distillate byproducts. These high temperature processes are expensive and have a high carbon footprint. For these reasons, alternative routes to propylene continue to attract attention.[12]

Other commercialized methods

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On-purpose propylene production technologies were developed throughout the twentieth century. Of these, propane dehydrogenation technologies such as the CATOFIN and OLEFLEX processes have become common, although they still make up a minority of the market, with most of the olefin being sourced from the above mentioned cracking technologies. Platinum, chromia, and vanadium catalysts are common in propane dehydrogenation processes.

Market

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Propene production has remained static at around 35 million tonnes (Europe and North America only) from 2000 to 2008, but it has been increasing in East Asia, most notably Singapore and China.[13] Total world production of propene is currently about half that of ethylene.

Research

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The use of engineered enzymes has been explored but has not been commercialized.[14]

There is ongoing research into the use of oxygen carrier catalysts for the oxidative dehydrogenation of propane. This poses several advantages, as this reaction mechanism can occur at lower temperatures than conventional dehydrogenation, and may not be equilibrium-limited because oxygen is used to combust the hydrogen by-product.[15]