propylene

{{main|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.Ashford's Dictionary of Industrial Chemicals, Third edition, 2011, {{ISBN|978-0-9522674-3-0}}, pages 7766-9

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%.{{cite web |url=http://www.dow.com/productsafety/finder/pro.htm |title=Product Safety Assessment(PSA): Propylene |publisher=Dow Chemical Co. |access-date=2011-07-11 |archive-url=https://web.archive.org/web/20130828163039/http://www.dow.com/productsafety/finder/pro.htm |archive-date=2013-08-28 }} In the United States, shale gas is a major source of propane.

In the Phillips triolefin or olefin conversion technology, propylene is interconverted with ethylene and 2-butenes. Rhenium and molybdenum catalysts are used:{{cite journal|last1=Ghashghaee|first1=Mohammad|title=Heterogeneous catalysts for gas-phase conversion of ethylene to higher olefins|journal=Rev. Chem. Eng.|volume=34|issue=5|pages=595–655|doi=10.1515/revce-2017-0003|year=2018|s2cid=103664623}}

:CH2=CH2{} + CH3CH=CHCH3 ->[][\text{Re, Mo} \atop \text{catalyst}] 2 CH2=CHCH3

The technology is founded on an olefin metathesis reaction discovered at Phillips Petroleum Company.{{cite journal | last1 = Banks | first1 = R. L. | last2 = Bailey | first2 = G. C. | title = Olefin Disproportionation. A New Catalytic Process | journal = Industrial & Engineering Chemistry Product Research and Development | volume = 3 |issue=3| pages = 170–173 | year = 1964 | doi = 10.1021/i360011a002}}{{cite encyclopedia|chapter=Metathesis|encyclopedia=Kirk-Othmer Encyclopedia of Chemical Technology|author=Lionel Delaude |author2=Alfred F. Noels |year=2005| doi=10.1002/0471238961.metanoel.a01|place=Weinheim|publisher=Wiley-VCH|isbn=978-0-471-23896-6}} Propylene yields of about 90 wt% are achieved.

{{main|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.

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.{{cite journal |doi=10.1016/j.joule.2017.07.008|title=Electrification and Decarbonization of the Chemical Industry|year=2017|last1=Schiffer|first1=Zachary J.|last2=Manthiram|first2=Karthish|journal=Joule|volume=1|issue=1 |pages=10–14|bibcode=2017Joule...1...10S |hdl=1721.1/124019|s2cid=117360588 |hdl-access=free}}

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.

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.{{cite journal|doi=10.1016/J.ENG.2017.02.006|title=New Trends in Olefin Production|year=2017|last1=Amghizar|first1=Ismaël|last2=Vandewalle|first2=Laurien A.|last3=Van Geem|first3=Kevin M.|last4=Marin|first4=Guy B.|journal=Engineering|volume=3|issue=2|pages=171–178|doi-access=free|bibcode=2017Engin...3..171A }} Total world production of propene is currently about half that of ethylene.

The use of engineered enzymes has been explored but has not been commercialized.{{cite web |url= https://greenchemicalsblog.com/2012/10/12/global-bioenergies-in-bio-propylene |website= Green Chemicals Blog |title= Global Bioenergies in bio-propylene |first= Doris |last= de Guzman |date= October 12, 2012 }}

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.{{cite journal | last1=Wu | first1=Tianwei | last2=Yu | first2=Qingbo | last3=Roghair | display-authors=etal | title=Chemical looping oxidative dehydrogenation of propane: A comparative study of Ga-based, Mo-based, V-based oxygen carriers | journal=Chemical Engineering and Processing - Process Intensification | volume=157 | year=2020 | issn=0255-2701 | doi=10.1016/j.cep.2020.108137 | page=108137| doi-access=free | bibcode=2020CEPPI.15708137W }}

Propylene is the second most important starting product in the petrochemical industry after ethylene. It is the raw material for a wide variety of products. Polypropylene manufacturers consume nearly two thirds of global production. Polypropylene end uses include films, fibers, containers, packaging, and caps and closures. Propene is also used for the production of chemicals such as propylene oxide, acrylonitrile, cumene, butyraldehyde, and acrylic acid. In the year 2013 about 85 million tonnes of propylene were processed worldwide.{{cite web |url=http://www.ceresana.com/en/market-studies/chemicals/propylene/ |title=Market Study: Propylene (2nd edition), Ceresana, December 2014|publisher=ceresana.com |access-date=2015-02-03}}

Propylene and benzene are converted to acetone and phenol via the cumene process.

Image:Cumene-process-overview-2D-skeletal.png

Propylene is also used to produce isopropyl alcohol (propan-2-ol), acrylonitrile, propylene oxide, and epichlorohydrin.{{Cite book |contribution = 8034. Propylene |year = 1996 |title = The Merck Index, Twelfth Edition |editor-last = Budavari |editor-first = Susan |pages = 1348–1349 |place = New Jersey |publisher = Merck & Co.}}

The industrial production of acrylic acid involves the catalytic partial oxidation of propylene.{{cite book |last1=J.G.L.|first1=Fierro (Ed.) |title=Metal Oxides, Chemistry and Applications |date=2006 |publisher=CRC Press |pages=414–455}} Propylene is an intermediate in the oxidation to acrylic acid.

In industry and workshops, propylene is used as an alternative fuel to acetylene in Oxy-fuel welding and cutting, brazing and heating of metal for the purpose of bending. It has become a standard in BernzOmatic products and others in MAPP substitutes,[http://www.worthingtonindustries.com/getmedia/ff77868e-b526-44ae-9064-e51aaa5ea02f/wc001-map-pro-premium-hand-torch-fuel For example, "MAPP-Pro"] now that true MAPP gas is no longer available.

Propylene resembles other alkenes in that it undergoes electrophilic addition reactions relatively easily at room temperature. The relative weakness of its double bond explains its tendency to react with substances that can achieve this transformation. Alkene reactions include:

• Polymerization and oligomerization
• Oxidation
• Halogenation
• Hydrohalogenation
• Alkylation
• Hydration
• Hydroformylation

Foundational to hydroformylation, alkene metathesis, and polymerization are metal-propylene complexes, which are intermediates in these processes. Propylene is prochiral, meaning that binding of a reagent (such as a metal electrophile) to the C=C group yields one of two enantiomers.

{{See also|Polypropylene}}

The majority of propylene is used to form polypropylene, a very important commodity thermoplastic, through chain-growth polymerization. In the presence of a suitable catalyst (typically a Ziegler–Natta catalyst), propylene will polymerize. There are multiple ways to achieve this, such as using high pressures to suspending the catalyst in a solution of liquid propylene, or running gaseous propylene through a fluidized bed reactor.{{Citation |last=Heggs |first=T. Geoffrey |title=Polypropylene |date=2011-10-15 |url=https://onlinelibrary.wiley.com/doi/10.1002/14356007.o21_o04 |encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry |pages=o21_o04 |editor-last=Wiley-VCH Verlag GmbH & Co. KGaA |place=Weinheim, Germany |publisher=Wiley-VCH Verlag GmbH & Co. KGaA |language=en |doi=10.1002/14356007.o21_o04 |isbn=978-3-527-30673-2 |access-date=2021-07-09|url-access=subscription }}

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In the presence of catalysts, propylene will form various short oligomers. It can dimerizes to give 2,3-dimethyl-1-butene and/or 2,3-dimethyl-2-butene.{{cite journal |doi=10.1021/acs.chemrev.0c00076 |title=Nickel Catalyzed Olefin Oligomerization and Dimerization |year=2020 |last1=Olivier-Bourbigou |first1=H. |last2=Breuil |first2=P. A. R. |last3=Magna |first3=L. |last4=Michel |first4=T. |last5=Espada Pastor |first5=M. Fernandez |last6=Delcroix |first6=D. |journal=Chemical Reviews |volume=120 |issue=15 |pages=7919–7983|pmid=32786672 |s2cid=221124789 |url=https://hal-ifp.archives-ouvertes.fr/hal-02954532/file/Nickel%20Catalyzed%20Olefin.pdf }} or trimerise to form tripropylene.

Propene is a product of combustion from forest fires, cigarette smoke, and motor vehicle and aircraft exhaust. It is an impurity in some heating gases. Observed concentrations have been in the range of 0.1–4.8 parts per billion (ppb) in rural air, 4–10.5 ppb in urban air, and 7–260 ppb in industrial air samples.

In the United States and some European countries a threshold limit value of 500 parts per million (ppm) was established for occupational (8-hour time-weighted average) exposure. It is considered a volatile organic compound (VOC) and emissions are regulated by many governments, but it is not listed by the U.S. Environmental Protection Agency (EPA) as a hazardous air pollutant under the Clean Air Act. With a relatively short half-life, it is not expected to bioaccumulate.

Propene has low acute toxicity from inhalation and is not considered to be carcinogenic. Chronic toxicity studies in mice did not yield significant evidence suggesting adverse effects. Humans briefly exposed to 4,000 ppm did not experience any noticeable effects.{{Cite web|last=PubChem|title=Hazardous Substances Data Bank (HSDB): 175|url=https://pubchem.ncbi.nlm.nih.gov/source/hsdb/175#section=Human-Toxicity-Excerpts-(Complete)|access-date=2021-07-09|website=pubchem.ncbi.nlm.nih.gov|language=en}} Propene is dangerous from its potential to displace oxygen as an asphyxiant gas, and from its high flammability/explosion risk.

Bio-propylene is the bio-based propylene.[https://www.roadtobio.eu/uploads/news/2017_October/RoadToBio_Drop-in_paper.pdf Bio-based drop-in, smart drop-in and dedicated chemicals][https://www.wur.nl/nl/Onderzoek-Resultaten/Onderzoeksinstituten/food-biobased-research/Oplossingen/Duurzame-bioplastics-op-basis-van-hernieuwbare-grondstoffen.htm Duurzame bioplastics op basis van hernieuwbare grondstoffen]

It has been examined, motivated by diverse interests such a carbon footprint. Production from glucose has been considered.{{Cite web|last=Guzman|first=Doris de|title=Global Bioenergies in bio-propylene|url=https://greenchemicalsblog.com/2012/10/12/global-bioenergies-in-bio-propylene/|access-date=2021-07-09|website=Green Chemicals Blog|date=12 October 2012|language=en-US}} More advanced ways of addressing such issues focus on electrification alternatives to steam cracking.

Propene is flammable. Propene is usually stored as liquid under pressure, although it is also possible to store it safely as gas at ambient temperature in approved containers.Encyclopedia of Chemical Technology, Fourth edition, 1996, {{ISBN|0471-52689-4}} (v.20), page 261

Propene is detected in the interstellar medium through microwave spectroscopy.{{cite journal|title=Discovery of Interstellar Propylene (CH2CHCH3): Missing Links in Interstellar Gas-Phase Chemistry |publisher=IOP |date=2007-08-10 |doi=10.1086/521398 |last1=Marcelino |first1=N. |last2=Cernicharo |first2=J. |last3=Agúndez |first3=M. |last4=Roueff |first4=E. |last5=Gerin |first5=M. |last6=Martín-Pintado |first6=J. |last7=Mauersberger |first7=R. |last8=Thum |first8=C. |display-authors=3|journal=The Astrophysical Journal |volume=665 |issue=2 |pages=L127–L130 |arxiv=0707.1308 |bibcode=2007ApJ...665L.127M |s2cid=15832967 |doi-access=free }} On September 30, 2013, NASA announced the detection of small amounts of naturally occurring propene in the atmosphere of Titan using infrared spectroscopy.{{cite web |date=2013-09-30 |title=Spacecraft finds propylene on Saturn moon, Titan |url=http://www.upi.com/Science_News/2013/09/30/Cassini-finds-ingredient-of-household-plastic-on-Saturn-moon/UPI-42881380571911/ |access-date=2013-11-12 |publisher=UPI.com}}{{cite web |title=Cassini finds ingredient of household plastic on Saturn moon |url=http://www.spacedaily.com/reports/Cassini_finds_ingredient_of_household_plastic_on_Saturn_moon_999.html |access-date=2013-11-12 |publisher=Spacedaily.com}}{{Cite journal |last1=Nixon |first1=C. A. |last2=Jennings |first2=D. E. |last3=Bézard |first3=B. |last4=Vinatier |first4=S. |last5=Teanby |first5=N. A. |last6=Sung |first6=K. |last7=Ansty |first7=T. M. |last8=Irwin |first8=P. G. J. |last9=Gorius |first9=N. |last10=Cottini |first10=V. |last11=Coustenis |first11=A. |last12=Flasar |first12=F. M. |date=2013-09-30 |title=Detection of Propene in Titan's Stratosphere |url=https://iopscience.iop.org/article/10.1088/2041-8205/776/1/L14 |journal=The Astrophysical Journal |volume=776 |issue=1 |pages=L14 |doi=10.1088/2041-8205/776/1/L14 |issn=2041-8205|arxiv=1309.4489 |bibcode=2013ApJ...776L..14N }} The detection was made by a team led by NASA GSFC scientist Conor Nixon using data from the CIRS instrument {{Citation |last1=Flasar |first1=F. M. |title=Exploring the Saturn System in the Thermal Infrared: The Composite Infrared Spectrometer |date=2004 |work=The Cassini-Huygens Mission: Orbiter Remote Sensing Investigations |pages=169–297 |editor-last=Russell |editor-first=Christopher T. |url=https://link.springer.com/chapter/10.1007/1-4020-3874-7_4 |access-date=2025-01-05 |place=Dordrecht |publisher=Springer Netherlands |language=en |doi=10.1007/1-4020-3874-7_4 |isbn=978-1-4020-3874-7 |last2=Kunde |first2=V. G. |last3=Abbas |first3=M. M. |last4=Achterberg |first4=R. K. |last5=Ade |first5=P. |last6=Barucci |first6=A. |last7=Bézard |first7=B. |last8=Bjoraker |first8=G. L. |last9=Brasunas |first9=J. C.|bibcode=2004chm..book..169F |url-access=subscription }}{{Cite journal |last1=Jennings |first1=D. E. |last2=Flasar |first2=F. M. |last3=Kunde |first3=V. G. |last4=Nixon |first4=C. A. |last5=Segura |first5=M. E. |last6=Romani |first6=P. N. |last7=Gorius |first7=N. |last8=Albright |first8=S. |last9=Brasunas |first9=J. C. |last10=Carlson |first10=R. C. |last11=Mamoutkine |first11=A. A. |last12=Guandique |first12=E. |last13=Kaelberer |first13=M. S. |last14=Aslam |first14=S. |last15=Achterberg |first15=R. K. |date=2017-06-20 |title=Composite infrared spectrometer (CIRS) on Cassini |url=https://opg.optica.org/ao/abstract.cfm?uri=ao-56-18-5274 |journal=Applied Optics |language=EN |volume=56 |issue=18 |pages=5274–5294 |doi=10.1364/AO.56.005274 |pmid=29047582 |bibcode=2017ApOpt..56.5274J |issn=2155-3165}} on the Cassini orbiter spacecraft, part of the Cassini-Huygens mission. Its confirmation solved a 32-year old mystery by filling a predicted gap in Titan's detected hydrocarbons, adding the C₃H₆ species (propene) to the already-detected C₃H₄ (propyne) and C₃H₈ (propane).{{Cite journal |last1=Maguire |first1=W. C. |last2=Hanel |first2=R. A. |last3=Jennings |first3=D. E. |last4=Kunde |first4=V. G. |last5=Samuelson |first5=R. E. |date=August 1981 |title=C3H8 and C3H4 in Titan's atmosphere |url=https://www.nature.com/articles/292683a0 |journal=Nature |language=en |volume=292 |issue=5825 |pages=683–686 |doi=10.1038/292683a0 |issn=1476-4687}}

• Los Alfaques disaster
• Inhalant abuse
• 2014 Kaohsiung gas explosions
• 2020 Houston explosion
• Titan (moon)

{{Reflist|30em}}

{{Alkenes}}

{{Molecules detected in outer space}}

{{GABAAR PAMs}}

{{Hydrides by group}}

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Category:Alkenes

Category:Monomers

Category:Commodity chemicals

Category:Petrochemicals

Category:Gases

Category:Allyl compounds