Propylene

Key takeaways

Propylene belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Propylene to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Propylene from memory before moving on to harder problems.

Reference excerpt

Propylene, also known as propene, is an unsaturated organic compound with the chemical formula CH3CH=CH2. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petroleum-like odor. Propylene is a product of combustion from forest fires, cigarette smoke, and motor vehicle and aircraft exhaust. It was discovered in 1850 by A. W. von Hoffmann's student John Williams Reynolds as the only gaseous product of thermal decomposition of amyl alcohol to react with chlorine and bromine.

Production

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. 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%. In the United States, shale gas is a major source of propane.

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

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. Propylene yields of about 90 wt% are achieved.

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 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.

Other commercialized methods 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 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. Total world production of propene is currently about half that of ethylene.

Research The use of engineered enzymes has been explored but has not been commercialized. 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.

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

Propylene is also used to produce isopropyl alcohol (propan-2-ol), acrylonitrile, propylene oxide, and epichlorohydrin. The industrial production of acrylic acid involves the catalytic partial oxidation of propylene. 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, now that true MAPP gas is no longer available.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Propylene

Start with the simplest possible case. Write down what Propylene claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Propylene before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Propylene ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Propylene

In research: Propylene appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Propylene in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Propylene is common in secondary-school and first-year university syllabi. It links to neighbouring topics Alkenes, Allyl compounds, Commodity chemicals, so understanding it makes those chapters shorter.
In everyday life: Look for Propylene outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Propylene in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Propylene means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Propylene out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Propylene in simple terms?

Propylene, also known as propene, is an unsaturated organic compound with the chemical formula CH3CH=CH2. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons.

Why does Propylene matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Propylene?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Propylene.