Propylene oxide is an organic compound with the molecular formula CH3CHCH2O.
This colourless volatile liquid is produced on a large scale industrially,
its major application being its use for the production of polyether polyols for
use in making polyurethane plastics. It is a chiral epoxide, although it is
commonly used as a racemic mixture. This compound is sometimes called
1,2-propylene oxide to distinguish it from its isomer 1,3-propylene oxide,
better known as oxetane. Production
Industrial production of propylene oxide starts from propylene. Two general
approaches are employed, one involving hydrochlorination and the other
involving oxidation. In 2005, about half of the world production was through
chlorohydrin technology and one half via oxidation routes. The latter approach is
growing in importance. = Hydrochlorination route=
The traditional route proceeds via the conversion of propylene to
chloropropanols: The reaction produces a mixture of
1-chloro-2-propanol and 2-chloro-1-propanol, which is then
dehydrochlorinated. For example: Lime is often used as a chlorine
absorber. = Co-oxidation of propylene=
The other general route to propylene oxide involves co-oxidation of the
organic chemicals isobutane or ethylbenzene. In the present of
catalyst, air oxidation occurs as follows:
CH3CH=CH2 + Ph-CH2CH3 + O2 → CH3CHCH2O + Ph-CH=CH2 + H2O
The coproducts of these reactions, t-butyl alcohol or styrene, are useful
feedstock for other products. For example, t-butyl alcohol reacts with
methanol to give MTBE, an additive for gasoline. Before the current US ban of
MTBE, propylene/isobutane was one of the most important production process.
= Oxidation of propylene= In April 2003, Sumitomo Chemical
commercialized the first PO-only plant in Japan, which produces propylene oxide
from oxidation of cumene without significant production of other
products. This method is a variant of the POSM process that uses cumene
hydroperoxide instead of ethylbenzene hydroperoxide and recycles the coproduct
via dehydration and hydrogenation back to cumene.
In March 2009, BASF and Dow Chemical started up their new HPPO plant in
Antwerp. In the HPPO-Process, propylene is oxidized with hydrogen peroxide:
CH3CH=CH2 + H2O2 → CH3CHCH2O + H2O In this process no side products other
than water are generated. Uses
Between 60 and 70% of all propylene oxide is converted to polyether polyols
for the production of polyurethane plastics. About 20% of propylene oxide
is hydrolyzed into propylene glycol, via a process which is accelerated by acid
or base catalysis. Other major products are polypropylene glycol, propylene
glycol ethers, and propylene carbonate. = Historic and niche uses=
Propylene oxide was once used as a racing fuel, but that usage is now
prohibited under the US NHRA rules for safety reasons. It has also been used in
glow fuel for model aircraft and surface vehicles, typically combined in small
percentages of around 2% as an additive to the typical methanol, nitromethane,
and oil mix. It is also used in thermobaric weapons, and microbial
fumigation. Fumigant
The United States Food and Drug Administration has approved the use of
propylene oxide to pasteurize raw almonds beginning on September 1, 2007,
in response to two incidents of contamination by Salmonella in
commercial orchards, one incident occurring in Canada and one in the
United States. Pistachio nuts can also be subjected to propylene oxide to
control Salmonella. Microscopy
Propylene oxide is commonly used in the preparation of biological samples for
electron microscopy, to remove residual ethanol previously used for dehydration.
In a typical procedure, the sample is first immersed in a mixture of equal
volumes of ethanol and propylene oxide for 5 minutes, and then four times in
pure oxide, 10 minutes each. Safety
Propylene oxide is a probable human carcinogen, and listed as an IARC Group
2B carcinogen. References
External links WebBook page for C3H6O
Propylene oxide at the United States Environmental Protection Agency
Propylene oxide - chemical product info: properties, production, applications.
Propylene oxide at the Technology Transfer Network Air Toxics Web Site
CDC - NIOSH Pocket Guide to Chemical Hazards