05 | 2010

Basics
Basics of Bio-Polyolefins
Polyethylene
H H
| |
— C — C —
| |
H H
n
Plastic Fuel Tank made from bio-PE
(Photo: Courtesy Braskem)
Ethylene
H H
\ /
C ═ C
/ \
H H
As it has almost become a habit, let’s start our ‘basics’ article with a look
into Wikipedia: A polyolefin is a polymer produced from a simple olefin
(also called an alkene with the general formula C n
H 2n
) as a monomer.
For example, polyethylene (C 2
H 4
)n (PE) is the polyolefin produced by polymerizing
the olefin ethylene H 2
C=CH 2
. Polypropylene (PP) is another common polyolefin
which is made from the olefin propylene. In some cases PE is produced
as a copolymer using butene, hexene or octene as comonomer.
Polyethylene
Polyethylene or polythene (IUPAC name polyethene or poly(methylene)) is the
most widely used plastic, with an annual production of approximately 80 million
metric tons (2008). Its primary use is within packaging [1]. And in bioplastics
MAGAZINE 01/2008 Dr. Thomas Isenburg wrote: Polyethylene is a plastic material
that has been known for more than 100 years. It is found in millions of applications
from simple film, through containers, to toys or technical components such as
plastic fuel tanks for cars.
Polyethylene was discovered by the chemist Hans von Pechmann in 1898. In
1933 polyethylene was successfully produced, at a pressure of 1400 bar and
a temperature of 170°C, at the ICI laboratories. For a large scale industrial
process these conditions were, however, difficult to produce and were highly
energy intensive. In 1953 polymer chemistry saw a major breakthrough. The
chemists Karl Ziegler and Giulio Natta succeeded in synthesising polyethylene
from ethylene at normal pressure using catalysts.
Ethylene
So it all starts with ethylene…
Ethylene is a chemical intermediate used to produce many different products,
besides polyethylene (PE), for example polyethylene terephthalate (PET),
polyvinyl chloride (PVC), and polystyrene (PS) can be named. Its current world
production capacity is around 115,000 tons per year, mainly (>98%) through the
petrochemical route based on steam cracking (thermal pyrolysis) of petroleum
liquids (naphtha, condensate, and gas oils) and natural gas feedstocks (ethane,
propane, and butane).
However, before the boom of petroleum started in the early 1950s, ethylene
was produced from ethanol. Interestingly, the first report that was published in
the literature about the catalytic dehydration of ethanol to ethylene dates from
1797.
Applying the catalytic dehydration of ethanol to produce ethylene is again
becoming more and more important. Especially in Brazil, with the building
of large-scale plants motivated by the Brazilian sugarcane based ethanol
competitiveness and by the low carbon footprint of the product obtained by this
route. Just a few weeks before publication of this issue of bioplastics MAGAZINE
Braskem started the manufacture of polyethylene on a large scale based on
Brazilian renewable ethanol.
52 bioplastics MAGAZINE [05/10] Vol. 5