Chemical Engineering November 2013 - 18

Braskem
Newsfront
Water
Inert
(adiabatic)
HoNor AwArd:
BrAskem
Sugarcane-based ethylene
and polyethylene
Polyethylene (PE) is the most commercialized
plastic in the world, with
annual production of approximately
70 million m.t., most of which is
produced from petroleum-based ethylene.
With the delivery of first lots
of Braskem's sugarcane-based PE in
early 2011, the company set a new
milestone for the CPI by producing
this commodity material from 100%
renewable resources. The achievement
was the culmination of years of
scientific and engineering teamwork.
Leveraging on Brazil's existing bioethanol
industry, which has been supplying
nearly 20% of the country's fuel
demands, Braskem developed a process
to utilize the 92.5 wt.% bioethanol
- that is used directly as fuel for cars
- to make ethylene, which is then polymerized
into various grades of PE.
In Braskem's process (Figure 4),
the ethanol dehydration reaction
is performed in the vapor phase in
randomly packed, fixed-bed reactors
with a heterogeneous catalyst, such
as alumina, silica-alumina or zeolites.
Fixed-bed reactors are operated
adiabatically. The temperature drop,
caused by the endothermic reaction,
is minimized by adding an inert heatcarrying
fluid along with ethanol
feedstock. A single reactor or, preferably,
multiple reactors in series are
typically used, with intermediate furnaces
to reheat the streams that feed
the next reactor.
After the dehydration reaction,
the raw ethylene product is quickly
cooled by a water quench to remove
the product water and condensable
polar substances, such as unreacted
ethanol and small amounts of acetaldehyde
and acetic acid. The crude ethylene
is then scrubbed with caustic to
remove traces of CO2. The ethylene
stream is then compressed, and dried
to produce a chemical-grade ethylene
with purity greater than 99%. When
polymer-grade ethylene is required,
the chemical-grade ethylene is further
purified to remove heavy and
light contaminants.
Effluents from the quench and
scrubbing towers contain mostly acetRaw
ethylene
Chemical
grade
ethylene
Polymer
grade
ethylene
Heavy
contaminants
Aqueous
effluent
Caustic
effluent
Reaction
Quench Scrubbing Drying
Purification
system
Figure 4. In Braskem's process, sugarcane-based ethanol is dehydrated to form
ethylene, which is then used to make polyethylene
aldehyde, diethyl ether and unreacted
ethanol. These components are removed
in a specially designed separation
system, which achieves a chemical
oxygen demand (COD) lower than
100 parts per million (ppm) and the
oxygenates are recovered for either recycling
in the plant, or used as fuel.
The proprietary dehydration technology
produces ethylene monomer
from ethanol in a very efficient way.
The carbon yield of the process is higher
than 98% and the small amount of byproducts
is recovered, supplying part
of the energy required by the process.
The process generates a final liquid
effluent consisting of water with less
than 10 ppm oxygenated compounds
permitting the aqueous effluent to be
easily treated or reused.
This bioethylene is used to produce
many grades of biopolyethylene in two
different polymer plants. The polymers
can be transformed in a variety
of products for a wide range of applications
including blow molding, injection
molding and films using the current
machinery that exists in plastics
processing industries.
Depending on the grade, the biopolyethylene
life cycle assessment indicates
the capture of 2.0-2.5 tons of
CO2 per ton of polymer from cradle-togate,
instead of the 1.9 tons of CO2 per
ton released by fossil-based PEs.
Today, bio-based ethylene and PE
are being produced in an industrial
unit with a 200,000-ton/yr bio-basedethylene
capacity that started up its
pre-operation in September 2010 in
Triunfo, Brazil. The commercialization
of biopolyethylene started in early
2011 using the " I'm Green " tradename,
supplying biopolyethylene resins to
global companies such as Toyota,
Danone, Shiseido, Tetra-pak, Chanel,
Coca-Cola, Johnson & Johnson and
18 ChemiCal engineering www.Che.Com november 2013
Natura. The bioethylene has also been
commercially supplied to Lanxess for
EPDM production since 2012.
HoNor AwArd:
eAstmAN CHemiCAl Co.
Perennial Wood
Wood is a preferred building material
because of its beauty, character,
workability and renewable nature.
Unprotected in outdoor applications,
however, it rots, decays, shrinks and
swells limiting its use. In February
2012, Eastman Chemical Co. commercialized
Perennial Wood - pine
that is chemically modified through
acetylation to change this paradigm
and offer builders, contractors and homeowners
real wood that lasts longer
than unmodified wood, has greater
dimensional stability and has greater
surface hardness.
This modified - not treated - wood
has a physical barrier against rot with
improved dimensional stability over
unmodified wood. Eastman introduced
Perennial Wood decking in February
2012 and Perennial Wood porch flooring
later in the year. Both products
come with a 25-year limited warranty
against rot, decay and movement.
Wood has a natural affinity for
water, stemming from a tree's need to
transport moisture through its vascular
system when alive. Part of this
affinity comes from hydroxyl groups
located throughout the lignin, cellulose
and hemicellulose structures.
Acetic anhydride (Ac2O) reacts with
these OH groups on components of the
cell wall, changing the hydrophilic OH
groups into more hydrophobic acetyl
groups, and making a permanent alteration
to the wood chemistry.
(wood)-OH + Ac2O → (wood)-OAc +
AcOH
Ethanol
Vaporization
Furnace
Crude
ethylene
NaOH
solution
Light
contaminants
http://www.Che.Com
Chemical Engineering November 2013

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