Styrene monomer (SM) is a valuable chemical
commodity used in many plastics and synthetic rubbers. Global
production is estimated around 25 million metric tons per
year.
The current styrene monomer technologies are over 70 years
old. All of the current SM technology offerings are based
on established, 2-step chemistry. First, benzene is alkylated
with ethylene over a solid acid catalyst to make ethylbenzene
(EB). Second, EB is dehydrogenated at high temperature (>600ºC)
over an iron oxide catalyst to styrene.
The reaction is thermodynamically limited and highly endothermic.
The high endothermic heat of reaction requires significant
input of energy.
Because all of the existing technologies are based on this
same chemistry, major improvements in process performance
are not likely, and achieving a competitive advantage is
difficult.
The ExSyM (Exelus Styrene Monomer
Technology) process is based on a different chemical route
to styrene that avoids the need for difficult and expensive
dehydrogenation. This alternate route uses the side-chain
alkylation of toluene with methanol. This route yields styrene,
hydrogen and water, as shown here.
ExSyM reduces the endothermic heat of reaction by 50% and
removes the thermodynamic limitation. This reaction pathway
has been investigated for over 30 years, but low product
yields have prevented it from being used commercially.
Through extensive research, Exelus has developed a new,
engineered solid catalyst that accelerates the side chain
alkylation reaction while greatly reducing the rate of methanol
decomposition. The formation of EB is also minimized. This
catalyst has shown product yields around 80% and a SM fraction
around 90%.
(part of New Chemistry page above)
Development Status
The process has been tested in bench-scale reactors. The
catalyst has shown no signs of deactivation and long-term
stability tests continue. Piloting is expected in Summer
2007.
New Chemistry
Process Benefits
Process Scheme and Performance
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