Chemistry Reference
In-Depth Information
process has been licensed to at least ten plants world-
wide. Liquid propylene and benzene are fed into the
reactor where propylation is completed. Any poly-
isopropylbenzene then is treated in a separate
reactor and transalkylated back to cumene. A series
of distillation columns are used to collect product
and recycle unwanted products. Using this process,
nearly stoichiometric yields are achieved as a result
of high propylene conversion, transalkylation of
polyalkybenzenes to cumene, high catalyst selectiv-
ity and insignificant formation of heavies. The high
yield results in less by-product and waste streams
than older processes. The catalyst itself, unlike sup-
ported phosphoric acid and aluminium trichloride, is
environmentally inert, requires no special packaging
or handling, can be removed readily from the reactor
and can be regenerated. The low temperature of
operation prevents the formation of significant
amounts of by-products. The purity of the cumene
produced is 99.97% or higher.
As the plant was converted to a more environ-
mentally friendly zeolite catalyst, the new process
showed improved product quality, lower production
costs, lower maintenance cost and reduced corro-
sion. The seven plants now in operation have a com-
bined capacity of over 3 million t year
-1
, which meets
more than 55% of the worldwide demand for
cumene. Two excellent accounts relating to this
topic include the article by Marcus & Cormier, 'Going
Green with Zeolites,' and a description by Meima
et al
. on the production of cumene [108,109].
Meima describes a number of processes to
cumene: Dow-Kellog process, CDTech process,
Mobil-Raytheon process (Badger), UOP process and
Enichem process. The CDTech process makes use of
catalytic distillation. The distillation of reactants
and products takes place in one vessel. The details
of many of these processes are often proprietary,
although it appears that all of these are based on
zeolitic-type materials. The ZSM-5 catalyst, for
example, is used in a number of process technolo-
gies, including cumene, ethylbenzene, xylene iso-
merisation and toluene disproportionation to olefin
recovery in the case of the petrochemical industry.
(a)
(b)
Fig. 6.9
Use of zeolite catalyst (a) in the industrial formation
of cumene (b).
Mobil introduced a new proprietary zeolite, MCM-
22, that gives high activity for the formation of
cumene. Presumably, the fine pore structure of the
zeolite helps to control the specificity of the reaction.
In Fig. 6.9 we show the fit of a cumene molecule
within ZSM-5 for comparison. I find it a somewhat
rewarding thought that careful design of catalysts
can, with skilful engineering methods, lead to large-
scale production as shown in Fig. 6.9. The engineer-
ing aspects were developed by Raytheon and the
4.5 Isodewaxing process (Chevron)
O'Rear & Scheurman [110] recently have described
the use of zeolite catalysis in Chevron. Isodewaxing
®
and Aromax
®
are two examples of zeolite catalysts
