Chemistry Reference
In-Depth Information
O
O
H
+
OCH
2
CH
3
OCH
2
CH
3
+
2CH
3
CH
2
OH
O
+ H
2
O
O
O
Scheme 6.17
Scheme 6.1
8
rapid esterification reaction with negligible amounts
of etherification. Using a resin catalyst eliminates
final ester contamination (from the sulfuric acid
using a homogeneous catalyst) and minimises efflu-
ent problems. The esterification processes (20 000
MPTA plant) for the production of the diethyl
maleate is a two-stage process involving an auto-
catalytic exothermic first stage to produce a
monoester, followed by a catalytic second stage to
produce the diester. The production of methyl esters
of natural fatty acids also has been developed using
a novel counter-current reactor design to operate at
conversions of 99.8% with a selectivity of >99%.
The C
10
-type fatty acids are esterified with methanol
and then hydrogenated to the linear alcohols. The
example of replacing a homogeneous catalyst
(sulfuric acid) with a heterogeneous catalyst is more
efficient, more cost-effective and environmentally
cleaner.
activity of this material per unit weight of Nafion
®
resin has been found to be up to 1000 times higher
than in the pure polymer. This has opened up the
potential applications dramatically. This work has
been summarized recently [90].
The use of ion-exchange resins for difficult alkyla-
tion reactions was almost non-existent [58]. One
reaction of interest is in the alkylation of benzene
with C
12
olefins for the formation of linear alkyl ben-
zenes. These materials, when sulfonated, represent
the basis of the detergents industry. In the current
commercial process, HF is used as the catalyst and
there is an obvious drive to replace this very
hazardous material with a solid acid catalyst. The
products of these reactions contain a mixture of
alkylbenzenes with the phenyl group attached to
different carbonatoms in the linear hydrocarbon
chain. The 2-phenyl isomer is the most preferred
product (see Scheme 6.18).
Branched isomers, which are the result of skeletal
isomerisation of the linear hydrocarbon chain, are
very undesirable due to lower biodegradability. It has
been shown recently that the Nafion
®
resin/silica
nanocomposite is a very active catalyst for this
reaction [90,91]. Conversions of 99% at 80°C are
obtained; the products contain >95% linear alkyl
benzenes and the rest (<5%) are the ca. 4%
branched alkylates from the ca. 4% branched olefins
(impurity in the feed), dimers of 1-dodecene and di-
substituted benzene. The linearity of the alkylation
using 1-dodecene is >99%. The nanocomposite cata-
lyst was approximately 400¥ more active than the
4.2 Nafion
®
/silica nanocomposites
Recently we have developed a highly active form of
Nafion
®
where the Nafion
®
resin is highly dispersed
within and throughout the porous silica network at
the tens of nanometres level [65]. The microstruc-
ture may be regarded as a porous silica network that
contains a large number of 'pockets' of very strong
acid sites (the Nafion
®
polymer) in domains of about
10-20 nm. This significantly increases the effective
surface area of the Nafion
®
resin particles by several
orders of magnitude and as a result the catalytic
