Chemistry Reference
In-Depth Information
(a)
(b)
as a fuel additive. Deutsche Texaco has commer-
cialised a process that uses a strong acid resin to
catalyse the direct hydration of olefins such as
propylene (in water) to produce the corresponding
alcohol. Macroreticular materials (e.g. Amberlyst
®
-
15) are preferred because they tend to foul less
readily than gels in long-term tests. The hydration
of isobutylene to
t
-butanol has been commercialized
by UOP/Huels in the early 1980s. The use of resin
catalysts in Europe and Japan in two plants alone
accounts for an annual production of at least 100 000
t year
-1
[71]. Ion-exchange resins are effective cata-
lysts for a number of dehydration-type chemistries.
These include the dehydration of
t
-butanol to
isobutylene and also the dehydration of butane diol
to tetrahydrofuran. This latter reaction has been
carried out by Davy-McKee as early as 1985 on
20 000 t year
-1
. Of course the most well-known reac-
tion is the formation of bisphenol A [72]. Degussa
also has demonstrated the use of strongly acidic
inorganic and organic ion-exchange resins in the for-
mation of 2-vinyl-4-hydroxymethyl-1,3-dioxolanes
[73]. These catalysts are based upon the poly-
condensation of a suitable alkyl-sulfonic-acid-
functionalised organosilane monomer (see Scheme
6.15). The catalyst is a solid with a siliceous matrix
and a high concentration of anchored ligand groups.
These kinds of catalysts are active for a number of
different types of reactions, such as the esterification
of free fatty acids, the esterification of acid anhy-
drides to form the corresponding diesters and the
condensation reaction to form bisphenol A.
Olah
et al
. recently have reported the use of
Nafion
®
as a highly efficient solid acid catalyst for the
Fig. 6.6
Scanning electron micrographs of: (a) microspherical
'macroreticular' resin; (b) Nafion
®
resin/silica nanocomposite.
similar characteristics to the macroreticular-based
resins although the pore structure is slightly smaller
(pore diameters are typically ca. 15-20 nm).
Commercial applications for ion-exchange resins
Ethers are widely used as octane boosters in the fuel
for motor vehicles. The most commonly used ethers
include: methyl
tert
-butyl ether (MTBE), ethyl
tert
-
butyl ether (ETBE) and
tert
-amyl methyl ether
(TAME). They are made by the addition of methanol
to isobutene, ethanol to isobutene and methanol to
2-methyl-1(or 2)-butene, respectively, over an acid
catalyst. Commercially, MTBE is produced in the
liquid phase over a macroporous sulfonic acid resin
catalyst, e.g. Amberlyst
®
-15, Dowex
®
or M32. The
macroporous resin is preferred due to the high
accessibility of its acid groups [66-68].
Longer chain alkyl ethers were prepared readily
by heating the corresponding alcohols (C
n
H
2
n
+1
OH,
n
> 3) in the liquid phase with Nafion resin catalyst
[69]. Amberlyst
®
resin catalyst is limited in this appli-
cation due to the temperature requirement, e.g.
>140°C. Nafion
®
resin also was an effective catalyst
for catalysing the condensation polymerisation of
alkane diols to form the corresponding polyether
glycols [70].
Ion-exchange resins (sulfonic-acid-modified poly-
styrenes) have been used commercially for a number
of years for the hydration of isobutylene to
t
-butanol.
Tert
-butyl alcohol may be used directly or indirectly
