Chemistry Reference
In-Depth Information
Fig. 13.1
The crude products obtained
after esterification of pentaerythritol
with a fatty acid, catalysed by PTSA
(
left
) and Envirocat EPIC (
right
).
PTSA catalysed
Envirocat EPIC catalysed
eliminating the effluent that results from decolouris-
ing treatments.
believed to be the first example of a true heteroge-
neous catalyst for aerobic oxidations [25]. It is a
highly efficient catalyst, typically using a 1% sus-
pension in the neat substrate to achieve catalysis of
the oxidation. The use of air or O
2
results in water
being produced as a by-product. Once the oxidation
is complete, the catalyst is removed from the reac-
tion mixture by filtration and the product can be
purified easily by distillation or crystallisation.
4.3 Oxidations
The oxidation of aromatic methyl and methylene
groups traditionally is performed using homogenous
cobalt salts in acetic acid, usually at high tempera-
ture and pressure [27]. Although air is used as the
oxidant, the resulting reaction mixture is highly
toxic and corrosive. The plants that perform these
reactions are built from expensive alloys and require
many safety features to be incorporated into the
system.
There are alternative methods of performing oxi-
dation that are highly efficient and can be performed
under very mild conditions. However, these pro-
cesses use high oxidation-state transition metals
(permanganate, dichromate) [28]. Even when these
metal salts are used catalytically, the secondary
oxidant (e.g.
t
-butyl hydroperoxide, 4-methylmor-
pholine-
N
-oxide) [29,30] is very expensive and toxic
and, when spent, an extensive work-up is required
to isolate the product from the reaction mixture.
Envirocat EPAD is a non-toxic and non-corrosive
powder. When launched onto the market it was
5 Activation of Envirocats
The clay-based Envirocats (EPZG, EPZ10, EPZE and
EPIC) are supplied in an
inactive
form. This is because
all clays and clay-based catalysts equilibrate with the
atmospheric humidity and typically contain 10%
(w/w) water. Activation of these catalysts is simply
a matter of removing the loosely bound water as-
sociated with the catalyst. The most convenient
method of activation is via azeotropic drying of a sus-
pension of the Envirocat either in the neat substrate
and/or in an inert hydrocarbon solvent for 2-3 h.
Should the activated catalyst become exposed to
moisture, azeotropic drying reactivates the catalyst.
Where this method of activation is not possible, there
is an alternative: thermal activation.
