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that the presence of an acid functionality in the catalyst may be essential to
accelerate the dehydration of 1-aminoethanol during the non-reductive
amination of ethanol.
102
The conversion of ethanol to 1,2-dichloroethane, which is an intermediate
for the synthesis of vinyl chloride monomer, formally consists of two steps:
(i) ethanol dehydration to ethylene and (ii) oxychlorination of the olefin to
the dichlorinated compound. Once again, in principle, the two reactions can
be carried out in sequence over a single bifunctional catalyst, with a catalyst
showing both acid features and redox properties.
103,104
On the other hand, a
two-step reaction with two catalytic beds in sequence, each one aimed at
fostering one specific reaction, can also be envisaged. This approach has
been described, for instance, in the case of glycerol oxidehydration to acrylic
acid (see below). This type of process configuration, which can be referred to
the intensification rules as listed in the green chemistry principles, is pos-
sible only when the co-product and by-products generated in the first section
do not interfere with the catalyst and reactions occurring in the second
catalytic bed. This avoids expensive separation procedures aimed at the
purification of the product which should serve as the reactant for the second
step carried out over the downstream catalytic section. On the other hand, if
all the reactants needed for reactions occurring over both catalytic beds are
co-fed all together at the top of the first bed, reactants for the second section
should not interfere with reactions occurring in the first section. If instead
this is the case, a differentiated feed, with reactants separation at the inlet of
the two beds, is alternatively recommended (Scheme 8.5).
d
n
4
r
4
n
g
|
3
.
Scheme 8.5 Possible reactor configuration for sequential reactions, including two
steps: (a) A
-
R + S; and (b) R + B
-
T.
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