Oxidation reactions Alkylation Application of copper chromite catalysts 1 Commercial application
method retained a spinel structure evidenced by the large amount of Cu
2+
species. In hydrogenolysis reactions, the precipitated catalyst showed a
higher catalytic activity than the impregnated catalyst. Thus, the reduced copper chromite spinel
structure, which constitutes a single phase, appears to be responsible for the high catalytic
activity in the hydrogenolysis of glycerol to propylene glycol.
Copper chromite catalysts are useful for a variety of chemical reactions in the processing of
oleo chemical feedstocks. Major oleo chemical applications include hydrogenolysis of fatty esters
to fatty alcohols including both methyl ester and wax ester processes, alkylation of alcohols with
amines and amination of fatty alcohols. The catalysts have unique performance for selective
hydrogenation of vegetable oils and can be used in the conversion of bio renewable feedstocks into
industrial chemicals. Dovell and Greenfield [113] used copper chromite as a catalyst for the
preparation of alkylaryl secondary amines by the reductive alkylation of a primary aromatic amine
with an aliphatic ketone in the presence of hydrogen eqn. 14.
ArNH
2
+ ORCR′ + H
2
→ ArNHRCHR′ + H
2
O 14 The
noble metals
cause both
nuclear hydrogenation and formation of alkylamines [114]
by hydrogenolysis of the carbon nitrogen bond between the alkyl group and the nitrogen atom in
the secondary amine i.e.: ArNHR + H
2
→ ArH + RNH
2
. Copper chromite catalysts avoid these undesirable side reactions, but a large amount of
ketone is reduced to the corresponding alcohol. Fatty alcohols are an important raw material
for surfactants as well as constitute one of the largest groups within the oleochemicals. The
fraction of natural fatty alcohols, i.e. fatty alcohols based on natural fats and oils, is steadily growing
[115]. The fatty alcohols can be produced by hydrogenation of fatty acid methyl esters, a
product from natural abundant coconut and palm kernel oils, to form high alcohol in the presence of
a CuCr
2
O
4
catalyst [116]. The hydrogenation of methyl esters and of fatty acids to form fatty
alcohols is given by the following general eqns. 15 and 16 respectively:
CuCr RCOOCH + 2H
2
↔ RCH
2
OH + CH
3
OH 15 Methyl ester Fatty alcohol
CuCr RCOOH + 2H
2
↔ RCH
2
OH + H
2
O 16 Fatty acid Fatty alcohol
Copper chromite catalyst also converts any unsaturated carbon double bonds so that only
saturated fatty alcohols are formed [87]. The hydrogenation process is carried out at 25 30 MPa
and a temperature of 250 300 C in a tubular
column.