Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Journal of Catalysis 209, 202–209 (2002)
doi:10.1006/jcat.2002.3617
Nickel–Magnesia Catalysts: An Alternative for the Hydrogenation
of 1,6-Hexanedinitrile
∗
∗
Marc Serra, Pilar Salagre,∗,1 Yolanda Cesteros, Francisco Medina,† and Jesu´s E. Sueiras†
∗
Facultat de Qu´ımica, Universitat Rovira i Virgili, 1.43005, Tarragona, Spain; and †Escola Te`cnica Superior d’Enginyeria Qu´ımica,
Universitat Rovira i Virgili, Av. Pa¨ısos Catalans, 26, 43007, Tarragona, Spain
Received January 8, 2002; revised March 21, 2002; accepted March 21, 2002
The main products of nitrile hydrogenation are usually
mixtures of amines (23, 24). The condensation reactions
between a highly reactive intermediate imine and the pri-
mary amine always lead to the formation of products such
as secondary and tertiary amines together with the pri-
mary amine (25). Catalysts based on Co, Ni, and Ru are
mostly used to produce primary amines (6, 7, 13, 14, 18,
26–29).
The addition of potassium in small amounts enhances
the selectivity of nickel catalysts toward primary amines
in adiponitrile hydrogenation (30–33). Other precursors,
such as hydrotalcites of Ni/Mg/Al, allow variation in the
MgO/Al2O3 ratio and, thus, allow control of the acidity of
the final catalysts (34, 35). When this ratio increases, the se-
lectivity to primary amines increases for the hydrogenation
of acetonitrile.
Two Ni–MgO systems were synthesized and characterized
as nickel catalysts for the hydrogenation of 1,6-hexanedinitrile
(adiponitrile) in the gas phase. The activity results were compared
with those obtained for a commercial Raney–Ni. All three cata-
lysts showed high selectivity to 1,6-hexanediamine, for a total
conversion with a maximum of 96% for the Ni–MgO catalyst,
which was made from a NiO–MgO solution. However, only Ni–
MgO catalysts showed high selectivity to 6-aminohexanenitrile (83
and 77%, respectively) and high conversion (87 and 85%, respec-
tively). The higher selectivity to 6-aminohexanenitrile could be
related to the presence of octahedral crystallites in the Ni–MgO
c
catalysts. ꢀ 2002 Elsevier Science (USA)
Key Words: nickel–magnesia catalysts; magnesia; adiponitrile;
dinitrile; 1,6-hexanedinitrile hydrogenation; 6-aminohexanenitrile;
1,6-hexanediamine.
From studies of the preparation conditions of NiO–MgO
systems, it is assumed that the reducibility of the corre-
sponding NiO phase and the final properties of the nickel
phase (size, morphology. . . ) are highly affected by the ten-
dency to form solid solutions of NiO–MgO (36–39). Ad-
ditionally, Ni/MgO catalytic systems have shown to have a
considerable inhibitory effect on the generation of graphitic
residues in several reactions (40).
In previous work (41), Ni–MgO systems showed high ac-
tivity for the hydrogenation of 1,4-butanedinitrile, with the
highest selectivity, 85%, to 4-aminobutanenitrile. We also
reported that the crystal morphology could induce certain
selectivity to the monoamine (42–45). However, the recent
literature on the hemihydrogenation of adiponitrile (4, 15,
17–19, 46–48) shows still difficulties in achieving selective
hydrogenation with high conversion.
Our goal was to obtain nickel systems that can cata-
lyze the hydrogenation of 1,6-hexanedinitrile and con-
trol the selectivity to 6-aminohexanenitrile and 1,6-
hexanediamine. Therefore, two Ni–MgO catalysts were
prepared and tested for the hydrogenation of adiponitrile.
Their catalytic results are compared with those obtained
for an usual industrial hydrogenation catalyst: Raney–Ni
(7, 13).
INTRODUCTION
Catalytic hydrogenation of nitriles is an important in-
dustrial route for the manufacture of a great variety
of amines (1–3), especially of 1,6-hexanediamine and 6-
aminohexanenitrile. This is confirmed by several recent
patents (4–15). The hydrogenation of adiponitrile to 1,6-
hexanediamine (16, 17) is an interesting industrial process
in the preparation of Nylon-6,6 and also in the obtaining of
6-aminohexanenitrile (18, 19), which is used in the prepa-
ration of caprolactam (precursor of Nylon-6) (20).
Caprolactam is mainly produced from cyclohexanone,
a process that generates 4.5 kg of ammonium sulfate per
kg of caprolactam produced. However, Rhodia is devel-
oping a new salt-free process to obtain caprolactam at
a lower cost than is needed for the current process. The
first step of this new process is the hemihydrogenation of
1,6-hexanedinitrile (adiponitrile) to 6-aminohexanenitrile
(21). This minimizes waste, one of the criteria of the green
chemistry for the manufacture and application of chemical
products (22).
1 To whom correspondence should be addressed. Fax: +34 977559563.
E-mail: salagre@quimica.urv.es.
202
0021-9517/02 $35.00
c
ꢀ 2002 Elsevier Science (USA)
All rights reserved.