Continuous Production of Dialkylamines by Selective Hydrogenation of Nitriles on a Nickel-Zeolite Catalyst

Article abstract of DOI:10.1134/S1070427217110088

Hydrogenation of aliphatic nitriles in the presence of nickel supported by NaX zeolite was studied. The data obtained were used to develop a continuous method for obtaining dialkylamines with the yield of the target product of up to 98%.

Full text of DOI:10.1134/S1070427217110088

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2017, Vol. 90, No. 11, pp. 1778−1782. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © Yu.V. Popov, V.M. Mokhov, S.E. Latyshova, A.O. Panov, M.Yu. Pletneva, 2017, published in Zhurnal Prikladnoi Khimii, 2017, Vol. 90,
No. 11, pp. 1470−1474.
SPECIFIC
TECHNOLOGICAL PROCESSES
Continuous Production of Dialkylamines by Selective
Hydrogenation of Nitriles on a Nickel-Zeolite Catalyst
Yu. V. Popov*, V. M. Mokhov, S. E. Latyshova, A. O. Panov, and M. Yu. Pletneva
Volgograd State Technical University, pr. Lenina 28, Volgograd, 400131 Russia
*e-mail: tons@vstu.ru
Received November 30, 2017
Abstract—Hydrogenation of aliphatic nitriles in the presence of nickel supported by NaX zeolite was studied.
The data obtained were used to develop a continuous method for obtaining dialkylamines with the yield of the
target product of up to 98%.
DOI: 10.1134/S1070427217110088
At the annual world’s production of more than
1.9 million tons (according to the data for 2013), aliphatic
amines C1–C6 are used in many fields of industry,
agriculture, and medicine [1, 2]. In turn, aliphatic
diamines are important half-products of organic synthesis.
For example, di-n-propylamine and di-iso-butylamine
are for the most part used in syntheses of herbicides.
Di-n-butylamine is used for synthesis of sulfonamide
vulcanization accelerators [1].
and aluminum oxide or a mixed aluminum-gallium
oxide. The conversion under atmospheric pressure at
a temperature of 125°C reached values of 10–100%,
with the selectivity with respect to diethylamine being
33–44%.
In [6], the role of a catalyst was played by nickel
supported by mesoporous silicon oxide modified with
zirconium. The process was performed under atmospheric
pressure at 135°C, with the conversion reaching a value of
11–31% and the selectivity with respect to diethylamine
being 25–39%.
Using the hydrogenation of nitriles in order to obtain
secondary amines is a possible alternative to the existing
industrial methods for their synthesis via alkylation of
ammonia by alcohols.
Palladium deposited on various supports (ZrO2, CeO2,
MgO, SiO2, Al2O3, ZnO, Ga2O3, and In2O3) was used
in the reaction of acetonitrile hydrogenation at 170°C
under atmospheric pressure. The conversion of the nitrile
reached values of 30–99%, with the selectivity with
respect to diethylamine being 25–48%.
It is known from the literature that the hydrogenation
of nitriles yields a mixture of primary, secondary, and
tertiary amines [3]. A promising way is to use catalysts
providing a selective synthesis of products. For example,
the authors of [4] described the selective hydrogenation
of aliphatic nitriles to give secondary amines in 94–100%
yield in the presence of Rh/C under atmospheric pressure
at a temperature of 25–60°C in the course of 6–24 h in
cyclohexane. The hydrogenation of aromatic nitriles
and cyclohexanecarbonitrile under similar conditions
selectively produced in 82–100% yield secondary amines
in the presence of both Pd/C and Rh/C [4].
Previously, we have studied [8] continuous processes
for hydrogenation of nitriles of varied structure on a
catalyst having the form of nanostructured agglomerates
of nickel particles, supported by a cracking catalyst
Ceokar-2. With the hydrogenation performed at 120–
260°C under atmospheric pressure , a mixture of products
was obtained, which included di- and trialkylamines, with
yields of secondary amines of 3 to 96%, depending on the
nitrile structure and temperature. The catalyst preserved
its activity during 15 h of continuous operation.
The gas-phase hydrogenation has been studied in most
detail for acetonitrile. For example, the authors of [5] used
as a catalyst nickel on supports containing tin phosphate
The methods described above have a number of
disadvantages, such as application of expensive and
1778

CONTINUOUS PRODUCTION OF DIALKYLAMINES
1779
hard-to-get materials, or a low formation selectivity of
the target product.
Hydrogenation of iso-butyronitrile (1a). The con-
ditional residence time of hydrogen was 40 s kgcat mol–1,
and that of nitrile 1a, 119 s kgcat mol–1. The reaction was
performed at 220°C. The conversion of nitrile 1a was
100%. The selectivity with respect to di-iso-butylamine
4a was 98%, and its yield, 98%. Mass spectrum (EI,
70 eV), m/e ((Irel, %): 130.0 (16) [M + 1], 128.7 (2) [M],
86.0 (100), 57.0 (30), 41.0 (30), 44.0 (19), 42.1 (10).
The selectivity with respect to N-iso-butylidene-iso-
butylamine 3a was 2%, and its yield, 2%. Mass spectrum
(EI, 70 eV), m/e (Irel, %): 128.0 (34) [M + 1], 126.8 (6)
[M], 84.0 (100), 41.0 (57), 56.9 (51), 56.0 (40), 42.0
(26), 70.0 (10).
The goal of our study was to develop a selective
method for continuous hydrogenation of nitriles into
secondary amines with gaseous hydrogen on a readily
available catalyst under mild conditions.
EXPERIMENTAL
We used the following reagents: propionitrile (99%),
n-butyronitrile (99%), nickel chloride hexahydrate
(99.3%), and sodium tetrahydroborate (97%) from
Alfa Aesar; iso-butyronitrile (99%) and n-valeronitrile
(88%) fromAcros Organics; NaX zeolite [TU (Technical
Specification) 2163-003-21742510–2004] from ReaKhim.
Hydrogenation of propionitrile (1b). The conditional
residence time of hydrogen was 40 s kgcat mol–1, and
that of nitrile 1b, 278 s kgcat mol–1. The temperature
was 220°C. The conversion of nitrile 1b was 100%.
The selectivity with respect to di-iso-butylamine 4b was
89%, and its yield, 89%. Mass spectrum (EI, 70 eV), m/e
(Irel, %): 102.0 (76) [M + 1], 100.8 (7) [M], 72.0 (100),
44.0 (87), 41.1 (32), 43.0 (27), 42.0 (17). The selectivity
with respect to tri-n-propylamine 6b was 8.5%, and its
yield, 8.5%, Mass spectrum (EI, 70 eV), m/e (Irel, %):
143.9 (10) [M + 1], 143.1 (1) [M], 113.9 (100), 85.9 (60),
58.0 (12), 43.9 (9), 115.0 (8), 142.0 (5). The selectivity
with respect to N-propylidenepropylamine 3b was 2.5%,
and its yield, 2.5%. Mass spectrum (EI, 70 eV), m/e
(Irel, %): 99.9 (21) [M + 1], 98.9 (6) [M], 69.9 (100), 42.0
(59), 41.0 (50), 43.0 (45).
A chromato-mass-spectral analysis was made on a
Saturn 2100 T/GC3900 instrument (electron impact EI,
70 eV).
A GLC analysis of the reaction mass was made on a
Kristallyuks-4000M chromatograph at theat = 100–210°C,
tevap = 250°C, Agilent HP-5 polar column, lcol = 50 m,
dcol = 0.32 mm, carrier-gas nitrogen, photoinization
detector (PID), tPID = 250°C.
An elemental analysis of the catalyst was made by
energy-dispersive X-ray spectroscopy (EDS) with a FEI
Versa 3D DualBeam instrument.
Catalyst preparation. A 2-g portion of the NaX
zeolite (1–1.5 mm fraction) was impregnated with an
aqueous solution of 0.5 g nickel chloride NiCl2·6H2O
in 4 mL of water in the course of 24 h. The impregnated
support was filtered off and washed with distilled water.
Nickel ions were reduced with three 0.1-g portions of
NaBH4 at a temperature of 22–25°C, with 2–3 mL per
portion.
Hydrogenation of n-butyronitrile (1c). The condi-
tional residence time of hydrogen was 40 s kgcat mol–1,
and that of nitrile 1c, 174 s kgcat mol–1. The reaction was
performed at 200°C. The conversion of nitrile 1c was
100%. The selectivity with respect to di-n-butylamine
4c was 85%, and its yield, 85%. Mass spectrum (EI,
70 eV), m/e (Irel, %): 130.0 (26) [M + 1], 128.7 (2) [M],
44.1 (100), 85.9 (39), 41.1 (31), 42.0 (17), 57.0 (62), 43.0
(5). The selectivity with respect to tri-n-butylamine 6c
was 13%, and its yield, 13%. Mass spectrum (EI, 70 eV),
m/e (Irel, %): 186.0 (16) [M + 1], 142.0 (100), 99.9 (90),
58.0 (60), 143.0 (10), 141.1 (8). The selectivity with re-
spect to butyl-1-idene-di-n-butylamine 3c was 2%, and
its yield, 2%. Mass spectrum (EI, 70 eV), m/e (Irel, %):
184.2 (2) [M + 1], 44.0 (100), 85.9 (49), 41.1 (12), 57.0
(55), 156.1 (4).
Hydrogenation. The reaction was performed in a
flow-through displacement reactor under atmospheric
pressure in the temperature range 120–240°C. The
reduced catalyst (2 g) was charged into the reactor in the
humid form between glass package layers, and water was
removed in a flow of hydrogen at 120°C immediately
before the reaction. The laboratory reactor has the form
of a tube made of 12Kh18N10T steel with inner diameter
of 9 mm and heating-zone height of 50 mm, placed in an
electric furnace. The temperature within the reactor was
measured with a thermocouple. The hydrogen flow rate
was controlled with a GV-7 hydrogen generator.
Hydrogenation of n-valeronitrile (1d). The condi-
tional residence time of hydrogen was 54 s kgcat mol–1,
and that of nitrile 1d, 418 s kgcat mol–1. The reaction was
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POPOV et al.
Scheme 1.
Scheme 2.
5a–5d
performed at 200°C. The conversion of nitrile 1d was
100%. The selectivity with respect to di-n-pentylamine
4d was 63%, and its yield, 63%. Mass spectrum (EI, 70
eV), m/e (Irel, %): 158.0 (36) [M + 1], 156.8 (2) [M], 44.0
(100), 100.0 (47), 43.0 (12), 41.0 (9). The selectivity with
respect to di-n-pentylamine 6d was 11%, and its yield,
11%. Mass spectrum (EI, 70 eV), m/e (Irel, %): 228.2 (14)
[M + 1], 170.0 (100), 114.0 (55), 58.0 (40), 171.0 (12).
The selectivity with respect to N-pentylidenepentylamine
3d was 1%, and its yield, 1%. Mass spectrum (EI, 70 eV),
m/e (Irel, %): 156.0 (100) [M+1], 98.1 (94), 41.0 (29),
42.0 (25), 56.0 (24). The selectivity with respect to
n-pentylamine 2d was 25%, and its yield, 24%. Mass
spectrum (EI, 70 eV), m/e (Irel, %): 87.8 (100) [M+1],
86.9 (19), 86.0 (6), 83.9 (2), 82.8 (1).
we obtained a catalyst whose surface contains, according
to the results of energy-dispersive X-ray spectroscopy,
5.6% Ni, 19.2% Si, 13.8%Al, 10.7% Na, and 50.66% O.
We used the catalyst to examine the hydrogenation
of iso-butyronitrile 1a, propionitrile 1b, n-butyronitrile
1c, and n-valeronitrile 1d in the temperature range 120–
240°C under atmospheric pressure. The composition and
structure of the products were confirmed by gas-liquid
chromatography and chromato-mass-spectrometry. It
was found the catalyst retained its activity after 15 h of
continuous operation.
The main reaction products at 180–240°C were
symmetric dialkylamines 4a–4d, formed by Scheme 1.
The corresponding tertiary amines were formed as by-
products by Scheme 2.
In all cases, insignificant amounts (1–5%) of
unsaturated products (imines 3a–3d and enamines 5a–5d)
were formed.
RESULTS AND DISCUSSION
The catalyst was produced by impregnation of a
support with an aqueous solution of nickel chloride, with
the subsequent reduction with NaBH4 in water, as this
was done in [8]. A zeolite of NaX brand (TU 2163-003-
21742510–2004) was chosen as the support. As a result,
We examined for the example of the reaction of
hydrogenation of nitrile 1a the influence exerted by
the process temperature and excess of hydrogen on the
conversion of the nitrile and selectivity with respect to
formation of a secondary amine (Fig. 1).
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CONTINUOUS PRODUCTION OF DIALKYLAMINES
1781
X, %
S, %
S, %
1
2
H2, mol mol–1 nitrile
T, °C
Fig. 1. (1) Conversion X of iso-butyronitrile 1a and (2) formation
selectivity S of di-iso-butylamine 4a vs. temperature T.
Fig. 2. Formation selectivity S of di-isobutylamine 4a vs. molar
excess of hydrogen H2 at 180°C.
At a temperature of 120°C, the conversion of nitrile
1a was 35%, with N-iso-butylidene-iso-butylamine 3a
being the main reaction product and iso-butylamine 2a
formed as a by-product with selectivity of 16%. When
the temperature was raised, the yield of di-iso-butylamine
4a increased and that of imine 3a and primary amine
2a decreased with increasing conversion of nitrile.
For example, the catalyzate contained at 180°C 57%
dialkylamine 4a, 23% imine 3a, and 20% amine 2a. The
full conversion of nitrile 1a was reached at 180°C, and
the maximum selectivity with respect to secondary amine
4a (98%), at 220°C. The high selectivity with respect to
dialkylamine can be attributed to the steric hindrance to
the formation of tri-iso-butylamine 6a.
nitrile : hydrogen molar ratio of 1 : 3. In this case, the
maximum specific output capacity for di-iso-butylamine
(0.007 mol s–1 kgcat) is reached at a specific molar
expenditure of the starting nitrile of 0.014 mol s kgcat.
Similar dependences were also observed in hydroge-
nation of nitriles with normal structure C3–C5 1b–1d. In
the case of hydrogenation of nitrile 1b, the 100% conver-
sion was reached at 220°C, with di-n-propylamine 4b be-
ing the main product with selectivity of 89%, In the case
of hydrogenation of nitrile 1c, the 100% conversion was
reached already at 200°C, with the formation selectivity
of di-n-butylamine 4c being 85%. In this case, the yield
and selectivity with respect to secondary amine 4c were
preserved at a conditional residence time of nitrile 1c in
the range 174–347 s kgcat mol–1 and conditional residence
time of hydrogen of 32–81 s kgcat mol–1, respectively. A
lower formation selectivity of di-n-pentylamine 4d was
observed for nitrile 1d. At 200°C and 99% conversion of
nitrile, dialkylamine 4d was obtained with selectivity of
63%. As by-products, we obtained tri-n-pentylamine 6d
and n-pentylamine 2d with selectivities of 11 and 24%,
respectively. In this case, raising the temperature further
to 220–240°C does not change the composition of the
catalyzate.
A study of the influence exerted by the molar excess
of hydrogen at 180°C (Fig. 2) demonstrated that, as the
iso-butyronitrile : hydrogen ratio is raised from 1 : 3 to
1 : 5, the selectivity with respect to secondary amine 4a
grows from 57 to 88% at a 100% conversion of nitrile 1a.
Raising the excess of hydrogen further has no effect on
the course of the process. At temperatures of 200°C and
more, this influence is not so significant: at ratios of 1 :
3 and 1 : 5, a 87% selectivity with respect to secondary
amine 4a is observed.
At a temperature of 220°C, we examined the
influence exerted by the conditional residence time on
the composition of products formed in hydrogenation
of nitrile 1a. It was found that the values of conversion
(100%) and selectivity (97%) are preserved at a conditional
residence time in the range 72–358 s kgcat mol–1 at a
CONCLUSIONS
A continuous process was developed for selective
catalytic hydrogenation of aliphatic nitriles C3–C5 into
the corresponding secondary amines in the presence of a
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optimal nitrile : H2 ratios, 1 : 3–1 : 8.
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