Catalytic Condensation of Carbonyl Compounds during the Synthesis of Cyclohexanone in the Production of Caprolactam

Article abstract of DOI:10.1134/S0965544118100122

Abstract: Kinetic features of the condensation processes of carbonyl and unsaturated impurities in cyclohexanone have been studied using model mixtures in a heterophase system in the presence and absence of phase-transfer catalysts. It has been shown that linear aldehydes are condensed with cyclohexanone in the heterophase system in the presence and absence of phase-transfer catalysts under mild conditions (30–50°C). Noncarbonyl unsaturated compounds (e.g., 2-cyclohexene-1-ol) can be removed only at temperatures above 100°C in the presence of acidic catalysts (e.g., high-temperature sulfonated cation-exchange resins). Unsaturated cyclic ketones are characterized by both alkylation reactions over acid catalysts and aldol condensation reactions in the presence of an alkali, thereby suggesting the possibility of their elimination at different cyclohexanone purification steps. The theoretical models built can be used to develop an effective cyclohexanone purification technology that will substantially enhance the manufacturability of high-purity caprolactam and polyamide.

Full text of DOI:10.1134/S0965544118100122

ISSN 0965-5441, Petroleum Chemistry, 2018, Vol. 58, No. 10, pp. 889–894. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © E.A. Martynenko, S.V. Levanova, I.L. Glazko, A.A. Morgun, 2018, published in Neftekhimiya, 2018, Vol. 58, No. 5, pp. 602–607.
Catalytic Condensation of Carbonyl Compounds during the Synthesis
of Cyclohexanone in the Production of Caprolactam
a,
a
a
a
E. A. Martynenko *, S. V. Levanova , I. L. Glazko , and A. A. Morgun
a
Samara State Technical University, Samara, 443100 Russia
*
e-mail: kinterm@samgtu.ru
Received May 24, 2017
Abstract—Kinetic features of the condensation processes of carbonyl and unsaturated impurities in cyclohex-
anone have been studied using model mixtures in a heterophase system in the presence and absence of phase-
transfer catalysts. It has been shown that linear aldehydes are condensed with cyclohexanone in the het-
erophase system in the presence and absence of phase-transfer catalysts under mild conditions (30–50°C).
Noncarbonyl unsaturated compounds (e.g., 2-cyclohexene-1-ol) can be removed only at temperatures above
1
00°C in the presence of acidic catalysts (e.g., high-temperature sulfonated cation-exchange resins). Unsat-
urated cyclic ketones are characterized by both alkylation reactions over acid catalysts and aldol condensation
reactions in the presence of an alkali, thereby suggesting the possibility of their elimination at different cyclo-
hexanone purification steps. The theoretical models built can be used to develop an effective cyclohexanone
purification technology that will substantially enhance the manufacturability of high-purity caprolactam and
polyamide.
Keywords: cyclohexanone, caprolactam, condensation, phase-transfer catalysis
DOI: 10.1134/S0965544118100122
During the oxidation of cyclohexane to cyclohexa-
In [9] we performed chromatographic–mass spec-
none in the production of caprolactam, a large num- trometric analysis of industrial cyclohexanone synthe-
ber of oxygen-containing impurities are formed— sis products . The impurities were identified by exist-
more than 50 compounds (saponifiable and unsapon- ing mass spectra from spectral databases. As a result, it
ifiable) which possess various reactivities [1–4]. This was shown that crude cyclohexanone contained about
complicates the selection of the optimum conditions 6 wt % unsaponifiable impurities including 3.1% com-
for the synthesis and purification of the target prod- pounds containing the aldehyde group, 1.5% com-
ucts.
pounds containing the keto group, 1.1% hydrocar-
According to published data [5–7], aldehydes (e.g., bons, and 0.1% unsaturated compounds. Some of
butanal, pentanal, and hexanal) and unsaturated com- them have both functional groups and unsaturated
pounds (e.g., 2-cyclohexene-1-one) are the most det- bonds in their molecule, e.g., 2-cyclohexene-1-one,
rimental unsaponifiable impurities that have negative 1-butoxy-2-cyclohexene, etc. When these compounds
influence on the quality of cyclohexanone and capro- enter the next production stages (oximation, Beck-
lactam. Linear aldehydes are formed as a result of the mann rearrangement, and polymerization) together
oxidation of n-butane, n-pentane, and n-hexane pres- with cyclohexanone, they form impurities, due to
ent in crude cyclohexane:
which the mechanical strength of the polyamide fiber
drops below the minimum requirements [10]. Thus, it
was found [6] that 2-cyclohexene-1-one transforms
into the corresponding unsaturated oxime and further
to the unsaturated lactam (azocycloheptene-2-one) at
the stage of Beckmann rearrangement. The latter
sharply decreases the quality of caprolactam; thus, the
permanganate number drops from 22500 to 2500 s
already at the concentration of the impurity of 25 mg
per 1 kg of caprolactam.
H
[
O]
CH3
H C
3
H3C
O
Unsaturated cyclic ketones are formed as a result of
both oxidation of cyclohexane and dehydrogenation
of cyclohexanol [8]:
OH
O
O
The aim of this work is to study the kinetic charac-
teristics and to find the optimum conditions for the
removal of unsaponifiable impurities for the purpose
–H2
–H2
889

8
90
MARTYNENKO et al.
Table 1. Processes and process conditions in the heterophase system
Process
Initial concentrations C , mol/L
T, °C
0
Reaction of 2-cyclohexene-1-ol (c-enol) with cyclohexanone C (c-enol) = 0.48 mol/L;
70–80
0
in the presence of and without PTC (TOMAC)
C (NaOH) = 2.5 mol/L;
0
C (PTC) = 0.01 mol/L;
0
Condensation of 2-cyclohexene-1-one (c-enone) with cyclo- C (c-enone) = 0.50 mol/L;
50–70
30–60
0
hexanone in the presence or absence of PTC (TOMAC)
C (NaOH) = 1.75 mol/L;
0
C (PTC) = 0.012 mol/L;
0
Condensation of hexanal (h-al) with cyclohexanone in the
presence or absence of PTC (TOMAC)
C (h-al) = 0.47 mol/L;
0
C (NaOH) = 1.75 mol/L;
0
C (PTC) = 0.012 mol/L;
0
of improving the quality of commercial-grade cyclo- representing aldehyde structures, and 2-cyclohexene-
hexanone and caprolactam.
1-one modeling unsaturated/carbonyl impurities.
Three systems of the condensation reaction of
cyclohexanone with unsaturated and aldehyde com-
pounds in a heterophase system in the presence of
alkaline, acidic, and phase-transfer catalysts (PTCs)
EXPERIMENTAL
The objects of the kinetic study were 2-cyclohex- were studied. Trioctylmethylammonium chloride
ene-1-ol as a model of unsaturated impurities, hexanal (TOMAC) was used as the PTC:
OH
O
OH
I
+
+
O
O
O
O
II
O
O
III
CH3
CH3
+
H C
3
O
Table 1 presents the conditions selected for study- vidual components synthesized for the purpose and
ing in the heterophase system.
thoroughly purified.
The catalytic studies were performed using model
mixtures composed of the industrial “oxidate” (cyclo-
hexane oxidation product after the stage of neutraliza-
tion and removal of the main amount of unreacted
cyclohexane, having the following composition:
The quantitative determination was performed by
means of GLC analysis on a Chromatec–Analitik
software–hardware complex on the basis of a Kristall-
2
000M chromatograph using the internal standard
method. For quantifying, a calibration coefficient was
determined for each of the compounds relative to a
standard. The standards used were pentanol-1 (for
3
8.8 wt % cyclohexane, 35.5 wt % cyclohexanone,
4.0 wt % cyclohexanol, and 1.7 wt % organic impuri-
2
ties) and the test substances 2-cyclohexene-1-ol,
2
-cyclohexene-1-ol) and hexanol-1 (for 2-cyclohex-
2
-cyclohexene-1-one, and hexanal. The volume ratio
ene-1-one and hexanal).
between the aqueous and organic phases was 1 : 1. A
The components were identified by the relative reactor equipped with a stirrer was charged with cyclo-
retention times of authentic pure substances or indi- hexanone, a model impurity under study, and a phase-
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CATALYTIC CONDENSATION OF CARBONYL COMPOUNDS
transfer catalyst, and the mixture was heated to a set
891
0.7
temperature and stirred until the complete dissolution
of the impurity and the catalyst. Then, an alkali solu-
tion preliminary heated to the required temperature
was rapidly introduced upon vigorous stirring.
Reagent-grade potassium hydroxide, analytical grade
sodium hydroxide, trioctylmethylammonium chlo-
ride (TOMAC) (assay >97.0 wt %), and sulfonated
cation exchange resin Amberlyst 70 (Dow Chemical)
were used as a catalyst.
0
0
0
0
0
.6
.5
.4
.3
.2
Without PTC
With PTC
0
.1
Samples were taken at certain time intervals simul-
taneously from the organic and aqueous phases in
equal amounts for the purpose of avoiding a change in
the ratio between the reagents. The concentration of
the impurity in the samples was analyzed by GLC.
50
100
150
0
Time, min
Fig. 1. Change in the 2-cyclohexene-1-ol concentration
with time in the condensation process without a phase-
transfer catalyst and in the presence of TOMAC. Condi-
Preliminarily, a set experiments on the determina-
tion of the influence of the stirrer rotational speed on
the reaction rate was conducted. All the subsequent
experiments were performed at a stirring speed of
tions: C(c-enol) = 0.48 mol/L, C (NaOH) = 2.5 mol/L,
0
C (PTC) = 0.012 mol/L, and T = 70°C.
0
~
3500 rpm, which corresponds to the kinetic region of
occur during saponification, and the presence of PTC
has no effect on the process. Making the conditions
harsher and changing the alkali (NaOH for KOH) also
did not affect the rate of the condensation reaction.
the process.
2
-Cyclohexene-1-ol was synthesized in this study
from cyclohexene in two steps according to the proce-
dure [11, 12]; the main substance content in the final
product was more than 85 wt % (according to GLC
A similar result was obtained in the case of the con-
data); T = 164–165°C. 2-Cyclohexene-1-one and densation reaction of 2-cyclohexene-1-ol with cyclo-
b
hexanal were purchased from Sigma-Aldrich and had hexanone under homogeneous conditions in the pres-
the purity of no less than 98.0 wt % according to GLC ence of KOH at 120°C. Thus, it can be concluded that
data.
the condensation of 2-cyclohexene-1-ol with cyclo-
hexanone in the presence of an alkali occurs neither
during saponification under mild conditions (about
The kinetics of condensation reactions in the het-
erophase system was studied in the temperature range
of 30–70°C (which is close to the conditions of the 70°C) nor at the step of distillation under more severe
saponification step in the industry) by the initial rates conditions (90–130°C); that is, the impurity cannot
using the isolation method [13].
be removed.
The condensation reactions of 2-cyclohexene-1-ol
with cyclohexanone in a homogeneous system in the
presence of the KOH catalyst and in a heterophase
system with the Amberlyst 70 catalyst were studied at
An experiment in metal ampoules (in airtight
cylindrical reactors made of stainless steel with a vol-
ume of 5 mL) was performed at 120°C in the presence
of potassium hydroxide and the acid catalyst
Amberlyst 70 for 2 h. The reactor was successively
charged with cyclohexanone, 2-cyclohexene-1-ol,
and the catalyst. Then the reactor was sealed and
placed in an air-bath oven. After expiration of the
reaction time, the reactor was cooled down and
unsealed, and the resulting products of the condensa-
tion reaction were analyzed by GLC.
1
20°C, thus simulating the conditions of the industrial
step of distillation in the temperature range of 90–
30°C.
1
RESULTS AND DISCUSSION
Reaction of Cyclohexanone with 2-Cyclohexene-1-ol
It was found that in the presence of acidic catalysts
The condensation reaction of cyclohexanone with
-cyclohexene-1-ol was conducted in a two-phase
(high-temperature macroporous sulfonated cation-
2
system with an aqueous NaOH solution in the pres- exchange resins), the condensation proceeded inten-
ence or absence of the PTC (TOMAC):
OH
sively, namely, the conversion of the reactant 2-cyclo-
hexene-1-ol was 87% and the apparent rate constant
for the condensation of 2-cyclohexene-1-ol with
O
O
OH
0
−1
cyclohexanone was k = 0.044 min at 120°C (Fig. 2).
H+
+
At the same time, it was found that the side self-
condensation reaction of cyclohexanone intensely
The results of the experiments are presented in proceeded under these conditions to yield dimers in an
Fig. 1. As is seen, this condensation reaction does not amount of up to 30 wt % over 120 min of the reaction:
PETROLEUM CHEMISTRY Vol. 58 No. 10 2018

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MARTYNENKO et al.
O
O
O
O
OH
2
+ H O
2
Reaction of Cyclohexanone with 2-Cyclohexene-1-one
The 2-cyclohexene-1-one molecule has an active carbonyl group, so that two types of reaction with cyclo-
hexanone can be assumed, (a) the aldol condensation or (b) the alkylation:
O
O
HO
O
O
a
b
O
+
O
O
To confirm this assumption, experiments on the con-
The results of the experiments are presented
densation of 2-cyclohexene-1-one with cyclohexanone in Fig. 3. As can be seen, the condensation reaction of
were performed in a two-phase system with an NaOH 2-cyclohexene-1-one with cyclohexanone is acceler-
aqueous solution in the presence or absence of the PTC. ated in the presence of the phase-transfer catalyst;
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
20
40
60
80
100 120 140
Time, min
Fig. 2. Change in the 2-cyclohexene-1-ol concentration with time in the process of condensation with cyclohexanone over the
Amberlyst 70 catalyst. Conditions: C(c-enol) = 0.6 mol/L, C (cat) = 10 wt %, and T = 120°C.
0
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CATALYTIC CONDENSATION OF CARBONYL COMPOUNDS
0.50
893
0.6
0.5
0.4
0.3
0.2
0
0.40
.45
Without PTC
With PTC
0.35
0.30
0.25
0.20
Without PTC
With PTC
0
0
.15
.10
0.05
0.1
0
10
20
30
40
50
60
Time, min
0
20
40
Time, min
60
80
Fig. 4. Change in the concentration of hexanal with time in
the process of its condensation with cyclohexanone in the
presence and absence of a phase-transfer catalyst. Condi-
tions: C (NaOH) = 1.75 mol/L, C (h-al) = 0.47 mol/L,
Fig. 3. Change in the 2-cyclohexene-1-one concentration
with time in the condensation process without a phase-
transfer catalyst and in the presence of TOMAC. Condi-
0
0
C (PTC) = 0.012 mol/L, and T = 30°C.
0
tions: C(c-enone)
= 0.50 mol/L, C (NaOH) =
0
1
.75 mol/L, C (PTC) = 0.012 mol/L, and T = 50°C.
0
Condensation of Aldehydes with Cyclohexanone
thus, the rate increases almost twofold and the conver-
The condensation of cyclohexanone with hexanal
sion over 1 h is about 70% versus 40% in the case of the was performed in a heterophase system with NaOH in
process without PTC.
O
the presence or absence of the TOMAC catalyst:
O
O
CH3
CH3
+
H C
3
O
It was shown (Fig. 4) that the use of the PTC also
Due to the presence of the active carbonyl group,
accelerated the condensation process by more than unsaturated cyclic ketones (2-cyclohexyl-1-one)
twofold; the conversion over 1 h was 70% versus 30%
in the case of the process in the absence of PTC.
0
.5
T = 30°C
T = 40°C
T = 50°C
T = 60°C
The kinetic studies were performed under the
pseudo-first-order conditions with respect to cyclo-
hexanone and the alkali (the reactant and the catalyst
were taken in eightfold and fourfold excesses, respec-
tively, relative to hexanal). The reaction order with
respect to the aldehyde was set to unity according to
published data [14]. The results are presented in
Figs. 5 and 6.
0.4
0
.3
.2
0
0.1
The apparent rate constants of the pseudo-first-
order reaction at various temperatures were estimated
for the heterophase process of hexanal condensation
with cyclohexanone (Table 2).
0
10
20
30
40
50
60
70
Time, min
Thus, the obtained results lead to the following
conclusions: linear aldehydes (hexanal) readily inter-
act with cyclohexanone under the alkali catalysis con-
ditions in the temperature range of 30–60°C, and the
rate increases almost twofold in the presence of PTC.
Fig. 5. Change in the concentration of hexanal with time at
different temperatures for the condensation process in the
presence of TOMAC. Conditions: C (NaOH)
=
=
0
1
.75 mol/L, C (h-al) = 0.47 mol/L, C (PTC)
0
0
0.012 mol/L, and T = 30–60°C.
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MARTYNENKO et al.
0
0
0
0
0
0
.7
.6
.5
.4
.3
.2
Unsaturated cyclic alcohols (2-cyclohexyl-1-ol)
react with cyclohexanone only under the conditions of
T = 30°C
T = 40°C
T = 50°C
acid catalysis at temperatures above 100°C.
ACKNOWLEDGMENTS
This work was supported by the Russian Founda-
tion for Basic Research, project no. 18-08-00307.
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Translated by E. Boltukhina
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