Intensification of cyclohexanone purification stage from impurities in caprolactam production using phase transfer catalysis

Article abstract of DOI:10.1134/S107042721407009X

Impurities in the oxidate, which was produced in the oxidation of cyclohexane in an industrial environment, were analyzed and identified. It is found that the amount of esters and ethers is 30% of the impurities produced, among which a cyclohexyl ethers amount is more than 50%. The process of purifying the oxidate from the impurities by hydrolysis in the presence of phase transfer catalysts and without them was studied. It has been shown that the use of trioctylmethyl ammonium chloride (Aliquat-336) in the the stage of saponification of esters enabled a removal of 90-96% of esters with reducing of reaction time in a 1.5-fold, in contrast to non-catalytic process.

Full text of DOI:10.1134/S107042721407009X

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2014, Vol. 87, No. 7, pp. 899−903. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © E.A. Martynenko, I.L. Glazko, S.V. Levanova, Yu.V. Portnova, 2014, published in Zhurnal Prikladnoi Khimii, 2014, Vol. 87, No. 7, pp. 907−912.
ORGANIC SYNTHESIS AND INDUSTRIAL
ORGANIC CHEMISTRY
Intensification of Cyclohexanone Purification Stage
from Impurities in Caprolactam Production
Using Phase Transfer Catalysis
E. A. Martynenko, I. L. Glazko, S. V. Levanova, and Yu. V. Portnova
Samara State Technical University, ul. Molodogvardeiskaya 244, Samara, 443100 Russia
e-mail: kinterm@samgtu.ru
Received March 14, 2014
Abstract—Impurities in the oxidate, which was produced in the oxidation of cyclohexane in an industrial
environment, were analyzed and identified. It is found that the amount of esters and ethers is 30% of the impurities
produced, among which a cyclohexyl ethers amount is more than 50%. The process of purifying the oxidate from
the impurities by hydrolysis in the presence of phase transfer catalysts and without them was studied. It has been
shown that the use of trioctylmethyl ammonium chloride (Aliquat-336) in the the stage of saponification of esters
enabled a removal of 90–96% of esters with reducing of reaction time in a 1.5-fold, in contrast to non-catalytic
process.
DOI: 10.1134/S107042721407009X
It is known that the quality of finished caprolactam di-
rectly depends on the quality of cyclohexanone, which is
intermediate in its production. Purification of cyclohexa-
none is paid much attention; complexity of the process
consists in the presence of a wide range of impurities
In industry there are several consecutive purification
stages of oxidate: neutralization of acids, saponification
(hydrolysis) of esters, and distillation. On saponification
stage, which proceeds in the presence of 5–10% aqueous
alkali solution, the amount of impurities is reduced as
a result of hydrolysis of esters.
–
3
–4
–1
resulted and in their low content (10 –10 mol L ).
Esters, aldehydes, alcohols, carboxylic acids, and
unsaturated peroxy compound are major impurities con-
tained in the cyclohexanone [1, 2]. Getting of a small
amount of these compounds to the finished cyclohexanone
can significantly affect a quality indicator such as the per-
manganate index (content of easily oxidized impurities).
However, in accordance with an experience of exist-
ing manufactures the removal of ester impurities can
be achieved only to 50–70% (with their concentration
in oxidate entering the saponification stage of about
1–1.5 wt %).
Previously [4], it was found that an increase in the
saponification temperature gives better removal of
esters, but this leads to the formation of condensation
products of cyclohexanone. It is shown that with in-
creasing the temperature from 30 to 120°C the amount
of the condensation products (resins) increases by
10 times.
Esters (mainly, difficult-to-saponify esters of mono-
carboxylic acids) in an oximation stage at treating with
hydroxylamine form hydroxamic acids, whose traces can
reach a distillation stage, where in the interaction with
the alkali they undergo Lossen rearrangement to form
the amine [3]:
8
99

900
MARTYNENKO et al.
Furthermore, at increasing the temperature the process
TOMAC, Aliquat-336), tetrabutylammonium bromide
([N(C H ) ]Br, TBAB), benzyltriethylammonium chlo-
should be carried out under pressure that requires a large
capital outlay due to changes in equipment design of the
process. Therefore, for enhancing the process it is neces-
sary to find other ways.
4
9 4
ride ([N(C H ) C H ]Cl, TEBAC).
2
5 3
7
7
RESULTS AND DISCUSSION
It is known that the rate of hydrolysis of esters in
a heterogeneous system, can be increased by using phase
transfer catalysts (PTC) [5–9]. As a result of studies of
the hydrolysis reactions of esters it was found that the
process using PTC is suitable for sterically hindered es-
ters, but in those cases where the ester has long carboxyl
acid side chain, carboxylate can form associates with the
cation of the catalyst, and the catalyst effect is reduced or
completely disappears. Thus, efficiency and mechanism
of the reaction under phase transfer catalysis should be
considered only relative to a specific reaction systems.
It is known that the efficiency of the catalyst depends
on its structure and reaction conditions. Thus, in neutral
or weakly alkaline media high lipophilic catalysts ofAli-
quat-336 or Catamine AB are active, but in systems with
strong alkali more hydrophilic catalyst such as TEBAC
are preferred [12]. In the study of 10% NaOH solution the
efficiency of both high lipophilic (TOMAC and TBAB)
and low lipophilic (TEBAC) catalysts were compared.
The study of ester saponification process under PTC
conditions was performed in a model system that was
a mixture close to industrial conditions (approximately
The study purpose is identification of impurities in the
oxidate entering the stage of saponification, investigation
of the ester saponification process in the presence of PTC.
4
0% of cyclohexane, 40% of cyclohexanol, 20% of cy-
clohexanone), in which modeling esters were added in
an amount of 5 wt % (calculation in term of the organic
substrate). The mixture was heated to a preset temperature
EXPERIMENTAL
(
70°C) and stirred until complete dissolution of ether, then
Analysis of oxidate (a product obtained by oxidation
of cyclohexane on the catalyst, cobalt naphthenate, at
a temperature 157–158°C, conversion 4.5–5%, selectivity
in term of a total amount of cyclohexanol and cyclohexa-
none 55–57%) was performed by gas chromatography-
mass spectrometry using a Shimadzu GCMS QP2010
Ultra device. Conditions for the analysis: capillary
column DB-1ms of 30 m × 0.25 mm, injector tem-
perature 250°C, column thermostating mode 60°C–
the catalyst and alkali solution (preheated to a desired
temperature) were rapidly added, and finally sampling
was conducted maintaining the ratio between the phases.
Samples were analyzed by the gas-liquid chromatog-
raphy. A sample preparation was performed as follows:
the sample was neutralized with hydrochloric acid until
neutral reaction to remove the residual alkali and the wa-
ter, then after anhydrous magnesium sulfate was added,
kept for 30 min and filtered off. In the obtained sample
the internal standard (dibutyladipate) was entered.
–
1
(
5 min)–10° min –260°C, carrier gas helium, a split
ratio 1/100.
Most components of oxidate entering hydrolysis stage
Chromatographic analysis was performed on a
software and hardware complex Hromatek-Analitik
based on a chromatograph Crystal-2000M with the
following parameters: capillary column with grafted
phase DB-1 of 101 m × 0.25 mm; column temperature
2
were identified by the mass spectra available of the spec-
tral database NIST (components nos. 1–20, 22, 25, 27,
3
1, 33) [10]. The remaining components were identified
by the products of fragmentation of the molecular ions
11]. Sum of ethers and esters was 30% of the impurities
[
–1
00°C–15° min –260°C; evaporator temperature 300°C,
produced, the amounts cyclohexyl among them was more
than 50%. The total amount of impurities in the oxidate
determined by gas-liquid chromatography was on aver-
age 1.5–2% (see the table). Two esters: dibutyl adipate
detector temperature 270°C; carrier gas helium; the split
ratio 1/80; analysis time 30 min.
The general PTC scheme for the hydrolysis of esters
using Starks model are shown in Scheme 1: the catalyst
passes through the phase interface performing permanent
transitions from phase to phase.
(DBA) and dicyclohexyl adipate (DCHA) were taken as
model objects of the most difficult-to-saponify esters.
Aqueous sodium hydroxide (5% in the case of DBA and
–
10% in the case of DCHA) was used as hydrolyzing agent;
It is known that when extraction of OH on the or-
trioctylmethyl ammonium chloride ([N(C H )CH ]Cl,
ganic phased are required, it is better to use ammonium
8
17
3
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 7 2014

INTENSIFICATION OF CYCLOHEXANONE PURIFICATION STAGE
Impurities in oxidate entering the saponification stage
901
a
Impuruties no.
Output time, min Concentration, %
Compound
1
2
3
4
5
6
7
8
9
2.54
2.80
0.76
15.76
0.89
8.94
0.50
2.39
6.09
2.51
1.69
3.21
1.56
2.94
2.61
1.33
3.90
13.08
0.44
0.49
1.12
2.46
4.29
0.39
5.56
0.99
6.62
0.80
1.59
0.74
2.76
0.65
0.56
0.33
1.16
0.90
Σ 100
n-Propylacetate
Methylcyclohexane
2.91
Ethylcyclopentane
3.09
1-Pentanol
3.19
Toluene
3.30
Cyclopentanol
3.95
Hexanal
4.77
1,2-Epoxycyclohexane
Ethylbenzene
5.05
10
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
6.31
2-cyclohexen-1-one
7.49
Cyclohexyl formate
8.08
Hexanoic acid
9.18
1,5-Pentanediol
9.44
Cyclohexylacetate
9.62
1,2-Cyclohexanediol
10.5
1,3-Cyclohexanediol
11.42
12.53
13.09
13.87
14.73
14.96
15.23
15.52
16.79
16.95
17.26
17.8
Cyclohexyl propionate
Hexyl pentanoate, pentylhexanoate
Cyclohexylbutanoate
1,6-Hexanedal
Cyclohexyl pentanoate
Hexylcyclohexyl ester
Dicyclohexyl ether
Adipic acid pentyl ester
Glutaric acid hexyl ester
2-(Cyclohexenyl)cyclohexanol
Glutaric acid monocyclohexyl ester
Cyclopentanecarboxylic acid pentyl ester
Succinic acid dicyclohexyl ester
1'-Hydroxy[1,1'- bicyclohexyl]-one-2
1,2'-dihydroxy[1,1-bicyclohexyl]
Bicyclohexyl-2,3'-dione
Cyclopentanecarboxylic acid cyclohexyl ester
Adipic acid butyl hexyl ester
18.35
18.55
18.63
19.17
19.67
20.35
a
Concentration are in the form of percentage of the total amoumt of the impurities equal to 1.5%.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 7 2014

902
MARTYNENKO et al.
Scheme 1.
determine compatibility with an organic substrate, the
surface active properties, which provide the transfer
of hydroxyl anions. All studied quaternary ammonium
salts showed in a varying degree the catalytic effect.
The greatest increase in the reaction rate was observed
for catalysts TBAB and TOMAC; TEBAC exhibited
less activity in the hydrolysis reaction, due likely to its
less lipophilicity.
Phase
interface
The effect of the PTC amount on the hydrolysis pro-
cess was studied on an example of the catalyst TOMAC
salt containing a lipophilic cation and anion, for which
(Fig. 2). It was found that in the studied concentrations
ΔG° (thermodynamic potential of ion transfer from the
T
–
–
–
TOMAC belongs to a class of phase transfer catalysts,
which do not block the interface. With increasing the PTC
concentration more than 1.5% significant darkening of
the reaction mixture occurs that may be associated with
resinification. Further studies were conducted using the
catalyst in the amount of 0.5 wt %.
aqueous phase to the organic) is very high (F , OH , Cl ,
Br , SO ).
–
2
–
4
Figure 1 shows results of experiments with different
catalysts. It is seen that the catalytic effect is due to the
chemical nature of alkyl groups composed PTC and
also associated with their length and structure, which
Fig. 2. DCHA change in concentration c (M) at time τ (min)
in hydrolysis in the presence of various amounts of PTC.
Conditions: c(DCHA) = 5, c(NaOH) = 10 wt %; 70°C.
c(PTC), wt %: (1) 0.2, (2) 0.3, (3) 0.5, (4) 0.6, (5) 0.8, (6)
1.2, (7) 1.4.
Fig. 1. Change DCHA concentration c (M) in time τ (min)
in hydrolysis in the presence of various PTC. Conditions:
c(DCHA) = 5, c(NaOH) = 10, c(PTC) = 0.5 wt %; 70°C.
(1) TEBAC, (2) TBAB, (3) TOMAC, (4) without a catalyst.
(b)
(a)
Fig. 3. Change of concentration of ester c (M) during the time τ (min) in hydrolysis without PTC (1) and in the presence of volumes (2)
at 70°C. Ester: (a) DBA, (b) DCHA. Conditions: (a) c(DBA) = 5, c(NaOH) = 5, c(PTC) = 1.5 wt %; (b) c(DCHA) = 5, c(NaOH) = 10,
c(PTC) = 1.5 wt %.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 7 2014

INTENSIFICATION OF CYCLOHEXANONE PURIFICATION STAGE
903
Saponification of DBA and DCHA was conducted in
ACKNOWLEDGMENTS
the presence of TOMAC. The results of the experiments
are shown in Fig. 3. As can be seen, the use of PTC
significantly accelerates the hydrolysis process: in the
case of DBA, the rate increases by 25 times (for 1.5 h
the conversion was 90% compared to 8% in the case of
non-catalytic process); and in the case of DCHA the rate
increases by 5 times (the conversion up to 70% achieved
for 1.5 h compared to 18 % of non-catalytic process).
The lower rate in the case of DCHA can be explained
by steric hindrances associated with the presence of two
bulk substituents at the carboxyl group:
This work was financially supported by the Ministry
of Education and Science of the Russian Federation
within the framework of the basic part of the state task
for Samara State Technical University (project 1015).
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1
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