Optimization of a cyclohexanone distillation stage in the presence of alkali

Article abstract of DOI:10.1134/S1070427211100156

Kinetics of two reactions: hydrolysis of esters and condensation of cyclohexanone in an alkaline environment, was studied in model mixtures. Derived kinetic equations were used to assess optimal parameters of proceeding cyclohexanone distillation in the presence of alkali.

Full text of DOI:10.1134/S1070427211100156

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2011, Vol. 84, No. 10, pp. 1767−1771. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © I.L. Glazko, S.V. Levanova, E.A. Martynenko, A.A. Sokolova, 2011, published in Zhurnal Prikladnoi Khimii, 2011, Vol. 84, No. 10,
pp. 1675−1679.
ORGANIC SYNTHESIS AND INDUSTRIAL
ORGANIC CHEMISTRY
Optimization of a Cyclohexanone Distillation Stage
in the Presence of Alkali
I. L. Glazko, S. V. Levanova, E. A. Martynenko,
and A. A. Sokolova
Samara State Technical Unversity, Samara, Russia
Received April 12, 2011
Abstract—Kinetics of two reactions: hydrolysis of esters and condensation of cyclohexanone in an alkaline
environment, was studied in model mixtures. Derived kinetic equations were used to assess optimal parameters
of proceeding cyclohexanone distillation in the presence of alkali.
DOI: 10.1134/S1070427211100156
It is known that the quality of commercial caprolac-
tam, obtained by oxidation of cyclohexane from cyclo-
hexanone by the oxidation scheme, depends on a quality
of the latter. The main impurities of cyclohexanone, which
reduce the caprolactam quality, are products containing
ether, aldehyde groups, unsaturated and macromolecular
compounds [1–3]. They are formed in an oxidation stage
and, remaining in cyclohexanone in distillation, continue
to participate in a various secondary reactions, increase
a permanganate index (PI) of target products, therewith
reducing quality and increasing losses.
the permanganate index [2]. However, it dramatically
increases an amount of condensation products of cyclo-
hexanone (Oil-X), which leads to an increase in its loss
(20–50 kg t–1 of cyclohexanone).
It is known that alkali can catalyze the hydrolysis reac-
tions as well as other processes occurring by nucleophilic
mechanism: decomposition, condensation, dimerization,
etc. So revealing of patterns of competing reactions pro-
ceeding in the presence of alkali at high temperatures is
topical to optimize the distillation stage of cyclohexanone
and to improve its quality.
Due to the constant increase in requirements for qual-
ity of caprolactam, much attention is paid to cleaning of
raw materials and intermediates, mainly, of cyclohexa-
none.
EXPERIMENTAL
Crude cyclohexanone (food of column 3A), cyclo-
hexanone-distilled prior to feeding and after feeding of
alkali in the distillation column were used as objects of
the study. Essential number, the value of the PI, and the
content of high-boiling impurities were determined in
the samples by standard methods. The results are shown
in Table 1.
At factories producing caprolactam, cyclohexane oxi-
dation is carried out following the scheme of extraction
of cyclohexanone from reaction mixture obtained after
oxidation by means of distillation: sequentially unreacted
cyclohexane is removed, then commercial cyclohexanone
and cyclohexanol, as well as high-boiling waste, Oil-X,
are extracted (Fig. 1).
It turned out that during the distillation in the presence
of alkali the essential number is reduced 3 times. This is
due to proceeding the hydrolysis of esters (Scheme 1).
To clean cyclohexanone from impurities in reflux
columns 3 and 3A for the selection of end product is
added 25–30% aqueous solution of alkali (KOH), which
promotes the hydrolysis of esters, thereby reducing
Along with the hydrolysis occur side reactions of
a cyclohexanone autocondensation, which resulted in
1767

1768
GLAZKO et al.
Cyclohexane
Alcohol fraction
2A
1
Reaction mixture
obtained after
oxidation
High boiling component
Cyclohexanone
2
Cyclohexanol
KOH
4
3
1A
5A
KOH
3A
4A
Oil-X
Fig. 1. Scheme of separation of products of cyclohexane oxidation.
Scheme 1.
a mixture of isomers, 2-(1-cyclohexenyl)cyclohexanone
(I) and (2-cyclohexylidene)cyclohexanone (II), as well
as heavier products of the condensation (III) that make
up the Oil-X (Scheme 2).
O
O
C
C
R
+ 2 KOH
OR
RO
Thus, it was necessary to study the kinetics of the
main reactions, hydrolysis and condensation, and choose
a mode in which a decrease in the impurity contained in
cyclohexanone without the formation of new, i.e., regimes
under which the following inequality holds r1>> r2, where
r1 is the reaction rate of hydrolysis according to Scheme 1,
O
O
r1
C
R
C
+ 2 ROH.
OK
KO
Table 1. Characteristics of the samples
Sample
Concentration of esters,
Content of high boiling
impurities, wt %
PI, units
–
M
Crute cyclohexane
0.0119
4.03
Cyclohexanone-distillate
before alkali delivery
0.008
20
18
0.369
0.346
after alkali delivery
0.0004
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 10 2011

OPTIMIZATION OF A CYCLOHEXANONE DISTILLATION STAGE
1769
Scheme 2.
r2, the reaction rate of condensation by Scheme 2.
components was performed by the subring of the indi-
vidual components synthesized for this purpose.
The kinetics was studied in model systems by the
method of initial velocities of isolation [4] under condi-
tions close to reality. The kinetics of the hydrolysis of es-
ters studied in a model mixture: dibutyladipinate–alcohol
(ethanol, cyclohexanol) solution of potassium hydroxide
in the temperature range 5–30°C, the concentration of the
ester (dibutyl adipata) cDBA, 1.77 mol l–1, the concentra-
tion of alkali ranged from 0.14–0.54 mol l–1.
The main kinetic characteristics of hydrolysis of
esters and the condensation of cyclohexanone (reaction
order by components, the observed rate constant in the
studied temperature ranges, activation energy) are given
in Table. 2.
Analysis of the obtained values indicates that the
hydrolysis of esters occurs at low temperatures at high
speed. Condensation processes start at temperatures
above 100°C and require a much longer time of contact.
To stop the hydrolysis the probes were taken in flasks
containing 5 ml of 0.1 N HCl and an amount of the hy-
drolyzed esters was analyzed by the reverse titration.
PID-1
The kinetics of cyclohexanone concentration was
studied on the model mixture of cyclohexanone–cyclo-
hexanol at temperatures 90–140°С in a range of alkali
concentration 1.8–7.65, cyclohexanone 2.11–4.58 mol l–1.
Cyclohexanol
The reactor was charged with a mixture of cyclohexa-
none–cyclohexanol, which was heated to a predetermined
temperature, and under vigorous stirring fine ground al-
kali was rapidly injected as a catalyst. Immediately after
injection, and complete dissolution of the alkali sampling
was begun. To stop the condensation reaction the samples
were cooled by placing them in ice water. The analysis of
product was performed on the chromatographic software
and hardware complex “Hromatek Analyst” based on
a chromatograph “Crystall-2000M” with the following
parameters: capillary column with a grafted phase OV-
101 m × 0.25 m, evaporator temperature 300°C, detector
temperature 300°C, column temperature 130–260°C,
heating rate 5°C min–1, carrier gas helium, the division
of flow 1/80; analysis time 55 min.
Dianones
Cyclohexanone
Trianones
Fig. 2. Cyclohexanone condensation products. (τ) yield time
(min).
Atypical chromatogram of the condensation products
of cyclohexanone is shown in Fig. 2. Identification of the
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 84 No. 10 2011

1770
GLAZKO et al.
Table 2. Kinetic characteristics of the reactions
Condensation of cyclohexanone
Hydrolysis of esters
Kfound × 103, M s–1
parameter
Т, K: 363
Kfound ×103, M s–1
parameter
0.05 ± 0.03
0.13 ± 0.02
0.40 ± 0.02
Т, K: 278
4.76 ± 0.03
6.35 ± 0.03
383
413
283
293
303
18.17 ± 0.04
39.96 ± 0.04
Equation of
reaction speed
(dc)/(dt)
Equation of
reaction speed
(dc)/(dt)
3.9 × 103exp(–50500/8.314T) ×
1.42 × 109exp(–61400/8.314T)cKOH ester
foundсKOH ester
c
=
c
KOHc2anone = kfoundс2anone
k
с
Ea, kJ mol–1
50.5 ± 2.9
Ea, kJ mol–1
61.4 ± 2.6
than 1 s; at 30°C, for 1.5 min.
The obtained kinetic equations were used to estimate
the optimal time required for maximum hydrolysis of
esters with a minimum yield of condensation products
of cyclohexanone (Fig. 3). It is seen that when the con-
centration of alkali cKOH = 0.13 wt % (0.0215 mol l–1)
the reaction at 100°C comletes for 0.5 min, at 30°C to
achieve the same conversion up to 45 minutes will take
up. When an amount of KOH increases to 0.26 wt %
(0.043 mol l–1), at 100°C hydrolysis proceeds for less
Using the kinetic equation of the condensation of
cyclohexanone, we calculated an amount of high-boiling
products formed at different temperatures and contact
times. The initial concentration of cyclohexanone was
85; water, 2; esters, 0.3 wt %. The results are presented
in Table. 3.
Under real conditions the distillation occurs in a tray
column, a calculated residence time of alkali in the col-
umn is about 2.6 h, temperature in a still is 90–130°С.
Data of Table 3 show that under conditions close to
real (temperature 120°C, contact time 2.6 h) the yield
of the condensation product dramatically grows. The
amount of the condensation products is about 28 kg t–1
of cyclohexanone that corresponds to parameters of the
real process (20–50 kg t–1).
CONCLUSIONS
(1) It was established that in practice by carrying out
the distillation in the presence of alkali, from the crude
cyclohexanone no more than 70–75% of ester impurities
may be removed.
(2) The concentration of alkali supplied should not
exceed the equivalent concentration, since the presence
of free alkali after removal of esters increases the yield
of the condensation products.
Fig. 3. Time τ (s) of reaching the quantitative hydrolysis of
esters (99% conversion) vs. temperature Т (°С) at various
alkali concentrations. cKOH (wt %): (1) 0.13 (0.0215 M), (2)
0.26 (0.043 M).
(3) The temperature distillation should not exceed
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OPTIMIZATION OF A CYCLOHEXANONE DISTILLATION STAGE
1771
Table 3. Yield of cyclohexanone condenation products at various temperatures of the process
Yield of cyclohexanone condenation products, kg t–1
сКОН = 0.13 wt % (0.0215 M)
сКОН = 0.26 wt % (0.043 M)
Т, °С
in the case of real time of
in the case of real time of
contact in a column,
2.6 h
at time required for reaching
99% conversion of esters
at time required for reaching
99% conversion of esters
contact in a column,
2.6 h
30
50
0.0006
0.0004
0.0003
0.0003
0.0002
0.00
0.01
0.02
0.08
0.18
0.0027
0.0021
0.0018
0.0010
0.0010
0.29
1.01
70
2.90
100
120
14.00
27.98
REFERENCES
120°C. When the temperature of the column in the still
grows, an amount of high-boiling components increases
by an order of magnitude.
1. Iogansen,A.V., Zelenskaya, L.G., and Semina, G.N., Khim.
Promyshlennost’, 1965, no. 39, pp. 20–21.
2. Lupanov, P.A., Chichagov, V.N., Chadaev, V.P. et al., Khim.
Promyshlennost’, 1975, no. 5, pp. 336–338.
ACKNOWLEDGMENTS
3. Kotel’nikova, T.S., Cand. Sci. (Chem.) Dissertation, 2009.
This work was part of the Federal Program “Scientific
and scientific-pedagogical personnel of innovative Rus-
sia” (2009–2013) NC-58P, GC P 206.
4. Shmid, R. and Sapunov, V.N., Neformal’naya kinetika (Non-
Formal Kinetics), Moscow: Mir, 1985.
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