- Email: [email protected]
Preparation of cumene hydroperoxide
Special Supplement to Chemical Engineering Science, vol. 3, 1954.
Preparation of cumene hydroperoxide J. P.
FORTUIN*
and H. 1. 'V ATERlIIAN
Laboratory of Chemical Engineering, Delft Technological University, Holland Summary-Cumene hydroperoxide has been prepared by liquid phase oxidation of eumene with molecular oxygen. The oxidation rates and yields are given of experiments carried out in a "Pyrex" reactor at 110-130°C. Copper was found to be a catalyst for this oxidation. Experiments carried out in a copper reactor showed an improvement in-reaction rate as well as in yields. At 120°C about 11.0% wt of cumenc hydroperoxide was formed in the liquid per hour in a yield of 95%. The kinetics of the reaction of cumene with oxygen have been studied. It is shown that the diffusion of oxygen in the hydrocarbon can influence the rate of reaction. The results indicated a reaction of zero order with respect to oxygen and first order with respect to cumene, The apparent activation energy of the non-catalytic oxidation of cumene was determined at 16 kcaljmole. For the continuous preparation of cumene hydroperoxide a tubular copper reactor has been developed. Evidence has been obtained that in the scaling up of such a reactor,the dissipation of the heat of reaction will not be a major problem. Resume-e-L'hydropcroxydc de cumenc a etc prepare par oxydation du cumene en phase liquide avec de I'oxygene moleculalrc, On donne les vitesses d'oxydation et les rendements obtenus dans des essais faits a 110-130°C dans un reacteur en verre Pyrex. II a ete trouve que Ic cuivre est un catnlyseur pour cettc oxydation, Les vitesses de reaction et les rendements obtenus dans un reacteur en cuivre etaient plus grands qu'en verre, A 120°C il s'est forme environ 11.6% en poids d'hydroperoxyde de cumene par heure, Ie rendement etant de 95%. Une etude a etc faite de Ia reaction du cumene avec I'oxygene. Elle a revelC que la diffusion de I'oxygene dans l'hydrocarbure peut influencer Ia vitesse de reaction. Les resultats ont indlque que In reaction est d'ordre zero par rapport a I'oxygene et d'ordre un par rapport au cumene, L'encrgie apparente d'activation de l'oxydation non-catalytlque du cumene a ete determinee ; sa valeur etait de 10 kenl/rnole. Pour la preparation continue de l'hydroperoxyde de eumene on a developpe un reacteur tubulaire en cuivre et il semble que l'aggrandissemcnt de ce reacteur ne donne pas des dlfflcultes insurmontables en ce qui concerne Ia dissipation de Ia chaleur, Zusammenfassung-Kumolhydroperoxyd wurde mittels Oxydation von Kumol mit molekularern Sauerstoff in der Fliissigkeitsphase hergestellt. Die Oxydationsge-chwlndlgkeiten und Ausbeutcn von in eincm Pyrex-Rcaktor bci 110·130°C durchgefllhrten Versuchen werden erwiihnt. Es stellte sich heraus, dass Kupfer diese Oxydation katalytisch beeinflusst. Versuche in cinem Kupferrcaktor wiesen eine Verbesserung der Iteaktlonsgcschwlndigkelt sowie der Ausbeuten auf. Dei 120°C wurde stiindlich, mit ciner Ausbeute von 95% 'etwa 11.6 Gew.% Kumolhydroperoxyd in der Fliissigkeit gebildet. Die Kinetik der Reaktion von Kumol mit Sauerstoff wurde untersucht, Es wurde naehgewiesen, dass die Diffusion von Sauerstoff in den Kohlcnwasserstoff die Reaktionsgeschwindigkeit beeinflussen kann, Die Ergebnisse zeigten eine Reaktion der nullten Ordnung hinsichtlich des Sauerstoffs und der ersten Ordnung hinsiehtlich des Kurnols, Die scheinbare Aktivierungsenergie der niehtkatalytischen Oxydation wurde zu 10 kealjmol bestimmt. Zum Zwecke der kontinuierliehen IIersteUung von Kumolhydroperoxyd wurde cin rohrfOrmiger Kupferreaktor entwiekclt. Es stelIte sich heraus, dass bel der Vergrossorung cines solehen Rcaktors die Abfuhr der Reaktionswiirrne keine besonderen Schwierigkeiten verursamt• ... Present address:
I{oninklijke/Shell-Laboratorium, Amsterdam.
60
J. P.
FonTUIN
and H. 1.
'VATEmIAN :
Preparation of eumene hydroperoxide
An important factor influencing the oxidation INTRODUCTION Cumene hydroperoxide has acquired technical rate is the purity of the feed, as small amounts importance as a polymerization catalyst and as of inhibitors (such as sulphur compounds, phenols, an intermediate in the "cumcne-process" for the aniline or styrenes) present in the hydrocarbon manufacture of synthetic phenol. The hydroper- may break the reaction chains. The oxidation reaction is generally preceded by oxide is now produced commercially by reacting an induction period. A maximum oxidation rate eumene in the liquid phase with oxygen or air. is only attained if a certain hydroperoxide conThe main results of our investigation into the centration is built up in the liquid. The induction preparation of phenol from cumene were preperiod can be eliminated by adding a hydroviously published [1]. It was shown that for this peroxide to the hydrocarbon to be oxidised before oxidation process the eumene should be very pure the reaction is started. so that inhibitors present in the base material These characteristics showed up clearly in our must be removed by a suitable chemical treatinvestigation, in which thoroughly purified cumene ment. The cumene could be readily autoxidized was used. in a copper reaction vessel, the copper wall of BASE MATERIALS the reactor acting as the oxidation catalyst. Cumene hydroperoxide was obtained as a solution The crude cumenc was distilled and then treated in an excess of unconverted cumene. In this with sulphuric acid followed by a treatment with solution the hydroperoxide was decomposed into aqueous mercuric acetate solution (sec Ref. 1). phenol and acetone by means of sulphur dioxide Physical constants of the eumene: b.p, 152·0as a catalyst. 152·5°C, n~ 1'41)13, lit. values b.p. 152'3°C and The present paper deals specifically with the n~ 1'4913 [2]. preparation of cumene hydroperoxide. The Commercial oxygen containing at least 99% O2 characteristics of the oxidation were first studied or filtered air were used as oxidants. in a "Pyrex" glass reactor. Subsequently, when :METIIOD OF ANALYSIS thc usc of copper as a catalyst had shown to lead to a better yield and a higher rate of reaction, a The hydroperoxide concentration in the oxidised copper vessel was taken for the oxidation. liquids was determined by an iodometric method The kinetics of the reaction of cumene with [3], The yield of the reaction was computed from oxygen were also studied. The results of this the hydroperoxide content and the total oxygen investigation were of interest for the design of a content of the liquid. reactor for the continuous preparation of cumene RESULTS, hydroperoxide. The performance of this tubular reactor was so encouraging that it is believed to Oxidation of 200 ml, of cumene with oxygen in be suitable for application on a larger scale. a stirred "Pyrex" glass apparatus (stirring speed 1,200 r.p.m.) at varying temperatures gave the LIQUID PHASE OXIDATION OF CUlIiENE results collected in Table 1. The induction period It is assumed that the autoxidation of hydroTable 1. carbons in the liquid phase proceeds according to Oxidation of cumene in a "Pyre.x" reactor a free radical chain mechanism, a hydroperoxide being the first oxidation product formed. AppreillaximullI oxidaciable yields can be achieved if the hydroperoxide Length oJ tioll rate % tvl. Yield remperatllrc illdllctioll period lqjdroperoxide is stable under the conditions of the reaction - as °C % hours formed per hour may for instance be the case with isopropylbenThe common oxidation zenc liydroperoxide, II 110 4·4 00·8 catalysts, i.e, the soluble salts of the transition 8-!·3 120 s-i I! metals, cannot be used here as they tend to 10,0 1 130 74'6 decompose the hydroperoxides formed.
61
CONFERENCE
ON
OXIDATION
Table 3.
was taken to be at an end when the maximum oxidation rate had established itself. 'When the oxidation was carried out with air instead of with oxygen, the maximum oxidation rate at rio-c was 4·1% wt of cum ene hydroperoxide formed per hour. Hence, about the same rate of oxidation was observed with air as with oxygen in this apparatus. The material balance of the oxidation was drawn up from an experiment carried out in the "Pyrex" reactor, in which cumcne was oxidized with oxygen at I20 0 e during 6 hours. The resulting liquid was carefully analysed. In Table 2 the results of the analyses are expressed as moles of material formed per 100 moles of cumene converted.
Oxidation oj cumene in a copper reactor, Temperature Oxidation rate % uit, cumcne DC hydroperoxideformed per hour 120 130
'Yield
11'(}
ll5 81
25·0
in this reactor. Before each experiment the inner surface of vessel and stirrer were rinsed with fuming nitric acid (spec. gr. 1·52), washed with water, and dried. The stirring speed was 880
r.p.m, At 120 0 e uniform, high yields were obtained in the copper reactor. The rate of production of eumene hydroperoxide under the conditions employed could be calculated at about 100-120 grams per litre per hour. For comparison two other reactors and stirrers were constructed, identical in shape to the copper reactor but now made of stainless steel and brass. Under exactly the same conditions the rates of cumene hydroperoxide formation appeared to be as follows:
7'able 2. Moles Of compounds found per 100 moles of cumene conuerled,
cumene hydroperoxidc dimcthylphenylcarbinol water ac etophenone methanol carbon dioxide
PROCESSES
80 '1 14·7 3·4 0·4 0'5 0 '3
in copper in brass in stainless steel
It is seen that the tertiary alcohol IX, IX dimethylphenyl-carbinol is the most important by-product formed. When the oxidation in the "Pyrex" reactor was carried out in the presence of 0·5 % wt of finely divided copper as a catalyst the maximum oxidation rate at nooe increased to 7'3% wt of cumene hydroperoxide formed per hour. The same catalytic effect of copper metal was observed when the oxidation was carried out in a copper vessel equipped with a copper stirrer, In this reactor the rate of reaction increased while the yield was higher than in the case of an oxidation in a glass reactor at the same temperature. The data are collected in Table 8. The experiments were done with 200 ml. of eumene and a supply of 25 litres of oxygen per hour. It should be noted that the experiment at 180 0 e gave a 25% conversion in the first hour of reaction and only an additional {)'4% in the second hour. No induction period was observed
22·3 ]7·2 4·1
The copper reactor showing definite advantages it was decided to make use of the copper catalyst to study the continuous preparation of cumene hydroperoxide. For the choice of the type of reactor a study was first made of the kinetics of the reaction of cumene with oxygen. KINETICS OF eUl\IENE OXIDATION
The experiments were made in a "Pyrex" glass reactor (sec Fig. 1). This small vessel permitted the oxidation of 0-8 gram mole of hydrocarbon per run at a constant temperature, which was maintained by placing the reactor in the vapour of a boiling liquid. Several variables were studied in this apparatus by measuring the rate of oxygen absorption under various conditions. The volume of oxygen absorbed was reduced to o°C and 760 mm mercury. 62
J. P.
FORTul~ and H . I. WATER)!AN : Preparation of cumcne hydroperoxidc
Above a certain critical stirring speed the maximum oxidation rote is no longer affected, and hence the real chemical reaction rate is then measured. Fig. 2 shows the oxygen absorption curves of two experiments carried out in the small reactor at 1l0·5°C with stirring speeds of 1,850 r.p.m, and 3,600 r.p.m., respectivel y, The slopes of the cur ves differ by 4 %. The critical stirring speed was about 2,500 r.p.m. in this apparatus, no further increase in the maximum rate beingobserved at higher velocities. All further experiments were carried out with a minimum speed of 8000 r.p.rn. (b) Concentration. of oxygen
CIRCULATING PUMP
Fig. 1. Assembly for kinetic experiments.
(a) Stirring speed When oxygen is bubbled through cumene at 100-120°C the oxidation rate will be governed partly by the rate at which the gas diffuses into the liquid. By rapid stirring the diffusion may be eliminated as the rate-determining factor.
J600
At IlO'5°C the maximum oxidation rate using pure oxygen (760 mm) as the oxidant amounted to 540 ml, of 02 absorbed per 9'3 gram mole. eumene per hour. The partial pressure of oxygen in the gas was now varied between 760 and 160 mm by mixing the gas with nitrogen. No decrease in the maximum oxidation rate was observed in this region of oxygen concentrations. Lower partial pressures of the oxygen were not studied. The reaction is apparently of zero order with respect to oxygen. It should be pointed out that the oxygen concentration might influence the oxidation rate if the gas diffusion has a determining effcct. In this case an increase in oxygen pressure, i.e. above atmospheric, might favour the rate of hydroperoxide formation.
(c) Concentration of hydrocarbon The effect of the hydrocarbon concentration on the oxidation rate was studied with mixtures of cumene and monochlorobenzcne, In Fig. 3 the maximum oxidation rates of these mixtures nrc plotted against their molar concentrations, It..is seen that the rate is about 'directly proportional to the concentration, indicating' a first order reaction with respect to cumene. The maximum oxidation rate of solutions of eumenc more dilute than 2 gram moles per litre could not be determined exactly owing to the low volume of oxygen absorbed per hour. '.
RPM.
.J TIME, HOURS
Jiig. 2. Effect of stirring speed.
63
CONFERENCE .O N
OXIDATION
PROCESS~S
Table 4.
MAXIMUM OXIDATION RATE
lUaximum oxidation
ml O;/JOg C/JMENE
Temperature
160
°c
140
ra(~
0/ cumene at several temperaturc.,.
J1Iaximum oxidation rate in tnl. of oxygen absorbed pcr 0 ·3 gram. mole of cumene per lIour
120
lJ7·Q 105·0 111 ·5
'KJO
80
250 3!l8 1>70
60 40
Using the formula E = R
20
~/;. T;.
In K. [4] a K2 mean value of 16 kcal per mol was found for the apparent activation energy of the reaction of cumcne with oxygen under these conditions. 1-
6 CONCENTRATION. GRAM MO'E/L/TRE
I
Fig. 3.
Effect of hydrocarbon concentration.
2
CONTINUOUS OXIDATION OF CUIIlENE
(d) Temperature
Oxygen absorption curves were determined at three different temperatures. 3% wt of cumene hydroperoxide was added to the eumene before these runs were started, with the object of shortening the induction periods. A very pure sample of cumene hydroperoxide was used for this purpose. It was proved in a blank experiment that the addition of the hydroperoxide did not affect the maximum oxidation rate of the cumene. OXYGEN A8SORPT/OI{ N 7.P
tn'
REACTION T
1500
1 : /II,5 .II : 105 JiI: 97
0C
«c
°c
1000
500
I
~
6
7
OXIDATION TIME. HOURS
Fig. 4.
Effeet of temperature.
Fig. 4 shows the results of the experiments. The maximum oxidation rates determined from the slopes of the curves arc given in 'I'able 4.
Following the results outlined in the preceding paragraphs an oxidation system was now developed for the continuous preparation of cumene hydroperoxide from cumene, A copper vessel of 400 ml. capacity provided with a high speed stirrer (2,000 r.p.m.) was used as the reactor. Cumene and the gas could be fed in and the oxidized liquid could' be discharged or circulated continuously. After one hour of reaction in this apparatus the oxidation of 200 ml cumcne at 120°C with an oxygen gas rate of 25 Iitres per hour resulted in a 20% wt cumene hydroperoxide solution. This means a production of approximately 180 grams of eumene hydroperoxide per litre per hour. However, when the experiment was continued with a continuous feed of fresh cumene the rate of hydroperoxide formation dropped rapidly within the next few hours to a value as low as 9 grams per litre per hour. It was shown that inhibition of the oxidation was caused by contamination of the cumene with packing materials, mainly from the stirrer. As it was known that eumene is very sensitive to traces of impurities and the contamination of material caused by such a high speed stirrer remained a problem, another reactor was designed without rotating parts. This reactor consisted of a vertical copper tube 1,250 mm long, internal diameter 24 mm (see Fi~. 5).
J. P.
FORTUIN
and H. I .
WATERMAN:
VENr GAS
" AIR INLEr CUMENE INLEr
Fig. 5.
Continuous oxidation of cumene.
Copper rings were used as the packing material for the flanges at both ends. Valves were made of brass with graphite on asbestos for packings. Before each experiment the inside of the copper tube was etched with fuming nitric acid (specific gravity 1'52), then washed with water and dried. For batch experiments the reactor was filled with 500 ml. of eumene per run. The results of some of these exp eriments are given in Table 5. In the experiments 2 and 4 the reactor was filled with copper turnings.
Preparation of cumcne hydr~peroxide
tubular reactor. In agreement with this, an even lower production rate was observed in experiments 3 and 4 where air was used as the oxidant. Super atmospheric pressures may be expected to be advantageous when a tubular reactor is used for this oxidation. Thc tubular reactor gave a satisfactory performance in continuous experiments. These runs were started by pressing 500 ml. of cumene into the reactor, heating to 120°C and thereupon oxidizing to the desired cumene hydroperoxide concentration. Then a continuous stream of eumcnc was introduced at the bottom; the excess liquid in the reactor soon passed the overflow through the cooler into the receiver. In a run of 111 hours with a feed of 190 ml. of cumene per hour a continuous stream of oxidized cumene was obtained in this way, with an average contcnt of 21 % wt of eumene hydroperoxide. It is assumed that baekmixing of liquid into the reactor took place here, so that the oxidation was carried out more or less under steady state conditions. The heat of reaction amounts to 27'7 keal per mole of cumene hydroperoxide formed [1]. In the last experiment about 37 grams of cumene hydroperoxide was formed per hour in a reactor of 0·5 litre. This means a production of approximately 0·5 mole per litre per hour or 13,850 cals heat generated per litre reaction volume per hour. About 840 grams of cumene has to be fed into such a reactor per hour, to get a solution of about 20% cumene hydropcroxide. When the cumene
In experiments 1 and 2, carried out with oxygen as the oxidant the rates of production of cumene hydroperoxide are 101 and 126 grams per litre per hour, respectively. This is lower than the 180 grams obtained with the just mentioned stirred reactor. Apparently, the diffusion of the oxygen in the liquid partly determines the rate of hydroperoxide formation in the
Table 5. Batch expcrimetl18 in the tubular reactor. .~
Experiment No. 1 2 11
4
Gas
Rate 1./lIr
oxygen oxygen air air
25 25 50 65
to.
Grams rumene lIydroperoxidc prepared per !lour
120 121 121 121
50'5 63 25·5 33
R eactor T emperatures
'I
t2
117 116 116 116
120 120 120 120
65
Remarks
copper turnings copper turnings
CONFERENCE
ON
OXIDATION
PROCESSES
is introduced cold, say at 20°C, an amount of heat of reaction ean be removed sufficiently 340 X 0'5 X 100 = 17,000 cals is needed to heat by: a. feeding cold cumene; b. jacketing the the cold feed to the reaction temperature of 120°C reactor tube and cooling with steam or water, (specific heat of cumene in the temperature range taking a certain temperature gradient. taken at 0·5 caljg 0c). Hence, the heat evolved The authors wish to express their gratitude to during the reaction can be controlled by feeding Dr. J. J. VERSTAPPEN for doing part of the the cumene at a slightly elevated temperature. experimental work. Thanks are due to the Even.If a higher oxidation rate can be obtained management of N. V. de Bataafsche Petroleum or if the eumene hydropcroxide is discharged at a lIlaatschappij, The Hague, for permission to higher concentration it may be expected that the publish this paper. REFERENCES
[1] FORTUIN, J. P. and WATERl\lAN, H. I.; Chern. Eng. Sci.l953 2182; FORTUIN, J. P.; Thesis, Delft, 1952. [2] FRANCIS, A. W.; Chern. Revs. 1948 42 126. ]3] WAGNEll, C. D., Ssrrrn, R. II. and PETERS, E. D.; Anal. Chern. 1047 19 076. [4] GEORGE, P., RlDEAL, E. K. and ROBERTSON, A.; Proc, Roy. Soc. (London) 1946 A 185293.
66
Preparation of cumene hydroperoxide J. P.
FORTUIN*
and H. 1. 'V ATERlIIAN
Laboratory of Chemical Engineering, Delft Technological University, Holland Summary-Cumene hydroperoxide has been prepared by liquid phase oxidation of eumene with molecular oxygen. The oxidation rates and yields are given of experiments carried out in a "Pyrex" reactor at 110-130°C. Copper was found to be a catalyst for this oxidation. Experiments carried out in a copper reactor showed an improvement in-reaction rate as well as in yields. At 120°C about 11.0% wt of cumenc hydroperoxide was formed in the liquid per hour in a yield of 95%. The kinetics of the reaction of cumene with oxygen have been studied. It is shown that the diffusion of oxygen in the hydrocarbon can influence the rate of reaction. The results indicated a reaction of zero order with respect to oxygen and first order with respect to cumene, The apparent activation energy of the non-catalytic oxidation of cumene was determined at 16 kcaljmole. For the continuous preparation of cumene hydroperoxide a tubular copper reactor has been developed. Evidence has been obtained that in the scaling up of such a reactor,the dissipation of the heat of reaction will not be a major problem. Resume-e-L'hydropcroxydc de cumenc a etc prepare par oxydation du cumene en phase liquide avec de I'oxygene moleculalrc, On donne les vitesses d'oxydation et les rendements obtenus dans des essais faits a 110-130°C dans un reacteur en verre Pyrex. II a ete trouve que Ic cuivre est un catnlyseur pour cettc oxydation, Les vitesses de reaction et les rendements obtenus dans un reacteur en cuivre etaient plus grands qu'en verre, A 120°C il s'est forme environ 11.6% en poids d'hydroperoxyde de cumene par heure, Ie rendement etant de 95%. Une etude a etc faite de Ia reaction du cumene avec I'oxygene. Elle a revelC que la diffusion de I'oxygene dans l'hydrocarbure peut influencer Ia vitesse de reaction. Les resultats ont indlque que In reaction est d'ordre zero par rapport a I'oxygene et d'ordre un par rapport au cumene, L'encrgie apparente d'activation de l'oxydation non-catalytlque du cumene a ete determinee ; sa valeur etait de 10 kenl/rnole. Pour la preparation continue de l'hydroperoxyde de eumene on a developpe un reacteur tubulaire en cuivre et il semble que l'aggrandissemcnt de ce reacteur ne donne pas des dlfflcultes insurmontables en ce qui concerne Ia dissipation de Ia chaleur, Zusammenfassung-Kumolhydroperoxyd wurde mittels Oxydation von Kumol mit molekularern Sauerstoff in der Fliissigkeitsphase hergestellt. Die Oxydationsge-chwlndlgkeiten und Ausbeutcn von in eincm Pyrex-Rcaktor bci 110·130°C durchgefllhrten Versuchen werden erwiihnt. Es stellte sich heraus, dass Kupfer diese Oxydation katalytisch beeinflusst. Versuche in cinem Kupferrcaktor wiesen eine Verbesserung der Iteaktlonsgcschwlndigkelt sowie der Ausbeuten auf. Dei 120°C wurde stiindlich, mit ciner Ausbeute von 95% 'etwa 11.6 Gew.% Kumolhydroperoxyd in der Fliissigkeit gebildet. Die Kinetik der Reaktion von Kumol mit Sauerstoff wurde untersucht, Es wurde naehgewiesen, dass die Diffusion von Sauerstoff in den Kohlcnwasserstoff die Reaktionsgeschwindigkeit beeinflussen kann, Die Ergebnisse zeigten eine Reaktion der nullten Ordnung hinsichtlich des Sauerstoffs und der ersten Ordnung hinsiehtlich des Kurnols, Die scheinbare Aktivierungsenergie der niehtkatalytischen Oxydation wurde zu 10 kealjmol bestimmt. Zum Zwecke der kontinuierliehen IIersteUung von Kumolhydroperoxyd wurde cin rohrfOrmiger Kupferreaktor entwiekclt. Es stelIte sich heraus, dass bel der Vergrossorung cines solehen Rcaktors die Abfuhr der Reaktionswiirrne keine besonderen Schwierigkeiten verursamt• ... Present address:
I{oninklijke/Shell-Laboratorium, Amsterdam.
60
J. P.
FonTUIN
and H. 1.
'VATEmIAN :
Preparation of eumene hydroperoxide
An important factor influencing the oxidation INTRODUCTION Cumene hydroperoxide has acquired technical rate is the purity of the feed, as small amounts importance as a polymerization catalyst and as of inhibitors (such as sulphur compounds, phenols, an intermediate in the "cumcne-process" for the aniline or styrenes) present in the hydrocarbon manufacture of synthetic phenol. The hydroper- may break the reaction chains. The oxidation reaction is generally preceded by oxide is now produced commercially by reacting an induction period. A maximum oxidation rate eumene in the liquid phase with oxygen or air. is only attained if a certain hydroperoxide conThe main results of our investigation into the centration is built up in the liquid. The induction preparation of phenol from cumene were preperiod can be eliminated by adding a hydroviously published [1]. It was shown that for this peroxide to the hydrocarbon to be oxidised before oxidation process the eumene should be very pure the reaction is started. so that inhibitors present in the base material These characteristics showed up clearly in our must be removed by a suitable chemical treatinvestigation, in which thoroughly purified cumene ment. The cumene could be readily autoxidized was used. in a copper reaction vessel, the copper wall of BASE MATERIALS the reactor acting as the oxidation catalyst. Cumene hydroperoxide was obtained as a solution The crude cumenc was distilled and then treated in an excess of unconverted cumene. In this with sulphuric acid followed by a treatment with solution the hydroperoxide was decomposed into aqueous mercuric acetate solution (sec Ref. 1). phenol and acetone by means of sulphur dioxide Physical constants of the eumene: b.p, 152·0as a catalyst. 152·5°C, n~ 1'41)13, lit. values b.p. 152'3°C and The present paper deals specifically with the n~ 1'4913 [2]. preparation of cumene hydroperoxide. The Commercial oxygen containing at least 99% O2 characteristics of the oxidation were first studied or filtered air were used as oxidants. in a "Pyrex" glass reactor. Subsequently, when :METIIOD OF ANALYSIS thc usc of copper as a catalyst had shown to lead to a better yield and a higher rate of reaction, a The hydroperoxide concentration in the oxidised copper vessel was taken for the oxidation. liquids was determined by an iodometric method The kinetics of the reaction of cumene with [3], The yield of the reaction was computed from oxygen were also studied. The results of this the hydroperoxide content and the total oxygen investigation were of interest for the design of a content of the liquid. reactor for the continuous preparation of cumene RESULTS, hydroperoxide. The performance of this tubular reactor was so encouraging that it is believed to Oxidation of 200 ml, of cumene with oxygen in be suitable for application on a larger scale. a stirred "Pyrex" glass apparatus (stirring speed 1,200 r.p.m.) at varying temperatures gave the LIQUID PHASE OXIDATION OF CUlIiENE results collected in Table 1. The induction period It is assumed that the autoxidation of hydroTable 1. carbons in the liquid phase proceeds according to Oxidation of cumene in a "Pyre.x" reactor a free radical chain mechanism, a hydroperoxide being the first oxidation product formed. AppreillaximullI oxidaciable yields can be achieved if the hydroperoxide Length oJ tioll rate % tvl. Yield remperatllrc illdllctioll period lqjdroperoxide is stable under the conditions of the reaction - as °C % hours formed per hour may for instance be the case with isopropylbenThe common oxidation zenc liydroperoxide, II 110 4·4 00·8 catalysts, i.e, the soluble salts of the transition 8-!·3 120 s-i I! metals, cannot be used here as they tend to 10,0 1 130 74'6 decompose the hydroperoxides formed.
61
CONFERENCE
ON
OXIDATION
Table 3.
was taken to be at an end when the maximum oxidation rate had established itself. 'When the oxidation was carried out with air instead of with oxygen, the maximum oxidation rate at rio-c was 4·1% wt of cum ene hydroperoxide formed per hour. Hence, about the same rate of oxidation was observed with air as with oxygen in this apparatus. The material balance of the oxidation was drawn up from an experiment carried out in the "Pyrex" reactor, in which cumcne was oxidized with oxygen at I20 0 e during 6 hours. The resulting liquid was carefully analysed. In Table 2 the results of the analyses are expressed as moles of material formed per 100 moles of cumene converted.
Oxidation oj cumene in a copper reactor, Temperature Oxidation rate % uit, cumcne DC hydroperoxideformed per hour 120 130
'Yield
11'(}
ll5 81
25·0
in this reactor. Before each experiment the inner surface of vessel and stirrer were rinsed with fuming nitric acid (spec. gr. 1·52), washed with water, and dried. The stirring speed was 880
r.p.m, At 120 0 e uniform, high yields were obtained in the copper reactor. The rate of production of eumene hydroperoxide under the conditions employed could be calculated at about 100-120 grams per litre per hour. For comparison two other reactors and stirrers were constructed, identical in shape to the copper reactor but now made of stainless steel and brass. Under exactly the same conditions the rates of cumene hydroperoxide formation appeared to be as follows:
7'able 2. Moles Of compounds found per 100 moles of cumene conuerled,
cumene hydroperoxidc dimcthylphenylcarbinol water ac etophenone methanol carbon dioxide
PROCESSES
80 '1 14·7 3·4 0·4 0'5 0 '3
in copper in brass in stainless steel
It is seen that the tertiary alcohol IX, IX dimethylphenyl-carbinol is the most important by-product formed. When the oxidation in the "Pyrex" reactor was carried out in the presence of 0·5 % wt of finely divided copper as a catalyst the maximum oxidation rate at nooe increased to 7'3% wt of cumene hydroperoxide formed per hour. The same catalytic effect of copper metal was observed when the oxidation was carried out in a copper vessel equipped with a copper stirrer, In this reactor the rate of reaction increased while the yield was higher than in the case of an oxidation in a glass reactor at the same temperature. The data are collected in Table 8. The experiments were done with 200 ml. of eumene and a supply of 25 litres of oxygen per hour. It should be noted that the experiment at 180 0 e gave a 25% conversion in the first hour of reaction and only an additional {)'4% in the second hour. No induction period was observed
22·3 ]7·2 4·1
The copper reactor showing definite advantages it was decided to make use of the copper catalyst to study the continuous preparation of cumene hydroperoxide. For the choice of the type of reactor a study was first made of the kinetics of the reaction of cumene with oxygen. KINETICS OF eUl\IENE OXIDATION
The experiments were made in a "Pyrex" glass reactor (sec Fig. 1). This small vessel permitted the oxidation of 0-8 gram mole of hydrocarbon per run at a constant temperature, which was maintained by placing the reactor in the vapour of a boiling liquid. Several variables were studied in this apparatus by measuring the rate of oxygen absorption under various conditions. The volume of oxygen absorbed was reduced to o°C and 760 mm mercury. 62
J. P.
FORTul~ and H . I. WATER)!AN : Preparation of cumcne hydroperoxidc
Above a certain critical stirring speed the maximum oxidation rote is no longer affected, and hence the real chemical reaction rate is then measured. Fig. 2 shows the oxygen absorption curves of two experiments carried out in the small reactor at 1l0·5°C with stirring speeds of 1,850 r.p.m, and 3,600 r.p.m., respectivel y, The slopes of the cur ves differ by 4 %. The critical stirring speed was about 2,500 r.p.m. in this apparatus, no further increase in the maximum rate beingobserved at higher velocities. All further experiments were carried out with a minimum speed of 8000 r.p.rn. (b) Concentration. of oxygen
CIRCULATING PUMP
Fig. 1. Assembly for kinetic experiments.
(a) Stirring speed When oxygen is bubbled through cumene at 100-120°C the oxidation rate will be governed partly by the rate at which the gas diffuses into the liquid. By rapid stirring the diffusion may be eliminated as the rate-determining factor.
J600
At IlO'5°C the maximum oxidation rate using pure oxygen (760 mm) as the oxidant amounted to 540 ml, of 02 absorbed per 9'3 gram mole. eumene per hour. The partial pressure of oxygen in the gas was now varied between 760 and 160 mm by mixing the gas with nitrogen. No decrease in the maximum oxidation rate was observed in this region of oxygen concentrations. Lower partial pressures of the oxygen were not studied. The reaction is apparently of zero order with respect to oxygen. It should be pointed out that the oxygen concentration might influence the oxidation rate if the gas diffusion has a determining effcct. In this case an increase in oxygen pressure, i.e. above atmospheric, might favour the rate of hydroperoxide formation.
(c) Concentration of hydrocarbon The effect of the hydrocarbon concentration on the oxidation rate was studied with mixtures of cumene and monochlorobenzcne, In Fig. 3 the maximum oxidation rates of these mixtures nrc plotted against their molar concentrations, It..is seen that the rate is about 'directly proportional to the concentration, indicating' a first order reaction with respect to cumene. The maximum oxidation rate of solutions of eumenc more dilute than 2 gram moles per litre could not be determined exactly owing to the low volume of oxygen absorbed per hour. '.
RPM.
.J TIME, HOURS
Jiig. 2. Effect of stirring speed.
63
CONFERENCE .O N
OXIDATION
PROCESS~S
Table 4.
MAXIMUM OXIDATION RATE
lUaximum oxidation
ml O;/JOg C/JMENE
Temperature
160
°c
140
ra(~
0/ cumene at several temperaturc.,.
J1Iaximum oxidation rate in tnl. of oxygen absorbed pcr 0 ·3 gram. mole of cumene per lIour
120
lJ7·Q 105·0 111 ·5
'KJO
80
250 3!l8 1>70
60 40
Using the formula E = R
20
~/;. T;.
In K. [4] a K2 mean value of 16 kcal per mol was found for the apparent activation energy of the reaction of cumcne with oxygen under these conditions. 1-
6 CONCENTRATION. GRAM MO'E/L/TRE
I
Fig. 3.
Effect of hydrocarbon concentration.
2
CONTINUOUS OXIDATION OF CUIIlENE
(d) Temperature
Oxygen absorption curves were determined at three different temperatures. 3% wt of cumene hydroperoxide was added to the eumene before these runs were started, with the object of shortening the induction periods. A very pure sample of cumene hydroperoxide was used for this purpose. It was proved in a blank experiment that the addition of the hydroperoxide did not affect the maximum oxidation rate of the cumene. OXYGEN A8SORPT/OI{ N 7.P
tn'
REACTION T
1500
1 : /II,5 .II : 105 JiI: 97
0C
«c
°c
1000
500
I
~
6
7
OXIDATION TIME. HOURS
Fig. 4.
Effeet of temperature.
Fig. 4 shows the results of the experiments. The maximum oxidation rates determined from the slopes of the curves arc given in 'I'able 4.
Following the results outlined in the preceding paragraphs an oxidation system was now developed for the continuous preparation of cumene hydroperoxide from cumene, A copper vessel of 400 ml. capacity provided with a high speed stirrer (2,000 r.p.m.) was used as the reactor. Cumene and the gas could be fed in and the oxidized liquid could' be discharged or circulated continuously. After one hour of reaction in this apparatus the oxidation of 200 ml cumcne at 120°C with an oxygen gas rate of 25 Iitres per hour resulted in a 20% wt cumene hydroperoxide solution. This means a production of approximately 180 grams of eumene hydroperoxide per litre per hour. However, when the experiment was continued with a continuous feed of fresh cumene the rate of hydroperoxide formation dropped rapidly within the next few hours to a value as low as 9 grams per litre per hour. It was shown that inhibition of the oxidation was caused by contamination of the cumene with packing materials, mainly from the stirrer. As it was known that eumene is very sensitive to traces of impurities and the contamination of material caused by such a high speed stirrer remained a problem, another reactor was designed without rotating parts. This reactor consisted of a vertical copper tube 1,250 mm long, internal diameter 24 mm (see Fi~. 5).
J. P.
FORTUIN
and H. I .
WATERMAN:
VENr GAS
" AIR INLEr CUMENE INLEr
Fig. 5.
Continuous oxidation of cumene.
Copper rings were used as the packing material for the flanges at both ends. Valves were made of brass with graphite on asbestos for packings. Before each experiment the inside of the copper tube was etched with fuming nitric acid (specific gravity 1'52), then washed with water and dried. For batch experiments the reactor was filled with 500 ml. of eumene per run. The results of some of these exp eriments are given in Table 5. In the experiments 2 and 4 the reactor was filled with copper turnings.
Preparation of cumcne hydr~peroxide
tubular reactor. In agreement with this, an even lower production rate was observed in experiments 3 and 4 where air was used as the oxidant. Super atmospheric pressures may be expected to be advantageous when a tubular reactor is used for this oxidation. Thc tubular reactor gave a satisfactory performance in continuous experiments. These runs were started by pressing 500 ml. of cumene into the reactor, heating to 120°C and thereupon oxidizing to the desired cumene hydroperoxide concentration. Then a continuous stream of eumcnc was introduced at the bottom; the excess liquid in the reactor soon passed the overflow through the cooler into the receiver. In a run of 111 hours with a feed of 190 ml. of cumene per hour a continuous stream of oxidized cumene was obtained in this way, with an average contcnt of 21 % wt of eumene hydroperoxide. It is assumed that baekmixing of liquid into the reactor took place here, so that the oxidation was carried out more or less under steady state conditions. The heat of reaction amounts to 27'7 keal per mole of cumene hydroperoxide formed [1]. In the last experiment about 37 grams of cumene hydroperoxide was formed per hour in a reactor of 0·5 litre. This means a production of approximately 0·5 mole per litre per hour or 13,850 cals heat generated per litre reaction volume per hour. About 840 grams of cumene has to be fed into such a reactor per hour, to get a solution of about 20% cumene hydropcroxide. When the cumene
In experiments 1 and 2, carried out with oxygen as the oxidant the rates of production of cumene hydroperoxide are 101 and 126 grams per litre per hour, respectively. This is lower than the 180 grams obtained with the just mentioned stirred reactor. Apparently, the diffusion of the oxygen in the liquid partly determines the rate of hydroperoxide formation in the
Table 5. Batch expcrimetl18 in the tubular reactor. .~
Experiment No. 1 2 11
4
Gas
Rate 1./lIr
oxygen oxygen air air
25 25 50 65
to.
Grams rumene lIydroperoxidc prepared per !lour
120 121 121 121
50'5 63 25·5 33
R eactor T emperatures
'I
t2
117 116 116 116
120 120 120 120
65
Remarks
copper turnings copper turnings
CONFERENCE
ON
OXIDATION
PROCESSES
is introduced cold, say at 20°C, an amount of heat of reaction ean be removed sufficiently 340 X 0'5 X 100 = 17,000 cals is needed to heat by: a. feeding cold cumene; b. jacketing the the cold feed to the reaction temperature of 120°C reactor tube and cooling with steam or water, (specific heat of cumene in the temperature range taking a certain temperature gradient. taken at 0·5 caljg 0c). Hence, the heat evolved The authors wish to express their gratitude to during the reaction can be controlled by feeding Dr. J. J. VERSTAPPEN for doing part of the the cumene at a slightly elevated temperature. experimental work. Thanks are due to the Even.If a higher oxidation rate can be obtained management of N. V. de Bataafsche Petroleum or if the eumene hydropcroxide is discharged at a lIlaatschappij, The Hague, for permission to higher concentration it may be expected that the publish this paper. REFERENCES
[1] FORTUIN, J. P. and WATERl\lAN, H. I.; Chern. Eng. Sci.l953 2182; FORTUIN, J. P.; Thesis, Delft, 1952. [2] FRANCIS, A. W.; Chern. Revs. 1948 42 126. ]3] WAGNEll, C. D., Ssrrrn, R. II. and PETERS, E. D.; Anal. Chern. 1047 19 076. [4] GEORGE, P., RlDEAL, E. K. and ROBERTSON, A.; Proc, Roy. Soc. (London) 1946 A 185293.
66