Reaet.Kinet.Catal.Lett. Vol. 65, No. 2, 349-354 (1998)
Jointlypublishedby Elsevier Scicaee B.V., Amsterdam and AkadoaaiaiKiad6, Budapest
RKCL3256 REACTION OF ALCOHOLS WITH a-OXIDES IN THE PRESENCE OF LAYERED DOUBLE CATALYSTS M.V. Zvereva, M.G. Makarov and A.E. Kapustin Russian Chemical-Technological University, Moscow 125267, Russia Priazovskiy State Technical University, Mariupol 341000, Ukraine
Received July 8, 1997 Accepted October 7, 1997
Abstract
The activity of Mg-AI basic heterogeneous catalysts in the reactions of alcohols with ethylene oxide was studied. The kinetics of alcohol oxyethylation was examined. The kinetic equation of the reaction was determined and the structure of products was studied. The distribution coefficients of the oxyethylation reaction products were calculated. A comparison of the catalytic activity of MgAI hydroxides and products of their thermal treatment was made.
Keywords: Oxyethylation, catalyst, solid base
INTRODUCTION
The reaction of ethylene oxide with alcohols has industrial significance. Solvents and monomers, non-ionogenic detergents and ms~ticides constitute the list of the organic products obtained on the basis of these reactions. The addition of a-oxides to alcohols is the basis for obtaining the desired product distribution: ROH
crrt4~ ~ ROCFO2H.4~ ko
C~4O
RO[~ 2 H
c~4o k2
etc.
The product composition depends on the ratio of rate constants of reaction stages kj/ko (distribution coefficient Cj = kj/ko) and the quantity of attached 0133-1736D8/US$12.00. 9 AkadoaxiaiKiad6, Budapest. All rights reserv~L
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ZVEREVA et al.: DOUBLE CATALYSTS
ethylene oxide (oxyethylation degree m). These parameters are interconnected by the ratio: du o no am N no + 2 , C j 9 ni 1
o
(1) dui dm
hi_ 1 9Ci_ 1 - n i
9C i
m
n o + ECj
9 1-
ni
1
where no is the molar fraction of the initial alcohol, N i is the molar franction of the i-th product, Ci is the distribution coefficient, Co = 1, and N is the quantity of products. The ratio of rate constants is defined by the nature of initial substances, the type of catalysis and the structure of the heterogeneous catalyst. The most widespread basic catalysts are alcoholates of Na and K. This is due to their low cost and good efficiency in the processes where high selectivity is not necessary (for example, they are used for the production of non-ionogenic detergents). However, processing of catalytic reactions in the presence of homogeneous catalysts certainly includes the preparation of initial catalytic system as well as the stage of the catalyst recovery. The application of heterogeneous catalysts allows to avoid these stages which frequently are difficult and power-intensive. It also allows changing the process technologies, increasing the effective concentration and, consequently, the reaction rate. It is also possible to go from periodic processes to continuous ones, to simplify the service of installations, to reduce environmental pollution. Acidic heterogeneous catalysts are well known and widely used in industry for organic synthesis. Very little in known about substances of basic nature, not used in industrial scale. The purpose of our work was to study inorganic anion-exchangers [1] (MgN-layered double hydroxide for example) as heterogeneous catalysts of alcohol oxyethylation. EXPERIMENTAL
To prepare layered double hydroxide [Mg2AI(OH)6]OH, a solution of Zn(NO3)2 and AI(NO3)3 in stoichiometric quantifies was added under intensive stirring to a solution containing a surplus of NaOH and NaHCO3 [2]. After precipitate formation over 72 h, it was washed on a filter until negative reaction \
ZVEREVAet al.: DOUBLECATALYSTS
351
for nitrate and then converted into the hydroxide form. Afterwards it was dried to a constant weight at 100~ Elemental analysis and thermogravimetric studies have shown that the structure of the catalyst corresponds to the formula [MgaATAl(OH)6,34]OH.2H20. X-ray powder pattern analysis has shown the results in Table 1, which are similar to those reported in Ref. [3].
Table 1
Interspace distances ofthermaUy treated catalysts Calcination temperature (~ 110 150 250 350 400 >450
doo3(A) 7.7 7.5 7.0 7.0 6.8 not defined
Thermogravimetric studies have shown that during the thermal processing a general reduction of the number of basic sites as well as their transformation from one type into another [1, 4] takes place. The reaction was carried out in a thermostated reactor equipped with a magnetic stirrer. The pressure in the reactor corresponded to the pressure of ethylene oxide and alcohol vapor at the given temperature, The contents of alcohol and products of ethylene oxide addition in the reaction mixture were established by gas-liquid chromatography. The kinetic experiments were described in detail elsewhere [4-5]. The reaction rate was controlled by the determination of ethylene oxide pressure using a manometric method. All experiments were conducted in the absence of solvent, in the appropriate alcohol. The initial concentrations of ethylene oxide were 0.070.7 mol/L, those of the catalyst 0.011-0.043 mol/L and the temperature 70-90~ RESULTS AND DISCUSSION The results obtained show that the logarithm of ethylene oxide pressure change is directly proportional to the reaction time. This testifies to first order in ethylene oxide. Effective rate constants were calculated from the kinetic results. They appear to be practically independent of the initial concentration of ethylene oxide. For various initial catalyst concentrations, a linear dependence of the effective rate constant on catalyst concentration was obtained. This fact shows first order in the catalyst as well. Kinetic results are presented in Table 2. We did not study
352
ZVEREVAetal.:
DOUBLECATALYSTS
the influence o f the alcohol concentration on the rate. W e assumed that the reaction order in alcohol is one, the same being true for other oxyethylation reactions, Experiments at various temperatures allowed to determine the activation parameters (Table 3).
Table 2
The reaction of ethylene oxide with butanol at different catalyst concentrations (Co - catalyst concentration (tool/L), kar and k~o are effective experimental and calculated rate constants (10.4 s'x), t = 90"C) Co
kar
k~o
0.043
4.95
5.20
0.033
3.52
3.88
0.022
2.35
2.63
0.110
1.27
1.33
Table 3
The reaction of ethylene oxide with butanol at various temperatures (C~ = 0.043 moUL; C~o= 0.078 tool/L; kar and k~o are the effective experimental and calculated rate constants (10-4 s"1) T (*C)
kar
k~o
70
1.76
1.87
go
z 75
3.19
90
4.95
5.20
The expression for the rate constant dependence on the reagent concentration and temperature is k~,to= A exp(-E/RT) Co CRoa
(2)
The kinetic dependences obtained are described b y the equation: R = kCoC~oC~oH where Caoais the alcohol concentration (mol/L).
(3)
ZVEREVA et al.: DOUBLE CATALYSTS
353
Table 4 compares the catalytic activities in butanol oxyethylation with homogeneous and heterogeneous basic catalysts. Table 4 Butanol oxyethylation with homogcnenus and heterogeneous catalysts Literature data [5]
Experimental data
T = 90~
T = 90"C
In A = 14.2
In A = 10.83 K = 1.73x10 "3
K = 1.01xl0 "3
E - - 60.01 0d/reel)
E-- 53.55 (L2/mol2 s)
(kJ/mol)
(L2/mol2 s)
The alcohol oxyethylation products were studied for various catalysts. After analysis of the reaction mixture composition, the distribution coefficients were calculated. The experimental data were processed on a computer by least squares minimization. It was established that an adequate description of experimental dependences is reached at k: = ks -- k4 ... etc. These values for various catalysts are listed in Table 5. Table 5 Distribution coefficients for ditferent catalysts (T = 125~ oxyethylation degree m = 3.5) Calcination temperature (oc)
Reaction time 0a)
C1
C2
150
0.5
2.33
2.95
325
6.0
1.70
1.46
400
7.5
2.13
2.11
450
8.5
2.38
2.25
The analysis of the results shows that the rate decreases with increasing catalyst treatment temperature. It is known that both Br6nsted and Lewis basic sites participate in the alcohol oxyethylation. The decrease in rate may be due to
354
ZVEREVAetal.: DOUBLECATALYSTS
the fact that the rate on a heterogeneous basic catalyst depends on the strength of basic sites and their concentration. The concentration of basic sites decreases with an increase in catalyst heat treatment temperature. The sample processed at T = 600~ practically did not contain Br6nsted basic sites, a n d an appreciable reaction rate in its presence was not observed. In Ref. [4] the following distribution coefficients were reported for basic homogeneous catalysis: C1 = 2.2 + 0.2; C2 = 2.41:1: 0.17. No acid sites were found on the catalyst surfaces. The distribution coefficients obtained experimentally were the same as the coefficients in homogeneous base catalysis. So, in this case the heterogeneity of the catalyst did not influence the reaction. Only in the reaction with the catalyst processed at T = 3250C, were the distribution coetficients somewhat lower. On the basis of the results obtained, it is possible to generalize a typically basic mechanism of the catalytic processes studied.
Acknowledgment. The authors are grateful to S. Miyata for samples of catalysts.
REFERENCES 1.
2. 3. 4. 5.
6.
A.E. Kapustin: Usp. Khim., 60, 2685 (1991). W.T. Reichle: Chemtech., 16, 58 (1993). V.KL. Constantine, T.J. Pinnavaia: Catal. Lett., 23, 361 (1994). M.N. Zvereva, A.A. Kozlov, A.E. Kapustin: m Prec. of Priazovsky State Technical University, 1,297 (1995). N.N. Lebedev,V.F. Shvets: in Prec. of Mendeleev University, 115, 87 (1980). V.F. Shvets,M.G. Makarov:Kinet Katal., 23, 847 (1982).
