27
Ind. fng. Chem. Fundam. 1985, 2 4 , 27-32 Corbett. W. E., Jr.; Luss. D. Chem. f n g . Sci. 1974, 29, 1473. Dadyburjor, D. B. AIChE J . 1982, 28, 720. Ernst, W. R.; Daugherty, D. J. AIChE J . 1978, 24, 935. Mlnhas, S.; Carberry, J. J. J . Catal. 1969, 74, 270. MorbMelll. M.: Servlda. A,: Varma. A. Ind. €nu. Chem. Fundam. 1982, 27, 278. Neogl, P. AIChE J . 1983, 28, 498. Neogl, P.; Ruckenstein, E. AIChE J . 1980, 26, 787. Ruckenstein, E. AIChE J . 1970. 76, 151.
-
Shadman-Yazdl, F.; Petersen, E. E. Chem. Eng. Sci. 1972, 27, 227. Thomas, C. L.; Barmby, D. S. J . Catal. 1968, 72, 341. Varghese, P.; Wolf, E. E. AIChE J . 1980, 26, 55. Welsz, P. B. CHEMTECH 1973, 498.
Received for review October 17, 1983 Revised manuscript received April 20, 1984 Accepted April 23, 1984
Generalized Statistical Model for the Prediction of Binary Adsorption Equilibria in Zeolites Douglas M. Ruthven' and Francis Wong+ Depatiment of Chemical Engineering, Universky of New Bruns wick. Fredericton, New Brunswick, Canada € 3 8 5A3
A simple generalized statistical thermodynamic representation of adsorption equilibrium isotherms is proposed and used as a basis for the prediction of binary equilibria from single-component isotherm data. Experimental single-component and binary equilibrium isotherms for sorption of cyclohexane-n heptane in 13X molecular sieves are presented, and the model is shown to provide a good representation of these data as well as of other binary equilibrium data available from the literature.
The problem of predicting binary or multicomponent adsorption equilibria from single-component isotherms is of great practical significance and has therefore attracted considerable attention. Among the more successful methods proposed are the ideal adsorbed solution theory (Myers and Prausnitz, 1965; Glessner and Myers, 1969) and the more recent extension of this approach to nonideal systems (Costa et al., 1981), the simplified statistical thermodynamic model (Ruthven, 1971; Ruthven et al., (1973), and the vacancy solution theory (Suwanayuen and Danner, 1980). A comparison of the predictions of several of these theories was presented by Danner and Choi (1978) and by Kaul(l982). The ideal adsorbed solution theory and the vacancy solution theory are generai classical thermodynamic approaches which do not depend on detailed physical models for the adsorbed phase. This is a significant advantage since an analysis of single component equilibrium data for zeolitic adsorbents reveals that none of the simple model isotherms is universally applicable. This has led Barrer and Coughlan (1968) and Kiselev (1968) to resort to the semiempirical virial expression to correlate equilibrium data. The virial isotherm is, however, of limited value in relation to the problem of predicting multicomponent equilibria since there is no obvious way to derive the required virial coefficients for a mixture from the single-component data. A simplified statistical model which depends on approximating the expressions for the configuration integral by simplified expressions involving the Henry constant and the molecular volume was suggested by Ruthven (1971) and extended to binary systems by Ruthven et al. (1973). The main assumptions of this model are as follows. (i) The adsorbed molecules are considered as confined within a particular cage of the zeolite with only relatively infrequent exchanges between molecules in neighboring cages. (ii) 'Irving Oil Ltd., Saint John, N.B. 0196-4313/85/1024-0027$01.50/0
The molecules within any particular cage are considered as delocalized and freely mobile within the free volume of the cage. (iii) Sorbateaorbate attraction is neglected. (iv) Sorbate-sorbate repulsion is accounted for by a reduction in the free volume of the cage. These assumptions appear reasonable, as a first approximation, for systems involving sorption of nonpolar molecules such as saturated hydrocarbons. For such systems, the model has been shown to provide a good representation of the single-component isotherms and a good prediction of the binary isotherms from the singlecomponent parameters (Ruthven and Loughlin, 1972; Loughlin et al., 1974; Ruthven, 1976; Holborow and Loughlin, 1977; Singhal, 1978; Danner and Choi, 1978). However, the assumptions upon which this model is based are clearly inappropriate for localized sorption. It is therefore not surprising that the model has been found to provide a poor prediction of the binary equilibrium isotherms for systems containing COz and/or C2H4(Holborow and Loughlin, 1977) since with these sorbates a significant degree of localization is to be expected. A more general semiempirical approach which retains the statistical approach but avoids the need to introduce a specific model for the adsorbed phase is therefore suggested as a means of correlating single-component isotherms and predicting binary equilibria from single-component data.
Theoretical Model We consider the system to be divided into a number of equivalent subsystems with each subsystem being statistically representative of the macrosystem. For a zeolitic adsorbent the subsystem may conveniently be taken as an individual cage within the framework. The grand partition function ( E ) for the system may then be written in the form E = 1 + Z I U + 22u2 + ... + 2,um (1) where 2, represents the configuration integral for an in0 1985
American Chemical Society
28
Ind. Eng. Chem. Fundam., Vol. 24, No. 1, 1985
dividual subsystem containing s sorbate molecules and is defined by 2, =
S!
exp[-Us trl, r2,..., r,)/kT] dr,, dr2, ..., dr, (2)
U(rl, r2,..., r3)represents the potential with the sorbate molecules located a t the positions represented by the position vectors rl, rz,..., r3and the integration is carried out over all possible configurations within the subsystem. m is the maximum number of molecules which can be contained within the subsystem and a = p / k T is the sorbate activity. The expression for the equilibrium isotherm is given by (Hill, 1960) Zla + A2a2+ ... + mZ,am c = - -a In (3) d In a 1 Z,U+ Z,a2 + ... + Z,am
+
To calculate the configuration integral by evaluation of eq 2 presents a formidable problem for all but the simplest of systems. However, without further approximation we may write the configuration integral in the following form "
0
1-
Z, = -RB
(4)
S!
in which R, is a temperature-dependent constant characteristic of the particular sorbate-sorbent system. For an ideal system in which the adsorbed molecules are not in any way affected by the presence of other molecules within the same cage, R, = 1.0. Values of R < 1.0 represent replusive interactions while R > 1.0 represents attractive forces between molecules, leading to a decrease in the overall potential. Since Zla = Kp, where K is the Henry constant, the expression for the isotherm becomes
Kp
+ (Kp)'R, + ... + ___ Kp
+ -2!1 (Kp)'R1+ ... + ((KPP m ~
-
This expression is similar to the virial isotherm in that it contains a number of empirical constants ( R J ,but unlike the virial isotherm these constants have a simple and well-defined physical significance. The extension to binary (or multicomponent) systems requires the introduction of further approximations since we now require expressions for the configuration integrals for subsystems containing i molecules of component A and j molecules of component B. The simplest approximation is to assume that in a cage containing i molecules of type A and j molecules of type B the configuration integral can be represented by
where s = i + j . This amounts to assuming that the interaction effect in the mixed subsystem is the geometric mean of the interactions which would be observed in subsystems containing the same number of molecules of either kind. This appears likely to be a reasonable approximation for many systems but may be expected to fail in extreme cases for molecules of very different size or where interactions are strong, e.g., when one species is slightly basic and the other species slightly acidic. Subject to this approximation the expression for the binary isotherm becomes
with a corresponding expression for cB. The summation is carried out over all possible values of i and j satisfying the constraint i + j Is. (For molecues of very unequal size some appropriate modification to the stipulation i + j I s may be required.) The number of terms required in the summation depends on the size of subsystem, the choice of which is to some extent arbitrary. In practice the size of the subsystem is selected to give a convenient number of terms in the summation-usually 3 or 4. In utilizing this method of predicting binary equilibria the following procedure is followed. (1)The Henry constants KA and KB are determined from the single-component isotherms. If the isotherm data extend to sufficiently low concentrations, the Henry constant may be obtained directly from the limiting slope. Otherwise, the Henry constant obtained by extrapolation of a plot of log (p/c) vs. c as recommended by Barrer and Lee (1968). (2) The single-component isotherms are matched to eq 5 (with K fixed) in order to determine the values of the parameters R1,R2,..., R, for each commponent. (3) The values of KA and KB together with the values of R1, ..., R, from the single-component isotherms are used to calculate the binary isotherm according to eq 7. For the success of this approach it is essential that the parameters derived from the single-component isotherms are accurate, and this makes it essential to avoid the choice of too large a subsystem. If the subsystem is too large, eq 5 will contain too many parameters to permit accurate evaluation of the individual R values. Thus, although a good fit of single-component isotherms may be obtained, due to compensation between the various terms in the expression, the individual R values will not be reliable. Unless the individual parameters are correctly determined one cannot expect to obtain a good prediction of the binary equilibrium. For similar reasons, it is essential to determine the Henry constant first rather than to attempt to determine simultaneously all parameters K and R1,..., R, by a multivariable optimization fit of eq 5 to the experimental single-component isotherm. In practice, due to the inevitable scatter of expermental data, two or three constants are about the maximum that can be evaluated with confidence from a single isotherm. This means that the size of the subsystem should be chosen to contain no more than about four molecules. Experimental Section A schematic diagram of the apparatus is shown in Figure 1. The adsorbent (6.2 g) was contained in a column within a thermostatically controlled oven. A gas circulating system with a metal bellows pump was used to circulate helium through the column. The circuit included an online gas sampling valve connected to the input of a small Gow-Mac chromatograph, a make-up system to admit He in order to maintain a pressure of 1atm within the circuit, and an injection port through which known volumes of liquid hydrocarbon were injected by microsyringe. The adsorbent was lls-in. Linde 13X pellets, ground and sieved to a particle size of 0.7 mm. The sieve was dehy-
Ind. Eng. Chem. Fundam., Vol. 24, No. 1, 1985 29 A
- I
5
I
409.K 'bH12
To helium tank
00 .-To junction
20
recorder
I t
To bubble flowmeter
Figure 1. Schematic diagram of the apparatus: A, B, valves; C, molecular sieve column containing 13X zeolite,D, detector block; Cg, gas chromatographic column containing chromosorb P and silicone oil DC200; GC, gas chromatography for analysis of the sampled gas; I, injection port, entry point for cyclohexane, heptane liquids; P, potentiometer, measured voltage (mV) of thermocouple; R, rotameters; Rp, recirculating pump (reciprocating,bellows type); SL, sample loop; SV, three-way gas sample valve; T, thermocoupling (chromel/alumel or type K).
LO DRESSL[RE
60
80
'OC
(TORR1
Figure 2. Experimental single-componentisotherms for sorption of cyclohexane and n-heptane at 409 K on 13X sieve showing fit of theoretical curves calculated according to eq 5 with parameters given in Table I. 2.5
I
Table I. Parameters for Single-Component Isotherms for Heptane and Cyclohexane in Linde 13X cyclohexane heptane 409 K 458 K 409 K 458 K 0.22 7.0 KO 1.33 0.91 1.07 R1 0.296 0.665 0.517 0.146 0.005 R2 0.038 0.003 a
Molecules/cage.torr.
drated at 375 "C for 48 h under a helium flow rate of 100 cm3/min. The column was then sealed, removed, and weighed in order to determine precisely the dry weight of adsorbent (6.22 g). The column was then reconnected and regenerated for a further period of 12 h to ensure complete removal of any traces of moisture. Preliminary calibration was required in order to determine the effective gas volume in the system. The system volume was considered to be composed of two volumes: V, at oven temperature. These volumes were determined according to the procedure described by Wong (1979). During an adsorption experiment the temperature of the adsorbent was set to the desired value and the He circulation was started. An aliquot of either the pure component or the desired mixture was then injected with a 1.0mL syringe. Circulation was continued for several hours until equilibrium was reached as judged by constancy in the peak areas of the chromatogram. If we know the initial quantity of sorbate injected, the weight of the sieve, the volume of the system, and the concentration in the gas phase (measured chromatographically), the adsorbed phase concentration may be found by straightforward mass balance. The procedure is repeated and in this way the entire isotherm may be obtained.
Results and Discussion Cyclohexane-Heptane on 13X Sieve. The experimentally determined single-component isotherms for cyclohexane and heptane at 409 and 458 K are shown in Figures 2 and 3. Replicate experiments showed good reproducibility. The parameters derived by fitting the isotherms to eq 5 in the manner outlined above are given in Table I.
00
L 20
40
60
PRESSURE
I TORR '
80
1
Figure 3. Experimental single-componentisotherms for sorption of cyclohexane and n-heptane at 458 K on 13X sieve showing fit of theoretical curves calculated according to eq 5 with parameters given in Table I.
Binary equilibria for the cyclohexane-heptane-13X system were determined over the total hydrocarbon pressure range 0-100 torr at three different molar ratios of the components (1:3, 1:1, 3:l). From these data the equilibrium adsorbed phase and gas-phase concentrations could be determined, at any desired total hydrocarbon pressure, by interpolation. Plots showing the binary isotherms at four selected total hydrocarbon pressures are shown in Figures 4 and 5 together with the theoretical curves calculated from eq 7 using the parameters derived from the single-component isotherms (Table I). It is evident that the theory provides a good representation of the experimental data. C2H4-C2HG-13X Zeolite. Detailed experimental equilibrium data for the system C2H4-C2H6in 13X sieves as well as single-component isotherms for the individual pure components have been presented by Danner and Choi (1978). These data were analyzed according to the procedure outlined above. However, in this system the saturation limit is about 5.5 molecules/cage. Therefore if the individual cage is taken as the subsystem, five R parameters are required. It proved difficult to calculate reliable values for this many parameters from a single isotherm although by careful choice of the initial estimates and the step size in the multivariable optimization routine it was
30
Fundam., Vol. 24, No.
Ind. Eng. Chem.
1, 1985
Table 11. Parameters from Single-Component Isotherms for CzHl and CzH, in 13X Sieve (Data of Danner and Choi, 1978) C2H6
C2H4
323 K
298 K
298 K
1. Based on Subsystem = 1 Cage 0.16 0.1 0.018 0.99 1.304 0.967 0.337 1.10-2 1.167 0.537 0.012 1.10 0.147 0.042 0.636 0.018 0 0
2. Based on 0.08 1.112 0.233
Molecules/cage.torr. CYCLOHEXPNE ( A i - H E P T A N E I B I - 1 3 X 439'K
' 5 TCQR
20
323 K 0.0089 1.013 1.024 0.543 0.225 0.172
Subsystem = Half Cage 0.0089 1.686 0.44
0.05 0.40 0.057
0.0045 0.897 0.564
Molecules/half cagestom.
7
P
"I-
32
C
OL
Ob
08
10
Figure 4. Comparison of experimental binary isotherm data with theoretical curves calculated according to eq 7 using parameters derived from the single-component isotherms; (cyclohexane-n-heptane-13X sieve at 409 K).
I CYCLOHEXANE
[ A I - HEPTPNE ! E l - 13X
I
'7
l:o
X
1.A
200
o
roc
600 9
eoo
L
I PRESSJRE
I TOQR i
Figure 6. Single-component isotherms of Danner and Choi (1978) for ethane in 13X sieve showing fit of theoretical curve calculated according to eq 5 with parameters given in Table 11. ETHYLENE .13X
I
l.o~~-
I
29E'K
15 TOQQ
I
2.01
3.0
2
02
C.r
0.b
0.0
'.0
Figure 5. Comparison of experimental binary isotherm data with theoretical curves calculated according to eq 7 using parameters derived from the single-component isotherms; (cyclohexane-n-heptane-13X Sieve at 458 K).
possible. To avoid this difficulty, the subsystem was redefined as a half cage, thereby reducing the number of R parameters to 2. (The concentrations (molecules/subsystem) calculated on this basis are doubled in order to express the concentration on a consistent basis as molecules/cage.) The resulting parameters derived from the single-component isotherms are given in Table 11. The single-component isotherms are shown in Figures 6 and
3
200
4 0 PRESSURE
600
800
TORR)
Figure 7. Single-component isotherms of Danner and Choi (1978) for ethylene in 13X sieve showing fit of theoretical curves calculated according t o eq 5 with parameters given in Table 11.
7. The theoretical binary equilibrium curves are compared with the binary isotherm data in Figure 8. The curves calculated with the half cage as the subsystem provide a good fit of the experimental binary data. The difference between the theoretical curves calculated using the full cage or the half cage as the subsystem is, however, small, indicating that at least within the present limits the precise choice of subsystem has only a relatively small effect on the isotherm predicitions.
Ind. Eng. Chem. Fundam., Vol. 24, No. 1, 1985
1
iTHYLEHE I A I - E T H A N E I S 1 - 1 3 X
31
Table 111. Parameters from Single-Component Isotherms for COz, CzH4,C3H8,and c-C3HGin 5A Zeolite a t 323 K (Derived from Data of Holborow, 1974) COP 0.645 0.223 0.061 0.002
K" R1
RZ R3
CzH4 1.183 0.032 0.026
C3HB 0.333 0.455 0.432 0
0
C-C&j 2.3 0.276 0.244 0
Molecules/cage.torr.
20
"0
02
06
04
E'hylene I A l - P r o p a n e l B 1 - S A 323'K E Torr
1 0
08
YA
Figure 8. Comparison of binary equilibrium data of Danner and Choi (1978) for CzH6-czH4-13Xsieve with theoretical curves calculated according to eq 7 wiih parameters derived from the single component isotherms (Table 11): (subsystem = 1 cage, -; subsystem = half cage, - - - - -).
I
ETHYLENE.51
8 Tor-
I
1
I CYCLOPROPANE.5A 323'K
.
20
Y
3 Y u
- o [
'
"
20
z
LO
60
'
y
80
"
LO
20
"
60
I
80
PRESSURE ITORRI 4
PROPANE - 5 A
1
'
0
4
YA
CARBON OlOXlDE.5A 323*K
f273'K
1
Figure 10. Comparison of binary equilibrium data of Holborow for COz-CzH4, CzH4-C3H8,and c-C3H6-CzH4in Linde 5A sieve at 323 K with theoretical curves calculated according to eq 7 with parameters derived from single-component isotherms (Table 111). *O C2.(' A I - ZjH8 - SA
k, Q
20
LO
60
80
I
.
0
100
PRESSURE
. 200
. 300
.
323K
I
LO0
I TORR I
Figure 9. Single-component isotherms of Holborow for COz, C2H4, C3H8,and c-C3H6in Linde 5A sieve at 323 K showing fit of theoretical curves calculated according to eq 5 with parameters given in Table 111.
CzH4-C3H8,C2H4-C02,c-C3H6X2H4-5A. Holborow (1974) has presented experimental single-component and binary equilibrium data for several light hydrocarbons and COz in Linde 5A sieves. Of the systems studied by Holborow, the only one which gave a good fit of the simple statistical model was propane-cyclopropane (Loughlin et al., 1974). The other systems all showed deviations to a greater or lesser extent (Holborow and Loughlin, 1977). The single component isotherms for CzH4,C3Hb COz, and c-C3H6in 5A zeolite at 323 K (Figure 9) were fitted to eq 5 in the manner noted above. The parameters so derived are summarized in Table I11 and the binary equilibrium curves calculated according to eq 7 using these parameters are compared with experimentalbinary isotherms in Figure 10. For these systems neither the ideal adsorbed solution theory nor the simple statistical model gave a staisfactory representation of the binary isotherm as may be seen from Figure 11, but with the present approach, good predictions of the binary isotherms are obtained. It may be seen that the values of the empirical parameters R1,Rz, ... in Tables 1-111 show the expected decrease in the sequence R1> Rz > > RS,.... In general R I1.0, indicating either that there
Figure 11. X-Y diagram for CzH4-C3H8-5A at 323 K showing prediction of ideal adsorbed solution theory (- - -) and present model (-).
is significant energetic heterogeneity within a cage (leading to occupation of less favorable sites at higher loading) or that replusive interactions between adsorbed molecules are more important than sorbate-sorbate attraction effects. The importance of energetic heterogeneity has been stressed recently by Myers (1983), but simply on the basis of present evidence it is not possible to decide whether energetic heterogeneity or sorbate-sorbate interaction effects are dominant. Conclusions The statistical approach to the modeling and correlation of equilibrium isotherms is based on well-established
32
Ind. Eng. Chem. Fundam. 1985, 2 4 , 32-39
thermodynamic principles, but the main difficulty with this approach is the problem of estimating the configuration integrals. In the approach proposed here, the configuration integrals are treated as empirical parameters which are derived from the experimental single-component isotherms. These values are then combined in order to estimate the configuration integrals required for the binary isotherm. The method is therefore semiempirical although it is based on well-established theoretical principles. The weakest point in the proposed approach is the use of the geometric mean to predict the configuration integrals for mixed subsystems. This is a reasonable approximation for mixtures in which the deviations from ideal behavior are not too large, since for such systems the interaction energies A-A, B-B, and A-B are not too different and geometric averaging can be easily justified. However, the approximation cannot be expected to hold for systems which show unusually strong A-B interactions and the model will therefore not give reliable predictions for highly nonideal systems which commonly show azeotrope formation. To properly account for the behavior of such systems would require the introduction of additional cross-coefficients characterizing the interactions between unlike molecules, and since such coefficients would have to be determined experimentally from the equilibrium data for the mixed system the predictive value of the model would be lost. However, this criticism applies equally to other currently available methods of prediction of mixture equilibria such as the vacancy solution theory (Kaul, 19821, and there is as yet no completely satisfactory method for the a priori prediction of mixture equilibria in highly nonideal systems. The approach proposed here, however, is straighforward and reasonably general. It has been shown to provide good predictions of the mixture isotherms for several moderately nonideal systems and has the potential for further extension to highly nonideal systems by the inclusion of additional coefficients. The empirical coefficients introduced here into the statistical model play a role analogous to the activity coefficients in the classical thermodynamic approach.
Nomenclature = activity (of component A or B) adsorbed phase concentration, molecules/cage k = Boltzmann's constant K (KA,KB)= Henry's law constant (of component A or B) P (PA,PB)= partial pressure (of component A or B) ri = position vector (eq 2) R, = coefficients defined by eq 4 U, = potential energy (eq 2) of adsorbed species XA,XB = mole fractions of A and B in adsorbed phase YA,YB = mole fractions of A and B in gas phase Zi = configuration integral of i molecules in a subsystem Registry No. Cyclohexane, 110-82-7;heptane, 142-82-5. a
(uA, ag)
c =
Literature Cited Barrer, R. M.; Lee, J. A. Surf. Sci. 1968, 72, 354. Barrer, R. M.; Coughlin, B. In "Molecular Sieves"; Society of Chemical Industry: London, 1968; p 233. Costa, E.; Sotelo, J. L.; Calleja. G.; k r r o n , C. AZChE J . 1981, 2 7 , 5. Danner, R. P.; Choi, E. C. F. Ind. Eng. Chem. Fundam. 1978, 17, 248. Glessner. A. J.; Myers, A. L. Chem. Eng. Prog. Symp. Ser. 1969, 65(96), 73. Hill, T. L. "Introduction to Statistical Thermodynamics"; Addison-Wesley: Reading, MA, 1960; p 132. Holborow, K. A. Ph.D. Thesis, University of New Brunswick, Frederiction N.B., Canada, 1974. Holborow, K. A,; Loughlin, K. F. Am. Chem. SOC. Symp. Ser. 1977, 4 0 , 379. Kaul, B. K. Paper 91b AIChE Annual Meeting, Los Angeles, Nov 1982. Kiselev, A. V. "Molecular Sieves"; Society of Chemical Industry: London, 1968; p 250. Loughlin, K. F.; Holborow, K. A.; Ruthven, D. M. AZChE Symp. Ser. 1974, 71(152), 24. Myers, A. L.; Prausnitz, J. M. AZChEJ. 1965, 11. 121. Myers, A. L. AZChE J . 1983, 29,691. Ruthven, D. M. Nature (London)Phys. Sci. 1971, 232(7), 70. Ruthven, D. M. AZChE J . 1978, 22, 753. Ruthven. D. M.; Loughiin, K. F.; Holborow, K. A. Chem. Eng. Sci. 1973, 28. 701. Ruthven, D. M.; Loughlin, K. F. J . Chem. Soc., Faraday Trans. 1. 1972, 68, 696. Slnghal, A. K. AIChE Symp. Ser. 1978, 14(179), 36. Suwanayuen, S.;Danner, R. P. AZChE J . 1980, 26, 68. Wong. F. MSc.E. Thesis, University of New Brunswick, Fredericton, N.B., Canada, 1979.
Received for review February 8, 1983 Revised manuscript received April 18, 1984 Accepted June 4, 1984
Heterogenizing Homogeneous Catalyst. 1. Oxidation of Acetaldehyde Tse-Chuan Chou' and Cheng-Chleh Lee Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan, ROC 700
The process of heterogenizing homogeneous Co3+ ion as catalyst for the liquid-phase oxidation of acetaldehyde to form peracetic acid was developed and studied. The reaction mechanism of acetaldehyde oxidation was proposed and the ratedetermining steps were experimentally identified. The results indicated that the selectivity of producing peroxides is very high and the decompositions of peroxides to form the side product, acetic acid, are insignificant. The rates of formation of peracetic acid obtained by using supported homogeneous Co3+ ion as a catalyst were different from those with homogeneous Co3+ ion as a catalyst.
Introduction The synthesis of peracetic acid (PAA)from acetaldehyde and oxygen by using Co3+ion as homogeneous catalyst in the liquid phase has been discussed in previous papers (Chou and Lin, l980,1982a, 1983; Chou and Lee, 1982b). The reaction scheme in the liquid phase can be summarized as
CH3CHO t 0 2
CO'+
CH CHO
CH~COJH
7 AMP
cow
CH3C02H t V2O2
2CH3C02H
(1
1
As shown in eq 1,the main byproduct is acetic acid, which is rapidly formed from the catalytic decomposition of the
0196-4313/85/1024-0032$01.50/00 1985 American Chemical Society
