180
I n d . Eng. Chem. Res. 1990, 29, 180-186
Larocca, M. Fast Catalytic Cracking with nickel and vanadium Contaminants. Ph.D. Dissertation, University of Western Ontario, London, Ontario, Canada, 1988. Leuenberger, E. L.; Moorehead, E. L.; Newell, D. F. Effect of Feedstock Type on FCC Overcracking. 1988 NPRA Annual Meeting, March 20, 1988; AM-88-51. Mann, R.; Thomson, G. Deactivation of a supported zeolite catalyst: simulation of diffusion, reaction and coke deposition in a parallel bundle. Chem. Eng. Sci. 1987,42,3. Mann, R.; Sharratt, H. P. N.; Thomson, G. Deactivation of a supported zeolite catalyst: diffusion, reaction and coke deposition in stoichastic pure networks. Chem. Eng. Sci. 1986,41 (41, 711. McElhiney, G. FCC catalyst selectivity determined from microactivity tests. Oil Gas J. 1988,35,Feb 8. Meisenheimer, R. G. A mechanism for the deactivation of trace metal contaminants on cracking catalysts. J . Catal. 1962,I , 356. Montgomery, J. A. Catalytic cracking. The effects of operational variables. The Davison Chemical Guide to Catalytic Cracking. Davison Chemical Division, 1970. Nace, D. M. Catalytic cracking over crystalline alluminosilicates I. Ind. Eng. Chem. Prod. Res. Dev. 1969a,8,1. Nace, D. M. Catalytic cracking over crystalline aluminosilicates 11. Ind. Eng. Chem. Prod. Res. Deu. 1969b,8, 1. Nace, D. M. Catalytic cracking over crystalline aluminosilicates. Ind. Eng. Chem. Prod. Res. Deu. 1970,9, 2. Nace, D. M.; Voltz, S. E.; Weekman, V. W. Application of a kinetic model for catalytic cracking. Effects of charge stocks. Ind. Eng. Chem. Process Des. Deu. 1971,10, 530. Nalltham, R. V.; Tarrer, A. R. Application of a catalyst deactivation model for hydrotreating solvent refined coal feedstocks. Ind. Eng. Chem. Process Des. Deu. 1983,22,645. Newson, E. Catalyst deactivation due to pore-plugging by reaction
products. Ind. Eng. Chem. Process Des. Deu. 1975,14, 1. Pine, L. A.; Maher, P. J.; Wachter, W. A. Prediction of cracking catalyst behaviour by a zeolite unit cell size model. J. Catal. 1984, 84,466. Szepe, S.;Levenspiel, 0.; Catalyst deactivation. In 0. Proc. European Fed., 4th Int. Cong. Chem. React. Eng.; Pergamon Press: New York, 1971. Tan, C. H.; Fuller, 0. M. A model fouling reaction in a zeolite catalyst. Can. J . Chem. Eng. 1970,48,4. Voltz, S. E.; Nace, D. M.; Weekman, V. W. Application of a kinetic model for catalytic cracking. Ind. Eng. Chem. Process Des. Dev. 1971,10, 4. Voorhies, A. Carbon formation on catalytic cracking. Ind. Eng. Chem. 1945,37,4. Weekman, V. W. A model of catalytic cracking conversion in fixed, moving, and fluid bed reactors. Ind. Eng. Chem. Process Des. Dev. 1968,7, 1. Weekman, V. W. Lumps, models and kinetics in practice. AIChE Monogr. Ser. 1979,2 1 , 75. Wheeler, A. Catalysis; Reinhold: New York, 1955; Vol. 2. Wojciechowski, B. W. A theoretical treatment of catalyst decay. Can. J. Chem. Eng. 1968,46,2. Wojciechowski, B. W. The kinetic foundation and practical application of the time on stream theory of catalyst decay. Cat. Reo. Sci. Eng. 1974,9 (l),79. Wolf, E. E.; Alfani, F. Catalyst deactivation by coking. Cat. Rev. Sci. Eng. 1982,24 (3), 329. Wollaston, E. G.; Haflin, W. J. What influences cat cracking. Hydrocarbon Process. 1975,93,9.
Receiued for reuiew March 24, 1989 Accepted October 3, 1989
Heterogenized Homogeneous Catalyst. 4. Catalyst with a Bias Active Site Distribution Tse-Chuan Chou,* Jin-Yen Lin, Chin-Huang Liang, and Jing-Shan Do Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan, Republic of China 70101
A heterogenized homogeneous catalyst with a bias active site distribution was investigated. The polymer supports of the catalyst with a bias active site distribution were designed and prepared by means of controlling the sulfonation reaction of the polystyrene resin. The results showed that the reaction rate of aldehyde oxidation increased with an increase of the film thickness with a bias active site of the catalyst particle and reached a maxima when the film thickness with a bias active site was equal to the catalytically effective thickness. The turnover number, however, decreased sharply with an increase of the film thickness with a bias active site of the particle. The results also showed that the reaction rate and the turnover number of aldehyde oxidation initiated by the heterogenized homogeneous catalyst with a bias active site distribution was larger and 100 times higher, respectively, than that of using a Co-type catalyst supported by the commercial resin. The behavior of the heterogenized homogeneous catalyst was much more improved when using the catalyst with a bias active site distribution. The oxidation of aldehydes in the liquid phase using metal ions as catalysts has been widely studied (Czytko and Bub, 1981; Chou and Lin, 1983; Emanuel et al., 1984; Hronec et al., 1985; Kuo and Chou, 1987a; Maslov and Blyumberg, 1976; McNesby and Heller, 1954). In general, the selectivity of producing organic peroxides using homogeneous metal ions as the catalyst was low. The yield as well as the selectivity of organic peroxides is much improved for the oxidation of aldehydes using a heterogenized homogeneous catalyst (Chou and Lee, 1985; Kuo and Chou, 1987b, 1988; Chou et al., 1987; Hwang and Chou, 1989). Because the lifetime of the free radical was very short, the free radical initiated by the heterogenized homogeneous catalyst was effective only on the thin film of the outer surface of a catalyst particle, i.e., the cata0888-5885/90/2629-0180$02.50/0
lytically efective thickness. For the oxidation of aldehydes, the catalytically effective thickness of a catalyst particle was found previously (Hwang and Chou, 1987). In general, a commercial polystyrene resin was thoroughly and uniformly sulfonated. By use of the commerical polystyrene resin as the catalyst support, the sulfonated anion easily and uniformly chelated with the metal ion throughout the whole particle. However, beyond a certain film thickness from the outer surface, there are many chelated-metal ions that are useless or are considered to be inactive because the initiated free radicals by these active sites cannot reach the bulk solution. Furthermore, a few papers also pointed out that the inside part of the sulfonated anion could very easily combine with water, which deactivated the heterogenized homogeneous catalyst Q 1990 American
Chemical Society
Ind. Eng. Chem. Res., Vol. 29, No. 2, 1990 181 (Chou and Liang, 1988). It is of interest to prepare the catalyst with a bias active site distribution to improve the heterogenized homogeneous catalyst. In this study, the prepared bias active site distribution resin was used as the support of the heterogenized homogeneous catalyst, and the uniform active site distribution resin (Dowex cationexchange resin) was also used as a support for the comparisons. n-Butyraldehyde and cobalt ion were chosen as the model compound and the catalytic metal ion, respectively, to study the characteristics and performance of the heterogenized homogeneous catalyst with a bias active site distribution. Theoretical Analysis The mechanism of forming per-n-butyric acid by oxidation of n-butyraldehyde in a higher pressure of oxygen, at room temperature, and using heterogenized homogeneous Co3+as the catalyst has been reported (Hwang and Chou, 1987; Kuo and Chou, 1987b, 1988). However, the thermal initiation and the hydration of metal ions as well as free radicals were considered. The reaction mechanism was modified as follows: 02(9)
-% 0 2 ( b )
(1)
adsorption of n-butyraldehyde RCHO(b)-% RCHO,,) catalytic initiation
-
+ s-Co3+
RCHO,,)
kc
RCO,,)
(2)
+ s-Co2++ H+
(3)
diffusion of the free radical RCO(,) -kRC6(b)
(4)
thermal initiation RCHO(b)+ 0 2 ( b ) -kRCO(b)+ HO2(b) propagation RCo(b) + 0 2 ( b ) k,_ RC03(b) RC63(b) + RCHO(b)
RCO&,)
(5)
(6) RC6(b)
(7)
decomposition
22RCO&b)
RCO,H(b) + RCHO(b) termination
+ -
RCO,,)
kt
inactive
k9
~ R c O , ( ~ ) inactive RcO,(~) S
kll
inactive
(8)
(9) (10) (11)
hydration KlS
s-Co3++ nlH20 * s-Co3+-.nlH20
(12)
K14
RC63(b) + nzHzO(b)* RC63.-n2H20(b) regeneration of catalyst RC03H(b)+ S-c02+ -% RC6,(b)
(13)
+ S-c03++ OH-(b) (14)
s-Co3+is supported Co3+. As shown in Figure 1,the RCO free radical which was generated within the pore of the catalyst particle diffused to the bulk solution and then reacted there with the dis-
bulk solution
Nemst layer
bciive site
Figure 1. Schematic diagram representing the structure of the gelular resin particle with a bias active site distribution.
solved oxygen. The material balance in a control volume inside the particle is shown as follows: -4aAr2A[RC6]/At = 4a(N,lr21,+Ar - N,1r21,) (kc[s-Co3+][RCHO],,) - k,[RC0](,))4ar2Ar (15) where N,, is the flux of RCO within the particle. Equation 16 can be obtained by simplifying eq 15: d[RCO](,)/dt = -l/r2 d(Nmlr2)/dr+ kC[~-Co3+][RCHO](,) - kJRCO](,) (16) Substituting N,, by the term -De d[RCO](,)/dr, eq 16 becomes d[RCO](,,/dt = D e / r 2d(r2 d[RCO](,)/dr)/dr + k,[s-Co3+][RCHO],,) - kJRCO](,) (17) The material balances of the species in the bulk solution were d[RC6](b)/dt= ( A / V ) ( - D ed[RCO]/dr(,,R) k3[RC01(b)[Od(b)+ kdRC031(b)[RCHOl(b) + k2[RCHO1(b) [ 0 2 1 (b) (18) d[RCO3I(b)/dt = k3[RCOl(b)[021(b) k4[RCO3l(b)[RCHOl(b)- 2k9[RC63l(bt - kll[RCO3l(b)[Sl (19) d[RCO3H](b)/dt = -k,[RCO3l(b)[RCHOl(b)- k5[RCO3Hl(b)[RCHOl(b)(20) where A and V are the catalytically effective outer surface of the particle and the volume of the solution, respectively, and [SI is the total area of the outer surface of the supported resin. Equations 17-20 can be expressed by the dimensionless form. The detailed procedures are presented in the Appendix. The results are shown as follows: Rc = k4[RCHOl(b)(-~ll[Sl+ [(k11[s1)2+ ((8~&3~gPD,0.5)/(r,k~5))[s-Co3+l [RCHo](b)]0.5]/(4kg) (21) where R, is the catalytic reaction rate of n-butyraldehyde oxidation. If (k,l[S])2 5))[s-Co3+][RCHO](b)]0.5)/(4kg)(22) or R,' = R, + k4kli[RCHOI(b)[SI/(4kg)= k,[RCHO] (b)(k&3p0,O5[ RCHO](b) [S-c03+] / (2kgr,k>5))0.5 (23)
182 Ind. Eng. Chem. Res., Vol. 29,No. 2, 1990 Table I. Effect of Sulfonation Time on the Capacity and Sulfur Content of a Bias Active Site Distribution Resin (Sulfuric Acid, 20 mL/g of Resin; Chloroform, 1 mL/g of Resin) sulfonation time, min temp, “C 40 10 40 20 40 40 80 40 10 60 20 60 40 60 80 60 10 80 20 80 40 80 80 80
S content, mol 0.093 0.132 0.183 0.251 0.167 0.334 0.794 1.59 1.11 1.36 3.66 4.81
%
capacity, mequiv/g 0.0086 0.012 0.016 0.041 0.032 0.170 0.511 1.210 0.996 1.239 3.501 4.378
Experimental Section A Pyrex glass vessel, a round-bottom flask with four necks, was used as the reactor for preparing the polymer supports. Prepurified styrene and divinylbenzene were introduced dropwise into the aqueous solution which contained CaC03 as the suspender and Na2S04as electrolyte. The polymerization reaction was initiated by 2,2’-azobis(isobutyronitril)(AIBN). After 3 h of a run, the resin was taken out, washed, and dried. Then the desired particle size of the resin was chosen as the polymer support (Bauman and Eichhron, 1974;Hohenstein and Mark, 1946; Wheaton and Harrington, 1952). The character of the resin was identified by elemental analysis, and the capacity, density, and the degree of cross-linking of the resin particles were also measured. The sulfonated resin was made by sulfonating the prepared resin with concentrated HzS04,which was diluted with a solvent, chloroform (Braun et al., 1972;Chee and Ihm, 1986;Gregor et al., 1951;Boundy, 1952). During the sulfonation reaction, the stirring rate and temperature were well controlled, respectively, at the desired values to get different degrees of sulfonation. The uniform and bias sulfonated resins could be used as the support for the heterogenized homogeneous catalyst. Then, the sulfonated resin could exchange with different concentrations of Co3+ to make the Co-type heterogenized homogeneous catalyst with a uniform or bias active site distribution. Both the uniform and bias active site Co-type resins were used as catalysts for the oxidation of n-butyraldehyde. The experimental procedures of n-butyraldehyde oxidation were described in previous reports (Hwang and Chou, 1987). Results and Discussion Effect of Temperature and Reaction Time on the Film Thickness with a Bias Active Site for Preparing the Catalyst. The characteristics of the resin with the bias active site distribution were affected by the reaction time and temperature of sulfonation. As shown in Table I, at the same sulfonation time, the highest temperature gave a larger sulfur content, which is the sum of SO2 and S03H functional groups, and a larger capacity, S03H functional group only, of the ion-exchange resin. Also indicated is that increasing the reaction time increased both the sulfur content and the capacity. At 40 “C, increasing the sulfonation time from 10 to 80 min increased the sulfur content from 0.093% to 0.251% and increased the capacity from 0.0086 to 0.041 mequiv/g, respectively. The results also revealed that the sulfur content was much larger than the capacity. This was possibly due to the generation of cross-linking sulfonyl group, SOz, that in-
Table 11. Effect of the Co3+Concentration of the Co-Type Catalyst Supported by Commercial Resin on the Reactivity” CCo3+,
mequiv/g resin 0.16 0.34 0.52 0.82 1.01
1.46 2.45 2.93 3.78 4.61
103~,,
M/min 1.08 1.55 1.78 2.27 2.45 2.93 3.84 4.23 4.57 4.99
T,,mol/ (mol-min) 29.3 18.0 13.9 11.5 9.68 7.85 6.46 5.94 4.92 4.30
D.
cm3/e 1.240 1.269 1.292 1.314 1.325 1.345 1.358 1.372 1.395 1.422
[RCHO], 2 M; temperature, 20 “C; Co-type resin, 0.5 g; O2 flow rate, 150 cm3/min; volume of solution, 150 mL.
hibited the formation of the sulfonic group, S03H. At 60 “C, which was almost the reflux or the highest temperature of sulfonation at atmospheric pressure, it was found that the sulfonyl group was easily formed and the sulfur content of the sulfonated resin was still larger than the capacity for the initial stage of a run, as shown in Table I. On the other hand, the main product of sulfonation shifted to the sulfonic group, and the capacity significantly increased from 0.032 to 1.210 mequiv/g when the sulfonation time increased from 10 to 80 min, as shown in Table I. A t 80 “C, however, the resin was broken into small pieces, which made both the sulfur content and capacity sharply increase with reaction time. Effect of Cobalt Ion Concentration, The effects of the cobalt ion concentration of the heterogenized homogeneous catalyst supported with the commerical resin on both the reaction rate and turnover number of n-butyraldehyde oxidation are shown in Table 11. The results indicated that the reaction rate monotonically increased to 2.93 X M/min when the concenfrom 1.08 X tration of cobalt ion increased from 0.16 to 1.46 mequiv/g. However, the turnover number (moles of product/ (mole of catalysteminute)) sharply decreased from 29.3 to 7.86 mol/(mol-min). The effect of the cobalt ion concentration on the reaction rate slowed down at higher cobalt ion concentrations. Further increasing the concentration of cobalt ion from 1.46 to 4.60 mequiv/g, the reaction rate of n-butyraldehyde oxidation only slightly increased from 2.93 X to 4.99 X M/min, and the turnover number only slightly decreased from 7.85 to 4.3 mol/(mol.min). The density of the Co-type resin increased with an increase of cobalt ion concentration as shown in Table 11. As shown in eq 23,the normalized catalytic reaction rate, R l , was proportional to the square root of the concentration of the catalyst. It could be simplified as follows: R,’ = KA1*[Co3+]o,5 (24) where K is a constant and AI* = ($,‘X’/sinh X”- 4‘, coth X”+ (44)2= k4/r;/De, X’=r’/rp, and X ” = 44(1 - X’), The turnover number, T,, can also be expressed as follows: T , = KA,*[CO~+]~.~ (25) where A2* = A , * / ( l - (1- XX)3) and XX = (rp - r ” ) / r p . By use of eqs 24 and 25 and for a given catalytically effective thickness and particle size, i.e., a given KAI* and KA2*,R,‘ and T , could be calculated, respectively, at a given concentration of the catalyst. The logarithmic plots of the normalized reaction rate and turnover number against the concentration of the catalyst resulted in straight lines, respectively, as shown in Figures 2 and 3. These indicate that the theoretical analysis was consistent
I
/--
Ind. Eng. Chem. Res., Vol. 29, No. 2, 1990 183 I
/ I /
KA; =0.0050
-5
-
a
0.0010
- -
3
11
*q-
0 0023
J
I
C = 250
2
1
e
2-
500
I
/
1
t
*
: Experimental
- :
Theoretical
I
0
-1
1
2
In [ s - c o + ~ ]
5000
Figure 2. Effect of cobalt ion concentration on the catalytic oxidation rate. [RCHO], 2 M, temperature, 20 "C; Co-type resin, 0.5 g; O2flow rate, 150 cm3/min; volume of solution, 150 mL.
I
*
Experimental
-
Theoretical
0 01
0 02
I - r'7rp Figure 4. Effect of sulfonation film thickness of different particle sizes on the reaction rate. Catalytically effective thickness, 0.01rP.
r----l
3i \
0 -1
0
I
I
0
1
i 2
In [s-cd3 ] Figure 3. Effect of cobalt ion concentration on the turnover number. [RCHO], 2 M; temperature, 20 "C; Co-type resin, 0.5 g; O2 flow rate, 150 cm3/min; volume of solution, 150 mL.
with the experimental results. Effect of the Film Thickness with an Active Site on the Reaction Rate and Turnover Number. At a given concentration of catalyst, the reaction rate and turnover number were proportional to AI* and A2*, respectively. Assuming that the catalytically effective thickness was O.O1rp and the rate of free-radical termination within the pores of catalyst particle was constant, the relationships of both Al* and A2* against film thickness with an active site were obtained as shown in Figures 4 and 5, respectively. The results indicated that the values of 4: which corresponded to the particle size were in the range 250-10000. The reaction rate or Al* monotonically increased and then reached a maximum and was constant with an increase of the film thickness with an active site or the sulfonation film thickness as shown in Figure 4. Figure 4 revealed that the n-butyraldehyde oxidation rate did not increase with an increase of the thickness of sulfonation when the thickness of sulfonation was larger than the catalytically effective thickness, i.e., the n-butyraldehyde initiated to form free radicals occurred at the outer surface film only. The turnover number or A2*, however, sharply decreased with an increase of the film thickness with an active site. For example, A2* decreased from 0.15 to 0.034 when 1 - r f f / r pincreased from 0.0012
I - rrY& Figure 5. Effect of sulfonation film thickness of different particle sizes on the normalized turnover number. Catalytically effective thickness, O.Olr,,.
to 0.01 at 4: = 1000. The turnover number decreased slowly with an increase of the thickness with an active site when the sulfonation thickness, 1 - r f f / r p was , further increased. For example, A2* decreased from 0.034 to 0.016 when 1 - r"/rP increased from 0.01 to 0.02 at 441 = 1000. A t a fixed 1 - r"/rP value, the turnover number or A2* significantly decreased with an increase of 4: or particle size. Effect of Co-Type Resin Capacity on the Rate and Turnover Number of Aldehyde Oxidation. The activity of the bias active site distribution catalysts obtained by sulfonating at 40 and 60 "C was tested by the nbutyraldehyde oxidation. The results were shown in Figures 6 and 7. When the concentration of the catalyst sulfonated at 40 "C increased from 0.0086 to 0.041 mequiv/g, the reaction rate of n-butyraldehyde oxidation monotonically increased from 1.81 X to 3.65 X M/min, but the turnover number slowly decreased from 839 to 358 mol/(mol.min). However, by use of the catalyst
184 Ind. Eng. Chem. Res., Vol. 29, No. 2, 1990 1300
- _ _ _ _ _ _ ~
35
-I4
E
-
-- 6 I
30
-5
E BOC -3
T
'4
F
X
0 I
s
L
400
i +
200
l5
>
C
-
e 10
- 1
i 3
11
5
-0
O L -
0
000
001
002
Capacity of
003
c0+3
004
00
005
150 cm3/min; volume of solution, 150 mL.
2 0
Capacity of
meq/g resin
Figure 6. Catalytic reactivity of Co-type resin sulfonated at 40 "C. [RCHO], 2 M; temperature, 20 "C; Co-type resin, 0.5 g; O2flow rate,
I
10
1
cOi3,
' 0
I
30
40
50
meq/g resin
Figure 8. Catalytic reactivity of Co-type resin with commercial resin or uniform site distribution as support. [RCHO], 2 M, temperature, 20 "C; Co-type resin, 0.5 g; O2flow rate, 150 cm3/min; volume of solution, 150 mL. Table 111. Comparisons of the Reactivity of Co-Type Resin Catalyst with Uniform and Bias Active Sites' capacity
of resin commercial type
C
C
k
600
t
1
sulfonated at 60 "C, 10 min
0
:
300-\
O L 00
, 03
06
Capacity of
1
09
cOi3
12
0 15
meq/g resin
Figure 7. Catalytic reactivity of Co-type resin sulfonated a t 60 "C. [RCHO], 2 M; temperature, 20 "C; Co-type resin, 0.5 g; O2flow rate, 150 cm3/min; volume of solution, 150 mL.
sulfonated at 60 "C, the reaction rate of aldehyde oxidation M/min to a maximum of 6.86 increased from 5.09 X X M/min when the concentration of the catalyst increased from 0.032 to 0.511 mequiv/g. Then the reaction rate of the aldehyde oxidation decreased from 6.86 X to 4.63 X M/min when the concentration of catalyst increased from 0.511 to 1.21 mequiv/g. However, the turnover number sharply decreased from 1260 to 135 mol/ (molamin) when the concentration of the catalyst is increased from 0.032 to 0.17 mequiv/g. The turnover number then slowly decreased from 135 to 16 mol/ (mol-min)when the concentration of the catalyst increased from 0.17 to 1.21 mequiv/g. It was found that the film thickness of the active site was smaller than the catalytically effective thickness for the catalyst sulfonated at 40 OC and less than 80 min. By use of this type of resin as the catalyst support, increasing the catalyst concentration or the film thickness with an active site increased the aldehyde oxidation rate and slowly decreased the turnover number as shown in Figure 6. The range of film thickness with an active site was also smaller than the catalytically effective thickness for the catalyst sulfonated at 60 "C and less than 40 min. By use of this type of resin as the support of the catalyst, the aldehyde oxidation rate monotonically increased and the turnover number sharply decreased, respectively, with an increase
HZO content, w t
of Co3+, 70 mequiv/g A' Bb 4.610 25.12 Oc 25.12 1.12d 0.032 6.63 Oc 6.63 0.04d
i03R,, T,,mol/ color M/min (mol-min) blue 2.78 4.02 violet 2.35 3.38 golden 5.19 1071 golden 3.12 685
"Before pretreatment of the catalyst. bAfter pretreatment of the catalyst. cPretreatment at 80 "C vacuum oven for 24 h. dPretreatment at 80 "C oven for 24 h. e [RCHO], 2 M temperature, 20 "C; Co-type resin, 0.3 g; O2 flow rate, 150 cm3/min; volume of solution, 150 mL.
of the film thickness with an active site. The results correlated well with the results of the calculation, as shown in Figures 4 and 5. When the film thickness with an active site was larger than the catalytically effective thickness, the reaction rate of aldehyde oxidation gradually decreased and was less than the results of calculation, as shown in Figure 7. The difference between the experimental results and the calculated ones might be due to the increase of the number of sulfonic groups on the resin particle. The sulfonic group increased the concentration of the adsorbed water, which could deactivate the reaction rate (Chou et al., 1987; Chou and Liang, 1988). Comparison of the Co-Type Catalysts with Uniform and Bias Active Site Distributions. The turnover numbers of the n-butylaldehyde oxidation were in the range 300-1200 mol/(mol*min)using the catalyst with a bias active site distribution, as shown in Figures 6 and 7, while the turnover numbers were in the range 5-30 mol/(mol.min) using the Co-type resin catalyst supported by commercial resin, as shown in Figure 8. A t 0.5 mequiv/g of resin capacity of Co3+,the reaction rate of nbutyraldehyde was 1.5 and 7.0 X lo9 M m i d respectively using the catalyst supported by the commercial resin and the resin with a bias active site as shown in Figures 7 and 8. The results reveal that the active site or Co3+ion immobilized on the resin is much more active for the catalyst with a bias active site distribution than that with a uniform active site distribution. Comparisonsof the activities of the catalysts supported by both commerical resin and resin with a bias active site
Ind. Eng. Chem. Res., Vol. 29, No. 2, 1990 185 distribution were summarized as shown in Table 111. The results showed that both the turnover number and the reaction rate of the aldehyde oxidation were quite different when using these two types of catalysts. The turnover number of the aldehyde oxidation when using the Co-type catalyst with a bias active site distribution prepared in this work was much larger than that when using the Co-type catalyst supported with a commercial resin. The characteristics of the heterogenized homogeneous catalyst were much more improved by designing the bias active site distribution.
Conclusions The performance of the Co-type resin catalyst with a bias active site distribution was evaluated by both experimental and theoretical analyses. The results indicated that the reaction rate of the aldehyde oxidation increased with an increase of the film thickness with an active site of the catalyst particle. However, further increasing the concentration or film thickness with an active site of the catalyst, the reaction rate was constant or decreased when the film thickness with an active site was larger than the catalytically effective thickness. Both the experimental and theoretical results showed that the turnover number decreased sharply with an increasing of the catalyst concentration or the film thickness with a bias active site. The turnover number also gradually decreased against catalyst concentration when the film thickness with an active site was larger than about 10% of the particle radius. Both the active site and turnover number using the catalyst supported by the commercial resin were much smaller than that of the resin with a bias active site distribution prepared in this work. The developed co-type resin catalyst with a bias active distribution was much more active than the catalyst supported by the commercial resin.
Y = dimensionless term of the species concentration in the bulk solution 2 = dimensionless term of the species concentration within the particle Greek Letters /3 = catalyst loading, 3WIpV
0 = dimensionless term of time
resin density, g/cm3 4 = dimensionless term of the square root of the reaction rate &= definition of [RCHO](~)O/[RCHO](,)~ p =
Subscripts b = bulk solution g = gas phase p = intra-particle phase s = resin surface
Appendix The material balance of the RCO free radical of a control volume within the particle of catalyst is shown as follows: 6[ RCO](,)/ b t = De/r2(6(r2b[RCO]),(
/ 6r)/br)
+
~,[S-CO~+][RCHO](~) - kJRCO](,) (A-1) Similarly, the material balances of RCO, RC03, and RC03H species in the bulk solution are shown as follows:
Acknowledgment The support of National Science Council and National Cheng Kung University are acknowledged.
Nomenclature A = effective outer surface Al* = [&X'/sinh X I ' - q5t coth X I ' + l]/4: Az* = AI*/Cl - (1- XX)3] De = effective diffusion coefficient f = effectiveness factor [i] = concentration of component i [ i ] = effective concentration of component i k-= reaction rate constant, M-' min-' K13 = equilibrium constant for the formation of the cobaltwater complex K14 = equilibrium constant for the formation of the RC03water complex = radius of the resin particle, dm = inner boundary of the catalytically effective thickness, dm r'' = inner boundary of the sulfonated film thickness, dm R, = reaction rate initiated by the catalyst, M m i d Rth = reaction rate initiated by the thermal initiation,M m i d S = inert surface t = reaction time, s T = reaction temperature, "C V = volume of solution, mL W = weight of resin, g X = dimensionless term of direction r X ' = dimensionless term of direction r' XX = dimensionless term of the sulfonated film thickness of the resin
9
where [RCHO](,)ois the initial concentration of n-butyraldehyde on the surface of the catalyst, Le., r = r ; [RCHO](b,ois the initial concentration of n-butyraldehy8e in the bulk solution; r'and rp are the catalytically effective radius and the radius of the catalyst particle, respectively; and W and p are the weight and density of the resin, respectively. On the basis of the dimensionless groups, eqs A-1-A-4 are rewritten as 6Zm1/60 = 1/X2 b ( X 2 bZm1/6X)/6X + d,2Zn1- b,"Zml (A-5) dYml/dO= -P/k(6Zm1/bX)Iz-1) - ds2Ym1 + 442Ym2Ynl - + $22Yn1 (A-6) dYmz/de e 93'Yml- b42y,2Yn1- 299*Ym~~ - P9112Ym2 (A-7) dYn2/de = '$42&yn1d?Yn2Yn1 (A-8)
186 Ind. Eng. Chem. Res., Vol. 29, No. 2, 1990
At pseudo steady state, dZml/dO, dYml/dO,and dY,/dO are equal to zero; then eqs A-5-A-7 are simplified as follows: I / X 2 d(X26Zm1/6X)/6X + @c2Zn1 - @:Zm, = 0 (A-9) @32ym1 + @?ym2ynl + @?ynl = 0 -p/@((azml/6x)lx=l) I
(A-10) &2Ym1 - d42ym2ynl - - 2&2Ym22 - P$112Ym2 = 0 (A-11)
A t a higher stirring rate, the external film diffusion resistance of the catalyst can be neglected, i.e., [RCHO](b) = [RCHO],,,. The lifetime of the. free radical within the catalyst particle is short, and RCO only exists in the thin film of the outer surface of the catalyst particle. The boundary conditions are
X
BC1:
= 1, z m 1 = l Y m l
(A-12)
x = x: zml= o
BC2:
(A-13)
From eqs A-9, A-12, and A-13, Zmlwas obtained as follows:
z,~= Cl/X exp(4,X) + Cz/X
exp(-&X)
+ (@c/@J2zn1 (A-14)
where
- X’)ll
(A-15)
C2 = @Ym1 exp($tX’) - (@c/$t)2[X’exp(@t)exp($,X’)]Zn1}/{2 sinh [&(l - X’)]) (A-16)
Equation A-10 is expressed as coth X ” - l)@Ymi+ (d,/9t)2Z”i(~tX’/Sinh X ” 4t coth X” + 1)J- &‘Yml + 42Ym~Yn1 - + 42’Ynl = 0 (-4-17)
-P/i[(@t
where X ” = dt(l - X’). Define Ymz = fYm2and f is the effectiveness factor of the free radical RC03. Combining eqs A-11 and A-17, Ymz is obtained: coth X ” - l ) Y n ~ l / 1)1+ [(P$ii2 + [42fo(@, coth X ” - 1)Yn1]/[@32+ P ( @ t coth X ” - 1)1)2+ [8@92@32(@22Yn1 - P/$(btX’/sinh X”-$Jt coth X ” + l)(@c/@t)2ZnJ1/[@~ + P ( & coth X ” - 1)]]o.5}/(4@92) (A-18)
Ym2 = (-P911~-
[@*‘f@(@t
[$? + P(@t coth X ” -
If
/3$11*
>> [ $ 4 2 f / 3 ( @ t coth X ” - 1 ) Y ~ ~ l /+[ @ P(&~ coth X ”
- l)],then
Ym2 = I-Pb11’ + [ ( P @ 1 1 2 ) 2 + [8$92@32(@22Yn1 X ” - $t coth X ” + 1)($c/$J2Zn1)l/ B/4(4tX’/sinh [Q3’ P(@tcoth X“- 1)]]o~5}/(4~g2) (A-19)
+
is large,
When the value of
(&X’)/(sinh X”) = (&X’)/[sinh &(l- X’)] q+
then (&X’/sinh X ” -
coth X ” = &
$J~coth
2
0
(A-20) (A-21)
X” + 1) is nearly equal to
-+t.
When the value of c#+~is much larger than /3(+t coth X ”
- 11, then Ym2 =
I-P@11’
dYmz/dO =
+ [ ( P ~ I I+~8&2[422Yn1 )~ +
I-P4112
Rth = d[RCO,H],b)/dt = k4(kz/2kg)0’5[02](b~5[RCHO](b)1’5 Rth
= k#o>5[RCHO](b)1’5
(A-25)
Case 2. Catalytic initiation only occurs, and there is absence of water R, = k4[RCHOI(b)l-kii[SI + [(8M3k9PD,0.5)[s-Co3+l(b)/ (rpk,0.5)]0.5) / (4kg) (A-26) Registry No. Co, 7440-48-4; n-butyraldehyde, 123-72-8.
Literature Cited Bauman, W. C.; Eichhron, J. Fundamental Properties of a Synthetic Cation Exchange Resin. J . Am. Chem. SOC.1974, 69, 2830. Boundy, R. H. Styrene: Its Polymers, Copolymers and Derivatives; Waverly Press: New York, 1952; pp 674-677. Braun, D.; Cherdron, H.; Kern, W. Techniques of Polymer Synthesis and Characterization; John Wiley and Sons Inc.: New York, 1972; p 264. Chee, Y. C.; Ihm, S. K. The Influence of Acid Site Distribution on the Catalytic Deactivation of Sulfonated Poly(styrene-divinyl benzene) Membrane Catalyst. J. Catal. 1986, 102,180. Chou, T. C.; Lee, C. C. Heterogenizing Homogeneous Catalyst. 1. Oxidation of Acetaldehyde. Ind. Eng. Chem. Fundam. 1985,24, 32.
Cl = (&Ymlexp(-@,X’) + ($c/$t)2[X’exp(-$t) e~p(-$~X’)lZ,~I/(2 sinh [&(l
Case 1. Thermal initiation only occurs, and there is absence of water and the inert surface
(P/3)(@z/&)Znil1°.51/ (469’) (-4-22) + [ ( P G I I ~+) ~8692[622Yn~+
( ~ /@ ) ( ~ , 2 / ~ t ) z n 1 l l ~ . ~ Y n 1 } /-( 4&~ 9J ~~)~ Y ~(A-23) IY~z
If [RCHO],,,, = K,[RCHO](,,,, then d[RCO,H] (b) / d t = kf[RCHOI(b)Hii[SI + [(kii[s1)2 + 8kg(kz[0zl(b)[RCHOl,b, + ( P D , 0 . 5 / r p ) ( k ~ 3 / k t 0 . 5 ) [ s - C o[RCHOl(b))1°.51/(4k9) 3+l (A-24)
Chou, T. C.; Lin, F. S. Effect of Interface Mass Transfer on the Liquid-phase Oxidation of Acetaldehyde. Can. J. Chem. 1983,61, 1295. Chou, T. C.; Liang, C. H. The Effects of Water and Inert Surface on the Oxidation of Benzaldehyde Catalyzed by Polymer Supported Co(II1). J . Chin. Inst. Chem. Eng. 1988, 19 (3), 137. Chou, T. C.; Liang, C. H.; Lu, M. K. The Effect of Water and Inert Surface on the Thermal Oxidation of Benzaldehyde. J . Chin. Inst. Chem. Eng. 1987, 18 (4), 229. Czytko, M. P.; Bub, G. K. Oxidation of Toluene by Cobalt(II1) Acetate in Acetic Acid Solution: Influence of Water. Ind. Eng. Chem. Prod. Res. Dev. 1981,20, 481. Emanuel, N. K.; Zaikov, G. E.; Maizus, Z. K. Oxidation of Organic Compounds: Medium Effect in Radical Reactions; Pergamon Press: New York, 1984. Gregor, H. P.; Bregman, J. I.; Gutoff, F.; Broadley, R. D.; Baldwin, D. E.; Overberger, C. G. Studies on Ion-Exchange Resins. Capacity of Sulfonic Acid Cation-Exchange Resins. J . Colloid Sci. 1951, 6 , 20. Hohenstein, W. P.; Mark, H. Polymerization of Olefins and Diolefins in Suspension and Emulsion. Part I. J . Polym. Sci. 1946, I (21, 127. Hronec, M.; Ilavsky, J.; Cvengrosova, Z. Kinetics and Mechanism of Cobalt-catalyzed Oxidation of p-Xylene in the Presence of Water. Ind. Eng. Chem. Prod. Res. Dev. 1985,24, 787. Hwang, B. J.; Chou, T. C. Heterogenizing Homogeneous Catalyst. 2. Effect of Particle size and Two Phase Kinetics Model. Ind. Eng. Chem. Res. 1987, 26, 1132. Hwang, B. J.; Chou, T. C. Bias Temperature Effect on the Characteristics of a Heterogeneous-Homogeneous Chain Reaction in a Semi-Batch Annular-Wall Reactor. Chem. Eng. Sci. 1989, in press. Kuo, M. C.; Chou, T. C. Kinetics and Mechanism of the Catalyzed Epoxidation of Oleic Acid with Oxygen in the Presence of Benzaldehyde. Ind. Eng. Chem. Res. 1987a, 26, 277. Kuo, M. C.; Chou, T. C. Heterogenized Homogeneous Catalyst. 3. Oxidation of Benzaldehyde in a Semibatch Tubular Wall Reactor. Ind. Eng. Chem. Res. 1987b, 26,1140. Kuo, M. C.; Chou, T. C. Benzaldehyde Oxidation Catalyzed by the Wall of a Tubular Bubble Column Reactor. AIChE J . 1988, 34 (6), 1034. Maslov, S. A.; Blyumberg, E. A. Liquid-Phase Oxidation of Aldehydes. Russ. Chem. Rev. 1976, 45 (2), 155. McNesby, J. R.; Heller, C. A. Oxidation of Liquid Aldehydes by Molecular Oxygen. Chem. Rev. 1954,54, 325. Wheaton, R. M.; Harrington, D. F. Preparation of Cation Exchange Resins of High Physical Stability. Ind. Eng. Chem. 1952,44 (8), 1796.
Received for review April 10, 1989 Accepted October 12, 1989
