Ind. Eng. Chem. Res. 1994,33, 2523-2529
2523
KINETICS, CATALYSIS, AND REACTION ENGINEERING Heterogenized Homogeneous Catalyst. 7. Comparisons of Thermal Oxidation and Heterogenized Homogeneous Co- and Mn-Type Resin Catalyzed Oxidation of Propionaldehyde LungChyuan Chen and Tse-Chuan Chou' Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan, ROC 70101
The oxidation of propionaldehyde initialized by thermal reaction, Co-type resin catalyst, and Mn-type resin catalysts was carried out. The results revealed that the yield of perpropionic acid was significantly increased by using Co- or Mn-type resin as catalyst instead of thermal initialization. A faster reaction rate was found by using Co-type resin as catalyst. However, a higher selectivity of perpropionic acid was obtained by using Mn-type resin as catalyst. The following rate equations were obtained when the propionaldehyde concentration and catalyst loading increased from 1.39 to 2.78 M and from 2 to 4g/L, respectively, a t 283 K: R,= 6.45 x [RCHO(b)11,41[S-CO~+]'-'~~~, for Co-type resin; R, = 4.98 x 10-3[RCHO(b)11~59[s-Mn3+10~41, for for thermal reaction. RCHO, s-Co3+,and s-Mn3+ Mn-type resin; R, = 1.08 x 10-4[RCHO(b)11.76, indicate propionaldehyde, Co-type resin, and Mn-type resin, respectively. The activation energies were found to be 75.8, 60.9, and 44.8 kJlmol using thermal, Co- and Mn-type resin catalysts, respectively. Mixing of Co- and Mn-type resins could not improve the selectivity of perpropionic acid.
Introduction Oxidation of hydrocarbon compounds in the liquid phase, such as the oxidation of cumene to peroxyl compound (Sotelo et al., 19851,toluene to benzaldehyde (Czykto et al., 19811, cyclohexane to adipic acid (Rao and Triukkoyilur, 19861, and cyclohexanone to adipic acid (Fredin and Perkel, 1980), has been given much attention industrially. Oxidation of aldehydes to peroxyl compounds is technically important. Aldehydes are easily oxidized to form organic peracids and carboxyl acids (Maslov and Blyumberg, 1976). Peracids with high oxidizing power can be used to produce epoxy compounds (Chou and Chen, 1991; Kuo and Chou, 19901, bleaching agents, detergents, and herbicides, etc. Several methods such as photolysis (Cocivera and Trozzolo, 1970; Maslov and Blyumberg, 1976), thermal autoxidation (Maslov and Blyumberg, 19761, and catalyzed oxidation (Chou and Lee, 1985; Hendricks et al., 1978; Hwang and Chou, 1987; Ivanov and Ivanov, 1985; Ohkatsu et al., 1977; Haber et al., 1981) were reported for the preparation of organic peracids from aldehydes. In general, poor yield was obtained by using a thermal autoxidation method. Metal ions, such as Co2+,Mn2+,and Fe3+,were used as homogeneous catalysts for the oxidation of aldehydes. These catalyzed reaction processes had the advantage of fast reaction and the disadvantage of poor selectivity of peracid since the high activity of the catalysts made the intermediate species, peracid and peroxyl free radical, be easily decomposed, therefore decreasing the selectivity of peracid. To improve the selectivity of peracids, Co-type resin was employed as catalyst in the presence of oxygen to oxidize aldehydes to peracids (Chou and Lee, 1985;
* Author to whom correspondence should be addressed. 0888-5885l94I2633-2523$Q4.5QlO
Hwang and Chou, 1987; Kuo and Chou, 1988; Chou and Yeh, 1992a,b). These previous results showed it a potential method to increase the selectivity of peracids. However, only Co-type resin was examined. It was wellknown that Mn3+ ion exhibited much activity on the oxidation of hydrocarbon in the liquid phase (Emanuel and Denison, 1967). Immobilizing Mn3+on resin for the catalytic oxidation of aldehydes was not reported. In this work, Mn-type resin was used to oxidize propionaldehyde to obtain perpropionic acid. The results of the selectivity of peracid and the reaction rate using Co- and Mn-type resins as catalysts and thermal reactions were compared. The kinetic models were also obtained in this work.
Experimental Section The preparation of the heterogenized homogeneous catalyst was reported previously (Chou and Lee, 1985). Resin was pretreated with hydrogen chloride, filtered, and dried in the oven. The resin catalysts were prepared by an ion exchanged method. First, 3 g of clean, dry H-type resin was dumped into a 0.5 M metal ion solution which was mixed by a magnetic stirrer and the temperature of the solution was controlled at 60 f 1 "C. The concentration of metal ion in the solution was analyzed by use of UV-vis spectroscopy and a pH meter to assure the completeness of exchange. Usually, it took about 112 h for the exchange process t o reach equilibrium. After the ion exchange was completed, the resin was separated from the solution by filtering. The exchanged resin was washed by water and dried at 80 "C in a vacuum oven for at least 5 days. The resins and cobalt(I1) acetate were purchased from Sigma Co. (Dowex-5OWXl2 and Dowex-50WX2) and Merck Co., respectively, The loading of metal ions on the resin were 4.95 and 3.41 mequivlg for Dowex-BOWX2 and Dowex-5OWX12, respectively.
0 1994 American Chemical Society
2524 Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994
Oxidations of propionaldehyde were carried out in a cylindrical Pyrex glass vessel with a diameter of 4.5 cm and a height of 20 cm and a Pyrex glass side arm with a porous gas disperser a t the bottom of the reactor. Magnetic stirring was provided for improving the mixing. Oxygen or nitrogen was directed into the reactor through the gas disperser and bubbled through the solution in the reactor. The gas flow rate was measured with a gas flowmeter. The reactor was vented to the atmosphere via a reflux condenser maintained at about -40 "C. The temperature of the reactor was kept constant within f 0 . 1 "C in a thermostat bath. All chemicals used were reagent grade. At the beginning of a run, the reactor was charged with both acetone as the solvent and a desired amount of catalyst and then oxygen at a fixed flow rate was bubbled through. When the temperature reached the desired value and steady state, the reactant, propionaldehyde, was added into the reactor. Sampling and analysis were performed periodically during the run. The concentration of propionic acid and perpropionic acid were determined by acid-base and iodometric titration (Greenspan and Mackellar, 1947),respectively.
Theoretical Analysis
2RCHO(b)
(v) propagation:
RCO,'(b)
(8)
+ RCHO(b) -RC03H(b)+ RCO'(b)
(9)
kl
+ S-
2RCO,'(b) RCO,'(b)
k8
inactive
k0
(10)
inactive
(11)
(vi) decomposition of peracid: RCO,H(b)
+ RCHO(b)
2RC02H(b)
-
+ s-co3+ RCOYP) + S - C O ~ ++ H+ (3) k,' RCHO(p) + s-Mn3+-RCOYp) + s-Mn2++ H+ (4) k3
(iii) RCO' free radical diffused from catalyst surface to the bulk solution: RCO'(p)%.!
RCO'(b)
(5)
(iv)RCO' free radical also generated thermally in the bulk solution:
+ O,(b) - RCO'(b) + HO,' k5
(6)
(12)
(vii) regeneration of catalysts:
+ S-c02+ k,,RCO; + s-c03+ + OH+ s-Mn2+5 RCO,' + s-Mn3++ OH-
RC0,H
(13) (14)
where S, s-C03+, s-Mn3+, and b and p indicate inert surface, Co-type resin, Mn-type resin, and the bulk phase and particle, respectively. If a chemical reaction is the rate-determining step and the system is a t steady state, the material balances of RCO'(b) and RCO$(b) in the bulk solution are expressed as d[RCO'(b)l = k,"[RCHO(p)] - k6[RCO'(b)l[0~(b)l dt
+
is expressed as
k,"
RCHO(b)
k6
(vi) termination:
k3"
(ii) RCO' free radical heterogeneously generated:
(7)
+ O,(b) -RCO,'(b)
RCO'(b)
RCO,H
Oxidation of aldehyde using heterogenized homogeneous Co-type resin as catalyst was investigated to be a free-radical scheme (Chou and Lee, 1985; Hwang and Chou, 1987; Kuo and Chou, 1988; Chou and Yeh, 1992a,b). The reaction mechanism includes initiation of free-radical, propagation, and termination reactions. The RCO' free radical was heterogeneously generated on the surface of Co-type resin and diffused to the bulk solution where it reacted with 0 2 to become peroxyl free radical RCO3'. Then, the peroxyl free radical reacted with aldehyde to form peracid and promoted the propagation reaction homogeneously. The peroxyl free radical RCO3' might terminate by combining with another or colliding with an inert surface. On the basis of similar redox behaviors of Mn3+ and Co3+ ions, the reaction mechanism of oxidation of aldehyde using Mn-type resin as catalyst was proposed as that of Co-type resin. (i) mass transfer of aldehyde and oxygen, respectively:
RCHO(P)
+ 02(b)-% 2RCOYb) + H202
+
= alz3[s-Co3+l BK,'[s-Mn3+l
(17)
where a,p, and Wi are the effective formation constants of RCO' free radical of eqs 3 and 4 and the thermal initiation, eqs 6 and 7, respectively, which can be expressed as
Wi = k,[RCHO(b)l[O,(b)l
+ k5'[RCHO(b)l2[O2(b)1 (18)
The [RCO$(b)] can be expressed as eq 19 by rearranging eqs 15 and 16: [RCO,'(b)l=
(","[RCHO(p)l + Wi}
0.5
(19)
2k8
The adsorption of aldehyde on the catalyst surface was assumed at equilibrium: [RCHO(p)l = K,[RCHO(b)I
(20)
Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994 2525 Then, eq 19 becomes
1.2 1 :peracid ,:total acid
The formation rates of propionic acid and perpropionic acid are expressed as eqs 22 and 23. 0.8
1
0.4
1
(22)
R, =
d[RCO H (b)l = k,[RCO,'(b)l[RCHO(b)l dt k,o[RCO3H(b)l[RCHO(b)l (23)
Let R, equal Ra plus 2R,, and let Rt equal R, plus Ra, which can be expressed as
R,= 2k,[RCO,'(b)l[RCHO(b)l
(24)
R,= k,[RC03'(b)l[RCHO(b)1 +
V."
Kio[RCO,H(b)I[RCHO(b)l (25) where Ra, R,, Rt, and R, are the formation rates of propionic acid, perpropionic acid, and total acid and the oxidation rate of aldehyde, respectively. Substituting eqs 21-24,
If the reaction is thermally initiated only, then eq 26 is rearranged to
R, =
(",[RCHO(b)I[O,(b)l + k,'[RCHO(b)l2[Oz(b)1l
2127
2k8
x
[RCHO(b)l (27) If the reaction is heterogeneously inititally by s-Co3+ only, then eq 26 is revised to eq 28 based on the neglecting of thermal initiation.
0
80 120 160 Time, min Figure 1. Typical product composition of propionaldehyde oxidation using Co-type resin as catalyst. Concentration of propionaldehyde 1.85M; temperature 283 K, oxygen flow rate 200 mumin; stirring rate 800 rpm; volume of solution 150 mL; Co-type resin 0.6 g. 40
the concentrations of total acid (i.e., the sum of perpropionic acid and propionic acid) and perpropionic acid increased linearly. After the steady reaction stage, the reaction rate slowed down and the concentration of total acid was almost a t a constant; however, the concentration of perpropionic acid reached a maximum and then decreased. The experimental results indicated that the termination of RC03' free radical was getting important and the formation rate of perpropionic acid was smaller than the decomposition rate during this stage. A 29% maximum ratio of concentrations of perpropionic acid to total acid was observed. The maximum ratio was larger than that of homogeneously Co3+ catalyzed reaction system, such as 5.0% for the oxidation of acrolein (Ohkatsu et al., 1967b).
Effect of Initial Propionaldehyde Concentration on Thermal Oxidation. Increasing the initial concentration of propionaldehyde from 1.39 to 2.78 M increased the oxidation rate and ratio of perpropionic acid formation rate (R,) to total acid formation rate (Rt) If the reacion is heterogeneously initiated by s-Mn3+ from 1.5 x to 6.3 x Wmin and 19.3 to 23.3%, only, then eq 26 becomes respectively, as shown in Figure 2. A logarithm plot of oxidation rate against initial propionaldehyde concenKJk3 0.5 gave a straight line with a slope of 1.76 as shown R, = 2k,( ( S - M ~ ~ + ) ~ . ~ [ R C H (29) O ( ~ ) I ~tration .~ in Figure 2. Accordingly, the oxidation rate could be expressed as If the reaction is initiated simultaneously by s-Co3+ and s-Mn3+,then eq 26 can be expressed as R, = 1.08 x 10-4[RCHO(b)11.76 (31) KAd3[s-Co3+1 KJk,'[s-Mn 3f 1 0.5 R, = 2k7 The initialized steps of thermal oxidation are shown 2128 in eqs 6 and 7,in which the activation energy of eq 7 is [RCHO(b>l1.' (30) the lowest and is most favorable to initiate the chain reactions at low temperature and the probability of Results and Discussion collision of eq 6 is the highest and is favorable at low propionaldehyde concentration. The reaction order Product Composition of the Oxidation of Prowould be 1.5 and 2 on the basis of eqs 6 and 7, pionaldehyde. Figure 1is a typical product composirespectively. Comparing the theoretical analysis with tion of the oxidation of propionaldehyde using Co-type the experimental results, eqs 6 and 7 are both possible. resin as catalyst. The reaction was faster after an Increasing concentration of proprionaldehyde increased induction period at the initial stage. Then, the reaction the formation and decomposition of perpropionic acid; took place at a steady state rate from 10 to 60 min, and
k,j
{
+
lx
2526 Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994
-7.5 - 23
h
h 0
5 -8.0
d
C
r;l
- 21
-9.0 1 0.3
1
0.5
I
1
0.7
I
0.9
k
'19 1.1
P
310.3
slope = -9115 Ea = 75.8 kJ/mol
I
40
30
0
-9.0 3.3
3.4
3.5
3.6
i 3.7
1000/T, K-' Figure 3. Effect of reaction temperature on thermal oxidation of propionaldehyde. Concentration of propionaldehyde 2.78 M; oxygen flow rate 200 mlimin; volume of solution 150 mL; stirring rate 800 rpm.
hence an optimum concentration of propionaldehyde was accomplished for getting the maximum RJRt ratio. Below this critical concentration, the ratio of RJRt increased with concentration of propionaldehyde. Effect of Reaction Temperature on Thermal Oxidation. Increasing reaction temperature from 5 to 20 "C significantly increased the oxidation rate from 2 x lop4 to 1.2 x M/min, and the RJRt ratio remained almost constant and was 23.5%as shown in Figure 3. Taking the Arrhenius plot yielded a straight line with slope of 9115, corresponding to an activation energy of 75.8 kJ/mol, as shown in Figure 3. This value of activation energy was reasonable compared with
2.1
2.5
[RCHO], M
Ln [RCHO] Figure 2. Effect of concentration of propionaldehyde on thermal oxidation of propionaldehyde. Temperature 283 K, oxygen flow rate 200 mlimin; volume of solution 150 mL; stirring rate 800 rpm.
1.7
Figure 4. Effect of initial concentration of propionaldehyde on the RdRt ratio of catalytic oxidation of propionaldehyde. Temperature 283 K; oxygen flow rate 200 mumin; volume of solution 150 mL; stirring rate 800 rpm; weight of catalyst 0.5 g.
other systems, such as 70.1 and 64.0 kJ/mol for oxidation of n-butyraldehyde (Chou et al., 1990) and isobutyraldehyde (Lu, 1988) by s-Co3+ resin catalysts, respectively. The ratio of RJRt almost at a constant showed that the formation and decomposition of perpropionic acid insignificantly changed with temperature for the thermal reaction. Effect of Initial Propionaldehyde Concentration on Catalytic Oxidation. Increasing the initial concentration of propionaldehyde from 1.39 t o 2.78 M increased the oxidation rate from 7.1 x to 18.7 x and 6.5 x to 19.2 x M/min using Coand Mn-type resins as catalysts, respectively. The ratio of RdRt increased from 39.8 to 44.2% with the propionaldehyde concentration from 1.39 to 1.85 M, and then decreased to 34.3% when the concentration of propionaldehyde increased to 2.78 M using Co-type resin as a catalyst as shown in Figure 4. A maximum RJRt ratio, 46.8%,at 2.31 M propionaldehyde was observed using Mn-type resin as catalyst. The logarithmic plot of oxidation rates against the initial propionaldehyde concentrations gave two straight lines with slopes of 1.41 and 1.58, and with intercepts of -5.41 and -5.57, respectively, using Co- and Mntype resins as catalysts as shown in Figure 5. The results showed that the reaction rates can be expressed as
R, = 4.47
x 10-3[RCHO(b)1'.41 for s-Co3'
(32)
R, = 3.81 x 10-3[RCHO(b)11.59for s-Mn3+ (33) The experimental results correlated well with eqs 28 and 29. The RJRt ratio significantly increased by using Co- and Mn-type resins as catalysts when compared with that of thermal reaction. This indicated that, applying heterogenized homogeneous Co- and Mn-type resins as catalysts, the yield of perpropionic acid significantly increased. The results also indicated that the Co-type resin showed a greater reactivity in the reaction
Ind. Eng. Chem. Res., Vol. 33,No. 11, 1994 2527
6o
-4.0
-4.3 h
6.e
d
v
2 p:
5 -4.6
\
40 -
2 30 -
-4.9
0 :s-coy+
.:s-Mn -6".W3
0.3
0.5
0.7 0.9 Ln [RCHO]
1.1
Figure 5. Effect of initial concentration of propionaldehyde on reaction rate of catalytic oxidation of propionaldehyde. Temperature 283 K, oxygen flow rate 200 mumin; volume of solution 150 mL; stirring rate 800 rpm; weight of catalyst 0.5 g.
than Mn-type resin. This discrepancy might be due to that the redox potential of Co3+/Co2+was 1.842 V vs NHE, which was larger than 1.51V vs NHE for Mn3+/ Mn2+. Hence, the Co-type resin was more effective in the initiation step to generate the RCO' free radical, eq 3, than the Mn-type resin, eq 4. Accordingly, the Cotype resin was more efficient to catalyze the reaction and developed a higher reactivity since the initiation step is the rate-determining step. The difference of selectivity between using Co- and Mn-type resins as catalysts might result from the facts that greater reactivity of the catalyst would increase the concentration of free radicals in the solution while increasing their recombination rate. Also, the Co-type resin showed a more destructive effect on the peroxyl species than Mntype resin. Based on the facts, the Co-type resin showed poor selectivity of the peroxy acid. Similar results were also reported by Ohkatsu et al. (1967a1,who studied the homogeneous Co3+ ion catalyzed oxidation of acrolein. Effect of Reaction Temperature on Catalytic Oxidation. Increasing temperature from 5 to 20 "C increased the oxidation rate from 10.5 x to 38.7 x Wmin and from 12.9 x to 35.3 x Wmin using Co- and Mn-type resins as catalysts, respectively. The ratio of RJRt was almost constant and is 35% using Co-type resin as catalyst. On the other hand, it decreased significantly from 53 to 39% using Mn-type resin as catalyst as shown in Figure 6. Taking the Arrhenius plot gave two straight lines with slopes of -7329 and -5390, corresponding to the activation energies of 60.9 and 44.8 kJ/mol, using Co- and Mntype resins as catalysts, respectively, as shown in Figure 7. These values were reasonable when compared with 45.5,41.1,and 83.2 kJ/mol for oxidation of n-butyraldehyde (Chou et al., 19901,isobutyraldehyde (Lu, 19881, and acetaldehyde (Hwang, 19841, respectively. The results indicated that n-aldehyde of more carbons and branched aldehyde showed lower activation energies which might result from the characteristic of electron donor of alkyl groups. However, more data were needed to confirm the findings. Mn-type resin exhibited smaller
Temp., K Figure 6. Effect of reaction temperature on the RJRt ratio of catalytic oxidation of propionaldehyde. Concentration of propionaldehyde 2.78 M; oxygen flow rate 200 mumin; volume of solution 150 mL; stirring rate 800 rpm; weight of catalyst 0.5 g.
Figure 7. Effect of reaction temperature on the reaction rate of catalytic oxidation of propionaldehyde. Concentration of propionaldehyde 2.78 M oxygen flow rate 200 mumin; volume of solution 150 mL; stirring rate 800 rpm; weight of catalyst 0.5 g.
activation energy than that of Co-type resin. This pointed out that Mn-type resin was favorable for reaction a t low temperature. The results also showed that Mn-type resin was more efficient for the selectivity of perpropionic acid a t lower temperature. Effect of Loadings of Catalysts on the Reaction. Increasing the loading of catalysts from 2.0 to 3.3 g/L increased the oxidation rate from 7.8 x lov3to 10.5 x Wmin and from 8.2 x t o 10.1 x Wmin using Co- and Mn-type resins as catalysts, respectively. The RdRt ratio decreased from 33.4to 29.7% and from 34.8 to 32.5% using Co- and Mn-type resins as catalysts, respectively, as shown in Figure 8.
:
2528 Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994
37
,40
17
38
\ \
16 C
'E \
\
-136
\
E
w33-
0
- 15
0
G
i
2 -
X
___\
29 -
34
w
2
42
rd
14
.:s-co~+ .:s-Mn3'
rate, theoretical :rate, experimental experimental
:R,/Rt,
25
0.3
0.2
0.5
0.4
13
0.6
0
loading, g
Figure 8. Effect of weight of catalyst on the RdRt ratio of catalytic oxidation of propionaldehyde. Concentration of propionaldehyde 1.85 M; oxygen flow rate 200 mumin; temperature 283 K volume of solution 150 mL; weight of catalyst 0.5 g. .:s-Mn3+, Ln(Ri)=0.41Ln(W)-4.31
Ln(Ri)=0.56Ln(W)-4.19
:s-Co3+,
-4.5
-4.6 h
d
t
/I
1
v
'
I
I
-4.9 -1.3
-1.1
-0.9
I
-0.7
I -0.5
Ln W Figure 9. Effect of weight of catalyst on reaction rate of catalytic oxidation of propionaldehyde. Concentration of propionaldehyde 1.85 M; oxygen flow rate 200 mumin; temperature 283 K, volume of solution 150 mL; weight of catalyst 0.5 g.
A logarithmic plot of oxidation rate against the loadings of resin catalyst yielded two straight lines with slopes of 0.56 and 0.41 using Co- and Mn-type resins as catalysts, respectively, as shown in Figure 9. The results can be expressed as
R,
0.015[S-C03+ 30.56
(34)
R,= 0 . 0 1 3 [ ~ - M n ~ ~ I ~ . ~ ~(35) Equations 34 and 35 correlated well with the theoretical analysis ones, eqs 28 and 29. The averaged value of kdk{ was found to be 1.66.
30
60
90
Mn c o n t e n t , wt% Figure 10. Effect of fraction of Mn-type resin on catalytic oxidation of propionaldehyde. Concentration of propionaldehyde 1.85M; oxygen flow rate 200 d m i n ; volume of solution 150 mL; temperature 288 K, weight of catalyst 0.5 g.
Effect of Co-Mn Mixing Type Resin. Increasing the content of Mn-type resin from 0 t o loo%, the to 14.4 x reaction rate decreased from 16.3 x Wmin. However, the RdRt ratio slightly increased from 32.0 to 35.5%as shown in Figure 10. The experimental results were smaller than these expected from eq 30 as shown in Figure 10. Several investigators (Kitajima et al., 1988; Okada and Kamiya, 1981; Shimizu et al., 1982) reported the enhancement of the catalytic activity by the addition of the second metal ion in the homogeneous reaction systems. However, the interactions of Co- and Mn-type resins were negative in this reaction system. The difference between the experimental and theoretical analysis results which were calculated from eq 30 is significant. The interaction between Co- and Mn-type resins, such as electron transfer, was not involved in the theoretical analysis. Also, the regeneration of s-Co3+by peroxy free radical was more difficult than that of s-Mn3+;i.e., the ratio [s-Co3+l/[s-Co2+l was smaller than [s-Mn3+l/[s-Mn2+l.Hence, the reaction rate significantly decreased and the RdRt ratio insignificantly increased with the content of Mn-type resin catalyst. Conclusion The experimental results showed that the yield of perpropionic acid was significantly increased using either Co- or Mn-type resin as catalyst when compared with thermal oxidations. The kinetic models were obtained. The reaction rates were proportional to 1.76, 1.41, and 1.59 orders of concentration of propionaldehyde and the activation energies were 75.8, 60.9, and 44.8 kJ/mol using thermal reaction, Co-type resin catalyst, and Mn-type resin catalyst, respectively. The reaction rates were proportional to 0.56 and 0.41 orders of loading of Co- and Mn-type resins, respectively. A faster reaction was obtained by applying Co-type resin than Mn-type resin as catalyst. However, a higher selectivity of perpropionic acid was obtained by employing Mn-type resin. Mixing of Co- and Mn-type resins did not significantly increase the selectivity of perpro-
Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994 2529 pionic acid. The reaction rate was slower than the theoretical analysis one when Co- and Mn-type resins were mixed and used as catalyst.
Acknowledgment The support of the National Science Council of ROC(NSC78-0402-EOO6-16) and of National Cheng Kung University is acknowledged.
Nomenclature (b) = bulk solution phase
(g) = gas phase ki = rate constants, min-l or (M-min)-l or M-2 min-l KA = adsorption equilibrium constant of propionaldehyde (p) = catalyst particle phase RCHO = propionaldehyde RCOOH = propionic acid RCO3H = perpropionic acid R, = propionic acid formation rate, Wmin R, = perpropionic acid formation rate, Wmin R, = oxidation rate, defined as R, + 2R,, M/min Rt = total acid formation rate, Wmin s-Co3+= Co3+-typeresin catalyst s-Mn3+= Mn3+-typeresin catalyst S = inert surface, m2 Wi = thermal initiation rate, Wmin [ ] = molar concentration, M Greek Letters
a = effective formation constant of eq 3 ,B = effective formation constant of eq 4
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Abstract published i n Advance ACS Abstracts, September
15, 1994.
