2212
I n d . Eng. Chem. Res. 1987,26, 2212-2215
Kinetics of the Air Oxidation of 1,2-Dichlorobenzene Suheyda Atalay* and H. Erden Alpay Department of Chemical Engineering, Ege University, Bornova, Izmir, Turkey
The kinetics of the air oxidation of 1,2-dichlorobenzene over a modified Vz05catalyst supported on kieselguhr was studied a t the temperature range 285-355 "C. The results could be described by 1 kinetic model of the redox mechanism of Mars and van Krevelen and by the reaction scheme consisting of a set of parallel reactions. The reaction rate is given as eq 1. The products of the oxidation of 1,2-dichlorobenzene (DCB) are maleic anhydride (MA), 2-chloromaleic anhydride (MCMA), 2,3-dichloromaleic anhydride (DCMA), 1,2,3-trichlorobenzene (TCB), 1,2,4-trichlorobenzene, carbon dioxide, hydrochloric acid, and water (Atalay, 1984). Of these products, especially maleic anhydride, 2-chloromaleic anhydride and 2,3-dichloromaleic anhydride are compounds of industrial importance (Buehler and BossEzrd, 1978; Ishimi et al., 1973; Gosselink et al., 1963; Whitfield and Friedman, 1973). DCMA and MCMA are used in production of fire retardant and antiallergic agents (Schneider et al., 1970). MA is produced by the catalytic air oxidation of benzene (Ioffe and Lyubarskii, 1962); Butler and Weston, 1963; Bielanski and Inglot, 1974), of butene and/or butadiene (Sunderland, 1976; Akimoto and Echigoya, 1975; Ai, 1971), of crotonaldehyde(Church and Bitta, 19631, and of furfural (Murthy and Rajamani, 1974). DCMA is prepared by oxidizing hexachlorobutadiene with SO3 (Simonov and Gazizov, 1978), chlorinating maleic anhydride (Eldred and Young, 1953), or using maleic anhydride and' thionyl chloride in pyridine (Relles, 1972). MCMA is also obtained from molten maleic anhydride and chlorine gas (Milone, 1945). Since these syntheses haven't sufficient industrial importance, in this study the object was to use an alternative source of a starting material for the production of DCMA and MCMA, and the most selective catalyst for the production of DCMA and MCMA was searched. Published data on the oxidation of o-DCB can scarcely be found in the literature. The only published work was a thesis by Akgerman (1977). In this work, gas-phase oxidation of o-DCB was studied over a Vz05 catalyst supported on Ti02 The results of this study showed that this reaction could be used to produce DCMA and MCMA and gave the best selectivity values at the temperature range 300-330 OC. By the addition of phosphorus and molybdenum to the Vz05catalyst, the selectivity of MA formation from butene or benzene was considerably increased (Ai, 1970,1971; Ioffe and Lyubarskii, 1962; Butler and Weston, 1963; Bielanski and Inglot, 1974). For this reason, in searching for the most selective catalyst, V205catalysts modified with MooB and P205as the active component were prepared on silica gel, kieselguhr or y-alumina supports. With these catalysts, selectivity expts. were carried out by holding the o-DCBlair ratio constant while varying the temperature and the weight of catalyst. At the end of the selectivity experiments, the catalyst, having kieselguhr as the carrier, and a composition of 72.45% Vz05,26.46% MOO,, and 1.09% Pz05for the active part, was found to be the most selective for the production of DCMA and MCMA. Following this investigation, kinetic experiments were carried using this selective catalyst at temperatures of 285, 300, 320,330, 340, 355 "C and at different feed flow rates for each temperature, neglecting the effects of heat and mass transfer. 0888-5885/87/2626-2212$01.50/0
Experimental Section The catalytic air oxidation of o-DCB to DCMA and MCMA was performed over the selective catalyst supported on kieselguhr having a composition of 72.45% V205, 26.46% MOO,, and 1.09% P205.The surface area measured by the BET N2adsorption method at -196 "C was 56.366 m2/g. The density of the catalyst measured experimentally was 1890 kg/m3. The catalyst pellets used in this study were cylinder shaped with a diameter of 12 mm and height of 1mm. The pellets were placed in the bed at the center of the reactor after they were divided into four equal parts. The equivalent pellet diameter was 6 mm. The flow diagram of the apparatus used is shown in Figure 1. The reactor was a Pyrex-glass tube of 25-mm i.d. and of 250-mm length. This tube was fitted into an electrically heated furnace, the temperature of which was controlled by a temperature controller. For this reason, an iron-constantan thermocouple which extended into the center of the catalyst mass was used. Since the depth of the catalyst bed and the diameter of the reactor were small, it is not wrong to say that the reactor was operated at isothermal conditions by controlling the temperature at the center of the catalyst bed and that the effect of heat transfer could be neglected. The flows of air and nitrogen were metered through flow meters. The nitrogen stream was passed into a saturator containing o-DCB. The temperature of the saturator was maintained at -1 deg of the desired temperature by an electrical heater controlled by a thermometer and an electronically operated relay. The nitrogen-o-DCB mixture was fed to the reactor through wired Pyrex-glass tubing held at 70-80 "C. Air was also heated similar to the nitrogen-o-DCB stream, and these were directed to the head of the reactor where the gases were mixed before passing down through the catalyst bed. The gas stream leaving the reactor was directed to a trapping system so that the reaction products could be collected for analysis. The trapping system consisted of two Dewar flasks arranged in series. The first trap was cooled with a mixture of ice and salt, and the second was cooled with liquid nitrogen. Between these traps, the sensor of the oxygen analyzer was placed, and the mole fraction of O2 in the gas mixture was measured at regular time intervals. These values were plotted as a function of time, and as a result the mole fraction of O2 at steady state was obtained. The gas leaving the second trap was directed to the atmosphere. At the end of the run (usually a run was of 8-h duration) the liquid and solid phases collected in the trapping system were washed out with acetone and analyzed by a JEOL JGG 1100 gas chromatograph with a flame ionization detector. The column used for the chromatographicanalysis was of stainless steel. 2-m length and 3-mm i.d. filled with Apiezon L or Apiezon M (supported on 80-100-mesh Chromosorb). Nitrogen was used as the carrier gas at a Q 1987 American Chemical Society
Ind. Eng. Chem. Res., Vol. 26, No. 11, 1987 2213
0.14
0.02 O'OL
t I I
I
Figure 1. Apparatus.
3
Table I. List of Experimental Conditionsa 109 x
T,
expt
"C
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
355 355 355 355 340 340 340 340 330 330 330 330 320 320 320 320 300 300 300 300 285 285 285 285
.
L
.
5
.
b
.
7
.
8
9
10
Total volumetric
-
I1
flow rate lml I s 1
Figure 2. Effect of the external diffusion.
FOG-DCB,
yo2 0.1925 0.1905 0.1900 0.1900 0.1935 0.1935 0.1915 0.1915 0.1925 0.1900 0.1920 0.1925 0.1932 0.1905 0.1921 0.1920 0.1952 0.1935 0.1962 0.1945 0.1958 0.1951 0.1953 0.1921
kmol/s
Oweight of catalyst = 2
1O2yoWDCB
1.816 2.747 3.275 4.054 1.709 1.999 4.187 4.645 1.955 2.154 2.468 4.063 2.600 3.617 4.832 7.503 2.234 2.307 3.508 3.951 1.745 3.014 2.457 2.647 X
0.4416 0.6665 0.7937 0.9808 0.4158 0.4860 1.0127 1.1221 0.5227 0.6534 0.6886 1.0315 0.6940 1.0925 1.2819 1.9766 0.5034 0.6162 0.8899 0.9643 0.4244 0.7309 0.5967 0.7705
YOO,
YNl
0.1967 0.1963 0.1960 0.1957 0.1968 0.1966 0.1956 0.1954 0.1953 0.1932 0.1944 0.1949 0.1950 0.1924 0.1938 0.1925 0.1965 0.1952 0.1970 0.1974 0.1968 0.1962 0.1964 0.1936
0.7988 0.7970 0.7960 0.7945 0.7991 0.7985 0.7943 0.7934 0.7994 0.8002 0.8055 0.7947 0.7981 0.7967 0.7933 0.7877 0.7984 0.7986 0.7941 0.7929 0.7990 0.7965 0.7976 0.7987
kg.
pressure of 0.4 kg/cm2. The temperature used for performing the analysis was 140 "C. The oxidation of o-DCB to DCMA and MCMA was studied at temperatures of 285,300,320,330,340, dnd 355 "C and at different feed flow rates. From the calculations reported here, it is observed that these conditions are sufficiently mild to avoid the effects of external and internal diffusions. consequently, it can be stated that the experiments were conducted under conditions where external and internal diffusional resistances were negligible. At the studied temperatures, to explain the reaction mechanism, oxidation products were identified as DCMA, MCMA, MA, TCB, hydrochloric acid, carbon dioxide, and water. All of the experimental conditions were summarized in Table I. All the kinetic runs were performed at atmospheric pressure.
Eliminations of External and Internal Diffusions Before the kinetic experiments were carried, the role of the physical steps of external and internal diffusion was checked. The role of the external diffusion was studied experimentally for the highest temperature (355 "C) by changing the total volumetric flow rate and keeping the catalyst weight and molar flow rate of o-DCB. The results (Figure 2) indicate that at the higher values of the volumetric flow rate of 7-8 mL/s, external diffusion effects
were negligible. This effect was also searched theoretically by the Hougen method (Yoshida et al., 1962) for the highest temperature where the maximum reaction rate was obtained. The role of internal diffusion was studied theoretically by calculating the effectiveness factor for the highest and the lowest temperatures employed. The results show that for this pellet diameter under the range of the parameters used in this study, the effect of internal diffusion could be neglected.
Results Since the kinetic experimental runs were carried under the conditions of the differential reactor, the reaction rate for o-DCB was defined as r,-DCB
= moles of o-DCB reacted/catalyst weight
In the same manner, the reaction rate for product i (MA, MCMA, or DCMA) was written as
ri = moles of o-DCB reacted to give i/catalyst weight With these definitions, kinetic experiments were evaluated. For this reason, molar flow rates of MA, MCMA, DCMA, and other reaction products were calculated iteratively using moles of oxygen consumed. Then the reaction rate of every step was calculated according to the above definitions. In this calculation, the overall oxidation scheme of o-DCB could be indicated as
E
C4C1203
Ce H E 12
C4HClOs
3.502
6.50~
C4H203
+
+ +
2C02 2C02 2C02
6 C o 2 -!- H 2 0
+
+
2H20
+ HCI + + 2HCI
H20
2HCI
Since the stoichiometry of every step in the oxidation of o-DCB shows a 1:l ratio of moles of o-DCB to moles of product i, the amount of product i formed could be taken as the number of moles of o-DCB reacted for the particular step considered. According to this evaluation, calculated reaction rates were given in Table 11. These rates were defined as experimental reaction rates.
Elaboration of the Kinetic Data In the interpretation of the kinetic experiments, the classical redox model of Mars and van Krevelen (1954) which was extensively applied in most of the studies of the hydrocarbon oxidation was used (Calderbank et al., 1977). Reaction rate expressions derived according to the redox
2214 Ind. Eng. Chem. Res., Vol. 26, No. 11, 1987
Table 11. List of Results of the Kinetic Experiments reaction rate, kmol/(kg of catalyst-s) expt
T,OC
102Y(o-DCB)h 0.3977 0.6038 0.7266 0.9148 0.3803 0.4490 0.9589 1.0680 0.4904 0.6154 0.6562 0.9931 0.6664 1.0570 1.2460 1.9390 0.5229 0.5927 0.8620 0.9301 0.4094 0.7105 0.5772 0.7459
356 355 355 355 340 340 340 340 330 330 330 330 320 320 320 320 300 300 300 300 285 285 285 285
1 2
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Y(O2)lm
0.1941 0.1926 0.1921 0.1918 0.1947 0.1945 0.1925 0.1923 0.1933 0.1909 0.1925 0.1927 0.1934 0.1903 0.1917 0.1903 0.1953 0.1937 0.1955 0.1941 0.1958 0.1949 0.1953 0.1921
107r0-DC8 1.388 1.993 2.136 2.112 1.129 1.179 1.731 1.739 0.939 0.954 0.909 1.183 0.812 0.930 1.080 1.122 0.644 0.691 0.865 0.839 0.487 0.659 0.632 0.664
mechanism were applied on the basis of the above-mentioned reaction scheme which was for parallel reactions. The kinetic model considered is represented by the relation r
o
-
(k1
-
+ k 2 + k3 + k 4 ) p m o - D C B k P O 2
-~ (4.5kl ~ ~ + 4k2 + 3 . 5 1 2 3 + 6 . 5 k , ) P m o . ~+c ~kgPno2 (1)
where k,, k,, k,, and k4 are kinetic constants of formation reactions of DCMA, MCMA, MA, and COP,respectively. Likewise, k, is the kinetic constant of the reoxidation step of the catalyst, and Po, are the partial pressures of o-DCB and oxygen, and m and n represent the reaction orders of o-DCB and oxygen, respectively. In the same manner, the reaction rate expressions for DCMA, MCMA, MA, and C02 formation steps may be written as ~ D C M A= rMCMA
=
@kipm0.~c~
(2)
@k2Pmo-DCB
(3)
rMA
Pk3Pmo-DCB
(4)
rco2 =
@k4Pm0-DCB
(5)
where k5Pn0, @
= kpo,
+ ( 4 . 5 k I + 4 k 2 + 3 . 5 k 3 + 6 . 5 k , ) p m , . ~ c ~(6)
For different values of m and n, the kinetic parameters which satisfy 1 - 6 derived for the redox model were evaluated by nonlinear regression based on Powell or Hooke Jeeves methods (Kuester and Mize, 1973) on the objective function N
N
1((ro-DCB)exptl i=l
- ( r ~ - D C B ) ~ a l ~ d+ )z
1=1
((rDCMA)exptl
-
N (rDCMA)calcd)z
+ ,E((rMCMA)exptl - (rMCMA)calcd)* + r=l
N ((rMA)exptl 1=1
- (rMA)calcd)z
ki, k29 k,, kip
- minimum
k5
1OsrDCMA
0.512 1.166 1.734 1.168 0.618 0.656 1.161 1.351 0.272 0.122 0.455 0.417 0.415 0.622 0.578 0.541 0.165 0.150 0.353 0.277 0.117 0.109 0.232 0.114
~@~MCMA 1.131 2.459 2.659 2.495 1.218 1.647 2.674 2.712 0.756 0.942 0.175 1.481 1.208 1.673 1.273 1.589 0.482 0.470 0.847 0.725 0.283 0.328 0.726 0.419
WrMA 0.592 1.196 0.664 0.723 0.422 0.570 0.784 0.744 0.250 0.315 0.446 0.592 0.363 0.518 0.441 0.514 0.158 0.124 0.246 0.198 0.124 0.084 0.229 0.134
107rco, 1.165 1.511 1.630 1.673 0.903 0.892 1.269 1.259 0.812 0.816 0.701 0.934 0.613 0.649 0.851 0.858 0.564 0.617 0.720 0.719 0.434 0.607 0.513 0.597
Table 111. Minimum Responses in the Alternate Models minimum resDonse model 1: model 2: model 3: model 4: T,"C m = n = 1 m = l : n = 0 . 5 m = 0 . 5 : n = l m = n = 0 . 5 355 340 330 320 300 285
74 15 34 19 2 3
74 15 35 19 3 3
570 508 77 116 54 4
Table IV. Kinetic Rate Constants, lO6ki (kmol/(kg of catalyst oatm))" T , "C k, k, k, 355 340 330 320 300 285
0.4048 0.3488 0.1702 0.1453 0.0736 0.0453
0.7695 0.7577 0.4984 0.3865 0.1950 0.1400
0.2711 0.2274 0.1864 0.1242 0.0559 0.0447
k, 5.1842 3.8667 3.6833 2.0138 1.9924 1.7317
586 523 76 120 55 4
k, 1.0916 0.7801 0.4728 0.4542 0.4497 0.4077
"m =,n = 1.
where N is the number of experiments. In the evaluation of these parameters for partial pressures of o-DCB and O,, logarithmic means of the reactor inlet and outlet conditions were used. Models having different values of m and n were searched by using the following criteria: (1)The values of the Tate constants should not be negative. (2) All the constants should be able to be represented by an Arrhenius-type equation. (3) The model should represent the experimental data satisfactorily. The minimum responses in all models tested were collected in Table 111. As it could be seen, models 1 and 2 were the best on the basis of minimum response and were in good agreement with the estimated parameter values. The kinetic rate constants calculated for model 1 were given in Table IV. Models 3 and 4 were evaluated for these kinetic parameters, and these values did not show the expected trend with the temperature change. Discussion and Conclusion The result obtained from models 1 and 2 is that there is a weak influence of the partial pressure of the oxygen
Ind. Eng. Chem. Res., Vol. 26, No. 11, 1987 2215 Table V. Kinetic Parameters
k,, kmol/ (kg of catalysts-atm) kl
k2 k3 k4
k6
hob,kmol/ (kg of catalyst.s.atm) 35.5156 1.7200 1.1868 1.7806 0.3230
Ei, kJ/kmol 83263.89 63841.35 67520.33 54566.01 54166.90
1o4(min response) 73.15 294.75 18.87 8449.07 726.00
on the reaction rate, while the influence of o-DCB seemed to be significant. To make the differential reactor assumption and to neglect the mass-transfer effects, all the experiments were done at a high and nearly constant partial pressure of oxygen. Therefore, the data could be fitted well with an order in oxygen of 1 or Further, this result showed that at the high partial pressures of oxygen, the reaction rate could be taken as pseudo first order in a partial pressure of o-DCB, but at the lower values, the influence of oxygen might be significant. For this reason, model 1 where m = 1, n = 1, could be taken as the best. This was in good agreement with the results obtained for various hydrocarbon oxidation reactions (Calderbank et al., 1977; Froment and Bischoff, 1979). The kinetic parameters evaluated for model 1were given in Table V. As can be seen in this table, the activation energies were quite similar to those given in the literature. In the air oxidation of benzene to maleic anhydride over the vanadium catalyst supported on kiselguhr, the activation energy was found to be 17 kcal/mol (Sampson and Shooter, 1965), and in this work the activation energies were found to be 19.9, 15.27, 16.15, and 13.05 kcal/mol for DCMA, MCMA, MA, and C02 steps, respectively. The values of the kinetic parameters found in this study were quite large when compared with the ones of the earlier study (Akgerman, 1977). It is hard to make a comparison between the values of the parameters since different catalysts were used in the two studies. The only result of this comparison could be stated as follows: The reaction was faster on a catalyst having TiOz as a support. In Table IV, the rate constant for the catalyst reoxidation step was smaller than that for the catalyst reduction step. This means that the catalyst reoxidation step is the controlling step. This is in accordance with the observations of Mars and van Krevelen (1954). Nomenclature E = activation energy, kJ/kmol F' = molar flow rate at reactor inlet, kmol/s KO = preexponential factor, kmol/(kg of catalyst-s-atm) K,, K,, k S ,k4, kS = kinetic constants for dichloromaleic anhydride, chloromaleic anhydride, maleic anhydride, carbon
dioxide, and catalyst reoxidation steps, kmol/(kg of cata1yst.s.atm) P = partial pressure, atm r = reaction rate, kmol/(kg of catalyst-s) T = temperature, "C W = catalyst weight, kg y = mole fraction yo = mole fraction at reactor inlet yo2 = oxygen mole fraction at steady state Subscripts
calcd = calculated DCMA = dichloromaleic anhydride exptl = experimental lm = Logarithmic mean MA = maleic anhydride MCMA = chloromaleic anhydride N2 = nitrogen o-DCB = o-dichlorobenzene O2 = oxygen Registry No. Vz05,1314-62-1; 1,2-dichlorobenzene, 95-50-1. Literature Cited Ai, M. Bull. Chem. Soc. Jpn. 1970,43, 3490. Ai, M. Bull. Chem. SOC.Jpn. 1971,44, 761. Akgerman, A. Assoc. Prof. Dissertation, Ege University, Izmir, Turkey, 1977. Akimoto, M.; Echigoya, E. Bull. Chem. SOC.Jpn. 1975, 48, 3518. Atalay, S. Ph.D. Thesis, Ege University, Izmir, Turkey, 1984. Bielanski, A.; Inglot, A. Bull. Acad. Pol. Sci. 1974, 22(9), 785. Buehler, N.; Bosshard, H. Ger. Offen. 2804, 1978. Butler, J. D.; Weston, B. G. J. Catal. 1963, 2, 8. Calderbank, P. H.; Chandrasekharan, C.; Fumagalli, C. Chem. Eng. Sci. 1977, 32, 1435. Church, J. M.; Bitta, P. Ind. Eng. Chem. Prod. Res. Deu. 1963,2,61. Eldred, N. R.; Young, D. M. J. Am. Chem. Soc. 1953, 75, 4338. Froment, G. F.; Bischoff, K. B. Chemical Reactor Analysis and Design; Wiley: New York, 1979. Gosselink, K. R.; Fay, H. E.; Loop, F. M. U S . Patent 3113, 1963. Ioffe, I. I.; Lyubarskii, A. G. Kinet. Katal. 1962, 3, 261. Ishimi, M.; Takanose, K.; Suzuki, T. Japan Kokai 7 356985, 1973. Kuester, L. J.; Mize, J. H. Optimization Techniques with Fortran; McGraw Hill: New York, 1973. Mars, P.; van Krevelen, T. Chem. Eng. Sci. Suppl. 1954, 3, 41. Milone, C . R. US. Patent 2 391 261, 1945. Murthy, M. S.; Rajamani, K. Chem. Eng. Sci. 1974, 29, 601. Relles, H. M. J. Org. Chem. 1972, 37, 3630. Sampson, R. J.; Shooter, D. Oxid. Combust. Reu. 1965, 1223. Schneider, J. A.; Pews, J. A.; Herring, R. G.; Jefferson, D. Ind. Eng. Chem. Prod. Res. Dew 1970, 9(4), 559. Simonov, V. D.; Gazizov, R. T. U.S.Patent 4067887, 1978. Sunderland, P. Ind. Eng. Chem. Prod. Res. Deu. 1976, 15(2), 90. Whitfield, R. E.; Friedman, M. Text. Chem. Color. 1973, 5(4), 76. Yoshida, F.; Ramaswami, D.; Hougen, D. A. AIChEJ. 1962,8(1), 5.
Received for review December 3, 1985 Revised manuscript received December 19, 1986 Accepted August 6, 1987
