Cyclohexanone and cyclohexanol are important intermediates in the
manufacture of caprolactam (serving as a monomer for nylon 6 polymer
formations) and adipic acid (serving as a monomer for nylon 66 polymer
formation; Berezin et al., 1966). The oxidation of cyclohexane is
carried out industrially at a temperature of 150-180[degrees]C and
pressure of 1.0-1.6 MPa in presence of Co salts (naphthenate, stereate,
oleate) as catalyst. The cyclohexane conversion is kept low (about 3-4%
per pass) as the cyclohexanol and cyclohexanone formed are more
susceptible for further oxidation to C[O.sub.2] (Berezin et al., 1966;
Emanuel et al., 1967). In literature, catalytic oxidation studies have
also been conducted using oxidants such as hydrogen peroxide, t-butyl
hydrogen peroxide (TBHP) other than molecular oxygen (Arends et al.,
1997; Carvalho et al., 1997; Schuchardt et al., 2001). Catalyst systems
studied other than cobalts salts are metal oxides, metal cations
incorporated in inorganic matrices such as silica, alumina, zirconia,
active carbon, zeolites (Lin and Weng, 1994) aluminophosphates
(Sakthivel and Selvam, 2002), and CoAPO-5 catalyst. The use of
carboxylic acids (except formic acid) as the solvent is necessary and
the use of propionic acid gives the highest reaction rate (Steeman et
al., 1961). Heterogeneous catalyst of cyclohexane exhibit leaching of
active metal ions, extreme reaction conditions (2 MPa pressure and
177[degrees]C temperature), and low activity (Suresh et al., 1988a). An
induction time, generally observed in the case of air oxidation of
cyclohexane, is reduced by adding promoters or co-reactants such as
acetaldehyde, cyclohexanone, cyclohexanol, and azobis (isobutyronitrile;
AIBN; Wen et al., 1997).
The mechanisms (see Figure 1) suggested in the literature assume
that cyclohexyl hydroperoxide (CHHP) is the intermediate formed in the
presence of transition metal salts (Suresh et al., 1988b; Tolman et al.,
1989; Wen et al., 1997) and is a multistage, free radical chain
reaction, comprising of initiation, chain propagation, and chain
termination step. Tolman et al. (1989), Spielman (1964), and Alagy et
al. (1974) developed a reaction scheme consisting of 154 reactions which
is impractical to analyze as it requires the determination of as many
number of rate constants simultaneously with high accuracy. Hence lumped
kinetic models which require lesser rate constants (Gange et al., 1981;
Pohorecki et al., 1992, 2001; Ponec, 2001; Anisia and Kumar, 2007) are
useful in analyzing reaction data.
[FIGURE 1 OMITTED]
In our present work, a macrocyclic binuclear monometallic copper
complex has been synthesized and is ionically bonded to the zirconium
pillared montmorillonite clay through ion exchange. The oxidation of
cyclohexane using heterogeneous complex catalyst without solvent and
cocatalyst has been studied in the temperature range 145-200[degrees]C.
In this article, it is shown that the Cu-Cu Homonuclear macrocyclic
complex catalyst serves as an effective catalyst for the oxidation of
cyclohexane and gives faster reaction with product specificity different
from Fe-Cu complex catalyst reported in our earlier work (Shul'pin,
Synthesis of CuCuL1 2([CH.sub.3]COO)
[O.sub.2][N.sub.2][C.sub.6][H.sub.4]).sub.2]] Macrocyclic Complex
The 2,6-diformyl-4-methylphenol needed for the macrocyclic complex
was prepared following the procedure given in literature (Serwicka and
Bahamwoski, 2004). The NMR Spectrum of the dialdehyde that we prepared
shows singlets at 11.42 (phenolic), 10.2 (aldehydic), 7.74 (aromatic),
and 2.36 ppm (methyl) and is consistent with the assigned structure and
matches with that given in literature (Serwicka and Bahamwoski, 2004).
In order to prepare the macrocyclic ligand, the
2,6-diformyl-4-methylphenol is reacted with 1,2-phenylenediamine in two
stages as follows and this gives two identical N202 sites on the formed
[FIGURE 2 OMITTED]
To a 50 ml, of NN-dimethylformamide at 40[degrees]C,
2,6-diformyl-4-methylphenol (1.95 g, 0.012 mol) and 1,2-phenylenediamine
(0.65 g, 0.006 mol) were added. To this solution cupric acetate (2.4 g,
0.012 mol) was added and the solution was stirred till the cupric
acetate dissolved completely. The solution was kept for 1 h and then
diethyl ether was added after which a precipitate appeared. The
precipitate was collected by filtration, dried and its FTIR spectrum in
Figure 2a shows the presence of functional groups C=N at 1533
[cm.sup.-1] and C=0 at 1668 [cm.sup.1].
The CuCuL1' (1.8 g, 0.0034 mol) obtained from the previous
step was dissolved in 30 ml, of methanol and to this solution,
1,2-phenylenediamine (0.37 g, 0.0034 mol) was added. The solution was
kept for 1 h and to this, diethyl ether was added. The precipitate that
appeared was collected by filtration and dried. The FTIR spectrum shown
in Figure 2b gave C=N at 1512 [cm.sup.-1] while a weak C=O peak
appearing at 1664 [cm.sup.-1].
[FIGURE 3 OMITTED]
Preparation of the Heterogeneous Catalyst
The acid (using HCl) treated montmorillonite was procured from
Ashapura Minechem Ltd. (Mumbai, India) and was first pillared using
zirconium ions and then was intercalated with the complex as shown in
Figure 3. The clay (20 g) was subjected to swelling by adding water (1
L) to the clay, and stirring it for 5 h and the mixture was finally
centrifuged and dried. In the next step, the clay was treated with NaCl
solution (1 M) and was aged for 24 h. The 20 g clay was separated,
dried, and then refluxed with freshly prepared zirconium oxychloride
(0.1 M) solution for 24 h at 100[degrees]C to obtain zirconium pillared
montmorillonite. It was separated and dried after loading zirconium salt
and its final weight was 28 g (an increase of 8 g). The final step is
the intercalation of the complex in the clay layers and is shown in this
figure. The clay (20 g) from this step was taken and refluxed with the
Cu-Cu complex (1 g) dissolved in acetonitrile (250 mL) for 24 h at
80[degrees]C. The final catalyst thus obtained was separated, washed
with acetone, dried and an increase in weight of 0.9 g was observed.
The oxidation reactions were performed in a high-pressure stainless
steel reactor with a capacity of 300 ml, equipped with gas delivery
system and sampling lines. The reactor was initially charged with 100
ml, cyclohexane, 1 g of catalyst, and 0.35 MPa oxygen, then heated to
the required temperature for the desired reaction time using oxygen as
the oxidant. An on/off controller was used for controlling the
temperature with a chrome alloy thermocouple for temperature sensing.
The products obtained after reaction were analyzed by gas chromatography
(GC) using a fused silica capillary column (0.25 mm x 50 m long film
having thickness 0.25 [micro]m) with flame ionization detector and the
gas chromatography-mass spectroscopy (GC-MS) was carried out using
Shimadzu QP-2000 instrument.
Test for the Absence of Cyclohexyl Hydroperoxide in the Reaction
The presence of CHHP in the product mixture can be demonstrated by
adding excess triphenylphospine to the product formed due to which the
former is converted to alcohol and can be detected as a peak
corresponding to the alcohol. The GC analysis of the reduced sample
confirmed the presence of CHHP molecule (Gange et al., 1981;
Shul'pin, 2002). In the presence of our catalyst, on carrying
similar experiments by adding triphenylphospine, the peak intensity of
the cyclohexanol in the GC analysis of the original product and the
reduced sample remains unchanged. Thus, it was concluded that in our
case there is no CHHP in the product mixture.
CHARACTERIZATION OF THE CATALYST
FTIR Analysis of the Complex
The FTIR analysis was carried out on a Bruker Vector 22 instrument
in the 4000-400 [cm.sup.-1] wave number range. The samples were ground
with KBr and pressed to 1 mm thick film. Examination of the FTIR spectra
was useful in showing the formation of the complex and its various
intermediates based on the frequencies of the C=N (1533 [cm.sup.-1]) and
C=O bond (1668 [cm.sup.-1]). The C=O bond weakens in the final step of
the complex synthesis when CuCuL1' is reacted with 1,
CHN Analysis of the Macrocyclic Complex
The CHN analysis was carried out in an elemental analyzer (CE 440
Leimann Labs, Inc., Exeter Analytical Inc., North Chelmsford, MA).
Helium was used as the carrier gas and 3-5 mg of the sample was required
for this analysis. The percent of Carbon, Hydrogen, and Nitrogen present
in the complexes were experimentally determined (Carbon 57.6%, Hydrogen
3.9%, and Nitrogen 6.9%) and these values were compared with calculated
theoretically. Since the complex was prepared using cupric acetate the
complex was assumed to have (C[H.sub.3]COO-) group and its molecular
formula was taken as CuCuL1 [(C[H.sub.3]COO).sub.2]
[C.sub.6][H.sub.4]).sub.2]] and the theoretical values were calculated
as Carbon 57%, Hydrogen 3.91%, and Nitrogen 7.83% which was within 5% of
the experimental values.
Thermogravimetric Analysis (TGA)
The TGA analysis was done using Perkin-Elemer instrument in
[N.sub.2] atmosphere. The CuCuL1 complex was heated from 40 to
900[degrees]C at the rate of 10[degrees]C/min and it was found that the
complex was stable upto 250[degrees]C (Figure 4). Similarly the TGA of
the final catalysts was done by heating the sample from 50 to
800[degrees]C at the rate of 10[degrees]C/min and it was found that it
was stable till 600[degrees]C (Figure 5). One can explain the enhanced
stability from the binding of the complex in the clay as follows. As
shown in Figure 6, the montmorillonite clay comprised of negatively
charged layers composed of two tetrahedral Si-O sheets. These formed
sandwiched octahedral Al sheet with oxygen atoms at the apex shared by
the octahedra with the tetrahedra. The excess negative charge was due to
the partial substitution of the [Al.sup.3+] by [Mg.sup.2+] and in order
to achieve electroneutrality, the layer charge is compensated by the
presence of cations such as [Na.sup.+] and [Ca.sup.2+] in the
interlayers (Bedioui,1995; Serwicka and Baharnwoski, 2004). These are
held together by weak dipolar and van der Waal forces and the distance
between them is known as basal spacing or c-spacing (Bedioui, 1995). In
Figure 6, the complex has been shown to be within the clay and the
energy of interaction between them is equivalent to the energy needed to
break an ionic bond. There has been a considerable interest in the
literature to predict the state of adsorbate in porous material and
determine the phase equilibria of these (Gelb et al., 1999). In order to
model these, it was assumed that the liquid was in a cage formed by the
porous substances. The state of the adsorbate depended upon the pore
geometry, the level of interaction between the liquid and pores and the
chemical and geometrical heterogeneity. The observed chemical and
thermal stability of the complex ionically bonded in the final catalyst
may well be attributed to the cage (Figure 6) effect produced by the
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
[FIGURE 7 OMITTED]
Energy Dispersive X-Ray Analysis (EDAX)
The EDAX analysis was carried out using FET QUANTA 200 Scanning
Electron Microscope (SEM) and for this, the samples were first coated
with gold under vacuum. It was found that the final catalysts contained
4.66 wt% copper.
Small Angle X-Ray Diffraction Analysis
Small angle X-ray diffraction measurements were done on ARL
X'TRA X-ray diffractometer (Thermo Electron Corporation, Waltham,
MA) equipped with Cu K[alpha] ([lambda] = 0.154 nm) radiation. The
voltage and the current applied to the X-ray tube were 45 kV and 20 mA,
respectively. The sampling width was set at 0.05[degrees] and the
scanning speed was 3[degrees]/min (2[theta]=2[degrees]-30[degrees]). The
X-ray diffraction patterns of the original montmorillonte clay and the
final catalyst (CuCuL1 complex supported on montmorillonite clay) are
given in Figure 7. The d-spacing was calculated from the 2[theta] value
of the peak corresponding to plane (001) and it was found that the
d-spacing of the original montmorillonite was 16.35
[Angstrom](2[theta]=5.4[degrees]) while the d-spacing of the final
catalyst was 30.84 [Angstrom](2[theta]=2.86[degrees]). From this, it
could be concluded that after the complex was loaded on montmorillonite
there was an increase in its d-spacing and hence the complex was
successfully intercalated between the layers of the clay.
RESULTS AND DISCUSSION
It was first demonstrated that there was no oxidation reaction in
presence of copper nitrate salt. For this, cyclohexane was charged with
the copper salt in the batch reactor, pressurized with oxygen and then
reacted. The reactor was found to give no conversion of cyclohexane. The
oxidation of cyclohexane with molecular oxygen in presence of Cu complex
catalyst was conducted in the temperature range 145-190[degrees]C to get
a high conversions. The above temperature range was chosen because below
145[degrees]C, the conversion was very low while above 190[degrees]C,
though the conversion was high, a large amount of undesired products (D)
were formed. From the GC and GC-MS analysis it was found that
cyclohexanone was formed as the major product while the by-products were
cyclohexanol and cyclohexene along with the undesired product (D). Based
on the feed and the product concentration the % overall cyclohexane
conversion = [N.sub.RC]/[N.sub.RF] x 100, % cyclohexanone selectivity =
[N.sub.PC]/[N.sub.RC] x 100, and % cyclohexanone yield =
[N.sub.PC]/[N.sub.RF] x 100 were calculated. In these, [N.sub.RC] was
the number of moles of cyclohexane consumed, [N.sub.RF], the number of
moles cyclohexane fed and [N.sub.PC], the number of moles of
cyclohexanone formed. Similarly the selectivity and the yield for
cyclohexanol and cyclohexene were calculated. The reaction was conducted
for 8 h and a drastic change in conversion and yield were observed
during the first 2.5 h of reaction. The overall conversion increased
from 9% to 23.6% when the temperature was increased from 145 to
190[degrees]C (480 min reaction time). At 145[degrees]C, only
cyclohexanone was formed as the product and after 480 min, the
conversion was 9% and the selectivity towards the formation of
cyclohexanone was 90.5%. When the temperature was increased to
160[degrees]C, cyclohexanol and cyclohexene were formed in small amounts
along with cyclohexanone as the major product. With increase in
temperature, the selectivity towards the formation of cyclohexanone and
cyclohexanol decreased. Cyclohexene was formed only in small amounts and
its selectivity was below 10% in the temperature range studied. The
yield of cyclohexanone and cyclohexanol increases with increase in
temperature so the decrease in the selectivity can be attributed to the
increase in rate of formation of the undesired product (D).
[FIGURE 8 OMITTED]
In our earlier work (Anisia and Kumar, 2007) oxidation of
cyclohexane was carried out using Fe-Cu complex catalyst. This gave very
low rate of reaction but highly specific to the formation of
cyclohexanone. In the present Cu-Cu complex catalyst the reaction was
atleast twice as fast but cyclohexene and cyclohexanol were formed in
addition to the main product. In this case the conversions of
cyclohexane as well as the yield of the products were found to approach
a steady state value with increase in time at all reaction temperatures.
To confirm that the metal complex is not leaching at the reaction
conditions studied, we carried out the following experiments.
I. The oxidation reactions were carried out using the spent
catalyst and the conversion was found to be the same as in the case of
the fresh catalyst. The reaction mass was checked for any copper salt
and was shown to have no metal.
II. From the product, the catalyst was filtered and the product
mixture was once again subjected to the same temperature and pressure.
The overall conversion was measured before and after the catalyst was
filtered and found to be unchanged indicating that there is no leaching
of the active species.
Reaction mechanism that have been found in literature are now
discussed. Moden et al. (2006) have investigated the kinetics and
mechanism of cyclohexane oxidation in presence of MnAPO-5 catalyst. They
have proposed that CHHP is an intermediate in cyclohexanol cyclohexanone
formation. Their combined rates of formation were found to be first
order in ROOH concentration and proportional to the redox active Mn
sites. Nunes et al. (2005) have studied the mechanism and kinetics of
cyclohexane oxidation (with iodosylbenzene) catalyzed by supramolecular
manganese (III) porphyrins. They proposed a mechanism in which the
cyclohexyl radical and OH groups combine rapidly to form cyclohexanol,
which is further oxidized to cyclohexanone. The free radical mechanism
of cyclohexane oxidation occurs through the formation of CHHP
intermediate, which decomposes to cyclohexanol and cyclohexanone
(present in almost equimolar amounts).
Since CHHP was shown not to be formed in the reaction mass, a
reaction mechanism (Figure 8) has been proposed with intermediate in the
adsorbed state. Oxygen is adsorbed on the ligand site (step 1) of the
catalyst and is assumed to reach equilibrium with oxygen to form an
activated species in the reaction mass. The reaction mechanism of this
figure is based on the product distribution obtained from the
experiments that were conducted and some of the pathways leading to the
formation of the products were taken to be reversible in nature as the
concentration of the products approached almost steady state values. The
cyclohexane molecule in presence of the activated catalyst first forms a
cyclohexyl radical anion intermediate, A (step 2). Intermediate A reacts
with oxygen molecule forming a peroxy radical anion intermediate, B with
the catalyst (step 3). This intermediate B forms cyclohexanone as shown
in step 4 of Figure 8. This also can react with another molecule of
cyclohexane forming cyclohexanone and cyclohexanol (see step 5). The
intermediate A reacts with oxygen forming cyclohexanone in step G and
cyclohexanol in step 7 and cyclohexane in step 8. Unidentified side
products (D) are also formed from intermediate A (step 9) and
cyclohexanone (step 10).
[FIGURE 9 OMITTED]
Following the reaction mechanism, we can write mole balance
equations for each component of the reaction as given in Table 1. Using
these equations, we carried out simulation employing Runge-Kutta 4
method (as needed for the Genetic Algorithm (GA) in this specific code
for optimal curve fitting) with [DELTA]t= 0.01 min for numerically
stable solution and calculated the concentrations of each component for
8 h of reaction time. The results were optimized with the experimental
values by using GA code and for this the objective function (OF) (given
below) was written as the sum of squares of the difference of simulated
and experimental values of cyclohexane, cyclohexanone cyclohexanol, and
OF = [([[CH].sub.sim] - [[CH].sub.exp]).sup.2] +
[([[CHone].sub.sim] - [[CHone].sub.exp]).sup.2] + [([[CHol].sub.sim] -
[[CHol].sub.exp]).sup.2] + [([[CHene].sub.sim] -
In this study, the fitness function is taken as 1/(1 + OF) and the
value of a string is known as the string's fitness which is
evaluated. The crossover and mutation probability were varied and
finally taken at 0.9 and 0.05, respectively. The random population was
created using a random number generator with a random seed equal to
0.887. The optimization was done for different temperatures and the
results of fitting the data of 180[degrees]C is shown in Figure 9. The
simulated concentrations overlap the experimental data and the best fit
activation energy and Arrhenius constants were determined and reported
in Table 2 In Figures 10 and 11, the concentrations of the intermediate
species obtained from simulation have been reported and it is observed
that these concentration fall due to fall in amount of oxygen (Figure
12) present in the reaction mass. This suggests that a higher oxygen
pressure would favour the forward reaction giving high yield of the
[FIGURE 10 OMITTED]
[FIGURE 11 OMITTED]
[FIGURE 12 OMITTED]
In the present work, a macrocyclic binuclear monometallic Copper
complex has been synthesized and has been ionically bonded with
zirconium pillared montmorillonite. From the small angle X-ray
diffraction patterns it can be concluded that the complex is
intercalated in the layers of montmorillonite as there is an increase in
the d-spacing (from 16.35 to 30.84 [Angstrom]) after loading of the
complex in the clay. The heterogeneous catalyst, thus prepared, was
stable at high temperatures as confirmed by the TG analysis. This
catalyst has been tested for its catalytic activity with the oxidation
of cyclohexane, in which cyclohexanone was obtained as a major product
and the by-products were cyclohexanol and small amounts of cyclohexene.
It was also confirmed that the metal complex was not leaching under the
conditions in which the reaction was conducted. The overall conversion
increases from 9% to 23.6% when the temperature was increased from 145
to 190[degrees]C (480 min reaction time). A reaction mechanism has been
proposed based on the product distribution. The optimal rate constants
were determined using GA and the concentrations obtained from simulation
were matched with the experimental data.
Manuscript received March 5, 2007; revised manuscript received
March 10, 2008; accepted for publication July 8, 2008
Alagy, J., P. Trombouze and H. Van Landeghem, "Designing a
Cyclohexane Oxidation Reactor," Ind. Eng. Chem. Proc. Des. Dev. 13,
Anisia, K. S. and A. Kumar, "Oxidation of Cyclohexane with
Molecular Oxygen in Presence of Characterized Macrocyclic Heteronuclear
FeCu Complex Catalyst Ionically Bonded to Zirconium Pillared
Montmorillonite Clay," J. Mol. Cat. A Chem. 271, 164-179 (2007).
Arends, W. C. E., R. A. Sheldon, M. Wallau and U. Schuchardt,
"Oxidative Transformations of Organic Compounds Mediated by Redox
Molecular Sieves," Angew. Chem. Int. Ed. Engl. 36, 1144-1163
Bedioui, F., "Zeolite-Encapsulated and Clay-Intercalated Metal
Porphyrin, Phthalocyanine and Schiff-Base Complexes as Models for
Biomimetic Oxidation Catalysts: An Overview," Coord. Chem. Rev.
144, 39-68 (1995).
Berezin, I. V., E. T. Denisov and N. M. Emanuel, "The
Oxidation of Cyclohexane," Transl. by K. A. Allen. Pergamon Press,
Carvalho, W. A., P. B. Varaldo, M. Wallau and U. Schuchardt,
"Mesoporous Redox Molecular Sieves Analogous to MCM-41,"
Zeolites 18, 408-416 (1997).
Emanuel, N. M., E. T. Denisov and Z. K. Maizus, "Liquid Phase
Oxidation of Hydrocarbons," Plenum press, New York (1967).
Gange, R. R., C. L. Spiro, T. J. Smith, C. A. Hamann, W R. Thies
and A. K. Shiemke, "The Synthesis, Redox Properties, and Ligand
Binding of Heterobinuclear Transition-Metal Macrocyclic Ligand
Complexes. Measurement of an Apparent Delocalization Energy in a
Mixed-Valent Copper (I) Copper (II) Complex," J. Am. Chem. Soc.
103, 4073-4081 (1981).
Gelb, L. D., K. E. Gubbins, R. R. Krishnan and M. S. Baratkowiak,
"Phase Separation in Confined Systems," Rep. Prog. Phys. 62,
Lin, S. S. and H. S. Weng, "Liquid Phase Oxidation of
Cyclohexane over CoAlPO-5," Appl. Catal. A Gen. 118, 21-31 (1994).
Moden, B., B. Zhan, J. Dakka, J. G. Santiesteban and E. Iglesia,
"Kinetics and Mechanism of Cyclohexane Oxidation on MnAPO-5
Catalysts," J. Catal. 239, 390-401 (2006).
Nunes, G. S., I. Mayer, H. E. Toma and K. Araki, "Kinetics and
Mechanism of Cyclohexane Oxidation Catalyzed by Supramolecular Manganese
(III) Porphyrins," J. Catal. 236, 55-61 (2005).
Pohorecki, R., J. Baldgya, W Moniuk, A. Kryysztoforski and Z.
Wojcik, "Liquid Phase Oxidation of Cyclohexane-Modeling and
Industrial Scale Process Simulation," Chem. Eng. Sci. 47, 2559-2564
Pohorecki, R., J. Baldgya, W Moniuk, W Podgorska, A. Zdrojkowski
and P. T. Wierzchowski, "Kinetic Model of Cyclohexane
Oxidation," Chem. Eng. Sci. 56, 1285-1291 (2001).
Ponec, V., "Alloy Catalysts: The concepts," Appl. Catal.
A Gen. 222, 31-45 (2001).
Sakthivel, A. and P. Selvam, "Mesoporous (Cr) MCM-41: A Mild
and Efficient Heterogeneous Catalyst for Selective Oxidation of
Cyclohexane," J. Catal. 211, 134-143 (2002).
Schuchardt, U., D. Cardoso, R. Sercheli, R. Pereira, R. S. da Cruz,
M. C. Guerreiro, D. Mandelli, E. V Spinace and E. L. Pires,
"Cyclohexane Oxidation Continues to be a Challenge," Appl.
Catal. A Gen. 211, 1-17 (2001).
Serwicka, E. M. and K. Bahamwoski, "Environmental Catalysis by
Tailored Materials Derived from Layered Minerals," Catal. Today 90,
Shul'pin, G. B., "Metal-Catalyzed Hydrocarbon
Oxygenations in Solutions: The Dramatic role of Additives. A
Review," J. Mol. Catal. A Chem. 189, 39-66 (2002).
Spielman, M., "Selectivity in Hydrocarbon Oxidation,"
AIChE J. 10, 496-501 (1964).
Steeman, J. W. M., S. Kaarsemaker and P. J. Hoftyzer, "A Pilot
Plant Study of the Oxidation of Cyclohexane of Air Under Pressure,"
Chem. Eng. Sci. 14, 139-149 (1961).
Suresh, A. K., T. Sridhar and O. E. Potter, "Autocatalytic
Oxidation of Cyclohexane-Modeling Reaction Kinetics," AIChE J. 38,
Suresh, A. K., T. Sridhar and O. E. Potter, "Autocatalytic
Oxidation of Cyclohexane-Modeling Reaction Kinetics", AIChE J. 38,
Tolman, C. A., J. D. Druliner, M. J. Nappa and N. Herron,
"Alkane Oxidation studies in DuPont's Central Research
Deapartment, Ch. X," In: C. L. Hill, Ed., "Activation and
Functionalization of Alkanes," John Wiley & Sons, Inc., New
Wen, Y, O. E. Potter and T. Sridhar, "Uncatalyzed Oxidation of
Cyclohexane in a Continuous Reactor," Chem. Eng. Sci. 52, 4593-4605
K.S. Anisia and A. Kumar * Department of Chemical Engineering,
Indian Institute of Technology, Kanpur 208016, India
* Author to whom correspondence may be addressed. E-mail address:
Table 1. Rate equation for each component
No Rate equation
1 d[[C.sub.6][H.sub.12]]/dt = -K[k.sub.1][[C.sub.6][H.sub.12]] +
[k.sub.2][[C.sub.6][H.sup.x-.sub.11] - [k.sub.5][[C.sub.6][H.sub.
2 d[[C.sub.6][H.sup.x-.sub.11]/dt = [k.sub.1][[C.sub.6][H.sub.12] -
[k.sub.2][[C.sub.6][H.sup.x-.sub.11] - [k.sub.3][[C.sub.6][H.sup.
x-.sub.11][[O.sub.2]] - [k.sub.6][[C.sub.6][H.sup.x-.sub.11]
[[O.sub.2]] + [k.sub.7][[C.sub.6][H.sub.10]O] - [k.sub.8][[C.sub.
6][H.sub.x-.sub.11][[[O.sub.]].sup.0.5] + [k.sub.9][[C.sub.6][H.
3 d[[C.sub.6][H.sub.11]O[O.sup.x-]]/dt = [k.sub.3][[C.sub.6][H.sup.
x-.sub.11][[O.sub.2]] - [k.sub.4][[C.sub.6][H.sub.11]O[O.sup.x-]
4 d[[C.sub.6][H.sub.10]O]/dt = [k.sub.4][[C.sub.6][H.sub.11]O[O.
sup.x-] + [k.sub.6][[C.sub.6][H.sup.x-.sub.11][[O.sub.2]] - [k.
sub.7][[C.sub.6][H.sub.10]O] - [k.sub.12][[C.sub.6][H.sub.10]O]
5 d[[C.sub.6][H.sub.12]O]/dt = [k.sub.5][[C.sub.6][H.sub.12]][[C.
sub.6][H.sub.11]O[O.sup.x-]] + [k.sub.8][[C.sub.6][H.sup.x-.
sub.11][[[O.sub.2]].sup.0.5] - [k.sub.9][[C.sub.6][H.sub.12]O]
6 d[[O.sub.2]]/dt = -[k.sub.3][[C.sub.6][H.sup.x-.sub.11]]
7 d[[O.sub.2]]/dt = -[k.sub.3][[C.sub.6][H.sup.x-.sub.11][[O.sub.
2]] - [k.sub.6][[C.sub.6][H.sup.x-.sub.11]][[O.sub.2]] + [k.sub.
7][[C.sub.6][H.sub.10]O] - [k.sub.8][[C.sub.6][H.sup.x-.sub.11]
[[O.sub.2].sup.0.5] + [k.sub.9][[C.sub.6][H.sub.12]O] - [k.sub.
8 d[D]/dt = [k.sub.11][[C.sub.6][H.sup.x-.sub.11]] + [k.sub.12]
Table 2. Arrhenius dependence on rate constants as determined from the
Rate constant E/R In A
[Kk.sub.l] 5.80E+03 9.00E+00
[k.sub.2] 6.60E+03 1.60E+01
[k.sub.3] 1.20E+04 2.70E+01
[k.sub.4] 1.00E+04 2.40E+01
k 1.40E+04 3.10E+01
[k.sub.7] 9.30E+03 9.20E+00
[k.sub.8] 1.50E+04 3.10E+01
[k.sub.9] 6.40E+03 4.70E+00
[k.sub.10] 1.50E+04 2.90E+01
[k.sub.11] 2.10E+04 4.00E+01
[k.sub.12] 6.20E+03 -1.10E+00