2571
Ind. Eng. Chem. Res. 1994,33, 2571-2577
Influence of Operational Variables on the Catalytic Behavior of Pt/Alumina in the Slurry-Phase Hydrogenation of Phenol Miguel A. Gutibrrez-Ortiz,' Alfonso Castano, M. Pilar Gonzlez-Marcos, Jose I. GutiBrrez-Ortiz, and Juan R. Gonzilez-Velasco Departamento de Ingenieria Quimica, Facultad de Ciencias, Universidad del Pais Vasco I Euskal Herriko Unibertsitatea, Apartado 644, E-48080-Bilbao, Spain
Hydrogenation of phenol in the liquid phase has been studied. The reaction system was a stirred tank reactor with the catalyst-highly dispersed platinudy-alumina prepared by adsorption from a n aqueous solution of H2PtCls-suspended as a slurry. I n order to prevent the mass transport steps to control the reaction rate, several experiments were carried out varying stirring rate, catalyst particle size, and catalyst weight. In the studied conditions, working with stirring rate above 9 Hz, catalyst particle size below 50 pm,and catalyst weight below 0.5 g assured the kinetic regime. The influence of pressure, temperature, and catalyst platinum content on both initial activity and selectivity was analyzed, for the chemically-controlled regime. Increasing total pressure was found to increase activity almost linearly and to decrease selectivity. The apparent activation energies for phenol consumption and cyclohexanone and cyclohexanol formation (from phenol) were determined.
Introduction Slurry-phase catalytic hydrogenation processes are often preferred industrially to gas-phase processes in the production of chemicals, mainly when selectivity is an important factor to consider (Chauvel and Lefebvre, 1989). In the production of cyclohexanone-intermediate in the manufacture of nylon-6 via ecaprolactam-by selective hydrogenation of phenol, though several gas-phase processes have been described (Grasshoff et al., 1981; Naumann et al., 1977; Oberender et al., 19731, the majority of the production is carried out in liquid phase (Areshide et al., 1971; Chauvel and Lefebvre, 1989; Inventa, 1968; Smeykal et al., 1967). The process requires both high activity and selectivity (GutierrezOrtiz, 19841, and is carried out using mainly group VI11 metal supported catalysts. This kind of processes, in which three phases are present-solid catalyst, liquid solvent, reactant (phenol) and products (cyclohexanone and cyclohexanol), and hydrogen gas-are rather complex, and though they are industrially used, not many studies have been devoted to them (Coussemant and Jungers, 1950; Kiperman, 1986; Kotova et al., 1988, 1991; Takagi et al., 1970; Zwicky and Gut, 1978). In this work, hydrogenation of phenol in the liquid phase carried out in a slurry-phase reactor with platinudalumina catalysts has been studied. The influence of variables such as stirring rate, catalyst weight, and catalyst particle size on reaction rate has been studied from a theoretical point of view and/or experimentally, in order to assure a chemically-controlledregime in the working conditions. The effect of hydrogen partial pressure, temperature, and catalyst metallic content on both initial activity and selectivity to cyclohexanone has been analyzed, for the chemically-controlled regime, and the apparent activation energies for phenol consumption and cyclohexanone and cyclohexanol formation have been determined.
Experimental Section Catalysts. A series of platinudalumina catalysts has been prepared by means of adsorption and anionic 0888-5885194/2633-2571$04.50/0
Table 1. Textural Properties of T-126 y-Alumina fresh calcined S, (BET), m2 g-l 151 186 Vp, cm3 g-l 0.30 0.37 rp (average), nm 3.0 2.9 r p (mode), nm 2.9 2.9 IEPS,pH 8.3 Table 2. Characteristics of Prepared Catalysts catal actual platinum catal particle no. content, wt % size, pm 1 0.63 30 2 0.43 43 43 3 0.91 4 2.86 43 5 0.63 115 6 0.81 235
D 1.19 0.82 1.09 1.06 1.19 1.05
exchange in aqueous solution of hexachloroplatinic acid, HzPtCls, as described elsewhere (Gutierrez-Ortizet al., 1993a,b). A commercial y-alumina, Girder Sud-Chemie T-126, milled, sieved and calcined a t 773 K for 4 h, has been used as catalytic support. The textural properties of the support have been determined by nitrogen adsorption-desorption at 77 K and neutralization at constant pH, and are listed in Table 1. Actual platinum content and dispersion of the prepared catalysts have been determined by atomic absorption spectrometry (AAS) and pulse chemisorption, respectively, and are shown in Table 2. Chemisorption measurements were carried out at 298 K, using hydrogen as adsorbate gas, in a n AMI-1 apparatus. Dispersion was calculated from the chemisorption results, assuming 0.5 Hz molecule adsorbed per surface platinum atom, as the surface to total platinum atom ratio:
D = NSINT
(1)
Kinetic Experiments. Hydrogenation of phenol in the liquid phase was carried out in a stirred tank reactor, described elsewhere (GutiBrrez-Ortiz et al., 1993a), with the catalyst suspended as a slurry. Temperature and pressure were kept constant during each run,and initially 200 cm3 of 50 w t % phenolmethylcyclohexanewas fed to the reactor together with 0 1994 American Chemical Society
2572 Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994
Table 3. Experimental Runs run no. N , Hz catal no. W ,g 1 4.2 3 0.5 2 9.2 3 0.5 3 10.8 3 0.5 4 11.7 3 0.5 5 12.2 3 0.5 6 12.2 1 0.5 5 0.5 7 12.2 8 12.2 6 0.5 9 12.2 3 0.25 10 12.2 3 0.75 11 12.2 3 1.0 3 0.5 12 12.2 13 12.2 3 0.5 14 12.2 3 0.5 15 12.2 3 0.5 16 12.2 3 0.5 17 12.2 3 0.5 2 0.5 18 12.2 19 12.2 4 0.17
P,MPa
T,K
2.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 2.8 1.0 1.96 3.23 2.76 2.78 2.84 2.8 2.8
373 373 373 373 373 373 373 373 373 373 373 373 373 373 333 353 393 373 373
-Tph
x
lo4,mol s-l 1.08 4.27 4.11 4.17 4.03 2.65 1.37 0.97 2.16 6.02 6.02 1.67 3.23 5.19 1.45 3.04 7.16 1.51 2.47
the catalyst. Hydrogen was continuously bubbling in the liquid mixture. The course of the reaction was determined by gas chromatographic analysis of liquid samples let out at intervals. The only products detected in the analysis, together with phenol and methylcyclohexane, were cyclohexanone and cyclohexanol. Activity was obtained by derivation of the curves concentration us time for phenol, cyclohexanone, and cyclohexanol at zero time, and has been expressed as initial reaction rate, ri, and initial turnover frequency, TOF,. Subscript i refers to hydrogen (ri = -rHz), phenol (ri = -rph), cyclohexanone (ri = r,,,), and cyclohexanol (ri = rod. Selectivity, S , was defined as the initial cyclohexanone to phenol reaction rate ratio, ron$-rph. The hydrogenation of phenol to cyclohexanone and cyclohexanol on Ptlalumina catalysts can be represented by the following scheme of reactions:
considered irreversible in the studied conditions. Initially, as no cyclohexanone is present in the reaction medium, the scheme can be reduced to
(3) The reaction system is rather complex, and several mass transfer steps could be limiting the reaction rate: (i)hydrogen diffusion within the gas bubble, (ii) hydrogen gas-liquid film diffusion around the gas bubble, (iii) reactant liquid-solid film diffusion around the catalyst particle, and (iv) reactant pore diffusion within the particle (Koopman et al., 1980; Roberts, 1976; Zwicky and Gut, 1978). In order to study the influence of different parameters on activity and selectivity, as well as to carry out a detailed kinetic study of the reaction system, it is necessary to assure a kinetic regime. Several experiments were performed in order to assure that in the working conditions the reaction rate was kinetically controlled, varying stirring rate from 4.2 to 12.2 Hz, catalyst weight from 0.25 to 1.0 g, and catalyst particle size from 30 to 235 pm.
TOF,h, s-l 4.01 16.85 16.22 16.46 15.89 13.79 7.14 4.47 17.05 15.84 11.88 6.57 12.73 20.49 5.72 12.01 28.25 16.82 9.39
S,molonemo1,h-l 0.546 0.481 0.492 0.494 0.476 0.524 0.660 0.617 0.481 0.615 0.615 0.633 0.530 0.475 0.322 0.365 0.485 0.480 0.661
- p ~ ,x
lo4,mol s-l 2.49 10.76 10.31 10.46 10.17 6.56 3.21 2.32 5.44 14.36 14.36 3.95 7.97 13.12 3.88 8.02 18.01 3.81 5.78
Once the kinetic regime was assured, several experiments were carried out t o determine the influence of pressure between 1.0 and 3.23 MPa, temperature between 333 and 393 K, and catalyst platinum content from 0.43to 2.86 wt % on both activity and selectivity. Table 3 gives a relation of the experimental runs.
Results and Discussion Mass Transfer Studies. The four diffusion steps were considered separately in order t o assure the absence of diffusion control of the reaction rate. Calculative approaches andor a series of experiments were carried out in order to assure the kinetic regime. When calculative approaches were used, their application will be illustrated with an example using the data and conditions listed in Table 4. The results of the example are summarized in Table 5 . When experiments were carried out, conclusions on the absence of mass transfer limitations will be supported with selectivity data. Step i, hydrogen diffusion within the gas bubble, presents no problems in our system, as the experiments were carried out with pure hydrogen. Step ii, hydrogen gas-liquid film diffusion around the gas bubble, has been studied considering two different aspects. On the one hand, this step is known to be strongly influenced by stirring rate, since stirring of the reaction mixture increases gas-liquid interfacial area by dispersing the hydrogen gas in the liquid phase. Taking this into consideration, a plot of the reaction rate us stirring rate, keeping the rest of the conditions constant, will be a horizontal line when there is absence of gas-liquid diffusion control. A similar behavior is expected for selectivity. Figure 1shows, for our system, that no dependence of initial activity and selectivity on stirring rate was found above 9 Hz. On the other hand, the reaction rate can be expressed as proportional to a driving force, concentration, and limited by three separate resistances in series: resistance to gas-liquid mass transport, resistance to liquidsolid mass transport (assuming spherical catalyst particles), and resistance to chemical reaction and pore diffusion (assuming a first order reaction as a first approximation), as follows (Roberts, 1976):
Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994 2673 Table 4. Parameters, Conditions, and References To Determine Mass Transfer Limiting Steps variable
value
referencesa
CH* Cph dp dlnaildlnxi DHZ
2.40 x 10-4molcm-3 mol 5.47 x 4.3 x 10-3crn 1 1.81 x cm2 s-' 5.04 x cm2 s-l
4 experimental experimental assumed Wilke and Chang (1) Wilke and Chang's and Wilke's equations (1) 3 3
Dph
hsHz hsph
g
M P T TPC
VbHl Vbmch Vbph VP W
Xi
e
IC
Pmch ICph
@a e1 Qmch QP Qph Qr
5
2.41 x 10-1 cm s-l 8.71 x 10-' cm s-l 981 cm c2 96.11 g mol-' 2.84 MPa 393 K 634.5 K 14.3 cm3 mol-' 140.4 cm3 mol-' 103.4 cm3 mol-' 0.4 cm3 g-' 0.5 g 1 0.52 3.2 x g cm-l s-' 1.3 x g cm-' s-l 6.3 x g cm-' s-' 1.79 g 0.93 g 0.68 g ~ m - ~ 1.31 g 1.17 g 2.76 g 4
other
Kay-type relation experimental experimental Kay-type relation (1) 1 Le Bas (1) Le Bas (1) experimental experimental assumed experimental Kendall-Monroe (1) Thomas (1) 1 3 Kay-type relation Lu's generalized chart (1) experimental Goyal et al. (1) experimental assumed 2
00
3
~
6
9
0.4
12
Stirring rate, Hz Figure 1. Dependence of -mZ(circles) and selectivity (triangles) on stirring rate (runs 1-5, Table 3).
a (1)Perry and Chilton, 1973. (2) Reid et al., 1987. (3) Roberts, 1976. (4) Shaw, 1987.
Table 5. Results Obtained for Calculative Approaches for Step iii and Step iv, Using Parameters Given in Table 4.
0""'"""""" 0 1
reaction rate, -pi, mol s-1 controlling step reactant estd exptl liquid-solid diffusion (iii) hydrogen 3.08 x 1.80 x phenol 2.54 x 10-l 7.16 x controlling step
reactant
estd. Thiele modulus, 9
pore diffusion (iv)
hydrogen phenol
3.86 0.24
This equation can be rearranged as
A plot of ~ / - T H ~us 1lW for a series of experiments in which all the conditions were held constant except the amount of catalyst added to the reactor is represented in Figure 2. It can be observed that for catalyst weight below 0.75 g (1/W above 1.33 g-l) the data can be represented by a straight line, with a small intercept corresponding to 1/(K &&Y;",g). The reciprocal of this value, about 8 x 10- f mol s-l, corresponds to the rate that would exist if the reaction were controlled by gasliquid mass transport. Thus, gas-liquid mass transport is probably controlling for the higher catalyst weights, and negligible (about 10% or less) for catalyst weight below 0.5 g. This conclusion is supported by Figure 3, in which the effect of catalyst weight on selectivity has been represented. Figures 1and 3 show that the presence of hydrogen gas-liquid mass transport controls produce an increase in the selectivity to cyclohexanone.
3
2
4
1/w, 8''
Figure 2. Plot of 1 4 - r ~ ~ us) 1/W (eq 5) (runs 5, 9, 10, and 11, Table 3). 0.65
0.6
-
1
I
tt
0.45 0.4
i1 0
0.25
0.5
0.75
1
1.25
w9 g Figure 3. Dependence of selectivity on catalyst weight (runs 5, 9, 10, and 11, Table 3). The influence of step iii, liquid-solid film diffusion around the catalyst particle, has been analyzed with calculative approaches. To favor liquid-solid mass transport, the catalyst particle velocity relative to the liquid must be as high as possible. This is favored by stirring rate to a certain extent, because it keeps the particles suspended in the liquid. However, in liquidphase processes the size of the catalyst particles is
2574 Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994
rather small, and they tend to move together with the liquid. Thus, increasing the stirring rate only makes the mixture go faster, even if baffles are being used, not increasing thus the relative particle-liquid velocity. Because of this, in the approaches used to calculate klsi (Roberts, 1976, Zwicky and Gut, 1978) we are using the following expression,
40
- 0.65
-
7-
30
-
obtained from Brian and Hales' correlation, in which the liquid velocity relative to the particles is considered to be the terminal velocity of a particle settling through a fluid, and the obtained value of Klsi has been multiplied by a factor of 2 to correct for the small velocity considered. If liquid-solid mass transport is controlling the reaction rate, and as steps i and ii have been proved not to be controlling, the observed rate would be given by
20
10
Table 5 shows the values of the dimensionless modulus (#) obtained by substitution of the corresponding parameters (Table 4) in eq 8 for both hydrogen and phenol. Usually, absence of pore diffusion control is assumed when values of 4 below 1 are obtained, and very severe pore diffusion control for 4 above 10. Table 5 shows that no pore diffusion control was found for phenol, but for hydrogen no definitive conclusion can be extracted as to the absence of pore diffusion control. Thus, some experiments were carried out varying the catalyst particle size. The results obtained are represented in Figure 4. We can see from Figure 4 that severe hydrogen pore diffusion control is found when catalyst particles above 100 pm are used. When particles below 50 pm were used, reaction rate was found to decrease with smaller particles. This effect is due to the presence of liquidsolid mass transport limitations: the smaller the par-
-8
-
0.5
6
-
0.45
' ~ ~ " " ' " " ' " " ' " ' ~ ~
50
150
100
200
0.4 250
Catalyst particle size, Frn
Figure 4. Dependence of TOFH,(circles) and selectivity (triangles) on catalyst particle size (runs 5-8, Table 3) (filled symbols correspond to run 6 , with the catalyst in a basket). 25 L
1
t
(7) Equation 7 was applied to both hydrogen and phenol in our experimental system. Table 5 shows that the reaction rates estimated for liquid-solid mass transport control are at least 1 order of magnitude above the experimental rates measured. Thus, we can assure absence of liquid-solid mass transport control of the reaction rate. The influence of step iv, pore diffusion within the catalyst particle, has been studied by both calculative approaches (Roberts, 1976; Zwicky and Gut, 1978) and experimentally. The calculative approach consisted in determining the dimensionless modulus 4, related to the effectiveness factor q. Assuming that temperature gradients inside the catalyst particle are negligible-which is very reasonable when working in the liquid phase, with very small catalyst particles, and the pores of the catalyst are filled with the liquid-the dimensionless modulus 4 can be evaluated, for a first order reaction, as
E
0.55
8
-
0
g
-
0 "
7 c
-2
8
0.6
-
20
T~
15
LLpp
e
10
5
0
0
2
1
3
PH , MPa I
Figure 5. Dependence of activity (circles) and selectivity (triangles) on hydrogen partial pressure.
ticles, the lower the relative particle-liquid velocity becomes (see comments to step iii). Because of this, the experiment with the smallest catalyst particles (run 6, Table 3) was repeated, but keeping the catalyst in a basket through which the liquid mixture was continuously circulating, assuring high relative particle-liquid velocity. This experiment is represented by the filled symbols in Figure 4. Thus, pore diffusion control could be considered negligible for catalyst particles below 50 pm. The presence of intraparticle diffusion control has been also found to increase selectivity. Summarizing the results, chemically-controlled regime is assured for stirring rate above 9 Hz, catalyst particle size below 50 pm, and catalyst weight below 0.5 g. The conditions of the following experiments were then chosen assuring the kinetic regime as 12.2 Hz, 43 pm, and 0.5 g. Pressure. The effect of pressure on catalytic activity has been analyzed carrying out a series of experiments in which the rest of the conditions were kept constant. The influence of hydrogen partial pressure, calculated taking into account the vapor pressure of the liquid mixture, on activity is represented in Figure 5 . Figure 5 shows that activity for phenol hydrogenation
Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994 2575 41
I
20
I
I
tl
1
t 4..
-
0 2.4
2.6
2.8
3
ld/T, K" Figure 6. Effect of temperature on activity. Circles, phenol; triangles, cyclohexanone; squares, cyclohexanol.
0.5
Z' 0.45 8 0
B
B oi
0.4
0.35
0.3 320
340
360 380 Temperature, K
400
Figure 7. Dependence of selectivity on temperature.
increased almost linearly as the hydrogen partial pressure was increased, in the studied range. As phenol hydrogenates both to cyclohexanone and cyclohexanol feq 31, the effect of this variable on selectivity to cyclohexanone was also studied. The results obtained are also visualized on Figure 5. Selectivity was found to decrease as hydrogen partial pressure was increased; i.e., hydrogen pressure favors the hydrogenation of phenol to cyclohexanol. Taking into account the effect of hydrogen pressure on selectivity, and considering that the previous studies on mass transfer have shown that hydrogen is always the first reactant to present mass transfer limitations, an increase in the selectivity to cyclohexanone, a t constant pressure and temperature, seems a good indicator of the presence of diffusional controls. Temperature. The influence of temperature on both activity and selectivity was also analyzed. Thus, several experiments were carried out varying operation temperature and keeping the rest of the conditions constant. Hydrogen partial pressure was kept constant considering the effect of temperature on the partial pressure of the liquid mixture. The results obtained are shown in Figures 6 and 7 for activity and selectivity, respectively. Figure 6 is a plot of ln(T0Fi) us 1/T. The slope of the straight lines obtained was used to determine the : phenol consumpapparent activation energies, E ~ for
:A'
4
1 0
0.65
0.45 0.4
0
2.5 Catalyst platinum content, wt%
0.5
1
1.5
2
3
Figure 8. Dependence of TOFph(circles) and selectivity (triangles) on catalyst platinum content.
tion, 27.44 kJ mol-l; for cyclohexanone formation, 35.55 kJ mol-'; and for cyclohexanol formation, 21.93 k J mol-l. The behavior of selectivity to cyclohexanol with temperature is visualized in Figure 7. The figure shows that selectivity increased as the operating temperature was increased. Thus, temperature was found to favor the formation of cyclohexanone. Catalyst Platinum Content. The effect of platinum content in the catalyst on activity and selectivity has also been analyzed. Several experiments were carried out using catalysts with platinum contents in the range 0.43-2.86 wt %. The dependence of activity and selectivity on catalyst platinum content has been represented in Figure 8. In order to prevent very high reaction rates in the system, i.e., very high concentration of active phase in the reactor, that would probably lead to hydrogen gas-liquid mass transfer limitations, only 0.17 g of the 2.86 wt %Pt catalyst was added to the reactor. If all platinum in the surface of the catalyst was equally active, the points in Figure 8 should be in a horizontal line. This is true for the 0.43 and 0.91 wt %Pt catalysts, but the catalyst with the highest platinum content presents lower activity. However, observing the behavior of selectivity, we can assure that a hydrogen mass transfer limitation is controlling reaction rate at this point: liquid-solid and/or intraparticle diffusion, because increasing catalyst platinum content increases the activity per unit weight of catalyst, -rJW, parameter included in eqs 7 and 8.
Summary and Conclusions The slurry-phase hydrogenation of phenol, using highly-dispersed platinudy-alumina catalysts prepared by adsorption from an aqueous solution of HzPtC16, has been studied in a batch reactor. Activity and selectivity have been determined for the initial reaction time. Both theoretical and experimental studies have been realized in order to assure the kinetic regime in the working conditions, analyzing the different mass transfer steps that could be limiting the reaction rate: (i) hydrogen diffusion within the gas bubble, fii)hydrogen gas-liquid film diffusion around the gas bubble, (iii) hydrogen and phenol liquid-solid film diffusion around the catalyst particle, and fiv)hydrogen and phenol pore diffusion within the catalyst particle.
2576 Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994
Mass transfer limitations, as phenol concentration in the liquid is high, have been found t o be mainly due t o hydrogen. The results of activity show that, in our working conditions, the kinetic regime is assured when a stirring rate above 9 Hz, an amount of catalyst below 0.5 g, and catalyst particle size below 50 pm are used, if catalyst platinum content is below 1wt 9%. Selectivity to cyclohexanone was found to be favored by the presence of mass transfer limitations; thus selectivity measurements were used to confirm the kinetic regime. For the kinetic regime, activity in the hydrogenation of phenol has been found to increase almost linearly as the hydrogen partial pressure was increased, in the studied conditions, while selectivity was found to decrease with hydrogen partial pressure. Thus, high hydrogen partial pressures favor the direct hydrogenation of phenol to cyclohexanol relative to cyclohexanone. This indicates that the reaction order for hydrogen is higher in the cyclohexanol than in the cyclohexanone formation. Hydrogen partial pressure is directly related to hydrogen concentration in the liquid, so the presence of hydrogen mass transfer limitations should produce the same effect as lowering hydrogen partial pressure: an increase in selectivity to cyclohexanone. This effect was confirmed by the experiments. The effect of temperature has been analyzed by determining the apparent activation energies, Ea', for phenol hydrogenation, cyclohexanone formation, and cyclohexanol formation. The calculated values are Eaph = 27.44 kJ mol-l, Ea,,, = 35.55 k J mol-l, and Ea01 = 21.93 k J mol-l, respectively. Selectivity has been found to increase as the temperature was increased. No dependence of catalyst platinum content has been found on activity. However, if very active catalysts are used with high metallic contents, mass transfer limitations are likely to appear in the system. As a final conclusion, higher selectivity to cyclohexanone will be obtained when low hydrogen partial pressure and high temperature are used, if we are working in the kinetic regime. Besides, selectivity will be improved if hydrogen mass transfer limitations are present.
N = stirring rate, Hz N S = number of platinum atoms in the catalyst surface per gram of catalyst NT = total number of platinum atoms per gram of catalyst P = total pressure, MPa PI = partial pressure of i, MPa r, = initial reaction rate for i, mol r p = pore radius of the catalyst support, nm S = initial selectivity to cyclohexanone, molonemolph-I S, = BET surface area of the support, m2 8-I T = temperature, K Tpc= pseudocritical temperature, K TOF, = initial turnover frequency for i, s-l Vb, = molar volume of i, cm3mol-l Vp = support or catalyst pore volume, cm3 g-l x, = molar fraction of i in the liquid X I = association parameter for i, dimensionless W = amount of catalyst added to the reactor, g
Acknowledgment
Literature Cited Areshide, K. J.; Sikharulidze, N. G.; Dzhaoshvili, 0. A. Process for Producing Cyclohexanone. British Patent 1,257,607, 1971. Chauvel, A.; Lefebvre, G. Petrochemical Processes. Technical and
The authors wish to thank Ministerio de Educacidn y Ciencia (DGICYT PB90-0645) and Uniuersidad del Pais Vasco1E.H.U. (UPV 069.310 EA2041921 for the
financial support in the realization of this work.
Nomenclature a, = activity of i in the liquid A,1 = gas-liquid interfacial area, cm2 C*H,~ =~concentration of hydrogen in the liquid in equi-
librium with concentration in the gas, mol cm-3
C,= concentration of i in the liquid, mol ~ m - ~ dp = catalyst particle size, cm D = platinum dispersion in the catalyst, defined as NS/NT D, = diffusion coefficient for i in the liquid, cm2 s-l E , = apparent activation energy, kJ mol-I g = acceleration due to gravity, cm s - ~ IEPS = isoelectric point of the solid, pH k,l= gas-liquid mass-transfer coefficient for hydrogen, cm S-1
kist
= liquid-solid mass-transfer coefficient for i, cm s-I k , = first-order reaction rate constant, cm3 s-l g-' M = molecular weight of the liquid, g mol-l M , = molecular weight of i, g mol-I
Greek Letters = effectiveness factor, dimensionless 0 = porosity of the catalyst particle, dimensionless p = liquid viscosity, g cm-1 ssl p, = viscosity of i, g cm-I s-l ea= apparent density of the catalyst particle (pores filled with liquid), g cm-3 el = density of i, g ~ r n - ~ el = liquid density, g cm-3 e p = apparent density of the catalyst particle (pores filled with air), g cm-3 er = actual density of the catalyst particle, g ~ r n - ~ t = tortuosity factor, dimensionless Q, = Thiele modulus, dimensionless Subscripts g = gas H2 = hydrogen i = hydrogen, phenol, cyclohexanone, cyclohexanol, or methylcyclohexane 1 = liquid mch = methylcyclohexane 01 = cyclohexanol one = cyclohexanone ph = phenol s = solid
Economic Characteristics. Znstitut Franqais d u Pitrole Publications; Editions Technip: Paris, 1989; 2 vols. Coussemant, F.; Jungers, J. C. La Cinetique de 1'Hydrogenation Catalytique des Phenols. Bull. SOC.Chim. Belg. 1950,59,295. Grasshoff, E.; Meye, H.; Naumann, H.-J.; Pohl, G.; Prag, M.; Schaefer, H.; Schubert, R. Verfahren zur Selektivhydrierung von Phenol zu Cyclohexanon. German Patent 150,999, 1981. Gutierrez-Ortiz, J. I. Hidrogenacion de Fenol a Ciclohexanona. Eleccion del Catalizador y Estudio Cinetico. W . D . Thesis, Universidad del Pais Vasco/E.H.U., Bilbao, 1984. Gutierrez-Ortiz, M. A.; Gonzalez-Marcos, J. A.; Gonzalez-Marcos, M. P.; Gonzalez-Velasco, J. R. Behavior of Highly Dispersed Platinum Catalysts in Liquid Phase Hydrogenations. Znd. Eng. Chem. Res. 1993a,32,1035. Gutierrez-Ortiz, M. A.; Gonzalez-Marcos, M. P.; Arnaiz-Aguilar, S.; Gonzalez-Marcos, J. A.; Gonzalez-Velasco, J. R. Surface Features and Catalytic Performance of PlatinudAlumina Catalysts in Slurry-Phase Hydrogenation. Znd. Eng. Chem. Res. 1993b,32,2457. Inventa A. G. fur Forschung und Patentvenvertung.Preparation of Cyclohexanone.British Patent 1,125,199, 1968. Kiperman, S. L. Some Problems of Chemical Kinetics in Heterogeneous Hydrogenation Catalysis. In Catalytic Hydrogenation; Cerveny, L., Ed.; Elsevier: Amsterdam, 1986.
Ind. Eng. Chem. Res., Vol. 33, No. 11, 1994 2577 Koopman, P. G. J.; Kieboom, A. P. G.; Van Bekkum, H. Mass Delft Prog. Transport in Liquid-Phase Hydrogenation. - Rep. 1980,>,24. Kotova, V. G.; Murzin, D. Yu.; Zyskin, A. G.; Kul’kova, N. V. Kinetics and Mechanism of Liauid-Phase Hvdroeenation of Phenol. Kinet. Catal. 1991,32, i17. Naumann, H.-J.; Schaefer, H.; Oberender, H.; Timm, D.; Meye, H.; Pohl, G. Entwicklung und Anwendung des Verfahrens der Selektiven Phenolhydrierung fiir die Herstellung von Cyclohexanon im VEB Leuna-Werke ‘Walter Ulbricht”. (Evolution and Use of the Procedures of Selective Hydrogenation of Phenol for the Manufacture of Cyclohexanone in VEB Leuna Werke “Walter Ulbricht”.) Chem. Tech. 1977,29,38. Oberender, H.; Schaefer, H.; Timm, D.; Baltz, H.; Blume, H.; Lunau, J.;Meye, H. Process for the Production of Cyclohexanone by Catalytic Hydrogenation of Phenol. British Patent 1,332,211, 1973. Perry, R. H.; Chilton, C. H. Chemical Engineers’Handbook, 5th ed.; McGraw-Hill: Tokyo, 1973. Reid, R. C.; Prausnitz, J. M.; Poling, B. E. The Properties of Gases and Liquids, 4th ed.; McGraw-Hill: New York, 1987. “
I
Roberts, G. W. The Influence of Mass and Heat Transfer on the Performance of Heterogeneous Catalysts in GasLiquid’Solid Systems. In Catalysis in Organic Synthesis; Rylander, P. N., Greenfield, H., Eds.; Academic Press: New York, 1976. Shaw, J. M. A Correlation for Hydrogen Solubility in Alicyclic and Aromatic Solvents. Can. J . Chem. Eng. 1987,65, 293. Smeykal, K.; Naumann, H.-J.; Schaefer, H.; Becker, K.; Veit, J.; Block, A. Process for the Production of Cyclohexanone by the Selective Hydrogenation of Phenol. British Patent 1,063,357, 1967. Zwicky, J. J.; Gut, G. Kinetics, Poisoning and Mass Transfer Effects in Liquid-Phase Hydrogenations of Phenolic Compounds over a Palladium Catalyst. Chem. Eng. Sci. 1978,33, 1363.
Received for review February 25, 1994 Revised manuscript received J u l y 19, 1994 Accepted July 29, 1994@
* Abstract published in Advance ACS Abstracts, October 1, 1994.
