Ind. Eng. Chem. Rod. Res. Dev. 1984, 23,44-50
44
Table VI. Thermal Stability of Modified AAP Supports. Single-Point Surface Area (m'/g) after Calcination at T ("C) 500 "C
800 "C
1000
compn 4Mg13AlOAP MgA8AP Mg8AAP A2AP 4Ca13AlOAP ZnA8AP
161 120 340 97 226 109
153 100 225 96 170
0 0
0
-
"C
1100 "C
-
-
95 91
-
-
0
-
mercial catalyst. Because this catalyst was supplied in the form of 1/16-in.extrudates, the test catalyst was formed to the same dimensions. Figure 2 shows the performance of these two catalysts over the course of the reaction. After the initial lining-out period, both catalysts showed little evidence of deactivation. In terms of average conversion per reactor load, the MgAAP-supported catalyst proved somewhat better, yielding an average conversion of 63% as compared with 43% for Ni-3266. Although the length of the test was not sufficient to make predictions as to the expected long-term life of the catalysts, it served as an indication that the experimental catalyst may be commercially viable. Conclusions Modifications of AAP by inclusion of the additional cations Mg, Ca, and Zn lead to supports with high prosities and high surface areas. These supports in combination with nickel result in highly efficient liquid-phase hydrogenation catalysts.
Y+3266 -- AR-43'
1
20
40
80
BO
Acknowledgment
120
100
Time , HI
Figure 2. Comparison of 20% Ni on 4Mg13AlOAP catalyst with commercial reference material. Condition detailed in text.
responding increase in crystallinity. From this, it is clear that the nature of the DTA exotherms is almost certainly the onset of phase separation, leading to crystallization and pore collapse with loss of surface area Studies of the effect of calcination temperature on the surface area of MgAAP have shown that high levels of modifier typically result in less thermally stable materials (Marcelin et al., 1983a). It should be pointed out, however, that although for the materials evaluated, the surface area and porosity properties were not modifier dependent; all the modifiers evaluated belonged to group 11. Those from other groups may indeed have different effecta on the surface properties. The performance of these materials for longer term activity was compared with that of the reference com-
The authors thank J. A. Tabacek, N. A. White, and R. H. Hazlett for their work in the preparation of the catalysts, R. L. Slagle, W. R. Grinder, N. C. George, and V. S. Sikora for performing the activity runs, and D. M. Regent for thermal analysis. Registry No. Magnesium, 7439-95-4; alumina, 1344-28-1; aluminum phosphate, 7784-30-7; nickel, 7440-02-0; calcium, 7440-70-2; zinc, 7440-66-6; cis-2-ethyl-2-hexena1,88288-45-3.
Literature Cited Campelo, J. M.; Garcia, A.; Luna, D.; Marinas, J. M. Appl. Catel. 1982a, 3,
315-325. Campelo, J. M.; Garcia, A.; Luna, D.; Marinas, J. M. Gazz. Chim. Its/. 1982b, 772, 221-225. Marcelin, G.;Vogei, R. F.; Swift, H. E. US. Patent 4365095, 1982. Marcelin, Q.; Vogel, R. F.; Kehi, W. L. "Preparation of Catalysts. 111". Elsevbr Science Publishers 6. V.; Amsterdam, l983a; pp 169-179. Marcelin, Q.; Vogei, R. F.; Swift, H. E. J . Catal. lB83b, 83, 42-49. Newme, J. W.; Heiser, H. W.; Ruseell, A. S.; Stumpf, H. C. "Alumina Properties"; Aiumlnum Company of America: Pittsburgh, PA, 1960. Vogel, R. F.;Marcelin G. US. Patent 4376067, 1983.
Received for review May 25, 1983 Accepted September 9, 1983
Reduction of Nitrobenzene to Aniline Jaime Wknlak' and Miriam Klein oepertment of Chemlcel E
w
~B , " Unhrwelty of the Negev, Beer-Sheva, Israel
Nitrobenzene was hydrogenated to aniline in the liquid phase, using Raney nickel, ruthenium on carbon, rhodium on carbon, rhodium on alumina, and nickel on Inert carrier catalysts. Raney nickel catalysis is a complex process that goes through azoxybenzene and arobenrene lntermedlates. All other catalysts yield aniline directly. Within the experimental range the reaction stopped at the aniline step; no cyclohexylamine was formed. Energy of actlvation for Raney nickel was 14.1 kcal/mol, and for palladium on carbon It was 9.7 kcal/mol. No plausible mechanism was found for reduction with Raney nickel.
Introduction Aniline is an important chemical in the m a n d a d w e of dyes and d-imtion accelerators and It is usu&y manufactured by fiereductionof nitrobenzene CGH5N02 + 3H2
+
CeH5NH2 + 2H20
0196-4321/84/1223-0044$01.50/0
From the data on AGfo of Dean (1973) it is possible to estimate the value of the equilibrium constant of the reaction a~ 1.53 X 1084 at 298 K indicating that the reaction may be considered irreversible for all practical purposes. Gharda and Sliepcevich (1960) studied the hydrogenation of nitrobenzene in the vapor phase at 400 OC over a 0 1984 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 1. 1984
copper catalyst and determined that the rate was proportional to the half-power of hydrogen pressure and nitrobenzene pressure. Rihani et al. (1965) hydrogenated nitrobenzene in the vapor phase at 275-350 OC over nickel and copper catalysts and found the same kinetic behavior as reported by Gharda. They reported an energy of activation of 16.5 kcal/mol. Several works have appeared on the liquid phase hydrogenation of nitrobenzene in the presence of suitable solvents to avoid phase separation. Samuelsen et al. (1950) hydrogenated nitrobenzene with Raney nickel that had been treated with chloroplatinic acid and found that nitrobenzene was converted quantitatively to aniline, without formation of intermediates. Scholnik et al. (1941) investigated the hydrogenation of nitrobenzene and the sodium salt as well as methyl and ethyl esters of nitrobenzoic acids, with Raney nickel activated with platinum chloride. Yao and Emmett hydrogenated nitrobenzene at room temperature and atmospheric pressure with colloidal palladium and rhodium (1959), with colloidal platinum (1961), and h e y nickel (1962). With nondegassed catalysts they found that nitrobenzene hydrogenated directly to aniline and that the rate was first order with respect to hydrogen pressure and that the order with respect to nitrobenzene varied between 0 and 1, depending on the catalyst concentration. The energy of activation was 12-15 kcal/mol when the order of reaction was between 0 and 1 for nitrobenzene, and 0-1.5 kcal/mol when the rate was determined by hydrogen diffusion through the solvent. Yao and Emmett (1959) also explored the influence of solvent nature on the rate and found that with ethanol-water and dioxanewater an increase in the amount of water changed the order of reaction with respect to nitrobenzene from 1 to 0. Taya (1962) used the same solvents in his work on the hydrogenation of p-nitrophenol in the presence of ruthenium and found that an increase in the amount of water increased the rate and changed the order. Litvin et al. (1975) made an extensive study on the influence of solvent on the rate of hydrogenation of p-nitrobenzoic acid with catalysts based on salts of rhodium, palladium, and ruthenium. Several publications claim that the conversion of nitrobenzene to aniline is not straightforward and goes through several intermediates. Yao and Emmett (1962) found that if Raney nickel was first degassed, azoxybenzene was formed together with aniline. Metcalfe and Rowden (1971) claimed that using butanol as a solvent and a palladium-silver alloy as a catalyst the activation energy varied between 5 and 25 kcal/mol depending on the silver content, and that the reaction went through stable intermediates such as hydroxybenzene, phenylhydroxylamine, azoxybenzene, and azobenzene. On the basis of this work Shebaldova et al. (1975) tried to hydrogenate nitrobenzene selectively to phenylhydroxylamine, using catalysts based on rhodium, palladium, and cobalt complexes. No aniline was produced, but azoxybenzene was found in increasing amounts. According to their results the following mechanism was proposed C,H,NO, + C,H,NO + C,H,NHOH -+ C,H,NH,
.1
J.
C,H,N=NC,H,
.1 0
Aniline was the only product when the catalyst was changed to iron or nickel. Debus and Jungers (1959) tried to describe the hydrogenation reaction of nitrobenzene by a complex scheme involving nitrosobenzene, azoxybenzene, azobenzene,
45
10% OV-17on ~achromQ 170'-2X)*C, 3'C/min Injection port 28OoC FID 2604 c P o Q d - B a c k e r 417
-
I
Figure 1. Typical GLC analysis.
phenylhydroxylamine, and hydrazobenzene. They found that their nickel catalyst deactivated strongly duiing the process probably by an oxidation step. On the basis of all these observations they proposed a mechanism similar to that of Haber (1898) considering that the relative rate of hydrogenation varied as follows: cgH a O >> CeHbNO2 > CeH5NHOH >> C G H ~ N and H ~ also C6HbN=NCeH, > CeHbN=N C&5 > CeHbNHNHCeHk 10 A recent publication of Burge et al. (1980) discusses the possible intermediates when the catalyst is Raney nickel. The Haber mechanism was adopted and the rate of disappearance of nitrobenzene was justified with zero-order kinetics. Rate constants were calculated for the different paths. By way of summary, it can be said that the hydrogenation of nitrobenzene has been studied in a wide range of conditions, in the liquid and vapor phase, with and without solvent, with different catalysts, and that its mechanism has not been fully elucidated. It is the purpose of this work to provide additional experimental evidence toward the possible mechanism. Equipment and Procedures Hydrogenation runs were made in a dead-end 3/4-gal batch autoclave, Model AF 150, manufactured by Autoclave Engineers for a working pressure of 5000 psig at 650 O F . A description of the experimental setup and the operating procedure have been given elsewhere (Wisniak et al., 1974). Samples were taken at prescribed intervals and analyzed by gas chromatography by use of the procedure described by Mejstrikova (1974). The apparatus used was a Packard-Becker Model 417 provided with a hydrogen flame ionization detector and an electronic irtegrater. The glass column was 6 f t long, 4 mm in i.d., filled with 10% OV-17 on 80/100 mesh Chrom Q. Operating conditions were 280 OC in the injector and in the detector. Column temperature was programmed from 170 t o 250 OC at 3O/min. Quantitative analyses were performed by using 2-chloro-4nitrotoluene dissolved in the ratio 1:4 in benzene as the internal standard. A typical chromatogram appears in Figure 1. Nitrobenzene, CP grade, was purchased from Frutarom, Israel. Raney nickel (W2) was obtained from Doduco Chemie, Elsenz, Germany. Platinum metal catalysts were purchased from Engelhard Industries, Newark, NJ, as 5% active metal on active carbon or alumina and had a bulk
46
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23,No. 1, 1984
Table I. Range of Operating Variables
-
920R PM 0 67%Raney-Ni
catalyst concentration: 2-20 g/L of nitrobenzene (Raney nickel) 0.25-1 g/L of nitrobenzene (palladiumic) pressure: 80-800 psig temperature : 100-210 "C agitation: 420-1300 rpm initial volume: 500-1500 mL
170°C 5 t
200PSig
@\
\
k/2 3=69D3(min-'
c
0
170'C 20ops1g
-
05"
-
0
a, c
1
i
6 01
A 1nC:InCokt olnCV=lnCoVo-kt
100
50
p7\ j ~
20
40
60
8c
100
120
ii0
150
200
250
Time i m i n l
Figure 3. Typical reaction with first-order kinetics. 1
101
160
Time [minl
Figure 2. Typical experiment with Raney nickel.
density of 28-31 lb/ft3 and surface of 1020 m2/g (Pd/C), 1036 m2/g (Ru/C), 976 m2/g (Rh/C), and 1190 m2/g (Ru/A1203). Catalyst G-49 was based on copper chromite; it contained 33% copper, 27% chrome, 11% barium, and was obtained from Girdler Sudchemie Katalysator GmbH, Munich, Germany. All catalysts were used as is without prior treatment. In all the following figures percentage catalyst refers to bulk catalyst per unit volume of nitrobenzene.
Results and Discussion About 80 runs were conducted int he variable range described in Table I. Analyses of the samples by GLC and NMR indicated the presence of nitrobenzene, aniline, azobenzene, and azoxybenzene only, and failed to detect other intermediates such as nitrosobenzene, phenylhydroxylamine, and hydrazobenzene. Typical results appear in Figures 2 and 3. It can be seen that the initial rate of nitrobenzene hydrogenation can be described reasonable well by the pseudo-first-order yeaction ( l / V ) ",/de = dCNB/dB = -kCNB (1) Influence of Agitation Rate. This parameter was studied in order to determine the conditions under which the rate was controlled by the physical or the chemical resistance. The results for h e y nickel reported in Figure 4 for two temperatures are representative of the general behavior that agitation speeds above 900 rpm did not affect the rate of reaction. These results, together with those obtained at different catalyst loadings, indicated that for agitation speeds above 900 rpm the system was probably controlled by the chemical reaction. Influence of Volume Changes. The hydrogenation of nitrobenzene in the liquid phase is somewhat unusual in that the changes in specific gravity that take place may cause an increase in volume of almost 24% for total conversion. This phenomenon affects not only the mathematical analysis of the process but may also change the nature of the agitation regime during the course of a given run. In order to study its physical significance,several runs were made at a fixed set of operating conditions while the
Agitation [R.F?M.l
Figure 4. Influence of agitation rate (Raney nickel).
920R PM 1339aRaney-NI 170%
0
2OOPSl g
; q , / , 0
a
0
,
500 Volume
loo0
,
;
1500
lmLl
Figure 5. Influence of volume change.
original amount of nitrobenzene was changed from 500 to 1500 mL (at 500 mL the impeller was located at the surface of the liquid phase). Most of the runs made in this work were made with an initial volume of lo00 mL and, as shown in Figure 5, the change in the initial rate constant is not significant. Another interesting problem that arose in this work was the opposing phenomena of volume increase because of reaction progress and volume decrease because of sampling. It was found that the net effect was a volume increase only if the initial rate constant (eq 1) was greater than 6 X min-'. Anyhow, it was found that for a larger portion of each run the change in volume could be described by a linear function with time V = V, + a0 (2)
Ind. Eng. Chem. Prod. Res. Dev., Val. 23, No. 1, 1984 47
-
920 R PM
4-
m Catalyst
2
[ g l L NE]
a c
10 0.5 2 5 5%Rh/AbO3 2
G-49 5% Pd/C 5%Rh/C
* c 0 0
A
c
A
0
0
1
I
Time
CminJ
Figure 6. Comparison between Catalysts.
E :
E
1
'0
Catalyst Raney-Ni
920RPM 2oopslg
c1
T e m p e r a t u r e I°C I
Figure 9. Influence of temperature (Raney nickel). 4 0-
920R P M 4gRaney-N& NB 2oopslg
C o t a l y s t weight [ g / ~NE1
Figure 7. Influence of catalyst loading ( h e y nickel).
where Vo is the initial volume and a is a constant. For a constant volume reaction eq 1 can be integrated to In C = In Co- kt (3) while if the volume varies according to eq 2 the integration changes to In CV = In CoVo- k t (4) The calculated values of C according to eq 2 and 4 appear in Figure 3 and show that both equations yield essentially the same results, particularly for the initial period. Catalyst Nature and Concentration. No reaction occurred with ruthenium on carbon and G-49 (copper chromite) catalysts. Rylander and Cohn (1960) reported the same result for ruthenium, althought Taya (1962) was able to hydrogenate p-nitrophenol with this catalyst. It is interesting to note that although copper chromite is unable to hydrogenate nitrobenzene in the liquid phase it will do it in the vapor phase (Rihani et al., 1961; Charda and Sliepcevich 1960). Figure 6 compares the activity of the different catalysts and from it we can infer that their activity changes in the order: 5% Pd/C > 5% Rh/C > 5% Rh/A1203 > Raney-Ni > G-49. Experiments with Raney nickel were conducted at 150 and 170 "C in the range 2-20 g/L of nitrobenzene (Figure 7) and with palladium on carbon at 170 "C and 0.25-1.0 g/L of nitrobenzene (Figure 8). For all catalysts except h e y nickel the reduction of nitrobenzene to aniline was direct and no intermediate products were detected. Figures 7 and 8 indicate that for each catalyst there is a linear range of concentration where the rate may be assumed to be chemically controlled. Temperature. The influence of this parameter was investigated with Raney nickel and 5% Pd/C catalysts. From Figure 9 it can be seen that for b e y nickel the rate increases up to about 170 "C and then starts to decrease. An Arrhenius plot of the same graph (Figure 10) yields an energy of activation of 14.1 kcal/mol in the range 1W170
r
20-
.-C
E 'N? \
0 X
c C
0 c
m C
0
0
t 1.9 21) 2J 2 2 2.3 2 4 2 5 2 6 2 7 2 8
Temperature 103/T1
