Ind. Eng. Chem. Res. 1987, 26, 1746-1750
1746
Registry No. Nafion-H, 39464-59-0; Indion-CXC-125, 69772-32-3; ZrOz, 1314-23-4; T i 0 2 , 13463-67-7; 2-H3CC6H4CH3, 95-47-6; C6H5CH=CH2,100-42-5; iron oxide, 1332-37-2; triflic acid, 6196-95-8; 1493-13-6; 1-(3,4-dimethylphenyl)-l-phenylethane, 1-(2,3-dimethylphenyI)-l-phenylethane, 81749-28-2.
t
W X
n
Literature Cited
0 W
z
W
a
>. VI
U.
0
z
0 a > W 0 z
s TIME (hours]
+ -
Figure 8. Comparison of activity of various acid catalysts: mole ratio of o-xylene:styrene, 5:l; catalyst, 5% (w/w) styrene (10% in the case of zirconia and titania); temperature, 100 "C; (A)zirconia triflic acid, (0) CER. (650 "C), (4) titania (500 OC), ( 0 )Nafion-H, (0)
The special behavior of zirconia deserves further investigation to determine the structure of acidic sites. The activity of zirconia was very comparable with that of CER and Nafion-H. In view of its lower cost and higher thermal stability as compared to the resin catalysts, the zirconia catalyst indeed appears promising for industrial applications. Acknowledgment
Arata, K.; Hino, M. Chem. Lett. 1978, 4, 325-326. Arata, K.; Hino, M. J . Chem. SOC.,Chem. Commun. 1979a, 24, 1148-1149. Arata, K.; Hino, M. Chem. Lett. 1979b, I O , 1259-1260. Arata, K.; Hino, M. Chem. Lett. 1979c, 5, 477-480. Arata, K.; Hino, M. J . Chem. SOC.,Chem. Commun. 1980, 18, 851-852. Arata, K.; Hino, M. Chem. L e t t . 1981, 12, 1671. Chaudhari, D. D.; Rajadhyaksha, R. A. J . Am. Oil Chem. SOC.1987a, in press. Chaudhari, D. D.; Rajadhyaksha, R. A. Bull. Chem. SOC.Jpn. 198713, in press. Eldon, E. S. US.3272879, 1966; Chem. Abstr. 1966, 65, 18417e. Friedman, B. S.; Patinkin, S. H. Friedal Crafts and Related Reactions; Olah, G. A . , Ed.; Interscience: London, 1964; Vol. I I , Part I , p 57. Gotoh, M.; Sato, A.; Shimizu, I. Ger. Offen. 3028 132, 1981: Chem. Abstr. 1981, 94, 174602d. SU 882980, Grigor'ev, V. V.; Grushin, A. I.; Prokofev, K. V. U.S.S.R. 1981; Chem. Abstr. 1981, 96, 145886k. Hasegawa, H.; Higashimura, T. Polym. J . ( T o k y o ) 1980, 12(6), 407-409. Malan, E. J . Appl. Chem. Biotechnol. 1972, 22, 959-965. Matsuzaka, E.; Sato, A.; Shimizu, I. Ger. Offen. 2818578, 1978; Chem. Abstr. 1978, 91, 39100m. Mitsubishi Gas Chemical Co., Inc. Jpn. Kokai Tokkyo Koho 80 113724, 1980; Chem. Abstr. 1980 94, 19186811. Torii, M. Ger. Offen. 2315256, 1973; Chem. Abstr. 1973, 80,84829q.
D.D.C. thanks the CSIR, New Delhi, for the award of a Senior Research Fellowship.
Received for review August 20, 1986 Accepted J u n e 11, 1987
Selective Catalytic Hydrogenation of Nitrobenzene to Phenylhydroxylamine Shrikant L. Karwa and Rajeev A. Rajadhyaksha* Department of Chemical Technology, University of Bombay, Matunga, Bombay 400 019, India
Selective hydrogenation of nitrobenzene to phenylhydroxylamine (PHA) is investigated on platinum-on-carbon catalyst under a wide range of operating conditions. Addition of dimethyl sulfoxide has been observed to improve the selectivity significantly. Selectivity to PHA was found to he higher a t lower reaction temperatures but was unaffected by change in hydrogen pressures from 7 to 21 atm. The selectivity was observed to he widely different in different solvents. The selectivity could be correlated with the dielectric constants of solvents. Selective hydrogenation of substituted nitroaromatics was also investigated. T h e selectivity to the respective hydroxylamines could be correlated with the electron-releasing tendency of the substituent. Palladium-on-carbon catalyst showed no selectivity for PHA. Selective catalytic hydrogenation of nitrobenzene to phenylhydroxylamine (PHA) is a reaction of considerable industrial importance since PHA can undergo rearrangement to yield a variety of industrially important products. In acidic conditions, depending on the reaction medium, PHA can be rearranged to a variety of substituted anilines such as p-aminophenol, p-anisidine, p-phenitidine, and p-chloroaniline (Rylander, 1979). Under alkaline conditions, PHA reacts with nitrosobenzene to form azoxybenzene (Russell et al., 1967) which undergoes simultaneous hydrogenation t o form hydrazobenzene. Hydrazo*Author to whom correspondence should be addressed.
0888-5885/87/2626-1746$01.50/0
benzene can be subsequently rearranged in acidic medium to benzidine (Venkataraman, 1952). Substituted nitroaromatics can undergo similar reactions to form trisubstituted aromatic compounds (Sone et al., 1980) and substituted benzidines (Lubs, 1955). Selective hydrogenation of nitroaromatics to corresponding hydroxylamine also has been exploited in several organic syntheses (Roblin and Winnek, 1940; DiCarlo, 1944; Fanta, 1953; Cavil1 and Ford, 1954; Sugimori, 1960; Schipper et al., 1961; Taya, 1966; Aeberli and Houlihan, 1967; Kauer and Sheppard, 1967; Yale, 1968; Barker and Ellis, 1970; Hodge , 1972). The most extensive study of partial hydrogenation of nitrobenzene to PHA has been reported by Rylander et al. C 1987 American Chemical Society
Ind. Eng. Chem. Res., Vol. 26, No. 9, 1987 1747
(1970). The study revealed that platinum-on-carbon is the most suitable catalyst for the reaction, and the selectivity can be considerably enhanced by addition of dimethyl sulfoxide (Me2S0)as a catalyst promotor. However, in this study, very high catalyst loading (5% by weight nitrobenzene of 5% Pt-on-C) was employed and all experiments were carried out at room temperature and hydrogen atmospheric pressure. The present paper reports an investigation of the above reaction under a wide variety of operating conditions. The reaction is investigated up to a hydrogen pressure of 21.4 atm. The effect of temperature on the rate and selectivity is also investigated. Various solvents have been employed and the selectivity to PHA is shown to be strongly dependent on the nature of solvent. The effect on selectivity is successfully correlated with molecular properties of the solvents. The effect of loadings of catalyst was also studied, and it is shown that the reaction can be carried out with as low as 0.15% (w/w) loading of the catalyst.
Experimental Section Experiments were carried out in a magnetically driven autoclave fitted with a gas-inducing type of agitator. The appropriate quantities of nitrobenzene, solvent, and catalyst were added to the clean and dry autoclave. A typical reaction charge consisted of 150 g of nitrobenzene and 350 g of solvent. Before heating the autoclave to the required temperature, it was repeatedly purged with hydrogen at room temperature. Once the required temperature was reached, it was pressurized with hydrogen and stirring was started. As hydrogen was consumed in the reaction, it was repleted so as to maintain a constant pressure. Temperature was controlled within fl K by regulating cooling water flow and the rate of heating. Samples of 2-3 mL were withdrawn through the sample outlet at regular time intervals and were analyzed on a Perkin-Elmer Series 10 HPLC using a 25-cm-long 10-pm Bondpack column. The eluent used was water-methanol mixture a t a flow rate of 0.027 mL/s. Methanol percentage in water was linearly increased from 0% to 80% in 480 s to yield a good resolution of PHA, aniline, nitrobenzene, hydrazobenzene, azoxybenzene, and azobenzene in the given order. All reagents used were of analytical grade. Results In light of the earlier results of Rylander et al. (1970)) the reaction was first investigated on platinum-on-carbon catalyst. The typical variation of the product composition at 14.6 atm and 333 K is shown in Figure la. During the early stages of the reaction, conversion of nitrobenzene to PHA (reaction 1) and to aniline (reaction 2) appears to occur as parallel reactions. As may be expected, PHA concentration exhibits a maximum. The maximum occurs a t almost complete conversion of nitrobenzene. This is followed by conversion of PHA to aniline (reaction 3). The reaction was subsequently investigated in the presence of Me,SO. Figure 1b shows the progress of reaction in the presence of Me2S0. The addition of MezSO clearly enhances the rate of formation of PHA relative to that of aniline although the overall rate of conversion of nitrobenzene is reduced. Figure 2 shows the variation of rate and selectivity with concentration of Me2S0. The selectivity of PHA increased from 26% without Me2S0 to 70% with 1.6% (w/w) MezSO. Further increase in MezSO concentration hardly improved the selectivity. The rate of reaction, however, dropped by a factor of 1.5-3 with addition of Me2S0. Subsequent experiments were carried out with 1.6% (w/w) MezSO concentration, which appears to be optimum.
1.0
VI
0.8
a D
?
-
0.6
NitrobRnrRne
-
-0- PHA Aniline
c
z
2
0.L
x
0.2
0 0
1200
ZLOO
L 00
3600
T i m e , s c c s __*
i b l with D M S O , I . 6 % I s / a )
A
Nilrobrnztnr
0
PHA
0
Aniline
-
I \
T"l,
S.CI
Predicted product
r
Figure 1. Typical variation of product composition. Reaction conditions: temperature, 333 K; pressure, 14.6 atm; initial concenimpeller tration, 30% (w/w)methanol; catalyst loading, 0.3% (w/w); speed, 33 rps.
:I 6
0
,
2~'
1.6 DMSO O o " c l n t l e t , o " ,
,
3.2 '/.1W/W)
,
L.0
+
,
L.8
;
p 1200
0.2
Figure 2. Effect of Me2S0 on rate of reaction and selectivity to PHA. Reaction conditions: temperature, 333 K; pressure, 14.6 atm; initial concentration, 30% (w/w)methanol; catalyst loading, 0.3% (w/w); impeller speed, 33 rps.
The effect of impeller speed on the rate of hydrogenation was investigated in the range 18-33 rps. The impeller speed was not observed to have any effect on the rate which indicates the absence of gas-liquid mass-transfer limitation in the given range of impeller speed. The catalyst loading was varied between 0.15% and 0.3% (w/w)
1748 Ind. Eng. Chem. Res., Vol. 26, No. 9, 1987
-10-
-11-
-12-
A€,=
12.38 k c a l / g m o i e
.s 1-13-
Time,rtcr
__I,
Figure 5. Effect of initial concentration. Reaction conditions: temperature, 333 K; MezSO concentration, 1.6% (w/w);catalyst impeller speed, 33 rps. loading, 0.3% (w/w); Table I. Effect of Solvents"
3.1
3.0
1x
.Kt
lo',
-
I
3.2
Figure 3. Arrhenius plots. Reaction conditions: 14.6 atm; initial concentration, 30% (w/w)methanol; Me2S0 concentration, 1.6% (w/w); catalyst loading, 0.3% (w/w); impeller speed, 33 rps. Hydropen pressure :
----
0
1 . 8 kg/cm' 21.4 kg/cm' 0
1200
2400
3500 Tim.,
SICS
1800
0
,/
6000
0
0
0
I
/
7200
-p
Figure 4. Effect of hydrogen pressure. Reaction conditions: temperature, 333 K; initial concentration, 30% (w/w)methanol; Me2S0 catalyst loading, 0.3% (w/w); impeller concentration, 1.6% (w/w); speed. 33 rps.
based on nitrobenzene. The rate was found to increase linearly with the loading without affecting selectivity. Below 0.15% (w/w) catalyst loading, the rate and selectivity were observed to be very poor which may be because of the presence of small quantities of catalyst poisons in the reagents. The reaction was studied a t different temperatures in the range 313-333 K. Figure 3 shows Arrhenius plots which indicate that reactions 1, 2, and 3 have activation energies of 9.72, 12.38, and 12.73 kcal/gmol, respectively (kinetic parameters were evaluated by using kinetic expressions described in the Discussion section). The selectivity to PHA improved from 70% a t 333 K to 78% a t 313 K. The effect of hydrogen pressure on reaction rate is shown in Figure 4. Reactions 1 and 2 were found to be dependent on pressure, while reaction 3 was independent.
solvent no solvent benzene ethyl acetate isobutyl alcohol methanol 18% w/w aq. methanol
dielectric const 2.27 6.00 18.70 32.6
max selectivity to PHA, mol % 15.6 11.5 22.0 67.0 70.0 76.0
time required to reach max PHA concn, s 9600 11100 9720 6300 2700 2280
'Reaction conditions: temperature, 333 K; pressure, 14.6 atm; initial concentration, 30% (w/w);catalyst loading, 0.3% (w/w); MezSO concentration, 1.6% (w/w); impeller speed, 33 rs.
The effect is quantitatively described by the kinetic expression given later. Selectivity to PHA was found to be independent of hydrogen pressure. Experiments were carried out a t different initial concentrations of nitrobenzene in methanol. The results obtained with initial concentrations in the range 20-50% (w/w) are shown in Figure 5. The amount of catalyst was increased in proportion to nitrobenzene concentration so that the loading of catalyst on the basis of the reactant remained constant. As can be seen from the figure, the rates of reactions 1 and 2 were unaffected by change in the nitrobenzene concentration; however, that of reaction 3 showed significant dependence. Contrary to the expectations, no change in selectivity to PHA was observed. But when no solvent was employed, the maximum selectivity dropped to 15.6%. The reaction was also investigated in various solvents. The maximum selectivity for PHA observed in different solvents and the time required to reach the same are given in Table I. It is apparent that the selectivity to PHA was significantly affected by the nature of solvent. Palladium-on-carbon (2% (w/w)) showed no selectivity to PHA with or without Me2S0. The hydrogenation of nitrobenzene was found to be zero order with respect to nitrobenzene, and aniline was observed to be the only product. The selective hydrogenation of o-nitrochlorobenzene, o-nitrotoluene, and o-nitroanisole was also investigated. The maximum selectivity to the corresponding hydroxylamines and the time required to reach the same are compared in Table 11. In all the above experiments, no formation of byproducts like azoxybenzene, azobenzene, and hydrazobenzene was observed.
Ind. Eng. Chem. Res., Vol. 26, No. 9, 1987 1749 Table 11. Selective Hydrogenation o f Substituted Nitroaromatics" max selectivity time required to hydroxylamine, to reach max selectivity, s nitroaromatics mol %
70 59 45 28
nitrobenzene o-nitrochlorobenzene o-nitrotoluene o-nitroanisole
2700 3720 4800 6300
Reaction conditions: temperature, 333 K; pressure, 14.6 atm; initial concentration, 30% (w/w)methanol; catalyst loading, 0.3% (w/w);MezSO concentration, 1.6% (w/w); impeller speed, 33 rsp.
Discussion The reaction product profile (Figure 1)tends to indicate that aniline and PHA are formed simultaneously from nitrobenzene and reactions 1 and 2 probably occur in parallel. Addition of MezSO suppresses the rate of both of the reactions; however, its effect on reaction 2 is considerably more significant, which leads to improved selectivity for PHA. Conversion of PHA to aniline occurs in series with reaction 1; it appears that adsorption of nitrobenzene is very strong as compared to that of PHA and hence reaction 3 is completely suppressed until nitrobenzene is almost fully consumed. This results in maximum PHA concentration at almost total conversion of nitrobenzene. Thus, the key to improve the selectivity to PHA seems to lie in suppressing reaction 2 and not reaction 3. On the basis of the above, it appears reasonable to divide the progress of the reaction into two parts. In the first part, only reactions 1 and 2 occur. The end of this period is marked by complete conversion of nitrobenzene. In the subsequent part, reaction 3 takes place. Thus, the reaction scheme for the present system can be described as follows: part
I
6
NHOH
+ 2H2
2@
+
H,O
(1)
(2) part
11.
The kinetic data were fitted to simple power law expressions on the basis of the above scheme. The kinetic expressions so obtained are part I YNHOHU)
= ~J'H,CNO~
Y N H ~ ( I )= -?NO?
W H ,
= klPH2CN02 + k 2 P H 2
part I1 Y N H ~ ( I I )= -YNHOH(II)
=
k,
The above expressions were found to be valid between 313 and 333 K and 7.8 and 21.4 atm of hydrogen pressure. The data obtained a t a constant concentration for Me2S0 of 1.6% (w/w) were used for the above kinetic analysis. The variation of concentrations predicted on the basis of the above kinetic expressions is compared with the experi-
mental data in Figure lb. The excellent agreement between the two lends further support to the proposed reaction scheme. The agreement was equally good in most other experiments. The results show that the selectivity of the reaction is significantly affected by change of solvent. Solvents are known to influence the hydrogenation reactions for a variety of reasons (Rylander, 1980; Cerveny and RugiEka, 1982; Rajadhyaksha and Karwa, 1986). A recent study by us (Rajadhyaksha and Karwa, 1986) reports that thermodynamic effects may play an important role in the effect of solvents. In light of this, it was considered worthwhile to investigate the correlation between thermodynamic interaction and the selectivity. It was not possible to estimate the activity coefficient of PHA in the various solvents since the UNIFAC parameters for the NHOH group are not reported. The dielectric constant of the solvent was therefore considered a parameter representative of intermolecular interaction. The values of dielectric constants of the various solvents are included in Table I. A very good correlation between the dielectric constant and the maximum yield of PHA is apparent. The correlation can readily be interpreted as follows. As the dielectric constant is increased, the interaction between PHA and the solvent becomes progressively favorable, which is also reflected in the increased solubility of PHA. This probably aids desorption of PHA in the solvent, preventing its further hydrogenation to aniline. The effect of initial concentration shown in Figure 5 is apparently inconsistent with the kinetics discussed above. On the basis of the kinetic expressions, one would expect that the rate of reaction 1should increase with an increase in initial concentration, while the rates of reactions 2 and 3, which are independent of concentration of nitrobenzene, should remain unaffected. This should result in an increase in selectivity for PHA. However, the results show that the rates of reactions 1 and 2 were unaffected, while that of reaction 3 showed an increase with an increase in the initial concentration of nitrobenzene. No simple explanation can be offered for this discrepancy. The kinetic expressions and the rate constants (Figure 3) accurately fit the data of a large number of experiments carried out with an initial concentration of 30% (w/w) nitrobenzene in methanol. The results presented in Figure 5 would suggest that the rate constants are probably dependent on the initial concentration of nitrobenzene, while the forms of the kinetic expressions remain applicable as suggested by the nature of variations of concentrations of different species with time. Such a change of rate constants with initial concentration has to be attributed to the accompanying change in the thermodynamic properties of the reaction medium. It is already shown that the rate constants of the different reactions involved in the above system are strongly affected by the change in solvent. The change in initial concentration from 20% (w/w) to 50% (w/w) can cause a significant change in the properties of the reaction medium similar to that caused by a change in solvent. Such an effect on the rate constant due to a change in initial concentration has been previously reported (Rajadhyaksha and Karwa, 1986). The additional substituent groups on nitrobenzene were also found to have significant effect on rate and selectivity. Both the rate and selectivity seem to decrease with the increasing electron-releasing capacity of the substituent. The presence of electron-releasing groups probably increases the strength of adsorption of the nitrogen-containing group on the metal. This would result in a decrease in the rate of desorption which may be expected to de-
Ind. Eng. Chem. Res. 1987, 26, 1750-1753
1750
crease the reaction rate and also increase the possibility of further hydrogenation of the hydroxylamine. Conclusions 1. The results indicate that formation of aniline, which is the principal side reaction in selective synthesis of PHA, occurs in parallel with the formation of PHA. Conversion of PHA into aniline is insignificant until all the nitrobenzene is converted. 2. Addition of MezSO suppresses the above parallel reaction and hence improves the selectivity. 3. The selectivity to PHA decreases with an increase in temperature but is unaffected by hydrogen pressure. 4. Solvent has significant effect on selectivity to PHA. The selectivity shows good correlation with the dielectric constant of solvent. 5. The other substituents on the benzene ring also have a marked effect on rate and selectivity. The rate and selectivity seem to decrease with an increase in electron-releasing effect of the substituent. Nomenclature C N O p = concentration of nitrobenzene at time t , gmol/cm3 k l = rate constant of reaction 1,cm3/[(ntm)(gof catalyst)(s)] k , = rate constant of reaction 2, gmol/[(dtm)(gof catalyst)(s)] k 3 = rate constant of reaction 3, gmoi/[(g of catalyst)(s)] P H I= hydrogen pressure, atm t = time, s Greek Symbols = rate of formation of aniline in part I, gmol/[(g of
YNH,(I)
catalyst)(s)] = rate of formation of aniline in part 11, gmol/ [ (g of catalyst)(s)] YNHOH(I) = rate of formation of PHA in part I, gmol/[(g of catalyst)(s)] +/NHOH(ID = rate of disappearance of I-XA in part 11, gmol/ [ (g of catalyst)(s)] - 7 N 0 2 = rate of disappearance of nitrobenzene, gmol/[(g of catalyst)( s ) ] YNH,(II)
Re&tW NO.PHA, 100-65-2; CsHbNO2, 98-95-3; Pt, 7440-06-4; (CHJZSO, 67-68-5; C&&3, 71-43-2; H3CCOZCH2CH3, 141-78-6; (H,C)ZCHCHzOH, 78-83-1; CHSOH, 67-56-1; H20, 7732-18-5; 2-OzNCsH,C1,88-73-3; 2-O~NCsH4CH3,88-72-2;~ - O ~ N C G H ~ O C H ~ , 91-23-6; P-HONHC,H,OCH,, 35758-76-0; 2-HONHC6H4CH3, 611-22-3; 2-HONHCsHdC1, 10468-16-3; CsH,NHz, 62-53-3.
Literature Cited Aeberli, P.; Houlihan, W. J. J . Org. Chem. 1967, 32, 3211-3214. Barker, G.; Ellis, G. P. J . Chem. SOC.C 1970, 2230-2233. Cavill, G . W. K.; Ford, D. L. J . Chem. SOC.1954, 565-568. Cerveny, L.; RuiiEka, V. Catal. Reu.-Sci. Eng. 1982,24(4),503-566. DiCarlo, F. J. J . Am. Chem. SOC.1944,66, 1420-1421. Fanta, P. E. J . Am. Chem. SOC.1953, 75, 737-738. Hodge, E. B. J . Org. Chem. 1972, 37, 320-321. Kauer, J. C.; Sheppard, W. A. J. Org. Chem. 1967, 32, 3580-3592. Lubs, H. A. The Chemistry of Synthetic Dyes and Pigments; Robert E. Krieger Publishing: New York, 1955. Rajadhyaksha, R. A,; Karwa, S. L. Chem. Eng. Sei. 1986, 41, 1765-1770. Roblin, R. 0.;Winnek, P. S. J. Am. Chem. SOC.1940,62, 1999-2002. Russell, G. A.; Geels, E. J.; Smentowski, F. J.; Chang, K.-Y.; Reynolds, J.; Kaupp, G. J. Am. Chem. SOC.1967,89(15), 3821-3828. Rylander, P. N.; Karpenko, I. M.; Pond, G. R. Ann. N. Y. Acad. Sci. 1970, I72(9), 266-275. Rylander, P. N. Catalytic Hydrogenation in Organic Syntheses; Academic: New York, 1979. Rylander, P. N. In Catalysis in Organic Synthesis 1978; Academic: New York, 1980. Schipper, E.; Chinery, E.; Nichols, J. J . Org. Chem. 1961, 26, 4 145-4 148. Sone, T.; Karikura, M.; Shininkai, S.; Manabe, 0. Chem. Abstr. 1980, 93, 26018. Sugimori, A. Bull. Chem. SOC.Jpn. 1960, 33, 1599-1600. Taya, K. Chem. Commun. 1966, 464-465. Venkataraman, K. The Chemistry of Synthetic Dyes; Academic: New York, 1952; Vol. I. Yale, H. L. J . Org. Chem. 1968, 33, 2382-2385.
Received for reuiew September 4, 1986 Accepted June 1, 1987
Comparison of ASTM Round-Robin Data on Particle Size Using Three Different Methods William H. Flank Union Carbide Corporation, Tarrytown Technical Center, Tarrytown, New York 10591
The Task Group on Particle Size of ASTM Committee D-32 on Catalysts has compiled round-robin data on a single lot of typical equilibrium fluidizable cracking catalyst microspheres. These data were obtained by different methods employing laser light scattering, electroconductive sensing, and a micromesh sieving technique. A total of 18 laboratories participated in all or part of these measurements. Size distribution curves were constructed by plotting particle size vs. cumulative percent finer than the indicated size. In the range 35-100 pm and from about 5 to 95 cumulative 70,the electroconductive sensing method data lie about 5-6 pm below those for the sieving method. T h e laser light scattering data curve lies between the other two curves in the range 35-60 pm and then falls at a progressively greater distance above the other two curves with increasing measured particle size. At 95 cumulative Ti, the laser light scattering curve is about 30 pm above the other two. This technique, then, appears to significantly overstate the size of particles above about 80 pm. Appropriate caution should be used in interpreting or comparing data obtained by this method. The Task Group on Particle Size of ASTM Committee D-32 on Catalysts has been working in the area of particle size measurement for a number of years. In the course of developing consensus standard methods for testing of particle size, round-robin data have been compiled on a single lot of the same material, a typical 0888-5885187/ 2626-1750$01.50/ 0
equilibrium fluidizable catalytic cracking catalyst designated Amoco CCC-408, using three different methods. These methods utilized an electroconductive sensing technique, which can employ instruments like the Coulter Counter and the Elzone system, a laser light scattering technique, which can employ instruments like the L&N 1987 American Chemical Society
