structed. In addition, the tables also contain the concentration of those species with very small concentrations which were not included on the graphs. 4
CbRBON MONOXIDE
Literature Cited
.o
.s
1.0
1.5
2 .o
MOLES CH4 PER MOLE SO0 REACTANT
Figure 5. Equilibrium composition of H20, COz, H2, and CO for the CH4-SOz system a t 600 K and 1atm. The initial gas composition was 0.1 atm of SO*, 0.025 to 0.1 atm of CH4, and 0.875 to 0.80 atm of inert.
yield of elemental sulfur is to be obtained, the ratio of sulfur dioxide to methane must be near 2. Figures S-1and S-2are very similar to Figure 4 and Figures S-3 and S-4 are similar to Figure 5. All four are included in the supplementary information. The supplementary information also includes Tables S-1 through S-4 which contain the data from which Figures 4, 5 , S-1, S-2, S-3, and S-4 were con-
Averbukh, T. D.. Radivilov. A. A.. Bakina, N. P.. Zh. Prikl. Khim. (Leningrad), 43, 35 (1970). Carnahan, B., Luther, H. A., Wilkes, J. O., "Applied Numerical Methods," p 321, Wiley, New York, N.Y., 1969. Detry, D., Drowart, J., Goldfinger, P.,Keller, H.. Rickert, H., Z.fhys. Chem. (FrankfurlamMain), 55, 314 (1967). Hsieh, Y. D., Atwood, G. A,, ind. Eng. Chem., Process Des. Dev., 15, 358 (1976). Kelley, K. K.. U.S. Bur. Mines Bull. No. 584, (1964). Lepsoe, R., ind. Eng. Chem.. 30, 92 (1937). Lewis, G. N., Randall, M., revised by Pitzer, K. S., and Brewer, L., "Thermodynamics," 2d ed, McGraw-Hill, New York, N.Y., 1961. Thacker, C. M., Miller, E., ind. Eng. Chem., 36, 182 (1944). Vilesov, N. G., Gorbatykl, G. A,, Khim. Prom., 42, 187 (1966). Walker, S. W., Ind. Eng. Chem., 38, 906 (1946). Washburn, W. E., Ed., "International Critical Tables of Numerical Data, Physics, Chemistry and Technology," Vol. 1, p 53, McGraw-Hill, New York, N.Y. 1926.
Receiued for reuiecu June 14, 1976 Accepted September 27,1976
Supplementary Material Available. Seven tables and four figures of equilibrium composition data (12 pages). Ordering information is given on any current masthead page.
COMMUNICATIONS
Effect of Catalyst Particle Size on Performance of a Trickle-Bed Reactor
This paper presents experimental data for the effect of catalyst particle size on the performance of a trickle bed reactor for hydrodesulfurization of 22% and 3 6 % reduced Kuwait crudes. The results were correlated well by the effective catalyst wetting model of Mears (1974) but not by the holdup model of Henry and Gilbert (1973).
Introduction In a recent series of papers, Henry and Gilbert (1973), Mears (1974),Paraskos et al. (1975),and Montagna and Shah (1975) analyzed holdup and effective wetting models for correlating data obtained in pilot scale hydroprocessing trickle bed reactors. Henry and Gilbert (1973) suggested that all the catalyst in a pilot scale trickle bed reactor is not effectively used. A pilot scale reactor, therefore, gives a poor performance when compared to a commercial reactor under equivalent reaction conditions. Henry and Gilbert (1973) attributed this to their low values of dynamic liquid holdup. Using the holdup correlation of Satterfield et al. (1969), they proposed that the performance of a trickle bed reactor which carries out a first-order reaction is given by In
cAi
a
( L )1/3( LHSV)-2/3( d ),
-2/3( u ) 113
CAo
(1)
Here C A and ~ C A are ~ the reactor inlet and outlet concentration of the reactant, L is the length of the catalyst bed, LHSV 152
Ind. Eng. Chem., Process Des. Dev., Vol. 16, No. 1 , 1977
is the liquid hourly space velocity, d, is the catalyst diameter, and u is the kinematic viscosity. Mears (1974) attributed the poor performance of the pilot scale reactor to incomplete catalyst wetting. Based on the wett6d packing area correlation of Puranik and the Vogelpohl (1974),he proposed an alternate relation for the reactor performance as
where u is the surface tension of liquid, uc is the critical value of the surface tension for the given packing, and 7 is the catalyst effectiveness factor. All other parameters in the above relation are the same as those in (1). For constant catalyst size and fluid properties, both relations 1 and 2 predict the same dependence of In ( C A ~ I C Aon J the catalyst bed length and the liquid hourly space velocity. Paraskos et al. (1975) and Montagna and Shah (1975) showed that for hydrodesulfurization and hydrocracking of various
a' K A T E 750'F K V T B 750'F
K A T B - 750'F K V T B - 750' F
0
KVTB.7903F
KVTB - 790'F
Experimental curves
Experimental curves
---
01' 01
\
0 A A
'Ao
L
L
L
L
L
-
1
1
dp i m m 1
I
N
I
,
Correlations basedon d p a 8 2 1 n C A o L t a n h i k d p ) CAO
Correlations basedon d p o s 2 1 n C A l ~ t a n h l k d p l
I
I
1
L-01
10
Figure 1. Experimental and the predicted catalyst size-conversion effects for the sulfur removal reaction.
Figure 2. Experimental and the predicted catalyst size-conversion effects for the nickel removal reaction.
crude residues and gas oils, the relation In ( C A ~ I C Aa~ ) Ln(LHSV) is generally valid; although the values of n and
Table I. Properties of the Feedstocks
m are somewhat dependent upon the nature of the reaction, reaction temperature, and nature of the feedstock and they are not always y3 and -2/3 as suggested by relations 1 and 2. The dependence of In ( C A ~ I C Aon ~ )the catalyst size and the fluid properties is different according to relations 1 and 2. In order to determine the more realistic of these two relations, ) of experimental measurements of In ( C A ~ I C Aas~ functions either catalyst size or fluid properties are needed. Henry and Gilbert showed that for saturation of aromatics in white oils In ( C A ~ / C A ~dp+I3. ) Mears suggested that this relation can be approximately obtained according to relation 2 if the reaction is severely limited by intraparticle diffusional processes. In this short paper we present some experimental data to further illustrate the true dependence of In ( C A ~ C Aon~ )the catalyst size. The data are taken in a reactor of constant catalyst bed length which is operating at constant liquid hourly space velocity. The catalyst size was varied by approximately one order of magnitude. The conversions of sulfur, nickel, vanadium, and asphaltenes were measured.
Experimental Section The experimental data were obtained for two residues from the same crude, and 22% reduced Kuwait crude (KVTB) and a 36% reduced Kuwait crude (KATB). The relevant properties of these crudes are illustrated in Table I. As expected, the concentrations of sulfur, nickel, vanadium, and asphaltene are proportionately higher in the 22% than in the 36% reduced Kuwait crude. The catalyst samples of this study were prepared by sizing down to the desired particle size ranges the same mother batch of commercially prepared hydrotreating catalyst. The hydrotreating catalyst consisted of the group 6-group 7 metal combination on alumina. The catalyst volume used in the present study was approximately 100 cm3. The details of the experimental apparatus and procedure are identical with the ones described recently by Montagna and Shah (1975). Results a n d Discussion The experimental data obtained in this study are briefly summarized in Tables I1 and 111. The data for 22% KVTB were obtained at two temperatures, 750 and 790 OF, while the data for 36% KATB were obtained a t 750 O F . The reactor
22% Reduced
Kuwait crude (KVTB) Specific gravity Gravity, "API Sulfur, % by wt Nickel, ppm Vanadium, ppm Asphaltenes (Cso insol.), % by wt Carbon residue, % by wt
1.025 6.5 5.43 33 99
36% Reduced Kuwait crude (KATB) 0.988 11.7 4.47 21
15.2
65 9.2
16.0
12.0
pressure in all the runs was maintained at 2000 psig. Recently Montagna and Shah (1975) have shown that for the present reaction conditions, backmixing would definitely not be important in the case of small catalyst sizes. For larger catalyst sizes (7 x 8 mesh and 12 x 14 mesh), backmixing could be important, but Figure 1of Montagna and Shah (1975) shows that this effect would not be very significant. The plots of In ( C A ~ I C Avs. ~ )d, obtained from these data for sulfur, nickel, vanadium, and asphaltene removal reactions are illustrated in Figures 1to 4, respectively. As shown in these figures, the data were well correlated by the relationship
The parameter k' is dependent on the intrinsic rate constant and diffusivity of the pertinent reactant within the catalyst (k' = yfi -where k is the intrinsic rate constant and D,ff is the effective diffusivity of the reactant in the catalyst). It should be noted that in deriving the above relation, it is assumed that the effectiveness factors for the various particle sizes can be defined as q = (tanh &/&), where C& is the standard thiele module. Although this expression for 7 is strictly valid for a slab geometry, Aris (1957) has shown that it can be applied to any particle geometry if a suitable value of d, is used. In the present study d,, as defined by Aris (1957),is used in relation 3. The parameter k' for each curve in Figures 1to 4 represents that value of k' which best correlates the experimental data. Ind. Eng. Chem., Process Des. Dev., Vol. 16, No. 1, 1977
153
Table 11. A Summary of Data for Desulfurization of 36% Reduced Kuwait Crude (2000 psig, 100 cm3 Catalyst Volume) Catalyst size, U.S. mesh Temperature, O F LHSV, h-l Hz rate, SCFhbl On-stream period, h Cq + recovery, %
7x8
12 X 14
20 X 25
35 X 40
750 1.04 4120 8-24 102.7
750 1.09 3960 8-24 103.4
148 0.94 4330 8-24 103.3
748 1.13 4440 8-24 102.7
18.9 1.68 13.5 34 5.37 11.25
20.4 0.81 7.7 12 2.73 11.71
20.3 0.78 4.1 5.9 1.48 11.43
20.6 0.74 2.2 1.6 0.98 11.65
Product Gravity, "API Sulfur, % by wt Nickel, ppm Vanadium, ppm Asphaltenes (Cs0 insol.), % by wt Hydrogen, % by wt
Table 111. A Summary of Data for Desulfurization of 22% Reduced Kuwait Crude (2000 psig, 100 cm3 of Catalyst) Catalyst size, U.S. mesh Temperature, O F LHSV, h-l H2 rate, SCF/bbl On-stream period, h Cd0 + recovery, %
7 x 8
7X8
12 X 14
12 X 14
20 X 25
20 X 25
35 X 40
35 X 4 0
749 0.51 4560 8-24 102.6
750 0.43 5407 8-24 104.4
750 0.5 5700 8-24 104.3
789 0.53 4090 8-24 104.8
753 0.55 3880 8-24 104
792 0.52 4200 8-24 103.9
750 0.53 4860 8-24 103.7
788 0.51 6200 8-24 105.5
21.6 0.42 4.7 9.3 4.36
19.1 0.56 1.5 2.2 2.21
22.7 0.28 0.8 0.1 2.54
18.4 0.54 0.8 0.4 1.63
23.1 0.13 0.6 0.3 2.33
11.78
11.51
11.76
11.59
11.85
Product Gravity, "API Sulfur, % by wt Nickel, ppm Vanadium, ppm Asphaltenes (Cso insol.), % by wt Hydrogen, % by wt
lo
15.4 2.09 21.5 44 9.23
20.8 12 27 1.16
18.5 0.65 1.6 10.1 5.03
11.19
11.77
11.82
1.1
E
J
1
i
4
i
A A 0 W
-
--I
01 01 dp imm I
1
1
1
1
1
0
1
J
KVTB-75eF KVTB-79O"F
Experimental curves Correlations baoedon d p o 8 ' 1 n ~ d t a n h I k d p 1
1
'A0
O'Ol- - A 0 1
10
10
dp imm I
Figure 3. Experimental and the predicted catalyst sh-conversion
effects for the vanadium removal reaction.
Figure 4. Experimental and the predicted catalyst size-conversion effects for the asphaltene removal reaction.
It is worthwhile to note briefly the physical significance of these k' values. For all reactions, k' values obtained for 36% KATB at 750 O F were almost the same as the ones for 22% KVTB at the same temperature. The magnitude of k' indicates the relative importance of pore diffusivity with respect to the intrinsic kinetic constant for the reaction. A smaller
value of k' implies a smaller importance of the pore diffusion limitation. Thus, as shown in Figures 1to 3, pore diffusion is more important for the demetallization reaction than for the desulfurization reaction. For desulfurization of 22% KVTB, a larger value of k' obtained at higher temperature was presumably due to the larger intrinsic rate constant a t higher
154
Ind. Eng. Chem., Process Des. Dev., Vol. 16, No. 1, 1977
temperature. Furthermore, for the demetallization reactions, severe intraparticle diffusional effects appear t o make k' insensitive to the temperature change in case of 22% KVTB. The liquid flow used in this study is about 0.05 kg/m2-s. At such a flow rate,'Figure 4 of Satterfield (1975) indicates that the catalysts are most likely incompletely wetted. Thus, relation 2 may be the most adequate representation of the physical situation for the present experiments. It should be noted that the accuracy of the power 0.82 on d, in relation 3 depends upon the validity of Puranik and Vogelpohl(l974) correlation for the present case. Within the accuracy of the present data, this power on d, appears to be reasonable. T h e power on d, in relation 1 is obtained from the holdup correlation of Satterfield et al. (1969). This correlation is obtained for flow of liquid down a string of spheres and its applicability to the present experimental system may be questionable. I t is clear from this study that relation 1cannot correlate the present data. Relation 2 predicts more realistic dependence of In (CA~,CAJon d, than that predicted by relation 1. Based on this study the effective catalyst wetting model appears to be more realistic than the holdup model. Nomenclature CA, = the reactor inlet concentration of A, g/cm3 C A= ~ the reactor outlet concentration of A, g/cm? d, = catalyst diameter, cm D ~ ~= f effective f diffusivity of A in the catalyst, cm2/s k = intrinsic rate constant for the reaction, l./s k' = a quantity proportional to,fcm
L = length of the catalyst bed, cm LHSV = liquid hourly space velocity, h-' u = kinematic viscosity of the liquid feedstock, cm2/s u = surface tension of the liquid feedstock, dyn/cm
Subscripts A = refers to sulfur, nickel, vanadium, or asphaltenes i = reactor inlet condition o = reactor outlet condition L i t e r a t u r e Cited Aris, R., Chern. Eng. Sci., 17, 167 (1962). Henry, H. C., Gilbert, J. B., Ind. Eng. Chem., Process Des. Dev., 12, 328 (1973). Mears, D. E., Adv. Cbem. Ser., No. 133, 218 (1974). Montagna, A., Shah, Y. T.. Ind. Eng. Cbem., Process Des. Dev., 14, 479 (1975). Paraskos, J. A., Frayer, J. A., Shah, Y . T., Ind. Eng. Cbem., Process Des. Dev., 14, 315 (1975). Puranik, S. S..Vogelpohl, A., Cbern. Eng. Sci., 29, 501 (1974). Satterfield, C. N. Pelossof, A. A., Sherwood, T. K., AIChE J., 15, 226 (1969). Satterfield. C. N., AIChEJ., 21, 209 (1975).
Gulf Research a n d Development Company Angelo A. Montagna Pittsburgh, Pennsylvania 15250 Yatish.T. Shah*' John A. Paraskos Received /or review March 26, 1976 Accepted July 26,1976
Author to whom correspondence should be sent at the Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pa., 15261.
LETTER T O THE EDITOR
Mass Transfer and Power Consumption in a Reciprocating Plate Extraction Column Sir: I t was brought to my attention by Dr. A. Karr that the word stroke (meaning twice the amplitude) should be used in the text to agree with the meaning of a in eq 2 and the values in Table I of Ioannu et al. (1976). Further, Dr. Karr suggested Table I Large holes and free area, Karr and Lo (1971)
Small holes and free area, present investigation
Methyl Isobutyl Ketone Dispersed, Water Extractant a (rnP 0.0125b 0.0125 0.009 0.009
f
(s-')u
Power (W/m")
4.75 226.0
4.63 210.0
2.0 166.0
1.6 42.0
Methyl Isobutyl Ketone Continuous, Water Extractant a (m)
f
(s-1)
Power (W/m3)
0.0125 4.75 226.0
-
0.010 1.68 108.
-
comparing the power consumption a t the minimum values of "HETS". We were reluctant to estimate point values of the power because of the approximate nature of eq 2. However, such comparison gives the results in the present Table I. It is also worthwhile to add that presence of solids in the system and/or ease of construction of plates (which favor plates with large holes and free area) should be considered together with the power consumption in comparing the two plate designs.
L i t e r a t u r e Cited loannou, J., Hafez, M.,Hartland. S.,Ind. Eng. Cbern., Process Des. Dev., 15, 469 (1976).
Department of Industrial and Engineering Chemistry Swiss Federal Institute o f Technology Zurich, Switzerland
Joachim Ioannou Mahmoud Hafez*' Stanley Hartland
-
Values corresponding to the minimum HETS. 3-in. column diameter based on earlier results by Karr (1959).
Address correspondence to this author at the Chemical Engineering Department, McMaster University, Hamilton, Ontario, Canada L8S 4L7. Ind. Eng. Chem., Process Des. Dev., Vol. 16, No. 1, 1977
155
