Energy & Fuels 1994,8, 227-233
227
Design of a Nickel-Tungsten Hydrocracking Catalyst L. C. Gutberlet,? R. J. Bertolacini,l and S. G. Kukes* Research and Development Department, Amoco Oil Company, P.O. Box 3011, Naperville, Illinois 60566 Received May 24, 1993. Revised Manuscript Received September 14, 1993@
Hydrocracking has become a major oil refining process since its introduction in 1961. Developing improved catalysts for industrial processes involves the proper balance between activity, selectivity, and catalyst life. Hydrocracking catalysts consisting of combinations of nickel and tungsten oxides supported on a low (135% ) alumina, silica-alumina matrix containing 35 5% Ultrastable Y zeolite were tested in a once-through mode. Catalyst performance was determined using a blend of light virgin and catalytic cycle oils for hydrocracking and a heavy catalytic cycle oil for denitrogenation. The best catalysts were estimated to be more than twice as active for hydrocracking as the reference ,catalyst; high selectivity to heavy naphtha, and near total denitrogenation and desulfurization were also achieved.
Introduction
Table 1. Catalyst Test Specifications
Hydrocracking has been a major refinery process since ita introduction in 1961.l The process has been installed by all major refiners, including Amoco.24 The process converts a variety of feedstocks to sulfur- and nitrogenfree saturated stable products with highly branched molecules. The products also have low melting points and high cetane numbers, excellent properties for diesel fuels, distillates, and jet fuels. The naphthas produced are excellent feedstocks for catalytic reforming to highoctane, low-sulfur gasolines. Because the products from hydrocracking virgin gas oils and catalytic cracking oils are sulfur and nitrogen free, contain little or no olefins, and are low in aromatics, they are valuable components to meet the new environmental regulations for reformulated transportation fuels. The major process configurations, single-and two-stage hydrocracking, have recently been reviewed by Ward.' Catalyst choices vary widely depending on the process configuration and refinery processing strategy. Although early commercial hydrocracking catalysts consisted of hydrogenation metals supported on amorphous acidic supports such as silica-aluminas of varying SiOz/A1203 ratios: these have been superceded by zeolite compositions for the acidic function and metals ranging from single noble metals, Pd and Pt, to combinations of group VI and VI11 metals for hydrogenation. Low-sodium composites are also required for thermal ~ t a b i l i t y . ~VerdrinelO has
Hydrocracking Activity Test 70% LCCO + 30% LVGO 19 g through 12,on 20 mesh (US. sieve) granules flowing hydrogen, 3 ms/h/kg catalyst, 20 h, 86 bar, 260 "C Once-through (fresh feed only) at 30 cms/h 1.38 Wo/h/Wc once-through 2 mS/L 86 bar (total) as required to give 77 wt % conversion 6-26 days arbitrarily chosen as 1.0 activity16 Denitrogenation Activity Test feed 100% HCCO catalyst charge 15 or 16 g through 20,on 40 mesh (U.S. sieve) manules catalyst flowing hydropen, 6 ma/h/kg catalyst, pretreatment 2 h, 86 bar, 260 "C oil flow once-through at 30 or 32 cm/h space velocity 1.90 Wo/h/Wc hydrogen flow once-through 3 m3/L exit gas pressure 86 bar (total) temperature 371 "C run length 7 days reference catalyst Harshaw Ni-4401E
* Address correspondence to this author. Fax:
708-420-3698. Retired. t Present address: Center for Catalytic Science and Technology, University of Delaware, Newark, DE 19716. 0 Abstract published in Advance ACS Abstracts, November 15,1993. (1) Nelson, W. L. Oil Gas J. 1967, March 20, 170. (2)Oil Gas J . 1967,January 9,58. (3)Oil Gas J. 1967,February 13,106. (4)Hydrocarbon Process. 1967,103. (5)Frye, C. G., Moffat, D. L., McAninch, H. W. Proceedings of the API Midyear Reforming Meeting, Houston, May 18,1970; pp 69-71. (6)Frye, C. G., Moffat, D. L., McAninch, H. W. Proceedings of the API Midyear Hydrocarbon Processing, May 1970; pp 103-105. (7) Ward, J. W. In Catalysts in Petroleum Reforming 1989,Trimm, D. L.,Ahshah, S.,Absi-Halabi, M., Bishara, A., Eds.; Elsevier: Amsterdam, 1990, pp 417-618. (8)Sullivan, R. F., Meyers, J. A. ACS Symp. Ser. 1975,No. 20,28-50. (9)Ward, J. W. Appl. Ind. Catal. Academic Press: New York, 1984; Vol. 3,pp 243-248. t
feed catalyst charge catalyst pretreatment oil flow space velocity hydrogen flow exit gas pressure temperature run length reference catalyst
reviewed the chemistry and physiochemical features of zeolites in catalysis and Heinemann" has reviewed technological applications of zeolites in catalysis including hydrocracking. Hydrocracking reactions and mechanisms have been reviewed by a number of authors including Weitkamp.12 It is our intent to show that the proper selection of metal combination and concentration is important for hydrocracking catalysts utilizing a thermally-stable zeolite in an amorphous silica-alumina matrix. The importance of these parameters in catalyst design and preparation has beeh recognized by industrial researchers ward's and Yan.14 In this study, we intend to show that the proper design of a single-stagehydrocracking (10)Verdrine, J. C. Solid State Chemistry in Catalysis; Grasselli, R. K., Brazdil, J. F., Eds.; ACS Symposium Series 279;American Chemical Society: Washington, DC, 1985;pp 16-273. (11)Heinemann, H. Catal. Rev. Sci-Eng. 1981,23,315-328. (12)Weitkamp, J. Akzo CataLSymp.(May-June 1988),Scheoeningen, The Netherlands. (13)Ward, J. W. Preparation of Catalysts III; Poncelet, G., Grange, P., Eds.; Elsevier: New York, 1983;pp 587-617. (14)Yan, Y. T. Ind. Eng. Chem. Res. 1990,29,1995-98.
0~~7-0624/94/2508-0227$04.50/0 0 1994 American Chemical Society
228 Energy &Fuels, Vol. 8, No. 1, 1994
Gutberlet et al.
Table 2. Feed Inspectionsa feed 100% HCCO 70% LCCO-30% LVGO ASTM distillation, "C IBP 212 203 246 10 vol % overhead 313 270 30 340 50 355 285 70 373 295 398 323 90 maximum 333 gravity, "API 17.1 27.5 refractive index, ~I.D*O 1.5507 1.5026 sulfur, wt % 0.77 0.25 159 nitrogen, ppm, total 736 hydrocarbon type, vol % paraffins 23.5 16.9 42.2 34.3 naphthenes 34.3 48.8 aromatics 'Catalyst testing was carried out in down-flow bench-scale equipment, a schematic drawing of which is shown in Figure 1. The reactor was 50 cm. long and had an internal diameter of 16 mm. The reactor was immersed in the molten salt bath, and the axial temperature profile was very nearly isothermal. Internal temperature measurement was obtained through an axial thermowell of 3 mm outside diameter.
catalyst produces a highly active and stable catalyst for processing moderately high nitrogen containing feedstocks to high yields of naphtha and high is0 to normal paraffin ratios, an indicator of high product quality. For this study, we have chosen a series of nickel-tungsten catalysts supported on a base of 35 5% Ultrastable Y zeolite dispersed in a low (13% ) alumina, silica-alumina matrix.
Experimental Section The nickel-tungsten catalysts were tested for both hydrocracking and denitrogenation activities. Operating conditions for each test are given in Table 1. In these test procedures, the catalyst was not presulfided. However, sulfiding occurred during the first phase of feedstock processing. The test feeds were a
blend of 70 vol % light catalytic cycle oil (LCCO) and 30 vol % light virgin gas oil (LVGO)for hydrocracking and heavy catalytic cycle oil (HCCO) for denitrogenation. Feed properties are given in Table 2. T h e hydrocracked product, both gas and liquid, was analyzed by flame ionization gas chromatography using an OV-1 column and Hewlett Packard chromatograph to determine the conversion of gasoline (193 "C, TBP) and lighter. The denitrogenated product was analyzed for total nitrogen by coulometry. Catalyst. The nickel-tungsten catalysts were prepared by impregnating the powdered base with an aqueous solution of nickel nitrate and ammonium metatungstate, using only enough solution t o fill the pore volume. The catalysts were then dried a t 120 "C, pilled with 4 % Sterotex, and calcined at 537 "C for 3 h. The catalyst pills (6 mm) were crushed to 12-20-mesh particles for the hydrocracking test and 20-40-mesh particles for the denitrogenation test. No diluent was used in either test. The catalyst base was 35 w t % Ultrastable Y sieve dispersed in low (13%) alumina silica-alumina, containing 0.31 wt % sodium. The nickel-tungsten catalyst compositions are given in Table 3.
Results
A summary of the hydrocracking and denitrogenation performances of each catalyst is given in Table 3 along with the heavy naphtha yields and the C r C 5 is0 to normal ratios. The hydrocracking activity test, as shown in Table 1, was carried out under a fixed set of operating conditions with only temperature being deliberately varied to maintain a conversion to gasoline and lighter product as close to 77 wt % conversion as possible. The observed temperature was corrected for deviations from 77 wt 7% conversion using zero order kinetics and an activation energy of 35 kcal. An additional correction to the temperature requirement was made for deviations in the gas flow (hydrogen partial pressure) using the empirical equation AT "C = 4.3(R - 2), R being the exit gas rate in standard cubic meters per liter of oil (m3/L). The
Table 3. Nickel-Tungsten Catalyst Compositions and Performance hydrocracking test catalyst
A B C D E F G H I J K L
M N 0 P
R S T U V W X Y AA
AB AC AD AE
composition, w t NiO WOa 10.0 0.0 10.2 2.5 14.5 8.6 16.8 5.0 15.8 5.0 16.6 2.7 8.7 2.8 4.2 8.5 6.3 1.4 12.8 1.4 2.1 6.3 4.2 16.4 3.0 9.6 1.5 9.5 4.7 16.0 2.4 16.2 17.1 1.6 1.6 25.7 3.4 26.8 16.4 1.0 1.0 6.2 1.6 22.6 32.7 1.6 4.0 13.0 2.1 16.2 3.4 31.7 25.2 2.7 15.0 2.0 2.0 15.0
%
base 90.0 87.3 76.9 78.2 79.2 80.7 88.5 87.3 92.3 85.8 91.6 79.4 87.4 89.0 79.3 81.4 81.3 72.7 69.8 82.6 92.8 75.8 65.7 83.0 81.7 64.9 72.1 83.0 83.0
temp, O C (77% conv) 419 361 371 362 361 356 364 364 363 355 364 360 361.5 356.5 360 354 353 357.5 356.5 354 361.5 357 362 359.5 356 362.5 358 356 357
activity wt basis
0.17 1.67 1.10 1.60 1.67 2.10 1.49 1.49 1.52 2.20 1.49 1.72 1.64 2.05 1.72 2.27 2.39 1.95 2.05 2.27 1.64 2.00 1.60 1.80 2.10 1.56 1.90 2.10 2.00
selectivity a t 385 "C, 77% conv heavy naphtha wt % 64.2 58.2 59.2 59.2 62.6 61.8 60.8 61.0 61.1 63.9 60.2 62.4 61.9 61.3 60.8 59.7 60.3 62.0 58.5 62.4 60.0 60.1 61.0 59.8 60.2 61.0 60.9 61.1 60.6
iso'normal c4
c6
1.59 1.50 1.67 1.51 1.68 1.62 1.85 1.67 1.84 1.62 1.58 1.59 1.64 2.04 1.74 1.96 2.07 1.66 1.71 1.72 1.74 1.64 1.63 1.59 1.96 1.94 1.62 1.52
5.36 7.01 4.52 4.92 4.09 5.05 6.09 7.00 3.88 5.77 5.29 4.87 4.31 3.91 3.95 3.87 3.50 3.65 3.35 4.61 3.69 3.24 4.07 3.99 3.58 3.20 3.75 4.15
denitrogenation test nitrogen, PPm 435 10 11 16 11 8 13 15 4 14 13 5 1.5 4 1 8 7 6 7 53 3 19 7 4 5 1.7 1.5 1.5
activity wt basis
0.36 1.34 1.32
-
1.24 1.32 1.39 1.28 1.25 1.55 1.27 1.28
1.50 1.77 1.55 1.85 1.39 1.42 1.46 1.42 0.96 1.60 1.20 1.42 1.55 1.50 1.74 1.77 1.77
Energy & Fuels, Vol. 8, No. 1, 1994 229
Nickel-Tungsten Hydrocracking Catalyst
Fern WPPLY
RUSKA PUMP
04 - 1 fi
I II II RUPTURE
IIII I
c . ow
I
bo cm LDNO 16 mm LD.
Figure 1. Bench-scale unit. .l 4
.12
10
F d 8
.08
f
'06
8
.04
f 0
.02
0
0
0.02
0.04
0.08
0.08
0.1 0
0.12
0.14
0.11
0.18
WO3. g-molWl 009 CATALYST
Figure 2. Hydrocracking activity contour diagram. hydrocracking temperatures for 77 wt % conversion listed in Table 3, represents an average value taken at 7 days on stream. Hydrocracking activity ( a )is related to the reaction rate constant (k)by the equation, k = ae-m/RT. Because the conversion is held at 77 w t %, the rate constant for the experimental catalyst ( c ) and the reference catalyst ( r ) are the same and a,e-'/RT = are-u/RT. Relative catalyst activity is then inversely related to the temperature requirement, i.e.,
a, p W R T , a , e-M/RTc For the reference catalyst, a Co-Mo supported on the same matrix as the experimental catalysts,'5 with an assigned activity of 1.0, and 7 day temperature requirement for 77 wt 5% conversion was 373 "C. Heavy naphtha yields, YO,at 385 O C and 77 wt % conversion were calculated from the observed data using -=-
~
~~
(15)Hensley, A. L.U.S. Patent 3,894,930.
230 Energy &Fuels, Val. 8, No. 1, 1994
Gutberlet et al. w
the equation: Y 0 = Y + 1 5 X 1 014 ( ~ - ~ ) + 9 X 1 0 8 ( & -
20
100 - c,
T + 273 where Y , T , and C are the observed heavy naphtha yield (wt %), temperature ("C), and conversion (wt %), respectively, and Co is at 77 % conversion. Heavy naphtha yields for the average temperature requirement at 7 days on stream can also be calculated with this equation. The calculated heavy naphtha yields and the is0 to normal ratios shown in Table 3 are average values for each run corrected to 385 "C and 77% conversion. In the denitrogenation activity test, as shown in Table 1,all operating conditions were held constant while the nitrogen content of the product was allowed to vary. The observed nitrogen contents were corrected for small deviations in reaction temperature using an empirical 2/3order kinetic equation and an activation energy of 11kcal, based on earlier work with the reference Harshaw catalyst, a sulfided nickel-tungsten supported on amorphous fluorided silica-alumina. Thus, the denitrogenation activity of the experimental catalyst is the ratio of its rate constant to that of the reference catalyst, which when freshly calcined has an assigned activity of 1.0 and gives a product containing 45 ppm nitrogen. Discussion
Od
a 1.o
0.5
0
1 .s
NW ATONIC wno
w
PA
1 1
1.4
01
As shown in Table 3, catalysts containing from 0 to 8.6 wt % NiO and 6.2 to 32.7 wt 5% W03 were evaluated.
Composition was varied with respect to the relative nickel and tungsten concentration as well as the total metal oxides deposited on the base. As aresult of the latter,the amount of base, which contains the active cracking component (US-Ymolecular sieve), varied from 92.8 to 64.9 wt %. Thus, while at low metals concentrations the catalyst activity is expected to improve as the metals loading is increased, at some point further increases in metal content should cause a loss in activity because of the decrease in molecular sieve content and pore plugging. Hydrocracking Activity. The response of activity to catalyst composition is shown by the contour diagram in Figure 2. The NiO and wO3 concentrations are the abscissa and ordinate, respectively. The NiO and W03 concentrations are given in g-mo1/100 g of catalyst to give an indication of surface coverage. Radiating from the origin are constant atomic ratios of the hydrogenation metals. The dashed line shown corresponds to an atomic ratio of three atoms of tungsten per atom of nickel. The data points, representing catalyst compositions, are keyed to Table 3 in which the hydrocracking activities are listed. The activity contours shown in Figure 2 range from 1.2 to 2.4. Because activity is based on the temperature requirement for constant conversion,these activity contours are in fact isotherms ranging from 369 OC at 1.2 activity to 353 "C at 2.4 activity. From Figure 2, the most active composition for hydrocracking is estimated to contain about 19 wt "6 total metal oxides with a W/Ni atomic ratio of about 3. Figure 3 shows the hydrocracking activity profiles obtained along the lines of constant Ni to W atomic ratio and total metal oxides content from the contour diagram indicated in Figure 2. Figure 3A shows the rapidity with which activity changes with Ni to W ratio at a total metal
a 0
8
ZD
15
10
NlO
15
UI
SS
+ wg. m.x
Figure 3. Hydrocracking activity profiles. 370
360
350
yo
0
2
4
6
8
10
12
14
16
18
20
22
24
26
MYS ON STRW
. 4
UTMYS CATMYS
- N; 1.5% NiO - 9.5% W 4 - 0; 1.?X NiO - 16.0% WO 3
Figure 4. Catalyst deactivation,
oxides level of 19 wt 5%. Figure 3B shows the rapidity with which activity changes as a function of total metal oxides at a fixed Ni to W atomic ratio of 0.33. Comparison of the two plota suggeststhat near the maximum in activity the Ni to W ratio has a greater influence on activity than the total amount of hydrogenation metals. Also shown in Figure 3, A and B, are the data from five catalysts (AA, AB, AC, AD, AE) from Table 3 which were not used in Figure 2 because of their consistently lower (about 10%) activity caused by a change in the zeolite
Nickel-Tungsten Hydrocracking Catalyst
Energy &Fuels, Vol. 8, No. 1, 1994 231
.12
.10
!
8B
.OO
.01
-U
F
m
.6
.04
z
.02
0 0
0.02
0.04
0.06
0.08
0.1 0
0.1 2
0.14
0.1 1
0.11
WOJ,g-moledl 009 CATALYST
Figure 5. Heavy naphtha yield at 385 O C .
composition of the matrix. This activity difference corresponds to a 2 "Cspread in temperature requirement. Replications in catalyst composition for two catalysts (AD and AE) gave a spread in temperature requirement of 1 "C. Thus the activity of the best nickel-tungsten catalyst should be about 2.3 with a variation of about f 5 % , Catalyst Deactivation. In most cases, the catalyst tests were run for less than 14 days, so a precise estimate of catalyst deactivation rate cannot be made. Typically, the deactivation, observed for the nickel-tungsten catalysts over this short period of operation, was never greater, and was frequently less, than that observed for the reference catalyst over the same time period. When two typical nickel-tungsten catalysts, N and 0, were run for 26 days, Figure 4,the measured deactivation rate was about 0.05 "C per day on average for both catalysts. This is about one-third that observed for the reference catalyst during the same operating period. Heavy Naphtha Yields. The yield of heavy naphtha at constant conversion (77 w t %) increases as the reaction temperature decreases. To determine if catalyst composition affects heavy naphtha yield, the comparison should be made at constant temperature. In Figure 5 the heavy naphtha yields calculated at 385 "C are shown for all the catalysts in Table 3. While the heavy naphtha yields vary from 58 to 64 w t %, no clear trend with catalyst composition is apparent, nor is there any clear relationship between heavy naphtha yield and hydrocracking activity. The solid contour in Figure 5 represents a hydrocracking activity of 2.0. The distributions of heavy naphtha yields inside and outside this activity contour are essentially the same. This can be more clearly seen in Figure 6 where the bar chart shows that the nickel-tungsten system gives a typical heavy naphtha yield of 61% as compared to the reference catalyst which gives a heavy naphtha yield of 59.4% with a standard deviation of about 1.8%. Iso/Normal Paraffin Ratios. Iso/normal paraffin ratios are indicators of the quality of the product boiling below heavy naphtha. In Figure 7 these ratios for butane
'
50
58
60 I1 62 X HEAW NAPHMA YlELO
0
ALLCATMYSTS
H
U T M W
63
64
>Z.OACTnmy
Figure 6. Distribution of heavy naphtha.
and pentane are plotted against catalyst composition with the solid contour representing a hydrocracking activity of 2.0. The values shown for each catalyst are averaged from observed data obtained between 70 and 84 w t 5% conversion. The iso/normal butane ratio showed no significant trend with catalyst composition. Furthermore, the observed values of 1.5-2.1 are similar to those obtained with the reference catalyst. Above 2.0 activity, the observed values were in the range of 1.52-1.96, while below an activity of 2.0, values of 1.51-2.07 were observed. The iso/normal pentane ratio is indicative of the quality of the light naphtha; the greater the isoparaffin content of light naphtha, the higher its octane number. Figure 7 shows that the iso/normal pentane ratio increases with increasing nickel content and decreasing tungsten. This can be seen more clearly in Figure 8 where iso/normal pentane is plotted separately against nickel and tungsten at constant compositions of each. For those catalysts
Gutberlet et al.
232 Energy & Fuels, Vol. 8, No. 1, 1994 .12
.10
E
i
I I ml
9’ z
.OS
.06
.M
.02
0 .12
.10
gE
-08
8
3
F
cI,
.06
.M
.02
0 0
.02
.M
.od
.os
.to
.12
.14
.16
Wg,g-moledlOOg CATALYST
Figure 7. Iso/normal paraffin ratios.
having hydrocracking activities of 2 or greater, the is01 normal pentane ratio average is 4.0, as compared to about 10 for the reference catalyst. Effect of Catalyst Sulfiding. An attempt was made to improve the iso/normal pentane ratio obtained with nickel-tungsten catalysts by presulfiding the hydrogenation metals to bring the hydrogenation and cracking activities of the catalyst into better balance. Catalyst AD was presulfided with 8 76 hydrogen sulfide in hydrogen at 4.4 bar and 260 OC and its hydrocracking performance evaluated with the following results: catalyst hydrocracking activity heavy naphtha, wt % at 385 O C iso/normal pentane ratio iso/normal butane ratio
sulfided 2.15 61.7 3.2 1.9
non-sulfided 2.10 61.1 3.8 - 1.6
Based on these data, presulfiding the catalyst has little or no effect on either activity or selectivity.
Denitrogenation Activity. The effect of catalyst composition on denitrogenation activity is shown in Figure 9. Although there is considerable random variation with composition, the best denitrogenation Catalysts are predominantly inside the hydrocracking activity contour of 2.0. Some of the variability in the data is due to uncertainty in the analytical measurement at very low nitrogen levels in the denitrogenated product. Under the conditions of the catalyst test, denitrogenation activities greater than 1.5 represent product nitrogen contents of less than 5 ppm. The reference with an activity of 1.0,would yield a product containing 45 ppm nitrogen under the same conditions. Desulfurization. For one of the more active catalysts (AE) the denitrogenated heavy catalytic cycle oil was also analyzed for sulfur content. This catalyst, contained 2.0 wt 74 NiO and 15.0 wt 9% WO3, had a denitrogenation activity of 1.77. Under denitrogenation test conditions, the sulfur in the product after 6 days on stream was 0.021 wt 7%, indicating about 97 % desulfurization.
Nickel-Tungsten Hydrocracking Catalyst
Energy &Fuels, Vol. 8, No. 1, 1994 233
0.00 .07
Q
3 2
3
.33 9.00
.67
.33 4.00
\
E!
.07
0
am
aw
0.01
Conclusions Designing an industrial catalyst involves more than developing a composition with high activity, although that is an important consideration for a commercial process such as hydrocracking. As this study has shown,the proper nickel and tungsten oxide ratios produce catalysts with high activity and selectivity with potential for long catalyst life. The highest activity catalysts are estimated to be 2.3 times more active for hydrocracking, on a weight basis, and twice as active, on a volume basis, as the reference catalyst. The heavy naphtha yield obtained with nickeltungsten may also be slightly higher. Because of its high hydrocracking activity and its approximately 50 % greater
o.oa
0.10
a12
0.14
ais
denitrogenation activity, nickel-tungsten has a broad range of applicability for refractory feedstocks. One potential disadvantage of nickel-tungsten is the low iso/normal paraffin ratios observed in the light naphtha, particularly the pentane. This would result in a somewhat lower octane number for this stream. Surprisingly, sulfiding the catalyst did not improve the is01 normal paraffin ratio nor did it significantly affect any of the other hydrocracking performance indicators. Acknowledgment. The authors thank Amoco Oil Co. for supporting this research. We also thank our collegues for their help and review of this manuscript.
