Superactive Nickel-Aluminosilicate Catalysts for Hydroisomerization and Hydrocracking of Light Hydrocarbons Harold E. Swift* and Edgar R. Black Gulf Research & Development Company. Pittsburgh, Pennsylvania 75230
Synthetic mica-montmorillonite (SMM), a layered-lattice dioctahedral clay, has cracking activity greater than amorphous silica-alumina, but less than that of Y zeolite. Nickel or cobalt is advantageously incorporated into the SMM structure during synthesis by isomorphous substitution for aluminum in the octahedral layer and/or as separate octahedral layers. Such nickel and cobalt SMM clays have higher surface areas than SMM and also exhibit significantly higher catalytic activities for light hydrocarbon reactions compared to SMM. For the hydroisomerization of a Cs/C,j paraffin fraction certain nickel SMM catalysts exhibit activities at least as great as that obtained with a Pd-H-mordenite catalyst. For the hydrocracking of hexane and raffinate, the activities are much higher than that obtained from a Pd-rare earth-Y zeolite catalyst
Introduction In a paper describing the structure and acidic properties of synthetic mica-montmorillonite (SMM) (Wright, et al., 1972) the lattice structure of this synthetic ammonium dioctahedral clay was compared to muscovite mica. The two materials differ in that SMM has irregularly interstratified expansible and nonexpansible layers before activation. Thermal activation of SMM causes deamination and a partially reversible loss of structure hydroxyl groups accompanied by a collapse of the interlayer spacing to 9.4 A. A pairwise loss of adjacent hydroxyls is hypothesized to account for the increased high temperature water sorption of activated SMM when lattice fluoride is present. The appearance of a hydroxyl band a t 3470 cm-l in the activated material is attributed to the presence of protons in the tetrahedral vacancies of the octahedral layer. Ammonia and pyridine adsorption experiments show the presence of both Lewis and Brrjnsted acidity, the relative amounts of each being dependent on the severity of previous outgassing. I t is claimed that SMM has cracking activity greater than amorphous silica-alumina, but less than Y zeolite (NL Industries Baroid Division Brochure). Mechanistic studies of hydrocarbon reactions over SMM were reported in an effort to gain insight why SMM is more active than silica-alumina (Hattori, et al., 1973). I t was suggested that the increased lability of the hydrogen atoms in SMM probably accounts for its enhanced cracking activity. The results of the current work show that a novel catalyst having great catalytic activity for the hydroisomerization and hydrocracking of light hydrocarbons can be prepared by incorporating nickel and cobalt into a structure for which SMM is a prototype. Experimental Section Details of the preparation and characterization of the 2:1 layer-lattice aluminosilicate clays containing six-coordinated nickel(I1) will be given in a forthcoming paper by Granquist and coworkers from the Baroid Division of NL Industries. Most of the nickel-substituted mica-montmorillonite clays reported in this paper were developed by and synthesized a t the Baroid Division of NL Industries, Houston, Texas; however, some of the catalysts were prepared a t our laboratory. A typical preparation of a nickel clay is as follows: 143.5 g of hydrated alumina, A1203.3H20 (Alcoa C 31, 64.9% A1203) was added with stirring to a polysilicic acid sol which was prepared by passing sodium silicate solution over a hydrogen resin. 106
Ind. Eng. Chern., Prod. Res. Develop.,Vol. 13, No. 2,1974
The volume of sol was chosen so as to contain 150 g of SiOz. Then 7.43 g of NH4F.HF was dissolved in this silica-alumina slurry, and 94.5 g of Ni(Ac)ze4H20 was dissolved in a minimum amount of water, added to the above slurry, and 29.8 g of aqueous ammonia (assaying 58.8% NH40H) was added with stirring. Upon gel formation, sufficient water was added to break the gel so that efficient stirring could continue. The proper volume of the final feed slurry was charged to a 1-gal stirred autoclave, heated quickly (1-1.5 hr) until the pressure lined-out a t 1250 psig (572°F) and was maintained a t this temperature and pressure for 3 hr. The product was cooled in a pressure vessel, removed, sheared in a blender to ensure homogeneity, and dried a t about 250°F. The final clay contained 6.75% nickel. Palladium was added to the clay either by impregnation or by exchange. In most cases an exchange procedure was used. A typical exchange procedure involved dispersing the oven-dried clay in enough water to give a slurry which was easy to stir and then adding an aqueous solution of (NH4)zPdC14. This mixture was stirred for approximately 16 hr at room temperature and then filtered. The filter cake was washed twice by redispersing it in deionized water and refiltering. The filter cake was oven-dried and sized to 10-20 mesh particles. Catalyst Evaluation. Catalysts were evaluated using two high-pressure screening units. Most of the hydroisomerization experiments were conducted in a 90-cm stainless steel reactor with an internal diameter of 8 mm and a total loading capacity of 36 cm3, Hydrocracking experiments were performed in a 33-cm stainless steel reactor with an internal diameter of 12 mm and a total loading capacity of 40 cm3. The normal catalyst charge was 8 cm3 for hydroisomerization and 15 cm3 for hydrocracking. The catalyst bed was diluted with quartz chips. Catalysts were pretreated overnight either by hydrogen reduction a t 650°F or sulfiding with a 2% H2S-98% Hz blend at 750°F. Reaction conditions for hydroisomerization were 400500"F, 0.5-4.0 LHSV, 2.5 Hz/HC mole ratio, and 450 psig pressure. Conditions used for hydrocracking were 550750"F, 1.5-4.0 LHSV, 2.5-4.0 Ha/hydrocarbon mole ratio, and 450 to 1000 psig pressure. n-Hexane (99 mole 90 pure) was used as the feedstock for most of the experiments. In addition, a raffinate was used as the feedstock for some of the hydrocracking experiments, and a C5/Cs simulated natural gasoline was used in the hydroisomerization studies. The compositions of these feedstocks are given in Table I. Raffinate is predom-
Table I. Feedstock Compositions
Component n-Butane Isopentane n-Pentane Cyclopentane 2,2-Dimethylbutane 2,3-Dimethylbutane 2-Methylpentane 3-Methylpentane n-Hexane Methylcyclopentane Cyclohexane Benzene C7 Paraffins Toluene c8+
Raffinate vol %" 0.1 1.2
1.3 1.6 2.5 4.1 21.3 16.9 26.4 5.1 0.4 0.5 16.7 1.6
Simulated natural gasoline, wt %
Table 11. Physical Properties of Ni-SMM Catalysts Evaluate&
19 .o 31 . O 0.5
2 .o
13.5 10.5 23.5
...
...
0.2
aAverage molecular weight is 88 g. inately a paraffinic stream which remains after aromatics are extracted from reformate. Liquid products were analyzed quantitatively using gas chromatography and gaseous products by mass spectrometry. Selectivity is defined as the weight per cent of the desired product(s) relative to the total weight of the products.
Catalyst A B C D E F G H
where each layer group is separated by cation exchange sites to maintain charge neutrality (Wright, et al., 1972). The aluminum ion is in tetrahedral (tetra) coordination in the silica-alumina layers and in octahedral (oct) configuration in the alumina layer. In all the clays discussed in this paper, x is approximately 1.5. Incorporation of nickel into the SMM structure occurs by substitution for octahedral aluminum; however, separate alumina and nickel octahedral layers may exist in the clays. Details of the synthesis and structural aspects of the nickel clays are beyond the scope of this paper and will be reported in the future by Granquist and coworkers. Table I1 gives the physical properties of the catalysts evaluated. As nickel is incorporated into the clay, there is a significant increase in surface area. This is in contrast to catalysts made by impregnation of SMM with metal ions which results in a considerable loss of surface area. The materials with varying nickel levels were evaluated for hexane hydroisomerization activity. The experimental results obtained at 500°F are given in Table I11 along with data for Pd-H-mordenite which has been reported to be very effective for this reaction (Adams and Rimberlin, 1967; Benesi, 1965, 1970). These data show the dramatic increase in catalytic activity and increased formation of high octane 2,2-dimethylbutane with increasing nickel concentration. The rate data given, which normalize the hexane conversion per unit weight of catalyst, show that the Pd-15% Ni-SMM catalyst is approximately 20 times more active than the Pd-SMM catalyst and approximately 1.7 times more active than Pd-H-mordenite. The catalyst prepared by impregnating 15 wt 70 nickel on SMM has lower activity than SMM, demonstrating the importance of having the nickel incorporated in the structure. It is important to have palladium impregnated or exchanged on Ni-SMM to obtain maximum hydroisomerization ac-
0 1 2
2
3 4 5 6
I*
Wt % F 1.21
0
6.75 14.3 15.0 21.6 26.4 30.5 35.7 15.0
0.50 0.61 1.01 0.73 0.53 0.28 0.37 1.01
Pd-rare earth-Y zeolitec 1% Pd-H-mordenitec
Surface area, m2/g 145 199 230 244 302 254 258 332 94 467 406
All samples calcined at 1000O F before analyses and contain approximately 0.7% Pd. b Catalyst made by impregnating SMM base (A) with nickel nitrate to incipient wetness, oven dried at 250°F for 16 hr and then calcined at l O O O O F for 10 hr. Surface areas obtained on formed materials after being calcined a t l O O O O F for 10 hr. Table 111. Hexane Hydroisomerization with SMM and Ni-SMM Catalysts at 50O0FQ
Results and Discussion The overall stoichiometry of the SMM unit cell can be represented by [(A1,)O"(A1,SiB~,)'e""02,(0H, F),]"- xNH,'
AP-. proximate Ni atoms/ unit W t % cell Ni
Selectivity to isomerized products, wt % c
2,2DMB/ Cs, wt %
Hexane conversion, wt %
Rateb 0.035 0.356 0.636 0.730 0.638 0.588 0.599 0.596 0.013 0.278
100 99 94 96 95 79 73 76
Jd
3.5 45 71 76 80 84 86 85 0.9 25
74
0.8 4.1 8.7 13.4 14.4 19.9 18.8
