USE OF PETROLEUM CATALYSTS

Abstract: Hycarbon feedstock containing nickel is subjected to a catalytic cracking process using a catalyst comprising zeolite, matrix and mixed oxide. The mixed oxide is selected from calcium, strontium and barium tin oxides and mixtures thereof.

Description: Field of the invention: The invention relates to cracking catalysts and to catalytic cracking, which is a major refinery process for the conversion of hydrocarbons to lower boiling fractions. More specifically, the invention relates to an improved process for cracking nickel containing feedstocks by using these catalysts. Background to the invention: Catalysts containing crystalline zeolites dispersed in an inorganic oxide matrix have been used for the catalytic cracking of petroleum-derived feedstocks for many years. During this time, it has been widely recognised in the industry that certain contaminants (notably vanadium, nickel, and iron), initially dissolved or dispersed in the hydrocarbon feedstock, are deposited on the catalyst during the catalytic cracking process, and the accumulated deposits lead to undesirable changes in the activity and selectively of the thus contaminated catalysts; see P.B. Venuto and E.T. Habib, Jr., Fluid Catalytic Cracking with Zeolite Catalysts, Marcel Dekker, Inc, New York, 1979, pages 10-11, and Kirk Othmer, Encylopedia of Chemical Technology, John Wiley & Sons, New York, Third Edn., 1981, Vol 17, page 82. Typically, the harmful effects noted have been increased yields of coke and hydrogen, a phenomenon ascribed to the action of the deposited metals as centres of dehydrogenation. These problems have become more acute as refiners have faced the need to process heavier feedstocks which contain increased amounts of the metal contaminants, and various strategies have been employed to alleviate the deleterious effects and facilitate smooth running of catalytic cracking units. These approaches have included (1) more frequent replenishment of the circulating catalyst inventory; (2) withdrawal of the regenerated catalyst and treatment with various chemicals to passivate the metals; (3) changes in design or operation of the catalytic cracker to reduce the poisoning activity of the contaminant metals; (4) addition to the feedstock of compounds of elements such as antimony, tin, barium, manganese, germanium and bismuth. Examples of these are found in the patent specifications US-A-4238362, US-A-4101417, GB-A-1598289, US-A-4377494, US-A-4367136 and US-A-3977963; and (5) incorporation in the zeolite composition of a passivating compound; thus, for passivation of vanadium or nickel, EP-A-0209240 recommends the addition of strontium carbonate and, for passivation of vanadium and nickel together, EP-A-0194536 recommends the addition of barium titanate, while for passivation of vanadium alone, EP-A-0204543 recommends the addition of a calcium, barium or strontium tin oxide. General description of the invention : The present invention provides a method of cracking nickel contaminated hydrocarbon feedstocks with a catalyst composition and use of the catalyst composition in such a method, which catalyst composition comprises a i) crystalline zeolite, ii) a matrix material, and iii) certain crystalline mixed oxides, derived from the heavier alkaline earth elements (calcium, strontium, barium) and tin, which oxides have themselves no harmful effects on the catalytic properties but are present in amounts sufficient to passivate the dehydrogenation properties of the contaminent nickel. Accordingly, the catalyst composition for use in accordance with the present invention comprises i) a crystalline zeolite, ii) a matrix material and iii) a mixed oxide selected from calcium, strontium and barium tin oxides and mixtures thereof. The mixed oxides include hydroxy stannates. The crystalline zeolite component, which is usually present in the range from about 5% to about 40% by weight, may generally be described as a crystalline, three dimensional, stable structure enclosing cavities of molecular dimensions. Most zeolites are based on aluminosilicate frameworks, the aluminium and silicon atoms being tetrahedrally coordinated by oxygen atoms. However, for the purposes of our invention we include as "zeolites" similar materials in which atoms of other elements are present in the framework, such as boron, gallium, germanium, chromium, iron, and phosphorus. Further we include materials such as pillared interlayered clays ("PILCS"), which have many of the catalytically valuable characteristics of the aluminosilicate zeolites. We also include all modifications to the above materials, whether obtained by ion-exchange, impregnation, hydrothermal or chemical treatments. Zeolites which can be employed in the catalysts for use in the methods of this invention can be natural or synthetic in origin. These naturally occurring zeolites include gmelinite, chabazite, dachiardite, clinoptilolite, faujasite, heulandite, analcite, levynite, erionite, sodalite, canorinite, mepheline, lazurite, scolecite, natiolite, offretite, mesolite, mordenite, brewsterite, fevierite, and the like. Suitable synthetic zeolites are zeolites A, B, E, F, H, J, L, Q, T, W, X, Y, Z, alpha, beta, omega, the EU types, the Fu types, the Nu types, the 2K types, the ZSM types, the ALPO types, the SAPO types, the L2 series, and other similar materials will be obvious. The effective pore size of the synthetic zeolites are preferably between 0.6 and 1.5 nanometers, and the preferred zeolites are those with the faujasite framework and silica/alumina ratios > 3, thus including synthetic zeolite Y and the various forms of Y which have been made more siliceous by chemical, hydrothermal or thermal treatments. In a preferred embodiment of the invention, the zeolite is converted to a form which is most applicable for catalytic cracking. In general this involves a sequence of ion-exchange and calcination treatments to introduce acid groups into the zeolite, stabilise the structure, and remove alkali metal cations. The prefered method of achieving this end, well known in the art, is to exchange the zeolite with solutions containing ammonium ions and/or rare earth ions (either a pure rare earth compound or a mixture). Such treatment can be carried out either on the zeolite before it is incorporated in the catalyst, or on the finished catalyst containing the zeolite, it can be carried out on a filter press, filter table, or filter belt, or by slurrying the zeolite/catalyst in a tank. The matrix into which the zeolite is incorporated can have a wide range of compositions. Suitable components include: naturally occurring or synthetic clays, including kaolin, halloysite and montmorillonite; inorganic oxide gels, including binary gels such as silica, silica-alumina, silica-zirconia, silica-magnesia, aluminium phosphates, or ternary combinations such as silica-magnesia-alumina; and crystalline inorganic oxides such as silica, alumina, titania, zirconia. Suitable mixed oxides for use as component (iii) are: The mixed oxide additive is a discrete component of the final catalyst, and is readily identifiable in the fresh catalyst by x-ray diffraction analysis. These materials are insoluble, and are not decomposed into their component oxides over a wide range of thermal and hydrothermal treatments, and, as such are readily identifiable in hydrothermally deactivated catalyst samples. Preferably the mixed oxide is present at a level of least about 0.1% by weight of the catalyst and up to about 20% by weight. The chemical form of the additive is central to determining the concentration in which it is used in the catalyst composition, or indeed its method of incorporation into the catalyst formulation. The additives used in methods of this invention can be prepared by various processes; for example, by calcination of intimate mixtures of the oxides or carbonates of the component elements, in the appropriate molar quantities, or by coprecipitation, or metathesis of salts of the appropriate elements. Conventional catalyst processing procedures encompass a wide range of pH conditions, typically pH 3 to pH 10, and require that any additives be resistant to such environments without themselves being decomposed, or resulting in changes in the properties of other catalyst components. The effect of additives not resistant to such environments can be to render the catalyst processing procedure inoperable, or to adversely affect both the physical and catalytic properties of the finished catalyst. As the form of the additives used in methods of the present invention are insoluble and inert to any catalyst processing procedures, the catalysts containing these additives may be prepared by any of the conventional methods used for the manufacture of FCC catalysts. For example, catalyst may be prepared by making an inorganic oxide sol at pH 3 and adding to this, aqueous slurries of the other catalyst components including zeolite and alkaline earth additive. The homogenised slurry can then be spray dried to produce catalyst microspheres, and washed free of soluble salts using for example aqueous ammonium sulphate and water. The catalyst compositions used in methods of this invention are employed in the cracking of nickel containing heavy hydrocarbon feedstocks, to produce gasoline, and light distillate fraction. Typical feedstocks would have an average boiling point greater than 316°C, and include such materials as gas oils, and residual oils. Because the catalysts used in methods of this invention are effective in cracking processes even when contaminated with nickel to levels in excess of 2000 ppm, these catalysts can be used to process feedstocks containing significantly higher concentrations of nickel than those employed in conventional catalytic cracking operations. These catalysts may be employed in any catalytic cracking process capable of operating with conventional microsphere fluid catalysts. Specific description of the invention The following examples illustrate the advantages of the invention. However, it is not intended that the invention be limited to the specific examples given. Example 1 (comparative) A catalyst was prepared by combining together 100 g Al₂O₃ 400 g Kaolin, and 270 g of CREHY (calcined Rare Earth/Ammonium exchanged zeolite Y), in 2895 g of a silica sol (8% SiO₂ w/w) at pH 3.2, to provide a homogeneous slurry. The slurry was then spray-dried to form catalyst microspheres with an average particle size of about 60 microns. The spray-dried catalyst was then washed with deionized water, 0.25 M ammonium sulphate, and finally deionized water, until the conductivity of the filtrate fell below 1 milli-mho. The washed catalyst was then dried at 100°C (Catalyst A). Example 2 A catalyst was prepared by combining together 100g Al₂O₃, 276g Kaolin, 124 g SrSnO₃, and 270 g of CREHY, in 2875 g of a silica sol (8% SiO₂ w/w) at pH 3.2, to provide a homogeneous slurry. The slurry was then spray-dried to form catalyst microspheres with an average particle size of about 60 microns. The spray-dried catalyst was then washed with deionized water, 0.25 M ammonium sulphate, and finally deionized water, until the conductivity of the filtrate fell below 1 milli-mho. The washed catalyst was then dried at 100°C (Catalyst B). Example 3 A catalyst was prepared by combining together 100g Al₂O₃, 300 g Kaolin, 100 g CaSnO₃, and 270 g of CREHY in 2875 g of a silica sol (8% SiO₂ w/w) at pH 3.2, to provide a homogeneous slurry. The slurry was then spray-dried to form catalyst microspheres with an average particle size of about 60 microns. The spray-dried catalyst was then washed with deionized water, 0.25 M ammonium sulphate, and finally deionized water, until the conductivity of the filtrate fell below 1 milli-mho. The washed catalyst was then dried at 100°C (Catalyst C). Example 4 A sample of catalyst of example 1, previously thermally treated to 538°C for 2 hr, was impregnated with 5000 ppm nickel according to the following procedure. 50 g of the thermally treated catalyst was slurried in 50 ml of a solution of 1.67 g nickel naphthenate in xylene in a rotary evaporator. The slurry was allowed to fully mix for 30 min at room temperature with constant agitation. The slurry was then dried under vacuum to yield the nickel impregnated catalyst. The impregnated catalyst was finally calcined at 538°C for 2 hr (Catalyst D). Example 5 50 g of catalyst of example 2, thermally treated to 538°C for 2 hr, was impregnated with 5000 ppm nickel using the procedure detailed in example 4. (Catalyst E). Example 6 50 g of catalyst of example 3, thermally treated to 538°C for 2 hr, was impregnated with 5000 ppm nickel using the procedure detailed in example 4. (Catalyst F). The above catalysts (A-F) were evaluated in a microactivity test (MAT) unit. Prior to testing, the catalyst samples were thermally treated at 538°C for 3 hrs, and then deactivated in steam at atmospheric pressure, at a temperature of 788°C for a period of 5 hrs. The cracking conditions used for the MAT were: The gasoil feedstock in these tests was characterised as follows: Distillation (°F) Specific Gravity (g/cc) was 0.907 These results demonstrate the presence of the strontium and calcium stannate reduce the dehydrogenation activity brought about by nickel contamination. Example 7 A zeolite based (CREHY) spray-dried catalyst was prepared containing CaSn(OH)₆ (1.1% w/w as CaO). This catalyst was impregnated with nickel, and deactivated under an atmospheric of steam in an equivalent manner to that described in the preceding examples. The catalytic performance of this sample (Catalyst G) was measured by MAT, and compared to an equivalent catalyst formulation containing no hydroxy stannate component (catalyst H). The results of these tests are shown in table II. This demonstrates the effectiveness of calcium hydroxystannate in reducing the dehydrogenation activity of contaminent nickel.

Claims: 1. A method of cracking nickel contaminated hydrocarbon feedstocks wherein the feedstock is contacted with a catalyst composition comprising: i) a crystalline zeolite, ii) a matrix material, and iii) a nickel passivating compound, characterised in that the nickel passivating compound is a mixed oxide selected from calcium, strontium and barium tin oxides and mixtures thereof. 2. A method according to claim 1, wherein the catalyst composition is contaminated with nickel at a level in excess of 2000 ppm. 3. A method according to claim 1 or 2, wherein the catalyst composition comprises from about 5% to about 40% by weight zeolite. 4. A method according to claim 1, 2 or 3, wherein the catalyst composition comprises from about 0.1% to about 20% by weight of mixed oxide. 5. Use of a catalyst composition in a method of cracking a nickel contaminated feedstock, which catalyst composition comprises i) a crystalline zeolite ii) a matrix material, and iii) a nickel passivating compound, characterised in that the nickel passivating compound is a mixed oxide selected from calcium, strontium and barium tin oxides and mixtures thereof. 6. Use according to claim 5, wherein the catalyst composition is contaminated with a level of nickel in excess of 2000 ppm. 7. Use according to claim 5 or 6, wherein the catalyst composition comprises from about 5% to about 40% by weight zeolite. 8. Use according to claims 5, 6 or 7, wherein the catalyst composition comprises from about 0.1% to about 20% by weight of mixed oxide.

Inventors: CHAPPLE, ANDREW PAUL
Applicants: UNILEVER N.V., UNILEVER PLC
Application year: 1988
Main classification: C10G11
IPC codes: C10G11