Fluid Cracking Catalyst Process Using a Zeolite Dispersed in a Magnesia-Alumina-Aluminum Phosphate Matrix

1. Field of the Invention

The present invention resides in a process for increasing gasoline yield and quality using a proprietary fluid cracking catalyst comprising a zeolite dispersed in a magnesia-alumina-aluminum phosphate matrix.

Around the turn of the century, motor vehicles in the United States began to appear in increasing numbers and gasoline obtained a degree of marketable value as a refinery product. Shortly thereafter, demand in the United States for motor fuels began to exceed the amount produced from refinery crude-oil runs geared for producing kerosene, fuel oils, etc., which were very much in demand at the time. Since then, the petroleum industry's most prominent problem has been inventing new and more efficient methods to meet the tremendous demand for gasoline without overproducing other petroleum products at the same time.

Due to the continually increasing demand for gasoline and the ever-shrinking supplies of crude cracking stocks, such as gas oils and the like, more attention has recently been directed to the catalytic cracking of heavier charge stocks such as petroleum residuals. These charge stocks, however, suffer from the disadvantage of having high metals content which is concentrated therein during a normal cracking process. The metals tend to deposit on catalysts and decrease the cracking characteristics thereof in a cracking process. The catalysts herein are particularly formulated to increase the gasoline yield and quality (i.e., BTX) from gas oils during a cracking process and additionally to catalytically crack petroleum residuals with high selectivity to gasoline production as well as having improved metals tolerant characteristics. Examples of typical metals which can be present during the cracking process include: nickel, vanadium, copper, chromium and iron.

2. Description of the Prior Art

The use of zeolitic cracking catalysts has become of increased importance in petroleum cracking processes due to the higher activity characteristics of these catalysts (see "Recycle Rates Reflect FCC Advances," by J. A. Montgomery, Oil & Gas Journal, Dec. 11, 1972, pp 81-86).

Several processes have been proposed in the past wherein zeolite catalysts are utilized to crack crude oils and petroleum residual feedstocks.

For example, U.S. Pat. No. 3,617,528; entitled "Hydrotreating Process and Catalyst;" issued to Hilfman on Nov. 2, 1971 discloses a hydrotreating process and a catalyst consisting of an alumina containing porous carrier material, a nickel component and a phosphorus component. The porous carrier is described as an adsorptive high surface area support. Suitable carrier materials include amorphous refractory inorganic oxides, for example, alumina, titania, zirconia, chromia, magnesia and the like.

U.S. Pat. No. 3,838,040; entitled "Hydrocracking with Zeolite in a Silica-Magnesia Matrix," issued to Ward on Sept. 24, 1974 relates to hydrocarbon conversion catalysts which are described as having increased activity and selectivity as well as improved physical characteristics. The catalysts consist of crystalline zeolitic aluminosilicates and silica-magnesia. It is to be noted that the prior art fails to appreciate the catalyst combination disclosed herein.

We have discovered a process for increasing the gasoline yield and quality in a petroleum cracking reaction by utilizing a catalyst possessing high activity and selectivity to gasoline production, as well as superior tolerance of high metals charge stocks. Particularly, our invention comprises a process for increasing gasoline yield in a petroleum cracking reaction by contacting a hydrocarbon feedstock under catalytic cracking conditions with a catalyst comprising a magnesia-alumina-aluminum phosphate matrix having an average pore radius of from about 10.degree. A to about 200.degree. A, preferably from about 75.degree. A to about 150.degree. A; a surface area ranging from about 100 M.sup.2 /g to about 300 M.sup.2 /g, preferably from about 125 M.sup.2 /g to about 250 M.sup.2 /g; and a pore volume of from about 0.3 cc/g to about 1.5 cc/g, preferably from about 0.7 cc/g to about 1.2 cc/g and wherein the magnesia-alumina-aluminum phosphate matrix has a mole percent ratio of from about 10:80:10 to about 25:10:65, especially from about 10:55:35 to about 20:35:45; and wherein said matrix retains at least 90% of its surface area when the matrix is additionally calcined at a temperature up to about 750.degree. C. for about 10 hours; said matrix being composited with from about 5 to about 50 weight percent, especially from about 5 to about 35 weight percent of a REY-zeolite.

This invention resides in an improved process for increasing the gasoline yield and quality in a catalytic cracking process of either light or heavy feedstocks which can contain a high metals content. Particularly, the process involves contacting a hydrocarbon feedstock with a catalyst comprising a REY-zeolite composited with a magnesia-alumina-aluminum phosphate matrix.

Typical zeolites or molecular sieves having cracking activity and which can be suitably dispersed in a matrix for use as a catalytic cracking catalyst are well known in the art. Suitable zeolites are described, for example, in U.S. Pat. No. 3,660,274 to James J. Blazek et al. The description of the crystalline aluminosilicates in the Blazek et al patent is incorporated herein by reference. Synthetically prepared zeolites are initially in the form of alkali metal aluminosilicates. The alkali metal ions are exchanged with rare earth metal ions to impart cracking characteristics to the zeolites. The zeolites are, of course, crystalline, three-dimensional, stable structures containing a large number of uniform openings or cavities interconnected by smaller, relatively uniform holes or channels. The effective pore size of synthetic zeolites is suitably between 6.degree. A and 15.degree. A in diameter. The overall formula for the zeolites can be represented as follows:

where M is a metal cation and n its valence and x varies from 0 to 1 and y is a function of the degree of dehydration and varies from 0 to 9, M is preferably a rare earth metal cation such as lanthanum, cerium, praseodymium, neodymium, etc., or mixtures of these.

Zeolites which can be employed in accordance with this invention include both natural and synthetic zeolites. These zeolites include gmelinite, chabazite, dachiardite, clinoptilolite, faujasite, heulandite, analcite, levynite, erionite, sodalite, cancrinite, nepheline, lazurite, scolecite, natrolite, offretite, mesolite, mordenite, brewsterite, ferrierite, and the like. The faujasites are preferred. Suitable synthetic zeolites which can be treated in accordance with this invention include zeolites X, Y, A, L, ZK-4, B, E, F, HJ, M, Q, T, W, Z, alpha and beta, ZSM-types and omega. The term "zeolites" as used herein contemplates not only aluminosilicates but substances in which the aluminum is replaced by gallium and substances in which the silicon is replaced by germanium.

The preferred zeolites for this invention are the synthetic faujasites of the types Y and X or mixtures thereof; however, the Y-type zeolites are superior when used herein.

It is to be noted that some X-type zeolite will be mixed with the Y-type zeolite due to the difficulty and cost involved in separating the two zeolites. It is additionally noted that the presence of small amounts of the X-type zeolite will not substantially impair the superior selectivity to gasoline production of the catalysts herein.

It is also well known in the art that to obtain good cracking activity the zeolites have to be in a proper form. In most cases this involves reducing the alkali metal content of the zeolite to as low a level as possible. Further, a high alkali metal content reduces the thermal structural stability, and the effective lifetime of the catalyst will be impaired as a consequence thereof. Procedures for removing alkali metals and putting the zeolite in the proper form are well known in the art as described in U.S. Pat. No. 3,537,816.

The crystalline aluminosilicate zeolites, such as synthetic faujasite, will under normal conditions, crystalize as regularly shaped, discrete particles of approximately one to ten microns in size, and, accordingly, this is the size range normally used in commercial catalysts. Preferably the particle size of the zeolites is from 0.5 to 10 microns and more preferably is from 1 to 2 microns or less. Crystalline zeolites exhibit both an interior and an exterior surface area, with the largest portion of the total surface area being internal. Blockage of the internal channels by, for example, coke formation and contamination by metals poisoning will greatly reduce the total surface area. Therefore, to minimize the effect of contamination and pore blockage, crystals larger than the normal size cited above are preferably not used in the catalysts of this invention.

The term REY-zeolites as defined herein is the Y-type zeolite that has undergone an ion exchange reaction with rare earth metal ions. The naturally occurring molecular sieve zeolites are usually found in the sodium form, an alkaline earth metal form, or mixed forms. The synthetic molecular sieves are normally in their sodium form, however, it should be understood that other alkali metal compounds can be substituted therefor. In their sodium form, the Y zeolites suitable for use herein correspond to the general formula:

wherein n is an integer of from about 3 to about 6 and x is an integer of from about 0 to about 9. It is to be noted that after the ion exchange reaction with the rare earth metals, the sodium content of the Y zeolite is from about 0.3 to about 1 molar percent, especially from about 0.5 to about 0.8 molar percent. When sodium is present above this molar range, it tends to deactivate the catalyst and to reduce the sodium content below 0.3 molar percent is too expensive to justify.

Rare earth metals can conveniently be substituted for the sodium in the Y zeolite above using conventional techniques and methods. A wide variety of rare earth compounds can be ion exchanged with the above sodium ions. Operable compounds include rare earth chlorides, bromides, iodides, carbonates, bicarbonates, sulfates, sulfides, thiocyanates, peroxysulfates, acetates, benzoyates, citrates, fluorides, nitrates, formates, propionates, butyrates, valecates, lactates, malanates, oxalates, palmitates, hydroxides, tartrates and the like. The preferred rare earth salts are the chlorides, nitrates and sulfates. It is to be noted that the only limitation on the particular rare earth metal salt or salts employed is that it be sufficiently soluble in the ion exchange fluid medium in which it is used to give the necessary rare earth ion transfer.

Representative of the rare earth metals are cerium, lanthanum, praseodymium, neodymium, illinium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, scandium, yttrium, and lutecium.

The rare earth metal salts employed can either be the salt of a single rare earth metal or mixtures of rare earth metals, such as rare earth chlorides of didymium chloride. As hereinafter referred to, unless otherwise indicated, a rare earth chloride solution is a mixture of rare earth chlorides consisting essentially of the chlorides of lanthanum, cerium, neodymium and praseodymium with minor amounts of samarium, gadolinium and yttrium. Rare earth chloride solutions are commercially available and the ones specifically referred to in the examples contain the chlorides of the rare earth mixture having the relative composition cerium (as CeO.sub.2) 48% by weight, lanthanum (as La.sub.2 O.sub.3) 24% by weight, praseodymium (as Pr.sub.6 O.sub.11) 5% by weight, neodymium (as Nd.sub.2 O.sub.3) 17% by weight, samarium (as Sm.sub.2 O.sub.3) 3% by weight, gadolinium (as Gd.sub.2 O.sub.3) 2% by weight, and other rare earth oxides 0.8% by weight. Didymium chloride is also a mixture of rare earth chlorides but having a lower cerium content. It consists of the following rare earths determined as oxides: lanthanum 45-56% by weight, cerium 1-2% by weight, praseodymium 9-10% by weight, neodymium 32-33% by weight, samarium 5-7% by weight, gadolinium 3-4% by weight, yttrium 0.4% by weight, and other rare earths 1-2% by weight. It is to be understood that other mixtures of rare earths are also applicable for the preparation of the novel compositions of this invention, although lanthanum, neodymium, praseodymium, samarium and gadolinium as well as mixtures of rare earth cations containing a predominant amount of one or more of the above cations are preferred since these metals provide optimum activity for hydrocarbon conversion, including catalytic cracking.

The matrix with which the REY-zeolite is composited is preferably a magnesia-alumina-aluminum phosphate of the general formula:

Normally, the magnesia-alumina-aluminum phosphate constituents are in a mole percent ratio range of from about 10:80:10 to about 25:10:65, preferably from about 10:55:35 to about 20:35:45. The above magnesia-alumina-aluminum phosphate matrix can be prepared according to techniques and methods normally used in the art. One such method is set forth in copending U.S. patent application Ser. No. 958,804, filed Nov. 8, 1978 to Kehl et al, the disclosure of which is incorporated herein by reference.

It is to be noted that the magnesia-alumina-aluminum phosphate matrix herein is characterized after calcination at 500.degree. C. for 10 hours, as amorphous and having an average pore radius of from about 10.degree. A to about 200.degree. A, preferably from about 75.degree. A to about 150.degree. A; a surface area ranging from about 100 M.sup.2 /g to about 350 M.sup.2 /g, preferably from about 125 M.sup.2 /g to about 250 M.sup.2 /g; and a pore volume of from about 0.3 cc/g to about 1.5 cc/g, preferably from about 0.7 cc/g to about 1.2 cc/g; and wherein said matrix retains at least 90% of its surface area when the matrix is additionally calcined at a temperature up to about 750.degree. C. for about 10 hours.

The REY-zeolite is composited with the magnesia-alumina-aluminum phosphate matrix from about 5 to about 50 weight percent, preferably from about 5 to about 35 weight percent, based on the weight of said matrix. The method of forming the final composited catalyst does not form a part of this invention, and any method well known to those skilled in the art is acceptable. For example, finely divided REY-zeolite can be admixed with finely divided magnesia-alumina-aluminum phosphate and the mixture spray dried using conventional methods to form the final catalyst. The above-described composite catalysts are highly selective to gasoline production and have a high tolerance to metals.

Typical feedstocks include light or heavy gas oils, light fractions of crude oil, heavy fractions of crude oil, or the like. Any type reaction vessel can be used in this invention which is normally used in the art. For example, U.S. Pat. No. 3,944,482 to Mitchell et al sets forth a suitable reaction vessel, reaction conditions, and process therefor, the teachings of which are incorporated herein by reference.

The weight ratio of catalyst to hydrocarbon feedstock is from about 4:1 to about 12:1, preferably from about 6:1 to about 10:1. The fresh hydrocarbon feedstock is generally preheated to a temperature of from about 316.degree. C. to about 371.degree. C., but is held below the vaporization point of said hydrocarbon feedstock. Additional heat required to achieve the desired reactor temperature is imparted to the reaction mixture by hot, regenerated catalyst.

The reactor linear velocity, should not be sufficiently high to induce turbulence or excessive backmixing, however, the reactor linear velocity must be sufficiently high so that substantially no catalyst accumulation or build up occurs in the reactor because such accumulation leads to backmixing.

Avoiding a catalyst build up in the reactor results in a very low catalyst inventory in the reactor, which results in a high space velocity. It is to be noted that conditions such as reactor size, etc., will determine the space velocity of the process. However, the space velocity herein is from about 35 to about 500 weight of hydrocarbon feedstock per hour per weight of catalyst, especially from about 50 to about 300 weight of hydrocarbon feedstock per hour per weight of catalyst. It is to be noted that the above conditions and description of operation are for a preferred fluid bed riser cracking operation.

The zeolite riser cracking conditions and system (known as FCC or fluid catalytic cracking) of this invention are described in greater detail in U.S. Pat. No. 3,617,512, the disclosure of which is incorporated herein by reference. However, the older conventional fluid bed operation or a fixed-bed operation can be used, the particular reaction condition, etc., are well known in the art and are not part of the present invention.

We have discovered that a magnesia-alumina-aluminum phosphate matrix, substantially as described herein, which has a low intrinsic cracking activity, interacts synergistically with a REY-zeolite, as herein described, to produce a cracking catalyst of high activity giving superior selectivity for gasoline production and quality.

The hydrocarbon feedstock used herein was a Kuwait gas oil having a boiling range of from about 260.degree. C. to about 426.degree. C. Inspections of this Kuwait gas oil are shown in Table I below.

A magnesia-alumina-aluminum phosphate matrix was prepared according to the following procedure:

A first solution was prepared by dissolving 96 grams of magnesium nitrate in 2 liters of water. A second solution was prepared by dissolving 1266 grams of aluminum nitrate in 4 liters of water. The two solutions must be clear. Next, the two solutions were combined and 90 grams of 85% phosphoric acid were added and the resulting mixture was agitated for about 5 minutes to form a final solution.

Approximately 3 liters of water were placed in a mixing vessel to provide a mixing medium. The above-described final solution was slowly added in combination with an aqueous solution of ammonium hydroxide (ratio=1:1) at relative rates to maintain the mixing medium pH at 9.0. The mixing medium was vigorously agitated during the addition period and continued for an additional 10 minutes thereafter to insure maximum contact of the mixing medium components. The mixture was then filtered, the precipitate was washed with 15 liters of water and dried.

The above-described magnesia-alumina-aluminum phosphate matrix, after calcination for 10 hours at 500.degree. C., is characterized by a surface area of 208 M.sup.2 /g, an average pore radius of 106.degree. A and a pore volume of 1.11 cm.sup.3 /g. It is to be noted that the large pore radius of the above matrix is highly beneficial for enhancing metals tolerance in the completed catalyst. The above matrix can be slurried with a REY-zeolite as defined herein to produce the desired catalyst.

A representative REY-zeolite catalyst was prepared according to the following procedure:

Into a 4-liter, 3-necked flask equipped with a mechanical stirrer, a water-cooled condenser and thermometer were added 2400 ml. of water heated to 80.degree. C., with stirring. To the water was added 800 grams of sodium Y zeolite and 564 grams rare earth chloride mixture comprising 48% cerium, 24% lanthanum, 5% praseodymium, 17% neodymium, 3% samarium, 2% gadolinium and 0.8% other rare earth compounds. It is to be noted that all percents are by weight. The temperature was maintained at 80.degree. C. for two hours with continued stirring and the reaction mixture was then filtered. The filtered REY-zeolite was reslurried with 2400 ml. of water and heated to a temperature of 80.degree. C. Next, an additional 564 grams of the above rare earth chloride mixture was added to the solution. The temperature was maintained at 80.degree. C. for two hours with stirring. The resulting REY-zeolite was filtered and washed with eight 1-liter batches of water.

The REY-zeolite was calcined at 538.degree. C. for 10 hours, slurried with 2400 ml. of water and heated to 80.degree. C. The procedure set forth above for the addition of the rare earth chloride mixture to the Y-type zeolite was repeated two additional times and the final reaction product was filtered and washed with eight 1-liter batches of water.

Next, the matrix produced in Example I was slurried and added to the REY-zeolite produced above. The slurry was then spray dried and calcined for 10 hours at 500.degree. C. to produce the desired catalyst. It is to be noted that the REY-zeolite content of the catalyst can be varied according to the wishes of the formulator, however, a weight percent of from about 5% to about 35% based on the total catalyst weight is desirable, especially 15 weight percent.

In Examples III to VII, a comparison was made between a REY-zeolite magnesia-alumina-aluminum phosphate catalyst, as defined herein, and similar commercially available catalysts. The catalysts were evaluated using a microactivity test (MAT) unit similar to the Standard Davison MAT (see Ciapetta, F. C. and Handerson, D. S. "Oil and Gas Journal," 65,88, 1967). Catalyst samples were tested at 482.degree. C., 15 weight hourly space velocity; 80 seconds catalyst contact time and a catalyst to oil ratio of 2.9. The charge stock was a Kuwait gas oil having a boiling range of from about 260.degree. C. to about 426.degree. C. (see Table I for inspection). The results are set forth in Table II below.

It is to be noted that the matrix material of this invention has a low intrinsic cracking activity but when composited with the REY-zeolites herein, interacts synergistically to produce a cracking catalyst of high activity which results in superior production of high quality gasoline.

In Examples VIII to XI the catalysts from Examples II and VII were examined using the above-described MAT unit test to determine the selectivity of BTX as a function of temperature. The reactor temperature was varied in accordance with the temperatures of Table III below, with the other parameters remaining the same. The results are set forth in Table III.

The above data indicate that the catalyst herein displays a marked increase in aromatics production with a modest increase in reaction temperature. This enhanced performance in combination with the catalyst thermal stability properties will permit production of gasoline having a higher octane number through the use of higher temperature processing conditions.

The catalyst of Example II was examined for metals tolerance by synthetically contaminating said cracking catalyst with several concentration levels of nickel and vanadium. The series was prepared by impregnating the catalyst with nickel and vanadium naphthates to metals levels of 1200, 1900, 3000 and 5000 parts per million (PPM) nickel equivalents. Parts per million nickel equivalents means the total PPM of nickel plus one-fifth of the total PPM of vanadium by weight deposited on the catalyst. The test procedure of Examples III to VII was followed with the following results:

The catalyst of Example VII was examined for comparison purposes in accordance with the procedure set forth in Examples XII to XVI. The results are tabulated in Table V below.

As can readily be seen from the above data the catalyst compositions of this invention are superior in its cracking activity; selective to gasoline yield and, additionally, exhibits excellent metals tolerance, attrition and thermal stability properties.

Obviously, many modifications and variations of the invention, as hereinabove set forth, can be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.