EP0107375B1

EP0107375B1 - Catalytic cracking process using powdered zeolite catalysts

Info

Publication number: EP0107375B1
Application number: EP83305769A
Authority: EP
Inventors: Nai Yuen Chen
Original assignee: Mobil Oil AS; Mobil Oil Corp
Current assignee: Mobil Oil AS; ExxonMobil Oil Corp
Priority date: 1982-09-28
Filing date: 1983-09-27
Publication date: 1986-05-28
Also published as: EP0107375A1; ZA837254B; AU559911B2; DE3363785D1; JPS5980489A; AU1955483A; BR8305308A; CA1218619A

Description

This invention relates to a catalytic cracking process using a crystalline zeolite of extremely small particle size as cracking catalyst.
Crystalline zeolites are extensively employed in commercial operations as catalyst for the production of gasoline. In practice they are combined with a suitable matrix, such as an inorganic oxide, to form either a bead suitable for use in moving-bed installations or a fluidizable catalyst particle suitable for use in FCC installations. Gas oil feed in contacted with the catalyst in a reactor until the catalyst is deactivated by deposition of coke. The catalyst is then passed through a regenerator in which the coke is burned off. Hot regenerated catalyst is then re-introduced into the reactor to contact the feed again. The cycle repeats continuously.
Such operations enjoy great commercial success and result in significant economic advantages. Nevertheless they do require a relatively large amount of catalyst in order to effect a satisfactory conversion of feed with satisfactory selectvity to gasoline. Current fluid riser cracking processes use catalyst-to-oil weight ratios of more than 5:1. The possiblity of discarding such large amounts of catalyst when coke-contaminated could certainly not be contemplated, particularly since the cracking reaction is endothermic and at least part of the heat necessary to conduct it must be obtained from combustion of coke in the regenerator and the subsequent introduction of the hot catalyst into the reactor.
Disclosures of catalytic cracking of gas oil with crystalline zeolites include U.S. Patent Nos. 3,140,249, 3,140,251 and 3,140,253, in which the particle size of the catalyst composite employed is either in the range of about 0.08 to 0.25 inches (2-6.35 mm) (for moving-bed operation) or the range of 10 to 150 microns (10-150 mm) (for FCC operation). The matrices employed include both catalytically active materials, such as silica-alumina, and catalytically inactive materials, such as silica. The circulation rate of such a catalyst composite is tied to its catalytic cracking function. Thus, for example, in a typical FCC operation, circulation rate of a matrix and circulation rate of a catalyst are inherently tied together and this rate is dependent on catalyst activity. The extent to which coke is removed in regeneration is directly tied to the restoration of the catalytic activity of the catalyst composite which, in turn, controls the rate of circulation of the catalyst into the cracking unit in order to maintain a stable operation.
GB-A-1,060,749 discloses a process for the catalytic conversion of hydrocarbons which comprises contacting the hydrocarbons at conversion conditions with a contact mass comprising two components, one of which is a particle form solid material which is catalytic or catalytically inert ranging from 200 mesh upwardly to 0.14 inch in diameter, the second component comprising a zeolitic molecular sieve conversion catalyst, said second component being in the form of particles ranging downward in diameter from 15 microns, said second component having at least some material of not more than 5 microns in diameter and sufficient of said second component to substantially coat the particles of the first named component and to adhere to the surfaces of the particles of the first named component.
According to the present invention a cracking process in which a hydrocarbon feed is contacted with a crystalline zeolite catalyst is characterized by the fact that said feed contacts both said catalyst, in the form of particles 0.01 to 5 I-lm in size and of an alpha activity of at least 500, and a hot, substantially catalytically inert solid in the form of particles 30 to 300 pm in size, whereafter said solid is separated and calcined and the resulting hot calcined solid recirculated to contact the feed, the weight ratio of zeolite catalyst to feed during the contacting being no greater than 0.1, preferably 40 to 2000 ppm. Preferred zeolites are zeolite X, Y, L, ZSN-5, ZSM-11, ZSN-12 and/or beta; preferred solids comprise sand, clay, dolomite, glass and/or metal, advantageously processing a surface area of at least 10 m²/g. In one embodiment the hot solid contacts unheated feed in which the zeolite catalyst is already dispersed; and at least part of the zeolite catalyst may, after contact with the feed, be separated therefrom, calcined and recirculated to contact the feed. Contact between catalyst, solids and feed usually occurs at a temperature of 300 to 650°C, with a residence time of 2 to 10 seconds at a solids:oil ratio of 5:1 to 12:1. It is preferred that the particle size of the zeolite be no greater than 2 pm.
The powdered zeolite can thus either be discarded or a portion of the same entering an air calcinerwith the heat carrier solids can be recovered from the flue gas via conventional means, such as by using an electrostatic precipitator amd/or bag filters, and recycled if desired. As can be seen, a key aspect of the invention is the separation of the catalytic cracking function from the circulating solids. Thus, the circulation rate of the solids is not tied to the catalytic activity but can be varied to the limit of the particular catalytic cracking unit being utilized, taking full advantage of its mechanical and material design. Thus, neither the circulating solids themselves or the rate at which they are recirculated are determined by properties of the crystalline zeolite, which need not be recycled at all or can be recycled at a rate which is different from the rate at which the solids are recirculated.
Since extremely small amounts of catalyst may be employed it is essential that the crystalline zeolite be highly active. As will be demonstrated in the examples, a zeolite having an alpha activity of 40 did not function in the process of this invention. The alpha test is described in The Journal of Catalysis. Vol. 4, pp. 522-529, August 1965.
Because the use of small particle size catalysts permits intimate contact of the catalyst with the feedstock, the amount of catlyst needed is greatly decreased. In the preferred practice of this invention, the catalyst-to-oil ratio is reduced from the conventional commercial operation of about 5:1 down to 40-2000 ppm per weight of oil - a reduction of more than 125,000-fold. Larger quantities of catalyst may be used but there is no particular added advantage to using more catalyst than is necessary effectively to catalyze the cracking of gas oil to gasoline.
The hot solids which are circulated to provide the necessary heat for the cracking reaction are not narrowly critical in nature, and since their circulation rate if divorced from the catalytic cracking activity of the powdered zeolite catalyst they can include such relatively low-cost substances as sand, dolomite, clay minerals, glass and metal particles. Thus, the preferred solid materials which are used as circulating heat carriers are materials which have substantially no catalytic cracking activity and their function would be merely to provide the necessary heat for the catalytic cracking reaction. However, it is to be understood that catalytically active materials, though not preferred, can also be used. Such materials include silica alumina, silica-zirconia, silica-titania, acid treated clays, etc. Although these materials do have catalytic cracking activity it is not as great as that of the powdered crystalline aluminosilicate zeolite so that, in effect, the heat transfer function and the catalytic function have still been separated although not to the extent that they would be were the heat carrier inert.
In one embodiment of this invention, it is preferred that the circulating solid have a high surface area, particularly when normally bothersome feeds such as heavy oils, resids or high metal containing feeds are used. The circulating solid of high surface area serves to trap out metal and coke. The preferred surface area should be greater than about 10 sq. meters/gm.
In another embodiment of this invention coke particles can serve as the circulating solids. Thus, the powdered superactive crystalline aluminosilicate zeolite may be dispersed in a coke gas oil or vacuum resid and introduced into a fluid coker.
Crystalline aluminosilicate zeolites which are useful in the novel process of this invention are extremely well known in the art and include zeolite X, Y, Beta, L, as well as mixtures of the above with smaller pore zeolites such as erionite, mordenite, ZSM-5, ZSM-8, ZSM-11 and ZSM-12 - providing they possess the appropriate alpha activity. The preferred crystalline aluminosilicate zeolites may include zeolite X and Y, particularly in their rare earth, acid, or rare earth-acid form. A mixture of zeolites can be used. One may commence the process with one zeolite then change it to another in order to meet product demand. Thus, for example, due to the fact that changes in catalyst composition can be made readily, it is possible to start with a maximum gasoline producing catalyst, such as rare earth Y and to quickly change to a maximum distillate catalyst such as dealuminized Y or to a dewaxing catalyst, such as zeolite ZSM-5 or to the use of a mixture of these catalysts in order to accommodate available charge stocks and market demand of the products.
In order to carry out the novel process of this invention, it is necessary that the heat carrier solid be of a particle size which is substantially in excess of the micron size of the powdered crystalline aluminosilicate zeolite. Since it is desired to separate the heat transfer function from the catalytic function, it is also necessary to be able to separate the heat circulating solids from the powdered crystalline aluminosilicate zeolite. To the extent that the heat circulating solids have a particle size greater than the powdered crystalline aluminosilicate zeolite, separation is easier. Thus, the expression "heat circulating solid" as used throughout the specification and claims is intended to mean a solid material which is preferably catalytically inert and which has a particle size of from 30 to 300 microns and even more desirably from 45 to 2000 microns. Blending of feedstock an catalyst may be carried out before the feedstock is introduced in to the reactor. In such a mode of operation, it is preferred to bypass or to eliminate the feed preheater in order to avoid catalyst deactivation. However, if it becomes necessary to use a feed preheate, another mode of operation is to disperse the catalyst in a separate cold hydrocarbon stream and inject it directly into the catalytic cracker whilst the remaining portion of the hydrocarbon feed, e.g. gas oil, is passed through the feed preheater.
Another advantage of the invention is that it is possible to incorporate additional functions into the circulating solids, such as S0₂ emission control by the use of antimony compounds or carbon monoxide combustion catalysts such as trace amounts of platinum or other well known materials which have an oxidation function.
The single figure of the Drawing is a schematic diagram of a process in accordance with the invention. A powdered crsytalline aluminosilicate is dispersed into a hydrocarbon feed and the mixture is fed into mixing zone 1 wherein it contacts hot solids such as sand, which enter into mxiing zone 1 through line 3. In mixing zone 1, the hot solids and the realtively cold catlayst-oil mixture are equilibrated and enter into reactor 2 wherein the hydrocarbon oil is catalytically cracked into lower molecular weight products such as gas oil. In general, the catalyst oil mixture moves rapidly through the reactor at a rate faster than that of the heat carrier solids. The products from rector 2 pass to a separator 4 where a gas liquid product is separated. This liquid product contains some of the micron or sub-micron size crystalline aluminosilicate zeolite, but the presence of these materials in the oil does not present any technical problems. The remaining portion of the powdered material, together with the solids, passes through line 5 into an air calciner 6 to which air is introduced through line 7. The powdered crystalline aluminosilicate zeolite passes through line 8 into filter 9 where it is recovered and either discarded or a portion recirculated back to reactor 3 through line 10. The hot solids from the air calciner 6 are recirculated to the mixing zone 1 through line 3.
The following examples illustrate the invention.

Feed preparation

In all the examples which follow, a waxy, high pour point Gippsland crude was used. Table 1 summarizes the properties of the crude oil. The oil was fractionated into a 420°F (215.5.OC) minus fraction, and a 420°F+ (215.5°C+) reduced crude fraction which included the residuum. The reduced crude was used as the feed without further purification or separation.

General test procedure

The reduced crude either neat or containing 400 to 2000 ppm of a dispersed acid cracking catalyst was charged into a fluidized bed reactor maintained at 510°C, at a rate of 1.13 gm/min. The reactor contained 50 ml (19 grams) of y-alumina particles which served as the heat transfer solids. The particles were fluidized by flowing 20 ml/min to 850 ml/min of helium depending on the activity of the dispersed catalyst and the oil residence time desired. Material balances were made at 10-minute intervals. To obtain a value of coke for the material balance, the oil was momentarily stopped and the reactor flushed with helium, after which the coke deposit on the heat transfer solids was burnt with a stream of 40% oxygen in nitrogen flowing at 400 ml/min and the combustion gas monitored with an IR detector for CO anbd C0₂ until all the coke was burnt. At the end of the burn, the reactor was flushed with helium before restarting the crude oil/dispersed catalyst feed pump.

Examples 1-3

In the following examples, the reactor was filled with 19 gms of fluid particles of y-alumina (60-120 mesh), a thermal background run was first made without any added dispersed catalyst. After the thermal run, the fed was changed to the one containing the dispersed catalyst. To prepare the dispersed catalyst, a 40/1 SiO_z/AI₂0₃ ZSM-5 was steam activated according to U.S. Patent No. 4,326,994 to an alpha value of 1600. The zeolite was in powdered form comprising submicron particles. It was dispersed in the oil at a concentration of 400 ppm.
In a second series of experiments, a superactive rare earth Y was prepared according to U.S. Patent No. 3,493,519 from a REY to an alpha value of 10,200.
The preparation was carried out contacting 52 grams of rare earth exchanged Y with 398.7 grams of 2.0 molar NH₄N0₃ for 96°C for one hour. The material was then steamed for one hour at 1000°F (538°C) with saturated steam followed by treatment with ethylene diaminetetraacetic acid (neutralized with ammonium hydroxide to a pH of 6.7). The treated material was then calcined at 1000°F (538°C) for one hour followed by ecxchange with 2 molar hot NH₄N0₃. The material was again calcined for one hour, exchanged with boiling NH₄NO₃ for one hour and washed with boiling water. The washed material was again exchanged with boiling NH₄NO₃ (2 molar) for one hour, washed with boiling water and dried overnight at 130°F (54.5°C).
The zeolite was in the powdered form, comprising particles of 2 µm or smaller. It was dispersed in the oil at a concentration of 2000 ppm.
Both the thermal run and the catalytic runs were made at 510-C and 1.13 gm oil/min and about 20 ml/ min of helium as the fluidizing gas. From the results shown in Table 2, high activity ZSM-5 and superactive REY are clearly effective catalysts for the dispersed cracking system.

Examples 4-6

In order to reduce thermal cracking, the following experiments were carried out at shorter vapor residence times by increasing the flow rate of the fluidizing gas from about 20 ml/min to about 850 ml/min. In addition to the thermal run, two catalytic runs were made under otherwise identical conditions with two high activity zeolite catalysts dispersed in the oil prepared as described previously. The results, as shown in Table 3, demonstrate that the conversion due to thermal reactions was greatly reduced and both high activity dispersed catalysts effected significant conversion of the feedstock to 420°F (215.5°C) minus cracked products.

Examples 7-9

In the last series of experiments, two commercial acid catalysts were used as the dispersed catalysts: a HZSM-5 steamed to an alpha value of 40, and a steam stabilized rare earth Y cracking catalyst (a = 0.5). These catalysts were evaluated in the presence of another batch of freshly prepared y-alumina which was more thermally active than the batch used in previous experiments, as indicated by its high methane yield. Results of the tests together with the thermal background run as presented in Table 4 show that these commercial acid catalysts were not effective when used in low concentration in the dispersed form. These experiments serve to demonstrate the importance of using catalysts possessing high intrinsic acid activity.

Claims

1. A cracking process in which a hydrocarbon feed is contacted with a crystalline zeolite catalyst, characterized in that said feed contacts both said catalyst, in the form of particles 0.01 to 5 µm in size and of an alpha activity of at least 500, and a hot, substantially catalytically inert solid in the form of particles 30 to 300 pm in size, whereafter said solid is separated and calcined and the resulting hot calcined solid recirculated to contact the feed, the weight ratio of zeolite catalyst to feed during the contacting being no greater than 0.1.

2. A process according to claim 1 wherein the weight ratio of catalyst to feed is 40 to 2000 ppm.

3. A process according to claim 1, or claim 2 wherein said zeolite is zeolite X, Y, L, ZSM-5, ZSM-11, ZSM-12 and/or beta.

4. A process according to any preceding claim wherein said solid comprises sand, clay dolomite, glass and/or metal.

5. A process according to any preceding claim wherein said solid has a surface area of at least 10 m²/g.

6. A process according to any preceding claim wherein the hot solid contacts unheated feed in which the zeolite catalyst is already dispersed.

7. A process according to any preceding claim in which at least part of the zeolite catalyst is, after contact with the feed, separated therefrom, calcined and recirculated to contact the feed.

8. A process according to any preceding claim wherein contact between catalyst, solids and feed occurs at a temperature of 300 to 650°C, with a residence time of 2 to 10 seconds at a solids:oil ratio of 5:1 to 12:1.