Preparation method for modified molecular sieve and modified molecular sieve-containing catalytic cracking catalyst

Abstract

A preparation method for modified molecular sieve and a modified molecular sieve-containing catalytic cracking catalyst. The preparation method comprises: mixing molecular sieve slurry, a compound solution containing ions of group IIIB metals of the periodic table of elements, organic complexing agent and/or dispersing agent and precipitating agent to obtain mixed slurry containing molecular sieve and precipitates of group IIIB elements in the periodic table of elements; and drying, and roasting or not roasting to obtain molecular sieve modified by the group IIIB elements. A weight ratio of group IIIB elements calculated based on oxides to molecular sieve dry basis is equal to (0.3-10):100, a molar ratio of organic complexing agent to ions of group IIIB metals is equal to (0.3-10):1, and a molar ratio of dispersing agent to the ions of group IIIB metals is equal to (0.2-16):1. Also related to is the catalytic cracking catalyst containing the modified molecular sieve prepared according to the method. The molecular sieve prepared by the method or the catalytic cracking catalyst containing same has good activity stability and heavy metal pollution resistance.

Claims

1. A preparation method of a modified molecular sieve, wherein the preparation method comprises: mixing a molecular sieve slurry, a compound solution containing Group IIIB metal ion of the periodic table, an organic complexing agent, a dispersant and a precipitating agent to obtain a mixed slurry containing the precipitate of Group IIIB element of the periodic table and the molecular sieve, followed by drying and optionally calcining, to obtain the Group IIIB element-modified molecular sieve, wherein the weight ratio of the Group IIIB element in terms of oxide to the molecular sieve on dry basis is 0.3 to 10: 100, the molar ratio of the organic complexing agent to the Group IIIB metal ion is 0.3 to 10: 1, and the molar ratio of the dispersant to the Group IIIB metal ion is 0.2 to 16: 1; wherein the mixing of the molecular sieve slurry, the compound solution containing the Group IIIB metal ion of the periodic table, the organic complexing agent, the dispersant and the precipitating agent is carried out by uniformly mixing the compound solution containing the Group IIIB metal ion of the periodic table, the organic complexing agent, the dispersant with the molecular sieve slurry, adding the precipitating agent and stirring for at least 10 minutes.

2. The preparation method according to claim 1, wherein the preparation method comprises: mixing the molecular sieve slurry, the compound solution containing Group IIIB metal ion of the periodic table, the organic complexing agent, the dispersant and the precipitating agent at a temperature of 5 to 100° C. and stirring for at least 10 minutes to obtain the mixed slurry containing the precipitate of Group IIIB element of the periodic table and the molecular sieve, followed by drying and optionally calcining, to obtain the Group IIIB element-modified molecular sieve, wherein the weight ratio of the Group IIIB element in terms of oxide to the molecular sieve on dry basis is 0.3 to 10: 100, the molar ratio of the organic complexing agent to the Group IIIB metal ion is 0.3 to 10: 1, and the molar ratio of the dispersant to the Group IIIB metal ion is 0.2 to 16: 1.

3. The preparation method according to claim 2, wherein the temperature is 5 to 60° C., and the stirring is carried out for 10 to 40 minutes to obtain the mixed slurry containing the precipitate of Group IIIB element of the periodic table and the molecular sieve.

4. The preparation method according to claim 2, wherein the weight ratio of Group IIIB element in terms of oxide to the molecular sieve on dry basis is 0.3 to 8: 100.

5. The preparation method according to claim 2, wherein the molar ratio of the organic complexing agent to the Group IIIB metal ion is 0.5 to 6: 1; the molar ratio of the dispersant to the Group IIIB metal ion is 1 to 11: 1.

6. The preparation method according to claim 2, wherein the precipitating agent is a substance capable of chemically reacting with the Group IIIB metal ion in the system and making the product thereof slightly soluble or insoluble in the system, in a chemical precipitation reaction.

7. The preparation method according to claim 6, wherein the precipitating agent is one or more of compounds capable of providing or generating hydroxide ions, carbonate ions, bicarbonate ions, phosphate ions, hydrogen phosphate ions, dihydrogen phosphate ions, or oxalate ions.

8. The preparation method according to claim 6, wherein the precipitating agent is one or more of oxalic acid, ammonium oxalate, ammonium carbonate, ammonium bicarbonate, carbon dioxide, aqueous ammonia, phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate and urea.

9. The preparation method according to claim 2, wherein the organic complexing agent is selected from one or more of formic acid, acetic acid, adipic acid, citric acid, tartaric acid, benzoic acid, ethylenediamine tetraacetic acid, salicylic acid and salts thereof, acetylacetone, diethanolamine, and triethanolamine.

10. The preparation method according to claim 2, wherein the dispersant is a surfactant having both lipophilic and hydrophilic properties in the molecule, which can uniformly disperse solid particles that are insoluble in the liquid while preventing the sedimentation and agglomeration of the solid particles, and form a material needed for stabilizing the suspension, and the dispersant does not form precipitates with the Group IIIB metal ion.

11. The preparation method according to claim 10, wherein the dispersant is selected from one or more of monohydric or dihydric alcohol having 2 to 8 carbon atoms, polyethylene glycol, cellulose derivative, polyacrylamide and derivatives thereof, and guar gum.

12. The preparation method according to claim 11, wherein the cellulose derivative is one or more of carboxymethylcellulose sodium, methyl hydroxyethyl cellulose, and hydroxypropyl methyl cellulose; and the monohydric or dihydric alcohol having 2 to 8 carbon atoms is one or more of ethanol, ethylene glycol, isopropanol, butanol, and methylpentanol.

13. The preparation method according to claim 2, wherein the condition for the calcination process is: calcining the molecular sieve in an atmosphere of 100% steam at a calcination temperature of 450-700° C. for a calcination time of 0.5 to 4 hours.

14. The preparation method according to claim 2, wherein the molecular sieve slurry is a sodium-reduced molecular sieve slurry.

15. The preparation method according to claim 9, wherein the organic complexing agent is selected from one or more of citric acid, ammonium citrate, ammonium dihydrogen citrate, diammonium hydrogen citrate, and ethylenediamine tetraacetic acid.

Description

DETAILED DESCRIPTION

(1) The present invention is further illustrated below by referring to the Examples, but the present invention is not limited to these examples.

(2) (A) The Analytical and Test Method Used in Examples

(3) 1. Sodium oxide, yttrium oxide, rare earth content: using X-ray fluorescence analysis.

(4) 2. Crystallinity and unit cell constant of the molecular sieve: using X-ray diffraction analysis.

(5) 3. Particle size: using laser particle size analyzer method.

(6) 4. Determination of catalyst activity: performed on Model CSA-B catalyst evaluation device produced by Huayang company. The catalyst was preliminarily aged at 800° C. in 100% steam for 6 h or 17 h, and the activity of the catalyst was measured using Dagang light diesel oil as a raw material at a reaction temperature of 460° C., a reaction time of 70 s, a catalyst loading of 5.0 g and a ratio of oil to solvent of 3.2:1.

(7) (B) Specifications of Raw Materials Used in the Examples

(8) 1. NaY molecular sieve, REUSY molecular sieve (RE.sub.2O.sub.3 content: 4.02%, Na.sub.2O content: 1.24%), NH.sub.4Y molecular sieve (Na.sub.2O content: 1.68%, subjected to hydrothermal calcination once), ZSM-5 molecular sieve (Na.sub.2O content: 0.10%), kaolin (ignition loss: 18.6%) or kaolin (ignition loss: 14.6%), diatomaceous earth (ignition loss: 15.4%), aluminum sol (containing 21.2 wt % of alumina) or aluminum sol (containing 19.4 wt % of alumina), pseudo-boehmite (ignition loss: 31.8%), boehmite (ignition loss: 17.0%), silica (white carbon black, ignition loss: 9.91%), ammonia (concentration: 18%), rare earth nitrate (RE.sub.2O.sub.3 230.5 g/L): all of which are industrial products, from Lanzhou Petrochemical Company catalyst plant.

(9) 2. Ammonium sulfate, citric acid, ammonium citrate, ethylene glycol, ethanol, ammonium oxalate, ethylenediamine tetraacetic acid, urea, diammonium hydrogen phosphate, lanthanum nitrate, cerium nitrate, yttrium nitrate, methyl hydroxyethyl cellulose: all of which are chemical reagents.

(10) 3. Hydrochloric acid: concentration of 36%, chemical reagent.

(11) 4. Synthesized yttrium-containing Y-type molecular sieve slurry Y-1: the molecular sieve slurry was prepared by the following process: (1) adding 1000 g of NaY molecular sieve (on dry basis) to 7 L of deionized water, adding thereto 350 g of ammonium sulfate while stirring, adjusting the pH value of the slurry to 3.4 with hydrochloric acid, and stirring the mixture at a temperature of 85° C. for 1 hour, followed by filtering and washing to obtain a filter cake; mixing the filter cake (798 g on dry basis) with 102 g of yttrium nitrate and 2.2 L of deionized water, stirring for 0.5 h, spray-drying, and hydrothermally calcining in a calciner in an atmosphere of 100% steam at a calcination temperature of 600° C. for a calcination time of 2 hours; (2) mixing the molecular sieve obtained in the step (1), ammonium sulfate and water in a weight ratio of molecular sieve (dry basis):ammonium salt:water=1:0.3:5 to form a slurry; stirring at 75° C. and pH=3.5 for 1 hour to obtain the synthesized yttrium-containing Y-type molecular sieve slurry Y-1.

EXAMPLE 1

(12) In the synthesized yttrium-containing Y-type molecular sieve slurry Y-1, 16 g of citric acid, 4 g of ethylene glycol, 54 g of yttrium nitrate and 128 g of ammonium oxalate were simultaneously added and stirred at a temperature of 55° C. for 20 minutes. The filter cake was filtered, washed, and calcined at 600° C. in an atmosphere of 100% steam for 2 hours to obtain the modified molecular sieve Z-1 of this Example.

(13) 600 g (on dry basis) of the molecular sieve Z-1 were added to 1.2 L of deionized water, and a molecular sieve slurry Z-1J was obtained after sand milling. 619 g of aluminum sol (containing 19.4 wt % of alumina), 1499 g of kaolin (ignition loss: 14.6%), 2.2 L of water were mixed and slurried, and then added to the molecular sieve slurry Z-1J, and stirring was continued for 30 minutes. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the catalyst C-1 of this Example.

EXAMPLE 2

(14) 798 g (on dry basis) of REUSY molecular sieve, 16 g (on dry basis) of ZSM-5 molecular sieve and water were mixed and slurried in the weight ratio of the molecular sieve (on dry basis):water=1:3 to form a molecular sieve slurry, 110 g of ethylenediamine tetraacetic acid and 104 mL of rare earth nitrate were added thereto, the pH value of the molecular sieve slurry was adjusted with aqueous ammonia to be in the range of 7.5 to 8.0, 23 g of ethanol was further added and the mixture was stirred at room temperature (25° C.) for 30 minutes. The filter cake was filtered, washed and dried at 200° C. to obtain the modified molecular sieve Z-2 of this Example.

(15) 600 g (on dry basis) of the molecular sieve Z-2 were added to 1.2 L of deionized water, and a molecular sieve slurry Z-2J was obtained after sand milling. 619 g of aluminum sol (containing 19.4 wt % of alumina), 1513 g of diatomaceous earth, and 2.2 L of water were mixed and slurried, and then added to the molecular sieve slurry Z-2J, and stirring was continued for 30 minutes. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the catalyst C-2 of this Example.

EXAMPLE 3

(16) 798 g (on dry basis) of REUSY molecular sieve and water were mixed in the weight ratio of the molecular sieve (on dry basis):water=1:3 to form a slurry, 155 g of urea and 85 g of lanthanum nitrate were sequentially added thereto and stirred at room temperature (25° C.), the pH value of the molecular sieve slurry was adjusted with aqueous ammonia to be in the range of 6.5 to 7.0, 14 g of ethylene glycol was further added and the mixture was stirred at room temperature (25° C.) for 1.5 hours, and then dried at 250° C. to obtain the modified molecular sieve Z-3 of this Example.

(17) 600 g (on dry basis) of the molecular sieve Z-3 were added to 1.2 L of deionized water, and the molecular sieve slurry Z-3J was obtained after sand milling. 1054 g of kaolin (ignition loss: 14.6%), 587 g of pseudo-boehmite, and 2.2 L of water were mixed and slurried. 60 mL of hydrochloric acid was added thereto and stirred for 1 hour. The molecular sieve slurry Z-3J was added and stirred for 15 minutes. Then 515 g of aluminum sol (containing 19.4 wt % of alumina) was added, and stirring was continued for 30 minutes to form a gel. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the catalyst C-3 of the present invention.

EXAMPLE 4

(18) 798 g (on dry basis) of NH.sub.4Y molecular sieve and water were mixed in the weight ratio of the molecular sieve (on dry basis):water=1:5 to form a slurry, 40 g of ammonium citrate, and 277 mL of rare earth nitrate were added thereto and stirred for 15 minutes, the pH value of the molecular sieve slurry was adjusted with aqueous ammonia to be in the range of 8.0 to 9.0, and stirring was continued for 1 hour at a temperature of 35° C. to obtain the modified molecular sieve Z-4 slurry of this Example. The modified molecular sieve Z-4 slurry was spray-dried to obtain the modified molecular sieve Z-4.

(19) 1030 g of kaolin (ignition loss: 14.6%), 440 g of pseudo-boehmite, 120 g of boehmite, and 2.2 L of water were mixed and slurried, 33 mL of hydrochloric acid was added thereto and stirred for 1 hour, and then 600 g (on dry basis) of the modified molecular sieve Z-4 slurry was added and stirred for 15 minutes. Then 619 g of aluminum sol (containing alumina of 19.4 wt %) was added and the stirring was continued for 30 minutes to form a gel. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the catalyst C-4 of the present invention.

EXAMPLE 5

(20) 798 g (on dry basis) of NH.sub.4Y molecular sieve and water were mixed in the weight ratio of the molecular sieve (on dry basis):water=1:3.5 to form a slurry, 70 g of diammonium hydrogen phosphate, and 64 g of cerium nitrate were added and stirred for 10 minutes, and then 30 g of ethylene glycol, and 15 g of ethanol were added and stirring was continued for 1 hour at a temperature of 15° C., the molecular sieve was spray-dried and hydrothermally calcinated in a calciner in an atmosphere of 100% steam at a temperature of 550° C. for a calcination time of 2.5 hours to obtain the modified molecular sieve Z-5 of this Example.

(21) 600 g (on dry basis) of molecular sieve Z-5 was added to 1.2 L of deionized water, and the molecular sieve slurry Z-5J was obtained after sand milling. 738 g of kaolin (ignition loss: 14.6%), 220 g of pseudo-boehmite, and 1.5 L of water were mixed and slurried. 19 mL of hydrochloric acid was added and stirred for 1 hour. Then the molecular sieve slurry Z-5J was added and stirred for 25 minutes, then 619 g of aluminum sol (containing 19.4 wt % of alumina) was added and the stirring was continued for 30 minutes to form a gel. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the catalyst C-5 of the present invention.

EXAMPLE 6

(22) 798 g (on dry basis) of NH.sub.4Y molecular sieve and water were mixed in the weight ratio of the molecular sieve (on dry basis):water=1:5 to form a slurry, 69.2 mL of rare earth nitrate was added and stirred for 10 minutes at a temperature of 25° C., Then 16 g of citric acid and 3 g of methyl hydroxyethyl cellulose were added and stirred for 10 minutes at a temperature of 25° C., and then 64 g of ammonium oxalate was added and stirring was continued for 15 minutes, the obtained molecular sieve was dried and hydrothermally calcined in a calciner in an atmosphere of 100% steam at a temperature of 650° C. for a calcination time of 2 hours to obtain the modified molecular sieve Z-6 of this Example.

(23) 500 g (on dry basis) of the molecular sieve Z-6 was added to 1.0 L of deionized water, and the molecular sieve slurry Z-6J was obtained after sand milling. 867 g of kaolin (ignition loss: 14.6%), 587 g of pseudo-boehmite, 222 g of silica, and 2.0 L of water were mixed and slurried. 50 mL of hydrochloric acid was added and stirred for 0.5 hour. Then the molecular sieve slurry Z-6J was added and stirred for 25 minutes, 870 g of aluminum sol (containing 19.4 wt % of alumina) was added and the stirring was continued for 30 minutes to form a gel. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the catalyst C-6 of the present invention.

EXAMPLE 7

(24) 69.2 mL of rare earth nitrate, 0.5 L of water, and 64 g of ammonium oxalate were mixed and stirred at 25° C. for 10 minutes, then 798 g (on dry basis) of NH.sub.4Y molecular sieve, 16 g of citric acid, 3 g of methyl hydroxyethyl cellulose and water were added. In the obtained mixed system, the weight ratio of the molecular sieve (on dry basis):water is 1:5, stirring was continued for 15 minutes, the obtained molecular sieve was dried and hydrothermally calcinated in a calciner in an atmosphere of 100% steam at a temperature of 650° C. for a calcination time of 2 hours to obtain the modified molecular sieve Z-7 of this Example.

(25) 500 g (on dry basis) of the molecular sieve Z-7 was added to 1.0 L of deionized water, and the molecular sieve slurry Z-7J was obtained after sand milling. 867 g of kaolin (ignition loss: 14.6%), 587 g of pseudo-boehmite, 222 g of silica, and 2.0 L of water were mixed and slurried. 50 mL of hydrochloric acid was added and stirred for 0.5 hour. Then the molecular sieve slurry Z-7J was added and stirred for 25 minutes, then 870 g of aluminum sol (containing 19.4 wt % of alumina) was added and the stirring was continued for 30 minutes to form a gel. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the catalyst C-7 of the present invention.

COMPARATIVE EXAMPLE 1

(26) In the synthesized yttrium-containing Y-type molecular sieve slurry Y-1, 16 g of citric acid, 4 g of ethylene glycol, and 54 g of yttrium nitrate were added and stirred at a temperature of 55° C. for 20 minutes. The filter cake was filtered, washed, and calcined at 600° C. in an atmosphere of 100% steam for 2 hours to obtain the comparative molecular sieve DZ-1.

(27) 600 g (on dry basis) of the molecular sieve DZ-1 was added to 1.2 L of deionized water, and the molecular sieve slurry DZ-1J was obtained after sand milling. 619 g of aluminum sol (containing 19.4 wt % of alumina), 1499 g of kaolin (ignition loss: 14.6%), and 2.2 L of water were mixed and slurried. Then the molecular sieve slurry DZ-1J was added and stirred for 30 minutes. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the comparative catalyst DC-1 containing the comparative molecular sieve DZ-1.

COMPARATIVE EXAMPLE 2

(28) In the synthesized yttrium-containing Y-type molecular sieve slurry Y-1, 54 g of yttrium nitrate and 128 g of ammonium oxalate were added and stirred at a temperature of 55° C. for 20 minutes. The filter cake was filtered, washed, and calcined at 600° C. in an atmosphere of 100% steam for 2 hours to obtain the comparative molecular sieve DZ-2.

(29) 600 g (on dry basis) of the molecular sieve DZ-2 was added to 1.2 L of deionized water, and the molecular sieve slurry DZ-2J was obtained after sand milling. 619 g of aluminum sol (containing 19.4 wt % of alumina), 1499 g of kaolin (ignition loss: 14.6%), and 2.2 L of water were mixed and slurried. Then the molecular sieve slurry DZ-2J was added and stirred for 30 minutes. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the comparative catalyst DC-2 containing the comparative molecular sieve DZ-2.

COMPARATIVE EXAMPLE 3

(30) The synthesized yttrium-containing Y-type molecular sieve slurry Y-1 was stirred at a temperature of 55° C. for 20 minutes. The filter cake was filtered, washed, and calcined at 600° C. in an atmosphere of 100% steam for 2 hours to obtain the comparative molecular sieve DZ-3.

(31) 600 g (on dry basis) of the molecular sieve DZ-3 was added to 1.2 L of deionized water, and the molecular sieve slurry DZ-3J was obtained after sand milling. 619 g of aluminum sol (containing 19.4 wt % of alumina), 1499 g of kaolin (ignition loss: 14.6%), and 2.2 L of water were mixed and slurried. Then the molecular sieve slurry DZ-3J was added and stirred for 30 minutes. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the comparative catalyst DC-3 containing the comparative molecular sieve DZ-3.

COMPARATIVE EXAMPLE 4

(32) According to the preparation method of a molecular sieve containing rare earth disclosed in Chinese patent CN99105792.9: 798 g (on dry basis) of REUSY molecular sieve, 16 g (on dry basis) of ZSM-5 molecular sieve and water were mixed and slurried in the weight ratio of the molecular sieve (on dry basis):water=1:3 to form a molecular sieve slurry, 110 g of ethylenediamine tetraacetic acid was added, and the pH value of the molecular sieve slurry was adjusted with aqueous ammonia to be in the range of 7.5 to 8.0. 23 g of ethanol was added, and stirred at room temperature (25° C.) for 30 minutes. The filter cake was filtered, washed, and dried at 200° C. to obtain the comparative molecular sieve DZ-4.

(33) 600 g (on dry basis) of the molecular sieve DZ-4 was added to 1.2 L of deionized water, and the molecular sieve slurry DZ-4J was obtained after sand milling. 619 g of aluminum sol (containing 19.4 wt % of alumina), 1513 g of diatomaceous earth, and 2.2 L of water were mixed and slurried. Then the molecular sieve slurry DZ-4J was added and stirred for 30 minutes. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the comparative catalyst DC-4 containing the comparative molecular sieve DZ-4.

COMPARATIVE EXAMPLE 5

(34) 798 g (on dry basis) of REUSY molecular sieve and water were mixed in the weight ratio of molecular sieve (on dry basis):water=1:3 to form a slurry, 85 g of lanthanum nitrate was added, and stirred at room temperature (25° C.), and the pH value of the molecular sieve slurry was adjusted with aqueous ammonia to be in the range of 6.5 to 7.0 and the stirring was continued at room temperature (25° C.) for 1.5 hours. It was dried at 250° C. to obtain the comparative molecular sieve DZ-5.

(35) 600 g (on dry basis) of the molecular sieve DZ-5 was added to 1.2 L of deionized water, and the molecular sieve slurry DZ-5J was obtained after sand milling. 1054 g of kaolin (ignition loss: 14.6%), 587 g of pseudo-boehmite, and 2.2 L of water were mixed and slurried. 60 mL of hydrochloric acid was added and stirred for 1 hour. Then the molecular sieve slurry DZ-5J was added and stirred for 15 minutes. 515 g of aluminum sol (containing 19.4 wt % of alumina) was added and stirring was continued for 30 minutes to form a gel. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the comparative catalyst DC-5 containing the comparative molecular sieve DZ-5.

COMPARATIVE EXAMPLE 6

(36) 798 g (on dry basis) of NH.sub.4Y molecular sieve and water were mixed in the weight ratio of the molecular sieve (on dry basis):water=1:5 to form a slurry, and stirred for 15 minutes, stirring was continued at a temperature of 35° C. for 1 hour to obtain the comparative molecular sieve DZ-6 slurry. The comparative molecular sieve DZ-6 slurry was spray-dried to obtain the comparative molecular sieve DZ-6.

(37) 1030 g of kaolin (ignition loss: 14.6%), 440 g of pseudo-boehmite, 120 g of boehmite, and 2.2 L of water were mixed and slurried. 33 mL of hydrochloric acid was added and stirred for 1 hour. Then 600 g (on dry basis) of the molecular sieve DZ-6 slurry was added and stirred for 15 minutes. 619 g of aluminum sol (containing 19.4 wt % of alumina) was added and stirring was continued for 30 minutes to form a gel. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the comparative catalyst DC-6 containing the comparative molecular sieve DZ-6.

COMPARATIVE EXAMPLE 7

(38) 798 g (on dry basis) of NH.sub.4Y molecular sieve and water were mixed in the weight ratio of the molecular sieve (on dry basis):water=1:3.5 to form a slurry, 70 g of diammonium hydrogen phosphate, and 64 g of cerium nitrate were added and stirred for 10 minutes, stirring was continued at a temperature of 15° C. for 1 hour, it was spray-dried and the obtained molecular sieve was hydrothermally calcinated in a calciner in an atmosphere of 100% steam at a temperature of 550° C. and a calcination time of 2.5 hours to obtain the comparative molecular sieve DZ-7.

(39) 600 g (on dry basis) of molecular sieve DZ-7 was added to 1.2 L of deionized water, after sanding treatment to obtain the molecular sieve slurry DZ-7J. 738 g of kaolin (ignition loss: 14.6%), 220 g of pseudo-boehmite, 1.5 L of water were mixed and slurried. 19 mL of hydrochloric acid was added and stirred for 1 hour. Then the molecular sieve slurry DZ-7J was added and stirred for 25 minutes, then 619 g of aluminum sol (containing 19.4 wt % of alumina) was added and the stirring was continued for 30 minutes to form a gel. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the comparative catalyst DC-7 containing the comparative molecular sieve DZ-7.

COMPARATIVE EXAMPLE 8

(40) According to a method for increasing rare earth content of the ultrastable Y-type zeolite disclosed in Chinese patent CN200510114495.1, 798 g (on dry basis) of NH.sub.4Y molecular sieve was calcined in an atmosphere of 100% steam at 600° C. for 1.5 hours to obtain an ultrastable Y molecular sieve. The ultrastable Y molecular sieve and water were mixed in the weight ratio of the molecular sieve (on dry basis):water=1:5 to form a slurry, 40 g of ammonium citrate was added and stirred at 35° C. for 1 hour, then it was washed and filtered and the filter cake was removed. The filter cake was mixed in the weight ratio of the molecular sieve (on dry basis):water=1:5, stirred and then 277 mL of rare earth nitrate was added thereto, and stirring was continued at 35° C. for 1 hour. It was filtered and dried to obtain the comparative molecular sieve DZ-8.

(41) 600 g (on dry basis) of the molecular sieve DZ-8 was added to 1.5 L of deionized water, and the molecular sieve slurry DZ-8J was obtained after sand milling. 1030 g of kaolin (ignition loss: 14.6%), 440 g of pseudo-boehmite, 120 g of boehmite, and 2.2 L of water were mixed and slurried. 50 mL of hydrochloric acid was added and stirred for 1 hour. Then the molecular sieve slurry DZ-8J was added and stirred for 15 minutes, then 619 g of aluminum sol (containing 19.4 wt % of alumina) was added and the stirring was continued for 30 minutes to form a gel. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the comparative catalyst DC-8 containing the comparative molecular sieve DZ-8.

COMPARATIVE EXAMPLE 9

(42) According to a method for preparing a novel rare earth ultrastable Y molecular sieve containing a vanadium-resistant component for catalytic cracking of heavy oil disclosed in Chinese Patent CN02103909.7, 798 g (on dry basis) of NH.sub.4Y molecular sieve and water were mixed in the weight ratio of the molecular sieve (on dry basis):water=1:5 to form a slurry, 64 g of ammonium oxalate was added and stirred at a temperature of 25° C. for 0.5 hour. Then 69.2 mL of rare earth nitrate was added and further stirred sufficiently for 15 minutes. It was filtered and washed with water, and the obtained molecular sieve was hydrothermally calcined in a calciner in an atmosphere of 100% steam at a temperature of 650° C. for a calcination time of 2 hours to obtain the comparative molecular sieve DZ-9.

(43) 500 g (on dry basis) of the molecular sieve DZ-9 was added to 1.0 L of deionized water, and the molecular sieve slurry DZ-9J was obtained after sand milling. 867 g of kaolin (ignition loss: 14.6%), 587 g of pseudo-boehmite, 222 g of silica, and 2.0 L of water were mixed and slurried. 50 mL of hydrochloric acid was added and stirred for 0.5 hour. Then the molecular sieve slurry DZ-9J was added and stirred for 25 minutes, then 870 g of aluminum sol (containing 19.4 wt % of alumina) was added and the stirring was continued for 30 minutes to form a gel. After homogenization, spray-drying and molding, calcining, washing with water and drying were carried out to obtain the comparative catalyst DC-9 containing the comparative molecular sieve DZ-9.

(44) Physical and chemical properties of the molecular sieves Z-1 to Z-7 prepared in Examples 1 to 7 and the molecular sieves DZ-1 to DZ-9 prepared in Comparative Examples 1 to 9 were analyzed and tested. The results obtained are shown in Table 1:

(45) TABLE-US-00001 TABLE 1 Properties of the modified molecular sieves Rare Unit Sodium Yttrium earth Crystal- cell oxide oxide oxide linity constant Item wt % wt % wt % wt % nm The molecular sieve Z-1 prepared by 1.54 5.80 — 69 2.457 Example 1 The molecular sieve Z-2 prepared by 1.20 — 7.10 47 2.457 Example 2 The molecular sieve Z-3 prepared by 1.21 — 8.05 45 2.457 Example 3 The molecular sieve Z-4 prepared by 1.56 — 7.98 43 2.454 Example 4 The molecular sieve Z-5 prepared by 1.52 — 3.02 53 2.452 Example 5 The molecular sieve Z-6 prepared by 1.61 — 1.98 56 2.450 Example 6 The molecular sieve Z-7 prepared by 1.61 — 1.98 55 2.450 Example 7 The molecular sieve DZ-1 prepared by 1.46 4.31 — 67 2.454 Comparative Example 1 The molecular sieve DZ-2 prepared by 1.51 5.78 — 68 2.457 Comparative Example 2 The molecular sieve DZ-3 prepared by 1.60 2.65 — 67 2.451 Comparative Example 3 The molecular sieve DZ-4 prepared by 1.19 — 4.02 51 2.455 Comparative Example 4 The molecular sieve DZ-5 prepared by 1.21 — 8.01 45 2.457 Comparative Example 5 The molecular sieve DZ-6 prepared by 1.65 — — 53 2.453 Comparative Example 6 The molecular sieve DZ-7 prepared by 1.51 — 2.98 52 2.452 Comparative Example 7 The molecular sieve DZ-8 prepared by 1.32 — 6.40 44 2.456 Comparative Example 8 The molecular sieve DZ-9 prepared by 1.48 — 1.81 54 2.450 Comparative Example 9

(46) The results in Table 1 show that, as compared with the molecular sieve DZ-1 prepared by Comparative Example 1, the sodium oxide content, crystallinity, and unit cell constant of the molecular sieve Z-1 prepared by Example 1 are comparable to the comparative molecular sieve DZ-1, but the yttrium oxide content of the molecular sieve is much higher than DZ-1 (1.49 wt % higher), indicating that the precipitating agent is indispensable in the preparation process of the modified molecular sieve of the present invention, which facilitates the precipitation of Group IIIB element of the periodic table on the molecular sieve. As compared with the molecular sieve Z-4 prepared by Example 4, the molecular sieve DZ-8 prepared by Comparative Example 8 has a low rare earth content in the molecular sieve and a low utilization of rare earth, since the filtration is carried out after the rare earth ion exchange, and there is a phenomenon that the rare earth that has not been exchanged to the molecular sieve is lost to the filtrate. The rare earth contained in the comparative molecular sieve DZ-8 enters the molecular sieve through ion exchange. Such rare earth renders the unit cells of the molecular sieve uneasy to shrink in the hydrothermal calcination process, so its unit cell constant is higher than that of the molecular sieve Z-4 prepared by Example 4. In addition, as compared with the molecular sieve Z-4 prepared by Example 4, the molecular sieve DZ-8 prepared by Comparative Example 8 incorporates the filtration treatment process of the molecular sieve, and the preparation process is relatively complicated. As compared with the molecular sieve Z-6 prepared by Example 6, the molecular sieve DZ-9 prepared by Comparative Example 9 is also problematic in that the rare earth is lost and the molecular sieve preparation process is relatively complicated, due to the filtration after the addition of rare earth to the molecular sieve. In the process of preparing molecular sieve Z-6 by Example 6, ammonium oxalate is mainly used as the precipitating agent for rare earth, but in the process of preparing molecular sieve DZ-9 by Comparative Example 9, ammonium oxalate firstly acts as a dealuminating agent to remove aluminum on the molecular sieve, and then reacts with the rare earth to precipitate the rare earth.

(47) In order to investigate the cracking activity and hydrothermal stability of the molecular sieves, the molecular sieves Z-1 to Z-7 prepared by Examples 1 to 7 and the molecular sieves DZ-1 to DZ-9 prepared by Comparative Examples 1 to 9 were respectively used, 5% (in terms of alumina) of aluminum sol (containing 21.2 wt % of alumina) binder, 30% of the molecular sieve (on dry basis), 65% of kaolin (ignition loss: 18.6%, on dry basis) and a suitable amount of deionized water were mixed evenly, homogenized, dried, crushed and sieved. 20 to 40 mesh particles were selected to test the activity of the catalyst after 17 hours of steam aging respectively. The test results are shown in Table 2.

(48) In order to investigate the heavy metal contamination resistance of the molecular sieves, the above 20 to 40 mesh particles were impregnated with 5000 μg/g of V, and 3000 μg/g of Ni (relative to the catalyst particles) by incipient-wetness impregnation method. The vanadium and nickel-contaminated particles were treated under the condition of 800° C. and 100% steam for 6 h. The activity of vanadium and nickel-contaminated catalyst after 6 h steam aging was tested. The test results are shown in Table 2:

(49) TABLE-US-00002 TABLE 2 The activity and heavy metal resistance of the catalysts prepared by the modified molecular sieves Activity after Activity Activity after vanadium and nickel preservation 17 h steam contamination and 6 h rate R1, Item aging, wt % steam aging, wt % wt % Catalyst containing the molecular sieve 69 55 80 Z-1 prepared by Example 1 Catalyst containing the molecular sieve 61 50 82 Z-2 prepared by Example 2 Catalyst containing the molecular sieve 62 52 84 Z-3 prepared by Example 3 Catalyst containing the molecular sieve 58 50 86 Z-4 prepared by Example 4 Catalyst containing the molecular sieve 50 39 78 Z-5 prepared by Example 5 Catalyst containing the molecular sieve 45 38 84 Z-6 prepared by Example 6 Catalyst containing the molecular sieve 45 37 82 Z-7 prepared by Example 7 Catalyst containing the molecular sieve 64 45 70 DZ-1 prepared by Comparative Example 1 Catalyst containing the molecular sieve 69 52 75 DZ-2 prepared by Comparative Example 2 Catalyst containing the molecular sieve 58 41 71 DZ-3 prepared by Comparative Example 3 Catalyst containing the molecular sieve 51 35 69 DZ-4 prepared by Comparative Example 4 Catalyst containing the molecular sieve 60 45 75 DZ-5 prepared by Comparative Example 5 Catalyst containing the molecular sieve 38 27 71 DZ-6 prepared by Comparative Example 6 Catalyst containing the molecular sieve 50 36 72 DZ-7 prepared by Comparative Example 7 Catalyst containing the molecular sieve 60 47 78 DZ-8 prepared by Comparative Example 8 Catalyst containing the molecular sieve 44 34 77 DZ-9 prepared by Comparative Example 9

(50) In Table 2, the activity preservation rate R1 is used to characterize the heavy metal contamination resistance of the molecular sieve. Definition: activity preservation rate R1=activity after vanadium and nickel contamination and 6 h steam aging/activity after 17 h steam aging×100%.

(51) The results in table 2 show that as compared with the molecular sieve DZ-1 to DZ-9 prepared by Comparative Examples 1 to 9, the catalysts prepared using the molecular sieves Z-1 to Z-7 prepared by Examples 1 to 7 of the present invention as the active component all have improved activity preservation rate R1, indicating that the modified molecular sieve of the present invention has a stronger vanadium and nickel contamination resistance.

(52) As compared with the molecular sieve DZ-1 prepared by Comparative Example 1, the catalyst prepared by using the molecular sieve Z-1 prepared by Example 1 of the present invention as an active component has a significantly higher (by 5%) 17 h activity than the comparative catalyst containing the molecular sieve prepared in Comparative Example 1. When the catalyst was contaminated by vanadium and nickel, the catalyst prepared by using the molecular sieve Z-1 prepared by Example 1 of the present invention as an active component has the activity after vanadium and nickel contamination and 6 h steam aging significantly higher by 10% than that of the comparative catalyst (the catalyst containing the molecular sieve DZ-1 prepared by Comparative Example 1), and the activity preservation rate R1 increased by 10%, indicating that the molecular sieve of the present invention containing the precipitated yttrium has a higher activity stability and resistance to vanadium, nickel contamination. As compared with the molecular sieve DZ-2 prepared by Comparative Example 2, the catalyst prepared by using the molecular sieve Z-1 prepared by Example 1 of the present invention as the active component has the 17 h activity comparable to that of the comparative catalyst containing the molecular sieve prepared in Comparative Example 2, but when the catalyst is contaminated with vanadium and nickel, the catalyst prepared by using the molecular sieve Z-1 prepared by Example 1 of the present invention as an active component has the activity after vanadium and nickel contamination and 6 h steam aging significantly higher by 3% than that of the comparative catalyst (the catalyst containing the molecular sieve DZ-2 prepared by Comparative Example 2), and the activity preservation rate R1 increased by 5%, indicating that the molecular sieve containing the precipitated yttrium prepared by using the organic complexing agent and the dispersing agent according to the present invention has a higher resistance to vanadium and nickel contamination. As compared with the molecular sieve DZ-3 prepared by Comparative Example 3, the catalyst prepared by using the molecular sieve Z-1 prepared by Example 1 of the present invention as an active component has the 17 h activity significantly higher by 11% than that of the comparative catalyst containing the molecular sieve DZ-3 prepared by Comparative Example 3; when the catalysts are contaminated with vanadium and nickel, the catalyst prepared by using the molecular sieve Z-1 prepared by Example 1 of the present invention as an active component has the activity after vanadium and nickel contamination and 6 h steam aging significantly higher by 14% than that of the comparative catalyst (the catalyst containing the molecular sieve DZ-3 prepared by Comparative Example 3), and the activity preservation rate R1 increased by 9%, indicating that the molecular sieve of the present invention containing the precipitated yttrium has higher activity stability and resistance to vanadium and nickel contamination. As compared with the molecular sieve DZ-4 prepared by Comparative Example 4, the catalyst prepared by using the molecular sieve Z-2 prepared by Example 2 of the present invention as an active component has the 17 h activity significantly higher by 10% than that of the comparative catalyst containing the molecular sieve prepared by Comparative Example 4; when the catalysts are contaminated with vanadium and nickel, the catalyst prepared by using the molecular sieve Z-2 prepared by Example 2 of the present invention as an active component has the activity after vanadium and nickel contamination and 6 h steam aging significantly higher by 15% than that of the comparative catalyst (the catalyst containing the molecular sieve DZ-4 prepared by Comparative Example 4), and the activity preservation rate R1 increased by 13%, indicating that the molecular sieve catalyst of the present invention containing the precipitated rare earth has higher activity stability and resistance to vanadium and nickel contamination.

(53) As compared with the molecular sieve DZ-5 prepared by Comparative Example 5, the catalyst prepared by using the molecular sieve Z-3 prepared by Example 3 of the present invention as an active component has the 17 h activity higher by 2% than that of the comparative catalyst containing the molecular sieve prepared by Comparative Example 5; when the catalysts are contaminated with vanadium and nickel, the catalyst prepared by using the molecular sieve Z-3 prepared by Example 3 of the present invention as an active component has the activity after vanadium and nickel contamination and 6 h steam aging significantly higher by 7% than that of the comparative catalyst (the catalyst containing the molecular sieve DZ-5 prepared by Comparative Example 5), and the activity preservation rate R1 increased by 9%, indicating that the molecular sieve catalyst prepared by using the dispersing agent and urea and aqueous ammonia precipitating agent has higher activity stability and resistance to vanadium and nickel contamination than the molecular sieve prepared by the precipitation technique using aqueous ammonia only.

(54) As compared with the molecular sieve DZ-6 prepared by Comparative Example 6, the catalyst prepared by using the molecular sieve Z-4 prepared by Example 4 of the present invention as an active component has the 17 h activity significantly higher by 20% than that of the comparative catalyst containing the molecular sieve prepared by Comparative Example 6; when the catalysts are contaminated with vanadium and nickel, the catalyst prepared by using the molecular sieve Z-4 prepared by Example 4 of the present invention as an active component has the activity after vanadium and nickel contamination and 6 h steam aging significantly higher by 23% than that of the comparative catalyst (the catalyst containing the molecular sieve DZ-6 prepared by Comparative Example 6), and the activity preservation rate R1 increased by 15%, indicating that the molecular sieve prepared by the present invention has higher activity stability and resistance to vanadium and nickel contamination than the molecular sieve without the precipitated rare earth.

(55) As compared with the molecular sieve DZ-7 prepared by Comparative Example 7, the catalyst prepared by using the molecular sieve Z-5 prepared by Example 5 of the present invention as an active component has the 17 h activity comparable to that of the comparative catalyst containing the molecular sieve prepared by Comparative Example 7; when the catalysts are contaminated with vanadium and nickel, the catalyst prepared by using the molecular sieve Z-5 prepared by Example 5 of the present invention as an active component has the activity after vanadium and nickel contamination and 6h steam aging higher by 3% than that of the comparative catalyst (the catalyst containing the molecular sieve DZ-7 prepared by Comparative Example 7), and the activity preservation rate R1 increased by 6%, indicating that the molecular sieve prepared by using the dispersing agent of the present invention has higher activity stability and resistance to vanadium and nickel contamination than the molecular sieve prepared by the precipitation technique using rare earth phosphate without dispersing agent.

(56) As compared with the molecular sieve DZ-8 prepared by Comparative Example 8, when the catalysts are contaminated with vanadium and nickel, the catalyst prepared by using the molecular sieve Z-4 prepared by Example 4 of the present invention as an active component has the activity after vanadium and nickel contamination and 6 h steam aging significantly higher by 3% than that of the comparative catalyst (the catalyst containing the molecular sieve DZ-8 prepared by Comparative Example 8), and the activity preservation rate R1 increased by 8%, indicating that the molecular sieve prepared by the present invention has higher activity stability and resistance to vanadium and nickel contamination than the molecular sieve without the precipitated rare earth.

(57) As compared with the molecular sieve DZ-9 prepared by Comparative Example 9, when the catalysts are contaminated with vanadium and nickel, the catalysts prepared by using the molecular sieve Z-6 and Z-7 prepared by Examples 6 and 7 of the present invention as an active component respectively have the activity after vanadium and nickel contamination and 6 h steam aging significantly higher by 4% than that of the comparative catalyst (the catalyst containing the molecular sieve DZ-9 prepared by Comparative Example 9), and the activity preservation rate R1 increased by 7% and 5% respectively, indicating that the molecular sieve prepared by using the complexing agent and the dispersing agent according to the present invention has higher activity stability and resistance to vanadium and nickel contamination than the molecular sieve prepared by the method of Chinese patent CN02103909.7 in the prior art.

(58) In order to further investigate the cracking activity and the hydrothermal stability of the catalysts, the catalysts C-1 to C-7 prepared by Examples 1 to 7 and the comparative catalysts DC-1 to DC-9 prepared by Comparative Examples 1 to 9 were respectively tested for the activity of catalysts after 17 h steam aging. The test results are shown in Table 3.

(59) In order to investigate the heavy metal contamination resistance of the catalysts, the catalysts C-1 to C-7 and the comparative catalysts DC-1 to DC-9 were respectively impregnated with 5000 μg/g of V, and 3000 μg/g of Ni (relative to the catalysts) by incipient-wetness impregnation method. The vanadium and nickel-contaminated catalysts were treated under the condition of 800° C. and 100% steam for 6 h, and tested for the activity of vanadium and nickel-contaminated catalyst after 6 h steam aging. The test results are shown in Table 3:

(60) TABLE-US-00003 TABLE 3 Activity and heavy metal resistance of the catalysts Activity after Activity after Activity 17 h steam vanadium and nickel preservation aging, contamination and 6 h rate R1, Item wt % steam aging, wt % wt % Catalyst C-1 prepared in Example 1 71 59 83 Catalyst C-2 prepared in Example 2 64 54 84 Catalyst C-3 prepared in Example 3 66 57 86 Catalyst C-4 prepared in Example 4 61 54 88 Catalyst C-5 prepared in Example 5 58 47 81 Catalyst C-6 prepared in Example 6 45 39 87 Catalyst C-7 prepared in Example 7 45 38 84 Comparative catalyst DC-1 67 48 72 prepared in Comparative Example 1 Comparative catalyst DC-2 prepared 71 54 76 in Comparative Example 2 Comparative catalyst DC-3 prepared 60 43 72 in Comparative Example 3 Comparative catalyst DC-4 prepared 54 38 70 in Comparative Example 4 Comparative catalyst DC-5 prepared 64 48 75 in Comparative Example 5 Comparative catalyst DC-6 prepared 41 30 73 in Comparative Example 6 Comparative catalyst DC-7 prepared 58 42 72 in Comparative Example 7 Comparative catalyst DC-8 prepared 61 48 79 in Comparative Example 8 Comparative catalyst DC-9 prepared 44 34 77 in Comparative Example 9

(61) In Table 3, the activity preservation rate R1 is used to characterize the heavy metal contamination resistance of the catalysts. Definition: activity preservation rate R1=activity after vanadium and nickel contamination and 6 h steam aging/activity after 17 h steam aging×100%.

(62) The results in table 3 show that as compared with the molecular sieve DC-1 to DC-9 prepared by Comparative Examples 1 to 9, the catalysts C-1 to C-7 prepared by Examples 1 to 7 of the present invention all have improved activity preservation rate R1, indicating that the modified molecular sieve catalysts of the present invention has a higher resistance to vanadium and nickel contamination.

(63) As compared with the catalyst DC-1 prepared by Comparative Example 1, the catalyst C-1 prepared by using the molecular sieve Z-1 prepared by Example 1 of the present invention as an active component has the 17 h activity significantly higher by 4% than that of the comparative catalyst DC-1 containing the molecular sieve prepared by Comparative Example 1; when the catalysts are contaminated with vanadium and nickel, the catalyst C-1 prepared by Example 1 has the activity after vanadium and nickel contamination and 6 h steam aging significantly higher by 11% than that of the comparative catalyst DC-1, and the activity preservation rate R1 increased by 11%, indicating that the catalyst of the present invention containing the precipitated yttrium has higher activity stability and resistance to vanadium and nickel contamination. As compared with the catalyst DC-2 prepared by Comparative Example 2, the catalyst C-1 prepared by Example 1 of the present invention has the 17 h activity comparable to that of the comparative catalyst DC-2 prepared by Comparative Example 2; when the catalysts are contaminated with vanadium and nickel, the catalyst C-1 prepared by Example 1 has the activity after vanadium and nickel contamination and 6 h steam aging significantly higher by 5% than that of the comparative catalyst (DC-2), and the activity preservation rate R1 increased by 7%, indicating that the molecular sieve catalyst containing the precipitated yttrium prepared with the organic complexing agent and the dispersing agent according to the present invention has higher activity stability and resistance to vanadium and nickel contamination. As compared with the catalyst DC-3 prepared by Comparative Example 3, the catalyst C-1 prepared by Example 1 of the present invention has the 17 h activity significantly higher by 11% than that of the comparative catalyst DC-3 prepared by Comparative Example 3; when the catalysts are contaminated with vanadium and nickel, the catalyst C-1 prepared by Example 1 of the present invention has the activity after vanadium and nickel contamination and 6 h steam aging significantly higher by 16% than that of the comparative catalyst (DC-3), and the activity preservation rate R1 increased by 11%, indicating that the catalyst containing the precipitated yttrium of the present invention has higher activity stability and resistance to vanadium and nickel contamination.

(64) As compared with the catalyst DC-4 prepared by Comparative Example 4, the catalyst C-2 prepared by Example 2 of the present invention has the 17 h activity significantly higher by 10% than that of the comparative catalyst DC-4 prepared by Comparative Example 4; when the catalysts are contaminated with vanadium and nickel, the catalyst C-2 prepared by Example 2 of the present invention has the activity after vanadium and nickel contamination and 6 h steam aging significantly higher by 16% than that of the comparative catalyst (DC-4), and the activity preservation rate R1 increased by 14%, indicating that the catalyst containing the precipitated rare earth of the present invention has higher activity stability and resistance to vanadium and nickel contamination.

(65) As compared with the catalyst DC-5 prepared by Comparative Example 5, the catalyst C-3 prepared by Example 3 of the present invention has the 17 h activity higher by 2% than that of the comparative catalyst prepared by Comparative Example 5; when the catalysts are contaminated with vanadium and nickel, the catalyst C-3 prepared by Example 3 of the present invention has the activity after vanadium and nickel contamination and 6 h steam aging significantly higher by 9% than that of the comparative catalyst (DC-5), and the activity preservation rate R1 increased by 11%, indicating that the molecular sieve catalyst prepared by using the dispersing agent and urea and the aqueous ammonia precipitating agent according to the present invention has higher activity stability and resistance to vanadium and nickel contamination than the molecular sieve catalyst prepared by the precipitation technique using aqueous ammonia only.

(66) As compared with the catalyst DC-6 prepared by Comparative Example 6, the catalyst C-4 prepared by Example 4 of the present invention has the 17 h activity significantly higher by 20% than that of the comparative catalyst DC-6; when the catalysts are contaminated with vanadium and nickel, the catalyst C-4 prepared by Example 4 of the present invention has the activity after vanadium and nickel contamination and 6 h steam aging significantly higher by 24% than that of the comparative catalyst (DC-6), and the activity preservation rate R1 increased by 15%, indicating that the catalyst prepared by the present invention has higher activity stability and resistance to vanadium and nickel contamination than the catalyst without the precipitated rare earth.

(67) As compared with the catalyst DC-7 prepared by Comparative Example 7, the catalyst C-5 prepared by Example 5 of the present invention has the 17 h activity comparable to that of the comparative catalyst DC-7; when the catalysts are contaminated with vanadium and nickel, the catalyst C-5 prepared by Example 5 of the present invention has the activity after vanadium and nickel contamination and 6 h steam aging higher by 5% than that of the comparative catalyst (DC-7), and the activity preservation rate R1 increased by 9%, indicating that the catalyst prepared by using the dispersing agent of the present invention has higher activity stability and resistance to vanadium and nickel contamination than the catalyst prepared by the precipitation technique using rare earth phosphate without dispersing agent.

(68) As compared with the catalyst DC-8 prepared by Comparative Example 8, when the catalysts are contaminated with vanadium and nickel, the catalyst C-4 prepared by Example 4 of the present invention has the activity after vanadium and nickel contamination and 6 h steam aging significant higher by 6% than that of the comparative catalyst (DC-8), and the activity preservation rate R1 increased by 9%, indicating that the catalyst prepared by the present invention has higher activity stability and resistance to vanadium and nickel contamination than the catalyst without the precipitated rare earth.

(69) As compared with the catalyst DC-9 prepared by Comparative Example 9, when the catalysts are contaminated with vanadium and nickel, the catalysts C-6 and C-7 prepared respectively by Examples 6 and 7 of the present invention have the activity after vanadium and nickel contamination and 6 h steam aging significant higher by 4-5% than that of the comparative catalyst (DC-9), and the activity preservation rate R1 increased by 10% and 7% respectively, indicating that the catalyst prepared by using the complexing agent and the dispersing agent according to the present invention has higher activity stability and resistance to vanadium and nickel contamination than the catalyst prepared by the method of Chinese patent CN02103909.7 in the prior art.

(70) In the preparation method of the modified molecular sieve provided by the Examples of the present invention, the particle size of the precipitates of Group IIIB elements in Examples 1 to 7 cannot be separately tested because the precipitates of Group IIIB elements and the molecular sieves are mixed together and are not isolated separately. In order to characterize the particle size of the precipitates of Group IIIB elements prepared by the method of the present invention, Examples 8-9 and Comparative Example 10 of the present invention provide quantitative data on the preparation and particle size of the precipitates of Group IIIB elements without addition of molecular sieves.

EXAMPLE 8

(71) 2 g of citric acid, 2.48 mL of rare earth nitrate and 75 mL of deionized water were mixed together to form a homogeneous solution, and 2 g of ammonium oxalate was added and stirred for 15 minutes to form a rare earth-containing precipitate slurry CD-1.

EXAMPLE 9

(72) 2 g of citric acid, 2.48 mL of rare earth nitrate and 75 mL of deionized water were mixed together to form a homogeneous solution, and 2 g of ethanol was added and stirred for 15 minutes to form a rare earth-containing precipitate slurry CD-2.

COMPARATIVE EXAMPLE 10

(73) A rare earth-containing precipitate slurry DCD-1 was prepared in the same manner as in Example 8, except that 2 g of citric acid was not added.

(74) The particle sizes of the rare earth precipitates of the rare earth-containing precipitate slurries CD-1, CD-2 and DCD-1 prepared by Examples 8 and 9 and Comparative Example 10 were tested respectively. The results are shown in Table 4.

(75) TABLE-US-00004 TABLE 4 Particle sizes of the rare earth precipitates Particle size, % Item D(V, 0.1), μm D(V, 0.5), μm D(V, 0.9), μm The rare earth-containing precipitate 1.17 6.78 15.13 slurry CD-1 prepared by Example 8 The rare earth-containing precipitate 1.16 9.08 20.53 slurry CD-2 prepared by Example 9 The rare earth-containing precipitate slurry 1.18 12.24 27.37 DCD-1 prepared by Comparative Example 10

(76) The results in Table 4 show that as compared with the rare earth-containing precipitate DCD-1 prepared by Comparative Example 10, the rare earth-containing precipitates CD-1 and CD-2 prepared by Examples 8 and 9 are smaller in particle size, indicating that the organic complexing agent and the dispersing agent can effectively reduce the particle size of the precipitates formed by the reaction of the rare earth with the precipitating agent in the present invention.