TREATMENT OF ZEOLITES

Abstract: The acid activity of catalysts comprising a zeolite, particularly a highly siliceous zeolite, in a matrix such as alumina is enhanced by treatment with aqueous monovalent fluoride followed by conversion of the zeolite to the hyd­ rogen form. Suitable monovalent cations are alkali metal, ammonium and hydrogen. It is preferred to convert to the hydrogen form by ammonium exchange followed by calcina­ tion.

Description: TREATMENT OF ZEOLITES This invention relates to the treatment of zeolites to enhance their acid activity. The ion exchange capacity of a crystalline aluminosilicate is directly dependent on its aluminum content: the more aluminum there is in a crystalline structure of the zeolitic kind, the more cations are required to balance the electronegativity thereof, and when such cations are of the acidic type, such as hydrogen, they impart high catalytic activity. On the other hand, highly siliceous zeolites having little or substantially no aluminum have many important properties and characteristics and a high degree of structural stability and have become candidates for use in various processes including catalytic processes. Materials of this type include highly siliceous zeolites such as ZSM-5 (US-A-3,702,886), ZSM-11 (US-A-3,709,979) and ZSM-12 (US-A-3,832,449) to mention a few. The silica-to-alumina ratio of a zeolite is often variable; for example, zeolite X can be synthesized with a silica-to-alumina ratio of from 2 to 3 and zeolite Y from 3 to about 6. In some zeolites, however, the upper limit of silica-to-alumina ratio is virtually unbounded. Zeolite ZSM-5 is one such material, its minimum silicato-alumina ratio being 5. US-A-3,941,871 discloses a crystalline zeolite essentially free of aluminum and exhibiting an x-ray diffraction pattern characteristic of ZSM-5. US-A-4,061,724, 4,073,865 and 4,104,294 describe microporous crystalline silicas or organo silicates of which the aluminium content is at impurity level. Because of the extremely low aluminum content of these highly siliceous zeolites their ion exchange capacity is correspondingly low. Therefore, when exchanged and processed in a conventional manner they are not as catalytically active as their higher aluminumcontaining counterparts. The invention permits the preparation of cata lysts from highly siliceous zeolites which have all the desirable properties inherently possessed by such mater ials yet have an acid activity which heretofore has only been manifested by materials having a higher aluminum content in their "as synthesized" form. According to the invention the catalytic activity of a catalyst comprising a crystalline zeolite In a matrix, the zeolite having an ion exchange capacity less than 0.7 meq./g and constituting from 25 to 75X wt. of a composite with the matrix, is enhanced by contacting the catalyst with a monovalent fluoride in an aqueous medium and thereafter converting the zeolite to the protonated (i.e. hydrogen or hydronium) form. The matrix is an inorganic oxide, preferably alumina, silica, boria and/or gallia, and the conversion to the protonated form may be by hydrolysis or by ammonium exchange followed by calcination. The invention is thus concerned with treatment of highly siliceous zeolites, particularly those of a silica-to-alumina ratio greater than 100, preferably greater than 500, up to and including those aforementioned highly siliceous materials where the silica-toalumina ratio is infinity or as reasonably close to infinity as practically possible, prepared from reaction solutions which involve no deliberate addition of aluminum. Trace quantities of aluminum are usually present in such materials due to the impurity of the reaction solutions. The invention also embraces treatment of those zeolites which have lattice elements other than silica and/or alumina associated therewith, such as boron, iron, chromium, etc. One procedure according to the invention is carried out by incorporating the crystalline zeolite into an alumina support matrix material and forming an extrudate of same, impregnating the extrudate under a vacuum (i.e. a pressure less than atmospheric pressure) with an aqueous solution of an alkali metal fluoride such as an aqueous solution of Lithium fluoride, sodium fluoride, potassium fluoride, rubidium fluoride or cesium fluoride, the solution being from about 0.1 to about 2 Normal, the vacuum impregnation being conducted at a temperature of from about OOC to about 1000C, preferably from about ambient to about 500C. The impregnated extrudate is then contacted with a warm, i.e. ambient to 1000C, preferably 600C to 800C, aqueous solution of from 0.1 to 2 Normal ammonium salt, e.g. 1N NH4N03, and thereafter calcined at a temperature of from about 2000C to about 6000C in an inert atmosphere of air, nitrogen, etc., at subatmospheric, atmospheric or superatmospheric pressures for from about 1 minute to about 48 hours. The amount of alkali metal fluoride which is utilized. is from about 0.05 to about 2 grams of alkali metal fluoride per gram of crystalline zeolite material in the extrudate. The ammonium salt solution contacting step may be conducted for a period of time of from about 1 hour to about 20 hours. The ammonium salt used is not narrowly critical and will normally be an inorganic salt such as ammonium nitrate, ammonium sulfate, ammonium chloride, etc. The support matrix material combined with the crystalline zeolite in the initial step may be in the form of a gel, if desired, and the relative proportion of zeolite component and support matrix material component, on an anhydrous basis, may vary with the zeolite content ranging from about 25 to 75 weight percent of the dry composite. An alternative procedure is carried out by compositing the zeolite, either before or after ion exchange, with an alumina support matrix material and, in a preferred embodiment forming an extrudate of same, reacting the composite or extrudate with a dilute aqueous solution of hydrogen fluoride of from about 0.1 to about 5 Normal, the reaction being conducted at a temperature of from about OOC to about 300C, preferably at about ambient temperature, for a time of less than about 60 minutes, preferably from about 10 minutes to less than about 60 minutes. The hydrogen fluoride reacted compos ite or extrudate is dried, usually by heating to about 1300C, and then treated (1) by contact with an ammonium salt solution, e.g. 1N NH4No3, (2) by hydrolysis and/or (3) by ammonolysis, and thereafter calcined at a temperature of from about 2000c to about 6000C in an inert atmosphere of air, nitrogen, etc., at subatmospheric, atmospheric or superatmospheric pressures for from about 1 minute to about 48 hours. The amount of hydrgen fluoride which is utilized is from about 0.02 to about 0.2 grams of hydrogen fluoride per gram of crystalline zeolite material in the composite or extrudate. A less than 5 weight percent HF solution is preferred. If the treatment step following hydrogen fluoride reaction is an ammonium salt solution contacting step, it may be conducted for a period of time of from about 1 hour to about 20 hours at a temperature of from about OOC to about 90 C. The ammonium salt used is not narrowly critical and will normally be an inorganic salt such as ammonium nitrate, ammonium sulfate, ammonium chloride, etc. If the ammonium salt solution is aqueous, it will be from about 0.1 to about 5 Normal, preferably about 1 Normal. If the treatment step following hydrogen fluoride reaction involves hydrolysis, the extrudate will be contacted with water at a temperature of from about 200C to about 5500C. When the hydrolyzing temperature is below 1000C, liquid water will be used. When the boiling point of water is exceeded, the extrudate may be purged with water saturated gas, e.g. helium. If the treatment step following hydrogen fluoride reaction involves ammonolysis, the composite or extrudate will be contacted with 0.1 to 5 Normal ammonium hydroxide at a temperature of from about OOC to about 90 C, or with moist or dry gaseous ammonia at a temperature of from about 500C to about 2000C. The support matrix material combined with the crystalline zeolite in the initial step of the present method may be in the form of a gel, if desired, and the relative proportion of zeolite component and support matrix material component, on an anhydrous basis, may vary with the zeolite content ranging from about 25 to about 75 weight percent of the dry composite. Extrusion of the composite is preferred at this point because it results in a more intimate mixture of components. A further procedure in accordance with the invention is carried out by incorporating the zeolite into a matrix of alumina, an alumina-silica mixture, gallia or boria, reacting the composite with concentrated aqueous solution of an ammonium halide, preferably a fluoride of from about 1 Normal to saturated (about 12 Normal), the reaction being conducted at a temperature of from about 00C to about 900C, preferably from about ambient to about 500C, for a time of less than about 60 minutes, preferably from about 10 minutes to less than about 60 minutes. The ammonium halide reacted composite is dried at about 110 to 1300C and then treated by contact with an ammonium salt solution, e.g. 1N NH4N03, at from about 0 to about 900C, and thereafter calcaned at a temperature of from about 2000C to about 6000C in an inert atmosphere of air, nitrogen, etc., at subatmospheric, atmospheric or superatmospheric pressures for from about 1 minute to abour 48 hours. The amount of halide salt which is utilized is from about 0.1 to about 0.5 grams of halide per gram of crystalline zeolite material in the composite. The treatment with the aqueous ammonium halide salt solution can be conducted for a period of time of from about 1 hour to about 20 hours. The ammonium salt used is not narrowly critical and will normally be an inorganic salt such as ammonium nitrate, ammonium sulfate, ammonium chloride, etc. The aqueous ammonium salt solution will be from about 0.1 to about 2 Normal. The support matrix material combined with the crystalline zeolite in the initial step of the present method may be in the form of a gel, if desired, and the relative proportion of zeolite component and support matrix material component, on an anhydrous basis, may vary with the zeolite content ranging from about 25 to about 75 weight percent of the dry composite. The fluoride employed according to the invention may take the form of a complex fluoroanion conforming to the formula: L(n-m)[MFn]e wherein L is an organis or inorganic ionic moiety such as, for example, (CH3)4N+ , Pt pyr2(NH4)2, NH4+ or Pt(NH4)4 2; MFn is a fluoroanion moiety comprising the element M; M is an element from Groups VB, VIB, VIIB, VIII, IIIA, IVA and VA of the Periodic Table of the Elements (Sargent-Welch Scientific Company) or a Rare Earth element, for example, boron, aluminum, gallium, silicon, phosphorous, antimony, bismuth, palladium, platinum, iridium, Iron, rhenium, molybdenum and tantalum; n is the co-ordination number of M; m is the valence of M and e is the valence or charge associated with L. Non-limiting examples of the fluoroanion moiety include BF4, A1F4 , PF6-, BiF4, A1F5 2, SiF62, SbF5 2, Fe 2, PtF62, ALF6-3, TaF8-3, and PdF7-3. Non-limiting examples of the compounds having a complex fluoroanion of the above formula L(n-m)[MFn]e include: ammonium tetrafluoroaluminate, ammonium hexafluorophosphate, ammonium tetrafluorobismuthate, ammonium pentafluoroaluminates, ammonium hexafluorosilicate, ammonium pentafluoroaluminates, ammonium hexafluorosilicate, ammonium pentafluoroantimonate, ammonium tetrafluoroferrite, ammonium octafluorotantalate, ammonium heptafluoropallidate, tetramethylammonium tetrafluoroborate, and ammonium tetrafluoroborate. The reaction may be conducted in a solvent med ium, i.e. solution, or as a solid-solid contact reaction and should be conducted at a temperature of from about -700C to about 800C and a pressure of from about -0.8 psig to about 50 psig. The product zeolite may, if desired, be hydrolyzed by contact with water at a temperature of from about 200C to about 5500C and/or contacted with an ammonium salt solution and calcined. If hydrolyzed and the hydrolyzing temperature is beloe 1000C at atmospheric pressure, liquid water may be used. When the boiling point of water is exceeded, such as when the hydrolyzing temperature exceeds 1000C at atmospheric pressure, the zeolite may be purged with water saturated gas, e.g. helium. The ammonium salt solution contacting step may be conducted, if desired, with an aqueous or nonaqueous solution of an ammonium salt, e.g. NH4N03, for a period of time of from about 1 hour to about 20 hours at a temperature of from ambient to about 1000C. The ammonium salt used is not narrowly critical and will normally be an inorganic salt such as ammonium nitrate, ammonium sulfate, ammonium chloride, etc. The hydrolysis and ammonium salt solution contacting steps, if conducted, may be conducted simultaneously when the ammonium salt solution is aqueous. The zeolite treated in accordance with the present method may, thereafter, be calcined at a temperature of from about 2000C to about 6000C in an inert atmosphere of air, nitrogen, etc., for from about 1 minute to about 48 hours. Of the zeolites advantageously treated in accordance herewith, zeolites ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 and ZSM-48 are particularly noted. ZSM23, -35. -38 and -48 are respectively defined by the xray data set forth in üS-A-4,076,842, 4,016,245 and 4,046,859 and EP-A-15132. Many of these zeolites possess a constraint index within the range 1-12, a property which can be employed to define zeolites to which the invention is applicable. The activity enhanced materials prepared according to the invention are useful as catalyst components for acid catalyzed organic compound conversion reactions. Such reactions include cracking of hydrocarbons, wherein the reaction conditions include a temperature of from about 3500C to about 6000C, a pressure of from about O to about 30 asia, and a weight hourly space velocity of from about 0.1 to about 10; and conversion of methanol to gasoline, wherein the reaction conditions include a temperature of from about 4000C to about 5000C, a pressure of from about 0 to about 1000 psig, and a weight hourly space velocity of from about 0.1 to about 20. It may be useful to composite the above-described activity enhanced crystalline zeolite with a matrix resistant to the temperature and other conditions employed in a conversion process. Suitable matrix materials are well known in the art and are described in our EP-A-1695. The following examples illustrate the present invention. EXAMPLE 1 Zeolite ZSM-5 prepared from a reaction mixture containing tetraalkylammonium ions and having a silicato-alumina mole ratio of about 26,000:1 (65 ppm framework alumina, 110 ppm bulk alumina and 0.23 percent sodium) was composited and extruded with Kaiser gammaalumina (Al203) to provide an extrudate of 65 wt.X ZSM-5 and 35 wt. X Al203, which was calcined for 30 minutes at 5380C. The calcined extrudate was vacuum impregnated with saturated aqueous sodium fluoride solution at a temperature of 250C. After 30 minutes contact, the extrudate was dried at 1300C and then contacted three times at about 800C with warm 1N NH4 NO3 solution (800C). The extrudate was hot water washed after each contacting with the warm ammonium salt solution. The extrudate was dried at 1300 and calcined for 30 minutes at 5380C and found to have an Alpha value of 70. The calcined estrudate subjected to impregnation had an Alpha value of less than 0.1. EXAMPLE 2 Example 1 was repeated, employing a zeolite prepared from a reaction mixture containing trimethyl E6- (trimethylarsonio)hexyl ammonium ions and having a silica-to-alumina mole ratio of greater than about 500. The product exhibited an Alpha value of about 23. As is known in the art, the Alpha value is an approximate indication of the catalytic cracking activ ity of the catalyst compared to a standard catalyst and it gives the relative rate constant (rate of normal hexane conversion per volume of catalyst per unit time). It is based on the activity of the highly active silicaalumina cracking catalyst taken as an Alpha of 1. The Alpha Test is described in The Journal of Catalysis, Vol. IV, pp. 522-529 (August 1965). EXAMPLE 3 A 0.6 gram sample of zeolite ZSM-5 having a silica/alumina mole ratio of about 26,000 (65 ppm framework alumina, 110 ppm bulk alumina and 0.23X sodium) was vacuum impregnated with 4 weight percent aqueous hydrogen fluoride (2 Normal) solution for reaction at a temperature of 250C. After 30 minutes reaction time, the zeolite material was dried at 1300C and treated three times with 1N NH4N03 solution, each treatment followed with water washing. The product was calcined at 5380C for 30 minutes in air. EXAMPLE 4 A 0.6 gram sample of pure gamma-alumina was reacted with hydrogen fluoride as in Example 3. A 0.3 gram portion of the hydrogen fluoride-reacted alumina was dried at 1300C and treated by hydrolysis by contact with liquid water at ambient temperature for 2 hours and then calcined at 5380C for 30 minutes. EXAMPLE 5 The remaining 0.3 gram portion of the hydrogen fluoride reacted alumina of Example 4 was dried at 1300C and treated with NH4N03 as in Example 3. The alumina product of this example was calcined at 5380C for 30 minutes. EXAMPLE 6 An aliquot of 65 parts of the untreated zeolite of Example 3 was combined and extruded with 35 parts of pure gamma-alumina (the same alumina as used in Example 4). The extrudate was reacted with hydrogen fluoride as in Example 3, dried at 1300C and treated with 1N NH4N03 solution three times followed each time by water washing. The extrudate product of this example was calcined for 30 minutes at 5380C. A sample of each product from Examples 3 to 6 was subjected to the Alpha Test to measure catalytic activity. The results are listed below: Example Product Description Alpha Value 3 Untreated Zeolite 0.015 3 Treated Pure Zeolite 0.2 4 Treated Pure Alumina 8 (with hydrolysis) 5 Treated Pure Alumina 10 (with ammonium salt treatment) 6 Treated Extrudate 101 (present method) EXAMPLE 7 The untreated zeolite used in Example 2 was composited with alumina and reacted with hydrogen fluoride as in Example 3. The hydrogen fluoride reacted composite is dried at 1300C and hydrolyzed by contact with liquid water at ambient temperature for 2 hours and then treated by ammonolysis involving contact with ammonia at 1500C for 30 minutes. The final composite product is than calcined at 5380C for 30 minutes in air. The original pure zeolite of this example exhibits an Alpha value of less than 1, while the final calcined composite provides an Alpha Value of about 100. EXAMPLE 8 Sixty-five parts of the untreated zeolite employed in Example 1 was combined and extruded with 35 parts of pure -alumina. A 0.6 gram sample of the extrudate was vacuum impregnated with a saturated solution of aqueous ammonium fluoride (approximately 12 Normal) for reaction at ambient temperature. After 30 minutes reaction time, the extrudate was dried at 1300C and treated three times with 1N NH4N03 solution, each treatment followed with hot water washing. The extruded product was then calcined at 5380C for 30 minutes in air. The sample was tested for hexane cracking (the Alpha Test) and constraint index. Results are shown below: CATALYST EVALUATION SAMPLE O < C.I. (650 F) Starting Extrudate 0.2 Final Product 140 3.9 -Alumina 0.2 Above results show enhanced Bronsted activity which can only result from addition of aluminum to the zeolite structure to create new acid sites. The invention is adaptable to the regeneration of spent zeolite catalysts no longer useful in such processes as cracking or dewaxing. These catalysts ordinarily will have been sufficiently treated by combustion as to be substantially free of carbon deposits, but will nevertheless have lost their activity. These catalysts, including zeolite materials which have been composited with silica, alumina, silica-alumina mixtures as well as other previously described matrix mixtures are subjected to ammonium halide (preferably fluoride) treatment followed by ion exchange with an aqueous solution of ammonium salts as described previously. EXAMPLE 9 Untreated ZSM-5 as used in Example 8 was converted to NH4-ZSM-5 by treating with 1.0 N NH4N03 at ambient temperature. A 2 gram sample af extrudate comprising 65 parts of the NH4-ZSM-5 and 35 parts of Kaiser gamma-alumina monohydrate was prepared by slurrying and extruding the components. The extrudate was then impregnated under vacuum (20 mm asia, -0.85 psig) and at a temperature of 250C with a saturated aqueous solution of ammonium tetrafluoroborate (NH4EF4). After 30 minutes contact, the extrudate was dried at 1300C and treated twice with cold NH4N03. It was then dried again, calcined at 5380C, ref fluxed for one hour with N04N03 and then washed with boiling water. The calcination and ref fluxing was repeated once more. The pro duct was subjected to the Alpha Test to measure catalyt ic activity. A sample of extrudate similarly prepared but not contacted with the complex fluoroanion contain- ing compound, was also tested for comparison purposes. The Constraint Index of the final product was also measured. The results of these tests are listed below: Alpha Value Constraint Index Starting Extrudate 1 Final Product 102 2.2

Claims: CLAIMS 1. A method of enhancing the activity of a catalyst comprising from 25 to 75X by weight of a crystalline zeolite having an ion exchange capacity less than 0.7 meq./g. and from 75 to 25Z by weight of an inorganic oxide matrix, which method comprises contacting the catalyst with a monovalent fluoride in an aqueous medium and thereafter converting the zeolite in the catalyst to the protonated form. 2. A method according to claim 1, wherein the matrix is alumina, silica, boria and/or gallia. 3. A method according to claim 1 or claim 2 wherein the contacting with the fluoride is acrried out at a temperature of O to 1000C. 4. A method according to any preceding claim wherein the duration of said contacting is up to 9 hour. 5. A method according to any preceding claim wherein the concentration of the flurode in said medium is 0.1 to 12N. 6. A method according to any preceding claim wherein the weight ratio of fluoride to zeolite during the contacting is 0.05 to 2.0. 7. A method according to any preceding claim wherein the fluoride is an alkali metal fluoride. 8. A method according to claim 7 wherein the concentration of fluoride in said medium is 0.1 to 2N and the fluoride/Zeolite weight ratio is 0.05 to 2.0. 9. A method according to any of claims 1 to 6 wherein the fluoride is hydrogen fluoride. 10. A method according to claim 9 wherein the contacting is carried out at O to 300C for from 10 to 60 minutes, the -concentration of fluoride in the medium is 0.1 to 5N and the fluoride/Zeolite weight ratio is 0.02 to 0.2. 11. A method according to any of the claims 1 to 6 wherein the fluoride is ammonium fluoride. 12. A method according to claim 11 wherein the contacting is carried out at O to 900C for from 10 to 60 minutes, the concentration of fluoride in the medium is 1 to 12N and the fluoride/zeolite weight ratio is 0.1 to 0.5. 13. A method according to any of claims 1 to 6 wherein the fluoride is a compound possessing a complex fluoroanion. 14. A method according to any preceding claim wherein the zeolite is converted to the protonated form by ammonium exchange followed by calcination at 200 to 6000C. 15. A method according to any of claims 1 to 13 wherein the zeolite is converted to the protonated form' by hydrolysis at a temperature of 20 to 5500C. 16. A method according to any preceding claim wherein the starting zeolite has a silica/alumina mole ratio greater than 100. 17. A method according to any preceding claim wherein the starting zeolite has a silica/alumina mole ratio greater than 500. 18. A method according to any preceding claim wherein the starting zeolite is one synthesised form a reaction mixture in which alumina is present only as an impurity. 19. A method according to any preceding claim wherein the starting zeolite contains lattice elements other than silicon and aluminum. 20. A method according to any of claims 1 to 19 wherein the zeolite is ZSM-5,-11,-12,-23,-35,-38 or -48. 21. A method according to any of claims 1 to 19 wherein the zeolite has a constraint index in the range 1 to 12. 22. Use of zeolites of enhanced activity, obtained by the method claimed in any preceding claim, as catalysts or catalyst components in the conversion of organic compounds.

Inventors: CHANG, CLARENCE DAYTON, MIALE, JOSEPH NICOLAS
Applicants: MOBIL OIL CORPORATION
Application year: 1983
Main classification: B01J29
IPC codes: B01J29, C01B39