TREATMENT OF ZEOLITES

Abstract: The acid activity of zeolites such as those of constraint index 1-12 is enhanced by treatment of the zeolite with salts of certain potential lattice elements under alkaline hydrother­ mal conditions to effect a reduction of silicon/non-silicon lattice element ratio.

Description: TREATMENT OF ZEOLITES The invention relates to the treatment of zeolites to enhance their activity. The silica-to-alumina mole 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; zeolite Y from 3 to about 6. In some zeolites, the upper limit of silica-to-alumina ratio is unbounded, as in the case of ZSM-5 wherein the silica-to-alumina mole ratio is at least 5. US-A-3,941,871 discloses ZSM-5 essentially free of aluminum. US-A-4,061,724, 4,073,865 and 4,104,294 describe microporous crystalline silicas or organosilicates wherein the aluminum content present is at impurity levels. Because of the extremely low aluminum content of such highly siliceous zeolites, their ion exchange capacity is not as great as materials with a higher aluminum content. Therefore, when these materials are contacted with an acidic solution and thereafter are processed in a conventional manner, they are not as catalytically active as their higher-aluminum counterparts. According to the present invention a method of in creasing the catalytic activity, alpha, of a crystalline zeolite having a constraint index of 1 to 12 and a lattice silicon/non-silicon atomic ratio of at least 20 comprises contacting the zeolite for a period of 1 hour to 30 days at a temperature of at least 1000C with an aqueous solution having a pH of 9 to 12 containing an ion of the formula M(OH)4 where M is Al, B, Fe, Cr or Ga, separating the zeolite from the solution and converting it to the protonated (ie. hydrogen or hydronium) form. Typical zeolites to which the invention may be applied are ZSM-5, -11, -12, -23, -35, -38 and -48, defined respectively by the x-ray data set forth in US-A-3,702,886, 3,709,979, 3,832,449, 4,076,842, 4,016,245 and 4,046,859 and EP-A-15132. Both aluminosilicate and other, e.g. boro-, chromo-, ferro- and gallosilicate, forms of such zeolites are contemplated as starting materials, as are their effectively pure silica forms. The invention may, from another aspect, be regarded as zeolite activation by contacting high silica zeolite under hydrothermal conditions with an alkaline metallate solution comprising at least one tetrahedrally bound hydroxylated metal late at a pH of about 9 to 12, and maintaining the zeolite in contact with the solution at elevated temperature under conditions to introduce tetrahedrally coorindated metallate into the crystalline zeolite. The technique is particularly advantageous for treating acid ZSM-5 type zeolites having a silica:alumina mole ratio greater than 50:1, in which case alkaline solutions containing aluminate anion may be employed under hydrothermal conditions at elevated temperatures. Nitrogenous bases, such as quaternary ammonium or amine compounds are preferred to maintain the aluminum ion in the desired state for treating the zeolites. The novel process of this invention permits the preparation of highly siliceous zeolites which have all the desirable properties inherently possessed by such high silica materials yet have an acid cracking activity (alpha value) which heretofore has only been manifested by materials having a higher aluminum content. The preferred starting material for the process of this invention is a high silica containing ZSM-5. The process is simple in nature and easy to carry out although the results obtained therefrom are dramatic. Nitrogenous bases andlor alkali metal cations can be employed to achieve a pH of at least 7. Preferably a pH greater than 9 up to about 13 is maintained with organic cations, such as amines or quaternary ammonium compounds. Being amphoteric, the ions of the metal M can be supplied by any suitable organic or inorganic salt such as chloride, sulfate, nitrate, acetate, etc. However, at a moderately alkaline pH, (eg. pH 9 to 12) a stable M(OH) 4 ion becomes available for hydrothermal treatment. This tetrahedral hydroxylated metallate ion is uniquely adapted for enhancing catalytic cracking activity. The hydroxylated metallates which are tetrahedrally coordinated in the zeolite crystalline structure according to the invention are Ga(OH) 4, Fe(OH) 4, Al(OH) 4, Cr(OH) 4 and B(OH)-4. The organic nitrogen-containing cation utilized In the hydrothermal solution can be a tetraalkylammonium cation, such as tetraethylammonlum, tetrapropylammonium, tetrabutylammonium, methyl triethylammonium, methyl tripropylammonium, as well as mixtures thereof. The nitrogenous base can include varlous primary, secondary or tertiary amines especially normal alkyl amines such as n-propylamine, n-butylamine. It Is advantageous to carry out the treatment at a pH of at least 7 up to about 13, and most preferably at a pH of 9 to 12. In addition to the organic bases, pH control can be accomplished by adding a suitable inorganic base such as sodium or ammonium hydroxide, to a solution of organic nitrogen-containing cation and aluminum ion. A particularly preferred embodiment, in the case where aluminum is to be introduced into the lattice, is to use an alkali metal aluminate as the source of aluminum ion. This anion species may be prepared in situ by adding a base such as sodium hydroxide to an aqueous solution of an aluminum salt such as aluminum sulfate, or by dissolving sodium alumina directly. The relative proportion of metal late ion and organic nitrogen-containing cation present in the solution is ndt narrowly critical and usually ranges from 1 to 150 grams of equivalent metal salt per liter of solution and 1 to 200 grams of organic compound per liter of solution. The most preferred solvent is water for reasons of economy and ease of operation; however, various cosolvents may be employed within the inventive concept. The amount of solution utilized to treat the zeolites is not critical and the solution to zeolite ratio can vary from 1 to 100 grams of solution per gram of zeolite. The amount of solution will vary as a function of its reaction kinetics concentration and desired enhancement of activity. The process is carried out by treating the zeolite as crystallized or after calcination with the above described solution at elevated temperatures ranging up to 3000C, preferably to 1600C, for periods of time ranging from 1 hour to 30 days, preferably from 1 to 5 days. The hydrothermal conditions may require superatmospheric pressures at above 1000C to maintain adequate ionizing medium to maintain the metallate ion. Autogenous pressure can be maintained by autoclave or the like. Ordinarily pressures of 100 kpa to 1000 kpa are satisfactory. Following the treatment, the zeolite may be further processed into its catalytically active form by conventional techniques, such as base exchange with appropriate cations such as hydrogen, ammonium, rare earth, and mixtures thereof. The zeolite is then advantageously calcined by heating to a temperature in the range of 200-6000C in an atmosphere such as air, nitrogen, etc., and atmospheric, subatmo spheric, or superatmospheric pressure for between about 1 and 48 hours. The zeolite can, if desired, be incorporated in a matrix by techniques well known in the art for use as a catalyst. Conventional binder matrices include inorganic oxides, such as silica, alumina, silica-alumina, etc. The following examples illustrate the invention. EXAMPLE 1 ZSM-5 of silica/alumina mole ratio 500 (A), 1600 (B) and > 30,000 (C) was treated with a solution prepared from 2.55 grams of sodium hydroxide, 10.0 grams of tetrapro pylammonium bromide and 7.2 grams of Al2(s04)3.14H20 and 115 grams of water under hydro-treating conditions: 1000C (2120F) for 6 hours at 1 atmosphere pressure. The solution to zeolite weight ratio was 3.4 parts of solution per part of zeolite, the pH 9.9. (Zeolites A and B, were calcined in nitrogen at 5400C (10000F) for 3 hours prior to treatment. Zeolite C was used as crystallized without calcination). The three zeolites were then processed into their active form by calcination in nitrogen at 5400C (10000F) followed by ammonium exchange with an aqueous solution of ammonium nitrate at ambient temperatures to remove sodium and/or excess aluminum ions. Finally, all three were air calcined at a temperature of 5400C (1000 F) for three hours. The three zeolites, before and after treatment, were evaluated for hydrocarbon cracking activity (alpha). (This test is described in Journal of Catalysis, Volume 4, pages 522-529, August 1965). The results obtained are shown in the following table: TABLE 1 Material A 9 C Zeolite ZSM-5 ZSM-5 ZSM-5 siO2/Al203 500:1 1600:1 > 30,000:1 Acid Acid Acid (as Form (calcined) (calcined) (crystal lized) i(Untreated acid form) 10 1.7 0.1 a(Treated acid form) 27 15 2.3 Enhancement, 2.7 8.8 23 It can be seen that the process of the invention resulted in a marked increase of activity. Thus, the ZSM-5 having a silica-to-alumina ratio of 500 had an alpha value of 10 prior to activation in accordance with the novel process of this invention, and thereafter its activity was raised to a value of 27. The effects of the alpha enhancement are more pronounced as the silica-to-alumina increases. COMPARATIVE EXAMPLES 2-8 The following comparative examples demonstrate that the simple addition of aluminum either by impregnation or exchange cannot achieve the activity enhancement of high silica zeolites. EXAMPLE 2 Four grams of type C low Al ZSM-5 (containing 50 ppm Al203) in its NH4 form are impregnated with solution of 0.03 g Al(NO3)3 9H20 in 2 g water. The wet zeolite mix is dried slowly, slugged and sized into 14/25 mesh. The resultant catalyst is activated at 5400C (10000F) for three hours. The alpha value is 0.38. EXAMPLE 3 Zeolite C catalyst is treated in ammonium form in a manner similar to those described in Example 2 except using 0.15 g Al(N03)3.9H20. The alpha value is 0.56. EXAMPLE 4 Ammonium Zeolite C is treated in a manner similar to Example 2 except using 0.3 g Al(N03)3).9H20. The alpha value is 0.81. EXAMPLE 5 Zeolite C is treated by impregnating 4 g of Type C low alumina ZSM-5 in its NH4 form with 0.13 g of NaAlO2 dissolved in 2 g of H2. The wet mix was dried at 110C (23)0F) for three hours and then calcined at 5400C (10000F) for three hours. The Na content of the sample was reduced by NH4 exchange. The sample was finally sized to 14/25 mesh and activated at 5400C (10000F) for three hours again. The alpha activity of the sample was 0.1. EXAMPLE 6 This catalyst is prepared in a similar manner as described in Example 5 except that the "as crystallized" low alumina ZSM-5 is used as base material. The alpha value was 0.43. EXAMPLE 7 Four grams of "as synthesized" low alumina ZSM-5 is exchanged with a solution of 1.5 g Al(N03)3.9H20 in 20 ml of H20. After mixing for 2 hours the sample is filtered, washed and dried. The sample is then sized to 14/25 mesh and calcined at 10000F for three hours and then exchanged with NH4N03 solution to remove Na to 0.02Z wt. The catalyst is finally activated in air at 5400 (10000F) for three hours. The alpha activity of the catalyst is found to be 0.24. EXAMPLE 8 This catalyst is treated in a similar manner to Example 7 except that 1.18 Al2(OH)5Cl is used instead of Al(N03)309H20. The alpha activity of the catalyst was found to be 0.31. The results obtained in Examples 2-8 are shown in Table 2, wherein it is demonstrated that the results obtained are distinctly inferior to the claimed invention as illustrated in Table 1. 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Claims: CLAIMS 1. A method for increasing the catalytic activity, alpha, of a crystalline zeolite having a constraint index of 1 to 12 and a lattice silicon/non-silicon atomic ratio of at least 20 which comprises contacting the zeolite for a period of 1 hour to 30 days at a temperature of at least 1000C with an aqueous solution having a pH of 9 to 12 containing an Ion of the formula M(OH) 4 where M is Al, B, Fe, Cr or Ga, separating the zeolite from the solution and converting It to the protonated form. 2. A method according to claim 1 wherein pH is determined by the presence of alkali or nitrogenous base. 3. A method according to claim 2 wherein the nitrogenous base is a tetraalkylammonium compound. 4. A method according to claim 2 wherein the nitrogenous base is an alkylamine. 5. A method according to claim 2 wherein the nitrogenous base is tetraethylammonium, tetrapropylammonium, tetrabutylammonium, methyltriethylammonium, methyltripropylammonium, propylamine and/or butylamine. 6. A method according to any preceding claim wherein the ion M(OH) 4 is derived from an organic or inorganic salt of M. 7. A method according to any of claims 1 to 5 wherein the ion Al(OH) 4 is derived from sodium aluminate. 8. A method according to claim 6 wherein the metal salt is present in a concentration of 1 to 150 gram equivalents per liter and a nitrogenous base is-present in a concentration of 1 to 200 g/liter. 9. A method according to any preceding claim wherein the aqueous solution/zeolite weight ratio is from 1 to 100. 10. A method according to any preceding claim wherein the zeolite is calcined at a temperature of 200 to 6000C before the contacting. 11. A method according to any preceding claim wherein the contacting is carried out at a temperature of 100 to 3000C. 12. A method according to any preceding claim wherein the contacting is carried out at a temperature of 100 to 1500C. 13. A method according to any preceding claim wherein the contacting is carried out at a pressure of 100 kpa to 10,000 kpa. 14. A method according to any preceding claim wherein the conversion of the zeolite to the protonated for is effected by hydrolysis or by ammonium exchange followed by calcination at 200 to 6000C. 15. A method according to any preceding claim wherein the non-silicon lattice element of the initial zeolite is other than aluminum. 16. A method according to any of claims 1 to 14 wherein the initial zeolite is an aluminosilicate having a silica/ alumina ratio greater than 500, preferably greater than 1600. 17. A method according to any preceding claim in which the initial zeolite is one synthesized from a reaction mixture in which aluminum is present only as an impurity. 18. A method according to any preceding claim in which the zeolite has a constraint index of 1 to 12. 19. A method according to any of claims 1 to 17 in which the zeolite is ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38 or ZSM-48. 20. Use as a catalyst, or catalyst component, for the conversion of organic compounds of a zeolite obtained by the method claimed inany of claims 1 to 19.

Inventors: CHU, POCHEN
Applicants: MOBIL OIL CORPORATION
Application year: 1983
Main classification: B01J29
IPC codes: C01B39, B01J29