Title:
"Synthetic Zeolite, in Particular for Catalytic Hydroisomerization of Higher Paraffins"
Kind Code:
A1


Abstract:
The invention relates to a zeolite of the ZSM-12 type, especially for the hydroisomerization of higher paraffins, which has a primary crystal size of <0.1 μm; as well as a specific volume, determined by mercury porosimetry at a maximum pressure of 4000 bar, of 30-200 mm3/g in a pore radius range of 4-10 nm; and which has further been prepared from a synthesis gel composition comprising an aluminum source, precipitated silica as a silicon source, TEA+ as a template, an alkali metal and/or alkaline earth metal ion source M having the valency n; in which the molar H2O:SiO2 ratio is selected between 5 and 15. The invention further relates to a catalyst comprising the above zeolite and its use.



Inventors:
Burgfels, Gotz (Bad Aibling, DE)
Kurth, Volker (Bad Aibling, DE)
Reimer, Alfred (Furth im Wald, DE)
Schmidt, Friedrich (Rosenheim, DE)
Wellach, Stephan (Assling, DE)
Application Number:
10/551606
Publication Date:
02/14/2008
Filing Date:
03/27/2004
Primary Class:
Other Classes:
208/138, 208/143, 208/244, 208/370, 423/705, 423/713, 208/112
International Classes:
C10G25/05; B01J29/70; B01J29/74; B01J35/02; C01B39/42; C10G45/64; B01J35/10
View Patent Images:
Related US Applications:



Primary Examiner:
JOHNSON, KEVIN M
Attorney, Agent or Firm:
SCOTT R. COX (LOUISVILLE, KY, US)
Claims:
What is claimed is:

1. 1-15. (canceled)

16. A process for producing a zeolite of the ZSM-12 type comprising preparing a synthesis gel in an aqueous solution or suspension, which comprises an aluminum source; a silicon source, comprising precipitated silica; TEA+ as a template; and an alkali metal or alkaline earth metal ion source M having a valency of n, wherein the molar H2O:SiO2 ratio of the gel is within the range from 5 to 15, crystallizing the synthesis gel under hydrothermal conditions, while being stirred, so as to obtain a solid; removing the solid from the solution, and utilizing the solid to produce the ZSM-12 type zeolite.

17. The process as claimed in claim 16, characterized in that the molar Mn/2O:SiO2 ratio in the synthesis gel is within the range from 0.01 to 0.045.

18. The process as claimed in claim 16, characterized in that the molar SiO2/Al2O3 ratio is within a range from 50 to 150.

19. The process as claimed in claim 16, characterized in that the crystallization of the synthesis gel is carried out at temperatures of from about 120 to 200° C.

20. The process as claimed in claim 16, characterized in that the solid is washed with demineralized water until the washing water has an electrical conductivity of less than 100 μS/cm.

21. The process as claimed in claim 16, characterized in that the crystallization time is from about 50 to 500 h.

22. The process as claimed in claim 16, characterized in that the solid is washed, dried, comminuted, and calcined.

23. The process as claimed in claim 22, characterized in that the calcination is carried out at a temperature of from 400 to 700° C., for a period of from 3 to 12 h.

24. The process as claimed in claim 16, characterized in that exchangeable cations present in the zeolite of the ZSM-12 type are exchanged by treating with an aqueous solution of an ammonium compound or of an acid, and the solid obtained after the ion exchange is washed, dried and subsequently calcined.

25. The process as claimed in claim 16, characterized in that the zeolite of the ZSM-12 type is shaped into a molding.

26. The process as claimed in claim 25, characterized in that a binder is added to the zeolite of molded product in an amount from 10 to 90% by weight, based on the total weight of the molded product.

27. The process as claimed in claim 25, characterized in that the molded product contains at least one transition group metal.

28. The process as claimed in claim 27, characterized in that the transition group metal comprises a noble metal.

29. 29-34. (canceled)

35. A zeolite of the ZSM-12 type which has a primary crystal size of ≦0.1 μm; and a specific volume, determined by mercury porosimetry at a maximum pressure of 4000 bar, of 30-200 mm3/g with a pore radius range of 4-10 nm.

36. The zeolite as claimed in claim 35, characterized in that the zeolite has a specific volume, determined by nitrogen porosimetry, in a pore radius range of 3-20 nm, of 0.05-0.40 cm3/g.

37. The zeolite as claimed in claim 35, characterized with a molar SiO2/Al2O3 ratio of from about 50 to 150.

38. The zeolite as claimed in claim 35, characterized with a molar M2/nO:SiO2 ratio of from 0.01 to 0.045.

39. The zeolite as claimed in claim 35, characterized wherein the primary crystals have been combined in agglomerates in a proportion of at least 30%.

40. The zeolite as claimed in claim 35, characterized in that the primary crystals have a mean diameter of from about 10 to 70 nm.

41. The zeolite as claimed in claim 39, characterized in that the agglomerates have cavities accessible from their surface or interstices between the primary crystals.

42. A catalyst for the conversion of organic compounds comprising the zeolite of claim 35.

43. The catalyst as claimed in claim 42, characterized in that it is in lump form.

44. The catalyst as claimed in claim 42, further comprising a binder in an amount of from 10 to 90% by weight, based on the total weight of the catalyst.

45. The catalyst as claimed in claim 42, characterized in that the catalyst contains at least one catalytically active component.

46. The catalyst as claimed in claim 45, characterized in that the at least one catalytically active component comprises a transition group metal.

47. The catalyst as claimed in claim 46, characterized in that the transition group metal comprises a noble metal.

48. The catalyst as claimed in claim 47, characterized in that the noble metal comprises platinum.

49. The catalyst as claimed in claims 45, characterized in that the catalytically active component comprises from 0.01 to 40% by weight of the catalyst based on the total weight of the catalyst.

50. A process for converting organic compounds comprising passing an organic feed stream over or through a catalyst bed comprising the ZSM-12 type catalyst of claim 42.

51. A process for hydroisomerization of higher paraffins having a carbon number greater than 5 carbon atoms, comprising passing a feed stream containing higher paraffins over through a catalyst bed comprising the ZSM-12 type catalyst of claim 42.

52. The process of claim 51 wherein the higher paraffin comprised n-octane.

53. The process of claim 50 wherein the organic compounds comprise aromatics.

54. The process of claim 51 wherein the hydroisomerization process is carried out in the presence of hydrogen at a temperature below 290° C.

55. The process of claim 51 wherein the hydroisomerization process is carried out at a pressure of 1 to 50 bar at a liquid hourly space velocity (LHSV) of from 0.1 to 10 l per hour.

56. A process for reforming utilizing the zeolite catalyst of claim 42.

57. A process for increasing the flowability of gas oils utilizing the catalyst of claim 42.

58. A process for catalytic or hydrogenating cracking and oligomerization or polymerization of olefinic or acetylenic hydrocarbons utilizing the catalyst of claim 42.

59. A process for alkylation utilizing the catalyst of claim 42.

60. A process for dehydrogenation and hydrogenation of organic compounds utilizing the catalyst of claim 42.

61. A process for the hydration or dehydration of organic compounds utilizing the catalyst of claim 42.

62. A process for the desulfurization of organic compounds utilizing the catalyst of claim 42.

63. A process for the conversion of alcohols and ethers to hydrocarbons and the conversion of paraffins or olefins to aromatics utilizing the catalyst of claim 42.

Description:
The invention relates to a zeolite of the ZSM-12 type, to a catalyst which is suitable in particular for the hydroisomerization of higher paraffins, to a process for producing such a zeolite of the ZSM-12 type or such a catalyst, and to the use of the catalyst.

The isomerization of paraffins is one of the most important refinery processes. Very recent legal restrictions in the use of aromatics and methyl tert-butyl ether in automotive gasoline are making the isomerization of higher paraffins (greater than C5) in particular one of the most important alternatives for increasing the octane number in automotive gasoline. This is especially true of the isomerization of C8 paraffins.

To date, it has not been possible to carry out such isomerizations owing to the excessively low selectivity, i.e. owing to the formation of large amounts of cracking products.

In recent times, a series of investigations of the use of zeolites as catalysts for hydroisomerization and hydrocracking of higher paraffins have been carried out. For instance, W. Zhang and P. G. Smirniotis (J. Catal. 182, 400-416 (1999)) report on the influence of the zeolite structure and its acidity on the selectivity and the reaction mechanism for the hydroisomerization and the hydrocracking of n-octane. The catalysts investigated were ZSM-12, USY and β-zeolites with varying Si/Al ratios. In the synthesis of the ZSM-12 zeolites, aluminum is removed from the zeolite by dealumination with hydrochloric acid in order to establish a certain Si/Al ratio. The thus produced zeolites were investigated for their surface acidity and their catalytic activity. At temperatures of more than 290° C., n-octane is converted at conversion rates of about 50% with selectivities of from 27 to 41% to isooctanes.

A. Katovic and G. Giordano (Chemistry Express, Vol. 6, No. 12, 969-972 (1991)) describe the synthesis of ZSM-12 zeolites from the following hydrogel system: x Na2O:y TEABr:z Al2O3:50 SiO2:1000 H2O (where 2.5<x<7.5; 3.5<y<10 and 0<z<1). In the preparation of ZSM-12 using precipitated silica, an Na2O/SiO2 ratio=0.1, a TEABr/SiO2 ratio=0.2 and an SiO2/Al2O3 ratio=100 were used. In order to obtain pure crystalline (Na-TEA)-ZSM-12, the following conditions are recommended: Si/Al in the region of 50, OH/TEA+ in the region of 1 and H2O/OH in the region of 100.

U.S. Pat. No. 5,800,801 describes an MTW zeolite, a process for its production and its use in the cracking of hydrocarbons. The MTW zeolite is also referred to as ZSM-12 zeolite. The zeolite has a certain x-ray diffraction pattern, and also a specific surface area of more than 300 m2/g. For the production of the MTW zeolite catalyst, an aqueous solution of sodium silicate is prepared, to which a solution of tetraethylammonium hydroxide and an aqueous solution of aluminum nitrate are added, the amounts of the individual components being selected such that: SiO2/Al2O3: >120 TEA+/SiO2: 0.2-0.95; H2O/SiO2: 20-300; OH/SiO2: 0.4-0.7.

U.S. Pat. No. 3,970,544 and DE 22 13 109 C2 describe ZSM-12 zeolites, processes for their preparation and their use for converting hydrocarbons. The SiO2/Al2O3 ratio in the ZSM-12 zeolites described is between 49 and 300. In the examples, the silicon source used is colloidal silicon oxide.

In the hydroisomerization of higher paraffins, large amounts of low molecular weight cracking products are formed. These side reactions are generally promoted by high temperatures, which are required in order to achieve industrially sufficient conversion rates.

It is therefore an object of the present invention to provide a zeolite of the ZSM-12 type which is suitable especially for use in a catalyst as is used, for instance, for the hydroisomerization of higher paraffins. It is a further object of the present invention to provide a catalyst which leads to higher yields of isoparaffins especially in the hydroisomerization of higher paraffins, and also affords advantageous results in other conversions of hydrocarbons.

This object is achieved with a zeolite of the ZSM-12 type as claimed in claim 1. Advantageous developments of the zeolite of the ZSM-12 type are the subject matter of the dependent claims. Furthermore, the invention provides a catalyst which comprises the inventive zeolite of the ZSM-12 type. Further developments of this catalyst are the subject matter of the claims dependent upon claim 8.

It has been found that, surprisingly, when a combination of certain features in the synthesis is complied with, particularly advantageous zeolites can be obtained, which are suitable, for example, especially for use in catalysts for the hydroisomerization of higher paraffins with high activity and good conversion, and it is possible to carry out the reaction even at comparatively low temperatures.

The invention therefore first provides a zeolite of the ZSM-12 type, especially for use in catalysts for the hydroisomerization of higher paraffins, which

    • (a) has a primary crystal size of ≦0.1 μm;
    • (b) a specific volume, determined by mercury porosimetry at a maximum pressure of 4000 bar, of 30-200 mm3/g in a pore radius range of 4-10 nm; and which has further been
    • (c) prepared from a synthesis gel composition comprising
      • c1) an aluminum source
      • c2) precipitated silica as a silicon source
      • c3) TEA+ as a template
      • c4) an alkali metal and/or alkaline earth metal ion source M having the valency n;
      • c5) in which the molar H2O:SiO2 ratio is selected between 5 and 18.

The inventive zeolite of the ZSM-12 type features a particularly high porosity. This is manifested clearly in the specific pore volume determined by mercury porosimetry, especially when it is placed in relation to the pore radius. In mercury porosimetry, the inventive zeolite of the ZSM-12 type exhibits, in a pore radius range of 4-10 nm, a specific volume of from about 30 to 200 mm3/g, preferably about 80-150 mm3/g, especially preferably about 100-130 mm3/g. ZSM-12 zeolites which have been produced using colloidal silica have a distinctly smaller specific pore volume in this pore radius range. Typical values for a pore radius range of 4-10 nm are in the region of about 3 mm3/g. In a pore radius range of 10-100 nm, the inventive zeolite of the ZSM-12 type has a specific pore volume of about 70-700 mm3/g, preferably about 150-550 mm3/g, especially preferably about 200-500 mm3/g. A zeolite of the ZSM-12 type produced using colloidal silica exhibits, in the pore radius range of 10-100 nm, typically a specific pore volume of about 40 mm3/g. The pore volume is determined by mercury porosimetry to DIN 66133 at a maximum pressure of 4000 bar (cf. Example 11). The aforementioned porosimetry values are determined on the zeolites which have been washed, dried and calcined according to Example 1. The above ranges for the specific volume also apply to the washed and dried but uncalcined zeolites.

The inventive zeolite of the ZSM-12 type has a high proportion of large pores, as obtainable only in the inventive composition according to claim 1. The inventive zeolite of the ZSM-12 type exhibits, in nitrogen porosimetry in the range of 30-200 Å, a specific volume of 0.05-0.40 cm3/g, preferably 0.10-0.35 cm3/g, especially preferably 0.15-0.30 cm3/g. It is assumed, without the invention being restricted to this assumption, that the above porosimetry of the inventive zeolite is also responsible for the high catalytic activity and reflects the numerous cavities between the small primary crystals. The specific pore volume is determined by nitrogen porosimetry according to DIN 661134 as specified in Example 12. The above porosimetry values may be determined on the dried uncalcined zeolites or preferably on the calcined zeolites. The above porosimetry values are determined on zeolites which have been washed, dried and calcined according to Example 1. The above ranges for the specific volume also apply to the washed and dried but uncalcined zeolites.

It has been found that it is particularly advantageous when the zeolite is synthesized directly with the desired SiO2/Al2O3 ratio by appropriately adjusting the amount of silicon source and aluminum source in the primary synthesis of the zeolite (in the synthesis gel composition). The SiO2/Al2O3 ratio in the synthesis gel composition corresponds approximately to the SiO2/Al2O3 ratio in the ZSM-12 zeolite. The SiO2 fraction in the synthesis gel composition deviates, in a manner familiar to those skilled in the art, generally by about ±10% from the fraction in the finished zeolite. Only in the event of very large or very small fractions of SiO2 are larger deviations observed. As a result, no subsequent dealumination of the zeolite to adjust the SiO2/Al2O3 ratio is required. The aluminum content of the zeolite of the ZSM-12 type thus does not subsequently have to be lowered by addition of acid and leaching of aluminum atoms. It is assumed that the inventive direct synthesis enables a homogeneous structure of the zeolite and prevents what is known as “extra-framework” aluminum, which is formed in the subsequent dealumination after the zeolite synthesis, and can disadvantageously influence the activity and selectivity of the ZSM-12 zeolite.

It has been found that, surprisingly, the inventive advantageous properties of the zeolite can be realized when the synthesis gel used to produce the zeolite fulfills certain requirements. For instance, TEA+ cations are used in accordance with the invention as a template (TEA=tetraethylammonium). Compared to this, MTEA+ is unsuitable (MTEA=methyltriethylammonium). Particular preference is given to using TEAOH as a template. In principle, it is, however, possible to use any starting materials which supply tetraethylammonium ions. For example, TEABr may also be used.

The molar TEA+/SiO2 ratio established in the synthesis gel is preferably selected at a low level. The molar TEA+/SiO2 ratio is preferably selected between about 0.10 and 0.18. In the synthesis gel composition, the molar SiO2/Al2O3 ratio is preferably established within the range of from about 50 to about 150.

The synthesis gel should preferably also have a comparatively low alkali metal and/or alkaline earth metal content, and the molar M2/nO:SiO2 ratio may advantageously lie between about 0.01 and 0.045. M2/nO is the oxide of the alkali metal or alkaline earth metal having the valency n. In addition, in accordance with the invention, a comparatively low molar ratio of H2O:SiO2 of from about 5 to 18, preferably from 5 to 13, in the synthesis gel is used. The metal ion M selected is preferably an alkali metal, especially preferably sodium.

Surprisingly, a considerable influence of the silicon source on the morphology and catalytic activity of the resulting ZSM-12 zeolite was found. For instance, in accordance with the invention, a precipitated silica is used which, in comparison to colloidal silica, has a lower reactivity. This also allows the mean size of the resulting primary crystals, which should be less than 0.1 μm in accordance with the invention, to be influenced. The precipitated silica preferably has a BET surface area of ≦200 m2/g.

It is important that the average size of the primary crystals in the inventive catalyst is comparatively low and is less than 0.1 μm. The primary crystal size may be determined from scanning electron micrographs, by analyzing a number of primary crystals with regard to length and width. The measured primary crystal sizes are then used to form the arithmetic mean. The primary crystals present in the inventive catalyst generally do not have any significant differences in their lateral elongation in comparison to their longitudinal elongation. Should this occur in the individual case, the largest and the smallest diameter of the crystal are averaged in the determination of the primary crystal size.

Specifically, the procedure is to produce scanning electron micrographs of the washed and dried (cf. Example 1) but uncalcined, template-containing ZSM-12 zeolite at a magnification of from 68 000 to 97 676 (instrument: Leo 1530; LEO GmbH, Oberkochen, Germany). On the micrographs, 30 primary crystals are selected which are clearly delimited from one another, and their longitudinal and lateral elongation is measured (cf. above) and the mean is determined therefrom. The diameters determined in this way are then used to form the arithmetic mean, i.e. the mean primary crystal size. The primary crystal size is substantially not influenced by calcining. The primary crystal size can therefore be determined directly after the synthesis of the zeolite of the ZSM-12 type, and also after the calcination.

The primary crystals preferably have a size in the range of from about 10 to 80 nm, more preferably in the range of from about 20 to 60 nm. The inventive catalyst thus comprises comparatively small primary crystals.

In a particularly preferred inventive embodiment, the primary crystals of the zeolite are combined at least partly to agglomerates. Advantageously, the primary crystals have been combined to agglomerates in a proportion of at least 30%, preferably at least 60%, especially preferably at least 90%. The percentage data are based on the total number of primary crystals.

When the above-described conditions and features are complied with in the synthesis of the inventive zeolite of the ZSM-12 type, an apparently particularly advantageous morphology of the agglomerates of the very small primary crystals is surprisingly obtained, which also positively influences the catalytic activity of the ZSM-12 zeolite. Afterward, the agglomerates preferably have a large number of cavities on their surface and interstices between the individual primary crystals. The agglomerates thus form a loose structure composed of primary crystals with cavities accessible from the agglomerate surface or interstices between the primary crystals. On scanning electron micrographs, the agglomerates appear as a sponge-like structure with a highly fissured surface which is generated by the loose coherence of the primary crystals. The micrographs preferably show relatively large spherical agglomerates which have a broccoli-like shape. The structured surface is formed from primary crystals which form a loose structure. Between individual crystals, cavities are formed, from which channels lead to the surface, which appear on the micrographs as darkly contrasted points on the surface. Overall, a porous structure is obtained. The agglomerates formed from primary crystals are preferably in turn joined to form larger, superordinate agglomerates, between which individual channels with larger diameter are formed.

In contrast, conventional zeolites of the ZSM-12 type exhibit, in scanning electron micrographs, a comparatively less structured and apparently smoother surface of the agglomerates. This is probably caused by the substantially lower porosity of the zeolite.

The inventive zeolite of the ZSM-12 type thus preferably forms an open agglomerate structure, i.e. a structure in which the primary crystals are not combined in such an ordered way that a substantially smooth or continuous surface of the agglomerates is obtained. Instead, the primary crystals form bridges between adjacent primary crystals, so that cavities are formed between adjacent primary crystals.

It is assumed, without any intention that the invention be restricted by this theory, that the particular agglomerate structure enables efficient access of the molecules to be converted to the active sites of the inventive catalyst and rapid transport of the converted molecules away from the active sites, and also particularly advantageous utilization of the catalytic activity even in the interior of the primary crystal agglomerates. For example, the high catalytic activity of the inventive catalysts in the hydroisomerization of paraffins is influenced by the efficient diffusion of the paraffins to the active sites in the primary crystal agglomerates, as a result of which the reaction kinetics and thus also the yield of branched hydrocarbons can be improved. This enables the hydroisomerization to proceed even at comparatively low temperatures with good conversion rates and substantially without side reactions which lead to the degradation of the carbon skeleton to form low molecular weight hydrocarbons.

The primary crystals of the inventive zeolite of the ZSM-12 type are thus preferably combined to agglomerates, the size of these agglomerates being highly variable, and it is also possible for a plurality of agglomerates to be combined to larger, superordinate agglomerates. In this case, the primary crystals are predominantly recognizable by scanning electron microscopy as delimited units, but are on the other hand joined over part of their surface with adjacent primary crystals to form agglomerates. Scanning electron micrographs reveal relatively large, broccoli-like structures with a highly structured surface, which have combined to larger, superordinate agglomerates. This structure is not significantly impaired or altered by the processing of the zeolite to the finished catalyst, especially by the calcining, comminution, etc.

In a preferred embodiment, the number of the primary crystals not bonded into agglomerates is minimized in the inventive zeolite of the ZSM-12 type. Agglomerates are understood to mean combinations of a plurality of primary crystals.

The inventive zeolite of the ZSM-12 type exhibits a high catalytic activity, especially in the hydroisomerization of higher paraffins. The invention therefore also provides a catalyst, especially for the hydroisomerization of higher paraffins, comprising a zeolite of the ZSM-12 type as described above. According to the invention, higher paraffins are understood to mean those having at least 5 carbon atoms.

In its simplest embodiment, the catalyst comprises only the inventive zeolite of the ZSM-12 type. To this end, the powder obtained in the preparation of the zeolite of the ZSM-12 type, which may also initially be further ground and adjusted to a certain particle size distribution, is, for example, pressed to moldings without binders.

However, the catalysts may additionally also comprise further components. For instance, the catalyst may comprise further meso- and/or microporous materials. Meso- and microporous materials are understood, for example, to mean molecular sieves, especially aluminophosphates, metalloaluminates, titanosilicates and metallosilicates, for example zeolites. The proportion of the meso- and/or microporous materials may be between 1 and 99% by weight based on the weight of the catalyst.

In a further inventive embodiment, the catalyst may be processed to moldings with the aid of a binder. In particular, the catalyst may have a binder content of from about 10 to 90% by weight, preferably from 20 to 70% by weight. The binder used may be any binder which is familiar to those skilled in the art and appears to be suitable, especially silicate materials, aluminum oxide, zirconium compounds, titanium oxide, and mixtures thereof, and materials, for example cement, clay, silica/alumina. Preferred binders include pseudoboehmite and also silicatic binders such as colloidal silicon oxide.

The inventive catalyst is suitable generally, but not exclusively, for conversion reactions of hydrocarbons. The properties of the catalyst may be modified by covering the catalyst with catalytically active components which influence its catalytic properties or which are themselves catalytically active. Suitable for this purpose are, for example, metals of the transition groups, particular preference being given here to the noble metals. Suitable examples are gold, silver, rhenium, ruthenium, rhodium, palladium, osmium, iridium and platinum, and mixtures and alloys thereof. Particular preference is given to platinum.

The catalytically active component is generally present in the catalyst in a proportion of from 0.01 to 40% by weight based on the total face of the catalyst. When the catalytically active component used is a noble metal, it is preferably present in the catalyst in a proportion of from 0.05 to 2% by weight.

The particular properties of the inventive catalyst are influenced significantly by the preparation of the catalyst, such as the composition of the synthesis gel, and also the use of precipitated silica. The invention therefore also provides a process for producing the above-described catalyst.

In the process according to the invention, a synthesis gel composition is produced which comprises, in aqueous solution or suspension:

    • a1) an aluminum source;
    • a2) precipitated silica as a silicon source;
    • a3) TEA+ as a template;
    • a4) an alkali metal and/or alkaline earth metal ion source M having the valency n; and
    • a5) the molar H2O:SiO2 ratio is set within the range from 5 to 15;
      the synthesis gel composition is crystallized under hydrothermal conditions so as to obtain a solid. The solid is removed, and optionally washed, dried and calcined.

The solid obtained in the process according to the invention corresponds to the above-described zeolite of the ZSM-12 type. It has primary crystals having a mean primary crystal size of <0.1 nm and exhibits, depending on the pore volume, the above-described distribution, determined by mercury porosimetry, of the specific pore volume.

As already explained in connection with the inventive zeolite of the ZSM-12 type and the catalyst, the silicon source used in the process according to the invention is precipitated silica and the template used is tetraethylammonium ions.

In relation to the aluminum source, there are no particular restrictions, so that it is possible in accordance with the invention to use all customary aluminum sources familiar to those skilled in the art. Suitable examples are activated alumina, γ-alumina, aluminum hydroxide, sodium aluminate, aluminum nitrate, or else aluminum sulfate. Particular preference is given to sodium aluminate, since it functions simultaneously as a source of alkali metal ions.

The alkali metal ion and/or alkaline earth metal ion source used may be any customary compounds familiar to those skilled in the art. The alkali metal used with particular preference is sodium. The alkali metal sources used are in particular alkali metal hydroxides, preferably sodium hydroxide.

The procedure in the synthesis is preferably to initially prepare a solution of tetraethylammonium hydroxide in demineralized water. Subsequently, the aluminum source, for example sodium aluminate, and also a source of alkali metal and/or alkaline earth metal ions M having the valency n, for example sodium hydroxide, is added to this solution, and the mixture is stirred until a solution of the constituents is obtained. Subsequently, the precipitated silica is added in portions to this solution to obtain a highly viscous gel. The synthesis of the zeolite is preferably carried out in a small amount of water as a solvent. To this end, the molar H2O:SiO2 ratio is adjusted within the range from 5 to 15.

The molar ratio of the silicon and aluminum sources in the synthesis gel composition corresponds substantially to the molar composition of the zeolite of the ZSM-12 type to be produced. In order to be able to take account of deviations, caused by the reaction kinetics, between the composition of the synthesis gel and the desired composition of the zeolite, it is possible optionally to carry out preliminary experiments to determine the suitable synthesis gel composition. Preference is given to establishing the molar M2/nO:SiO2 ratio in the synthesis gel composition in the oxidic preparation method within a range from 0.01 to 0.045. The molar SiO2:Al2O3 ratio in the synthesis gel composition is preferably established within the range from 50 to 150.

The synthesis gel composition is stirred until a homogeneous gel is obtained. The crystallization is subsequently carried out under hydrothermal conditions, i.e. at a temperature of more than 100° C. and a pressure of more than 1 bar. To this end, the synthesis gel is stirred in a suitable pressure vessel. The crystallization is carried out preferably at temperatures of from about 120 to 200° C., especially preferably from about 140 to 180° C. The crystallization is particularly suitably carried out at a temperature of about 160° C. The crystallization time is preferably from about 50 to 500 h, in particular from about 100 to 250 h. The crystallization time is influenced, for example, by the crystallization temperature. Under these synthesis conditions, a solid is obtained which has primary crystals having a mean primary crystal size of not more than about 0.1 μm.

The crystallized product is subsequently removed from the mother liquor. To this end, the reaction mixture can be filtered, for example, with the aid of a membrane filter press. However, other processes for removing the solid may likewise be carried out. A removal may, for example, also be effected by centrifugation. The removed solid is subsequently washed with demineralized water. The washing operation is preferably carried out until the electrical conductivity of the washing water has fallen below 100 μS/cm.

The removed solid is subsequently dried. The drying is carried out, for example, under air in customary drying apparatus. The drying temperature is selected, for example, within the range from 100° C. to 120° C. The drying time is generally in the range from about 10 to 20 h. The drying time is dependent upon the moisture content of the removed solid and on the size of the batch. The dried solid may subsequently be comminuted in a customary manner, in particular granulated or ground.

To remove the template, the solid may be calcined. The calcination is carried out with ingress of air, the temperatures selected being within the range from 400 to 700° C., preferably from 500 to 600° C. The time for the calcination is generally selected to be between 3 and 12 h, preferably 3 and 6 h. The times for the calcination relate to the time for which the zeolite is kept at the maximum temperature. Heating and cooling times are not taken into account.

The content in the catalyst of exchangeable cations, especially alkali metal ions, may be influenced, for example, by treatment with suitable cation sources such as ammonium ions, metal ions, oxonium ions and mixtures thereof, and the exchangeable ions, especially alkali metal ions, present in the inventive zeolite of the ZSM-12 type may be exchanged. The catalyst laden with the corresponding ions may subsequently be washed again and dried. The drying is carried out, for example, at temperatures of from 110 to 130° C. for a time of from 12 to 16 h. In order to convert the catalyst into an acid-activated form in the event of an exchange for ammonium ions, the catalyst may also be calcined, for which, for example, temperatures in the range of from 460 to 500° C. can be employed for a period of from 6 to 10 h. Finally, the catalyst may also be ground.

The catalyst may be used in powder form. However, the catalyst is preferably processed to moldings in order to increase the mechanical stability and for better handling. To this end, the inventive zeolite of the ZSM-12 type, as detailed above, may, for example, be pressed to corresponding moldings with or without addition of binders. However, the shaping may also be effected by other processes, for example by extrusion. In this case, the resulting powder is shaped after addition of a binder, for example pseudoboehmite, to moldings. The moldings may subsequently be dried, for example at temperatures of from 100 to 130° C. optionally, the moldings may also be calcined, for which temperatures in the range from 400 to 600° C. are generally used.

Especially in the case of use for hydrogenations, dehydrogenations and hydroisomerizations, the catalyst is also covered with suitable activating compounds (active components). The active components can be added in any way familiar to those skilled in the art, for example by intensive mixing, vapor deposition, saturation or impregnation with a solution, or incorporation into the zeolite. Preference is given to covering the catalyst with at least one transition group metal, especially preferably with at least one noble metal. To this end, the catalyst is impregnated, for example, with a corresponding solution of a transition group metal or of a noble metal. For the coverage with platinum, a suitable example is an aqueous H2PtCl6 solution. The impregnation solution is preferably adjusted in such a way that the impregnation solution is taken up fully by the catalyst. The catalysts are subsequently dried, for example, at temperatures of from about 110 to 130° C. for from 12 to 20 h and calcinated, for example, at from 400 to 500° C. for from 3 to 7 h.

The inventive catalyst is suitable in particular for a modification of hydrocarbons. For instance, the inventive catalyst is suitable for reforming cuts from mineral oil distillation, for increasing the flowability of gas oils, for isomerizing olefins or aromatic compounds, for catalytic or hydrogenating cracking and also for oligomerization or polymerization of olefinic or acetylenic hydrocarbons. Further applications are alkylation reactions, transalkylation, isomerization or disproportionation of aromatics and alkyl-substituted aromatics, dehydrogenation and hydrogenation, hydration and dehydration, alkylation and isomerization of olefins, desulfuration, conversion of alcohols and ethers to hydrocarbons and conversion of paraffins or olefins to aromatics. In particular, the catalyst is also suitable for isomerization and hydroisomerization of naphthenes. The invention therefore also provides for the use of the above-described catalyst for the conversion of organic compounds, especially hydrocarbons.

Particular preference is given to the hydroisomerization of higher paraffins. Higher paraffins are understood to mean saturated linear hydrocarbons having a carbon number of more than 5 carbon atoms, in particular of at least 7 carbon atoms. In particular, the catalyst is suitable for the hydroisomerization of n-octane.

The hydroisomerization is preferably carried out in the presence of aromatics, in particular of benzene.

The hydroisomerization is carried out in the presence of hydrogen, preferably at temperatures below 290° C., preferably at from about 230 to 260° C., in particular at about 250° C. The pressure is carried out in the hydroisomerization preferably within a range of from 1 to 50 bar at a liquid hourly space velocity (LHSV) of from about 0.1 to 10 l per hour of hydrocarbon fed or of the hydrocarbon-containing mixture per liter of catalyst.

The invention is illustrated in detail with reference to the examples which follow.

EXAMPLE 1

Synthesis of ZSM-12 (Inventive)

For the production of the ZSM-12 zeolite, a synthesis gel composition was prepared which had the following composition:


8.5952 H2O:SiO2:0.0099 Al2O3:0.0201 Na2O:0.1500 TEAOH

TEAOH=tetraethylammonium hydroxide

271.2 g of sodium aluminate and 99.1 g of NaOH were dissolved with stirring in 9498.3 g of an aqueous solution of tetraethylammonium hydroxide (35% by weight) and 15905.3 g of water. The solution was initially charged in a pressure vessel of capacity 40 l which was equipped with a stirrer. With vigorous stirring, 10 226.1 g of precipitated silica having a specific surface area of 170 m2/g were added in small portions. A highly viscous gel was obtained which had a pH of 13.7 at 24.0° C. The pressure vessel was closed and the contents were heated to 163° C. over 12 h and then kept at this temperature for a total reaction time of 155 h. In the pressure vessel, a pressure of 13 bar was established.

After 155 h had passed, the pressure vessel was cooled to room temperature. The solid product was removed from the mother liquor by filtration and subsequently washed with demineralized water until the conductivity of the washing water was below 100 μS/cm. The filtercake was dried at 120° C. with ingress of air over 16 h and subsequently calcined with ingress of air. For the calcination, the dried solid was heated initially to 120° C. at a heating rate of 1 K/min and kept at this temperature for 3 h. Subsequently, the solid was heated to 550° C. at a heating rate of 1 K/min and this temperature was maintained for 5 h.

The analysis by x-ray diffraction showed that ZSM-12 had formed. The scanning electron microscopy analysis showed agglomerates having a diameter of about 0.8 μm which had formed from small primary crystals, and the agglomerates exhibited a broccoli-like structure.

EXAMPLE 2

Ion Exchange

920 g of the zeolite ZSM-12 obtained in Example 1 were suspended in a solution of 349.60 g of NH4NO3 in 4250.40 g of demineralized water and stirred for 2 h. The solid was removed by filtration and the filtercake washed four times with 500 ml each time of demineralized water. Subsequently, the washed filtercake was slurried again in a fresh solution of 349.60 g of NH4NO3 in 4250.40 g of demineralized water and stirred for 2 h. The solid was again removed by filtration and washed with demineralized water until the conductivity of the washing water had fallen below 100 μS/cm. The filtercake was subsequently dried under air at 120° C. over 14 h and then calcined under air. To this end, the washed and dried filtercake was heated to 480° C. at a heating rate of 1° C./min and then kept at this temperature for 8 h.

Yield: 916.7 g.

The chemical and physical analysis gave the data reported in Table 1:

TABLE 1
Analysis of the inventive zeolite of the ZSM-12
type
Ignition loss7.9%by wt.
Naa)27ppm (wt.)
Ala)0.99%by wt.
Sia)47.1%by wt.
n(SiO2)/n(Al2O3)91
Ca)163ppm (wt.)
Fea)239ppm (wt.)
Spec. surface areab)415m2/g
a)based on the ZSM-12 ignited at 1000° C.
b)BET surface area to DIN 66131

EXAMPLE 3

Production of Moldings by Extrusion

330 g of the ZSM-12 zeolite obtained in the acidic form in Example 2 were mixed over 15 min in a kneader with 156.3 g of commercial pseudoboehmite as a binder with addition of 294 g of demineralized water, and processed to a plastic mass. The mass was kneaded for a further 10 min and then 21.0 g of mold release oil (steatite oil) were added. The mass was subsequently extruded to moldings (d= 1/16″). The moldings were dried under air at 120° C. over 16 h and subsequently calcined under air. To this end, the moldings were initially heated to 120° C. at a heating rate of 1° C./min and kept at this temperature for 2 h. Subsequently, the temperature was increased to 550° C. at a heating rate of 1° C./min and the moldings were kept at this temperature for 5 h. The moldings were cooled to room temperature and then comminuted to a mean size of 3 mm. The catalyst had the chemical and physical properties reported in Table 2:

TABLE 2
Properties of an extruded inventive zeolite of
the ZSM-12 type (binder: pseudoboehmite)
BinderAl2O
Binder content25%by wt.
Ignition loss8.8%by wt.
Naa)17.4ppm (wt.)
Ca)381ppm (wt.)
Spec. surface areab)363m2/g
a)after ignition at 1000° C.
b)BET surface area to DIN 66131

EXAMPLE 4

Production of Moldings Comprising a Silicate Binder

300 g of the ZSM-12 zeolite in the H+ form obtained in Example 2 were mixed in a kneader with 473.7 g of colloidal silica having a weight fraction of 25% silica and dried with cold air until a plastic mass formed. The plastic mass was kneaded for a further 10 min and then 6.0 g of methylcellulose were added. Subsequently, the mass was extruded (d= 1/16″). The extrudates were dried under air at 60° C. over 16 h and then calcined with ingress of air. To this end, the dried extrudates were heated initially at a heating rate of 1 K/min to 600° C. and kept at this temperature for 5 h. The extrudates were subsequently comminuted to a granule having a mean length of 3 mm.

b) Ion Exchange

349.5 g of the granulated extrudate obtained under a) were introduced into a sieve and the sieve was immersed into a solution of 158.32 g of NH4NO3 in 2103.44 g of demineralized water. The granule was left in the solution at room temperature over 1.5 h, in the course of which the sieve was regularly removed briefly from the solution in order to improve the ion exchange. The granule was removed from the NH4NO3 solution and washed with demineralized water until the conductivity of the washing water had fallen to below 50 μS/cm. The granule laden with ammonium ions was dried under air at 120° C. over 16 h and subsequently calcined. For the calcination, the dried granule was heated initially at a heating rate of 1 K/min to 600° C. and kept at this temperature for 5 h.

The properties of the catalyst are summarized in Table 3:

TABLE 3
Properties of an extruded inventive catalyst of
the ZSM-12 type (colloidal silica binder)
BinderSilicon dioxide
Binder content30%by wt.
Ignition lossa)5.1%by wt.
Nab)44 ± 10ppm (wt.)
Cb)100 ± 20ppm (wt.)
Pore volume (Hg)c)0.38cm3/g
Spec. surface aread)345m2/g
a)1000° C./3 h
b)uncalcined
c)Hg method to DIN 66133
d)BET surface area to DIN 66131; multipoint method (p/po = 0.004 − 0.14)/conditioning: 350° C./3 h; under reduced pressure

EXAMPLE 5

Comparative Example

Example 1 was repeated, except that colloidal silica was used instead of precipitated silica. The synthesis gel composition was selected as follows:


8.5952 H2O:SiO2:0.0099 Al2O3:0.0201 Na2O:0.1500 TEAOH

A solid was obtained which, in addition to ZSM-12 zeolite, contained ZSM-5 zeolite in a content of 30%. The solid was analyzed by scanning electron microscopy. From the scanning electron micrographs, the average diameter of the ZSM-12 primary crystals was determined to be 50-70 nm. The primary crystals formed by combination of tightly packed, continuous agglomerates. The proportion of the continuous agglomerates in the total number of agglomerates was more than 20%.

EXAMPLE 6

Comparative Example

A ZSM-12 zeolite, as described by S. Ernst, P. A. Jacobs, J. A. Martens, J. Weitkamp; Zeolites, 1987, Vol. 7, 458-62, was produced. The zeolite was produced using methyltriethylammonium bromide (MTEABr). The zeolite powder had an SiO2/Al2O3 ratio of 108. Scanning electron micrographs under 1980- to 20 000-fold magnification showed rice grain-shaped crystals having an average length of from 0.5 to 13 μm.

As described in Example 2, the zeolite powder was converted to the acidic H+ form by ion exchange with NH4NO3 and subsequent calcination.

EXAMPLE 7

Production of Catalysts Laden with Platinum

The zeolites in the H form obtained in Examples 2 and 6 were each pressed to tablets without further additives with the aid of a Carver laboratory press at a pressure of 18 tonnes. These tablets were crushed and the granules of sieve fraction 0.5-1.0 mm were removed. These granules were covered with 0.5% by weight of platinum by impregnating with 30% H2PtCl6 solution. The granule was subsequently dried at 120° C. for 16 h and then calcined at 450° C. for 5 h. The properties of the granules are compiled in Table 4.

TABLE 4
Properties of an inventive catalyst of the ZSM-12
type laden with platinum
ZeoliteExample 2Example 6
ShapeGranule, 0.5-1.0 mmGranule, 0.5-1.0 mm
Hgc) pore volume; cm3/g0.500.49
Pore size distribution
>1750 nm (% by vol.)2.215.26
1750-80 nm (% by vol.)51.8287.56
80-14 nm (% by vol.)29.005.51
14-7.5 nm (% by vol.)16.971.67
Spec. surface areaa)401281
(m2/g)
a)BET surface area to DIN 66131; multipoint method (p/po = 0.004-0.14)/conditioning: 350° C./3 h; under reduced pressure
c)HG method to DIN 66133

EXAMPLE 8

Isomerization

The platinum catalysts obtained according to Example 7 were tested in a microreactor with pure n-heptane. The test conditions were as follows:

Reactor diameter:8 mm
Catalyst weight:2.0 g
Catalyst size:sieve fraction of the granulated
material of from 0.5 to 1.0 mm
Pressure:20 bar
Temperature:250° C.
WHSV:2.18 h−1
H2:n-heptane (molar):1.3:1

The reactor was started up as follows: First, air was introduced at atmospheric pressure at a rate of 33.33 ml/min, and then the reactor was heated from room temperature to 400° C. This temperature was maintained for 1 h and then the temperature was lowered from 400° C. to 250° C. The air stream was then interrupted and replaced by a nitrogen stream (33.33 ml/min) for 30 min. The nitrogen stream was finally replaced by a hydrogen stream (33.33 ml/min) for 30 min. The pressure was then increased to 20 bar of H2, and then pure n-heptane was introduced and the product stream was analyzed by gas chromatography. The peak areas of all C1 to C7 components were measured every 30 min. The peak areas of all i(so)-heptanes (e.g. methylhexanes, dimethylpentanes, etc.) were combined and denoted as i(so)-heptane areas. The parameters are defined as follows:


Conversion (%)=(1−area(n-heptane)/total area)×100


Selectivity (%)=(area(i-heptane)/total area−area(n-heptane))×100


Yield (%)=(area(i-heptane)/total area)×100

The inventive catalyst exhibited steady state conversion and yield of 40% at virtually 100% selectivity. Cracking of the n-heptane to smaller molecules only took place in small fractions. The comparative catalyst exhibits no significant conversion of n-heptane at 250° C. The inventive catalyst exhibits a higher activity and converts n-heptane with very high selectivity even at low temperatures.

EXAMPLE 9

Example 1 was repeated, except that the composition of the synthesis gel was adjusted to the following ratio:


7.8918 H2O:SiO2:0.0091 Al2O3:0.0185 Na2O:0.1377 TEAOH

The crystallization time was increased to 175 hours. Otherwise, the process procedure corresponded to the sequence described in Example 1. A crystalline solid was obtained which was composed of ZSM-12. The solid was analyzed by scanning electron microscopy. The scanning electron micrograph reveals agglomerates which have a broccoli-like structure (open agglomerates). The proportion of closed agglomerates in the total number of agglomerates is less than 10%, while the open agglomerates correspond to a proportion of more than 90%.

EXAMPLE 10

The platinum catalysts obtained according to Example 7 were tested in a microreactor with pure n-octane. The test conditions were as follows:

Reactor diameter:8 mm
Catalyst weight:2.0 g
Catalyst size:sieve fraction of the granulated
material of from 0.5 to 1.0 mm
Pressure:20 bar
Temperature:245-250° C.
WHSV:2.25 h−1
Molar H2:n-heptane1.3:1
ratio:

The reactor was started up as follows: First, air was introduced at atmospheric pressure at a rate of 33.33 ml/min, and then the reactor was heated from room temperature to 400° C. This temperature was maintained for 1 h and then the temperature was lowered from 400° C. to 250° C. The air stream was then interrupted and replaced by a nitrogen stream (33.33 ml/min) for 30 min. The nitrogen stream was subsequently replaced by a hydrogen stream (33.33 ml/min) for 30 min. The pressure was then increased to 20 bar of H2, and then pure n-octane was introduced and the product stream was analyzed by gas chromatography.

In this test, the peak areas of all C1 to C8 components were determined every 30 min. The peak areas of all iso-octanes (e.g. methylheptanes, dimethylhexanes . . . ) were combined and denoted as isooctane areas. The parameters are defined as follows:


Conversion (%)=(1−area (n-octane)/total area)×100


Selectivity (%)=(area(isooctane)/total area−area(n-octane))×100


Yield=(area(isooctane)/total area)×100

The catalyst was tested in the microreactor for 110 hours, in the course of which the activity and the selectivity were determined at 245 and 250° C.

The inventive catalyst (Example 7 in conjunction with Example 2) showed an extremely high conversion rate of more than 85% and a selectivity after 10 hours of 80% at 250° C. At 245° C., the conversion was 70% and the selectivity 85%.

In contrast, the comparative catalyst (Example 7 in conjunction with Example 6) exhibited a considerably lower selectivity and conversion rate. A comparative catalyst produced according to Smirniotis, J. of Catalysis 182, 400-416 (1999) had a very low conversion rate on the corresponding conditions. Only at higher temperatures of about 290° C. was an acceptable conversion rate and selectivity observed.

EXAMPLE 11

The solids obtained in Examples 1, 5 and 9 were analyzed for their specific volume by mercury porosimetry to DIN 66133. The experimental conditions were as follows:

InstrumentPorosimeter 4000; Carlo Erba, IT
Sample preparation30 min under reduced pressure at
room temperature
Maximum pressure4000 bar
Contact angle141.3°
Hg surface tension480 dyn/cm

The values found for the samples are listed in Table 5.

TABLE 5
Specific volume of zeolites calcined according to
Example 1, measured by mercury porosimetry
Use of colloidalUse of precipitatedUse of precipitated
silica (Ex. 5)silica (Ex. 9)silica (Ex. 1)
Pore radiusrel. % bymm3/grel. % bymm3/grel. % bymm3/g
range (nm)vol.spec.vol.vol.spec.vol.vol.spec.vol.
1.9-10 5.5271414117139
 4-100.52.51212114115
 10-1008.3414040336295
100-200321582222122180
 200-1000462261414116131
1000-75008.24010101974
Total1004921001007100819

The loose structure and thus the high fraction of cavities between the primary crystals is shown in the mercury porosimetry in the range of pore radii of from 1.9 to 100 nm. The calcined inventive zeolite from Examples 1 and 9 exhibits a specific volume of from about 110 to 125 mm3/g in mercury porosimetry in the range from 4 to 10 nm. The calcined comparative example (ZSM-12 zeolite, produced using colloidal silica, Example 5) has a specific volume of 2.5 mm3/g in the range from 4 to 10 nm. In the range from 10 to 100 nm, the inventive zeolites of Examples 1 and 9 have a specific volume of from 300 to 400 mm3/g. The zeolite from Example 5, employed for comparison, exhibits a specific volume of 41 mm3/g in the range from 10 to 100 nm.

EXAMPLE 12

The zeolites obtained in Examples 1, 5 and 9 were analyzed for their pore radius distribution by nitrogen porosimetry to DIN 66134. The experimental conditions were selected as follows according to the manufacturer's instructions and the evaluation was carried out by the method of “Dollim./Heal”.

InstrumentSorptomatic 1900; Carlo Erba, IT
Sample preparation16 h/250° C./reduced pressure

The values found for the samples are reported in Table 6.

TABLE 6
Specific volume of zeolites calcined according to
Example 1, determined by nitrogen porosimetry (cf. above)
Use of colloidalUse of precipitatedUse of precipitated
silica (Ex. 5)silica (Ex. 9)silica (Ex. 1)
Specific418.37393.59439.00
surface
area m2/g
Pore-0.21760.56140.4758
specific
volume cm3/g
at p/p0 = 0.9999
spec.vol/fractionspec.vol/fractionspec.vol/fraction
Pore radiusradiusin theradiusin theradiusin the
rangerangevolumerangevolumerangevolume
 10-30 Å0.045 cm3/g76%0.031 cm3/g13%0.045 cm3/g20%
30-200 Å0.014 cm3/g24%0.211 cm3/g87%0.185 cm3/g80%
Total0.059 cm3/g100%0.242 cm3/g100%0.230 cm3/g100%

Nitrogen porosimetry in the 10-200 Å range clearly shows the differences in the two structures. In the region of very small pores having a pore radius in the range of 10-30 Å, which are characteristic of compact-structure agglomerates, both the inventive zeolite (Examples 1 and 9) and the zeolite from Example 5 employed as a comparison have a volume of about 0.04 cm3/g. However, the inventive zeolite has in this range only approx. 15% of the total volume for the range of 10-200 Å under consideration, while the volume of 0.04 cm3/g in this range for Example 5 corresponds to a fraction of the total pore volume (10-200 Å) of 76%. In agreement with the mercury porosimetry, the differences between the inventive zeolite (Examples 1 and 9) and Example 5 become clear in the pore radius range of 30-200 Å in particular. In nitrogen porosimetry in the range of 30-200 Å, the calcined inventive zeolite exhibits a specific volume in the range of about 0.18-0.21 cm3/g. In the Example 5 employed as a comparison, a specific volume of only 0.014 cm3/g was found in this range, which means that the zeolite for Example 5 exhibits a distinctly smaller fraction of cavities between the primary crystals.