Title of Invention	PROCESS FOR PREPARING A HYDROPHOBIC ZEOLITE
Abstract	A process for preparing a hydrophobic zeolite comprising calcining a starting zeolite having a silica to alumina molar ratio of at least 20, at a temperature in the range of from 650°C to 1000°C in the presence of steam and under a turbulent condition with respect to flow pattern of the zeolite for at least 15 minutes thereby producing the hydrophobic zeolite.

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FORM 2 THE PATENTS ACT 1970 [39 OF 1970] COMPLETE SPECIFICATION [See Section 10 and Rule 13] "PROCESS FOR PREPARING A HYDROPHOBIC ZEOLITE" PQ HOLDINGS INC., of 103 Springer Building, 3411 Silverside Road, Wilmington, Delaware 19803, United States of America, The following specification particularly describes the nature of the invention and the manner in which it is to be performed:- This application claims the benefit of U.S. Provisional Application No. 60/122,697, filed March 3, 1999, the entire disclosure of which is hereby incorporated by reference. FIELD OF INVENTION This invention relates to zeolites that are useful as adsorbents or catalyst supports. In particular, it involves production of a hydrophobic zeolite. BACKGROUND OF THE INVENTION Most zeolites are hydrophilic (water attracting) and thus have higher preference for sorption of water than for organic materials. However, the highly siliceous zeolites tend to be hydrophobic (organic-attracting). Hydrophobic zeolites are useful in selected applications such as removal of volatile organic compounds from water-containing/ environments. Hydrophobic zeolites tend to have a relatively small number of catalytically active acid sites. These low acidity zeolites are sometimes useful in catalytic processes where cracking reactions must be minimal. In order to measure the hydrophobicity of a zeolite, we have developed a Hydrophobicity Index screening test. A Hydrophobic ity Index (H) is calculated from the ratio of mass sorption of organic compound to mass sorption of water at specific partial pressures for the two adsorbates; thus Hc = Se/Sw for cyclohexane over water and Hn = Sn/SH for n-hexane over water. Highly hydrophilic zeolites will have H values of less than 1.0. Highly hydrophobic zeolites will have H values of substantially greater than 1.0. Selection of the adsorbent depends upon the pore opening of the zeolite structure of interest. It is well known that zeolites with 10-membered or less metal atoms ring openings will not adsorb substantial amounts of cyclohexane. For these zeolites, e.g. ZSM-5, ZSM-ll, etc., n-hexane is much more efficacious choice for the organic adsorbent. Moreover, the partial pressure at which the adsorbtion is measured can have an effect on the absolute amount of adsorption of any component and also the hydrophobicity index value. For the purpose of defining the conditions at which the index is measured (the adsorbate and the partial pressures) we have adopted the following convention: Hc07/05 refers to an index where cyclohexane adsorption at 7 torr is referenced to water adsorption at 5 torr. Similarly, Hn07/05 refers to an index where n-hexane adsorption at 7 torr is referenced to water adsorption at 5 torr. SUMMARY OF THE INVENTION A hydrophobic zeolite can be prepared by calcining a precursor zeolite with silica to alumina molar ratio at least 20, under high temperature and the presence of steam and under turbulent conditions with respect to flow pattern of the zeolite. In particular, a novel hydrophobic zeolite Y is provided by this method having a Hydrophobicity Index (HcOn/os) of greater than 20. DETAILED DESCRIPTION OF THE INVENTION We have found that by calcining zeolites under a turbulent condition, high temperature and in the presence of steam, a hydrophobic zeolite can be prepared. Turbulent condition arises from intimate admixture of the solid and the gas phase such that the characteristic flow pattern of the solid can be considered turbulent. These zeolites are more hydrophobic than zeolites that can be prepared by steam calcining a zeolite under non-turbulent conditions. Examples of hydrophobic zeolites that can be prepared by this method include, for example, zeolite Y, and zeolite beta. These zeolites are considered to have interconnecting pores of at least two-dimensions, preferably interconnecting two or three-dimensions, more preferably three-dimensions. The precursor (starting material) zeolites useful in preparing the hydrophobic zeolites have a silica to alumina molar ratio of at least 20, preferably from about 25, to about 150. The calcination temperature is in the range of from about 650°C, preferably from about 700°C, to 1000°C, preferably to 850°C in the presence of steam. The steam is preferably present in an amount of at least 10% by volume. In particular, we have found that by preparing the zeolite by calcining a zeolite having silica to alumina greater than 20, particularly stabilized zeolite Y under a turbulent condition, high temperature and in the presence of steam, a hydrophobic zeolite, particularly a stabilized zeolite Y having a Hydrophobicity Index (He07/0S) of greater than 20, preferably at least 25, can be prepared. The very hydrophobic zeolite products of our invention are prepared from zeolites having the structure of zeolite Y that is stabilized. These very hydrophobic zeolites have Hydrophobic ity Index (Hc07/05) of greater than 25, preferably greater than 30: The ultrahydrophobic materials have a Hydrophobicity Index (Hc07/05) of greater than 30, preferably equal to or greater than about 35. It has been surprisingly found that a very hydrophobic zeolite Y material can be prepared from a precursor material with a moderate silica to alumina molar ratio (bulk silica to alumina ratio) in the range of from 25, preferably from about 40, to about 150, preferably to about 120. It has also been surprisingly found that an ultrahydrophobic zeolite Y material can be prepared from a precursor having silica to alumina molar ratio of greater than about 60, preferably greater than about 75, preferably greater than about 85. The hydrophobic zeolite Y material of the invention can be produced by calcining a stabilized Y zeolite having a unit cell size within the range of less than 24.40 preferably less than 24.35, more preferably less than 24.30, most preferably less than 24.27, to preferably greater than 24.15, under turbulent conditions at a temperature within the range of from about 650°C, preferably from about 700OC, to 1000°C, preferably to 850°C in the presence of steam. The steam is preferably present in an amount of at least 10% by volume. Turbulent condition as herein referred to is a condition in which there is sufficient mix between solid phase and gas phase in which the gas flows through the dispersed solid phase without a discernable interface. The condition is not turbulent if the gas phase flows over a stationary solid such that there is a discernable interface between the solid and the gas. While not wishing to be bound by theory, we believe that superior contacting of the solid involved with the reactive gas atmosphere directly leads to the high hydrophobicity characteristic of the present invention. We believe that this condition is met when a substantial portion of the solid particles are continuously and completely surrounded by the reactive gas mixture. This condition can be described as a flow rate such that a significant fraction of the solid articles have reached the point where they have at least just been suspended and set in motion by the action of the gas. Such a velocity has often been described as the minimum fluidization velocity. This often occurs at Reynolds numbers (NRe') less than about 10 (DpGmf/u) . This phenomenon! has been described by the following relationship (Leva, "Fluidization," p. 63, McGraw-Hill, New York 1959): where Gmf = fluid superficial mass velocity for minimum fluidization, lb./(sec.)(sq.ft.) Dp = particle diameter, ft. gc = dimensional constant, 32.17 (lb.)(ft.)/(lb.force)(sec.2) pf = fluid density, lb./cu.ft. ps = solids density, lb./cu.ft. 5 = particle shape factor, dimensionless Emf = voidage at minimum fluidization, dimensionless μ = fluid viscosity, lb. / (ft.) (sec. ) Alternately, this has been described by a similar equation (Perry, "Chemical Engineers'Handbook," 4th Edition, p. 4-25, McGraw-Hill, New York): where Gmf = fluid superficial mass velocity for minimum fluidization, lb./(hr.)(sq.ft.) Dp = particle diameter, ft. pf = fluid density, lb./cu.ft. p8 = solids density, lb./cu.ft. μ = fluid viscosity, lb. / (ft.) (sec. ) For the invention process, it is preferable to calcine under a minimum fluidization velocity through at least substantial portion of zeolite particles in contact with gas phase where flow rate has a Reynolds number of at least 5, preferably at least 10. Substantial portion of zeolite particles are in contact with the gas phase when at least 50%, preferably 85%, more preferably 95%, most preferably 100% of the zeolite particles are in contact with the gas phase. To produce a turbulent condition, for example, a fluidized bed calciner or ebulating bed calciner, such as those available from such companies as Procedyne (New Brunswick, N.J.) and A. J. Sackett & Sons (Baltimore, Maryland) , and others can be used. This is not meant to be an exhaustive list of equipment but only to provide description of the types of equipment that are suitable for the process described. The equipment should be operated with sufficient flow of gas phase to produce turbulence in the solid and at a temperature and steam partial pressure effective to produce a hydrophobic zeolite of the invention. The starting stabilized zeolite Y can be prepared from zeolite NaY. Zeolite NaY can be produced by any conventional manner from water, a source of alumina, a source of silica, and sodium hydroxide. The resulting NaY zeolite has silica to alumina molar in the range of 4.0 to 6.0. Stabilization of this material is accomplished by combination ion exchange and steam calcination with at least one step of each. One way to prepare such zeolite is described in U.S. Patent No. 5,059,567 which disclosure is hereby incorporated by reference and another in U.S Patent No. 4,477,336, which disclosure is also incorporated by reference. In one method to prepare the starting material, the NaY can be ion-exchanged with ammonium solution, such as ammonium sulfate one or" more times, washed and dried. The ammonium ion-exchanged zeolite can be calcined at a temperature in the rang;e of 550°C to 800oC_in the presence of steam. This zeolite is then further ion exchanged with an ammonium solution and then recalcined in a similar temperature range. Following this calcination, the resultant zeolite is dealuminated by contact with mineral acid under conditions such that the desired silica to alumina molar ratio is achieved. The novel hydrophobic zeolite Y of the invention has a unit cell size in the range of from 24.15, preferably from 24.20, to 24.35, preferably to 24.28 angstrom. The surface area of these novel hydrophobic zeolite Y materials is preferably at least 500, more preferably at least 6C0 square meters per gram. The silica to alumina (chemical) molar ratio is substantially unchanged from the stabilized precursor zeolite. Organic adsorption is at least 10% by weight at a pressure of 7 torr. Without wishing to be bound by any particular theory we speculate that the exceptionally high degree of hydrophobicity obtained in zeolite materials by the process of this invention may be due to the changed nature of the interaction between the zeolite solids and the reactive gas atmosphere. In the turbulent fluid bed the degree of intimacy of contact between all solid particles and the hydrothermally reactive gas phase is much greater than can be effected in a static bed or in the mildly roiled bed of powder found in a rotary kiln. The typical rotary kiln is operated as a continuous process with a constant feed of powder entering one end of a heated tube and a constant flow of processed material discharged from the other. The steam or air/steam mixture used in a counter-current flow to treat the zeolite powder, according to the teachings of prior art, largely passes over the bed of solids making its most effective contact only with the solids exposed at the bed surface by the slow turnover with rotation of the calciner tube. In such equipment excessive turbulence must normally be prevented so as to avoid entrainment of solids in the gas phase and loss of material from the kiln. It is known that the combination of water and high temperature promotes the hydrolysis of framework Al out of the zeolite structure thus eliminating framework charge centers according to the following reaction: (1) [A104] , H* + 3H20 = [(OH) J + A1(0H)3 where [A104"] indicates the anionic charge- center in the tetrahedral framework lattice and [(OH)J indicates the "hydroxy-nest" framework vacancy created by hydrolysis to generate non-framework Al{3H)3 and related species. The -OH groups in the vacancy are attached to Si atoms in the lattice. This treatment removes sites at which polar water molecules can be held by ion dipole interaction. Water can also be bound to the solid by interaction with residual hydroxyl groups (-0H) by H-bonding. Thermal treatment alone eliminates most hydroxyl groups in zeolite materials at temperatures between 500-650°C as indicated by TGA analysis. The hydroxyl elimination reaction can be written in simplest form as: (2) sSi-OH + HO-Sis = =Si-0-Si= + H20 However, we have discovered that this reaction is not sufficient to substantially complete the elimination of hydrophyllic centers for zeolites. We have discovered surprisingly that contacting the zeolite with steam under turbulent conditions, at temperature of above 650oC with steam produces zeolites that are highly hydrophobic. We now speculate that the forced elimination of hydroxyl groups at high temperature can generate significant strain in the siloxane bonds thus formed. Framework vacancies are especially susceptible to the Eormation of strain centers. Such strained bonds possess varying degrees of partial polarization and this residual molarity provides sites for sorption of water and reversal of reaction (2) when the zeolite material is exposed to aqueous vapor again under milder thermal conditions. To minimize such polarized strain sites within the zeolite structure it is necessary to promote the release of strain to a substantial degree by a time dependent annealing process. The annealing mechanism may involve a continuous and reversible breaking and forming of bonds allowing the whole crystal structure to undergo a progressive relaxation towards minimized residual strain. This mechanism is most effectively catalyzed by the well known "mineralizing action" of water vapor. Hydrothermal treatment of zeolite materials in a urbulent fluidized bed without tangibly identifiable phase loundaries appears to drive the hydrophobization process in eolite materials to a degree that has not been recognized ireviously and which is not attainable by treatment of non-luidized material for comparable times under equivalent Lydrothermal conditions. Since we believe that the optimum nnealing process involves a uniform minimization of esidual strain energy throughout the structure of each rystal there is reason to suppose that the mechanism will e most effective for treatments that expose zeolite articles and particularly crystals to uniform conditions of eat transfer and contact with water vapor that is ndependent of any direction in space due to equipment or owder bed configuration. While it would not be surprising o find differences in the response of different crystal tructures to this isotropic environmental condition we elieve the treatment given to zeolites by the process of his invention is expected in every case to move the material in the direction of enhanced hydrophobicity. These novel zeolites can be useful as adsorbent for organics. EXAMPLES The following examples illustrate certain embodiments of our invention. These examples are not provided to establish the scope of the invention, which is described in the disclosure and recited in the claims. The proportions are in parts by weight (pbw) , percent by weight, moles or equivalents. X-Ray Diffraction The x-ray diffraction patterns of the Y zeolites prepared in the examples were determined. Relative crystallinity was determined by ASTM test method, D3 906-97, standard test method for determination of relative X-ray diffraction intensities of faujasite-type zeolite-containing materials. The lattice constants were determined by ASTM method, D3 942-97, standard test method for determination of unit cell dimension of a faujacite-type zeolite. The sharp peaks of the XRD spectra of zeolite Y prepared by our method also indicates their good crystallinity and lack of defects or. amorphous material. Surface Area The surface areas of the zeolite samples were determined by the ASTM test method (D3663-92) . This method utilizes a modification of the gas adsorption technique of surface area measurement described by Brunauer, Emmett and Teller, (BET) . Zeolite were calcined in air at 500°C for a period of 4 hours and then degassed by heating in vacuum at 350°C to remove sorbed vapors. The samples were then cooled to liquid nitrogen temperature. The quantity of nitrogen adsorbed at low pressure is determined by measuring the pressure difference after the introduction of a fixed volume of nitrogen to the sample. Under these conditions, nitrogen is sorbed into zeolite micropores. The volumetric sorption measurement is measured at pressure levels of P/Po between 0.02 and 0.05. The magnitude of the nitrogen sorbed is calculated using the BET equation. Mass Sorption Mass sorption of water and the organics (cyclohexane or n-hexane) were measured using an RXM-100 Multifunctional Catalyst Testing & Characterization Machine from Advanced Scientific Design, Inc. For the water sorption test, approximately 2 0mg of zeolite samples were used. Zeolites were well dried prior to measurement. Samples were pretreated by heating the sample from 20 °C to 500 °C at 20°C/min under rough vacuum and held at 500°C for 1 hour under high vacuum. The reactor containing the sample is maintained at 25°C using a water bath. The total water adsorption is measured first by introducing water vapor at an initial pressure resulting in the desired final pressure after 5 minutes adsorption. To obtain a full isotherm 10 to 12 final pressure points are measured at final pressures between 0.5 and 12 torr with the last point being approximately 12 torr. In order to correct for the condensation of water vapor on the walls, an empty reactor was run similarly and subtracted from the test results to obtain net adsorption. For the organic sorption tests, approximately lOOmg of zeolite samples were used. Zeolites were well dried prior to measurement. Samples were pretreated by heating the sample for 20°C to 500°C at 20°C/min under rough vacuum and held at 500°C for 1 hour under high vacuum. The reactor containing the sample is maintained at 25°C using a water bath. The total organic adsorption is measured first by introducing organic vapor at an initial pressure resulting in the desired final pressure after 3 minutes adsorption. To obtain a full isotherm 6 to 8 final pressure points are measured at final pressures between 0.5 and 4 5 torr with the last point being approximately 4 5 torr. Chemis Analysis v 5.04 program was used to generate the isotherm. The data used for calculation of the hydrophobicity index were chosen at 5 torr for water and 7 torr for cyclohexane to ensure values were at monolayer coverage. An alternative method was used for measurement of some of the samples, using a Landolt type sorption apparatus. (Landolt, George R., Analytical Chemistry, 43., 613 (1971).) The samples were pretreated by heating the sample in a vented muffle furnace with 3°C/min. ramp and held at 520°C for 4 hours. The cyclohexane sorption measurements were done at 40mm (torr) pressure at ambient temperature (21-25°C). Sorption was measured by mass difference after equilibrium has reached (typically after about 20 minutes) . The water sorption measurements were done at 11 torr pressure at ambient temperature or in a constant humidity desiccator containing a saturated solution of magnesium nitrate. A correlation to convert the data generated by the alternative method to the pressure points used for the RXM-100 method was derived empirically from data generated from the RXM method at multiple pressure points. Methanol Adsorption Methanol adsorption measurements were measured using an RXM-100 Multifunctional Catalyst Testing & Characterization Machine from Advanced Scientific Design, Inc. 80 to 100 mg of zeolite samples were used. Zeolites were well dried prior to measurement. Samples were pretreated by heating the sample for 20°C to 500°C at 20°C/min under rough vacuum and held at 500"C for 1 hour under high vacuum in a BET reactor. The reactor containing the sample is maintained at 25°C using a water bath. Methanol vapor is introduced at about 4 0 torr and the pressure is recorded initially and after stabilization reading 3 to 5 minutes interval. This step is repeated until the desired final pressure is reached. Chemis Analysis v 5.04 program was used to generate the isotherm. Base Titration Approximately 10 grams of zeolite (lOOmL H,0) was titrated using aqueous 1M NH4OH solution to a final pH of approximately 9 ± 0.01. pH Treatment NH40H solution was used to treat zeolite to an appropriate pH level for sufficient time to achieve a stable pH. Calcination Method 1 This is the process of the invention. Zeolite was introduced to a conical shape fluid bed design calciner (FBC), and heated to a temperature of 1380-1420°F (750-770°C) under fluidizing conditions using a steam/air mixture and held at the temperature for specified typical time intervals from 3 0 minutes to 4 hours. The steam/air fluidizing mixture is in the approximate range of 60/4 0 to 80/20. Steam flow is then discontinued and the fluidization medium is switched to air alone. The product is then transferred to a cooler with air alone over about 30 minutes time. Calcination Method 2 This is a comparative process using a rotary calciner where the calcination occurred without turbulence. 15 pounds of zeolite is loaded into a 55" long by 15" long diameter drum that contains two 1" baffles located opposite each other. The calciner with the drum is heated to about 750"F while the drum is rotated at 6 RPM. The typical heat up time is 3 H hours. 100% steam is maintained by injecting 18 mis/minute H20 and no air into the rotating drum. The steam contact time is 1-2 hours. Steam and/or air was injected above the bed of zeolite powder such that there was a discernible interface between the gas phase and the solid phase. Calcination Method 3 This is a comparative process under fixed bed condition. The system consist of an alloy vessel (sample chamber) contained within a top-vented muffle furnace to which air and steam is supplied. The furnace is heated from 1100C to 760°C. The vessel is supplied with steam varying in water content (air/water), made from a steam generator with temperatures ranging from 400°C-450°C. Steam is added to the sample chamber at about 250°C. The airflow is at 500 ml/min. The volume percent of steam is regulated by the flow of liquid water to the steam generator. The furnace is heated to the desired calcination temperature. Steam is forced through the sample by the design of sample holder and chamber. The sample holder is an open 10 cm diameter steel cylinder with 1.4 cm height that can hold approximately 15-25 grams of zeolite. The zeolite is supported on a bed of quartz mat fiber on top of the perforated steel bottom sample holder that allows steam to flow uniformly through the sample. Starting Stabilized Zeolite Y Material A A similar process to Example 1 of U.S. Patent No.5,059,567 was used, except ammonium chloride was used instead of ammonium sulfate. Hc07/05 of this zeolite material A is approximately 6-8. The properties of the precursor zeolites are given in Table 1 below. Lattice constant of A was 24.24. Starting Stabilized Zeolite Y Material B A similar process to starting material A was used, except the aluminum sulfate exchange step was eliminated. Hc07/o5 °f this zeolite material B is approximately 7-9. The properties of the precursor zeolites are given in Table 1 below. Lattice constant of B was 24.25-24.26. Examples 1-14 These examples illustrate the preparation of the hydrophobic zeolite Y of the invention. Starting material zeolites A or B described above were calcined under various conditions as listed in Table 1 below. Calcination Method 1 was used to calcine these material to produce products of this invention. Product properties are listed in Tables 1-2,4-5 below. COMPARATIVE EXAMPLE A This is a comparative example where starting material B was calcined using Calcination Method 2. Properties of the starting material, process conditions and product properties are listed in Tables 3, 4 and 5 below. COMPARATIVE EXAMPLE B This is a comparative example where starting material A or B were calcined using Calcination Method 3 . Properties of the starting material, process conditions and product properties are listed in Tables 3, 4 and 5 below. COMPARATIVE EXAMPLE C This is a comparative example where the Hydrophobicity Index of a commercially available zeolite Y having a silica to alumina molar ratio of 200, HSZ-390HUA, from Tosoh Corporation was measured. The result is listed in Table 3. Example 15 - Adsorption of Methanol on Hydrophobic Zeolite Y of the Invention The physisorption of methanol (MetOH) on the hydrophobic zeolite Y of the invention of Example 3 resulted in unusual adsorption isotherms at temperatures from 0 to 60°C. These Type 5 or Type S isotherms showed a sharp adsorption, step near p/p0 - 0.2 which is markedly different from the Type 1 adsorption isotherms usually observed on microporous materials and also from the Type 3 isotherms typical for the adsorption of alcohols or water on most hydrophobic surfaces. Except one paper, U. Muller, K. K. Unger, Characterization of Porous Solids (Ed. by K. K. Unger et al., Elsevier, Amsterdam) 101 (1988), that describes the adsorption of N2 on ZSW5 at around 77K, we have not found any report in the open literature that describes a sharp adsorption step near p/p0 - 0.2 for any adsorbate on microporous silicates or aluminosilicates (zeolites) . As Table 6 indicates the adsorption of MetOH gives a Type 1 adsorption isotherm on starting stabilized zeolite Y material A which is a parent compound of hydrophobic zeolite Y. Acetone, H20 and cyclohexane have also Type 1 isotherms on the hydrophobic zeolite Y of the invention. The adsorption isotherms are grouped into classes originally proposed by Brunauer, Deming, Deming, and Teller, (BDDT), (1) S. Brunauer, L. S- Deming, W. S. Deming, E. Teller, Journal of American chemical Society. 62, p. 1723 (1940), sometimes referred to as Brunauer, Emmett, and Teller (BET), (2) S. Brunauer, P. H. Emmett, E. Teller, Journal of American Chemical society. 60, p. 309 (1938),or similarly Brunauer, (3) S. Brunauer, The Adsorption of Gases and Vapours, Oxford University Press (1945),and further described by Gregg and Sing (4) S. J. Gregg, K. S. W. Sing, Adsorption, Surface Area and Porosity, 2nd Edition, Academic Press, Inc. (1982) Chapter 1. Molecular modeling results indicate that the odd shape of the MetOH adsorption isotherms on the hydrophobic zeolite Y of the invention can be directly related to the specific structure of dealuminated Y zeolite. The visualization of the adsorption process on the aluminum free Y zeolite suggests that only a small number of MetOH molecules can accumulate in the bent corners of the supercages at MetOH vapor pressures p/p0 0.1. These hydrophobic zeolite Y of the invention are useful as adsorbents for polar hydrocarbon materials, particularly alnnhol. TABLE I TABLE 2 Methanol Adsorption Data TABLE 3 (1) Empirical number generated from Hc40/11 measured values. (2) Measured as Hc07/05 values. TABLE 4 Base Titration Pata * Due to slight over titration (pH about 9.08) not counted in average. TABLE 6 We Claim: 1. A process for preparing a hydrophobic zeolite comprising calcining a starting zeolite having a silica to alumina molar ratio of at least 20, at a temperature in the range of from 650°C to 1000°C in the presence of steam and under a turbulent condition with respect to flow pattern of the zeolite for at least 15 minutes thereby producing the hydrophobic zeolite. 2. The process as claimed in claim 1 wherein the starting zeolite has a silica to alumina molar ratio of at least 40. 3. The process as claimed in claim 1 wherein steam partial pressure is at least 10 volume percent. 4. The process as claimed in claim 1 wherein the starting zeolite is an interconnecting two-dimensional zeolite or an interconnecting three-dimensional zeolite. 5. The process as claimed in claim 4 wherein the starting zeolite is an interconnecting three-dimensional zeolite. 6. The process as claimed in claim 5 wherein the starting zeolite is zeolite Y having a unit cell size greater than 24.15 angstrom and less than or equal to 24.40 angstrom. 7. The process as claimed in claim 6 wherein the starting zeolite is zeolite Y having a unit cell size less than or equal to 24.30 angstrom. 8. The process as claimed in claim 1 wherein the starting zeolite is calcined under a minimum fluidization velocity through at least substantial portion of zeolite particles are in contact with gas phase whose flow rate has a Reynolds number of at least 5. 9. The process as claimed in claim 1 wherein the turbulent condition is produced by calcining the starting zeolite in a fmildized calciner. 10. The process as claimed in claim 9 wherein the starting zeolite is an interconnecting three-dimensional zeolite. 11. The process as claimed in claim 10 wherein the starting zeolite is a zeolite Y having a unit cell size of less than or equal to 24.40 angstrom. 12. The process as claimed in claim 11 wherein the zeolite Y is prepared by ammonium-exchanging a NaY zeolite and dealuminating the ammonium-exchanged Y zeolite. Dated this the 16th day of August, 2001 [JAYANTA PAL] Of Remfry & Sagar ATTORNEY FOR THE APPLICANT[S]

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