NZ224450A - Method for preparing a low acidity refractory oxide-bound zeolite catalyst - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £24450 NEW ZEALAND PATENTS ACT, 1953 No.: Date: COMPLETE SPECIFICATION METHOD FOR PREPARING A ZEOLITE CATALYST BOUND WITH A REFRACTORY OXIDE OF LOW ACIDITY ■*1 We, MOBIL OIL CORPORATION, a corporation organised under the laws of the State of New York, United States of America, of 150 East 42nd Street, New York State of New York, United States of America, hereby declare the invention for which -ir/ we pray that a paten be granted to me"/us, and the method by which it is to be perfoi _ to be particularly described in and by the following statement: - (followed by page la) cc ' 0^ -£—^r2r56 METHOD FOR PREPARING A ZEOLITE CATALYST BOUND WITH A REFRACTORY OXIDE OF LOW ACIDITY BACKGROUND OF THE INVENTION This invention relates to a method for preparing a mechanically stable zeolite catalyst composition possessing a refractory oxide binder of low acidity, e.g., a silica binder.

The term "zeolite" as used herein designates the class 5 of porous crystalline silicates, which contain silicon and oxygen atoms as the major components. Other framework components can be present in minor amount, usually less than about 14 mole %, and preferably less than 4%. These components include aluminum, gallium, iron, boron, etc., and combinations 10 thereof. The crystalline aluminosilicates constitute an especially well known type of zeolite.

It is well known that extrusion is one way of obtaining a zeolite-containing material which has a high degree of strength for various applications, both catalytic and non-catalytic. 15 Some aluminosilicate zeolites have long been used as catalysts for a wide variety of organic conversion processes. In general, aluminosilicate zeolites are incorporated with a matrix, or binder, material in order to impart mechanical stability thereto. The most commonly used matrix materials 20 have included alumina and/or clays since these materials are fairly easy to extrude and provide extrudates of good physical strength.

It has long been recognized that silica is a desirable matrix and that it possesses advantages over alumina for some 25 catalytic reactions. In this connection, U.S. Patent No. \ 4,013,732 specifically discloses ZSM-5 with a silica matrix and w U.S. Patent Nos. 3,843,741 and 3,702,886 broadly disclose the use of ZSM-5 with a silica matrix. f U.S. Patent No. 4,582,815 describes a method for preparing silica-rich solids said to possess improved crush strength compared to that of known silica-bound materials. The method comprises mixing silica-rich solids, preferably a mixture of silica with a zeolite such as ZSM-4 (Omega), ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48, Beta, X, Y, L, ferrierite, raordenite, dachiardite, clinoptilolite, offretite, erionite, gmelinite or chabazite with water and an alkali metal base such as sodium hydroxide or a basic salt such as an alkali-metal carbonate, borate, phosphate or silicate as an extrusion aid followed by mulling, extruding and subsequently drying the extrudate. It is thought that substitution of alkali metal for hydrogen in the silanol groups on the surfaces of siliceous materials such as the foregoing zeolites is responsible for their improved crush strength. The resulting extrudate is said to possess superior crush strength and sufficient integrity to withstand treatments with acids so that it is possible to steam, acid extract or calcine them. To avoid trapping the alkali metal of the extrusion aid in the extrudate, the alkali metal is ordinarily removed by exchange under acidic conditions using dilute nitric acid in 1M ammonium nitrate solution.

Silica-bound zeolite catalysts prepared in accordance with the method described in U.S. Patent No. 4,582,815 are indicated to be useful in hydrocarbon conversions such as hydrocracking, isomerization, hydrogenation, dehydrogenation, polymerization, reforming, catalytic cracking and catalytic if*-hydrocracking. (N It has now been discovered that a low acidity ^ refractory oxide-bound zeolite possessing excellent mechanical stability and low binder acidity, making it especially useful as a catalyst for certain kinds of hydrocarbon conversions, can be prepared by a method which comprises: 3 -- a) providing a substantially homogeneous mixture of zeolite, water and a low acidity refractory oxide binder containing at least an extrusion-facilitating amount of said binder in a colloidal state to provide an extrudable mass, said 5 mixture being substantially free of added alkali metal base and/or basic salt; b) extruding the extrudable mass resulting from step (a); c) drying the extrudate resulting from step (b); and 10 d) calcining the dried extrudate resulting from step (c).

The calcined extrudate can be subjected to other operations such as base exchange, dealumination, steaming and impregnating with catalytically active metal(s), the details of1 15 which are well known in the art.

Unlike alumina binders, low acidity refractory oxide binders such as silica do not interact with zeolites to any appreciable extent. Consequently, zeolites can be bound with low acidity refractory oxides in accordance with the method of 20 this invention without increasing the zeolite's intrinsic activity as might occur with an alumina binder. •• In some types of hydrocarbon conversions, e.g., hydroprocessing, reforming, catalytic cracking and catalytic hydrocracking, the use of low-acidity refractory oxide-bound 25 zeolites having lower levels of inherent activity than their alumina-bound counterparts can result in lower coke production and significant increases in cycle length. On the contrary, the zeolite's intrinsic catalytic activity may actually be decreased by binding the zeolite with low acidity refractory (jw 30 oxides, such as silica. More particularly, zeolite activity ^ may be reduced by binding zeolites such as ZSM-5, Y, Beta, etc. with low acidity refractory oxides such as SiC>2 and TiC^.

It is believed that this reduction in activity is a result of a chemical reaction of the binder with the zeolite, whereby high ,• 0% d, £L ** -f-4256 — 4 acidity oxides such as alumina in the zeolite framework become replaced by low acidity refractory oxides from the binder. For example, zeolites with a silica to alumina molar ratio of 70 or 1 V less may become enriched with framework silicon content by binding the zeolite with silica and treating the mixture at elevated temperatures. Zeolites treated in this manner may exhibit lower exchange capacities, hexane cracking (e.g., as measured by alpha value) and toluene disproportionation activities, and shifts in x-ray diffraction patterns. 10 When employed in a low pressure hydrocracking (LPHC) process, a silica-bound, low sodium, framework dealuminated zeolite Y, e.g., ultrastable Y (USY) zeolite, has been found to provide significantly better results than a comparable alumina-bound USY zeolite.

Since the low acidity refractory oxide-bound zeolite catalysts of the present invention are capable of maintaining their structural integrity in low pH solutions, the zeolite dispersed in such a binder can be treated with an acid solution to effect dealumination. This effectively results in a 20 reduction in manufacturing costs of low acidity zeolite catalysts since extrudates are easier to handle than powders.

The method of this invention is not limited to any particular zeolite and in general may be employed with all metallosilicates, particularly the aluminosilicates whether or 25 not previously dealuminated to increase the framework silica:alumina ratio. Typical zeolites include ZSM-4 (Omega), ZSM-5; ZSM-11, ZSM-12, ZSM-20, ZSM-23, ZSM-35, ZSM-48, ZSM-50, Beta, X, Y and L as well as ferrierite, mordenite, dachiardite, clinoptilolite, offretite, erionite, gmelinite and chabazite.

The original cations associated with each of the zeolites utilized herein can be replaced by a wide variety of other cations employing techniques well known in the art. Typical replacing cations including hydronium, ammonium, alkyl ammonium and metal cations. Suitable metal cations include ,'NS £ X i - \ 224 450 F-4236 — 5 — ; O metals such as rare earth metals, as well as metals of Groups IIA and B of the Periodic Table, e.g., zinc, and Group VIII of the Periodic Table, e.g., platinum and palladium. As referenced herein the Periodic Table is that published by Fisher Scientific Company as Cat. No. 5702-10.

Typical ion-exchange techniques call for contacting f.:; 5 the selected zeolite with a salt of the desired replacing cation. Although a wide variety of salts can be employed, particular preference is given to chlorides, nitrates and sulfates. Representative ion-exchange techniques are disclosed in a wide variety of patents including U.S. Patent Nos. 3,140,249; 3,140,251; and 3,140,253.

Following contact with a solution of the desired replacing cation, the zeolite is then preferably washed with water and dried at a temperature of 65-315°C (150-600°F) and thereafter calcined in air, or other inert gas, at a 15 temperature of 260-815°C (500-1500°F) for 1 to 48 hours or more. Catalysts of improved selectivity and other beneficial properties can be obtained by subjecting the zeolite to treatment with steam at elevated temperatures ranging from 260 0 to 650°C (500 to 1200°F) and preferably from 400 to 540°C (750 to 1000°F). The treatment can be accomplished in an atmosphere of 100% steam or in an atmosphere consisting of steam or ammonia and some other gas which is essentially inert to the zeolites. A similar treatment can be accomplished at lower iZj temperatures and elevated pressure, e.g., from 180 to 370°C ,/<?• o%. (350° to about 700°F) at from 1000-20000 kPa (10 to 200 jjy atmospheres). 1*2 I If so desired, the zeolite can be treated with v. * >i ''%$■ rO't' reagents prior to steaming and with organics still contained from synthesis to remove alumina from the outside surface, or calcined in air or inert atmosphere to remove the organics and then ion exchanged to the ammonium form or other desired metal exchanged form. It is a special attribute of the low acidity refractory oxide-bound zeolite extrudate herein that it has sufficient integrity to withstand treatment with acids so that if-4256 -- 6 — it is possible to extrude an aluminosilicate zeolite such as zeolite Y and steam, acid extract, calcine or effect combinations thereof to produce a stable high silica-to-alumina Y in an easily handled form. Processes for dealuminizing Y are well known in the art, i.e., see Rabo, Zeolite Chemistry and Catalysis, ACS Monograph 171(1976) Chapter 4.

The binder material used herein can be selected from among any of the low acidity refractory oxides of metals of Groups IVA and IVB of the Periodic Table of the Elements. Particularly useful are the oxides of silicon, germanium, titanium and zirconium with silica being especially preferred. Combinations of such oxides with other oxides are also useful provided that at least about 40 weight percent, and preferably at least 50 weight percent, of the total oxide is one or a combination of the aforesaid Group IVA and/or Group IVB metal oxides. Thus, mixtures of oxides which can be used to provide the binder material herein include silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, silica-titania, titania-zirconia, silica-alumina-thoria, silica-alumina- zirconia, silica-alumina-magnesia and silica-magnesia-zirconia.

It is an important requirement of the method of the invention herein that the low acidity refractory oxide contains at least an extrusion-facilitating amount of the oxide in colloidal form, preferably with water as the dispersant. In general, however, at least part of the low acidity refractory oxide is added in dry particulate form, e.g. amorphous precipitated silica, so as to control the moisture content of the binder/zeolite/water mixture at a level to ensure f!hJ satisfactory extrusion. Preferably the moisture content of th# mixture does not exceed 50%, and preferably is at least 40%, by, weight. No alkali metal base or basic salt is added to the mixture.

The colloidal Group IVA and or Group IVB metal oxide component of the binder can represent anywhere from 1 to 90 weight percent or more of the total binder. For example, in the case of silica, amounts of colloidal silica ranging from 2 5 to 60 weight percent, preferably 5 to 50 weight percent, of the total binder generally provide entirely acceptable results.

The relative proportions of zeolite and low acidity refractory oxide binder can vary widely, with the zeolite content ranging from between 1 to 99 weight percent, and more 10 usually in the range of from 4 to 90 weight percent, of the total extrudate (dry basis).

Extrudates of 1/16 inch (1.6mm) obtained in accordance with this invention typically have a crush strength of from 5 to 24 pounds (2 - 11kg) when the crushing force is applied over 15 a 1/8 inch (3.2mm) length. This is equivalent to a crush strength range of 40 to 192 lb/linear inch (700 - 3430kg/ni). In addition, the low acidity refractory oxide-bound extrudates of this invention are also characterized by a high porosity, i.e., between 0.43 to 1 cc/gram (measured by mercury 20 porosimeter and helium absorption).

The extrudates of this invention can find utility in a wide variety of processes which are both catalytic and noncatalytic. Quite obviously, the materials can be used as sorbents. Additionally, the materials can be used as catalysts 25 for a wide variety of organic conversions. Moreover, since a low acidity refractory oxide, such as silica, has low catalytic activity, the incorporation of a zeolite in the silica can lead to some unusual catalytic effects. The low acidity refractory oxide can also be used as a support for a catalytic material, 30 e.g., a hydrogenation component such as platinum, palladium, cobalt, molybdenum, iron, tungsten, nickel or mixtures of the same. The catalytic metals in the form of their oxides or salts can also be added to the low acidity refractory oxide during the mulling step with pH adjustment, if necessary, to -7 I ^ _ - A ' ) o F-4&& -- 8 - stabilize the colloidal oxide component of the mixture. In particular, the low acidity refractory oxide-bound zeolite extrudates of the invention find utility in catalytic cracking, typically under conditions including a temperature of at least 5 315°C (600°F), generally 400-600°C (750°-1100°F), and pressures between 100 and 1500 kPa (atmospheric and 200 psig). If desired, the cracking can be conducted in the presence of hydrogen, preferably with the hydrogen partial pressure being no greater than 7000 kPa.

The invention will now be more particularly described with reference to the Examples, in which all parts are by weight unless otherwise specified.

Example 1 (Comparative) This example illustrates the preparation of an 15 alumina-bound USY catalyst to provide a basis for comparison with silica-bound USY catalysts prepared in accordance with the method of this invention (Examples 2-6). On a dry basis, 65 weight parts of USY zeolite (Z-14US, W.R. Grace) were intimately admixed with 35 weight parts finely divided alpha 20 alumina monohydrate (Kaiser SA) and an extrudable mass was obtained by mulling. The moisture content of the mix was adjusted to 46-48 weight percent by addition of deionized water. After additional mulling, the resulting paste was extruded using a 2" (5cm) Bonnot extruder to yield 1/16" 25 (1.6mm) diameter extrudates. The extrudates were subsequently dried at 121°C (250°F) for 18 hours in air and then calcined at 540°C (1000°F) for 3 hours in air flowing at 3 or 5 v/v/min. Heating rates of 2 or 3°C/min (3 or 5°F/min) we: used.

I I U 1M336- — 9 — Examples 2-6 65 parts of USY powder were mixed with 35 parts of (dry basis) of silica consisting of various ratios of an amorphous precipitated silica (PPG Industries HiSil 233 EP) and colloidal silica and were mulled to produce an homogeneous 5 mix. The moisture content of each mix was adjusted to 42-47 weight percent with deionized water. Each mix was extruded using a 2" (5 cm) Bonnot extruder and the extrudate treated substantially the same as described in Example 1. Since the alpha activity of the bound USY extrudate (as measured by the 10 alpha test) was less than 10, the extrudate was ammonium exchanged to remove sodium employing a three step ammonium exchange/calcination procedure. After ammonium exchanging at room temperature for 1 hour with 5 ml/g circulating IN ammonium nitrate, the extrudate was washed and dried at 121°C (250°F) in 15 air and subsequently calcined at 540°C (1000°F) for 3 hours in dry flowing air. This procedure was repeated three times so that the acidity of the catalyst (as measured by the alpha test) increased to a level of 250 to 300 and the sodium content was reduced from 1.8-1.9 to 0.1-0.2 wt %. The calcinations 20 were performed in a relatively anhydrous environment to preclude any significant steaming of the catalyst.

In these Examples, the effect of colloidal silica content on the physical properties of the zeolite was evaluated by varying the amount of colloidal silica in the extrusion mix 25 from 17.5 weight percent to 2.2 weight percent (on a dry basis). Additional amorphous precipitated silica was added to maintain a 65/35 zeolite/binder weight ratio (on a dry basis). The physical properties of the alumina and silica /V bound catalysts of Examples 1-6 are set forth in Table 1.

While two commercial sources of colloidal silica were used, a \\2- clear correlation was observed between crush strength and colloidal silica content demonstrating the critical role of colloidal silica as a binding agent. © 0 .) TABLE 1 Properties of Bound USY Catalysts Example 1 2 3 4 6 Wt. % Amorphous precipitated Silica 0.0 17.5 26.2 .6 .6 32.8 Wt i Colloidal Silica 0.0 17.5 8.8 4.4 4.4 2.2 Colloidal Silica Source (Alumina- EM EM EM Ludox, Ludox, bound) Science Science Science HS-30 HS-30 Sodium Content, ppm 870 1170 945 1580 1580 1650 Alpha Activity 300 266 255 279 321 263 Unit Cell Size, Angstroms 24.52 24.51 24.52 ND 24.61 24.56 Density, g/cc Real 2.73 2.38 2.35 2.32 2.35 2.33 Particle 0.94 0.89 0.90 0.84 0.84 0.84 Surface Area, M2/g 476 439 409 434 413 430 Pore Volume, cc/g 0.70 0.70 0.68 0.68 0.76 0.77 Avg. Pore Diameter, A 59 64 67 63 74 71 PSD, % of Pores with 0-30 A Diameter 36 33 33 32 33 27 -50 7 4 3 2 1 2 50-80 4 4 4 3 3 80-100 6 4 3 3 2 2 100-150 9 8 7 7 6 200-300 2 9 13 300+ 27 32 29 28 33 39 Crush Strength (lb/in) 65 84 77 71 87 53 (kg/m) 1161 1500 1375 1268 1554 946 EXAMPLES 7-9 65 Weight percent zeolite beta (on a dry basis) in the form of a powder was mulled with 35 wt parts of combined amorphous precipitated silica (HiSil 233 EP) and colloidal silica to produce a homogeneous mix. To facilitate admixture, the moisture content of the mix was adjusted to 45-49 weight percent by adjusting the amount of deionized water added. Two different amounts of colloidal Si02 were added to obtain extrudable mixes while maintaining a 65/35 zeolite/binder weight ratio. The resulting mixes were extruded to yield 1.6mm (1/16") diameter extrudates. The extrudates were dried at 121°C (250°F) for 18 hours and were subsequently calcined at 540°C (1000°F) for 3 hours in nitrogen flowing at 3 or 5 v/v/min. This was followed by a 3 hour calcination at 1000°F (540°C) in air flowing at 3 or 5 v/v/min. Next, each extrudate was exchanged twice at room temperature for 1 hour with a 5 ml/g circulating IN ammonium nitrate solution. After washing the extrudate was then calcined at 540°C (1000°F) for 3 hours in air flowing at 3 or 5 v/v/min.

For purposes of comparison, the physical properties of the foregoing extrudate (Examples 8 and 9) were compared with those of a commercially available alumina-bound zeolite beta (Example 7).

The physical property data are set forth in Table II as follows: >' TABLE 2 Physical Properties of Bound Beta Catalysts Example 7 8 9 Wt.% Amorphous Precipita- ted Silica 0 17.5 26.2 Wt.% Colloidal Silica 0 17.5 8.8 (HS-30) Moisture Content, % 45.7 48.1 Sodium Content, ppm ND 765 . 670 Alpha Activity 325 344 342 Density, g/cc Packed 0.50 ND 0.52 Real 2.58 2.33 2.34 Particle 0.89 0.87 0.82 Surface Area, m2/g 480 421 428 Pore Volume, cc/g 0.74 0.71 0.80 Avg. Pore Diameter, Angstroms 61 68 75 Crush Strength kg/m (lb/inch) 1321(74) 1536(86) 679(38) ND = not determined u The foregoing data clearly show the effects of the 20 colloidal silica as binding agent. The physical properties of the silica-bound zeolite Beta catalyst are similar to those of the alumina-bound zeolite Beta.

Examples 10 to 12 Silica-bound ZSM-5 extrudates (Examples 11 and 12) were prepared substantially as described in Examples 8 and 9. The physical properties of the silica-bound ZSM-5 extrudates and those of a commercial alumina-bound ZSM-5 extrudate (Example 10) are set forth in Table 3 as follows: TABLE 3 Physical Properties of Bound ZSM-5 Catalysts Example 11 12 Wt. 1 Amorphous precipita 0 17.5 26.2 ted silica Wt. % Colloidal Silica (HS-30) 0 17.5 8.8 Sodium Content, ppm 415 56 75 Alpha Activity about 220 168 155 Density, g/cc Real 2. , 63 2.30 2.31 Particle 0. 91 0.96 0.87 Surface Area, m2/g 338 283 287 Pore Volume, cc/g Avg. Pore Diameter, Angstroms 0. 71 0.60 0.72 84 85 101 Crush Strength kg/m (lb/inch) ND 1143(64) 554(31) ND = not determined F-*236- Examples 13-17 Previous examples demonstrate that silica-bound catalysts prepared by the extrusion method of this invention retain their structural integrity upon calcination and ammonium exchange. An important advantage of silica-bound zeolite catalysts is that the extrudates can be acid treated without losing their structural integrity. Thus, the silica-bound USY catalyst of Example 3 was steamed for 10 hours at 540°C (1000°F) to reduce the alpha activity from 255 to 50-60 and to reduce the unit cell size from 24.52 to 24.35 Angstroms. The steamed extrudate (Example 13) was then treated for 4 hours in a IN HN03 solution at 55oC or 85oC (Examples 14-17). As a result of the acid treatment, the alpha activity was reduced to 6 and the unit cell size was reduced to 24.25 Angstroms as determined by x-ray analysis. Good crystallinity was retained (greater than about 50%). More importantly, however, equivalent crush strengths were obtained before and after steaming and acid treatment. The data are summarized in Table 4 as follows: C) TABLE 4 Physical Properties of Acid Treated Si02-Bound USY Catalysts Example 3 13 14 16 17 HN03 concentration - - IN IN IN IN IN IN Treatment Temp., oC - - 55 55 85 85 85 85 Treatment Time, Hrs. - - 4 4 4 4 4 4 ml of HN03/g Cat.

- - Unit Cell Size, A 24.52 24.36 24.30 24.27 24.35 24.26 24.25 24.28 Crystallinity, % ND 65 65 ND 60 55 55 55 Alpha Activity 255 52 76 6 83 6 6 Crush Strength, lb/in 77 ND ND 81 ND 74 82 56 (kg/m) 1375 ND ND 1140 ND 1321 1464 1000 Na, wt% (-11) 0.11 0.05 0.01 0.04 0.01 0.05 0.08 Si02, wt$ (83.3) 83.3 ND 97.2 95.4 97.2 97.2 97.2 A1203. wt% (13.6) 13.6 ND 2.8 6.6 2.1 2.3 2.2 Ash, wt% (97.6) 97.6 98.5 98.9 98.7 98.9 98.7 98.9 Surface Area, m2/g 409 - 480 488 495 ND = not determined Example 18 A sodium exchanged zeolite Y (NaY) was extruded with silica in a 65/35 zeolite binder ratio. This extrudate was prepared by mixing, on a dry basis, 65 weight parts of NaY with 17.5 weight parts amorphous precipitated silica (HiSil 233 EP) and 17.5 weight parts of colloidal silica (HS-30). After mulling and water addition as appropriate, the resulting homogenous mixture paste was extruded to 1/16" diameter extrudate. The extrudate was dried at 121°C. 1 gram of this catalyst was calcined at 538°C for four hours under high nitrogen purge such that in-situ steaming of the material was avoided. The calcined silica bound catalyst was analyzed by x-ray diffraction along with the uncalcined silica bound catalyst.

X-ray diffraction data was collected at the Brookhaven National Laboratory, National Synchrotron Light Source on the X13A powder diffractometer. The diffractometer employs parallel beam geometry with a Ge(lll) incident beam monochromater and a Ge(220) analyzer crystal. Data was obtained with a 2-theta step scan of 0.01 degrees, 2 second count times per step, a theta scan of 2 degrees per step, and an x-ray wavelength of 1.3208 Angstroms. The 2-theta zero and x-ray wavelength were calibrated with a National Bureau of Standards silicon metal standard. D-spacings were obtained from the measured data with a second derivative peak search algorithm. The lattice parameters were refined with a standard least-squares refinement program.

For both samples, the expected orthorhombic unit cells were obtained. The a values obtained as well as the calculated o estimated standard deviations (esd) were: a0 esd r, jjL Uncalcined Catalyst 24.6611 0.0005 jj ilN Calcined Catalyst 24.6568 0.0006 9 F-+236 — 17 -- ~~ The difference between the two aQ values is 0.0043 whereas the sigma p calculated from the esd's, equals 0.0008. On statistical grounds, the limit of significance between the two '""P unit cells is 5.51 sigma. From a normal distribution chart, at significance levels of greater than 3.89 sigma the probability is less than 0.0001 that two equal unit cells would be found to differ to by 0.0043 Angstroms. This establishes the level of confidence at greater than 99.9999% that the two unit cells are statistically different. The calcined silica extrudate shows 10 the unit cell contraction consistent with silica insertion into the framework of the zeolite in place of framework alumina.

Example 19 (Comparative) To show the importance of controlling the moisture content of the extrudable mass, a zeolite beta/silica mix was prepared 15 with a 65/35 weight ratio as in examples 8 and 9 but using only colloidal silica as the low acidity, refractory oxide source. Thus, to 397.3g of zeolite beta crystals (ash content 75.5%), 538.5g of colloidal silica (Ludox HS-30) were gradually added and mulled. However, the resulting paste was too wet (moisture 20 content 50.4 I) to be extruded.

Example 20 The process of Example 19 was repeated but with ratio of the zeolite beta (ash content 75.5%) to colloidal silica (ash content 30%) increased to 82.5/17.5 to produce mixtures in 25 which the moisture content was at a level suitable for extrusion. The results are shown in Table 5 below: O

Claims (6)

- 18 - Table 5 Physical Properties of Silica-Bound Zeolite Beta Zeolite content, wt.! 82.5 Silica content (BiSil), wt.! 0 Silica content (Ludox), wt. % 17.5 Moisture content (actual), wt.! 46.5 44.61 43.6 Solids content (actual), wt.% 53.5 55.41 56.4 Solids content (target), wt.% 53.0 55.0 56.0 Crush strength, lb/inch 68 76 70 kg/m 1214 1357 1250 Density,g/cc Particle 0.89 0.91 0.92 Real 2.34 2.34 2.36 Surface area, mz/g 513 503 508 Pore volume, cc/g 0.70 0.67 0.67 1 Estimated from target moisture content. - 19 - 224450 WHAT<£/WE CLAIM IS;

1. A method for preparing a low acidity refractory oxide-bound zeolite catalyst which comprises: a) providing a substantially homogeneous mixture of zeolite, water and a low acidity refractory oxide binder containing at least an extrusion-facilitating amount of said binder in a colloidal state to provide an extrudable mass, said mixture being substantially free of added alkali metal base and/or basic salt; b) extruding the extrudable mass resulting from step (a); c) drying the extrudate resulting from step (b); and, d) calcining the dried extrudate resulting from step(c); and wherein the low acidity refractory oxide binder is an oxide of an element of Group IVA or Group IVB of the Periodic Table.

2. The method of Claim 1 wherein at least part of the low acidity refractory oxide binder is added as a dry particulate material.

3. The method of Claim 1 wherein the low acidity refractory oxide binder is silica.

4. The method of claim 3 wherein the content of silica (dry basis) from colloidal silica represents from 1 to 90 weight percent of the total binder.

5. The method of claim 3 wherein the content of silica (dry basis) from colloidal silica represents from 5 to 50 weight percent of the total binder.

6. The method of claim 1 wherein the moisture content of the extrudable mass does not exceed 50% by weight. 7 • The method of claim 1 wherein the moisture content of the extrudable mass is 40-50% by weight. 8, The method of claim 1 wherein the zeolite content (dry basis) represents from 1 to 99 weight percent of the total extrudate. - ;; • .V i * ' t;9. The method of claim 1 wherein the zeolite content (dry basis) represents from 40 to 90 weight percent of the7'Y;total extrudate. V 2 1 MAR !990;224450;— 20 —;10. A method for preparing a low acidity refractory oxide-bound zeolite catalyst according to any one of claims 1 to 9, substantially as herein described with reference to the examples.;5 ^... .0. l.Ur...;Sy^Hts/their authorised Agents., A. J. PARK. & SON.;P'r/U <^o •*