GB1586985A - Crystalline zeolite hp - Google Patents

Description

(54) CRYSTALLINE ZEOLITE HP (71) We, TEXACO DEVELOPMENT CORPORATION, a corporation organised and existing under the laws of the State of Delaware, United States of America, of 135 East 42nd Street, New York, New York 10017, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to crystalline aluminosilicates. In particular, it relates to a novel crystalline aluminosilicate and its preparation.

Synthetic crystalline aluminosilicates constitute well known materials which have heretofore been employed as selective adsorbents, supports and catalysts. In general, such crystalline materials have been grown under designated conditions of temperature and time from alkali oxide, aluminum oxide, silica and water precursors. The simplest source materials for preparing the more common crystalline aluminosilicates i.e., the type A, X and Y zeolites, are sodium aluminate, sodium silicate and for the more siliceous X and Y types, an additional source of silicate ions. (The terms crystalline aluminosilicates and zeolites are used herein interchangeably and refer to the same crystalline materials.) Most of the synthesis procedures now in use are tailored to the specific zeolites being prepared.

Crystalline zeolites occur in nature and these natural materials were utilized in early investigations of their-crystalline structure. Barrer, one of the early investigators, carried out the synthesis of numerous crystalline aluminosilicates using hydrothermal techniques which comprised introducing the reactant mixture into an autoclave and maintaining the mixture for extended periods of time at elevated temperatures as high as 400-450"C.

Subsequent investigation by others, such as Milton, accelerated the efforts for the commercial production of synthetic crystalline aluminosilicates.

Type A, Type X and Type Y zeolites are among the most useful synthetic crystalline aluminosilicates in use today. The Type A zeolite finds use in gas drying and in one of its particularly preferred embodiments, in an industrial process for separating normal paraffins from hydrocarbon mixtures. The catalytic properties of the Type X and Type Y zeolites have resulted in their commercial use in a variety of industries. By compositing the Type X or Type Y zeolite with an amorphous siliceous matrix, a catalyst is produced which has been found particularly useful in the fluid catalytic cracking of petroleum hydrocarbons.

The composition of these crystalline zeolites is: Type of Zeolite Chemical Analysis A Na96 [(A102)96 (SiO2)96] . 216H2O X Na86 [(AlO2)86 (SiO2)1(6] . 264H2O Y Na56 [(A102)56 (SiO2)136] . 250H2O Breck and Flanigen in their paper "Synthesis and Properties of Union Carbide Zeolites L, X and Y" present a correlation between the lattice constant of zeolite X and zeolite Y and the number of aluminum atoms in the unit cell. (This paper was read at the conference on molecular sieves held at the Universtiy of London on April 4-6, 1967 and published at pages 47-60 of "Molecular Sieves" which is a collection of the papers read at this conference and published by the Society of the Chemical Industry, London, S.W.1 in 1968.) In their paper, these authors describe the unit cell as containing 192 atoms of silicon and aluminum and define the zeolite Y structure as containing less than about 76 aluminum atoms per unit cell and the zeolite X structure as having from about 77 to 96 aluminum atoms.

Extrapolation of this correlation shows a lattice constant of 25.02 , for a zeolite having a 1:1 SilAl ratio, i.e., 96 aluminum atoms.

Dempsey, Kuhl and Olson, J Phys. Chem, 73, 387 (1969) present a correlation somewhat different from that of Breck and Flanigan. Their correlation between aluminum content of the zeolite and lattice constant shows discontinuities in the correlation at specific compositions which they attribute to a high degree of ordering in the lattice at these points. Extrapolation of their data shows a lattice constant of 25.13 A for a 1:1 SilAl atomic ratio.

In neither article do the authors present examples for aluminum content per unit cell above 87 atoms. In Breck and Flanigen the upper limit of the data shows a lattice constant of 24.95 A. at 86.5 aluminum atoms while Dempsey, KuhI and Olson show a lattice constant of 24.99 A. for 86.2 aluminum atoms. The differences in lattice constant are explained by the different methods of measurement employed.

In these articles there is an implied limit of unit cell composition at a 1:1 ratio of Si to Al atoms because of the so-called "Avoidance Rule" of Lowenstein which says that, in aluminosilicate-type structures, aluminum ions do not occupy adjacent positions in the lattice. This- then limits a Si-Al- structure to a 1:1 atomic ratio since a lower ratio would require the aluminum ions to occupy adjacent positions.

A number of procedures have been described for producing synthetic zeolites. These processes require the preparation of aqueous mixtures containing oxides of sodium, silicon and aluminum within certain definite mole ratio limitations. Each process requires that this aqueous mixture be subjected to certain conditions to effect crystallization of the desired zeolite species. U.S. 2,847,280 discloses the aging of an aqueous mixture of the oxides having certain definite mole ratios at a temperature not above 100OF (37.8"C) for at least 8 hours and then hydrotreating the mixture under autogenous pressure at a temperature of 150-325"F. (65.6 - 162.8 C) to produce zeolite A.U.S. 2,882,243 of Milton discloses another process of producing zeolite A wherein an aqueous mixture of the oxides in specific mole ratios is maintained at 20-175"C until crystallization occurs. U.S. 2,982,612 of Barrer et al.

discloses still another process of producing zeolite A by maintaining a certain aqueous mixture of oxides at 60-100 C to effect crystallization.

Other aqueous oxide mixes produce zeolite X or Y under proper conditions. U.S.

2,882,244 of Milton teaches that certain aqueous oxide mixes will produce zeolite X by maintaining the mix at 20-120"C, while the mixtures disclosed in U.S. 2,979,381 of Gottstine et al produce the same zeolite species when aged at ambient temperature for at least two hours and maintained at 185-2500F (85-121.1"C) for at least 1l/2 hours. The more siliceous aqueous mixtures of oxides disclosed in U.S. 3,130,007 of Breck yield zeolite Y when the mix is digested at ambient temperature for 24-32 hours and then maintained at 90-105 C for 25-65 hours.

The aging (digesting) and hydrothermal steps employed in the prior art to prepare synthetic zeolite A, X and Y were conducted under atmospheric or autogenous pressure. In no event were pressures in excess of 35-50 psig (0.2-0.3 MPa) considered as being either necessary or useful in preparing these materials. Neither were the effects of high pressures investigated for any beneficial results which might be obtained when preparing these crystalline aluminosilicates.

New processes for preparing crystalline aluminosilicates including those employing high pressures, might other significant advantages over processes presently employed, particularly if the crystalline aluminosilicate prepared thereby would have useful properties not found in crystalline aluminosilicates prepared heretofore.

Broadly this invention is directed to novel crystalline aluminosilicates and their method of preparation. More particularly, by employing pressures above 20,000 psig (ca. 138 MPa), preferably in excess of 40,000 psig (about 276 MPa) in the hydrothermal step, and in the optional aging step, of a crystalline aluminosilicate preparation, a zeolite having a structure similar to a zeolite X but having a higher aluminum content and exhibiting properties not found in zeolite X, is obtained.

The present invention will be readily understood by reference to the accompanying figures in which: Figure 1 presents the phase diagram of the zeolite species in the Na2O-SiO2 Al203 system when the crystallization conditions are 200OF (93.3 "C) and 50,000 psig (ca.

345 MPa).

Figure 2 presents the phase diagram of Breck and Flanigen for the zeolite species in the Na2O-SiO2-Al2O3 system when the crystallization conditions are 200OF (93.3"C.) and atmospheric or autogenous pressure.

Broadly, we have found that the use of high pressure during the synthesis of zeolite crystalline aluminosilicates produces a zeolite having a structure similar to that of zeolite but containing more aluminum atoms, having a higher lattice constant than that generally observed for zeolite X and exhibiting properties not found in zeolite X. More particularly, we have found that an aqueous mixture of oxides, which would, under techniques employed by the prior art, produce a zeolite A, will, by the utilization of pressures in excess of 20,000 psig (ca. 138 MPA), preferably above 40,000 -psig (about 276 MPa), during the hydrothermal portion and the optional aging portion of the synthesis produce. a zeolite which may generally be termed an aluminum-rich zeolite X.To distinguish this material from zeolite X prepared heretofore, we have designated this material zeolite HP.

Thus, this invention is directed not only to the process of preparing this zeolite but also to the zeolite itself. Zeolite HP is distinguishable from both zeolite X and zeolite Y, to which it is most closely related in the zeolite family, by having a unit cell which contains more aluminum atoms than possible heretofore and having a lattice constant larger than that reported for measurements on specific samples of zeolite X. Not only does this high aluminum zeolite X differ from other zeolites in its increased ease of ion exchange and depth of exchange, but it exhibits novel catalytic and absorptive properties not exhibited heretofore by the prior art zeolites.

Initially, this invention is directed to a process for preparing zeolite HP which comprises: a. forming an aqueous mixture of sodium aluminosilicate having a composition sufficient to establish ratio of silicon atoms to aluminum atoms of from 0.25. to 1.0, b. maintaining said aqueous mixture at a pressure above 20,000 psig (ca. 138 MPa), preferably above 40,000 psig (ca. 276 MPa), and a temperature of 150-350"F.

(65.6-176.7"C) for at least three hours, and c. recovering zeolite HP as the resulting solid product.

Optionally, and preferably we have found that the quality of the zeolite produced by this process is substantially improved if the aqueous mixture of step (a) is aged at high pressure and not above 100OF, preferably at aboutambient temperatures, prior to the hydrothermal crystallization of step (b).

The aging step comprises: aging said aqueous mixture for at least 8 hours at a pressure above 20,000 psig (ca. 138 MPa), preferably above 40,000 psig (ca. 276 MPa), and a temperature not above 100OF (37.8"C.).

In addition, this invention is directed to the zeolite produced by the processes described above. Further, this invention is directed to a synthetic zeolite crystalline aluminosilicate having a lattice constant of at least 25.02 and a ratio of silicon atoms to aluminum atoms in the unit cell of below 1.0.

In preparing zeolite HP an aqueous solution of sodium aluminosilicate serves as the starting material. This mixture is an aqueous solution of the oxides, Na2O, Al203 and SiO2, or materials whose chemical compositions can be. completely represented as mixtures of these oxides, in specified ranges of their mole ratios to produce a mixture wherein the atomic ratio of silicon to aluminum is from 0.25 to 1.0. This mixture may also be described as one which when subjected to the zeolite synthesis preparation techniques of the prior art, including for example, atmospheric or autogenous pressure, would produce zeolite A.

In preparing the aqueous mixture of sodium aluminosilicate for use in the process of the invention, any prior art method and formulation used to prepare a zeolite A synthesis mix may be employed, provided that the synthesis mixture has a ratio of silicon atoms to aluminum atoms of 0.25 to 1.0. One aqueous mixture which we have found to be particularly useful is disclosed in U.S. 2,847,280 and is formulated by reacting an aqueous solution of sodium silicate with CO2, SO2, H2S, the sodium hydrogen salts of their corresponding acids, (i.e., sodium bicarbonate, sodium bisulfite and sodium hydrosulfide), or mixtures thereof, to form hydrous silica and a by-product sodium salt and then adding sodium aluminate to the mixture in an amount sufficient to establish silicon to aluminum atomic ratio of from 0.25 to 1.0.These reactants may be mixed under room temperature conditions and stirred until a thick creamy reaction mixture is formed.

In another embodiment, an aqueous solution sodium aluminate'and sodium hydroxide is combined with an aqueous solution of sodium silicate to produce a mixture in conformity with the atomic ratio range set forth above. This solution is the preferred mixture disclosed in Milton's U.S. patent 2,882,243 for preparing a zeolite A.

In still another embodiment, a synthesis mixture of sodium aluminosilicate which is particularly useful in preparing zeolite HP is formulated by mixing together rapidly an aqueous solution of sodium silicate and an aqueous solution of sodium aluminate.

Hydrochloric acid is then added with rapid mixing to produce a uniform gel.

Although zeolite HP is produced by utilizing a high pressure hydrothermal treatment of the synthesis mix, as explained above, a purer product is obtained if an aging treatment, also conducted at high pressure, is performed prior to the hydrothermal crystallization step.

A method of preparing zeolite HP which includes both high pressure aging and high pressure hydrothermal treatment is therefore a particularly preferred embodiment of this invention.

Following the preparation of the aqueous mixture of sodium aluminosilicate, the mixture is, optionally, subjected to aging under high pressure and then hydrothermal treatment under high pressure in order to produce zeolite HP. The pressures that are necessary are substantially higher than those employed heretofore in the synthesis of zeolitic crystalline aluminosilicates. We have found that at pressures of 20,000-40,000 psig (about 138 - about 276 MPa), increasing amounts of zeolite HP are observed in the crystalline product which is a mixture of zeolite A and zeolite HP. We find that pressures in excess of 40,000 psig (about 276 MPa) produce sufficient quantities of zeolite HP in the desired quality.Although pressures far in excess of 40,000 psig (about 276 MPa) may be used to produce zeolite HP, those skilled in the art will appreciate that preparation costs will increase significantly when excessively high pressures are employed. Thus zeolite HP of good quality may be obtained at preparation pressures as high as 80,000 psig (ca. 552 MPa) but economic considerations hardly justify use of such a preparation pressure. We have found that a pressure of about 50,000 psig (ca. 345 MPa) is particularly useful.

The high operating pressures described above for use in the zeolite synthesis must be maintained during the hydrothermal step of the preparation and during the optional aging step preceding the hydrothermal step. Although it is, for operating reasons, usually more convenient to use the same pressure in both steps, this is not critical and the pressures may be different in the aging and hydrothermal treatments provided the pressure in both steps is above 20,000 psig (ca. 138 MPa) and preferably above 40,000 psig (ca. 276 MPa). Time and temperature are the other operating variables which must be controlled during the zeolite synthesis.Thus, we have found that the high pressure aging should be conducted at not above 100OF, preferably at about room temperature, for at least 8 hours, preferably from 8 to 170 hours, and most preferably from 24 to 72 hours. The high pressure hydrothermal treatment is conducted by maintaining the mixture at a temperature of 150-350"F (65.6 162.8"C) for at least three hours, preferably for 4-24 hours.

The synthetic crystalline aluminosilicate obtained in the high pressure synthesis process of the invention has a structure similar to that of zeolite X but possesses many distinguishing characteristics from this commercially available species of zeolite. The lattice constant for zeolite HP is significantly higher than that for zeolite X. We have found that lattice constants of at lest 25.02 A. are obtained for the zeolites produced in the high pressure synthesis of the invention when the atomic ratio of silicon to aluminum in the synthesis mix is from 0.25 to 1.0. In fact, the range of lattice constant for zeolite HP appears t6 be generally from 25.02 to 25.10 .

Chemical analysis and ion exchange data of zeolite HP indicate a lower than 1:1 ratio of silicon to aluminum. Because of the "Avoidance Rule", it is unlikely that aluminum ions would occupy adjacent positions in the lattice as required for such a composition. It is possible that the excess aluminum, as alumina, is occluded in the large cages of zeolite HP where it displays ion exchange capability. However, there is no visible evidence of such occlusion in the X-ray studies of this zeolite. The possibility must be considered, therefore, that exceptions to the "Avoidance Rule" may occur at the synthesis conditions employed in synthesising zeolite HP.If the lattice constants do represent aluminum contents below the 1:1 relationship predicted by the "Avoidance Rule" the fact that a limit is approached at about 25.10 would indicate that the exception could occur only at favored sites in the lattice.

Zeolite HP has a variety of uses. As obtained in its synthesis, zeolite HP is in its sodium form. This material finds utility after being ion exchanged with various cations such as calcium, potassium and some of the rare earths. Zeolite HP differs from zeolite X in increased ease of ion exchange and depth of exchange. Thus, not only is it easier to replace sodium in zeolite HP by utilizing fewer number of exchanges but the amount of residual sodium remaining after the exchange is substantially less than that obtained with zeolite X.

Further, subsequent absorption-desorption steps with zeolite HP show peaks which are much sharper and with less tailing than is obtained with zeolite X. This very high degree of ion exchange permits- very high loading of rare earth cations into the zeolite HP structure.

Thus, when utilized as a cracking catalyst, high equilibrium activities are readily achieved.

When zeolite HP, in its rare earth form, is composited with a siliceous matrix, an improved catalytic cracking catalyst having initial high activity is produced. In its lanthanum exchanged form, zeolite HP may be employed to crack hydrocarbons, such as gas oil, utilizing conventional catalytic cracking conditions.

The following examples serve to illustrate this invention: Example I 100 grams of PQ 'N' grade sodium silicate (containing 36.5 wt. % Na2Si4O9) were diluted with 120 cc of distilled water to produce a 30:1 ratio of water to SiO2. Carbon dioxide, in the form of dry ice, was then added in small quantities and replenished, at such a rate that no large excess was ever present, until a gel formed, at which point the remaining bits of dry ice were removed. Excess CO2 was avoided since it could convert the sodium present to sodium bicarbonate rather than the desired sodium carbonate.The bicarbonate would neutralize a portion of the sodium being added in the next step as sodium aluminate and would interfere with subsequent crystallization. 55 grams of commercial sodium aluminate, containing 95 wt.% 2 NaAlO2 3H2O, was dissolved in water to produce about a 30:1 mole ratio of water to salt and in an amount sufficient to produce about a 1:1 ratio of silicon to aluminum atoms when added to the gelled mixture. The aqueous solution of sodium aluminate was added to the gel with rapid mixing to produce a smooth creamy mixture after about 10 minutes of stirring. The mixture approximates the mixtures disclosed in U.S. Patent No. 2,847,280 which upon subsequent aging at room temperature and hydrothermal treatment at autogenous pressures and elevated temperatures produced zeolite A.

To evaluate the effect of high pressure on zeolite crystal formation the creamy mixture was divided into five portions. One portion served as a control and was subjected to aging at atmospheric pressure and hydrothermal treatment at 225OF (107.2"C) and autogenous pressure. The remaining four portions were subjected to various combinations of aging at atmospheric or elevated pressure and hydrothermal treatment at autogenous pressure or elevated pressure. In all instances the elevated pressure was 50,000 psig (about 345 MPa).

The high pressure studies were run in a reaction vessel constructed of Inconel (Registered Trade Mark) having a 347 stainless steel liner and a working cavity of approximately 13/4 inch ID x 26 inches. Synthesis mixes in 347 stainless steel vessels were placed in the working cavity and subjected to elevated pressures and temperatures. Mixes subjected to elevated temperatures and autogenous pressures were placed in screw capped 316 stainless steel vessels having a 200 cc capacity. The screw capped vessels were then placed in circulating air ovens under thermostatic control.

The results of these tests are set forth in Table I below: TABLE I High Pressure Preparation of Crystalline Zeolites Crystalline Produce Based Aging Hydrothermal Treatment on X-ray Analysis Temp. Press Temp Press Run Time of psig Time of psig No. hr. ( C) MPa) hr. ( C) (MPa) 1(1) 20 Ambient Atmos. 16 225 Auto.(2) Type A 2 20 Ambient Atmos 6 200 50,000 Type A (93.3) (ca. 345) 3 20 200 50,000 6 200 50,000 High Al Type X (93.3) (ca. 345) (93.3) (ca. 345) (Type HP) 4 72 Ambient 50,000 16 225 Auto. Type A (ca. 345) (107.2) 5 - No Aging - 6 200 50,000 High Al Type X (93.3) (ca. 345) (Type HP) Notes: (1) Control (2) Autogenous An additional run, Run 6, was made to determine the stability of Type 4A zeolite.A quantity of commercial Type 4A manufactured by the Linde Company together with some water was charged to the reaction vessel which was then pressured to 50,000 psig (ca 345 MPa) and heated to 2000F (93.3"C) for 24 hours. The type 4A sieves were recovered unchanged.

In each of the five runs a crystalline zeolite produce was obtained. Run 1 approximates the procedure disclosed in U.S. patent 2,847,280. As expected, when the aging and hydrothermal treatments were conducted under the moderate conditions of the prior art, zeolite A was prepared. Since the aging portion of the precedure is believed to result in nucleation of the favorite species for the particular composition of a synthesis mix, it was not surprising that the exceedingly high pressures utilized during the hydrothermal treatment of Run 2 did not produce other than zeolite A. Run 3, on the other hand, employed high pressures of 50,000 psig (ca. 345 MPa) in both the aging and the hydrothermal treatment and produced a zeolite type which was not expected - a zeolite similar to zeolite X but having an unusually high aluminum content.Run 4 might have demonstrated that the nucleation under high pressure would produce a Type X zeolite even if the hydrothermal treatment was conducted under moderate conditions. If nucleation did occur under high pressure it was not stable once the influence of pressure was removed since a Type A zeolite was produced in Run 4. Run 5 was conducted with no aging but a hydrothermal teatment at high pressure. Although a high aluminum content Type X zeolite was produced.in Run 5 it was of a visibly poorer quality than that which was obtained in Run 3.

The material from Run 3 was subjected to further examination under X-ray diffraction.

Calculations using this X-ray data shows the X type material from Run 3 had a lattice constant, aO, of 25.04 + 0.01 A. This is very close to the predicted value of 25.02 A by Breck & Flanigen for a Type X zeolite with a 1:1 Si to Al ratio. Chemical analysis of the Run 3 product gave a ratio of Si to Al of 1.16:1; however, this analysis did not distinguish between zeolite and any amorphous material which may have been present. The synthesis mix used in these runs had a Si to Al ratio of 0.96:1.

The results of Run 3 were confirmed by repeating this run with identical results being obtained in terms of the zeolite type. The lattice constant for the crystalline zeolites obtained from these runs, Runs 7 and 8, was:

Run 7 25.06 + 0.01 Run 8 25.04 + 0.01 Example II 200 grams PQN grade sodium silicate (365 wt.% NaSi4O9) was diluted to 400 cc with distilled water. 282 grams of Nalco #2 stablilized sodium aluminate (Na2O/Al203 = 1.45/1) ("Nalco" is a Registered Trade Mark) was diluted to 400 cc with distilled water. The two solutions were mixed rapidly to obtain a uniform consistency. Then 42 cc of commercial concentrated hydrochloric acid (12 N) diluted to 100 cc were added and the mixture blended until uniform. The gel had a Si/Al atom ratio of 0.79.The gel was charged to the high pressure vessel, aged for 20 hours at room temperature under 50,000 psig (ca. 345 MPA) hydrostatic pressure, then heated to 2000F (93.3"C) for 6 hours. A zeolite product was collected by filtration and washed with one liter of distilled water. The product yield was 134 grams. X-ray diffraction measurements showed that the zeolite had a lattice constant of 25.07 .

Example 111 Comparisons of the high pressure zeolite of Run 3 with Type X and Type Y zeolites were made.

Structure determinations of the zeolites were based on X-ray powder patterns. These tests were used both for identification and determination of lattice constants.

The data published by Breck and Flanigen show a correlation between lattice constant and the number of aluminum atoms in the unit cell of the Type X and Y class of zeolites in the hydrated form.

Lattice constant determinations are carried out by measuring selected lines in the back reflection regeneration of the X-ray pattern. Normally the lattice constant given is an average value for the a0 from the lines measured. X-ray measurements were made on the zeolite from Run 3 and commercially available Type X zeolite. The results are presented in Table II below. The first set of data was obtained from the same Miller indices while the second set of data utilized different line identifications.

TABLE II Lattice Constant, aO, Data Based On X-ray Powder Patterns (a) Based on same lines Back reflection line indent Run 3 Zeolite Type X Zeolite Miller Indices d value a0 d value a0 25, 5, 1 0.9826 25.07 0.9795 24.99 24. 6. 2 1.0095 25.06 1.0267 24.99 24, 2, 2 1.0367 25.06 1.0339 24.99 (b) Based on different lines Miller Indices d value a0 Miller Indices d value a0 26, 6, 4 0.9293 25.07 26, 8, 4 0.9088 24.99 26, 4, 2 0.9505 25.07 26, 4, 4 0.9395 25.00 The zeolite of Run 3 obtained under high pressure and from an aluminum-rich synthesis mixture exhibits a lattice constant as high as 25.07.This represents an aluminum richness in the zeolite of nearly 10% if the lattice constant correlations of Breck and Flanigen are accepted. Such a composition is supported by chemical analysis of the Run 3 zeolite HP whose typical analysis is as follows: Si/Al ratio, calculated from X-ray 92/104 Si/Al ratio, chemical analysis 92/104 Chemical analysis also showed the following oxide composition for the sodium form of the Run 3 zeolite HP.

Mole Wo Na2O 26.4 Al203 26.0 SiO2 47.6 Example IV To further investigate the effect of pressure during the aging and hydrothermal synthesis steps of crystalline aluminosilicate formation, a series of runs was made wherein the pressure was studied over a range of 15,000-50,000 psig (about 103 to 345 MPa). Two synthesis mix compositions were prepared as in Example I. Synthesis mixture A has a Si/Al atom ratio of 0.98/1. Synthesis mixture B had a Si/Al of 0.87/1. In each run the same high pressure was maintained during the aging and the hydrothermal steps and each synthesis mixture was investigated during each run. Further, acontrol was run simultaneously with each high pressure study. Thus, each run consisted of four parts.A high pressure synthesis of mixture A plus a control employing mixture A and a high pressure run with mixture B plus a control employing mixture B. Four pressure levels were investigated - 15,000, 30,000, 40,000 and 50,000 psig (ca. 103, 207, 276 and 345 MPa) with repeat runs for the 40,000 and 50,000 psig (ca. 276 and 345 MPa) tests. The product from each run was analyzed by X-ray techniques to identify the type of zeolite obtained. The results of runs 9 to 14 are presented in Table III below: TABLE III Pressure Experiments Product Identification (X-ray) Type Zeolite Aging Synthesis Press Synthesis Synthesis Run No. psig (MPa) Temp Press Temp, F ( C) Mixture A (1) Mixture B (2) 9 15,000 (c a. 103) Rm 15,000 (c a. 103) 220 (93.3) A A Control Atm. Rm Auto 225(107.2) A A + Amor.

10 30,000 (c a. 207) Rm 30,000 (c a. 207) 200 (93.3) A to X A Control Atm Rm Auto 225 (107.2) A A 11 40,000 (c a. 276) Rm 40,000 (ca. 276) 200 (93.3) A, X, HP A, X, HP Control Atm Rm Auto 225 (107.2) A A 12 50,000 (c a. 345) Rm 50,000 (c a. 345) 200 (93.3) HP, ao=25.04 HP, ao=25.07 Control Atm Rm Auto 225 (107.2) A A 13 40,000 (c a. 276) Rm 40,000 (c a. 276) 200 (93.3) A, X, HP A, X, HP Control Atm Rm Auto 225 (107.2) A A 14 50,000 (c a. 345) Rm 50,000 (c a. 345) 200 (93.3) HP, ao=25.04 HP, ao=25.06 Control Atm Rm Auto 225 (107.2) A A Notes: (1) Synthesis Mixture A - Si/Al = 0.98/1 (2) Synthesis Mixture B - Si/Al = 0.87/1 The runs conducted at 15,000 and 30,000 psig did not result in significant quantities of a Type X zeolite being produced.Although Runs 11 and 13, at 40,000 psig, did result in appreciable amounts of X Type zeolites being formed, Type A zeolite was also formed as well as some HP type zeolite. Runs 12 and 14 at 50,000 psig produced the aluminum-rich zeolite HP with no Type A zeolite being present. The lattice constant for the zeolite obtained with Mixture A in Runs 12 and 14 was the same as that obtained in Run 3 where the synthesis mixture had a ratio of 0.94/1. The higher aluminum content of synthesis mixture B gave an increase in lattice constant in Runs 12 and 14.

Example V A number of runs were made to study the effect of the silicon to aluminum ratio. The atom ratio was varied from 0.32/1 to 1.14/1. In Runs 23 and 24 the desired ratio was obtained by additions of sodium orthosilicate. In each run the aging was conducted at 50,000 psig (ca. 345 MPa) and room temperature for 20 hours while the hydrothermal step was conducted at 50,000 psig (ca. 345 MPa) at 2000F (93.3"C) for six hours. A control was run on each synthesis mixture wherein the aging was conducted at atmospheric pressure and the hydrothermal synthesis at autogenous pressures and 225OF (107.2"C). The product obtained from each high pressure run and control was identified for zeolite type by X-ray.

The results are presented in Table IV below: TABLE IV EFFECT OF CHANGES IN Al/Si RATIO OF SYNTHESIS MIXTURES Test Conditions: Aging-50,000 psig (ca. 345 MPa), Rm, Temp, 20 Hrs Synthesis-50,000 psig (ca. 345 MPa), 200OF (93.3"C) Control Aging-Atm Press, Synthesis-Autogenous Pressure, 225OF (107.2"C) Product Identification (X ray) Run No.Preparation Si/Al Atomic Ratio Zeolite Type 15 Pressure 0.98/1 HP, a0 = 25.04 t 0.01 Control 0.98/1 A 16 Pressure 0.87/1 HP, a0 = 25.07 t 0.01 Control 0.87/1 A 17 Pressure 0.87/1 HP, a0 = 25.06 t 0.01 Control 0.87/1 A 18 Pressure 0.98/1 HP, a0 = 25.04 t 0.01 Control 0.98/1 A Zeolite Type Run No. Preparation Si/Al Ratio Product X ray Identification 19 Pressure 0.56/1 HP to A, a0 = 25.07 t 0.01 Control 0.56/1 A 20 Pressure 0.32/1 HP to A Poor Quality Control 0.32/1 A 21 Pressure 1.49/1 Weak X Control 1.49/1 X, a0 = 24.87 22 Pressure 1.16/1 X, a0 = 24.99 + 0.01 Control 1.16/1 80% x, 20%A 23 Pressure 1.05/1 Very weak X Control 1.05/1 Weak X, Phillipsite 24 Pressure 1.14/1 Good X, a0 = 24.87 + 0.01 Control 1.14/1 Mod Weak X; St'd X Zeolite products were obtained in all cases but in some runs the yields were very poor.

There was no significant increase in the lattice constant for the zeolites where the silicon to aluminum mole ratio was below 0.87 to 1. However, there was a consistent change in lattice constant below this ratio extending into the silicon rich mixes which supports the conclusion of aluminum richness in the zeolites from the high aluminum mixes: Example VI A sample of the high aluminum zeolite (zeolite HP) prepared by the process of this invention and having a lattice constant of 25.06 t 0.01 (a portion of the material prepared in Run No. 7) was subjected to absorption tests together with a standard sample of zeolite X obtained from the Linde Company. Adsorptions of these two zeolites were determined and compared using a dual column chromatography.Slurries of the two zeolites were absorbed on Chromasorb P to give a 1:3 ratio of zeolite to packing in the two columns. A flow of helium was passed through each column while it was heated to an elevated temperature.

Then a quantity of an adsorbable material was introduced into the helium and the adsorption characteristics of each of the zeolites studied. The results obtained are presented in Table IV below.

The general adsorption characteristics of the zeolite HP and the zeolite X appear to be about the same with the major diference lying in the ease of desorption. The zeolite HP desorbed more quickly with the desorption peaks visibly demonstrating less tailing, i.e., a cleaner desorption. The exclusion by both sieves of perfluoro tributyl amine indicates that the pore openings are larger than 10 A., since this material is a standard one for measuring maximum pore openings of this size.

TABLE V Absorption Data - High Pressure Zeolite Column I - Zeolite HP Column II - Zeolite X Compound Temp C Behavior Time Behavior Time In Flow of He Desorb Peak 10 Min Benzene 350 Desorb Peak 10 Min Desorb Peak 25 Min Decahydronaphthalene 350 Desorb Peak 24 Min Desorb Peak 50 Min Diphenylmethane 350 Not Desorb 26 Not Desorb 26 Triisopropylbenzene 300 Not Desorb 24 Not Desorb 24 350 Not Desorb 16 Not Desorb 20 (C4F9)3N @ 350 Desorb with Air Desorb with Air Peak Peak 350 Desorb with Air Desorb with Air Peak Peak Example VII The ion exchange characteristics of Zeolite HP were studied and compared with the ion exchange properties of a standard zeolite X using the same concentration of exchange solutions and the same number of exchanges.The properties of the two zeolites were as follows: TABLE VI Zeolite Properties Zeolite HP Zeolite X Lattice Constant, a0 25.06 t 0.01A 24.95 + 0.04 Si/Al Ratio, X ray 0.92/1 1.09/1 Si/Al Ratio, Chem 0.96/1 1.12/1 Each zeolite was exchanged using calcium potassium and lanthanum salts. Each was compared for degree of exchange.and correspondence of the X ray patterns of the exchanged materials to X-ray pattern standards.

The calcium exchange utilized calcium formate as the exchange salt. Twenty five grams of the air equilibrated zeolites were treated with 200 ml of a 1.0 normal solution of the salt for 30 minutes at 1600F for each exchange. A total of five exchanges was carried out. The zeolites were washed with 500 ml of distilled water between exchanges and with 1000 ml after the final exchange. Finally the samples were washed with 100 ml of acetone and air dried.

X-ray patterns of the products corresponded with that of a known Ca X zeolite except for small line shifts. Chemical analyses revealed that the zeolite HP was exchanged to greater extent than the zeolite X. These data are: %Na20 toCaO %SiO2 %Al2O3 Si/Al Ratio Zeolite HP 0.1 18.5 41.4 37.6 0.93 Zeolite X 1.2 15.5 46.2 32.4 1.20 A second experiment using only three exchanges reduced the sodium (as sodium oxide) in the zeolite HP to 0.9 weight per cent, a degree of exchange superior to the zeolite X under the first set of exchange conditions.

The potassium exchange was conducted in a similar manner using the chloride as the exchange salt. The results of these exchanges are as follows: %Na2O %K2O Si/Al Ratio Zeolite HP 1.03 25.7 0.96 Zeolite X 1.3 21.6 1.15 Again the zeolite HP shows a higher degree of exchange for equivalent treatment.

The lanthanum exchange used the nitrate as the exchange salt and followed the exchange procedures recommended in Linde Molecular Sieves Technical Bulletin "Ion Exchange and Metal Loading Procedures". As with the previous two experiments there was a significant difference in depth of exchange for a given set of conditions.

Analytical data for the lanthanum exchanged zeolites are: %Na2O %La203 Si/Al Ratio Zeolite HP 0.5 32.2 0.98 Zeolite X 1.1 28.4 1.18 Zeolite HP differs from zeolite X in increased ease of ion exchange and depth of exchange.

Example VIII A number of synthesis mixes having various atom ratios of Al to Si were prepared in a manner similar to that of Example II to develop a phase diagram to show the distribution of zeolite species in the Na7O-SiO2- Awl703 system where the hydrothermal treatment to effect crystallization was conducted at 50,000 psig (ca. 345 MPa) and 200OF (93.3"C). The resultant species included conventional X, zeolite HP as well as other known species obtained in prior art synthesis processes. The phase diagram obtained is presented in Figure 1. The data points are indicated by circles on this triangular plot. Lattice constant measurements for some of the zeolites were obtained and are noted in Figure 1 adjacent to the data points.

Figure 1 bears a striking resemblance to the zeolite phase diagram presented in Figure 2 which shows the phase diagram for zeolites obtained when the crystallization is performed at atmospheric or autogenous pressure and 200OF (93.3"C). The most significant difference is that there is no zeolite A species in the phase diagram of Figure 1 where the high pressure crystallization of the invention is employed. It appears that the area occupied by zeolite A in Figure 2, appears as zeolite HP in Figure 1. The line between zeolite X and zeolite HP in Figure 1 is dotted since its exact location has not been determined. Thus the data point evidencing a lattice constant of 24.96 A is identified as zeolite X indicating that the transition line may well be located below this point.

WHAT WE CLAIM IS: 1. A process for preparing a synthetic zeolite which comprises maintaining an aqueous mixture of sodium alumino-silicate having a silicon to aluminum atomic ratio of from 0.25 to 1.0, at a pressure above 20,000 psig (ca. 138 MPa) and a temperature in the range from 150 to 3500F (65.6-176.7"C) for at least three hours.

2. A process as claimed in Claim 1 wherein the pressure is from 40,000 psig (ca. 276 MPa) to 80,000 psig (ca. 552 MPa).

3. A process as claimed in Claim 1 wherein the time is from 4 to 24 hours.

4. A process as claimed in any preceding Claim wherein the aqueous mixture is aged for at least 8 hours at a pressure above 20,000 psig (ca. 138 MPa) and a temperature not above 100OF (37.8"C), before the temperature is increased to the range from 150 to 350OF.

5. A process as claimed in Claim 4 wherein the aqueous mixture is aged at a pressure from 40,000 psig (ca. 276 MPa) to 80,000 psig (ca. 552 MPa).

6. A process as claimed in Claim 4 or 5 wherein the aqueous mixture is aged for from 24 to 72 hours.

7. Synthetic zeolite prepared by a method as claimed in any preceding Claim.

8. A synthetic crystalline zeolite, having a lattice constant of at least 25.02 , and an atom ratio of Si to Al in the unit cell below 1.0.

9. A synthetic crystalline zeolite as claimed in Claim 8 wherein the lattice constant is from 25.02 to 25.10 A.

10. A hydrocarbon conversion process which comprises contacting a hydrocarbon charge under catalytic cracking conditions with a zeolite as claimed in any of claims 7 to 9.

11. A process as claimed in Claim 1 substantially as hereinbefore described with reference to any of Examples I, II, IV, V and VIII.

12. A synthetic crystalline zeolite as claimed in Claim 8 substantially as hereinbefore described with reference to any of Examples I, II, IV, Vand VIII.

13. A hydrocarbon conversion process as claimed in Claim 10 substantially as hereinbefore described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. resultant species included conventional X, zeolite HP as well as other known species obtained in prior art synthesis processes. The phase diagram obtained is presented in Figure 1. The data points are indicated by circles on this triangular plot. Lattice constant measurements for some of the zeolites were obtained and are noted in Figure 1 adjacent to the data points. Figure 1 bears a striking resemblance to the zeolite phase diagram presented in Figure 2 which shows the phase diagram for zeolites obtained when the crystallization is performed at atmospheric or autogenous pressure and 200OF (93.3"C). The most significant difference is that there is no zeolite A species in the phase diagram of Figure 1 where the high pressure crystallization of the invention is employed. It appears that the area occupied by zeolite A in Figure 2, appears as zeolite HP in Figure 1. The line between zeolite X and zeolite HP in Figure 1 is dotted since its exact location has not been determined. Thus the data point evidencing a lattice constant of 24.96 A is identified as zeolite X indicating that the transition line may well be located below this point. WHAT WE CLAIM IS:

1. A process for preparing a synthetic zeolite which comprises maintaining an aqueous mixture of sodium alumino-silicate having a silicon to aluminum atomic ratio of from 0.25 to 1.0, at a pressure above 20,000 psig (ca. 138 MPa) and a temperature in the range from 150 to 3500F (65.6-176.7"C) for at least three hours.

2. A process as claimed in Claim 1 wherein the pressure is from 40,000 psig (ca. 276 MPa) to 80,000 psig (ca. 552 MPa).

3. A process as claimed in Claim 1 wherein the time is from 4 to 24 hours.

4. A process as claimed in any preceding Claim wherein the aqueous mixture is aged for at least 8 hours at a pressure above 20,000 psig (ca. 138 MPa) and a temperature not above 100OF (37.8"C), before the temperature is increased to the range from 150 to 350OF.

5. A process as claimed in Claim 4 wherein the aqueous mixture is aged at a pressure from 40,000 psig (ca. 276 MPa) to 80,000 psig (ca. 552 MPa).

6. A process as claimed in Claim 4 or 5 wherein the aqueous mixture is aged for from 24 to 72 hours.

7. Synthetic zeolite prepared by a method as claimed in any preceding Claim.

8. A synthetic crystalline zeolite, having a lattice constant of at least 25.02 , and an atom ratio of Si to Al in the unit cell below 1.0.

9. A synthetic crystalline zeolite as claimed in Claim 8 wherein the lattice constant is from 25.02 to 25.10 A.

10. A hydrocarbon conversion process which comprises contacting a hydrocarbon charge under catalytic cracking conditions with a zeolite as claimed in any of claims 7 to 9.

11. A process as claimed in Claim 1 substantially as hereinbefore described with reference to any of Examples I, II, IV, V and VIII.

12. A synthetic crystalline zeolite as claimed in Claim 8 substantially as hereinbefore described with reference to any of Examples I, II, IV, Vand VIII.

13. A hydrocarbon conversion process as claimed in Claim 10 substantially as hereinbefore described.