Title of Invention	A METHOD FOR THE MANUFACTURE OF FAUJASITE
Abstract	The invention relates to the manufacture of LSX faujasite. The industrial manufacture of LSX faujasite is improved by carrying out the aging and the crystallization of the gel with stirring with an Archimedean screw stirrer. In particular, the duration of the aging is shortened considerably without affecting the crystallinity of the final product.

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The present invention relates to the manufacture f zeolites, more specifically faujasites with a low silica ontent. The term faujasites is used here to refer to a rroup of mineral species characterized by their crystallographic topographic structure, an excellent account of which can be found in the work by Donald W. Breck "Zeolite mlecular Sieves", published by John Wiley and Sons, 1974 -op. 92 ff. The so-called Lowenstein rules requires that they lave an Si/Al ratio which is higher than or at least equal to L. Customarily the following distinctions are made: . X faujasites with Si/Al . y faujasites with Si/Al >1.5. The classical X faujasites have an Si/Al ratio 12. The physical characteristics of the faujasites (exchange capacity, nitrogen adsorption, etc.) evolve as a Exinction of the Si/Al ratio. The present invention relates to faujasites with an Si/Al ratio equal to 1, which are called the LSX faujasites (in English low silica X faujasites). Of all the faujasites which can be considered, these are the ones which possess the maximum possible number of tetrahedral aluminum ions per crystalline unit, and as a result, they potentially have the highest number of adsorption sites for a great variety of molecules such as CO2 N2 etc. Within the present specification, the term LSX faujasite is to be uderstood to indicate a zeolitic species whose Si/Al ratio is measured as 1 ± 0.05, where values below 1 reflect the analytical uncertainties in the measurement of this ratio, and higher values reflect either the same analytical uncertainty or a tolerable discrepancy in the purity of the product. The synthesis of faujasites comprises two distinct steps; the first (aging) in which precursor seed crystals appear, and the second (crystallization) is a phase of growth of crystals from these seeds. The course of these steps depends on numerous physical and chemical factors which are not entirely understood. The conditions of the medi\im determine the type of seeds formed and consequently the type of zeolite. It is known that the difficulties of the synthesis of faujasites increase when their Si/Al ratio decreases, and that traditional methods fail for the preparation on a large scale of faujasites with an Si/Al ratio of 1. In particular, from a pure sodium medium the zeolite NaA is obtained, and it is necessary to introduce a certain quantity of potassium ions to synthesize the faujasite structure; it is recognized that the faujasite structure can be obtained for Na/Na + K ratios in the synthesis gel of 0.7-0.8^. The synthesis of such zeolites with low Si/Al ratio has been described in the French Patent No. 2,357,482. Very generally, the zeolites are prepared by crystallization of silicoaluminiu aqueous compositions formed by a mixture of solutions of alkaline aluminates and sodium silicate at a temperature between room temperature and a temperature below their boiling point. With regard to the Stirring conditions in these media, one is torn between two contradictory imperatives. Stirring means favouring exchanges of matter and heat, and preventing the syneresis of the forming crystals. The other option is not to stir; in fact it has been observed in the synthesis of faujasites that stirring systematically leads to certain disturbances, particularly a defect in the crystallinity of the zeolite, which was reported by R.M. Barrer (see Hydrothermal Chemistry of Zeolites, Academic Press, 1982, p. 171). It can also be observed, independently of insufficiency of crystallinity, that parasitic phases appear; these phases form as a result of destruction due to stirring of certain unstable seeds. It is thought that, in these cases, local shearing can promote the appearance of certain seeds and the disappearance of certain others (see, for example, D.E.W. Vaughan, Chem. Eng. Prog., 48(2), 1988, pp. 25-31). In practice, for the industrial manufacture of LSX, inspiration is obtained from the teaching of G.H. Kuhl (Zeolites, September, 1987, vol. 7, pp. 451-457) and one omits stirring, resigning oneself to longer aging and crystallization durations and thus to unsatisfactory industrial profitability. It has now surprisingly been found that the conditions of the manufacture of LSX faujasite can be considerably improved by the use, as stirring means, of an Archimedean screw, a device which is well-known to persons skilled in the art, an example of which is given in the entry in Ullmann's Encyclopedia of Industrial Chemistry, VCH 1988, vol. B2, pp. 25-5. The present invention accordingly provides a method for the manufacture of a faujasite of the LSX type using an Archimedean screw stirrer for stirring the ingredients in gel form. The method according to the invention is suitable to be carried out industrially. An Archimedean screw stirring device suitable for use in the method of the present invention is illustrated in the accompanying drawing. Referring to the drawing, there is shown a stirring device, whose moving part comprises a vertical axle (A) aroxind which a helicoidal blade (H) with pitch (s) is wound and,'whose fixed part comprises a cylindrical wall (P) which is open at its two ends forming a guide tube surrounding the envelope of the blade and having a diameter (Dp) . The helicoidal blade is circiimscribed by a cylinder generated by revolution of the blade and having a diameter (D) . The Archimedean screw stirrer is housed in a reactor (R) with diameter (Dr) and height (hr). The guide tube is entirely immersed in the gel of starting ingredients in the reactor (R) . To allow circulation of fluxes in the reactor, the height of the guide tube (hp) is less than the filling height of the reactor. It is preferred that these two heights are in a ratio of less than 0.95. The guide tube itself is shorter than the blade so that the latter, in its rotation, is able to entrain the gel from the top to the bottom of the reactor. For its correct operation, an apparatus design is recommended in which the following relations are approximately observed: 0.3 Dr s Dp 0.3DrsD s - D The stirring speeds are generally slow; they may vary from a few rpm to several tens of rpm. They are selected according to the usual criteria used by persons skilled in the art (rapidity of the exchanges of heat and matter, limitation of the decanting effect, rheology of the medium) and suitably so that the device does not impose on the gel an average shearing in the tank of more than 25 sec-1. With such a device, one advantageously proceeds to the synthesis of LSX faujasite by working with gels whose initial alumina, silica, NaOH and potash composition is such that one has, in mole ratios: Na2O/(Na2O + K2O) : 0.7-0.8 H2O/Al2O3: 91-130 SiO2/Al2O3 1.8-2,2 (Na2O + K2O)/Al2O3: 5.5-8. In this manner the overall duration of the industrial manufacturing process can be considerably reduced, with aging processes at approximately 30-60°C occurring over durations of 10-40 hours, and crystallizations at 50-100°C taking 1-5 hours. Various combinations of these steps of aging and crystallization are possible, and they are part of the present invention. Accordingly the present invention provides a method for the manufacture of a faujasite of the LSX type which method comprises aging and crystallization of a gel whose mole composition meets the following conditions: Na2O/(Na2O + K2O): 0.7 ~ 0.8 H2O/Al2O3: 91 - 130 SiO2/Al2O3:1.8-2.2 (NaaO + K2O) /AI2O3: 5.5 - 8, the gel during its aging and crystallization being stirred by means of an Archimedean screw stirrer. The invention is further illustrated with reference to the following Examples. Example 1 -Synthesis of the LSX zeolite on a laboratory scale Preparation of the gel: Solution of sodium and potassium aluminate: demineralized water: 3 50 g 50% NaOH solution: 638 g 50% potash solution: 340 g This solution is heated at 115°C, and the following is added: hydrated alumina (gibbsite type) 146 g After dissolution and cooling, the water lost to evaporation is added. Solution of sodium silicate: demineralized water: 880 g sodium silicate; 440 g In a 2.5-L reactor, the two solutions are mixed by means of a deflocculating turbine at 2000 rpm for 5 min to obtain a homogeneous gel. This composition corresponds to the following stoichiometry: 4.87 Na2O: 1.63 K22O: 2 SiO2: 1 Al2O3: 130 H2O After mixing the reagents, NaOH silicate and sodio-potassic aluminate, the gel is allowed to mature for 20 h at 50oC, and then crystallization is carried out for 4h at 95oC, the aging and the crystallization being carried out under different stirring conditions as indicated in Table 1 below. The results obtained are expressed in crystallinity values measured by the toluene adsorption capacity at 25°C at a partial pressure of 0.5, expressed with respect to a faujasite having a toluene adsorption capacity equal to 24%, used as reference for a 100% crystallinity. / It is observed that: the passage of the synthesis from the static medium to a dynamic medium causes a loss of crystallinity depending on the type of stirrer. The use of the Archimedean screw as a mixing tool allows the preservation of an optimal crystallinity, while at the same time ensuring an effective transfer of heat and matter; the average anhydrous composition of the crystals is: (0.75-0.77) Na2O/(0.23-0.25) K2O/(1. 9-2 .1) SiO2/1 Al2O3 The composition does not differ appreciably depending on whether the LSX is synthesized in a dynamic reactor or in a static medium; the average size of the crystals and the granulometric distribution determined by scanning electron microscopy (SEM) are not different (median diameter approximately 6μm) . Example 1 bis - Alteration of the toluene index with increase in the stirring speed The conditions of the preceding example are reproduced, except that the gel is subjected to permanent stirring generated by an Archimedean screw stirrer for the aging period rotating at different speeds and generating the corresponding shearing rates reported in Table 2 below. The 5 final product is tested for its toluene adsorption capacity at a partial pressure of 0.5 and at 25°C. These results indicate the regular degradation of the LSX with the increase in the stirring speed during the aging. Example 2 - Synthesis of the LSX zeolite on an industrial scale Preparation of the reagents: the reagents are prepared as in Example 1, but using kilogram amounts rather than gram amounts. The solution of aluminate is poured into a 3 m-3 reactor, and then, while mixing, the solution of silicate is added, during which operation the mixture first remains clear (for approximately 2 min) and then it starts to gel. The stirring is continued for an additional 5 min. The conditions of aging and crystallization and the results obtained are summarized in Table 3 below. It can be seen that: the use of a classical stirrer (of the "plane propeller" type) does not allow a product with good crystallinity to be obtained; the industrial operation in the static mode is much slower than on the laboratory scale; the gel undergoes considerable syneresis; which prevents close contact between the reagents and can explain the increase in the duration of the aging; the Archimedean screw allows the preservation of the duration of the synthesis obtained in the laboratory while producing LSX with comparable quality (granulometry, chemical composition and crystallinity). WE CLAIM: 1. A method for the manufacture of a faujasite of the LSX type which method comprises aging and crystallization of a gel whose mole composition meets the following conditions; Na2O/(Na2O + K2O): 0.7 - 0.8 H2O/Al2O3: 91 -130 SiO2/Al203: 1.8-2.2 (Na2O + K2O) /AI2O3: 5.5 - 8, the gel during its aging and crystallization being stirred by means of an Archimedean screw stirrer. 2. The method according to Claim 1, in which the shearing generated in the gel by the Archimedean screw is less than 25 sec-1 3. The method according to Claim 1 or 2 in which the aging takes from 10-40 hours at temperatures of 30-60°C and the crystallization from 1 -5 hours at temperatures of 50 - 100°C. 4. A method for the manufacture of a faujasite such as herein described and exemplified with reference to accompanying drawings.

Documents:

1558-mas-1997 abstract-granded.pdf

1558-mas-1997 claims-granded.pdf

1558-mas-1997 description (complete)-granded.pdf

1558-mas-1997 drawings-granded.pdf

1558-mas-1997- abstract.pdf

1558-mas-1997- claims.pdf

1558-mas-1997- correspondence others.pdf

1558-mas-1997- correspondence po.pdf

1558-mas-1997- description complete.pdf

1558-mas-1997- drawings.pdf

1558-mas-1997- form 1.pdf

1558-mas-1997- form 26.pdf

1558-mas-1997- form 3.pdf

1558-mas-1997- form 4.pdf