BE599134A - - Google Patents

Description

       

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  Process for preparing crystalline zeolites.



   The present invention relates to a process for the synthesis of crystalline aluminosilicates having a zeolitic structure of a rigid three-dimensional network, a size of uniform pores and well-defined intra-crystalline dimensions, so that only molecules of one shape and size. A suitable size can be transported in any direction between the outer phase and the interior of the crystalline zeolite. In other words, the invention relates to an improved process for preparing a crystalline aluminosilicate zeolite of molecular sieve type.

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  In one aspect of the invention, this is aimed at a continuous process for the preparation of solid aluminosilicates of the molecular sieve type consisting of porous crystals in which the pores of the crystals have uniform dimensions and in particular a dimension of about 4 A when 'it is sodium aluminosilicate.



   Molecular sieve type aluminosilicates are known to be essentially dehydrated forms of crystalline zeolites containing varying amounts of sodium, calcium and aluminum with or without other metals.



  All or part of the sodium or calcium ions normally contained in the structure of the molecular sieve can be exchanged with a number of other ions. The ions of sodium, calcium, metals introduced by exchange of these, silicon, aluminum, and oxygen contained in these zeolites are arranged in the form of an aluminosilicate according to a :: loti: crystalline defined and uniform. The building contains a large number of small cavities, connected by a number of even smaller orifices, cavities and orifices which are strictly uniform in size.



   Molecular sieves of the A series and molecular sieves of the X series are currently commercially available. The A series molecular sieves comprise materials which meet the following composition expressed as oxides: 1.0 + 0.2 M2O : Al2O3: 1.85 + 0.5 SiO2: Y H2O n in which M is a metal of groups I or II or a transition metal from the periodic table, hydrogen or the ammonium radical, n represents the valence of M and X is any number up to about 6. A zeolite

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 synthetic known as molecular sieve 4A is a crystalline sodium aluminosilicate having an effective pore size of about 4 A.

   In hydrated form, this material is chemically characterized by the formula
 EMI3.1
 of unit cell: Na12 (Al02) 12 (Si02) 12, 27 i0. The synthetic zeolite known as molecular talais 5A is a crystalline aluminosilicate having channels
 EMI3.2
 of about 5 A in diameter and in which s / sodium ions or more, out of the 12 sodium ions of the last formula above, are replaced by calcium, of course at the rate of one calcium ion for 2 sodium ions. A crystalline sodium aluminosilicate having pores or channels of about 13 A in diameter is also commercially available under the name 13X Molecular Garnis.

   The letter X
 EMI3.3
 serves to distinguish the intra-atosic structure Ge ce Lcolitïse from that of cries t; .; ::: '. , :: "E: n tiO # '18S ci-aesrus. Iors of its Li-on, -e pro4..¯ ¯ 3X cori-nt cb:.' Ea e r6; onc the cell forzrule = nizail.e '"(: 10) 5 (i, J) 106 ,,' ::. the formula --ellu'-, 00 00 l06 '\ ""' -: v, The synthetic zc-olith known as lt nor dc té, .Üs.:. oJ.écu.lé :. ire 10X is a criszaiîi alurài = 1osilicazE having an effective pore diameter of e: -. 7 about 10 j. "e1 :. in which a substantial increase in sodium ions of; 3i-odui7c 13X have been replaced by calcium.



   All of the molecular sieves listed above have heretofore been prepared in these batch type operations. A synthesis of the A-series molecular sieves using a method of this type is described in US Pat. No. 2,882,243, April 21, 1959.



  A synthesis of the X series molecular sieves is described
 EMI3.4
 in U.S. Patent No. 2,882,244, April 21, 1959.

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   These previously known methods are mandatory. ment carried out in discontinuous operations. This is not sure. taking into account the complex structure of crystals, which usually require a relatively long time to form from the disordered components originally distributed at random throughout the solid phase and the liquid phase of the crystal. reaction mixture. It will be understood that the search for a process for the continuous preparation of molecular sieves, leading to an industrial operation easier to monitor and to a greatly increased production volume, constitutes an interesting objective.



   The main subject of the invention is a process making it possible to increase the speed of production of molecular sieves based on crystalline aluminosilicates, it also comprises a continuous process for the preparation of molecular sieves applied more particularly to molecular sieves of the A series and in particular to molecular sieve 4A.



   These and other objects which will become apparent hereafter are achieved in accordance with the invention! which is based on a new process for increasing the speed of production of the A series molecular sieves, this process allows to prepare the A series molecular sieves continuously It was surprisingly found that the technique used in the process of the invention was not applicable to the synthesis of the X series molecular sieves. The reason for this difference is not fully understood but it appears to be due to a difference in the mechanism of crystal growth. for both types of molecular sieves.

   It has been established, in accordance with the invention;

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 that the introduction of a certain amount of a series A molecular sieve into the initial reaction mixture used for the preparation of this type of molecular sieve unexpectedly helped to promote and increase the rate of crystallization of the molecular sieve product. In particular it has been found that the introduction of a certain amount of crystalline sodium aluminosilicate having a uniform pore structure consisting of pores of about 4 A in diameter, i.e. 4A molecular sieve , to the reaction mixture used for the preparation of this molecular sieve caused an unexpected increase in the rate of crystallization of the desired molecular sieve.

   Since the A-series molecular sieves are originally prepared as the sodium salt, the above process can be used to advantage to increase the rate of production of the A-series molecular sieves in general.



  The strong increase in crystallization rate thus obtained makes it possible to continuously prepare the 4A molecular sieve and the other molecular sieves of the A series.



   In one embodiment, the invention relates to an improved process for preparing a molecular sieve based on crystalline aluminosilicate characterized by pores of uniform dimensions, and corresponding to the formula: 1.0 + 0.2 M2O: Al2O3: 1.85 # 0.5 SiO2:

   Y H2O n in which M represents at least one member of the group consisting of hydrogen, the ammonium radical, the metals of groups I and II of the periodic table and the metals

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 transition of this classification, n represents the val- uence of M, and Y can be any number up to 6, from a reaction mixture containing sodium oxide, silica, Illumine and water, a mixture whose composition, expressed in moles of oxides, meets the following conditions:
The Na2O / SiO2 ratio is between 0.8 and 3.0
The SiO2 / Al2O3 ratio is between 0.5 and 2.5
The H2O / Na2O ratio is between 35 and 200.



   This mixture is maintained at a temperature between about 20 and about 175 ° C. until crystals of sodium aluminosilicate having the composition indicated above are formed, then these crystals are separated from the mother liquor and at least part of their sodium ions is exchanged with ions of M, this process being characterized by the introduction into the reaction mixture, before the end of crystallization, of a sufficient quantity, in general at: Joins about 1 % of the final weight of sodium aluminosilicate crystals obtained, to increase the rate of crystallization of said mixture.



   In another embodiment, the invention comprises a continuous process for synthesizing a solid sodium aluminosilicate molecular sieve consisting of porous crystals in which the pores of the crystals are uniform in size and in fact one size. of pore size of about 4 A, a process according to which a reaction mixture containing sodium oxide, silica, alumina and water is continuously prepared, having a composition, in moles of oxides , which meets the following requirements:

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The Na2O / SiO2 ratio is between 0.8 and 3.0.



   The SiO2 / Al2O3 ratio is between 0.5 and 2.5.



   The H2O / Na2O ratio is between 35 and 200.



   The mixture is maintained at a temperature between 20 and 175 ° C, until crystals of the above composition form; a portion of the crystalline slurry obtained is continuously withdrawn, the crystalline slurry withdrawn is continuously introduced into fresh reaction mixture, in an amount sufficient to increase the rate of crystallization; and the crystals are continuously separated from the remainder of the crystalline slurry.



   In another embodiment, the intention is to take a continuous process of syrthesis of a solid calcium aluminosilicate based molecular sieve consisting of porous crystals in which the pores have a uniform size.
0 of about 5 A, by continuous exchange 0 'at least about 40% of the sodium ions of the sodium crystalline aluminosilicate, obtained as described above, with calcium ions.



   A series molecular sieves basically consist of a three-dimensional edifice of silica and alumina tetrahedra. Silicon and aluminum ions share oxygen atoms in such a way that the ratio oxygen atoms to the total number of aluminum and silicon atoms is equal to 2. The electro- valence of the aluminum-containing tetrahedron is balanced by the inclusion in the crystal of a cation, for example a an alkali metal cation or an alkaline earth metal cation. This balance can be expressed by a formula in which the ratio of Al2 to the number of various cations, such as Ca, Sr, Mg, Na2, K2 or Li2 is equal to unity. A

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 cation can be exchanged in whole or in part for another cation by these ion exchange techniques.



   Such molecular sieves of the A series are characterized by a composition, expressed as oxides, corresponding to the following formula:
 EMI8.1
 1.0 + 0.2 il20: i120. 1.85 + 0.5 SiO.,: Y H20 n in which M is hydrogen, the ammonium radical, a metal from group I or from group II of the periodic table such as sodium, potassium, silver , cadmium, lithium, mercury, calcium, magnesium and strontium or a transition metal of the periodic classification such as nickel, cobalt, platinum, chromium, iron, scandium, titanium, vanadium,
 EMI8.2
 manganese, vttrium, zirconiu.::::L, niobium, -nolyt- dene, ruthenium, 'e rhodium, iJallé :: 8iuJl, -Hafniu, tçlL21e, tungsîcne, rhJnlUT! 1'oe: iu .. or iriciiLt: 11;

   n represents the valence of, <1, and Y can be any number up to about 6. Such olecular tees are originally prepared in the sodium form of the crystals. In general, the preparation process consists in heating, in aqueous solution, an appropriate mixture of oxides, or of materials whose chemical composition can be represented in their entirety as a mixture of the oxides Na2O '
 EMI8.3
 Al 20 3-Y 8102 'and Ii20. The product which crystallizes in the hot mixture is separated therefrom and washed with water until the excess alkali has been removed. After heating until dehydration, the product is ready for use.

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   Reagents suitable for the preparation of Series A sodium zeolites include silica sols, silica gels, silicic acid or sodium silicate as sources of silica. Alumina can be obtained from activated alumina, gamma alumina, alpha alumina, aluminum trihydrate or sodium aluminate.



  As the source of sodium ion, sodium hydroxide will preferably be used because it also helps to regulate the pH. The reaction solution has a composition, expressed as a mixture of oxides, in the range of 0.5 to 2.5 for the SiO2 / Al2O3 ratio, 0.8 to 3.0 for the NaO / SiO ratio and 35 to 200 for the H2O / Na2O ratio.



  The ratio values specified above and in particular the value of the SiO / Al2O3 ratio seem to be critical factors of the process of the invention because a composition expressed as a mixture of oxides and dispensing with the following conditions: -. SiO2 / Al2O3 ratio is between 3 and 5, the Na2O / SiO2 ratio is between 1.2 and 1.5, and the H2O ratio is between 35 and 200 yes is of a type normally used in the preparation of molecular sieves of the X-series, is not sensitive to the seeding technique used in the invention with success on reaction mixtures meeting the compositions specified.



   The reaction mixture of specified composition is placed in a suitable reactor and the reactants are then heated for a sufficient time. The reaction time must be sufficient to allow crystallization of the amorphous gel which initially forms. A suitable method of preparation is to first prepare a solution.

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 tion of sodium aluminate and sodium hydroxide and then adding, with rapid stirring, an aqueous solution of sodium silicate.

   Although satisfactory crystallizations can be brought about at temperatures ranging from 20 to 175 ° C., at pressures equal to or greater than atmospheric pressure and corresponding to the vapor pressure in equilibrium with the mixture at the reaction temperature, it is generally carried out successfully crystallization at a temperature of about 100 C.



  For temperatures between 20 and 175 ° C, an increase in temperature causes the reaction rate to increase and therefore the reaction time to decrease. Once the formation of the zeolite crystals is complete the crystals retain their physical structure, and it is not necessary to maintain the reaction temperature high in order to obtain maximum yield of crystals.



   After formation, the crystalline zeolite is separated from the mother liquor, usually by filtration or centrifugation. The crystal mass is then washed, preferably with salt-free water, on the filter, until the wash water in equilibrium with the zeolite reaches a pH of 9 to 12. It is then dried. crystals at a temperature between about 25 and 150 C.



  Substantially complete dehydration is achieved by calcination in air at a temperature of 350 ° C or higher.



  The use of temperatures substantially above about 525 ° C. should be avoided, since the elevated temperatures cause destruction of the physical structure and loss of sorption properties. If we want, we can

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 use pressures lower than atmospheric pressure, but it is preferred to dehydrate at atmospheric pressure. rendering dehydration, it is advantageous to sweep the water vapor formed in the heating zone with a stream of air or another gas.



   In accordance with the invention, it has been found that the presence in the reaction mixture for the formation of molecular sieve 4A of a certain amount of a crystalline molecular sieve of the series A previously formed, dramatically improved the crystallization rate of the forming 4A molecular sieve. The series A molecular sieve present in the reaction mixture may be a 4A sieve or a 4A sieve which has undergone prior cation exchange with hydrogen, ammonium, a Group I or II metal or a transition metal. of the periodic table as indicated above.

   For example, the 5A tolecular sieve can be used. It was found that the mass of this sieve crystal 4A produced per unit time increased as the amount of crystal product present in the reaction mixture was increased. It was further found that the specific surface area of the crystalline product was directly proportional to its mass and that the crystal size of the 4A molecular sieve produced was constant and uniform.



   The crystalline molecular sieve introduced into the reaction mixture can be obtained from a number of origins, including molecular sieve previously prepared, dried and calcined, or crystals taken during growth, or

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 crystals that have stopped growing but are still contained in the mother liquor. A particularly advantageous method is to recycle a part of the reaction product obtained, containing the crystalline material, as seed crystals into the feed stream, without separating the crystalline solid from the aqueous phase. Indeed, it is not necessary that the seed crystal of the sieve 4A be isolated and dried before use.

   This latter observation makes possible a continuous process for the synthesis of 4A molecular sieves and hence a continuous process for the preparation of the other different molecular sieves of the A series.



   The amount of crystalline 4A or other A-series molecular sieve added to the reaction mixture can vary widely. The use of an amount as small as 1% by weight relative to the final weight of crystals produced is sufficient to seed and significantly decrease the time required to induce the transformation of the reaction slurry into crystals of the zeolizhe of the series. A. Although such small amounts have a real effect, the use of larger amounts, between 10 and 20% by weight, will significantly decrease the time required to transform the slurry of amorphous solids into the crystalline form. wanted.

   Accordingly, if it is desired to prepare crystalline zeolite A by a batch process, the finding that crystallization of this type of zeolite can be reproducibly induced by the addition of gel, as described herein. and that by operating in this way an advanced stage of crystallization is achieved

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 in a shorter time, constitutes a clear improvement of the batch type process.



   In the embodiment of the invention relating to a continuous operation using the seeding technique described above, the reproducible induction of recrystallization constitutes an essential characteristic. In this aspect of the invention relating to a continuous operation in which a portion of crystalline zeolite suspended in its mother liquor is recycled to the slurry reaction mixture, the quantity of recycled products may be sufficiently small so that after instantaneous mixing with the constituents forming the zeolite the content of the mixture of crystals introduced in this way is such that it represents 10% of the final crystalline product capable of forming from the mixture.

   However, it is advantageous and therefore preferable to add larger portions of the crystalline zeolite suspended in the mother liquor to the fresh crystallization components, generally amounts between 10 and 90% of the total crystalline product. final.



   The advantageous use of a mixture of crystalline zeolite suspended in its mother liquor to form fresh crystalline zeolite is based on the discovery of the highly unusual crystallization rate characteristics of the A-series zeolite. Specifically, the rate of crystallization of a new crystal, once a substantial amount of crystals already present in the reaction mixture has been shown to obey a law of growth in.

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 "population" best expressed by the following equation: log Cf =
Cj where Cf and Ci indicate the rate of crystallization in the slurry reaction mixture, or the rate of final and initial crystallization, respectively, in a time interval t.

   Cf and Ci are both expressed by the ratio: Weight ¯ of crystals in the unit volume of the slurry x 100 Weight of crystals plus the weight of residual crystallizable solids in the unit volume of the slurry
After mixing with fresh crystallization reagents, the crystallization rate is initially reduced in the reaction mixture to a value of i. This freshly formed mixture reaches, after a residence time of 1 in the reactor, a concentration Cf. k is a constant, the value of which depends on the temperature and on the sodium hydroxide concentration.



   Figure 1 of the accompanying drawing shows a suitable system for the continuous production of A series molecular sieves. In this figure, sodium silicate in aqueous solution is introduced into mixer 12 from vessel 10 through line 11. The solution mixed sodium aluminate-sodium hydroxide coming from the container 13 is also introduced into the mixer 12 through line 14. The two solutions undergo intimate mixing in the apparatus 12. After mixing, the product is carried through 15 to the reactor 16 in which crystallization of sodium alumhosilicate takes place. The product leaves the reactor through line 17.

   Part of the reaction mixture containing

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 the crystals are recycled to the reactor through lines 18, 19 and 20 to increase the rate of crystallization in the reactor. The stream of the reaction mixture which passes through line 17 is passed to filter 21 which separates the crystalline product from aqueous base.



  The latter, consisting of a sodium hydroxide-sodium aluminate filter, is withdrawn through line 22 and recycled to receptacle 13 through line 23. During or after this recycling, the recycled stream can be reinforced by adding aluminate. sodium and / or sodium hydroxide. The crystalline product obtained by the filter 18 can be washed on filter or led through 24 to a washing zone 25 in which the crystalline product is washed until it is. free from water soluble impurities. The washed product is then sent through line 26 to a drying zone 27 maintained at a temperature between about 25 and about 150 ° C.

   The product is sent after drying to a calcination zone 29 via a conduit 28 and it is subjected to substantially complete dehydration by heating to a temperature between approximately 350 and 525 C. The product coming from the calcination zone via the conduit 30 is 4A molecular sieve. As an alternative to the above process, and when it is desired to obtain 5A sieve or other A series molecular sieve, the crystalline sodium aluminosilicate from wash zone 25 is sent to a porous endless belt. 32 through a pipe 31. In the first part of its passage over the endless belt, the sodium aluminosilicate is sprayed with a suitable ion exchange solution.

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 in which, the ion replaces all or part of the sodium ions of the crystalline sodium aluminosilicate.

   This exchange solution is sent to the spray device 34 through line 33. After passing through the spraying zone, the product whose ion has been exchanged is transported by the porous endless belt through a zone. washing. In this area, water from line 35 is sprayed by device 36 in order to effectively wash the product until it is free of water soluble impurities. The spent exchange solution and the washing water are collected in the tank 37 and withdrawn through the line 38, however the washed aluminosilicate is sent from the endless belt to a drying zone 40 via a plane. incl. '39.

   After drying, the crystalline aluminosilicate is sent to a calcination zone 42 via line 41. After dehydration by calcination, the molecular sieve is withdrawn via line 43.,
In the operation described above, the sodium ions can be replaced. crystalline sodiuri aluminosilicate originally produced in whole or in part by other cations upon treatment with the exchange solution. These exchange ions include other monovalent or -bivalent cations such as lithium and magnesium, metal ions from the first group of the periodic table such as potassium and silver,

     metal ions of the second group such as calcium, zinc and strontium, transition ions such as --nickel, cobalt and other ions such as ammonium ion with which sodium zeolite

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 of the A series reacts as with metals in that they replace sodium ions without causing any visible change in the basic structure of the crystalline zeolite. The ion exchange can conveniently be effected by spraying the sodium aluminosilicate or otherwise contacting with a solution of an icnisable compound of the ion to be introduced. by exchange in the molecular sieve. After such treatment, the product obtained is, as indicated above, washed with water and dried and calcined.



   Sodium zeolites of the A series which have undergone an exchange with calcium or magnesium ions admit molecules of larger size than the original tarais. An unusual feature of zeolites that have been resized with calcium or magnesium ion is that the opening of the pores does not take place gradually, as the sodium ions are released. so: .t replaced by calcium ions, but, on the contrary, it occurs in a relatively narrow lining of composition.

   When the ion exchange has taken place at a rate of at least 25%, the substance has substantially the same pore characteristics as the sodium seolite of series A, i.e. a pore diameter about
0 4 A. However when the exchange rate exceeds about 40%, the pore characteristics become those of calcium magnesium zeolites of the A series, that is, a pore diameter of about 5 # In general substances exchanged with a divalent ion such as zeolites of zinc, nickel and strontium

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 have pore size characteristics similar to those of the A-series calcium and magnesium zeolites.

   Substances containing a monovalent ion such as the lithium zeolites of the A series, on the other hand, have pore size characteristics similar to those of the sodium zeolites of this series.



   It has further been found, in accordance with the invention, that the final crystallization rate can be increased by increasing the concentration of the sodium hydroxide solution used as the crystallization medium. It has been established that the rate of crystallization increases as the concentration of sodium hydroxide is increased in the crystallization medium. Thus, when the concentration of sodium hydroxide:; - in the crystallization -iilieu. is less than normal for NaOH), the crystallization rate is quite slow.

   On the other hand, solutions which are very concentrated in sodium hydroxide, for example 3 to 5 times normal, require the use of an apparatus resistant to caustic products, which constitutes an economic weakness of the process using such solutions. It has been found, in accordance with the invention, that it is particularly advantageous to maintain the concentration of the sodium hydroxide solution used as crystallization medium in the approximate concentration zone of 1.1 to 2.0 N.



   In the process of the invention, it is generally preferred to use soluble starting reagents to prepare crystalline sodium aluminosilicate, e.g.

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 example of aqueous solutions of sodium aluminate and sodium silicate. The initial reaction mixture obtained by mixing these solutions is an amorphous gel of sodium aluminosilicate which, in the presence of sodium hydroxide, undergoes crystallization into the desired crystals of molecular tarais 4A. It is therefore possible to operate by first preparing the amorphous sodium aluminosilicate gel, isolating and drying it and introducing it into a solution of sodium hydroxide at the preferred concentration indicated above. .



  However, it is essential for the success of the operation that the reaction mixture used has a composition expressed as oxide soles which meets the following requirements:
The report . O / SiO2 must be between J, 3 and 3.0.



   The SiO2 / Al2O3 ratio must be between 0.5 and 2.5.



   The H2O / Na2O ratio should be between 35 and 200.



   It will be understood that the amount of crystalline sodium aluminosilicate introduced in accordance with the process of the invention into the initial reaction mixture should be such as to increase the rate of crystallization of the desired crystalline sodium aluminosilicate in the mixture. reaction. The particular amount of crystalline aluminosilicate introduced can vary within wide limits but is in general a function of the type of particular apparatus used.



   The following examples illustrate the invention without however limiting it.

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  EXAMPLE 1
A mixture of 800 ml of 1.1N aqueous sodium hydroxide solution at 100 ° C. and 27.2 g (as dry matter) of an amorphous sodium aluminosilicate is placed in a suitable reaction apparatus. The latter consists of 45 mole percent silica and 27.5 mole% alumina and 27.5 mole% sodium oxide. The mixture is stirred and samples are taken periodically. They are washed with water and swept with nitrogen at a temperature of 360 C.

   The amount of crystalline sodium aluminosilicate having a uniform structure consisting of pores of about 4A in diameter, that is to say crystals of 4A molecular weight, contained in the different samples is determined by the capacity of water sorption. The results of the examinations are collated in Table I, below.



   TABLE I
 EMI20.1
 
<tb> Exchange- <SEP> Time <SEP> of exchange- <SEP>% <SEP> in <SEP> weight
<tb>
<tb> tillon <SEP> tillonnage, <SEP> of <SEP> sieve <SEP> 4A
<tb>
<tb> hours <SEP> in <SEP> the screen
<tb>
 
 EMI20.2
 ¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯ tillon
 EMI20.3
 
<tb> 1 <SEP> 2.50 <SEP> 14.3
<tb>
<tb>
<tb>
<tb> 2 <SEP> 2.75 <SEP> 20.2
<tb>
<tb>
<tb>
<tb>
<tb> 3 <SEP> 3.00 <SEP> 26.9
<tb>
<tb>
<tb>
<tb>
<tb> 4 <SEP> 3.25 <SEP> 39.6
<tb>
<tb>
<tb>
<tb>
<tb> 5 <SEP> 3.50 <SEP> 56.8
<tb>
<tb>
<tb>
<tb>
<tb> 6 <SEP> 3.75 <SEP> 82.3
<tb>
<tb>
<tb>
<tb>
<tb> 7 <SEP> 4.00 <SEP> 100
<tb>
 

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The reaction illustrated by the figures in the table above is typical of a normal reaction carried out without seeding.

   The results are also shown graphically in Figure 2 of the accompanying drawing, in which the transformation of the amorphous material into the crystalline molecular sieve 4A is shown as a function of the reaction time.



  EXAMPLE 2.



   A reaction mixture was prepared as described in Example 1, however, in this example, 27.2 g of 4A molecular sieve was added to the sodium hydroxide solution along with the sodium aluminosilicate. amorphous sodium. The added molecular sieve was previously dehydrated by flushing nitrogen at 360 ° C. for 4 hours. As in Example 1, samples of the mixture are taken at different time intervals and the amount of 4A molecular sieve in the solid samples is determined, as well as the rate of conversion of the amorphous material to the sieve. molecular. The results of this test are shown in Table II, below.



   TABLE II
 EMI21.1
 
<tb> Exchange- <SEP> Time <SEP> of exchange- <SEP>% <SEP> in <SEP> weight <SEP> of <SEP> Rate <SEP> of
<tb>
<tb> tillon <SEP> tillonnage, <SEP> sieve <SEP> 4A <SEP> in <SEP> transform
<tb>
<tb> ¯¯¯¯¯ <SEP> hours <SEP> sample <SEP> mation <SEP>%
<tb>
<tb>
<tb>
<tb>
<tb> 1 <SEP> 0 <SEP> 58.8 <SEP> 0
<tb>
<tb>
<tb>
<tb>
<tb> 2 <SEP> 0.25 <SEP> 70.7 <SEP> 28.9
<tb>
<tb>
<tb>
<tb>
<tb> 3 <SEP> 0.50 <SEP> 93.6 <SEP> 84.6
<tb>
<tb>
<tb>
<tb>
<tb> 4 <SEP> 0.75 <SEP> 99 <SEP> 97.5
<tb>
<tb>
<tb>
<tb> 5 <SEP> 1.00 <SEP> 100 <SEP> 100
<tb>
 

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As in Example 1, 27.2 g of amorphous sodium aluminosilicate was made into 4A molecular sieve.

   However, the reaction in this example lasted 45 minutes for a conversion rate of 97.5% instead of about 4 hours in example 1. The results of this example are also shown graphically in figure 2.



  EXAMPLE 3
A reaction mixture was prepared as described in Example 1. The 4A molecular sieve crystals were allowed to grow for 3.5 hours after which 27.2 g of amorphous sodium aluminosilicate was added to the reaction mixture. This note is considered to be the time z 'ro with regard to
 EMI22.1
 sample collection :: 'or1s. The quantity of 4A molecular sieve contained in the solid samples is determined, as well as the rate of transformation into percentage.
 EMI22.2
 hundred of matter a ::. or) he in crystalline tānis. The results of this test are shown below.



   TABLE III
 EMI22.3
 
<tb> Exchange- <SEP> Time <SEP> of exchange- <SEP>% <SEP> er. <SEP> weight <SEP> of <SEP> Rate <SEP> of
<tb>
 
 EMI22.4
 tillon tillonnage, 1 *? is 4A in transform: a- ¯¯ ininutes 1sample%
 EMI22.5
 
<tb> 1-1 <SEP> 36.3
<tb>
<tb>
<tb> 2 <SEP> 0 <SEP> 21.0 <SEP> 0
<tb>
<tb>
<tb>
<tb>
<tb> 3 <SEP> 10 <SEP> 23.5 <SEP> 3.2
<tb>
<tb>
<tb>
<tb>
<tb> 4 <SEP> 20 <SEP> 28.4 <SEP> 9.4
<tb>
<tb>
<tb>
<tb>
<tb> 5 <SEP> 30 <SEP> 34.0 <SEP> 16.5
<tb>
<tb>
<tb>
<tb> 6 <SEP> 40 <SEP> 45.6 <SEP> 31.2
<tb>
<tb>
<tb>
<tb>
<tb> 7 <SEP> 50 <SEP> 55.9 <SEP> 44.2
<tb>
<tb>
<tb>
<tb>
<tb> 8 <SEP> 60 <SEP> 70.2 <SEP> 62.3
<tb>
<tb>
<tb>
<tb>
<tb> 9 <SEP> 70 <SEP> 86.0 <SEP> 82.2
<tb>
<tb>
<tb>
<tb> the <SEP> 80 <SEP> 98.0 <SEP> 97.5
<tb>
<tb>
<tb>
<tb>
<tb> 11 <SEP> 90 <SEP> 99.6 <SEP> 99,

  5
<tb>
 

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The results of this example, showing that the crystals in the growth stage also serve as seeds for transformation of the amorphous product into the crystalline molecular sieve 4A, are shown graphically in Figure 2.



  EXAMPLE 4
A race reaction mixture described in Example 1 is prepared. The mixture is allowed to react for 5 hours so that crystallization is complete.



  At the end of this time, 27.2 g of anhydrous amorphous sodium aluminosilicate were introduced and samples were taken from the reaction mixture as described above. The time of adding the amorphous product is considered time zero from a sampling point of view. The amount of molecular sieve 4A and the degree of conversion in% of the amorphous material to crystalline sieve in each of the samples is shown in the table below.



     TABLE IV
 EMI23.1
 
<tb> Exchange- <SEP> Time <SEP> of exchange- <SEP>; <SEP> in <SEP> weight <SEP> of <SEP> Rate <SEP> of <SEP> trans-
<tb>
<tb>
<tb>
<tb> tillon <SEP> tillonnage, <SEP> sieve <SEP> 4A <SEP> in <SEP> formation,
<tb>
<tb>
<tb>
<tb> ¯¯¯¯¯minutes¯¯¯¯ <SEP> sample <SEP>%
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 1-1 <SEP> 100 <SEP> -
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 2 <SEP> 0 <SEP> 49.5 <SEP> 0
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 3 <SEP> 10 <SEP> 58.0 <SEP> 16.8
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 4 <SEP> 20 <SEP> 75.5 <SEP> 51.5
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 5 <SEP> 30 <SEP> 83.7 <SEP> 67.7
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 6 <SEP> 40 <SEP> 94.0 <SEP> 88,

  0
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 7 <SEP> 50 <SEP> 100 <SEP> 100
<tb>
 

 <Desc / Clms Page number 24>

 
The above results which are also shown graphically in Figure 2, show that reaction mixtures which have fully reacted are also suitable to serve as a source of seeds for the transformation of amorphous product into molecular taxis 4A, without having to. necessary to separate the solid and liquid phases of the reaction mixture.



  EXAMPLE 5
Amorphous sodium aluminosilicate is prepared from solutions of sodium aluminate and sodium silicate. in the presence of 4A molecular sieve crystals. For this purpose, an aqueous solution of 22.9 or of sodium aliate in 200 ml of water is heated to 100 C. Then 11.2 g of molecular ta.is 4A are added, followed immediately by stirring. , 44.7 g of sodium metasilicate monohydrate dissolved in 200 water at 100 C. The silica / alumina ratio existing in the mixture is the same as in the amorphous product used in the preceding examples.

   The aqueous phase is comparable in alkalinity to that of the previous examples.



  Samples of the reaction mixture were taken at various intervals and the amount of 4A molecular sieve they contained and the rate of conversion of the amorphous material to crystalline molecular tanis determined by analysis. The results obtained for each sample are shown in the table below.

 <Desc / Clms Page number 25>

 



  -TABLE V
 EMI25.1
 
<tb> Sample- <SEP> Sample time <SEP> <SEP>% <SEP> in <SEP> weight <SEP> Rate <SEP> of <SEP> trans-
<tb>
<tb>
<tb> lon <SEP> tillonnage, <SEP> of <SEP> sieve <SEP> 4A <SEP> formation, <SEP>%
<tb>
<tb>
<tb> hours <SEP> in <SEP> the sample
<tb>
 
 EMI25.2
 ¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯ tillon ¯¯¯¯¯.¯¯¯¯¯
 EMI25.3
 
<tb> 1 <SEP> 0 <SEP> 47 <SEP> 0
<tb>
<tb> 2 <SEP> 0.25 <SEP> 51.5 <SEP> 8.5
<tb>
<tb> 3 <SEP> 0.50 <SEP> 61.2 <SEP> 26.8
<tb>
<tb> 4 <SEP> 0.75 <SEP> 78.8 <SEP> 60.0
<tb>
<tb> 5 <SEP> 1.00 <SEP> 93.5 <SEP> 87.7
<tb>
<tb> 6 <SEP> 1.25 <SEP> 100 <SEP> 100
<tb>
 
The comparison of the figures above with those of example 1,

    shows that the transformation of fresh amorphous sodium aluminosilicate to crystalline 4A molecular sieve was influenced by the presence of 4A seeds.



    EXAMPLE 6
 EMI25.4
 By operating as: nwe described in lexe.bple 1, 45 g of dry amorphous sodium aluminosilicate are dispersed in 1600 ml of 0.8N sodium hydroxide solution.



  This amorphous material has essentially the same composition as that used in the preceding examples. The content of the samples taken in crystalline molecular sieve 4A is determined by X-ray diffraction techniques. The results obtained are shown below.

 <Desc / Clms Page number 26>

 



  TABLE VI
 EMI26.1
 
<tb> Sample- <SEP> Sample <SEP> time <SEP>% <SEP> in <SEP> weight <SEP> of
<tb>
<tb>
<tb> lon <SEP> tillonnage, <SEP> sieve <SEP> 4A <SEP> in
<tb>
<tb> ¯¯¯¯¯¯¯ <SEP> hours <SEP> sample
<tb>
<tb>
<tb>
<tb>
<tb> 1 <SEP> 3.0 <SEP> traces
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 2 <SEP> 3.5 <SEP> 5
<tb>
<tb>
<tb>
<tb>
<tb> 3 <SEP> 4.0 <SEP> 7
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 4 <SEP> 4.5 <SEP> 8
<tb>
<tb>
<tb>
<tb>
<tb> 5 <SEP> 5.0 <SEP> 12
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 6 <SEP> 5.5 <SEP> 21
<tb>
<tb>
<tb>
<tb>
<tb> 7 <SEP> 6.0 <SEP> 41
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 8 <SEP> 6.5 <SEP> 64
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 9 <SEP> 6.75 <SEP> 73
<tb>
 
It will be understood in Figure 3 in which the above results have been graphically represented,

   that the time required for complete crystal growth increases as the concentration of the sodium hydroxide solution increases.



  EXAMPLE 7
By operating as described in Example 6, 45 g of dry amorphous sodium aluminosilicate are dispersed in 800 ml of a 1.6 N solution of sodium hydroxide.



  As in the previous examples, the samples are analyzed by X-ray diffraction. The results are set out in Table VII below.

 <Desc / Clms Page number 27>

 



  TABLE VII
 EMI27.1
 
<tb> Sample- <SEP> Sample <SEP> time <SEP>% <SEP> in <SEP> weight <SEP> of <SEP> sieve
<tb> tillon <SEP> tillonnage, <SEP> 4A <SEP> in <SEP> the sample hours <SEP> lon
<tb>
<tb> 1 <SEP> 0.5 <SEP> 6
<tb>
<tb> 2 <SEP> 1.0 <SEP> 33
<tb>
<tb> 3 <SEP> 1.5 <SEP> 76
<tb>
<tb> 4 <SEP> 2.0 <SEP> 84
<tb>
<tb> 5 <SEP> 2.5 <SEP> 90
<tb>
<tb> 6 <SEP> 3.0 <SEP> 91
<tb>
 
These results are also represented graphically in Figure 3.



  EXAMPLE 8
Working as described in Example 6, 45 g of dry amorphous sodium aluminosilicate are dispersed in 1200 ml of 1.2N sodium hydroxide solution.



  The samples are analyzed by ray diffraction. The results obtained are shown in Table VIII below and in Figure 3.

 <Desc / Clms Page number 28>

 



  TABLE VIII
 EMI28.1
 
<tb> Sample <SEP> Sample <SEP> taken <SEP>% <SEP> in <SEP> weight <SEP> of <SEP> sieve
<tb> ¯¯¯¯¯¯¯¯¯ <SEP> after <SEP> hours <SEP> 4A <SEP> in <SEP> sample
<tb>
<tb> 1 <SEP> 0.5 <SEP> 0
<tb>
<tb> 2 <SEP> 1.0 <SEP> 6
<tb>
<tb> 3 <SEP> 1.5 <SEP> 8
<tb>
<tb> 4 <SEP> 2.0 <SEP> 16
<tb>
<tb> 5 <SEP> 2.5 <SEP> 50
<tb>
<tb> 6 <SEP> 3.0 <SEP> 80
<tb>
<tb> 7 <SEP> 3.5 <SEP> 84
<tb>
<tb> 8 <SEP> 4.0 <SEP> 94
<tb>
   EXAMPLE 9
A reaction is carried out exactly as described in Example 6, but mixing 0.9 g of molecular sieve 4A with the amorphous sodium aluminosilicate before adding this to the hydroxide solution. sodium.

   The proportions used correspond to a conversion rate of approximately 2% at the start of the reaction. The different samples are analyzed by X-ray diffraction and the results of these examinations are shown in Table 9, below, and in Figure 4.

 <Desc / Clms Page number 29>

 



  TABLE IX
 EMI29.1
 
<tb> Sample <SEP> Sample <SEP>% <SEP> in <SEP> weight <SEP> of <SEP> Rate <SEP> of <SEP> trans-
<tb>
<tb>
<tb> sampled <SEP> sieve <SEP> 4A <SEP> in <SEP> formation <SEP>% <SEP>
<tb>
<tb>
<tb> ¯¯¯¯¯¯¯¯¯ <SEP> after <SEP> hours <SEP>: <SEP> sample
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 1 <SEP> 0.5 <SEP> traces
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 2 <SEP> 1.0 <SEP> traces
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 3 <SEP> 1.5 <SEP> 3 <SEP> 1
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 4 <SEP> 2,0 <SEP> 5 <SEP> 3
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 5 <SEP> 2.5 <SEP> 5 <SEP> 3
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 6 <SEP> 3.0 <SEP> 9 <SEP> 7
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 7 <SEP> 3.5 <SEP> 15 <SEP> 13
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 8 <SEP> 4.0 <SEP> 28 <SEP> 26
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 9 <SEP> 4,

  5 <SEP> 42 <SEP> 40
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 10 <SEP> 5.0 <SEP> 62 <SEP> 60
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 11 <SEP> 5.5 <SEP> 82 <SEP> 80
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 12 <SEP> 6.0 <SEP> 91 <SEP> 89
<tb>
 
It will be seen from the figures in this table that the medium containing 2% crystals by weight results in low production since it takes another 3.5 hours to produce a further 13% crystals. In contrast to this result it takes 0.5 hour to produce 13% crystals if there are already 15% at the start of the reaction.



   EXAMPLE 10
A reaction was carried out as described in Example 1, but using 400 ml of 1.1N aqueous sodium hydroxide solution instead of 800 ml. Samples are taken and analyzed as previously described. The results are shown in the table below.

 <Desc / Clms Page number 30>

 



  PAINTINGS.
 EMI30.1
 
<tb>



  Sample <SEP> Sample <SEP> taken <SEP>% <SEP> in <SEP> weight <SEP> of <SEP> sieve
<tb> ¯¯¯¯¯¯¯¯ <SEP> after <SEP>: <SEP> neures <SEP> 4A <SEP> in <SEP> sample
<tb>
<tb> 1 <SEP> 3.00 <SEP> 12.7
<tb>
<tb> 2 <SEP> 3.25 <SEP> 7.7
<tb>
<tb> 3 <SEP> 3.50 <SEP> 29.2
<tb>
<tb> 4 <SEP> 3.75 <SEP> 45.3
<tb>
<tb> 5 <SEP> 4.00 <SEP> 82
<tb>
<tb> 6 <SEP> 4.25 <SEP> 98
<tb>
 
Comparison of the figures in the table above with those in Table 1 shows that as the volume of the sodium hydroxide solution decreases, the induction period for crystallization of the molecular sieve 4A increases.



  EXAMPLE 11
A solution of 21.8 g of sodium aluminate dissolved in 200 ml of water is placed in a suitable reaction apparatus. This solution is heated to the boil and a boiling solution of 109 g of sodium metasilicate monohydrate in 320 ml of water is added with stirring.



  Samples are taken periodically, filtered, washed with water and flushed with nitrogen at 360 ° C. The weight% 13X molecular sieve in each of the samples is determined by cyclohexane sorption. . The results obtained are shown below.

 <Desc / Clms Page number 31>

 



  TABLE XI
 EMI31.1
 
<tb> Sample <SEP> Sample <SEP> taken <SEP>% <SEP> in <SEP> weight <SEP> of <SEP> sieve
<tb>
<tb> ¯¯¯¯¯¯¯¯ <SEP> after <SEP>: <SEP> hours <SEP> z¯¯¯ <SEP> 13X <SEP> in <SEP> sample
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 1 <SEP> 2.00 <SEP> 13.6
<tb>
<tb>
<tb>
<tb>
<tb> 2 <SEP> 2.25 <SEP> 23.8
<tb>
<tb>
<tb>
<tb>
<tb> 3 <SEP> 2.50 <SEP> 36.4
<tb>
<tb>
<tb>
<tb>
<tb> 4 <SEP> 2.75 <SEP> 52.7
<tb>
<tb>
<tb>
<tb>
<tb> 5 <SEP> 3.00 <SEP> 70.0
<tb>
<tb>
<tb>
<tb> 6 <SEP> 3.25 <SEP> 91.0
<tb>
<tb>
<tb>
<tb>
<tb> 7 <SEP> 3.50 <SEP> 94
<tb>
 EXAMPLE 12
Reaction was carried out as described in Example 11: after 2.5 hours 45% of the amorphous sodium aluminosilicate had passed to a crystalline 13X molecular sieve.

   Fresh solutions of sodium aluminate and sodium silicate are then added in order to produce a fresh amorphous gel of mass equal to the initial amorphous gel of sodium aluminosilicate. The moment at which this addition is made is considered as time zero for the taking of samples. The results obtained on the analysis are shown below.

 <Desc / Clms Page number 32>

 



  TABLE XII
 EMI32.1
 
<tb> Sample <SEP> Sample <SEP>% <SEP> in <SEP> weight <SEP> of
<tb> taken <SEP> after: <SEP> sieve <SEP> 13X <SEP> in <SEP> Conversion
<tb>
<tb>
<tb> 1 <SEP> 0 <SEP> 24.3 <SEP> [alpha]
<tb>
<tb> 2 <SEP> 0.50 <SEP> 31.0 <SEP> 9.7
<tb>
<tb> 3 <SEP> 1.00 <SEP> 40.1 <SEP> 20.9
<tb>
<tb> 4 <SEP> 1.50 <SEP> 53.7 <SEP> 38.8
<tb>
<tb> 5 <SEP> 1.75 <SEP> 62.3 <SEP> 50.3
<tb>
<tb> 6 <SEP> 2.00 <SEP> 78.5 <SEP> 71.6
<tb>
<tb> 7 <SEP> 2.25 <SEP> 80.5 <SEP> 74
<tb>
 
The figures above show that the 13X molecular sieve is not as sensitive to. Seemennement as molecular sieve 4A.

   Further, it is evident that seeding prevents the complete transformation of CI (- amorphous sodium aluminosilicate to crystalline sieve: 13X. Seeding has furthermore been observed to result in the formation of another crystalline product. different from the 13X product which ultimately leads to an impure product. Consequently, the method described is not applicable to the continuous synthesis of α-series molecular sieves but only applies to aluminoslicates having the crystalline structure and characteristics. molecular sieves of the A series.



   In order to show that the dimension: of the crystals is constant throughout the growth, the following operation is carried out.

 <Desc / Clms Page number 33>

 



  EXAMPLE 13
A 4A molecular sieve sample was used as the seed for the preparation of fresh 4A sieve. Part of the product obtained in the reaction is in turn used as a seed for the second preparation. A total of seven preparations are made, using in each case, as seeds, a fraction of the product of the previous reaction. If the growth of fresh molecular sieve was due to the uniform deposition of a new crystalline phase on the crystals used as seeds, the crystals obtained in the 7th preparation should be appreciably larger than the crystals used as seeds in the seed. first reaction.

   The ratio of seed crystals to amorphous gel used in each reaction is such that the final cubic crystals would have to have a ridge 10 times larger than the initial seed if crystal growth were to take place in this manner. Examination of the initial and final crystals by electron microscopy did not reveal any appreciable difference in the dimensions of the crystals. As a result, the observed mode of crystal growth is quite unusual and unexpected. Usually, as will be appreciated, seed crystals undergo a marked increase in size as they nourish the growth of new crystals.



   Some general relationships applicable to embodiments of the invention in which crystalline zeolite suspended in its mother liquor is added to the reaction mixture is indicated below. In a typical installation, the volume of the reactor, i.e.

 <Desc / Clms Page number 34>

 the volume of the apparatus 16 of Figure 1 is denoted by "V" measured in liters. The total flow rate through the reactor can be referred to as "F" measured in liters / hour. Referring to Figure 1, this flow rate is also the outlet flow through line 17.

   The flow rate "F" is linked to the basic flow rate law given previously by the relation: V = #
F
The net output flow rate of the installation in kg / hour, that is to say the productivity of the portion of current passing through line 17 and sent to filter 21, is given by the relation: (Cf- Ci) ¯¯¯¯¯ x F x S = Net crystal flow rate in kg / hour.



   100 in which S is the sum of the weights in kg of the crystals and the crystallizable gel contained per liter of slurry.



  In the usual operations, S will have the same value at the inlet line 15, in the reactor 16, and in the recycle line 19. If the installation operates in such a way that the crystallized product is at a lower crystallization rate. at 100%, as can be done the net output rate of crystallized solids different from the net output rate of crystals becomes (Cf-Ci) x F x S = Net output rate of crystallized solids in kg / hour.



   Cf
The advantageous use of the medium described can be illustrated from the relationships indicated above. For an installation comprising a 3785 liter reactor, intended to produce solids at a crystallization rate.

 <Desc / Clms Page number 35>

 tion of 90%, and operating with the equivalent of 1.2 N NaCH as in Example 8.



     V = 3785 liters
K = 0.97 hour-1
Cf = 90%
S = 0.037 kg / 1 As F = V and # = 1 # k log C
Ci the net output rate of crystallized solids in kg / hour
 EMI35.1
 = Cf '- C 1 kA -a Cf Log C f Ci -Cq 135 1.5 90 -Ct x 135 = (90-Ci) x Log.2Q 90 Zo g C f = (90-C: L) XCC ii Figure 5 shows how the net output rate, i.e. the portion of current sent to filter 21 in the system shown in Figure 1, increases as Ci increases, by recycling large amounts of the product stream which serves to provide the crystallization medium.



   The flow rate of the producing fraction of the current
F output 17 which goes to filter 21 can be referred to as product and can be calculated by the expression: Fproduct, kg / h = Net outflow rate of crystallized solids
As can be seen in Fig. 5, the product F value increases as the media recycle rate is increased to give larger Ci values.



   The recycling rate of the medium, derived by the pipes 18, 19 and 20 of FIG. 1, can be designated by Fmilieu.

 <Desc / Clms Page number 36>

 



   The rate of recycling of the medium necessary to produce the desired value Ci can be deduced: from the following considerations.



   (a) The weight of crystalline solids introduced by
 EMI36.1
 hour in 15 is FmiJ.ieu x S x C: r 13 (b) The total weight of crystalline solids p1Z sciM # of the crystallisables introduced per hour in 15 is F x::., (c) The resulting rate of crystalline & tiQBL sp. The ratio aE of the currents introduced at 15 is, in percentage, the ratio of (a) to (b) multiplied by 100; this coiLs * - et2ze ëgxl.a # ment the value of Ci.
 EMI36.2
 



  F midpoint has S x ±. x ICC 100 = 1.



  F x S or F medium = Ci Je F = Ci x k 7 in cf Cf log C-r Ci for the numerical application mentioned above,
 EMI36.3
 F medium Ci x 40.8 log .20 Ci as shown in figure 5.
 EMI36.4
 Thus, the example illustrated shows that the. :: rista: U.i.- tion in a medium consisting of crystalline zeolite suspended in its mother liquor constitutes a highly efficient process, the efficiency increasing when the
 EMI36.5
 ratio of medium to constituents of: fo:

  r # .t1cm of the crystals increases. It will naturally be understood that the
 EMI36.6
 Operating conditions can be chosen so as to produce less than 90% or more than 90% of solid crystallized products, the value 90% being simply given as an illustration.


    

Claims (1)

ABSTRACT. Process for increasing the rate of crystallization of a crystalline sodium or calcium aluminosilicate characterized by the following points, taken alone or in combination: 1 An effective amount of crystalline aluminosilicate is added to a reaction mixture intended for the production of a crystalline sodium or calcium aluminosilicate having a uniform structure consisting of pores of about 4 A in diameter and the composition of which expressed in moles of oxides meets the following conditions: The Na2O / SiO2 ratio is between 0.8 and 3.0. The SiO2 / Al2O3 ratio is between 0.5 and 2.5. The H2O / Na2O ratio is between 35 and 200, before the end of crystallization. 2 The reaction mixture originally contains an amorphous sodium aluminosilicate in aqueous sodium hydroxide solution at a concentration of 1.1 to 2.0 N and an effective amount of crystalline sodium aluminosilicate is added thereto. 3 A molecular sieve consisting of solid sodium aluminosilicate in the form of porous crystals in which the pores of the crystals have a uniform size is prepared by maintaining the reaction mixture at a temperature between about 20 C and about 175 C. until crystals are formed; the crystals are separated from the mother liquor and before the end of the crystallization reaction is introduced into the reaction mixture a sufficient amount of the aluminosilicate molecular sieve to increase the rate of crystallization of said reaction mixture. 4 The reaction mixture is continuously prepared <Desc / Clms Page number 38> based on sodium oxide, silica, alumina and water, part of the crystalline slurry obtained is continuously withdrawn, this withdrawn portion is continuously introduced into fresh reaction mixture, in an amount sufficient to increase the rate of crystallization of the mixture; and the crystalline product is continuously separated from the remaining crystalline slurry. 5 The molecular sieve is characterized by uniformly sized pores and has the following formula: EMI38.1 1.0 + 0.2 MO: g12o3: 1.85 0.5 8i02: Y H20 nn wherein M is at least one member of the group consisting of hydrogen, ammonium, metals of groups 1 and II of the periodic table and the transition metals of the periodic table, n represents the valence of M and Y is any number up to about 6; the crystals are separated from the mother liquor and at least part of the sodium ions they contain are exchanged for ions of M. 6 Crystalline sodium aluminosilicate is chemically characterized in its hydrated form by the formula. EMI38.2 Na12 (Al02) 12 (8i02) 12, 27 H2O The process is used for the synthesis of a crystalline sodium aluminosilicate: an amorphous sodium alumina silicate is contacted with an aqueous solution of 1.1 to 2.0 N sodium hydroxide, and effect crystallization in the presence of an additional amount EMI38.3 of said crystalline sodium aluminosilicate sufficient to cause seeding of said mixture and EMI38.4 to thereby increase the rate of conversion of amorphous sodium aluminosilicate to crystalline sodium aluminosilicate. <Desc / Clms Page number 39> The operation is continuous and the seeding of the fresh reaction mixture is carried out by means of recycling of a part of the crystalline mixture obtained in the reaction. 9 The reaction mixture is obtained by mixing sodium aluminate, sodium silicate and sodium hydroxide. 10. The part of the obtained crystalline mixture which is removed from the reaction zone is filtered, the filtrate is reused as sodium aluminate and sodium hydroxide, and the crystals are dried and calcined. The amount of crystalline mixture recycled for inoculation of the fresh mixture corresponds to about 10 to 90% of the final crystalline product. A calcium aluminosilicate molecular sieve consisting of porous crystals in which the pores are uniform in size of about 5 A is prepared by exchanging at least 40% of the sodium ions of the crystalline sodium aluminosilicate for calcium ions. 13 The initial reaction mixture is carried out by an intimate mixture of aqueous streams of (1) sodium silicate and (2) sodium aluminate and sodium hydroxide *