BE534425A - - Google Patents

Description

       

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   The present invention relates to an adsorbent of the molecular sieving type and more particularly to a synthetic crystalline form of sodium aluminum silicate, to its derivatives and to the processes for the manufacture and activation of these adsorbents. .



   The main object of the present invention is to provide an adsorbent of the molecular sieving type having improved adsorbing properties, and particularly a crystallized metallic alumino-silicate, possessing remarkable properties and a very high adsorption capacity, as well as a convenient and efficient method of making and activating the novel absorbent according to the invention.



   The naturally occurring hydrated metal aluminosilicates are referred to as zeolites. Synthetic absorbents according to the invention have compositions similar to those of some of the natural zeolites, so that the term "zeolite" seems to apply appropriately to the adsorbents according to the invention. However, there are clear differences between synthetic and natural materials. In order to distinguish one from the other, the synthetic crystallized sodium aluminosilicate according to the invention will be designated by the term “zeolite X”.



   Some adsorbents, including zeolite X, selectively adsorb molecules depending on their size and shape and are referred to as "molecular sieves". Molecular sieves have an available sorption zone within a large number of regularly sized pores of molecular order. With such an arrangement, molecules of a certain size and shape enter the pores and are adsorbed, while molecules that are larger or differently shaped are excluded.



  Not all adsorbents behave like molecular sieves. Common adsorbents like charcoal and silica gel, for example, do not exhibit molecular sieving action.



   Zeolite X basically consists of a three-dimensional edifice of tetrahedra from SiO4 to AlO4. These tetrahedra are crosslinked by sharing oxygen atoms so that the ratio of oxygen atoms to the total of aluminum and silicon atoms is equal to 2 or O / (Al + Si) = 2.



  The electrovalence of each tetrahedron containing aluminum is balanced by the inclusion in the crystal of a cation, for example an alkali or alkaline earth ion. This balance can be expressed by the formula: Al2 (Ca, Sr, Ba, Na2, K2) = le. One cation can be exchanged for another by the ion exchange techniques described below. The spaces between the tetrahedra are occupied by water molecules before dehydration.



   Zeolite X can be activated by heating so as to remove water of hydration. Dehydration results in crystals interwoven with channels of molecular dimensions which provide a very large surface area for adsorption of foreign molecules. The interstitial channels have a dimension such that, at the narrowest points, molecules whose maximum dimensions of the projected minimum cross-sections are greater than those of heptacosafluorotributylamine do not enter the channels.



  Factors influencing the occlusion by crystals of activated zeolite X are the size and polarizing power of the interstitial cation, the polarizability and polarity of the occluded molecules, the size and shape of the adsorbed molecule relative to those of the channels, the duration and severity of dehydration and desorption, and the presence of foreign molecules in the interstitial channels. Of course, the rejection characteristics of zeolite X are just as important as the adsorption or positive adsorption characteristics. For example, if we have to separate the

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 benzene from heptacosafluorotributylamine (C4H9) 3N, it is also essential that the crystals refuse heptacosafluorotributylamine as they adsorb benzene.



   One feature of the invention is the relatively simple process for preparing zeolite X. Although many cations can be present in the zeolite X molecule, it is preferable to synthesize the sodium form of the crystal, since reagents are readily available and soluble in water. Sodium in the sodium form of zeolite X can be readily exchanged with other treatments, as will be seen. In principle, the preferred process involves heating a suitable mixture, in aqueous solution, of the oxides or materials whose chemical composition can be fully represented as mixtures of the oxides Na2O, Al2O3, SiO2 and H2O, suitably to a temperature of d. 'approximately 100 C. for a period of up to 90 hours or more.

   The product which crystallizes from the hot mixture is filtered off, washed with distilled water until the washing water in equilibrium with the zeolite has a pH of 9 to 12. After activation, for example by drying, the material is ready to operate as a molecular sieve.



   The Applicant has found that a temperature of about 100 ° C. is particularly advantageous in this process. This temperature is easy to maintain, high enough to actually activate the reaction, while being low enough to give crystals of high water content which, after activation, have a high adsorption capacity.



   Zeolite X can be distinguished from other zeolites and silicates by its X-ray diffraction spectrum carried out on the powder and by some of its physical characteristics. The X-ray diffraction spectrum of various ion-exchanged forms of X zeolite are described below. Composition and density are among the characteristics that have been shown to be the most important in identifying zeolite X.



   The basic formula of all crystallized zeolites in which M is a metal and n its valence can be represented as M2O: Al2O3: X SiO2: Y H2O. In general, a particular crystallized zeolite has values of X and Y within a specified range.



  The value of X for a particular zeolite varies somewhat due to the aluminum and silicon atoms occupying essentially equivalent positions in the lattice. Small variations in the relative numbers of these atoms do not significantly change the crystal structure or the physical properties of the zeolite. For zeolite X, numerous analyzes have shown that an average value of X is about 2.5 and generally between 2.5 ¯ 0.5.



   The value of Y is not necessarily invariable for all samples of zeolite X, particularly in the case of the various forms of ion exchange of zeolite X, this because the various exchangeable ions have different dimensions and, since they there is no significant change in the dimensions of the crystal lattice as a result of the ion exchange, there is more or less * space available in the pores of the zeolite X to accommodate the water molecules.



   The average value of Y determined by heating the fully hydrated sodium zeolite to 500 ° C. under a pressure of about 0.1 mm. is 6.2. Zeolite X partially exchanged with lithium and zeolite

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 Sodium X partially exchanged with magnesium gives a higher Y value, which is about 7.2 for the fully hydrated form. A Y value of about 8 can be obtained for an X zeolite fully exchanged with magnesium or lithium. The partially exchanged X zeolites with calcium and barium have Y values of approximately
6.4 and 6.2 and, if the exchange is complete, about 7.



   In the zeolite X obtained by synthesis according to the preferred process, the ratio Na2O / Al2O3 should be equal to 1. If all of the excess base present in the mother liquor is not removed by washing the precipitated product , the analysis may show a ratio greater than 1, and if the washing is carried too far, some exchange of sodium with hydrogen ions may occur, the ratio then becoming less than 1.



   It has been found that due to the ease with which the exchange with hydrogen takes place, the ratio is, for zeolite X, of:
M2O n = 0.9 0.2, Al2O3 = 0.9 ¯ 0.2, M representing a metal and n its valence. A typical composition of sodium X zeolite expressed as oxides is 0.9 Na2O / Al2O3 / 2.5 SiO2 / 6.1 H2O.



   Thus, the formula for zeolite X can be written as follows: (0, 9 ¯ 09.2) M2O: Al2O3: (2.5 + 0.5) SiO2: Y H2O n
In this formula M represents a metal, n its valence and Y can have any value up to 8, depending on the identity of the metal and the degree of hydration of the crystal.



   The pores of zeolite X are normally filled with water, and in this case the above formula represents the chemical composition of zeolite X. When there is material in the pores other than water, l The chemical analysis shows a lower value of Y and presents it with other adsorbates. The presence in the crystal lattice of volatile material at temperatures below about 600 ° C. does not appreciably alter the useful value of zeolite X as an adsorbent, the pores usually being free of these materials after activation by heater.



   The bulk densities of the fully hydrated samples of the various forms of zeolite X are determined by floating the crystals on liquids of appropriate densities. The technique and liquids applied are set forth in an article entitled "Density of Liquid Mixture", published in "Acta Crystal lographica", 1951, vol. 4, p. 565. These densities, in grams per cubic centimeter, are as follows: sodium zeolite X, 1.93: lithium zeolite X, 1.89; Rubidium X zeolite, 2.15; Magnesium zeolite X, 1.95; Calcium zeolite X, 1.96; Barium zeolite X, 2.31; Cerium X zeolite, 2.15. The accuracy of these measurements is 41.1 g./cc.



   Representative reagents applied in the manufacture of the sodium form of zeolite X are silica gel, silicic acid, colloidal silica or sodium silicate as a source of silica. Alumina can be supplied by activated alumina, gamma alumina, alumina

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 sodium trihydrate or aluminate. The sodium ion can be supplied by sodium hydroxide, which also aids in pH adjustment. It is preferable that the reagents are soluble in water. A solution of the reagents in the appropriate proportions is placed in a container, suitably made of glass or metal. The container is closed to prevent water loss and the reagents are heated for the desired time.

   A convenient and preferred method of preparing the mixture of reagents is to make an aqueous solution containing sodium aluminate and sodium hydroxide and add it, preferably with stirring, to an aqueous solution of sodium silicate. The system is stirred until homogenization or dispersion in the almost homogeneous state of the gel possibly formed. Stirring can be stopped after this mixing, since there is no need to stir the reaction mass during the formation and crystallization of the zeolite. The initial mixing of the ingredients is conveniently done at room temperature, but this is not essential.



   The Applicant has found that a crystallization temperature of about 100 ° C. is particularly advantageous in this process. This temperature is easy to maintain. It is high enough to facilitate the reaction and low enough to give crystals with a high water content which, after activation, have a high adsorption capacity. Satisfactory results have been obtained with reaction temperatures not exceeding about 21 ° C. and reaching about 120 ° C., at atmospheric pressure or at a pressure corresponding at least to the vapor pressure of water at equilibrium with mixing at higher temperature. Any suitable heating device such as an oven, sand bath, oil bath or double wall autoclave can be used.

   For reasons of convenience, in the laboratory, glass containers containing the reagents are kept immersed in a boiling water bath giving a temperature of about 100 C. In industrial production, double-walled steam-heated containers provide a convenient way to control the temperature. For temperatures between room temperature (21 C.) and 120 C. increasing the temperature increases the speed of the reaction and decreases its duration. For example, sodium zeolite X is obtained in 88 hours at 50 ° C., in approximately 6 hours or less at 100 C. and in approximately one and a half hours at 120.

   Once the zeolite crystals have been formed, they retain their structure, and maintaining the reaction temperature for a time longer than the time required to obtain the maximum yield of crystals is not detrimental up to 100 C. C Thus, zeolite X, which can be completely crystallized in six hours at 100 ° C., can remain in contact with the mother liquor at 100 ° C. for another 50 to 100 hours, without apparent change in yield or structure. crystals.



   When the reaction period is complete, the zeolite crystals are filtered off. The reaction magma can be filtered at reaction temperature, if desired, but it is preferable to cool it to room temperature before filtration. The filtrate or mother liquor can be reused after re-establishing the appropriate amounts of reagents so as to obtain a suitably proportioned mixture of reagents. The mass of zeolite crystals is washed, preferably with distilled water and conveniently on a filter, until the wash water coming out in equilibrium with the zeolite has a pH of 9 to 12.



   The crystals are then dried, conveniently in an oven, at a temperature of between 25 and 150 ° C. approximately. This drying is sufficient to perform X-ray analysis and chemical analysis. In practice,

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 it is not necessary to carry out a separate drying, since this takes place at the same time as the activation. Individual crystals of zeolite X appear cubic. Most of these crystals have a size of 0.1 to 100 microns.



   For the synthesis of zeolite X, it has been found that the composition of the reaction mixture is critical. The crystallization temperature and its duration are important variables involved in the yield of crystallized material. Under certain conditions, for example too low a temperature and too short a time, no crystalline material occurs. Extreme conditions can also give rise to materials other than zeolite X.



   Table I which follows gives specific examples of the production of the sodium form of zeolite. The mixtures and the treatments described give zeolite X crystallized in principle pure, except in operation 5 where the presence of traces of another crystalline form of sodium aluminosilicate with zeolite X is observed.

   In Table 7, the pressure of "solution A" denotes an aqueous solution of sodium silicate containing about 20% by weight of Na2O and 32% by weight of SiO2: the expression "solution B" denotes an aqueous solution of sodium silicate containing about 7.5% by weight Na2O and 25.8% by weight SiO2, and the expression "solution C" is a colloidal suspension of silica in water containing about 29 , 5% by weight of SiO2.

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 TABLE I.
 EMI6.1
 
<tb>
<tb>



  Oxide <SEP> ratio
<tb> Temp. <SEP> SiO <SEP> / <SEP> Na2O / <SEP> H2O /
<tb>
 
 EMI6.2
 OP n Reagents C. Duration A1263. S102. Na20 1 10 g. NaAlO + 32 g. ground. A + 5, 5 ge NAH + 135 ca. H20 100 z7 h. 3.0 1, 3 38 2 10 g. NaAlO2 + 32g. ground. A + 5i5 g. NaOH + 185 cc. H20 100 47 h. 3.0 1.3 50
 EMI6.3
 
<tb>
<tb> 3 <SEP> 20 <SEP> g. <SEP> NaA102 <SEP> + <SEP> 64 <SEP> g. <SEP> ground. <SEP> A <SEP>
<tb>
 
 EMI6.4
 + llg. NaOH + 310 cc. H20 60 65 h. 3.0 1.3 41
 EMI6.5
 
<tb>
<tb> 4 <SEP> 50 <SEP> g. <SEP> NaAl02 <SEP> + <SEP> 160 <SEP> g. <SEP> ground. <SEP> A
<tb> + <SEP> 27.5 <SEP> g. <SEP> NaOH <SEP> + <SEP> 775 <SEP> ce. <SEP> H20 <SEP> 100 <SEP> 15 <SEP> h. <SEP> 3.0 <SEP> 1.3 <SEP> 41
<tb> 5 <SEP> 18.4 <SEP> g. <SEP> NaA102 <SEP> + <SEP> 278 <SEP> g. <SEP> ground.
<tb>
 
 EMI6.6
 



  B + 34.2 g. NaOH + 88 cc. H2O 100 6 hrs. II, 4 0.72 18 6 15.9 g. A12 03 .3 H2O + 31 g.
 EMI6.7
 
<tb>
<tb> ground. <SEP> B <SEP> + <SEP> 47.4 <SEP> g. <SEP> NaOH <SEP> + <SEP> 52
<tb> cc. <SEP> H2O <SEP> 100 <SEP> 24 <SEP> h. <SEP> 14.5 <SEP> 0.65 <SEP> 17
<tb> 7 <SEP> 5 <SEP> g. <SEP> NaA102, <SEP> 114 <SEP> g. <SEP> ground. <SEP> C-
<tb>
 
 EMI6.8
 + 29, 'g. NaOH + 36 cc. H20 50 ll j. 20 0, 72 17
 EMI6.9
 
<tb>
<tb> 8 <SEP> 10 <SEP> g. <SEP> NAAlO2 <SEP> + <SEP> 59 <SEP> g. <SEP> ground. <SEP> A
<tb> + <SEP> 94 <SEP> cc. <SEP> H2O <SEP> 100 <SEP> 47 <SEP> h. <SEP> 5, <SEP> 6 <SEP> 0.76 <SEP> 29
<tb> 9 <SEP> 20 <SEP> g. <SEP> NaA102 <SEP> + <SEP> 59 <SEP> g. <SEP> ground. <SEP> A
<tb>
 
 EMI6.10
 + 11 g. NaOH + 270 g.

   H20 120 read 5 h. 3.0 lu3 38 The sodium form of zeolite X was produced at 100 ° C., sensitive
 EMI6.11
 ment free of impurities, using actual mixtures the compositions of which, expressed as mixtures of oxides, are between the following limits:
 EMI6.12
 sio2 / Ai203 3 - 5 Na2O / sio2 1.2 - 1.5
H2O / Na2O 35 - 60
Zeolite X has also been produced in admixture with other crystallized sodium aluminosilicates and crystallized alumina from reactants in proportions outside these limits.



  Zeolite X was thus produced as a mixture with a crystalline form of sodium aluminum silicate while maintaining reaction mixtures at 100 ° C., the compositions of which, expressed as mixtures of oxides, are between the following limits:

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 EMI7.1
 Si02 / Al203 2 - 40 Na20 / Si02 0.6 - 6
H2O / Na2O 10 - 30
Likewise, zeolite X mixed with yet another form of sodium aluminosilicate can be obtained by maintaining reaction mixtures at 100 0, the compositions of which, expressed as oxide ratios, are between the following limits:

   
 EMI7.2
 Si 2 / Al 2 3 2.4 - 30 Na20 / Si02 0.4 - 6.5
H2O / Na2O 10 - 90
Zeolite X mixed with another crystalline form of sodium aluminosilicate was likewise produced by maintaining reaction mixtures at 100 ° C. whose compositions, expressed as oxide ratio, are between the following limits
 EMI7.3
 Si 2 / Al 203 3 - 15
Na2O / SiO2 4 - 7 H20 / Na20 30 - 70
Zeolite X mixed with yet another crystalline form of sodium aluminosilicate was also produced by maintaining at 100 ° C. a reaction mixture of initial composition:

   
 EMI7.4
 Si02 / A1203 3.4 Na20 / Si02 1.8 H20 / Na20 28
When X zeolite mixed with other materials has been prepared, the X-ray diffraction spectrum of the mixture can be reproduced by simple proportionate addition of the spectra of the individual pure components.



   Other properties, for example the molecular sieve selectivity of zeolite X, are among the properties of the mixture as long as zeolite X itself is in the mixture.



   The adsorbents referred to here include not only the sodium form of zeolite X obtained by synthesis from a sodium-aluminum-silicate-water system with sodium as the exchangeable cation, but also crystalline materials obtained by partial or complete exchange. sodium by another cation. The sodium cations can be replaced in whole or in part by ion exchange with other monovalent, divalent or trivalent cations. Monovalent ions, which are both smaller than sodium, such as lithium, and larger, such as potassium and ammonium, freely enter the structure of zeolite X and exchange with other cations possibly present. The same is true of divalent ions smaller than sodium, such as magnesium, and larger, such as strontium and barium.

   Cerium is an example of a trivalent ion entering into the structure of zeolite X.



   The spatial arrangement of atoms of aluminum, silicon and o-

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 xygen constituting the fundamental lattice of the zeolite crystal remains in principle unchanged by the partial or complete replacement of the sodium ion by other cations. X-ray spectra of the ion-exchanged zeolite forms show the same major lines at essentially the same positions, but show some differences in the relative intensities of the x-ray lines obtained due to the ion exchange.



   Among the forms of zeolite X obtained by direct synthesis and ion exchange are the sodium, lithium, potassium, hydrogen, silver, ammonium, magnesium, calcium, zinc, barium, cerium and manganese forms.



  For convenience, these materials will be indicated by the chemical symbol of the cation associated with the letter X. The sodium form is thus Na2X, the calcium form CaX and the ceric form Ce2X3.



   Ion exchange of the sodium form of zeolite X (Na2X) or other forms of zeolite X can be accomplished by conventional ion exchange methods. The preferred continuous process consists of packing zeolite X into a series of vertical columns each of which bears a suitable support at the base; an aqueous solution of a soluble salt of the cation to be introduced into the zeolite is passed successively through the beds and the flow from the first bed is changed into the second when the zeolite present in the first bed has been changed by exchange in the desired proportion.



   In order to obtain an exchange with hydrogen, water or an aqueous acid solution such as hydrochloric acid can conveniently be used. For the exchange with sodium, a solution of sodium chloride is used. Other suitable reagents are: for exchange with potassium, an aqueous solution of potassium chloride or an extended solution of potassium hydroxide; for exchanges with lithium, magnesium, calcium, ammonium, nickel or strontium, aqueous solutions of the chlorides of these elements; exchange with zinc, silver or cerium, an aqueous solution of their nitrate, and for manganese a solution of a manganous salt.

   Although the most convenient is to use aqueous solutions of the cation exchange compounds, other solutions containing the desired cations or hydrated cations can be used.



   In a typical case of exchange by separate operation, 8 g are mixed in a beaker. of sodium zeolite X (Na2X) and 380 cc. of a 0.05 M aqueous solution of barium chloride. The mixture is stirred for 2.5 minutes and the crystals are collected by filtration. The X-ray spectrum of the crystals is characteristic of the X zeolite and analysis shows that 55% of the sodium ions have been replaced by barium ions at the ratio of one barium ion to two sodium ions.



   If an exchange operation is repeated by increasing the stirring time to 4.5 minutes before filtration, the degree of replacement of the sodium ions by barium ions is brought to 64%.



   In another case, 15 g are mixed. of sodium zeolite X and 500 cc. of distilled water containing 34.7 g. of barium chloride and heated at 100 ° C. for one hour, then filtered. The crystals thus obtained are treated again in the same manner and a barium X zeolite is obtained in which 93% of the sodium ions originally present have been replaced by barium ions.



   A glass exchange column is packed without tamping, up to 70 cm. in height of 37 g. of sodium zeolite X in tablets. 2.75 liters of a 0.05 M aqueous solution of zinc nitrate are passed through the column over a period of a little over five hours. The chemical analysis of the zeolite thus exchanged indicates a replacement of 47% of the sodium ions by

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 zinc ions, in the ratio of one atom of zinc to two of sodium. By varying the concentration of zinc or other exchange ion, or the temperature, ion exchange up to almost 100% of the sodium ions can be achieved.



   Among the ways to identify zeolite X and to distinguish this zeolite from other zeolites and other crystalline substances, the X-ray diffraction spectrum has proved to be an interesting means. The X-ray diffraction spectrum (powder) is obtained by standard techniques. The radiation is the doublet K u of copper; a Geiger counter recording spectrophotometer is used. The heights of the maxima I and the positions as a function of 20 where 0 is the Bragg angle are read from the spectrophotometer graph. We calculate by this means the relative intensities 100 1 where 10 is the intensity
1 0 of the strongest or maximum line, and d (obs) the interplanar space in angstroms corresponding to the recorded lines.



   Table A gives the values relating to the X-ray diffraction spectra (on powder) of sodium X zeolite (Na2X), of calcium zeolite CaX at 89% exchange, of silver zeolite X (Ag2X) at 85% exchange, ceric zeolite X (Ce2X3) at 77% exchange, lithic zeolite X (Li2X) at 59% exchange, ammonium zeolite X [(NH4) 2X] 81% exchange and barite zeolite X (BaX) at 93% exchange. This table gives the values 100 1 and d (obs) in angstroms for the observed lines
1 for the different forms of X zeolites with different ions exchanged.

   The X-ray spectrum indicates a cubic cell with dimensions of 24.5 angstroms to 25.5 angstroms. A separate column shows the sum of the squares of the Miller indices (h2 + k2 + I2) for a cubic cell, corresponding to the lines observed in the X-ray diffraction spectra. The ao values of each particular zeolite are also shown.



   The relative intensities and line positions differ only slightly in the various exchanged forms of X zeolites. The spectra all show substantially the same lines and all meet the requirements of a cubic cell of approximately the same size. . The spatial arrangement of the atoms of silicon, oxygen and aluminum, i.e. the arrangement of the tetrahedra of AlO4 and SiO4, is essentially the same for all forms of zeolite X. The appearance of a few less important lines of disappearance of others, from one form of zeolite X to another, is attributable to the different dimensions and different numbers of cations present in the various forms, these differences causing some expansion or contraction of the crystals .

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  TABLE A
 EMI10.1
 
<tb>
<tb> CaX <SEP> Ag2CX <SEP> BaX <SEP> Ce2X3
<tb> (h2 + k2 + 12) <SEP> 100 <SEP> d (obs) <SEP> 100 <SEP> d (obs) <SEP> 100 <SEP> d (obs) <SEP> 100 <SEP> d (obs)
<tb> 1/10 <SEP> angst. <SEP> 1/10 <SEP> angst. <SEP> 1/10 <SEP> ang. <SEP> 1/10 <SEP> ang.
<tb>



  3 <SEP> 100 <SEP> 14.37 <SEP> 100 <SEP> 14.37 <SEP> 100 <SEP> 14.43 <SEP> 100 <SEP> 14.42
<tb> 8 <SEP> 9 <SEP> 8.79 <SEP> 2 <SEP> 8, <SEP> 82 <SEP> 7 <SEP> 8.84 <SEP> 2 <SEP> 8.81
<tb> 11 <SEP> 4 <SEP> 7.51 <SEP> 6 <SEP> 7.54 <SEP> 81
<tb> 12 <SEP> 29 <SEP> 7.21
<tb> 16 <SEP> 16 <SEP> 6.23 <SEP> 13 <SEP> 6.25 <SEP> 4 <SEP> 6.24
<tb> 19 <SEP> 16 <SEP> 5.71 <SEP> 27 <SEP> 5.73 <SEP> 18 <SEP> 5, <SEP> 72 <SEP>
<tb> 27 <SEP> 5 <SEP> 4.79 <SEP> 2 <SEP> 4.80 <SEP> 6 <SEP> 4.80 <SEP> 7 <SEP> 4.80
<tb> 32 <SEP> 11 <SEP> 4.40 <SEP> 6 <SEP> 4.41 <SEP> 4, <SEP> 42 <SEP> 4 <SEP> 4.41
<tb> 35 <SEP> 3 <SEP> 4.22
<tb> 36 <SEP> 3 <SEP> 4.16
<tb> 40 <SEP> 2 <SEP> 3,936 <SEP> 10 <SEP> 3,948
<tb> 43 <SEP> 20 <SEP> 3.8 <SEP> 9 <SEP> 3.805 <SEP> 45 <SEP> 3.810 <SEP> 38 <SEP> 3.808
<tb> 44 <SEP> 2 <SEP> 3,754 <SEP> 11 <SEP> 3,760 <SEP> 89 <SEP> 3,767 <SEP> 4 <SEP> 3,767
<tb> 48 <SEP> 2 <SEP> 3,

  593 <SEP> 5 <SEP> 3,603 <SEP> 7 <SEP> 3,606
<tb> 51 <SEP> 2 <SEP> 3,486 <SEP> 3 <SEP> 3,494 <SEP> 9 <SEP> 3,499 <SEP> 4 <SEP> 3,499
<tb> 56 <SEP> 12 <SEP> 3.328 <SEP> 11 <SEP> 3.335 <SEP> 28 <SEP> 3.339 <SEP> 18 <SEP> 3.339
<tb> 59 <SEP> 3 <SEP> 3,241 <SEP> 6 <SEP> 3,250 <SEP> 11 <SEP> 3,253 <SEP> 3 <SEP> 3,253
<tb> 67 <SEP> 4 <SEP> 3.041 <SEP> 10 <SEP> 3.051
<tb> 68 <SEP> 2 <SEP> 3.027
<tb> 72 <SEP> 8 <SEP> 2,934 <SEP> 7 <SEP> 2,941 <SEP> 14 <SEP> 2,944 <SEP> 10 <SEP> 2,944
<tb> 75 <SEP> 6 <SEP> 2.875 <SEP> 12 <SEP> 2.882 <SEP> 19 <SEP> 2.887 <SEP> 13 <SEP> 2.886
<tb> 76 <SEP> 17 <SEP> 2,869
<tb> 80 <SEP> 7 <SEP> 2,783 <SEP> 25 <SEP> 2,792 <SEP> 68 <SEP> 2,795 <SEP> 13 <SEP> 2,794
<tb> 83 <SEP> 4 <SEP> 2,732 <SEP> 4 <SEP> 2,739 <SEP> 13 <SEP> 2,742 <SEP> 4 <SEP> 2,744
<tb> 88 <SEP> 6 <SEP> 2,653 <SEP> 5 <SEP> 2,662 <SEP> 10 <SEP> 2,663 <SEP> 8 <SEP> 2,663
<tb> 91 <SEP> 4 <SEP> 2,

  610 <SEP> 9 <SEP> 2,617 <SEP> 7 <SEP> 2,620 <SEP> 7 <SEP> 2,620
<tb> 96 <SEP> 12 <SEP> 2,549 <SEP> 24 <SEP> 2,551 <SEP> 4 <SEP> 2,552
<tb> 99 <SEP> 5 <SEP> 2.512
<tb> 104 <SEP> 1 <SEP> 2,440 <SEP> 3 <SEP> 2,451
<tb> 107 <SEP> 20 <SEP> 2,418
<tb> 108 <SEP> 5 <SEP> 2,396 <SEP> 9 <SEP> 2,207 <SEP> 26 <SEP> 2,406
<tb> 115 <SEP> 6 <SEP> 2.182 <SEP> 7 <SEP> 2.331
<tb> 116 <SEP> 4 <SEP> 2,140 <SEP> 4 <SEP> 2,323
<tb> 128 <SEP> 3 <SEP> 2,202 <SEP> 2 <SEP> 2,119 <SEP> 27 <SEP> 2,210 <SEP> 10 <SEP> 2,210
<tb> 131 <SEP> 2 <SEP> 2.175 <SEP> 5 <SEP> 2.184
<tb> 136 <SEP> 3 <SEP> 2,139 <SEP> 12 <SEP> 2,140 <SEP> 7 <SEP> 2,140
<tb> 138 <SEP> 2 <SEP> 2,112 <SEP> 5 <SEP> 2,121
<tb> 140 <SEP> 25 <SEP> 2,113
<tb> 144 <SEP> 1 <SEP> 2.074
<tb> 155 <SEP> 1 <SEP> 2,000
<tb> 160 <SEP> 2 <SEP> 1.975
<tb> 163 <SEP> 3 <SEP> 1.954 <SEP> 3 <SEP> 1.956
<tb> 164 <SEP> 1 <SEP> 1.945
<tb> 168 <SEP> 1 <SEP> 1,

  921
<tb> 172 <SEP> 6 <SEP> 1,908
<tb> 176 <SEP> 4 <SEP> 1.882 <SEP> 6 <SEP> 1.885
<tb> 179 <SEP> 1 <SEP> 1.859
<tb> 187 <SEP> 1 <SEP> 1,821 <SEP> 7 <SEP> 1,829
<tb> 195 <SEP> 1 <SEP> 1,784 <SEP> 3 <SEP> 1,790
<tb> 200 <SEP> 2 <SEP> 1,761 <SEP> 7 <SEP> 1,768 <SEP> 4 <SEP> 1,769
<tb> 204 <SEP> 6 <SEP> 1,751
<tb>
 

 <Desc / Clms Page number 11>

 
 EMI11.1
 
<tb>
<tb> 211 <SEP> 2 <SEP> 1,714
<tb> 236 <SEP> 8 <SEP> 1,628
<tb>
 
 EMI11.2
 243 3 1, 597 3 1.60 in 11.604 3 1, 604 0 0 0 0 ô = 24.90 A ao = 24.96 A a 0 = 2q., 99 A a 0 = 24.99 A
 EMI11.3
 
<tb>
<tb> (NH4) 2X <SEP> Li2X <SEP> Na2X
<tb> h2 + k2 + 12 <SEP> 100 <SEP> 1/10 <SEP> d (obs) <SEP> 100 <SEP> 1/1 <SEP> d <SEP> (obs) <SEP> 100 < SEP> 1/1 <SEP> d <SEP> (obs)
<tb> <SEP> angst. <SEP> angst.

   <SEP> angstroms
<tb> 3 <SEP> 100 <SEP> 14.41 <SEP> 100 <SEP> 14.37 <SEP> 100 <SEP> 14.47
<tb> 8 <SEP> 16 <SEP> 8.85 <SEP> 18 <SEP> 8.79 <SEP> 18 <SEP> 8.85
<tb> 11 <SEP> 10 <SEP> 7.53 <SEP> 14 <SEP> 7.49 <SEP> 12 <SEP> 7.54
<tb> 19 <SEP> 15 <SEP> 5.73 <SEP> 20 <SEP> 5.70 <SEP> 18 <SEP> 5.73
<tb> 27 <SEP> 6 <SEP> 4.81 <SEP> 7 <SEP> 4.79 <SEP> 5 <SEP> 4.81
<tb> 32 <SEP> 14 <SEP> 4.42 <SEP> 11 <SEP> 4.40 <SEP> 9 <SEP> 4.42
<tb> 35 <SEP> 1 <SEP> 4.23 <SEP> 1 <SEP> 4.21 <SEP> 1 <SEP> 4.23
<tb> 40 <SEP> 5 <SEP> 3,953 <SEP> 5 <SEP> 3,931 <SEP> 4 <SEP> 3,946
<tb> 43 <SEP> 19 <SEP> 3,813 <SEP> 23 <SEP> 3,794 <SEP> 21 <SEP> 3,808
<tb> 44 <SEP> 2 <SEP> 3,773 <SEP> 3 <SEP> 3,749 <SEP> 3 <SEP> 3,765
<tb> 48 <SEP> 2 <SEP> 3,610 <SEP> 1 <SEP> 3,590 <SEP> 1 <SEP> 3,609
<tb> 51 <SEP> 2 <SEP> 3,500 <SEP> 2 <SEP> 3,482 <SEP> 1 <SEP> 3,5
<tb> 56 <SEP> 17 <SEP> 3.341 <SEP> 22 <SEP> 3,

  324 <SEP> 18 <SEP> 3.338
<tb> 59 <SEP> 2 <SEP> 3,257 <SEP> 2 <SEP> 3,239 <SEP> 1 <SEP> 3,253
<tb> 67 <SEP> 4 <SEP> 3.056 <SEP> 6 <SEP> 3.040 <SEP> 4 <SEP> 3.051
<tb> 72 <SEP> 10 <SEP> 2,948 <SEP> 10 <SEP> 2,933 <SEP> 9 <SEP> 2,944
<tb> 75 <SEP> 13 <SEP> 2,889 <SEP> 22 <SEP> 2,874 <SEP> 19 <SEP> 2,885
<tb> 80 <SEP> 11 <SEP> 2,797 <SEP> 9 <SEP> 2,782 <SEP> 8 <SEP> 2,794
<tb> 83 <SEP> 3 <SEP> 2,746 <SEP> 3 <SEP> 2,730 <SEP> 2 <SEP> 2,743
<tb> 88 <SEP> 9 <SEP> 2,667 <SEP> 9 <SEP> 2,653 <SEP> 8 <SEP> 2,663
<tb> 91 <SEP> 1 <SEP> 2,623 <SEP> 3 <SEP> 2,609 <SEP> 3 <SEP> 2,620
<tb> 96 <SEP> 1 <SEP> 2,553 <SEP> 1 <SEP> 2,542 <SEP> 1 <SEP> 2,550
<tb> 104 <SEP> 1 <SEP> 2.451
<tb> 108 <SEP> 4 <SEP> 2.407 <SEP> 6 <SEP> 2.395 <SEP> 5 <SEP> 2.404
<tb> 123 <SEP> 1 <SEP> 2,256 <SEP> 1 <SEP> 2,244 <SEP> 1 <SEP> 2,254
<tb> 128 <SEP> 4 <SEP> 2,210 <SEP> 3 <SEP> 2,200 <SEP> 3 <SEP> 2,

  209
<tb> 131 <SEP> 2 <SEP> 2,183 <SEP> 2 <SEP> 2,175 <SEP> 3 <SEP> 2,182
<tb> 136 <SEP> 2 <SEP> 2,140 <SEP> 3 <SEP> 2,139 <SEP> 2 <SEP> 2,141
<tb>
 
 EMI11.4
 13 9 1 2.121 2 2.110 2 2.120
 EMI11.5
 
<tb>
<tb> 144 <SEP> 2 <SEP> 2,084 <SEP> 2 <SEP> 2,074 <SEP> 1 <SEP> 2,083
<tb> 147 <SEP> 1 <SEP> 2,060
<tb> 155 <SEP> 1 <SEP> 2.007
<tb> 164 <SEP> 1 <SEP> 1.952 <SEP> 2 <SEP> 1.945 <SEP> 1 <SEP> 1.952
<tb> 168 <SEP> 1 <SEP> 1,929 <SEP> 2 <SEP> 1,920 <SEP> 1 <SEP> 1,928
<tb> 179 <SEP> 2 <SEP> 1,860
<tb> 184 <SEP> 1 <SEP> 1,842
<tb> 187 <SEP> 1 <SEP> 1,829 <SEP> 2 <SEP> 1,820
<tb> 195 <SEP> 1 <SEP> 1,790 <SEP> 1 <SEP> 1,789
<tb> 200 <SEP> 2 <SEP> 1,767 <SEP> 2 <SEP> 1,760 <SEP> 2 <SEP> 1,767
<tb> 211 <SEP> 3 <SEP> 1,721 <SEP> 5 <SEP> 1,713 <SEP> 3 <SEP> 1,721
<tb> 236 <SEP> 1 <SEP> 1,628 <SEP> 1 <SEP> 1,621
<tb> 243 <SEP> 3 <SEP> 1,604 <SEP> 5 <SEP> 1,596 <SEP> 3 <SEP> 1,

  603
<tb>
<tb> ao <SEP> = <SEP> 25.01 <SEP> A <SEP> ao <SEP> = <SEP> 24.88 <SEP> A <SEP> ao <SEP> = <SEP> 24.99 <SEP> A
<tb>
 

 <Desc / Clms Page number 12>

 
The most significant values of d for zeolite X are given in Table B.



   TABLE B.



   D-value of reflection in angstroms
 EMI12.1
 
<tb>
<tb> 14.42 <SEP> ¯ <SEP> 0.2
<tb> 8.82 <SEP> 0.1 <SEP>
<tb> 4.41 <SEP> ¯ <SEP> 0.05
<tb> 3.80 <SEP> ¯ <SEP> 0.05
<tb> 3.33 <SEP> ¯ <SEP> 0.05
<tb> 2.88 <SEP> ¯ <SEP> 0.05
<tb> 2.79 <SEP> ¯ <SEP> 0.05
<tb> 2.66 <SEP> ¯ <SEP> 0.05
<tb>
 
Occasionally, additional lines not belonging to the spectrum of zeolite X appear together with the characteristic lines of zeolite X. This indicates that there is one or more crystalline materials in admixture with zeolite X in the treated sample.



  Additional materials can often be identified as being in the initial reagents in the synthesis of the zeolite, or as other crystalline substances. When the X zeolite is heat treated at temperatures between 100 and 600 C. in the presence of water vapor or other gases or vapors, the relative intensities of the lines present in the X-ray spectrum may be. appreciably altered from those observed in the spectra of the unactivated X zeolite. Small changes in the position of the lines can also occur under these conditions. These changes in no way affect the identification of these X-ray spectra as relating to the X zeolite.



   The particular technique and / or apparatus used, humidity, temperature, orientation of powder crystals, and other variables, as is well known to those skilled in crystallography or X-ray diffraction, can cause certain variations in the currents and positions of the lines.

   These changes, even in the rare cases where they are significant, do not pose identification problems for an x-ray specialist. Thus'. the results given here to identify the zeolite X lattice do not exclude those materials which, due to the mentioned or known variables, do not show all the lines or show additional lines which are admissible in the cubic system of the zeolite X , or show a slight displacement of these lines so as to give a slightly larger or smaller reticular parameter.



   A simple test described in "American Mineralogist", vol. 28, p. 5451 1943, allows rapid control of the silicon / aluminum ratio in zeolite X. According to the description of the test, the three-dimensional lattice zeolites containing aluminum and silicon in an Al / Si atomic ratio = 0, 67 or more give a gel when treated with hydrochloric acid. Zeolites with smaller aluminum / silicon ratios break down in the presence of hydrochloric acid and precipitate silica. When mixing about 0.2 g. powdered sodium zeolite X with water and about 2 cc. of concentrated hydrochloric acid and when heated, a solid, almost clear gel forms.



   The zeolites contemplated here exhibit adsorption properties.

 <Desc / Clms Page number 13>

 exceptional tion among the known adsorbents. Common adsorbents, such as charcoal and silica gel, exhibit adsorption selectivities based primarily on the boiling point or critical temperature of the adsorbates. In contrast, the activated zeolite X exhibits selectivity based on the size and shape of the adsorbate molecule. Among the molecules of adsorbates whose size and shape are such as to allow adsorption by zeolite X, the latter shows a strong preference for those which are polar, polarizable and non-saturated.

   Another property of zeolite X which contributes to its exceptional position among adsorbents is that of adsorbing large amounts of adsorbates even at very low pressures, very low partial pressures or very low concentrations. One of these adsorption characteristics or a combination of several of these characteristics or others can make zeolite X useful in many gas or liquid separation processes which do not currently involve the use of adsorbents. The use of zeolite X makes it possible to carry out in a more efficient and more economical manner many processes currently using other adsorbents.



   Common adsorbents like silica gel and charcoal do not show any appreciable molecular sieving action as do the various forms of zeolite X. This sieving action of sodium zeolite X is shown in the following table in which P represents the vapor pressure of the adsorbate at 25 C. In this table, as well as others appearing during this description, the expression "adsorbed weight%" refers to the percentage increase in weight of the adsorbent . The adsorbents are activated by heating under reduced pressure so as to remove the adsorbed material. Throughout this specification, the activation temperature of zeolite X is 350 ° C. and the absolute pressure to which it is heated is less than about 0.1 mm. of mercury, unless otherwise specified.

   Likewise, the pressure given for each adsorption is the pressure of the adsorbate under the adsorption conditions, unless otherwise indicated.
 EMI13.1
 
<tb>
<tb>



  Adsorbat <SEP> Temp. <SEP> Pressure <SEP> Weight <SEP> adsorbed <SEP>% <SEP>
<tb> C <SEP> mm. <SEP> Hg <SEP> on <SEP> Na2X
<tb> Octane <SEP> 25 <SEP> 11 <SEP> 30.0
<tb> Benzene <SEP> 25 <SEP> 45 <SEP> 25.0
<tb> m-dichlorobenzene <SEP> 25 <SEP> P <SEP> 35.5
<tb> Heptacosafluorotri- <SEP> 23 <SEP> P <SEP> <SEP> 2,2
<tb> butylamine
<tb>
 
These results show that the porous structure of sodium zeolite X allows free access for molecules of octane, benzene and dichlorobenzene, which are thus easily adsorbed. On the other hand, it does not allow access to heptacosafluorotributylamine. This adsorption behavior makes it possible to separate mixtures of heptacosafluorotributylamine and larger molecules with benzene, toluene, octane or other kinds of molecules small enough to be adsorbed.



   Measurements made using various forms of zeolite X exchange show that the pore size varies from one form to another.



  Lithium X zeolite, sodium zeolite X, and calcium zeolite X all adsorb diphenylmethane, but the adsorption rates and equilibrium adsorption capacities are different, as shown below.

 <Desc / Clms Page number 14>

 
 EMI14.1
 
<tb>
<tb> Adsorbent <SEP> Temp. <SEP> C. <SEP> Pressure <SEP> Weight <SEP>% <SEP> of <SEP> diphenylmethane
<tb> adsorbed <SEP> in <SEP> 9 <SEP> hours
<tb>
 
 EMI14.2
 Na2X 25 Po ...

   5.9
 EMI14.3
 
<tb>
<tb> Li2X <SEP> 25 <SEP> Po <SEP> 11.1
<tb> CaX <SEP> 25 <SEP> Po <SEP> 15.7
<tb>
   # Po is the vapor pressure of diphenylmethane at 25 C,
These results show that replacing the sodium ions present in the original sodium X zeolite with half the calcium ions of about the same size opened the pore structure sufficiently to allow freer access of the diphenylmethane. A slightly less pronounced enlargement of the dimensions of the pores is obtained by replacing a number of sodium ions by a standard number of small lithium ions.



   The adsorption properties of zeolite X can be modified by partially filling the pores of zeolite X with 8 * molecular species different from that of which the adsorption is being studied. This effect is shown by the adsorption of acetylene on fully activated Na2X and on Na2X samples partially loaded with water.
 EMI14.4
 
<tb>
<tb>



  Condition <SEP> of <SEP> Na2X <SEP> Weight <SEP>% <SEP> of <SEP> C2H2 <SEP> adsorbed <SEP> on <SEP> Na2X
<tb>
 
 EMI14.5
 ¯¯¯¯¯¯¯¯¯¯¯¯¯¯ to 700 mm. îg and 25 C.
 EMI14.6
 
<tb>
<tb> completely <SEP> enabled <SEP> 15
<tb> Charged <SEP> with water <SEP> to <SEP> 5% <SEP> in <SEP> weight <SEP> 12.4
<tb> Charged <SEP> with water <SEP> to <SEP> 15% <SEP> in <SEP> weight <SEP> 7.2
<tb>
 
Another exceptional property of zeolite X is its marked preference for polar, polarizable and unsaturated molecules, of course provided that these molecules are of such a size and shape that they can enter the system. pores. This is in contrast to what happens with charcoal and silica gel, the selectivity of which is based on the volatility of the adsorbate.

   The following table compares the adsorptions of water, a polar molecule, of carbon dioxide, a polarizable molecule, and acetylene, a non-saturated molecule, on charcoal, silica gel and sodium zeolite X.
 EMI14.7
 
<tb>
<tb>



  Adsorbat <SEP> Temp. <SEP> Pressure <SEP> ¯¯¯¯¯¯¯ Weight <SEP>% <SEP> adsorbed
<tb> 0 C <SEP> mm. <SEP> Hg <SEP> Na2X <SEP> Gel <SEP> of <SEP> silica <SEP> Charcoal <SEP> of <SEP> wood
<tb> Water <SEP> 25 <SEP> 0.2 <SEP> 25.7 <SEP> 1.6 <SEP> 0.1
<tb> Acetylene <SEP> 25 <SEP> 50 <SEP> 10.6 <SEP> 2.1 <SEP> 2.5
<tb> Carbonless <SEP> 25 <SEP> 50 <SEP> 15.7 <SEP> 1.3 <SEP> 2.2
<tb>
 
The affinity of zeolite X for the adsorbate is all the greater as the degree of polarity, polarizability and unsaturation is higher. This is shown by the following results relating to a series of C2 and C3 hydrocarbons adsorbed on sodium zeolite.

 <Desc / Clms Page number 15>

 
 EMI15.1
 
<tb>
<tb>



  Pressure, <SEP> mm, <SEP> Hg. <SEP> Temp. C <SEP> Weight <SEP>% <SEP> adsorbed <SEP> on <SEP> Na2X
<tb> C2H6 <SEP> C2H4 <SEP> C2H2
<tb> 5 <SEP> 25 <SEP> 0.2 <SEP> 1.4 <SEP> 6.6
<tb> 25 <SEP> 25 <SEP> 0.8 <SEP> 6.1 <SEP> 9.8
<tb> Weight <SEP>% <SEP> adsorbed <SEP> on <SEP> Na2X
<tb> C3H8 <SEP> C3H6
<tb> 1 <SEP> 25 <SEP> 0.8 <SEP> 6.0
<tb> 5 <SEP> 25 <SEP> 3.1 <SEP> 10.6
<tb>
 
The adsorption selectivity of zeolite X for polar molecules relative to non-polar molecules is shown in the following table which compares carbon monoxide, a polar molecule, with argon, a non-polar molecule whose dimension and volatility are much the same.
 EMI15.2
 
<tb>
<tb>



  Adsorbat <SEP> Temp <SEP>. C. <SEP> Pressure, <SEP> mm. <SEP> Hg <SEP> Weight <SEP>% <SEP> adsorbed <SEP> on
<tb> ¯¯¯¯¯¯¯ <SEP> ¯¯¯¯¯¯¯ <SEP> ¯¯¯¯¯¯¯¯¯¯¯¯¯ <SEP> BaX
<tb> Argon <SEP> -75 <SEP> 500 <SEP> 5.0
<tb> Oxide <SEP> of
<tb> carbon-75 <SEP> 500 <SEP> 10.0
<tb>
 
The selectivity of zeolite X for an unsaturated aromatic hydrocarbon, toluene, compared to a saturated cyclic hydrocarbon, cyclohexane, is illustrated by the following results:

   
 EMI15.3
 
<tb>
<tb> Pressure, <SEP> mm.Hg. <SEP> Temp. <SEP> C. <SEP> Weight <SEP>% <SEP> adsorbed <SEP> on <SEP> Na2X
<tb> Toluene <SEP> cyclohexane
<tb> 0.05 <SEP> 25 <SEP> 13.0 <SEP> 7
<tb> 0.10 <SEP> 25 <SEP> 19.7 <SEP> 12.3
<tb>
 
Organic sulfur compounds are generally more polar or polarizable than their hydrocarbon counterpart, so that organic sulfur compounds can be selectively adsorbed in mixtures with hydrocarbons of approximately the same composition and degree of unsaturation. Thus, thiophene and benzene have about the same volatility and are difficult to separate by distillation, whereas zeolite X can effect the separation by selective adsorption of thiophene.



  As a demonstration, 6.6 g of powdered Na2X are placed in 12 g. of a mixture containing 24.3% thiophene and 75.7% benzene. It is shaken for a short time and it is observed that the thiophene concentration of the supernatant liquid is reduced to 21.4%. In another test, vapors containing 0.44% thiophene are passed in benzene over a bed of Na X; the outgoing vapors contain only 0.19% thiophene.



   The selectivity for a given adsorbate molecule is modified by ion exchange in sodium zeolite X. Thus, for a particular adsorbate, one of the many cationic forms of zeolite X, such as barium zeolite X, may be a better adsorbent than other cationics of zeolite X. Furthermore, the relative selectivity between the various cationic forms of zeolite X changes with temperature or with increasing frequency.

 <Desc / Clms Page number 16>

 the pressure at which the adsorptions are effected. Here are various illustrations of these effects.
 EMI16.1
 
<tb>
<tb>



  AdsorbatTemp. <SEP> Pressure <SEP> Weight <SEP>% <SEP> adsorbed
<tb> C <SEP> mm.Hg. <SEP> Na2X <SEP> CaX <SEP> MgX <SEP> BaX <SEP> MnX <SEP> Li2X <SEP> Ce2X3
<tb>
 
 EMI16.2
 Water 25 0.04 - 22.9 - 20.1 1913 - 13.1
 EMI16.3
 
<tb>
<tb> 25 <SEP> 4.5 <SEP> 29.3 <SEP> 33.3 <SEP> 34.2 <SEP> 25.8 <SEP> 31.9 <SEP> 31.8 <SEP> 27 , 1
<tb>
 
 EMI16.4
 Oxide of ¯75 25 5.4 4.5 carbon 25 5.4 - 891 4.5 - ls8
 EMI16.5
 
<tb>
<tb> 0 <SEP> 25- <SEP> 2.5 <SEP> - <SEP> 0.8 <SEP> 0.8 <SEP> - <SEP> 0.0
<tb> o <SEP> 750 <SEP> - <SEP> 5,1 <SEP> - <SEP> 6,8 <SEP> 4, <SEP> 2 <SEP> - <SEP> 1,9
<tb> Nitrogen <SEP> -75 <SEP> 738 <SEP> - <SEP> 9.0 <SEP> - <SEP> 10.8 <SEP> 8.6 <SEP> @ <SEP> 5.3
<tb>
 
 EMI16.6
 n-hexane 25 20 1.9, 2 - 18, 3 15, 8 1 d, 9 tes 16.1 methylcyclo-
 EMI16.7
 
<tb>
<tb> hexane <SEP> 25 <SEP> 38 <SEP> 20.7 <SEP> - <SEP> 24.4 <SEP> 16.8 <SEP> 20.0 <SEP> 21.3 <SEP> 17 ,

  6
<tb>
 
The high degree of selectivity exhibited by zeolite X for polar, polarizable and unsaturated molecules makes zeolite X more useful in separating polar molecules from less polar or non-polar molecules, polarizable molecules from less polarizable or non-polarized molecules. -polarisables, and 'unsaturated molecules less non-saturated molecules or saturated molecules.



   Zeolite X shows selectivity for adsorbates, provided that they can enter its porous network according to the points
 EMI16.8
 boiling point of said adsorl3a-ts, as well as their polarity, their peelability and their degree of unsaturation. For example, hydrogen is not strongly adsorbed at room temperature because its boiling point is too low. A non-polar saturated molecule of ethane adsorbs somewhat more strongly at room temperature than the polar carbon monoxide molecule because of the much lower boiling point effect of carbon monoxide. (-192 C) than that of ethane (-88 C.) outweighs the effect of the higher polarity of carbon monoxide.



   Another important characteristic of zeolite X is its property of adsorbing large amounts of adsorbates at low pressures, partial pressures or concentrations of adsorbates. This property makes zeolite X useful in removing adsorbable impurities from gas and liquid mixtures because its adsorption capacity is relatively high even when the material being adsorbed is at a low concentration. It is also possible to efficiently recover compounds existing in very low proportions in the mixtures. The following table gives examples of high adsorption at low pressures by zeolite X, with comparative results for silica gel and charcoal. .

 <Desc / Clms Page number 17>

 
 EMI17.1
 
<tb>
<tb>



  Adsorbat <SEP> Temp. <SEP> C <SEP> Pressure <SEP> ¯¯¯¯¯¯ Weight <SEP>% <SEP> adsorbed
<tb> mm. <SEP> Hg. <SEP> Na2H <SEP> Gel <SEP> silica <SEP> Carbon <SEP> of <SEP> b.
<tb>



  Water <SEP> 25 <SEP> 0.02 <SEP> 14.5 <SEP> 0.7 <SEP> 0.4
<tb>
 
 EMI17.2
 25 0.1 23.1 1.2 - 25 4.5 32.3 11.4 2.7 25 Po 39.5 42.9 24.1 co2 25 1.6 3.7 0.5 0.5
 EMI17.3
 
<tb>
<tb> 25 <SEP> 80 <SEP> 18.0 <SEP> 0.6 <SEP> 2.3
<tb> 25 <SEP> 750 <SEP> 26.3 <SEP> 4.6 <SEP> 10.0
<tb> SO2 <SEP> 25 <SEP> 0.7 <SEP> 30.2 <SEP> - <SEP> 1.7
<tb> 25 <SEP> 12 <SEP> 38.1 <SEP> - <SEP> 10.7
<tb> 25 <SEP> 696 <SEP> 42.9 <SEP> - <SEP> 61.6
<tb> H2S <SEP> 25 <SEP> 0.5 <SEP> 115, <SEP> -
<tb> 25 <SEP> 11 <SEP> 22.6
<tb> 25 <SEP> 400 <SEP> 35.0
<tb> NH3 <SEP> 25 <SEP> 0.6 <SEP> 5.9 <SEP> 1.9 <SEP> 0.3
<tb> 25 <SEP> 9 <SEP> 12.7 <SEP> 5.9 <SEP> 0.4
<tb> 25 <SEP> 700 <SEP> 19.7 <SEP> 12.9 <SEP> 8.3
<tb> C2H2 <SEP> 25 <SEP> 4.9 <SEP> 6.6
<tb> 25 <SEP> 9.8 <SEP> 1.7 <SEP> 2.0
<tb> 200 <SEP> 13.3 <SEP> 2.2 <SEP> 4.0
<tb>
 
 EMI17.4
 740 14.7 2.2 4.9
 EMI17.5
 
<tb>
<tb> C2H4 <SEP> 25 <SEP> 37 <SEP> 7,

  1 <SEP> 2.1 <SEP> 4.4
<tb> 160 <SEP> 10.1 <SEP> 2.7 <SEP> 7.1
<tb> C2H6 <SEP> 25 <SEP> 25 <SEP> 0.8 <SEP> 0.0 <SEP> 3.3
<tb> 300 <SEP> 8.3 <SEP> 0.6 <SEP> 8.8
<tb> 700 <SEP> 10.2 <SEP> 1.4 <SEP> 11.4
<tb> C3H6 <SEP> 25 <SEP> 0.1 <SEP> 2.2 <SEP> 0.1
<tb> 2 <SEP> 8.5 <SEP> 0.3
<tb>
 
 EMI17.6
 48 14.9 3 1 11.6
 EMI17.7
 
<tb>
<tb> C3H8 <SEP> 25 <SEP> 4 <SEP> 2.6 <SEP> 0.1
<tb> 3H8 <SEP> 25 <SEP> 11.1 <SEP> 0.8
<tb> 700 <SEP> 14.6 <SEP> 6.5 <SEP> i-C4H10 <SEP> 25 <SEP> 0.2 <SEP> 2.4 <SEP> 0.0 <SEP> -
<tb> 5.5 <SEP> 11.5 <SEP> 0.7 <SEP> 15.9
<tb> 400 <SEP> 18.4 <SEP> 11.8 <SEP> 27.2
<tb> C4H8-1 <SEP> 25 <SEP> 0.1 <SEP> 9.9 <SEP> 0.4 <SEP> -
<tb> 5 <SEP> 17.0 <SEP> 2.2 <SEP> 12.5
<tb>
 
 EMI17.8
 350 19.6 15.5 28.9
 EMI17.9
 
<tb>
<tb> n-C6H14 <SEP> 25 <SEP> 0.18 <SEP> 4.8 <SEP> -
<tb> (hexane <SEP> n) <SEP> 0.22 <SEP> 10.2 <SEP> - <SEP> -
<tb> 20 <SEP> 19,

  2 <SEP> - <SEP> Cyclohexane
<tb> C6H12 <SEP> 25 <SEP> 0.03 <SEP> 4.8 <SEP> -
<tb>
 
 EMI17.10
 0.18 17.5 - -
 EMI17.11
 
<tb>
<tb> 45 <SEP> 19.6
<tb> Toluene
<tb> C6H5CH3 <SEP> 25 <SEP> 0.03 <SEP> 7.5
<tb>
 
 EMI17.12
 0.08 18.0 - -
 EMI17.13
 
<tb>
<tb> 27 <SEP> 26.8 <SEP> -
<tb>
 

 <Desc / Clms Page number 18>

 
 EMI18.1
 
<tb>
<tb> Adsorbat <SEP> Temp. <SEP> C <SEP> Pressure <SEP> Weight <SEP>% <SEP> adsorbed
<tb> mm. <SEP> Hg. <SEP> Na2X <SEP> Gel <SEP> silica <SEP> Carbon <SEP> of <SEP> b.
<tb>



  CO <SEP> 0 <SEP> 50 <SEP> 0.8 <SEP> -
<tb> 298 <SEP> 3.2 <SEP> -
<tb> 750 <SEP> 5.1
<tb>
 
 EMI18.2
 CH30H 25 0.01 6.6 1.3 0.0
 EMI18.3
 
<tb>
<tb> 0.08 <SEP> 14.5 <SEP> 3.8 <SEP> 0.3
<tb> 1.2 <SEP> 21.7 <SEP> 9.3 <SEP> 1.6
<tb> 90 <SEP> 24.1 <SEP> 28.4 <SEP> -
<tb>
 
 EMI18.4
 
<tb>
<tb> Weight <SEP>% <SEP> adsorbed
<tb> Na2X <SEP> BaX <SEP> CaK <SEP> K2X
<tb> Nitrogen <SEP> -196 <SEP> 5 <SEP> 24.8
<tb> Nitrogen <SEP> -196 <SEP> 195 <SEP> 21.9 <SEP> 27.5
<tb> Oxygen <SEP> -196 <SEP> 56 <SEP> 34.0
<tb> Argon <SEP> -196 <SEP> 146 <SEP> 42.0 <SEP> 34.1 <SEP> 43.7
<tb> Krypton <SEP> -183 <SEP> 17 <SEP> 73
<tb> Hydrogen <SEP> -1 <SEP> 96 <SEP> 100 <SEP> <<SEP> 1
<tb> Helium <SEP> -196 <SEP> 100 <SEP> <<SEP> 1
<tb> Oxide <SEP> of
<tb> carbon <SEP> - <SEP> 75 <SEP> 500 <SEP> 15.8
<tb> Nitrogen- <SEP> 75 <SEP> 500 <SEP> 9.6 <SEP> 10 <SEP> 10.0 <SEP> 7,

  9
<tb> Oxygen <SEP> -75 <SEP> 500 <SEP> 5.2 <SEP> 6.5 <SEP> 6.5 <SEP> 5.8
<tb> Argon <SEP> -75 <SEP> 500 <SEP> 5.1 <SEP> 5.1 <SEP> 5.0
<tb> Oxygen <SEP> 25 <SEP> 500 <SEP> <<SEP> 1 <SEP>
<tb> Hydrogen <SEP> 25 <SEP> 500 <SEP> <<SEP> 1
<tb> Oxide <SEP> of
<tb> carbon <SEP> 25 <SEP> 500 <SEP> 1.8
<tb> Methane <SEP> 25 <SEP> 500 <SEP> <<SEP> 1
<tb> Nitrogen <SEP> 25 <SEP> 500 <SEP> <<SEP> 1
<tb>
 
These results show that water is more strongly adsorbed than any of the other materials at comparable temperatures and pressures, and illustrate one of the main uses of zeolite X, namely the removal of water from mixtures containing it. .



   An example of the application of this property of strong adsorption at low pressures is the drying of an air stream containing only small initial amounts of water. If, for example, air contains water under a partial pressure of 0.1 mm, of mercury, the zeolite X adsorbs about 23% by weight of water. Under similar conditions, silica gel adsorbs only about 1% by weight of water. This property can also be applied to the removal of traces of ethylene, acetylene, propylene and other by-product gases or waste gas streams.



   This table also demonstrates the low adsorbability of hydrogen and helium on zeolite X compared to that of oxygen, nitrogen, argon and krypton and shows the application of zeolite X to the separation of very volatile gases such as hydrogen, helium and neon from less volatile gases such as oxygen, nitrogen, argon, krypton and xenon,
The table shows that at -75 C. nitrogen is adsorbed more strongly than oxygen and argon and oxygen more strongly than argon, which allows the separation of nitrogen from mixtures with the oxygen and argon and

 <Desc / Clms Page number 19>

 the separation of oxygen from mixtures with argon, using zeolite X.



   The table also shows that at the same temperature (25 C. in the table) acetylene is more strongly adsorbed at a given pressure than are oxygen, nitrogen, hydrogen, carbon monoxide. , carbon dioxide, methane and ethylene. Thus, acetylene can be removed from mixtures comprising these less strongly adsorbed gases by means of zeolite X.



   Likewise, ethylene is more strongly adsorbed than oxygen, nitrogen, hydrogen and carbon monoxide, and zeolite X can be used in the separation of ethylene mixtures from its ethylene mixtures. with the other named gases.



   It is seen that carbon monoxide is adsorbed selectively with respect to hydrogen, nitrogen, oxygen, argon and methane, demonstrating the possibility of the application of zeolite X to the separation of carbon monoxide from any of these other gases.



   Carbon dioxide is more strongly adsorbed than hydrogen, helium, nitrogen, oxygen, methane, ethane and ethylene. Likewise, sulfur dioxide is selectively adsorbed from mixtures with hydrogen, nitrogen, oxygen, ethylene, carbon monoxide, and carbon dioxide. This also applies to mixtures of hydrogen sulfide with hydrogen, nitrogen, oxygen, carbon monoxide, carbon dioxide, methane, ethylene, propane, butane and pentane . Ammonia is more strongly adsorbed than hydrogen, nitrogen, oxygen, carbon monoxide, carbon dioxide, methane, and ethane.



   Another advantage of this high adsorption at low pressures is the possibility of carrying out adsorption processes at higher temperatures than is generally done with common adsorbents. The adsorptive power of physical adsorbents decreases with increasing temperature so that while the adsorption capacity of any adsorbent may be sufficient at a certain temperature, it may be insufficient at a higher temperature. On the contrary, the strongly adsorbent X zeolite in principle retains its capacity at high temperatures.



  For example, the table below gives the adsorption isotherms for water on calcium zeolite X at 25 and 100 C. and it is seen that this zeolite adsorbs more water at 100 C. than silica gel at 25, in most of the pressure range.
 EMI19.1
 
<tb>
<tb>



  Pressure <SEP> Weight <SEP>% <SEP> adsorbed <SEP> to <SEP> 25 C <SEP> Pressure <SEP> Weight <SEP>% <SEP> adsorbed <SEP> to <SEP> 100 C.
<tb> mm <SEP> Hg. <SEP> Gel <SEP> silica <SEP> NaX <SEP> mm <SEP> Hg <SEP> Gel <SEP> silica <SEP> Na2X
<tb> 0.1 <SEP> 1.2 <SEP> 23.1 <SEP> 0.6 <SEP> 0.2 <SEP> 9.6
<tb> 4.5 <SEP> 11.4 <SEP> 32.3 <SEP> 4.5 <SEP> 0.6 <SEP> 15.8
<tb> Po <SEP> 42.9 <SEP> 39.5 <SEP> Po <SEP> 15 <SEP> 20.9
<tb>
 
Po is the vapor pressure of water at 25 C.



   The activation, reactivation or regeneration methods applicable with zeolite X differ from those used with common adsorbents. Zeolite X can be activated initially by heating in air or vacuum, or in another suitable gas. Temperatures of about 700 ° C were found to be satisfactory for activation. Under similar conditions, most of the adsorbents are partially or totally destroyed by heating or oxidized by air.

   The conditions applied to the desorption of an adsorbate of zeoli-

 <Desc / Clms Page number 20>

 te X vary with the adsorbate, but usually one or more means such as raising the temperature and reducing the pressure, partial pressure or concentration of the adsorbate in contact with the adsorbent are used. Another method is to displace the adsorbate by adsorption of another more strongly retained adsorbate. It is thus possible to displace the acetylene adsorbed on a bed of zeolite X by adsorption of water.



   Zeolite X can be used as an adsorbent for the above purposes in any suitable form. Thus, a column of crystallized material in powder gives excellent results, as well as a column of granules obtained by pressing a mixture of zeolite X with a suitable binding agent such as clay.


    

Claims (1)

ABSTRACT. As a new industrial product, synthetic crystalline adsorbent material, characterized by the following points, separately or in combinations: 1) it has the composition, expressed in oxides, (0.9 + 0.2) M20: A1203: (2.5 + 0.5) Si02: Y H20 n in which M is a cation having a valence not exceeding 3, n is the valence of M, and Y is a number not exceeding 8, the atoms of matter being arranged in the form of a cell in such a way that the X-ray powder diffraction spectrum of matter gives for the value of the interplanar spacing of the recorded lines, or the value of the reflection expressed in angstroms, a number between 14.42 and 2.66 approximately. 2) said material is a metallic alumino-silicate with a cubic cell ridge having a length of 24.5 to 25.5 angstroms; 3) the size of the crystals is 0.01 to 100 microns; 4) the ratio of silicon atoms to aluminum atoms in the aluminum silicate portion of the material is at least 2 to 3; 5) the ratio of silica to alumina in the silicate is between 2 and 3; 6) M is sodium, calcium, magnesium, lithium or barium; 7) at least part of the sodium of the sodium alumino-silicate is replaced by potassium, calcium, magnesium, lithium or barium; 8) Since M is sodium, the length of the edge of the cubic cell is 24.99 angstroms and the density of matter is 1.93; 9) M being calcium, the length of the edge of the cubic cell is 24.90 angstroms and the density of the material is 1.96; la) M being magnesium, the length of the edge of the cubic cell is 25 angstroms and the density of the material is 1.95; 11) Since M is lithium, the length of the edge of the cubic cell is 25 angstroms and the density of the material is 1.89; 12) Since M is barium, the length of the edge of the cubic cell is 24.99 angstroms and the density of matter is 2.30. <Desc / Clms Page number 21> II - Process for the preparation of a metal alumino-silicate as above, characterized by the following points, separately or in combinations; 13) an aqueous sodium-aluminum-silicate mixture is made according to the molar ratios, counted as oxides, of: EMI21.1 S10 / toi 3, 0 - 5, 0 Na2O / SiO2 1.2 - 1.5 H2O / Na2O 35-60 and this mixture is maintained at a temperature between 20 and 120 ° C. for a period such that crystals having the specified ray diffraction spectrum are obtained; 14) The temperature is kept at 100 C. 15) the crude crystals are washed with water until the pH of the washing water is 9 to 12; 16) application to the preparation of a metallic alumino-silicate EMI21.2 that as in I, comprising contacting the sodium aluminosilicate prepared as above with a solution containing a cation other than sodium, of a valence not exceeding 3; so as to partially or totally replace the sodium with said other cation; 17) said replacement cation is lithium, hydrogen, potassium, silver, ammonium, magnesium, calcium, zinc, barium, cerium or manganese; 18) the molar ratio of the mixture of oxides applied to the preparation is: EMI21.3 Si02 / A1203 2 - 40 Na2O / SiO2 0.6 - 6 H2O / Na2O 10 to 30 19) said ratio is: EMI21.4 Si02 / A1203 2.4 - 30 Na20Si02 0.4 to 6.5 H2O / Na2O 10 to 90 20) the said ratio is: EMI21.5 Si02A1203 3 to 15 Na2O / SiO2 4 to 7 H2O / Na2O 30 to 70 III - Process for applying the crystallized adsorbent synthetic material obtained by means of the process as above to the separation of molecules whose minimum cross section is less than that of heptacosafluorotributylamine from a mixture with molecules of a Larger minimum cross-section, said method being characterized by the following, separately or in combination: 21) the mixture is brought into contact with the crystalline material which adsorbs the molecules of smaller cross section; <Desc / Clms Page number 22> 22) the mixture containing organic sulfur compounds and other compounds, at least part of the sulfur compounds is adsorbed; 23) the mixture containing hydrogen and one or more of the following gases: hydrogen, nitrogen, oxygen, carbon monoxide, carbon dioxide, methane, ethylene, propane, butane or pentane, at least part of the hydrogen sulphide is adsorbed; 24) the sulfur compound present in said mixture is sulfur dioxide; 25) the mixture containing carbon dioxide and one or more gases such as hydrogen, helium, nitrogen, oxygen, methane, ethane and ethylene, at least part of the carbon dioxide is adsorbed; 26) the mixture containing a relatively volatile gas such as hydrogen, helium or neon and a relatively non-volatile gas such as oxygen, nitrogen, argon, krypton or xenon, a portion at least relatively volatile gas is adsorbed; 27) the mixture containing ammonia and hydrogen, nitrogen, oxygen, carbon monoxide, carbon dioxide, methane or ethane, one part less ammonia is adsorbed; 28) the mixture containing a saturated organic compound and an unsaturated organic compound, the latter is adsorbed at least in part; 29) said mixture contains ethylene and ethane, or propylene and propane; 30) the mixture containing an ethylenic compound and an acetylenic compound, at least part of the latter is adsorbed; 31) the mixture containing an aromatic compound and a saturated organic compound, at least part of the aromatic compound is adsorbed; 32) the mixture containing a polar compound and a less polar compound, at least part of the compound of higher polarity is adsorbed; 33) the gas mixture containing nitrogen, oxygen and argon, is contacted with the adsorbent material at a temperature below zero degrees, at least part of the nitrogen being adsorbed; 34) said mixture containing only oxygen and argon, at least part of the oxygen is adsorbed; 35) the adsorbent crystalline synthetic material is partially dehydrated before use; 36) The adsorbed material is collected from the absorbent by heating the latter, if desired under reduced pressure, or by washing with a suitable solvent of the adsorbate.