LIIMATTA ERIC W
| DD107428A1 | 1974-08-05 | |||
| FR2319577A1 | 1977-02-25 | |||
| FR2381716A1 | 1978-09-22 | |||
| EP0435625A2 | 1991-07-03 |
| 1. | A method for producing a crystalline syntheti faujasite of the zeolite "X" type comprising the steps of: i) separately preparing a sodium silicate solution and a sodium aluminate solution; ii) admixing the sodium silicate solution and the sodium aluminate solution at high shear until a mixture results having a ratio of sodium oxide to silica of 0.4:1 to 1:1; silica to alumina of 25:1 to 1.5:1; and water to sodium oxide of 20:1 to 50:1; iii) heating said mixture to a temperature of abou 80 to 120°C in the absence of any further mixing for a period of time sufficient to produce the desired crystalline faujasite of the zeolite "X" type; and iv) recovering said zeolite "X" . |
| 2. | The method according to Claim 1 wherein said high shear is produced by mechanical mixing. |
| 3. | The method according to Claim 2 wherein said mechanical mixture is a bladetype operating at a tip speed of from 5 feet/sec to 100 feet/sec. |
Field of the Invention
In general, the present invention relates to the production of zeolites.
Description of the Prior Art
Certain naturally occurring hydrated metal aluminum silicates are called zeolites. The synthetic adsorbents of the invention have compositions similar to some of the natural zeolites. The most common of these zeolites are sodium zeolites. Zeolites are useful as detergent builders, cracking catalysts and molecular sieves, Zeolites consist basically of a three-dimensional framework of Si0 4 and A10 4 tetrahedra. The electrovalence of each tetrahedra containing aluminum is balanced by the inclusion in the crystal of a cation, for example, a sodium ion. This balance may be expressed by the formula Al/Na - 1. The spaces between the tetrahedra are occupied by water molecules prior to dehydration.
Zeolites "X" and "Y" may be distinguished from other zeolites and silicates on the basis of their X-ray powder diffraction patterns and certain physical characteristics. The X-ray patterns for several of these zeolites are described below. The composition and density are among the characteristics which have been found to be important in identifying these zeolites.
The basic formula for all crystalline sodium zeolites may be represented as follows:
Na 2 0:A1 2 0 3 :xSi0 2 :yH 2 0.
In general, a particular crystalline zeolite will have values for x and y that fall in a definite range. The value x for a particular zeolite will vary somewhat since
the aluminum atoms and the silicon atoms occupy essentiall equivalent positions in the lattice. Minor variations in the relative numbers of these atoms do not significantly alter the crystal structure or physical properties of the zeolite. For zeolite X, an average value for x is about 2. with the x value falling within the range 2.5±0.5.
The value of y is not necessarily an invariant f all samples of zeolites. This is true because various exchangeable ions are of different size, and, since there i no major change in the crystal lattice dimensions upon ion exchange, the space available in the pores of the zeolite t accommodate water molecules varies.
The average value for y determined for zeolite X is 6.2. The formula for zeolite X may be written as follows:
0 . 9±0 . 2Na 2 0 : A1 2 0 3 : 2 . 5±0 . 5Si0 2 : yH 2 0 ;
II .y. I"I may be any value up to 8 for zeolite X.
The pores of zeolites normally contain water. The above formulas represent the chemical analysi of zeolite X. When other materials as well as water are in the pores, chemical analysis will show a lower value of y and the presence of other adsorbates. The presence in the crystal lattice of materials volatile at temperatures below about 600°C, does not significantly alter the usefulness of the zeolites as an adsorbent since the pores are usually freed of such volatile materials during activation.
Among the ways of identifying zeolites and distinguishing them from other zeolites and other crystalline substances, the X-ray powder diffraction patter has been found to be a useful tool. In obtaining X-ray powder diffraction patterns, standard techniques are employed. The radiation is the Ka doublet of copper, and a Geiger counter spectrometer with a strip chart pen recorder is used. The peak heights, I, and the positions as a
function of 2fi where θ is the Bragg angle, are read from the spectrometer chart. From these, the relative intensities, 100I/I 0 , where I 0 is the intensity of the strongest line or peak, and d the interplanar spacing in A corresponding to the recorded lines are calculated.
X-ray powder diffraction data for sodium zeolite X are given in Table A. 100I/I 0 and the d values in angstroms (A) for the observed lines for zeolite X are also given. The X-ray patterns indicate a cubic unit cell of dimensions between 24.5 A and 25.5 A. In a separate column are listed the sum of the squares of the Miller indices (h 2 + k 2 + l 2 ) for a cubic unit cell that corresponds to the observed lines in the X-ray diffraction patterns. The a 0 value for zeolite X is 24.99 A, where a 0 is the unit cell edge.
TABLE A
The more significant d values for zeolite X are given in Table B.
TABLE B
MOST SIGNIFICANT d VALUES FOR ZEOLITE X d Value of Reflection in A
14.45 ± 0.2
8.85 ± 0.1
7.55 ± 0.1
5.75 ± 0.1
4.42 ± 0.05
3.80 ± 0.05
3.33 ± 0.05
2.88 ± 0.05
2.79 ± 0.05
2.66 ± 0.05
Occasionally, additional lines not belonging to the pattern for the zeolite appear in a pattern along with the X-ray lines characteristic of that zeolite. This is an indication that one or more additional crystalline materials are mixed with the zeolite in the sample being tested.
Frequently, these additional materials can be identified as initial reactants in the synthesis of the zeolite, or as other crystalline substances. When the zeolite is heat treated at temperatures of between 100°C and 600°C, in the presence of water vapor or other gases or vapors, the relative intensities of the lines in the X-ray pattern may be appreciably changed from those existing in the unactivated zeolite patterns. Small changes in line positions may also occur under these conditions. These changes in no way hinder the identification of these X-ray patterns as belonging to the zeolite.
The particular X-ray technique and/or apparatus
employed, the humidity, the temperature, the orientation of the powder crystals and other variables, all of which are well known and understood to those skilled in the art of X- ray crystallography or diffraction can cause some variation in the intensities and positions of the lines. These changes, even in those few instances where they become large, pose no problem to the skilled X-ray crystallographe in establishing identifies. Thus, the X-ray data give herein to identify the lattice for a zeolite, are not to exclude those materials, which, due to some variable mentioned or otherwise known to those skilled in the art, fail to show all of the lines, or show a few extra ones tha are permissible in the cubic system of that zeolite, or sho a slight shift in position of the lines, so as to give a slightly larger or smaller lattice parameter.
A simple test described in American Mineralogist, Vol. 28, Page 545, 1943, permits a quick check of the silicon to aluminum ratio of the zeolite. According to the description of the test, zeolite minerals with three- dimensional network that contains aluminum and silicon atom in an atomic ratio of Al/Si = 2/3 = 0.67, or greater, produce a gel when treated with hydrochloric acid. Zeolite having smaller aluminum to silicon ratios disintegrate in the presence of hydrochloric acid and precipitate silica. These tests were developed with natural zeolites and may vary slightly when applied to synthetic types.
U. S. Patent No. 2,882,244 describes a process fo making zeolite X comprising preparing a sodium-aluminum- silicate water mixture having an Si0 2 /Al 2 0 3 mole ratio of from 3:1 to 5:1, an Na 2 0/Si0 2 mole ratio from 1.2:1 to 1.5:1, and an H 2 0/Na 2 0 mole ratio of from 35:1 to 60:1, maintaining the mixture at a temperature of from 20°C to 120°C until zeolite X is formed, and separating the zeolite X from the mother liquor. In U. S. Patent No. 3,119,659, a kaolin clay and sodium hydroxide are formed into a compact body, dried,
reacted in an aqueous mixture at a temperature of from 20°C to 175°C until a zeolite is formed. Zeolite X is formed in a reaction mixture having an Na 2 0/Si0 2 molar ratio of 5:1, and an H 2 0/Na 2 0 molar ratio of 30:1 to 60:1. Zeolite Y is formed in a reaction mixture having an Na 2 0/Si0 2 molar ratio of 0.5:1, an Si0 2 /Al 2 0 3 molar ratio of 7:1, and an H 2 0/Na 2 0 molar ratio of 20:1 to 40:1.
U. S. Patent No. 4,440,366 relates to a process for producing a crystalline synthetic faujasite wherein an activated sodium silicate system is provided by mixing a sodium silicate solution with a seed amount of the faujasite to be produced and the activated sodium silicate system is reacted with a sodium aluminate solution under controlled conditions to thereby form the desired crystalline synthetic faujasite.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Zeolite X is the name given to synthetic zeolites having the crystal structure of the naturally occurring mineral, faujasite having an Si0 2 /Al 2 0 3 ratio of less than 3. In general, a sodium silicate solution and a sodium aluminate solution are each separately prepared. Sand is dissolved in a sodium hydroxide solution at a pressure of at least 100 psig and a temperature of at least 130°C to produce a sodium silicate solution having a silica to sodium oxide molar ratio of between 2.0:1 and 2.8:1 for preparing zeolite X. Any other suitable process for preparing the sodium silicate solution may be used. Any suitable process for preparing the sodium aluminate solution may also be used. All the literature claims in zeolite preparation call for adequate agitation. It is generally understood that continuous agitation during the zeolite crystallization process controls the size of the particle. This is especially important for large volume commercial zeolite production where small particle size is critical. However,
we surprisingly discovered that during zeolite X preparation, agitation during zeolite crystallization is actually disadvantageous. Also for the production of zeolite X with particle sizes in the range of 0.5-5 microns, one can eliminate agitation during the long crystallization periods. It was also discovered that the particle size of the final product can be controlled by agitation in the ver early stages of the zeolite X preparation.
Preferably, the sodium silicate solution can be added slowly to the sodium aluminate solution. The solutions can be at elevated temperatures (such as 60°C) or at room temperature at the time of addition. It is important in the process of the present invention to have the sodium aluminate and sodium silicate solutions mix unde high shear conditions. This high shear rate causes the gel that initially forms from the admixture of reactants to be broken into a lower viscosity material, i.e., a viscosity o around 18 cp at 100 s "1 . The term high shear rate as used in this application means mechanical mixing with tip speeds of 75-2,000 ft/min. The time until such low viscosity material forms and after which high shear mixing can be stopped is from about one minute to about five hours with ten minutes being preferred. After the low viscosity material is produced, it is agitated under high shear for 1- 20 minutes.
The reaction mixture for zeolite X has the following molar ratios: sodium oxide to silica--0.4 :1 to 2:1, silica to alumina--2.2 to 3.5:1, and water to sodium oxide--20:1 to 70:1; and preferred molar ratios of 1:3 to 1.7:1, 2.6:1 to 3.0:1, and 30:1 to 45:1, respectively, and most preferred molar ratios of 1.4:1, 2.8:1, and 36.4:1, respectively.
The system is heated to a temperature of about 80°C to 125°C and preferably about 90°C to 105°C. No agitation is necessary at this time nor is it desirable because of attendant problems associated with the
crystallization process, e.g., reaction plugging. The temperature is maintained until the desired crystalline synthetic faujasite is formed, normally about an hour. The oil bath heating step may be performed at temperatures of about 0°C to 90°C for about four to six hours. Such lower temperatures require longer heating times.
Zeolite X Production
The experimental conditions and results for those experiments where zeolite X was the desired product are listed in Table C.
The following detailed experimental procedures are examples of the above.
EXAMPLES 1-10 Examples 1-10 were carried out in the absence of agitation during the crystallization periods. The samples were prepared by pouring appropriate amounts of solution from stock solutions of sodium aluminate (3.3% Al and 6.0% Na) , sodium silicate (12.8% Si and 10.2% Na) , 50% NaOH and water to among 500 grams of reactants. The reactants were blended in a 1000 ml beaker using a 1 " D Cowles blade attached to a Dispermat CV. The reactants were sheared at approximately 2000 rpm until the thick gel that forms is broken into a fairly low viscosity material. The samples were then poured into glass containers and heated with no agitation at 90°C for 60+ hours. The following table summarizes this data.
TABLE C
REACTION SUMMARY
Exp. Prod. Na Al Si Rxn. Rxn. % Part. No. No. Temp. Time Zeolite Size X
1 42-3 5.91 1.74 3.13 90 68 Hr 114 3.42
2 43-1 6.11 1.74 3.13 90 68 Hr 111 2.73
3 43-2 6.31 1.74 3.13 90 68 Hr 109 6.18
4 43-3 5.74 1.74 2.93 90 68 Hr 119 4.78
5 43-4 5.89 1.74 2.93 90 68 Hr 119 4.16
6 43-5 6.09 1.74 2.93 90 68 Hr 120 4.28
7 43-6 6.29 1.74 2.93 90 64 Hr 116 4.23
8 44-1 5.78 1.69 3.25 90 64 Hr 115 4.31
9 44-2 5.94 1.74 3.34 90 64 Hr 111 3.95
10 44-3 6.14 1.74 3.34 90 64 Hr 116 3.91
11 44-4 6.34 1.74 3.34 90 64 Hr 110 3.35
12 42-3 5.91 1.74 3.13 115 1.5 Hr 73 15.3
13 43-1 6.11 1.74 3.13 115 1.5 Hr 60 81.3
14 43-2 6.31 1.74 3.13 115 1.5 Hr 74 26.8
15 43-3 5.74 1.74 2.93 115 1.5 Hr 88 44.5
16 43-4 5.89 1.74 2.93 115 1.5 Hr 74 57.0
17 43-5 6.09 1.74 2.93 115 1.5 Hr 79 13.7
18 43-6 6.29 1.74 2.93 115 1.5 Hr 68 26.9
19 44-1 5.78 1.69 3.25 115 1.5 Hr 98 18.4
20 44-2 5.94 1.74 3.34 115 1.5 Hr 81 255.0
21 44-3 6.14 1.74 3.34 115 1.5 Hr 84 76.5
22 44-4 6.34 1.74 3.34 115 1.5 Hr 48 167.0
Under no agitation, the zeolite X produced has mean particle size in the range of 2.73 to 6.18 um.
All the reactants may be blended together under high shear at room temperature and after the gel is formed,
the gel can be transferred to a simple container equipped with no agitation capability for crystallization to complete. Elevated temperatures in the crystallization reactor is preferred. The incentive for this process is in lower equipment costs.