Abstract:
The present invention relates to a process for producing a crystalline synthetic faujasite of the zeolite &#34;Y&#34; type wherein an activated system is provided by mixing a sodium silicate solution with a seed amount of zeolite &#34;Y&#34; type synthetic faujasite and the activated system is reacted with a sodium aluminate solution under controlled conditions to thereby form a low water reaction mixture or system and then a crystalline synthetic faujasite of the zeolite &#34;Y&#34; type.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     In general, the present invention relates to the production of synthetic faujasites or zeolites and more especially to Zeolite Y. 
     2. 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 frame work of SiO 4  and AlO 4  tetrahedra. The tetrahedra are crosslinked by the sharing of oxygen atoms so that the ratio of oxygen atoms to the total of the aluminum and silicon atoms is equal to two or 0/(Al+Si)=2. 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. 
     Zeolite 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.sub.2 O.Al.sub.2 O.sub.3.xSio.sub.2.yH.sub.2 O. 
    
     In general, particular crystalline zeolite will have values for &#34;x&#34; and &#34;y&#34; that fall in a definite range. The value &#34;x&#34; for a particular zeolite will vary somewhat since the aluminum atoms and the silicon atoms occupy essentially equivalent positions in the lattice. Minor variations in the relative number of these atoms do not significantly alter the crystal structure or physical properties of the zeolite. For zeolite Y, an average value for &#34;x&#34; is about 4.5 with the &#34;x&#34; value falling within the range 4.5±0.5. 
     The value of &#34;y&#34; is not necessarily an invariant for all samples of zeolites. This is true because various exchangeable ions are of different size, and, since there is no major change in the crystal lattice dimensions upon ion exchange, the space available in the pores of the zeolites to accommodate water molecules varies. 
     The formula for zeolite Y may be written as follows: 
     
         0.9±0.2Na.sub.2 O.Al.sub.2 O.sub.3.4.5±1.5SiO.sub.2.yH.sub.2 O; 
    
     and, &#34;y&#34; may be any value up to 9. 
     The pores of zeolites normally contain water. 
     The above formulas represent the chemical analysis of zeolite Y. When other materials as well as water are in the pores, chemical analysis will show a lower value of &#34;y&#34; 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 pattern has been found to be a useful tool. In obtaining X-ray powder diffraction patterns, standard techniques are employed. The radiation is the Kα 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 2θ 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 &#34;d&#34; the interplanar spacing in Å corresponding to the recorded lines are calculated. 
     X-ray powder diffraction data for sodium zeolite Y are given in Table A. Relative Intensity (100I/I 0 ) and the &#34;d&#34; values in angstroms (Å) for the observed lines for zeolite Y are shown. 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. 
     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 indicated 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 pattern. 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. 
     
                       TABLE A______________________________________X RAY DIFFRACTIONPATTERN FOR SYNTHETIC FAUJASITE(ZEOLITE Y)                   Relativeh.sup.2 + k.sup.2 + l.sup.2           d (Å)                   Intensity______________________________________3               14.29   1008               8.75    911              7.46    2419              5.68    4427              4.76    2332              4.38    3540              3.91    1243              3.775   4748              3.573   451              3.466   956              3.308   3759              3.222   867              3.024   1672              2.917   2175              2.858   4880              2.767   2083              2.717   788              2.638   1991              2.595   11108             2.381   6123             2.232   2128             2.188   4131             2.162   3139             2.099   5144             2.062   3164             1.933   2168             1.910   3179             1.850   2187             1.810   2192             1.786   1195             1.772   2200             1.750   4211             1.704   5______________________________________ 
    
     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 variations 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 crystallographer in establishing identities. Thus, the X-ray data given 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 that are permissible in the cubic system of that zeolite, or show a slight shift in position of the lines, so as to give a slightly larger or smaller lattice parameter. 
     A simple test described in &#34;American Mineralogist,&#34; 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 a three-dimensional network that contains aluminum and silicon atoms in an atomic ratio of Al/Si=2/3=0.67, or greater, produce a gel when treated with hydrochloric acid. Zeolites 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. Pat. No. 2,882,244 describes a process for making a synthetic faujasite of the type of zeolite X comprising preparing a sodium-aluminum-silicate water mixture having an SiO 2  /Al 2  O 3  mole ratio of from 3:1 to 5:1, an Na 2  O/SiO 2   mole ratio from 1.2:1 to 1.5:1, and an H 2  O/Na 2  O 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. Pat. 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. A synthetic faujasite of the type of zeolite Y is formed in a reaction mixture having an Na 2  O/SiO 2  molar ratio of 1.5:1, an SiO 2  /Al 2  O 3  molar ratio of 5:1, and an H 2  O/Na 2  O molar ratio of 30:1 to 60:1. Zeolite Y is formed in a reaction mixture having an Na 2  O/SiO 2  molar ratio of 0.5:1, an SiO 2  /Al 2  O 3  molar ratio of 20:1 to 40:1. 
     U.S. Pat. No. 3,920,789 discloses a process for making zeolite Y using elevated temperatures and pressures for the crystallization stage followed by very rapid cooling of the reaction mass. 
     In U.S. Pat. No. 3,130,007, zeolite Y is formed by preparing an aqueous sodium alumino silicate mixture having a certain composition, maintaining the mixture at a temperature of 20° C. to 125° C. until zeolite Y is formed, and separating the zeolite Y from the mother liquor. Table B shows reaction mixture compositions that produce zeolite Y. 
     
                       TABLE B______________________________________U.S. PAT. NO. 3,130,007REACTION MIXTURE COMPOSITIONS FOR ZEOLITE YNa.sub.2 O/SiO.sub.2          SiO.sub.2 /Al.sub.2 O.sub.3                    H.sub.2 O/Na.sub.2 O______________________________________0.20-0.40      10-40     25-600.41-0.60      10-30     20-600.61-1.0        7-30     20-600.6-1.0         8-30     12-901.5-1.7        10-30     20-901.9-2.1        10        40-90______________________________________ 
    
     U.S. Pat. No. 3,130,007 indicates in Column 2, lines 35-42, the necessity of using an active silica source by specifying that aqueous colloidal silica sols or reactive amorphous solid silicas are preferred. 
     In U.S. Pat. No. 4,016,246, zeolite Y is formed by preparing an aqueous alumino silicate reaction mixture by mixing an alumina component and an Na 2  O component with an active hydrate sodium metasilicate to form a certain reaction mixture, than heating the mixture at a temperature of 20° C. to 120° C. until zeolite Y is formed. Table C shows reaction mixture compositions that produce zeolite Y. 
     
                       TABLE C______________________________________U.S. PAT. NO. 4,016,246REACTION MIXTURE COMPOSITIONS FOR ZEOLITE YNa.sub.2 O/SiO.sub.2          SiO.sub.2 /Al.sub.2 O.sub.3                    H.sub.2 O/Na.sub.2 O______________________________________0.28-0.30      8-10      20-700.30-0.31      8-12      20-700.31-0.32      8-14      20-700.32-0.34      8-16      12-900.34-0.40      7-40       12-1200.4-1.0        5-50       12-1200.7-1.0        31-50      12-120______________________________________ 
    
     U.S. Pat. No. 4,016,246 also discusses the significance of using an activated source of sodium silicate. In such patent an active hydrated sodium metasilicate is prepared by carefully hydrating sodium metasilicate under specified conditions. 
     U.S. Pat. No. 4,166,099 discloses a process for preparing crystalline aluminosilicate zeolites, particularly synthetic faujasites such as zeolite type X and zeolite type Y utilizing especially prepared nucleating centers or seeds. Such seed preparation is lengthy and involved. 
     U.S. Pat. No. 4,164,551 discloses a process for making zeolite Y also utilizing specifically prepared nucleating centers. 
     From the prior art, one would assume that zeolite Y cannot be made from reaction mixtures having a relatively low water to silica ratio. A H 2  O/SiO 2  ratio of at least about 40:1 would seem to be required to produce zeolite Y of a sufficiently high crystallinity. 
     U.S. application Ser. No. 299,878 filed on Sept. 8, 1981, now U.S. Pat. No. 4,400,366, discloses a process for making synthetic faujasites of the Zeolite Y type of an exceptionally high crystallinity. Such process requires a substantial water to silica ratio in the reaction mixture. This application is specifically incorporated herein. 
     The present invention is a modification of this process for making a high crystalline Zeolite Y. Although an excellent or superior Zeolite Y can be made by this exemplary process, substantial amounts of water are required. Present commercial specifications for zeolite Y for most uses do not require such high crystallinity zeolites. 
     It is therefore an important object of the present invention to provide a synthetic faujasite of the zeolite Y type which meets current specifications for crystallinity for commercial application and which process utilizes a reduced amount of water. 
     It is another object of the present invention to provide a process for producing a commercially acceptable zeolite Y which is more economical than present processes. 
     Still another object is to provide a zeolite Y product which has high crystallinity and yet which can be manufactured at reduced costs. 
     Other objects and advantages of the invention will be more readily apparent from a reading of the description hereinafter. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to the preparation of synthetic faujasites, namely zeolite Y, wherein a seed quantity of bulk zeolite Y is mixed with sodium silicate and a relatively small amount of water with agitation for up to about five hours at ambient temperature. The entire system is cooled to about -5° C. to 0° C. and sodium aluminate which has been precooled to about 0° C. is added. The system is warmed up to ambient temperature and then held at such temperature for up to about 24 hours. The mixture is then heated to about 80° C. to 120° C. and reacted at such temperature with stirring until the desired crystalline product is formed. Zeolite Y is then filtered out and dried in an oven. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Zeolites X and Y are names given to synthetic zeolites having the crystal structure of the naturally occurring mineral, faujasite. Zeolite X is the name for those compounds having an SiO 2  /Al 2  O 3  ratio of less than 3 while zeolite Y is the name for those compounds with a ratio of 3 or greater. Zeolite Y is known to have ratio upwards to 7 but those with SiO 2  /Al 2  O 3  in the range of about 4.5 to 5.5 are of greatest importance. The process of this invention is for making a zeolite Y. 
     The seed used in making a zeolite Y is a relatively small quantity of a zeolite Y from a previously prepared bulk batch. 
     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 1.7:1 and 5.0:1 for preparing zeolite Y. 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. 
     An activated system is prepared by mixing a relatively small amount of the seed or bulk zeolite of the type of zeolite Y with sodium silicate. 
     Faujasite seed may be used in amounts of about one percent to ten percent by weight of the mixture. Amounts below five weight percent do not produce as effective yields. The amount of seed zeolite used is not critical other than that it should be a sufficient amount to provide the necessary activation of the sodium silicate system. Larger amounts may be used since the zeolite is in the final product, but obviously, as weight percent of seed goes above ten, the economics of the process diminishes. 
     A mixture of faujasite and sodium silicate provides a suitable activated system. Activation is accompanied by agitation, with stirring being adequate. Agitation is continued at ambient temperature up to about three hours. Longer time may be used if desired, but should be unnecessary, The mixture or system is then cooled to about -5° C. to about 0° C. Temperature and times may be varied, but the activation period or mixing of bulk or seed zeolite with sodium silicate must be at least about one-half hour. 
     Preferably, the sodium aluminate solution is independently cooled to a temperature of about 0° C. and then slowly added with agitation to the sodium silicate system. While mixing, the temperature of the system is maintained at or near 0° C. Mixing is continued from about five minutes to about five hours. 
     After addition of the sodium aluminate is completed, agitation is stopped and the system is warmed to ambient temperature. The mixture is then allowed to stand at such temperature up to about sixteen hours. A standing time of about six to sixteen hours is usually necessary in preparing zeolite Y. 
     The reaction mixture comprises a sodium silicate mother liquor and an amorphous sodium alumino silicate pigment and for zeolite Y, the mixture or system has the following molar ratios: sodium oxide to silica 0.5:1 to 1:1; silica to alumina-10:1 to 15:1; and water to sodium oxide-17:1 to 30:1; and, preferably molar ratios of 0.6:1 to 0.8:1, 10.5:1 to 12.5:1 and 10:1 to 15:1, respectively, and, most preferred molar ratios of 0.7:1, 12.5:1, and 25:1, respectively. 
     After standing, the system is heated to a temperature of about 80° C. to 120° C. and preferably about 90° C. to 105° C. The mixture is reacted at similar temperatures. An oil bath is conveniently used, agitation with stirring or by other suitable means is appropriate. 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. 
     In one preferred process, about 1.8 parts of zeolite Y powder, on a dry weight basis, are mixed with 100 parts by weight of sodium silicate, and stirred at ambient temperature for about three hours. The mixture is then cooled to about -4° C. About 25.5 parts of sodium aluminate is independently cooled at about 0° C., then added slowly with vigorous agitation to the system while maintaining the temperature at or near 0° C. After addition of the sodium aluminate is complete, agitation is stopped and the system is warmed to ambient temperature. The system is then allowed to stand at such temperature for about 16 hours. The system is then heated in a 110° C. oil bath to a temperature of about 90°-100° C. with stirring. This temperature is maintained for about one hour after which solid zeolite Y is filtered out, dried in an oven and recovered. 
     A linear relationship exists between product silica to alumina ratio and the silica utilization. This latter is limited to about 10-20 weight percent to produce the desired 4.5 ratio product. An alumina to water ratio of about 1:200 is all that is required. 
    
    
     The invention is further illustrated by the following examples which set forth various methods and compositions. 
     EQUIPMENT 
     The reaction vessel was a 3-neck, 300 ml, round-bottom flask. An Ace Glass, Teflon, single-blade, ground glass, joint stirrer was used in the center position. This was driven by an electric motor. The shaft rpm was 200 except during reactant mixing when it was increased to 500 rpm. One neck was equipped with a thermometer. The other neck allowed use of a dropping funnel (syringe needle for those experiments where materials were added during the cool period when the thermometer was replaced with a condenser) during mixing and a condenser during the cook period. The products were filtered on fine frit-glass filter funnels and dried in a 115° C. oven. 
     EXPERIMENTAL PROCEDURE 
     Seed activation was in a sealed vessel submerged in a 90° C. oil bath. This was for 3 hours using the seed and sodium silicate. The system was stirred continuously. The product was then removed, cooled and mixed with water (if any used) in a 300 ml 3 mesh round bottom flask equipped with a thermometer and stirrer. The third neck was stoppered and the liquids cooled to -5° C. with slow agitation. The stopper was removed and the agitation increased to about 400 rpm on the stirrer while the sodium aluminate was dropped in over a period of about 20 minutes. This was done using a 60 ml syringe and a Sage Syringe pump set at 150×0.1. The cooling bath was then removed, the stirrer shut off and the third neck closed with a reflux condenser. The unit stood at ambient temperature for 16 hours then was heated, with stirring, using an oil bath at 105° C. Heating up to 90° C. took about 20 minutes and reflux was continued for 6 hours. The solids were then filtered out, washed in distilled water and dried at 115° C. for 16 hours. 
     REAGENTS 
     Sodium aluminate had a composition of 13.95 percent Na 2  O and 12.8 percent Al 2  O 3 . 
     
         ______________________________________Blend 1     38 grams of Commercial Silicate &#34;A&#34;       46.3 grams of Commercial Silicate &#34;B&#34;Blend 2     83.7 grams of Commercial Silicate &#34;C&#34;       8.3 grams of Commercial Silicate &#34;B&#34;Blend 3     49.4 grams of Commercial Silicates &#34;C&#34;       35.6 grams of Commercial Silicate &#34;B&#34;Silicate &#34;A&#34;       12.7 percent Na.sub.2 O       23.0 percent SiO.sub.2       balance H.sub.2 OSilicate &#34;B&#34;       30.0 percent SiO.sub.2       balance H.sub.2 OSilicate &#34;C&#34;        9.7 percent Na.sub.2 O       23.0 percent SiO.sub.2       balance H.sub.2 O______________________________________ 
    
     SEED PREPARATION 
     Seed samples are identified as a, b and c, and were prepared by following U.S. Pat. No. 4,166,099, Example 1, Method A. Other seed samples b and c were bulk product prepared as the experiment number listed and ground in a mortar with a pestle. Although not wishing to be bound by any particular theory, it is believed that the seed or bulk product is activated when mixed with a sodium silicate solution; however, it is only important that an activated system be prepared. The terms seed activation or activated seed are used herein to describe the step of mixing or contacting the seed or bulk product with a sodium silicate solution or a sodium silicate solution containing caustic and/or water. 
     For the experiments seed activation was accomplished by refluxing the ground seed, i.e. bulk product, in sodium silicate, with rapid stirring for a period of three hours. 
     ZEOLITE Y PRODUCTION 
     Following the experimental conditions described hereinbefore, the results are described in Table I. 
     
                                           TABLE I__________________________________________________________________________  Weight                     SilicateRun    Percent       Reaction Mixture Sodium                             RatioNo.   Seed*  Seed**       or System (Moles)                        Silicate                             SiO.sub.2 /Na.sub.2 O__________________________________________________________________________1  a   10   8.5Na.sub.2 O.Al.sub.2 O.sub.3.12.5SiO.sub.2.333.8H.sub.2                        &#34;A&#34;  1.872  a   10   8.2Na.sub.2 O.Al.sub.2 O.sub.3.12.0SiO.sub.2.145.0H.sub.2                        &#34;A&#34;  1.873  a   10   4.5Na.sub.2 O.Al.sub.2 O.sub.3.12.5SiO.sub.2.111.0H.sub.2                        Blend 1                             4.614  a   10   8.5Na.sub.2 O.Al.sub.2 O.sub.3.15.7SiO.sub.2.333.8H.sub.2                        &#34;C&#34;  2.355  a   10   8.5Na.sub.2 O.Al.sub.2 O.sub.3.15.7SiO.sub.2.198.0H.sub.2                        &#34;C&#34;  2.356  b   10   8.2Na.sub.2 O.Al.sub.2 O.sub.3.12.0SiO.sub.2.145.0H.sub.2                        &#34;A&#34;  1.877  b   10   6.3Na.sub.2 O.Al.sub.2 O.sub.3.10.7SiO.sub.2.145.0H.sub.2                        &#34;C&#34;  2.358  b   10   6.3Na.sub.2 O.Al.sub.2 O.sub.3.12.0SiO.sub.2.148.8H.sub.2                        Blend 2                             2.649  c   10   6.3Na.sub.2 O.Al.sub.2 O.sub.3.10.7SiO.sub.2.145.0H.sub.2                        &#34;C&#34;  2.3510 a   10   4.5Na.sub. 2 O.Al.sub.2 O.sub.3.12.5SiO.sub.2.333.8H.sub.2                        Blend 3                             4.61__________________________________________________________________________   Sodium    Sodium   Silicate    Aluminate          Additional  CrystallinityRun   Amount    Amount          Water Product                      As Percent                             RatioNo.   (Grams)    (Grams)          (Grams)                (Grams)                      of Standard                             SiO.sub.2 /Al.sub.2 O.sub.3__________________________________________________________________________1  94.3  23.1  95.7  16.9  178    3.52  90.7  23.1  --    12.3  103    3.43  49.2  13.5   2.9  --    45     4.54  123.3 23.1  70.6  12.5  166    3.75  123.3 23.1  --    11.1  24     --6  90.7  23.1   0.1  11.0  85     3.37  83.8  23.1  --    11.5  74     3.38  92.0  23.1  --    11.9  70     3.49  83.8  23.1  --    10.8  115    --10 85.0  23.1  112.7 16.0  Amorphous                             --__________________________________________________________________________ *Seed a  Linde 13X Commercial Zeolite Y b  Zeolite Y Product from Run 1 c  Zeolite Y Product from Run 2 **Based on theoretical product with SiO.sub.2 /Al.sub.2 O.sub.3 at 4.5 an 100 percent utilization 1.65 grams 
    
     The present invention provides an economical process for producing a commercially acceptable Zeolite Y. In such process, cooling cost, reflux costs, handling costs and investment costs are all reduced. The present invention also enables a larger quantity of product to be produced in the same equipment. 
     Zeolite Y made by the process has a crystallinity as good or better than the present commercially acceptable standard. 
     The Zeolite Y of the present invention has particular utility as a catalyst or catalyst base. 
     The foregoing disclosure and description of the invention is illustrative and explanatory thereof and various changes in the illustrated process may be made within the scope of the appended claims without departing from the spirit of the invention.