Micro-particulate aluminosilicate and process for producing the same

Abstract: A micro-particulate aluminosilicate suitable for use as an ion exchanger, adsorbent or the like has a mean particle size of not greater than 3 µm (micrometers), preferably not greater than 1 µm , as measured by precipitation particle size distribution measuring method. The micro-particulate aluminosilicate is produced by a process having the steps of preparing an aqueous solution as a solvent, the aqueous solution containing a water-soluble polymer dissolved therein; adding to the aqueous solution a metal hydroxide or a metal salt, a metal aluminate and colloidal silica as essential components and stirring the mixture to uniformly disperse the essential components so as to form a cake; and synthesizing the micro-particulate aluminosilicate by allowing the cake to mature followed by heating.

Description: The present invention relates to a process of producing a micro-particulate aluminosilicate. In general, it has been well known to synthesize zeolite artificially as an aluminosilicate by using a metal hydroxide or a metal salt, an aluminate of a metal and colloidal silica. Nowadays, zeolite is finding a spreading use in various industrial fields because of its useful functions and characteristics such an ion exchanging of metal ions, sieving of molecules, adsorption of gases such as carbon dioxide, nitrogen oxide and sulphur oxide, reactive catalytic action and so forth. Although natural zeolite is available, the proportion of artificially synthesized zeolite used is increasing because of the large impurity content and lack of uniformity of particle size of natural zeolite. As one of process for synthesizing zeolite, it has been attempted to bring a metal hydroxide or a metal salt, an aluminate of a metal and colloidal silica into reaction in an aqueous solution. This process does not necessitate any specific equipment because it relies upon a simple mechanism of reaction conducted in an aqueous solution and, therefore, has been widely adopted as a synthesizing process for an artificial mass-production of zeolite at a low cost. In recent years, there is an increasing demand for artificial production of designed aluminosilicate particles, e.g., uniformalization of particle size, refining of particles, increase in the purity and polygonal particle configuration approximating spherical in place of conventional cubic or rectangular form particles, in order to cope with current requirements for enhancement of ion-exchanging ability, ion-exchanging speed, adsorbability and adsorption speed. This synthesis process for producing aluminosilicate in an aqueous solution, however, suffers from the following disadvantages. Namely, the speed of growth of crystals after generation of crystal nuclei is high because of the low viscosity of the solvent, so that the mean particle size in terms of particle size distribution measured by precipitation method is as large as 6 µm. In addition, the particle sizes are distributed over a wide range. Thus, the above-described process could not provide ultra-fine aluminosilicate particles of a mean particle size not greater than 4 µm and having a narrow range of particle size distribution. EP-A-0115680 discloses a process for providing synthetic ZSM-5 zeolite catalysts comprising mixing a precursor for an alumina hydrate, a precursor for silica hydrogel, an alkali metal hydroxide and water together with an organic templating reagent, and thereafter heating the reaction product under autogenous conditions. According to one aspect of the present invention, there is provided a process for producing a micro-particulate aluminosilicate comprising the steps of: preparing an aqueous slurry of a metal hydroxide or metal salt, a metal aluminate and colloidal silica as essential components in an aqueous solution of a water-soluble polymer; stirring the slurry to disperse uniformly said essential components so as to form a cake; and thereafter allowing said cake to mature followed by heating; characterised in that said water-soluble polymer is gelatin. Said process may provide a micro-particulate aluminosilicate having a mean particle size of not greater than 3 µm (micrometers) as measured by precipitation particle size distribution measuring method. The mean particle size of the micro-particulate aluminosilicate may be not greater than 1 µm (micrometers) as measured by precipitation particle size distribution measuring method. Typically, the addition of the metal hydroxide or metal salt, metal aluminate and colloidal silica may be conducted by adding the colloidal silica to the aqueous solution in which the gelatin is uniformly dissolved, stirring the mixture to uniformly disperse the colloidal silica, and thereafter gradually adding aqueous solutions of the metal hydroxide or metal salt and the metal aluminate; the cake may be obtained by conducting as necessitated a strong agitation of the mixture after addition of the metal hydroxide or metal salt and the metal aluminate. According to the invention, an aqueous solution dissolving gelatin may advantageously be used as the solvent. This solvent may provide an effective means for suppressing drastic growth of aluminosilicate particles in reaction taking place in the aqueous solution so as to form a large quantity of ultra-fine particles of uniform particle size. The metal hydroxide or metal salt suitably used in the process of the present invention may be selected from those which are ordinarily used for synthesis of zeolite, such as sodium hydroxide, potassium hydroxide, calcium hydroxide, strontium hydroxide, ferrous or ferric chloride, nickel chloride, and so forth. Examples of the metal aluminate typically used are sodium aluminate, potassium aluminate, calcium aluminate, cobalt aluminate and other aluminates which are ordinarily used for synthesizing zeolite. One of these aluminate may be used alone or two or more of them may be used simultaneously. The process of the present invention may provide ultra-fine aluminosilicate particles of a mean particle size not greater than 3 µm with a high degree of uniformity of the particle size, for the following reasons. In the process of the invention, the field of generation of crystals is a polymeric viscous solution, i.e., an aqueous solution of gelatin. Therefore, the reaction reagent reacts while being surrounded by the gelatin dissolved as a solvent in the aqueous solution. Therefore, the growth of crystals may be retarded in the process for forming zeolite from amorphous matter as a precursor of zeolite, as compared with the case where the reaction process in a less-viscous aqueous solution as in the conventional process. Thus, the crystals may grow steadily and slowly, allowing generation of a greater number of nuclei. Growth of such nuclei also takes place under the retarded condition. The aluminosilicate in accordance with the present invention, needless to say, may or may not contain a large quantity of amorphous matter as the precursor of zeolite. The present invention may be carried out for production of various types of zeolite which can be synthesized in aqueous solution system, such as zeolite A, zeolite X, zeolite Y, zeolite Z, zeolite ZSM-5 and moldenyte. According to the invention, it may be possible to produce artificial aluminosilicate particles of ultra-fine and uniform particle size, by virtue of retardation of growth of crystals offered by the use of an aqueous solution of a gelatin as the solvent. Thus, according to the present invention, it may be possible to effect a control of the whole reaction for generating zeolite from an amorphous matter as a precursor, which control has been materially impossible by the conventional process which uses a mere aqueous solution. Consequently, the present invention seeks to produce ultra-fine aluminosilicate particles of a mean particle size not greater than 3 µm and having a narrow particle size distribution of several micrometers (µm). The ultra-fine aluminosilicate particles of narrow particle size distribution may have large surface areas and rounded polygonal configurations approximating spheres. Consequently, ion exchanging ability may be improved as compared with products of conventional process. According to the invention, it may be possible to obtain functional ultra-fine aluminosilicate particles which can cope with demands of various fields. Following is a description by way of example only and with reference to the accompanying drawings of methods of carrying the present invention into effect. In the drawings:- Figure 1 is a graph showing crystallization ratio of reaction product in Experiment I conducted by using aqueous solution of gelatin as a solvent. Figure 2 is a graph showing the state of generation of zeolite in Experiment I. Figure 3 is a graph showing particle size distribution of a reaction product in Experiment II. Figure 4 is a graph showing compositions of reaction products in Experiment III. Figure 5 is graph showing particle size distribution of reaction product in Comparative Experiment IV conducted by using an aqueous solution of polyvinyl alcohol as the solvent. Figure 6 is a graph showing ion-exchanging ability of the reaction product in Experiment V. Figures 7A and 7B are electron-microscope photographs of particle construction of reaction product obtained in Experiment I using a solvent having gelatin content of 0.0 wt%, as observed at moments 1 hour and 10 hours after commencement of the reaction, respectively. Figures 7C and 7D are electron-microscope photographs of particle construction of reaction product obtained in Experiment I using a solvent having gelatin content of 10.0 wt%, as observed at moments 1 hour and 10 hours after commencement of the reaction, respectively. Figure 7E is an electron-microscope photograph of construction of particle in amorphous portion of reaction product obtained in Experiment I using a solvent having gelatin content of 10.0 wt%, as observed at a moment 10 hours after commencement of the reaction, respectively. Figure 8 is a diagram showing particle size distribution of production Experiment VI. Figure 9 is a diagram showing particle size distribution of a Comparative Example of Experiment VI. Figures 10A and 10B are electron-microscope photographs showing respectively the particle constructions of reaction products in Experiment VI and a Comparative Experiment. Figure 11 is a graph showing particle size distribution of production Experiment VII. Figure 12 is a graph showing particle size distribution of product in a Comparative Experiment to be compared with Experiment VII. Figures 13A and 13B, respectively are electron-microscope photographs showing constructions of particles of products in Experiment VII and the Comparative Experiment; and Figure 14 is a graph showing the ion-exchanging ability data measured by Experiment 8. The invention will be more fully understood from the following description of Experiments in which an electron-microscope model JEM 4000 or model T-330A EX produced by Nippon Denshi kabushiki Kaisha was used for microscopic observation of reaction products. Used also was a centrifugal precipitation particle size measuring apparatus model SA-CP3 produced by kabushiki Kaisha Shimazu Seisakusho. Experiment I Each of a plurality of triple-inlet flasks was charged with 40 cc of water, and 4 gram(g) of sodium hydroxide, 2 g of sodium aluminate and 14 g of 40 wt% aqueous solution of colloidal silica were mixed in the water, followed by addition of gelatin as the water-soluble polymer. The amount of addition of gelatin was varied to provide aqueous solutions of different gelatin concentrations: namely, 0.0 wt%, 0.1 wt%, 0.5 wt%, 1.0 wt%, 3.0 wt%, 5.0 wt%, 7.5 wt% and 10.0 wt%. After being stirred, the aqueous solutions were allowed to mature for 1 hour at the room temperature, and was made to react by being heated to and maintained at 100°C, with the reaction time varied up to 10 hours. The reaction product obtained through 10-hour reaction was filtrated and the filtrate was rinsed with water followed by drying,whereby white crystals were obtained. The white crystals were confirmed to be faujasite, through a powder X-ray diffraction analysis. It was also confirmed that the crystals are zeolite Y, as a result of measurement of lattice constant. Fig. 1 shows the yields of the reaction products. It will be seen that the yield decreases drastically when the gelatin content exceeds 5.0 wt%, thus proving effect of gelatin to retard generation of zeolite Y. Aluminosilicate samples were obtained by filtering the reaction products produced with gelatin contents of 0.0 wt%, 1.0 wt%, 7.5 wt% and 10 wt%, as obtained at moments 1 hour, 2 hours, 5 hours, 8 hours and 10 hours after commencement of reaction,. Changes in the rates of generation of zeolite were observed on these filtrates to obtain results shown in Fig. 2. Filtrated matters of aluminosilicate other than crystallized zeolite Y were amorphous and were confirmed to be constituted by aluminosilicate of extremely fine particles having several hundreds of Å, through an X-ray diffraction analysis. Fig. 2 shows the yields of these reaction products. It will be seen that the yield decreases drastically when the gelatin content exceeds 5.0 wt%, thus proving effect of gelatin to retard generation of zeolite Y. Experiment II Particle size distributions were measured on the different samples of zeolite Y obtained with gelatin contents of 0.0 wt%, 0.1 wt%, 1.0 wt% and 7.5 wt%. The results are shown in Fig. 3. It is to be noted, however, the zeolite Y obtained by the use of the aqueous solution containing 7.5 wt% of gelatin was formed through a 20-hour reaction to obtain a yield of 98 %. From Fig. 3,it will be understood that, in the sample obtained with the aqueous solution which did not contain gelatin (comparative example), the particle sizes were wide-spread from 0.66 µm to 42.1 µm, and the particle size of cumulative 50 % was 4.71 µm. In contrast, all the samples prepared by using aqueous solutions containing gelatin showed narrower ranges of particle size distribution as measured by precipitation method, as well as smaller mean particle size (cumulative 50 %). More specifically, the samples produced by using aqueous solutions of gelatin contents of 0.1%, 1.0% and 7.5% respectively showed mean particle sizes of 3.55 µm, 1.97 µm and 1.70 µm. This clearly shows that the samples of zeolite Y produced by using aqueous solutions containing gelatin have higher degrees of uniformity of particle size than the sample produced without using gelatin. It is also understood that smaller width of particle size distribution and, hence, a greater degree of uniformity of the particle size are obtained when the gelatin content in the aqueous solution is increased. Furthermore, an electron-microscopic observation of the thus-obtained crystals showed that the crystal configuration is rounded, i.e., approaches an octo-face structure, as the gelatin content is increased, as will be seen from Fig. 7. It is also confirmed that the mean particle size of zeolite Y decreases in accordance with a rise in the gelatin content. Experiment III Samples of zeolite Y were produced under the same reaction conditions as Experiment I while varying the amounts of sodium aluminate and 40 wt% aqueous solution of colloidal silica, and regions in which zeolite Y is obtainable in single phase were examined in each of the cases of the gelatin content being 0.0 wt%, 1.0 wt% and 10.0 wt%, the results being shown in reaction composition chart in Fig. 4. As will be understood from Fig. 4, when gelatin was not used, zeolite Y was obtainable only in the form of a mixture with herechelite and could not be obtained as a single phase, in the region where the content of silicon oxide was 2.5 mol% or less. In contrast, when gelatin was used in amount of 1.0 wt%, zeolite Y as single phase could be obtained even when the content of silicon oxide was reduced to 1.0 mol%. Reduction in the silicon oxide content means increase in the aluminum oxide content in zeolite Y, which suggests enhancement of the ion-exchanging ability and catalytic activity of the zeolite Y. In the case where the gelatin content was increased to 10.0 wt%, single phase of zeolite Y could be obtained even in a region of further decreased silicon oxide content. It is thus understood that addition of gelatin widens the region of generation of zeolite Y as compared with the case where gelatin is not added. Thus, zeolite Y having higher aluminum content can be obtained easily by the use of gelatin. Comparative Experiment IV Each of a plurality of triple-inlet flask was charged with 28 cc of water in which were added 0.5 g of sodium hydroxide, 1.5 g of sodium aluminate and 30 g of 40 wt% aqueous solution of colloidal silica. Then, polyvinyl alcohol (saponification value 98.5%, polymerization degree 2400) was added to the respective mixtures so as to form aqueous solutions having polyvinyl alcohol contents of 0.0 wt% and 0.1 wt%. The aqueous solutions were then stirred and allowed to mature for 15 hours at the room temperature. The reaction products were then filtered and the filtrates were rinsed with water followed by drying, whereby samples white powders of zeolite A were obtained. The particle size distributions of these samples were measured to obtain results as shown in Fig. 5. It will be seen that the sample obtained by using polyvinyl alcohol provides a narrower range of particle size distribution and smaller particle size, as compared with the sample obtained without using polyvinyl alcohol. It was also confirmed through another experiment that the use of polyvinyl alcohol widens the region of generation of zeolite, as in the case where gelatin is used. Experiment V Experiment V was conducted to examine the ion exchanging ability of the product, by using th samples of ultra-fine aluminosilicate particles obtained in Experiment I. The ion-exchanging ability was measured by putting the sample in an aqueous solution of strontium chloride and calculating the amount of strontium consumed through exchange of ions. The results of the measurement are shown in Fig. 6. As will be seen from this Figure, the sample obtained with reaction time being zero exhibits only a small ability of ion exchange. In contrast, the amorphous phases obtained through 1-hour or longer reactions showed ion exchanging ability equivalent or superior to that of zeolite. It is to be specifically pointed out that superior ion exchanging ability is developed by the phase obtained at a moment 1 hour after the commencement of reaction, i.e., before generation of zeolite is confirmed. In view of this fact, electron-microscopic photos were taken of the reaction products obtained at moments 1 hour and 10 hours after the commencement of the reaction, for each of the samples obtained with gelatin contents of 0.0 wt% and 10.0 wt%, respectively. These photos are shown in Figs. 7A to 7D. It will be seen from Fig. 7C that the sample produced with the use of 10.0 wt% gelatin exhibits an amorphous phase composed of extremely fine particles of a particle size around 500 Å (= 50 nm) at the moment 10 hours after the commencement of the reaction. These extremely fine particles forming amorphous phase were scattered and left on the surface of static water for 48 hours. The particles were held afloat without substantial precipitation. The amorphous phase showed a transparency substantially equivalent to that of colloid. Experiment VI A reaction vessel made of a stainless steel having an internal volume of 5 ℓ was charged with 1200 cc of water and 103 g of gelatin. The mixture was stirred to allow gelatin to be uniformly dissolved in water, thus forming a water-soluble solvent. Then, 540 g of 40 wt% aqueous solution of coloidal silica was added to the solvent and stirred so as to be uniformly dispersed in the solvent. Meanwhile, an aqueous solution was prepared by dissolving 160 g of sodium hydroxide and 56 g of sodium aluminate in 370cc of water. The thus-prepared aqueous solution was gradually added to and mixed with the solvent containing the above-mentioned dispersed phase at 30°C, and the mixture was strongly agitated by a strong shearing homo-mixer go as to form a cake. The cake was then left for 1 hour at the room temperature for maturing and was then heated to and maintained at 100°C for 10 hours for reaction. The reaction product was filtered and the filtrate was rinsed with water, followed by drying, whereby white powder of zeolite Y was obtained. The particle size distribution of this zeolite Y was measured, the results being shown in Fig. 8. As will be seen from this Figure, an unrealistically small mean particle size of 0.73 µm, as well as very narrow particle size distribution of 0.5 to 2.0 µm,was obtained. In addition, the proportion of particles having particle sizes not greater than 1 µm was as large as 80%. As a comparative example VI, zeolite Y was synthesized by the same process as Experiment VI except that gelatin was not added. Fig. 9 shows the results of measurement of particle size distribution of the thus obtained comparative example of zeolite. It will be seen that the comparative example has a mean particle size of 3.96 µm which much greater than that of the product of Experiment VI. The particle size distribution with also was 0.8 to 10 µm, which also is much greater than that of the product of Experiment VI. Figs. 10A and 10B show electron-microscopic photos of the product of Experiment VI and the product of the comparison example. It will be seen that the product of Experiment VI,synthesized by using gelatin dissolved in the solvent, exhibits much smaller particle sizes with higher degree of uniformity, as well as rounded polygonal configurations approximating spheres, as compared with the product of comparison example prepared by the conventional; process employing no gelatin. Thus, the superiority of the product produced by Experiment VI in accordance with the present invention is proved not only from the results of measurement but also through electron-microscopic observation. Experiment VII Aluminosilicate was synthesized and white powder of zeolite A was obtained by the same process as Experiment VI except that the amounts of coloidal silica, sodium aluminate and sodium hydroxide were respectively changed to 300 g, 187 g and 62 g. The particle size distribution of this zeolite A was measured, the results being shown in Fig. 11. As will be seen from this Figure, an unrealistically small mean particle size of 0.75 µm, as well as very narrow particle size distribution of 0.4 to 2.0 µm,was obtained. In addition, the proportion of particles having particle sizes not greater than 1 µm was as large as 80%. As a comparative example VII, zeolite A was synthesized by the same process as Experiment VII except that gelatin was not added. Fig. 12 shows the results of measurement of particle size distribution of the thus obtained comparative example of zeolite. It will be seen that the comparative example has a mean particle size of 6.81 µm which much greater than that of the product of Experiment VI. The particle size distribution with also was 1.0 to 10 µm, which also is much greater than that of the product of Experiment VI. Figs. 13A and 13B show electron-microscopic photos of the product of Experiment VI and the product of the comparison example. It will be seen that the product of Experiment VII, synthesized by using gelatin dissolved in the solvent, exhibits much smaller particle sizes with higher degree of uniformity, as well as rounded polygonal configurations approximating spheres, as compared with the product of comparison example prepared by the conventional process employing no gelatin. Thus, the superiority of the product produced by Experent VII in accordance with the present invention is proved not only from the results of measurement but also through electron-microscopic observation. Experiment VIII Next step, examine the ion-exchanging ability of the products of the Experiments VI and VII comparing with the products of the comparison examples of the Experiments VI and VII. The ion-exchanging ability was measured by putting 0.1g of the product in 1000ppm of an aqueous solution of strontium chloride measured correctly and stirring under the room temperature and skimming above liquid and measuring a concentration of strontium-ion survived in the liquid by the Atomic Absorption Analysis. By calculating the results of the measurement, each amounts of strontium ion-exchanging by mg equivalent per 100g each samples were shown by Fig. 14. The Fig.14 shows that the zeolite produced by the Experiment VI and VII have a rapid reaction velocity, comparing to the zeolite produced by the comparison example VI and VII, and some zeolite have a high ion-exchanging ability, thus it is proved that this invention is superior.

Claims: A process for producing a micro-particulate aluminosilicate comprising the steps of: preparing an aqueous slurry of a metal hydroxide or metal salt, a metal aluminate and colloidal silica as essential components in an aqueous solution of a water-soluble polymer; stirring the slurry to disperse uniformly said essential components so as to form a cake; and thereafter allowing said cake to mature followed by heating; characterised in that said water-soluble polymer is gelatin. A process as claimed in claim 1 characterised by adding said colloidal silica first to said aqueous solution in which said water-soluble polymer is uniformly dissolved, stirring the mixture to disperse uniformly the colloidal silica, and thereafter adding gradually aqueous solutions of said metal hydroxide or metal salt and said metal aluminate; and in that said cake is obtained by conducting a strong agitation of the slurry after addition of said metal hydroxide or metal salt and said metal aluminate. A process as claimed in claim 1 or claim 2 wherein said aqueous solution contains up to 10%wt gelatin. A process as claimed in claim 1, claim 2 or claim 3, characterised in that said aqueous solution contains 7.5%wt gelatin. A process as claimed in claim 1, claim 2, claim 3, or claim 4, characterised in that said aqueous solution contains 5%wt gelatin. A process as claimed in claim 1, claim 2, claim 3, claim 4 or claim 5, characterised in that said aqueous solution contains 3%wt gelatin. A process as claimed in claim 1, claim 2, claim 3, claim 4, claim 5 or claim 6, characterised in that said aqueous solution contains 1.0%wt gelatin. A process as claimed in claim 1, claim 2, claim 3, claim 4, claim 5, claim 6 or claim 7, characterised in that said aqueous solution contains 0.5%wt gelatin. A process as claimed in claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim 7 or claim 8, characterised in that said aqueous solution contains 0.1%wt gelatin.

Inventors: ARAI KOZO, GOTO YOSHIAKI, ARAI, KOZO, GOTO, YOSHIAKI
Applicants: TOKUSHU KIKA KOGYO KK, TOKUSHU KIKA KOGYO CO., LTD.
Application year: 1991
Main classification: C01B39
IPC codes: C01B39, B01J39