WO2006022704A1

WO2006022704A1 - Zeolite a with submicron-size particles

Info

Publication number: WO2006022704A1
Application number: PCT/US2004/025993
Authority: WO
Inventors: Ernest Senderov; Richard J. Hinchey; Philip Connolly
Original assignee: Pq Holding, Inc.
Priority date: 2004-08-11
Filing date: 2004-08-11
Publication date: 2006-03-02

Abstract

Compositions containing zeolite A of sub-micron particle size and of a narrow particle size distribution are provided. A method for making the sub-micron zeolite A includes a two-step process of 1) forming an activated silicate containing a low level of aluminate and 2) subsequently adjusting the composition of the activated silicate to make a final reaction mixture having a stoichiometry suitable for zeolite A formation.

Description

ZEOLITE A WITH SUBMICRON-SIZE PARTICLES

FIELD OF THE INVENTION

This invention relates to zeolites. More particularly, it relates to zeolite A having a small particle size suitable for use in detergent compositions.

BACKGROUND OF THE INVENTION

Zeolites, as is commonly known in the art, are crystalline aluminosilicates having fully cross-linked open framework structures built of tetrahedral, corner- sharing SiO₄ and AIO₄ groups. Zeolites belong to the class of minerals referred to generally as tectosilicates, and their crystalline architecture can be idealized as being constructed from silicon atoms in tetrahedral, four-fold coordination with oxygen atoms in a 3-dimensional lattice. Each silicon atom in the structure has a nominal 4⁺ charge and shares 4 oxygen atoms (each having a nominal charge of 2^") with other silicon atoms in the crystal lattice.

Substitution of the isoelectronic Al³⁺ for Si⁴⁺ in the framework creates a charge imbalance on the lattice that must be rectified by the incorporation of additional cations close by Al sites. Steric accommodation of the hydrated cations directs the crystallization of aluminosilicates towards the formation of more open structures containing continuous channels or micropores within the crystal. These structural micropores in the anhydrous zeolites allow the passage and adsorption of molecules based on size giving the materials molecular sieving properties. The cations themselves are not part of the crystal framework and can usually be replaced by equivalently charged species without damage to the lattice. In zeolite A, the pore size is large enough to permit the facile passage and exchange of cations in aqueous solutions. The as- synthesized forms of zeolite A exhibit a highly selective exchange affinity for Ca²⁺ ions, the primary cation found in potable "hard" water in the United States, and this gives it particular value as a water "softening" builder in detergent powder formulations.

For many zeolite applications, usage of small particle zeolite would be advantageous. However, conventional methods of zeolite A synthesis lead to relatively large crystals in the several-micron size range. Even if small primary crystals are formed, they usually intergrow into aggregates with diameters exceeding several microns.

Zeolites, and zeolite A in particular, could be used to advantage in liquid detergent formulations, but conventional zeolite particles are too large to remain in suspension without settling and separation as a solid phase. Sedimentation of zeolite solids, requiring re-dispersion prior to use, places liquid formulations containing zeolites at a marketing disadvantage. Availability of a zeolite material consisting substantially of submicron particles would allow the formulation of liquid detergents containing stable suspensions of zeolite solids.

Zeolites are also useful in other applications such as fillers for plastics, paper and composite materials. Zeolite A is particularly useful as a thermal stabilizer in PVC and CPVC. In such applications it is especially beneficial to functional performance if the zeolite material consists of very small particles having an average size of one micron or less and being essentially free of particulates with sizes greater than 5-10 micron.

Zeolites can be made by a number of processes, such as are described in U.S. Patent Application Publication No. US 2001/0053741 Al. Processes for making zeolite A by such methods essentially comprise mixing together alkaline aqueous solutions of sodium silicate and sodium aluminate to form amorphous aluminosilicate gels, which are heated for a time and converted to a crystalline aluminosilicate with an ideal anhydrous oxide composition of: 2SiO₂ ^■ AI₂O₃ ^• Na₂O, having a characteristic x-ray diffraction pattern and commonly referred to as sodium zeolite A, zeolite A, 4A, or LTA in the IUPAC structure type convention. Typical as-made zeolite A contains associated water, and can be expressed by the following formula:

Na₂O • AI₂O₃ ^■ 2.0SiO₂ • 4.5H₂O. SUMMARY OF THE INVENTION

In one aspect, the invention provides a composition containing submicron zeolite¹ A. The zeolite A has a laser light scattering particle size distribution according to the following ranges:

D (V, 0.99) is at most 1.2 μm; D (V, 0.9) is at most 0.8 μm; D (V, 0.5) is at most 0.6 μm; D (V, 0.1) is at most 0.4 μm; and has a particle size variation coefficient of at most 40%. An X-ray powder diffraction pattern of the zeolite A shows a full width at half maximum of at most 0.17° 2Θ and a crystallinity of at least 80%.

In another aspect, the invention provides a method for producing a composition comprising zeolite A. The method includes performing in sequence the steps of: a) combining water, sodium silicate, sodium aluminate, and sodium hydroxide in amounts according to the following ranges of mole ratios:

Na₂O/AI₂O₃ = 6-60 H₂O/AI₂O₃ = 100-600 SiO₂/AI₂O₃ = 8-75 to form a first reaction mixture; b) maintaining the first reaction mixture for an aging time, and at an aging temperature, selected to provide an activated silica; c) mixing together the activated silicate and an adjustment mixture comprising water, sodium hydroxide, sodium aluminate, and sodium silicate in amounts as needed to provide a crystallization mixture having a mole ratio composition as follows:

Na₂O/AI₂O₃ = 3.5-30 H₂O/AI₂O₃ = 100-600 SiO₂/AI₂O₃ = 1.6-7.5; and d) maintaining the crystallization mixture for a crystallization time, and at a crystallization temperature, sufficient to form the zeolite A.

In another aspect, the invention provides zeolite A made by the foregoing method.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a scanning electron micrograph of a zeolite product according to the invention.

Fig. 2 shows particle size distribution plots for three zeolite products according to the invention, and a plot for one prior art zeolite.

Fig. 3 is a comparison of particle size distribution from SEM and laser light scattering.

DETAILED DESCRIPTION OF THE INVENTION

The invention will next be illustrated with reference to the figures. Such figures are intended to be illustrative rather than limiting and are included herewith to facilitate the explanation of the present invention.

The invention provides compositions containing zeolite A having a substantially submicron particle size and a narrow particle size distribution, and a process for making such a zeolite. The particle size distribution (PSD) can be represented in terms of the volume fraction of the sample that is less than a specified size in μm, as measured by laser light scattering. The volume size fractions D (V, 0.1); D (V, 0.5); D (V, 0.9); and D (V, 0.99) correspond to the top size for the 10, 50, 90, and 99 percentile volume fractions, respectively. Better properties are typically provided by a product with narrower range or, by other words, with more uniform particle size distribution. The relative uniformity of PSD can be characterized by the variation coefficient, which is calculated in percent by the following equation.

Variation coefficient (%) = Standard deviationxlOO/volume mean diameter Zeolite A according to the invention typically has a particle size distribution (determined by the procedure described below in Example 1) wherein:

D (V, 0.99) is at most 1.2μm,

D (V, 0.9) is at most 0.8 μm,

D (V, 0.5) is at most 0.6 μm, and

D (V, 0.1) is at most 0.4 μm.

Variation coefficient is at most 40%.

More typically, the particle sizes range as follows:

D (V, 0.99) is not higher 0.8 μm,

D (V, 0.9) is not higher than 0.6 μm

D (V, 0.5) is not higher than 0.4 μm

D (V, 0.1) is not higher than 0.3 μm

Variation coefficient is at most 30%

Thus the average particle size is smaller, and the particle size distribution is significantly narrower, than that of zeolite A prepared by conventional methods. Fig. 1 is a scanning electron microscopy (SEM) image showing an exemplary zeolite A according to the invention, revealing zeolite A particles less than 1 μm in size. Fig. 2 shows the particle size distribution of three typical zeolite A samples, according to the invention, with essentially all of the particles being less than 1 μm in size. The zeolites were those obtained in Example 1 below (2 hrs crystallization at 95°C), Example 2 (3 hrs crystallization at 100⁰C), and Example 3 (3 hrs crystallization at 95⁰C). A commercial zeolite A, Valfor^® 401F, is shown for comparison. SEM analysis, in combination with light scattering particle size analysis, allows another defining characteristic of the zeolite A of this invention, the degree of aggregation, to be measured. The degree of aggregation (DA) may be calculated according to the following equation:

DA = Diaser scattering/DsEM where Dι_aSer scattering is the equivalent spherical volume mean particle size determined by laser light scattering, and D_SEM is the equivalent spherical volume mean particle size determined by scanning electron microscope.

In some embodiments of the invention, the degree of aggregation of the zeolite A is less than 3.0. More typically, it is less than 2.0. Zeolite A according to the invention typically has an external surface area of at least 30 m²/g_/ as measured by the N₂ adsorption BET method.

Compositions containing zeolite A according to the invention may be solid products (for example dry powders or compacted dry powders in the form of briquettes or other shapes) containing the zeolite, or they may be aqueous dispersions of the zeolite. Either of these forms may optionally contain other ingredients such as may be suitable for any of a variety of applications. It has been found that zeolites according to the invention provide aqueous dispersions having good stability. By "good stability," it is meant that there is relatively little settling out of the zeolite from the dispersion, and/or any settling that does occur is easily reversed by mild agitation.

A two-stage process is used for making zeolite A according to the invention. In the first stage, activated silicate is formed by reaction of excess sodium silicate with aluminate under conditions of relatively high pH. The reaction mixture is allowed to age for a short period of time. Subsequently, in the second stage, an adjustment mixture is combined with the activated silicate. This adjustment mixture contains the balance of the Na-aluminate needed to bring the resulting total batch composition to a stoichiometry appropriate for forming zeolite A . Maintenance of the resulting mixture under time and temperature conditions suitable for forming crystalline zeolite A completes the second stage. The product may then be isolated by any of the usual techniques known in the art. Crystallization is considered to be complete when X-Ray Diffraction (XRD) analysis indicates that the degree of conversion of the starting amorphous gel into crystalline product has reached a maximum and stopped changing. Either or both of the activated silicate and the final gel composition may be essentially organic-free, by which it is meant that no organic compounds are purposely included in the formulation. This is a distinct advantage over processes that require the use of organic ingredients such as tetramethylammonium hydroxide to achieve small zeolite particle size. Such organic materials must, before use in many applications, be removed by calcination or by other means before the zeolite can be used, for example as an adsorbent or ion exchanger. Such a step is not necessary when zeolite A is made according to the invention in the absence of organic compounds. In addition, the zeolite A particles of this invention show very little aggregation of the primary crystallites into larger aggregate particles, which would require mechanical milling or other means of reducing the particle size for applications requiring a substantially submicron zeolite.

Ratios of Ingredients

It has been found that when at least a certain proportion of total formulation silicate is provided by the activated silicate, the zeolite product made by the process is consistently high purity zeolite A having a very small particle size, typically less than 1 μm. Preferably at least 50% of the total silicate is provided in activated silicate, more preferably at least 75%, still more preferably at least 95%, and most preferably 100%. The resulting zeolite product typically contains greater than approximately 80 wt%, more typically >90 wt%, preferably >95 wt% zeolite A (determined by XRD according to the method provided in Example 1 below), and therefore less than approximately 20, 10, and 5 wt% of an aluminosilicate impurity, respectively. Further, XRD analysis of the zeolite A shows a narrow full width at half maximum (FWHM) for the characteristic peaks found at 24.0°, 27.1°, 29.9°, and 34.2° 2Θ. Typically, the average FWHM for these peaks is at most 0.17° 2Θ. The crystallinity of the zeolite A phase in the product is typically at least 80%, more typically at least 90%, and most typically at least 95% relative to Valfor^® 100, a standard commercial zeolite A available from PQ Corporation of Valley Forge, PA.

As used herein, the term "mole ratio" as applied to ratios involving Na₂O, AI₂O₃, H₂O, and SiO₂ means ratios based on the total mole amounts of sodium, aluminum, water, and silicon in the composition, regardless of the form in which these materials occur. Thus, for purposes of this patent, these materials are treated equally for purposes of determining "mole ratios" regardless of whether they are in the form of soluble species or whether they are bound in the form of a zeolite or other insoluble material.

Mole ratios of ingredients in the activated silicate may range within the following limits:

Na₂CVAI₂O₃ = 6-60; typically 10-30 H₂CVAI₂O₃ = 100-600; typically 200-500 SiO₂/AI₂O₃ = 8-75; typically 10-25

Mole ratios of ingredients in the total batch composition, i.e. after addition of the adjustment mixture, may range within the following limits:

Na₂O/AI₂O₃ = 3.5-30; typically 5-10 H₂O/AI₂O₃ = 100-600; typically 130-200 SiO₂ZAI₂O₃ = 1.6-7.5; typically 1.8-2.5

In one exemplary embodiment of the invention, the mole ratios of ingredients in the activated silicate are as follows:

Na₂O/AI₂O₃ = about 17 H₂O/AI₂O₃ = about 300 SiO₂/AI₂O₃ = about 15

In some exemplary embodiments of the invention, the total batch composition is in the range:

Na₂O/Al₂O₃ = 5.5-8.5 H₂O/AI₂O₃ = 140-150 SiO₂/AI₂O₃ = 1.9-2.0 Process for Making the Zeolite The general process of this invention may be carried out in a number of ways. In preparing the activated silicate, the sodium silicate and aluminate reagents can be added to a reaction vessel sequentially. The order of addition is not critical, but lower initial viscosities are observed by the addition of silicate to aluminate, thereby leading to better mixing. Vigorous agitation is desirable during aluminate reagent addition to ensure immediate dispersion of the aluminate in the silicate solution and the general absence of localized volumes of concentrated aluminate. Alternatively, both reagents may be added simultaneously, e.g. by "jet" mixing, or by using a static in-line mixer, thereby providing high velocity, turbulent mixing conditions.

Without desiring to be bound to any particular explanation or theory, the applicants believe that the two-stage sequence of gel make-up limits the formation of polycrystalline agglomerate particles in the product of this invention. In zeolite synthesis according to prior art methods, the formation of gel particles with an AI₂O₃-rich composition close to that of zeolite A is thought to allow multiple nucleation events to occur during a certain period of the crystallization stage within individual gel particles and on the surface of growing crystals. The resulting intergrowth of crystallites creates robust, polycrystalline aggregates much larger in size than the individual crystallites, which is undesirable according to the present invention. By doping a source of soluble silica with a moderate amount of soluble aluminate, the silicate reagent is converted to strongly alkaline, silica rich, aluminosilicate sol/solution. While the overall composition is silica rich, the very high alkalinity in the system favors a low SiO₂/AI₂O₃ in the colloidally dispersed solid phase. It is believed that the colloidal solids in the activated silicate consist predominantly of vast numbers of zeolite nuclei or precursors in dynamic equilibrium with a solution phase principally composed of highly charged monomeric silica species. This alumina- activated sol is then combined with the aluminate adjustment reagent, at a nominal SiO₂/AI₂O₃ stoichiometry appropriate to the formation of zeolite A. The presence of a large number of nuclei or nuclei precursors accelerates simultaneous formation of small crystals, reducing or eliminating nucleation on the crystal surfaces and reducing or preventing intergrowth. Surprisingly, the gel which is formed by this procedure can then be aged at ambient temperature for a time before heating or heated directly to convert the gel material into very small and largely discrete crystallites of zeolite A. This occurs without significant formation of the large particle, intergrown, agglomerates characteristic of the zeolite material formed by conventional prior art synthesis methods.

When zeolite A is made as described above, it is believed that huge numbers of nuclei are contributed to the synthesis mixture (i.e. the final reaction mixture containing all of the ingredients) by the activated silicate reagent. These crystalline moieties may act as sites for precipitation of amorphous aluminosilicate solids from solution. Such a precipitation of the bulk of amorphous aluminosilicate directly on multiple discrete sites may inhibitthe formation of larger gel particles, which are thought to be centers for formation of larger, intergrown, polycrystalline, agglomerates. In addition, the formation of small particle size material may also be aided by the high alkalinity of the solution phase favoring formation of a flocculated aluminosilicate solid rather than the extended open network of amorphous aluminosilicate gel that is characteristic of conventional synthesis. It has been found that aging of the .,. activated silicate for a limited period of time prior to addition of the adjustment mixture provides a narrower particle size distribution than when no aging occurs. This is consistent with a time-dependent process for formation of precursors or nuclei. However, excessive delay in the addition of the adjustment mixture may result in the formation of an impurity phase. Without wishing to be bound by any particular theory or explanation, this may be due to the composition domain in the activated silicate being outside the domain that favors the exclusive nucleation and growth of zeolite A. If sufficient nuclei of an impurity phase are formed in the activated silicate, these nuclei may continue to grow even after the addition of the adjustment mixture initiates the crystallization of zeolite A.

Regardless of the exact mechanisms involved, there will be an optimal aging time before addition of the aluminate adjustment mixture to achieve minimum particle size and avoid phase contamination in the final product. The optimum time will vary considerably depending upon the exact conditions of preparation of the activated silicate reagent, including inter alia the temperature, agitation, and exact formulation used. Conditions that would favor zeolite crystal growth, such as elevated temperature and prolonged agitation, should be avoided so as to maximize the concentration of nuclei or precursor species in the silicate at the point when the aluminate adjustment reagent is added. Typically, aging of the activated silicate may be conducted at a temperature between about 15 and 4O⁰C, more typically between about 20 and 35°C. The aging is typically performed for a period of time ranging between about 0.5 and 8 hours, more typically between about 1 and 3 hours. In one exemplary embodiment, aging is performed for 1.5 hours at 25°C.

After the adjustment mixture is added, the total batch composition may optionally be aged, typically at approximately 20-40⁰C, for a period of time as long as about 170 hours, typically about 2-30 hours, and more typically about 6-24 hours.

Following the addition of the adjustment mixture and the optional aging period, the mixture is brought to a crystallization temperature typically in the range of 30-120⁰C, more typically about 50-110⁰C, and most typically about 90-100⁰C in order to effect crystallization to form the zeolite. The crystallization time is typically between about 0.25 and 48 hours, more typically between about 0.5 and 20 hours, and most typically between about 0.5 and 3 hours. Heating to the desired temperature can be accomplished by methods known in the art including steam sparging, heating of vessel walls or pumping the gel through a heat exchanger.

Progress of the crystallization may be monitored by x-ray diffraction analysis and comparison of selected peak areas or intensities with fully crystalline standards. Upon determination that crystallization is complete, it is desirable that the product solids be promptly cooled by a water quench or by heat exchangers or separated from the mother liquor by filtration. It is known generally in the art that, in some situations, over-digestion of a zeolite in its liquor can promote the formation of undesirable crystalline impurity phases or be otherwise detrimental to zeolite performance in ion exchange applications. The product zeolite may be flocculated in the high ionic strength mother liquor solution, which makes the material filterable in conventional equipment. The washed filter cake may be dried by heating in conventional equipment such as a flash dryer, or it may be reslurried and dried in a spray dryer as is known in the art. The evaporation of water during the drying process invariably generates capillary tension between the discrete submicron particles. This tension draws the particles together, forming persistent larger agglomerates. For this reason it is preferable to re-slurry the filter cake in a concentrated aqueous dispersion (30-50%) to preserve the nanoparticle nature of the product. Alternatively, if a dry powder of submicron zeolite A is desired, a surface active agent may be added to the reslurried filter cake to inhibit the aggregation of the submicron particles during drying. In some embodiments, compositions containing zeolite A according to the invention may be aqueous dispersions, for example dispersions comprising between 20 and 70 wt% of the zeolite in water, optionally with a dispersing agent to maintain dispersion stability. Suitable dispersing agents, which may typically be present at a level up to about 5 wt%, and may for example include polyacrylic acids or salts thereof, polyethers, polyalcohols, and copolymers of polyacrylic acid and a polyether.

Sodium Silicate Solution

Sodium silicate solution for use according to the invention may be prepared by any means known in the art, for example by combining aqueous NaOH with any highly reactive silica solid. Preferred silica reagents by reason of their lower cost are any of the variety of soluble sodium silicate solutions of commerce that are known and used in the art to prepare zeolites. For example, soluble sodium silicates having SiO₂/Na₂O mole ratios ranging from 1 to 4 can be used, and commercial silicate solutions or sodium silicate glass of one particular ratio can be combined with NaOH or NaOH solutions to generate solutions with lower ratio as is known in the art. Silicate solutions having a SiO₂ZNa₂O mole ratio of about 3.3 (commonly known as "waterglass" solution) are generally available at relatively low cost and consist of a mixture of monomeric and polymeric silica species. Used as such, this reagent favors the formation of a silica-rich primary gel when a reactive aluminate solution is slowly added to it. In addition, sodium silicate powders like those produced by PQ Corporation can be used. Reactive amorphous silica powders may also be used, such as can be prepared by acid precipitation from sodium silicate or generated as residual solids by the acid extraction of Al from clays. Other suitable reactive silicas include varieties of amorphous silicas, available from Degussa Corporation of Parsippany, NJ or PPG Industries Inc. of Pittsburgh, PA, and calcined rice hulls. Additional suitable reactive silicas are well known to those skilled in the art. As used herein, the term "sodium silicate solution" will be understood to include aqueous mixtures of reactive silicas with NaOH.

Sodium Aluminate Solution

Sodium aluminate solution for use according to the invention may be prepared by any method known in the art, for example by dissolving AI₂O₃ • 3H₂O, also known as alumina trihydrate (ATH) Or AI(OH)₃, in aqueous NaOH. The composition of this solution can be varied over a considerable range in terms of weight percent Na₂O or AI₂O₃ dissolved. Compositions that provide stable solutions at ambient temperatures are described in a binary phase diagram well-known in the art, such as for example as published in the Kirk- Othmer Encyclopedia of Chemical Technology, Fourth Edition, Vol. 2, p. 269 (1992). The aluminate solution can be prepared and analyzed and stored for later use or it can be prepared to a specific formulation as a batch for each batch synthesis of zeolite. Methods of making sodium aluminate solutions are well known in the art, and are described for example in U.S. Patent Application No. 09/810,914. For the purposes of this invention it is necessary that essentially all of the alumina in the Na-aluminate reagent be fully dissolved. Sodium aluminate having a Na₂O/AI₂O₃ ratio of >1 is typically used.

When aluminate is prepared in bulk, it is frequently the practice to meter the requisite quantity of analyzed solution into a batch feed tank. A silicate batch feed tank can similarly be supplied with a requisite quantity of sodium silicate solution of a specific composition. Alternatively, commercial sodium aluminate such as is produced by the Southern Ionics Company of Mobile, AL can be also be used. Detergent Formulations

Zeolites of the present invention may be particularly useful as ingredients in liquid detergent formulations. Accordingly, the invention also comprises a detergent composition comprising from 0.1% to 99% by weight of a builder system comprising at least the zeolite of this invention and, optionally, an auxiliary detergent builder salt, and from about 0.1% to about 99% by weight of at least one detergent adjunct other than the builder system, as are known in the art. Such detergent adjuncts include, but are not limited to, detersive surfactants, bleaches and bleach activators, enzymes and enzyme stabilizing agents, suds boosters or suds suppressers, anti-tarnish and anticorrosion agents, soil suspending agents, soil release agents, germicides, pH adjusting agents, non-builder alkalinity sources, chelating agents, organic and inorganic fillers, solvents, hydrotropes, optical brighteners, dyes, perfumes, fabric treatment agents such as polyamide-polyamines, abrasives.

Detergent compositions in general are described in U.S. Patent Nos. 4,605,509 and 4,274,975, both to Corkill et al., and in published PCT Application Serial Number WO/43482, to Burckett-St Laurent et al, all of which are incorporated herein by reference. Exemplary formulations include, inter alia, an aluminosilicate and one or more anionic, nonionic, zwitterionic, or other surfactants. Detergent formulations of this invention may be in any form, including but not limited to liquid suspensions, gels, or powders, and may be useful in any cleaning application, for example as a laundry or dishwashing detergent.

EXAMPLES Example 1

A 66.62 g sample of commercial sodium aluminate, produced by Southern Ionics (19.50 wt% of Na₂O; 23.40 wt% of AI₂O₃) was mixed in a one- half gallon stainless steel beaker with 271.90 g of 50 wt% caustic and combined with 320.80 g of de-ionized water. A 480.09 g portion of N-silicate, commercially produced by PQ Corporation (8.90 wt% of Na₂O; 28.66 wt% of SiO₂), was added to that solution with agitation. Mole ratios of components in this silicate solution were Na₂O:AI₂O₃:SiO₂:H₂O= 17.0:1:15.0:299.9. After mixing, agitation was stopped and the silicate solution was left to age for 1.5 hr.

Separately, 1400.00 g of de-ionized water, 650.11 g of 50 % caustic and 433.00 g of sodium aluminate were combined with stirring in a 2 gallon plastic bucket. To this aluminate solution was added the activated silicate solution (after aging for 1.5 hr) with vigorous agitation, using a high-sheer "Premier" disperser (lOOOOrpm, 10 min). After adding the silicate solution to the aluminate, an additional 224.20 g of de-ionized water was used to rinse the beaker. The mole ratios in the final gel mixture were Na₂OiAL₂O₃ISiO₂IH₂O = 7.0:1.0:2.0:150.0.

The gel mixture was distributed into five tightly closed 1 liter Teflon^® bottles. The bottles stayed on the bench at room temperature for 21 hrs, and then four of them were installed on a rotating (30 rpm) wheel inside a furnace preheated to 95°C. The fifth bottle was opened immediately, the gel from inside was dropped into a triple-volume excess of room temperature de-ionized water to quench an ongoing reactions within the gel, and the mixture was placed on the Buchner funnel to separate alkaline solution and wash the filter- cake with water until the pH was about 11.5. The four bottles in the furnace were subsequently taken off after certain time periods of heating and their contents quenched, separated, and washed in an analogous manner.

The wet filter-cakes were analyzed for particle size distribution on a Malvern Mastersizer S Long Bed instrument. Each sample was prepared for measurement by dispersing in water to form a 50% (w/w) dispersion. This dispersion was then irradiated with ultrasonic energy for 4 minutes using a Cole Palmer Model CV26 Ultrasonic Processor. This dispersion was added drop-wise to the Malvern sampler until an obscuration of less than 18% (and preferably less than 13%) is obtained. The sampler pump and stirrer were set at 70%. The particle size distribution was calculated using the 3OHD presentation (particle refractive index = 1.5295+ 0.10Oi, in water RI =1.333). The product was dried (HO⁰C) and further characterized by XRD, SEM and X-ray fluorescence (XRF). XRD analysis was performed on a Philips X'Pert MPD X-Ray Diffractometer PW 3040 instrument. Monochromatized CuKa radiation was used. A sample was scanned stepwise at a rate of 0.02° 2Θ per second for each step. For calculation of the crystal Unity, five peaks were chosen with 2Θ at 21.6, 24.0, 27.1, 29.9 and 34.2°. The computer-reported peak areas, resulting from subtracting the integrated baseline intensity from the integrated peak intensity of a sample, were compared with those of the certified sodium zeolite A standard (Valfor^® 100, commercial product of PQ Corporation) having a crystal size of several microns. The percent crystallinity was calculated from the summed intensities (J):

% Crystallinity = (∑Jsam_ple/∑Js_taπ_dar_d)XlO0

Peaks at 24.0, 27.1, 29.9, and 34.2° 2Θ were also used to determine the average peak widths (FWHM) calculation.

SEM imaging was performed on an FEI DB235 focused ion beam instrument, in electron beam mode. Particle size analysis was performed using Scion Image (release Beta 4.0.2) software. Measurements were performed such that the reported numbers reflect the length of an edge of the cubic shaped crystals. The volume mean crystal dimension a_v was calculated using the relation: a_v = [∑n*a,7∑n]^1/3 where n is the number of particles with dimension a], and ai is the crystal dimension (edge length) measured by SEM.

Thus the SEM particle size measurement treats particles as cubes, and in order to compare the SEM results with those obtained by the laser light- scattering technique, which treats particles as spheres, the SEM data were converted to "equivalent sphere" data by multiplying by a factor of 1.24, which is the ratio of the diameter of any sphere to the edge of a cube of equal volume. The number of crystals involved in the measurements varied from 140 to 300.

Unheated gel appeared to be amorphous, but gel products of 1, 2, 3 and 4 hrs digestion were represented by sodium zeolite A phase, with no impurities detectable by XRD, and with relative crystallinities of 81%, 85% (FWHM = 0.12° 2Θ), 78% and 83 %, respectively. Elemental analysis (by XRF) indicated that these crystalline products had a composition close to NaA stoichiometry. Particle size distributions (by light scattering technique) for the 1, 2, 3 and 4 hr samples were also similar: D(V, 0.10) = 0.3 μm; D(V, 0.50) = 0.4 μm; D(V, 0.90) = 0.6 μm; D(V, 0.99) = 0.8; Variation coefficient = 30%. Thus all of the products were of submicron-sized particles.

An SEM image of the submicron crystals of the 2-hr product is seen in FIG. 1. It is evident that the population of particles is formed by grains of variable size, but average cube edge size is 0.14 ±0.05 μm, which corresponds to an equivalent spherical volume mean diameter of 0.19±0.06 μm. This evaluation is in reasonable agreement with the mean volume diameter of 0.42±0.13 μm calculated from light scattering. The small difference between particle sizes calculated by the two methods indicates that the degree of aggregation of primary crystals was insignificant (DA = 2.2).

Similarly, the results of a N₂ BET surface area determination (41 m²/g) for the same sample indicated a calculated diameter of equivalent uniform spherical particles of about O.lμm. Thus all of the measurements presented above indicate a very small, submicron size range of the primary crystals and particles in the zeolite A made by this exemplary process according to the invention.

Example 2

A 37.9 g portion of commercial sodium aluminate, produced by Southern Ionics (19.50 wt% of Na₂O; 23.40 wt% of AI₂O₃), was mixed with 91.3 g of 50 wt% caustic and combined with 234.5 g of de-ionized water. A 333.2 g portion of JL-silicate, (16.78 wt% of Na₂O; 0.20 wt% Of Al₂O₃: 25.22 wt% Of SiO₂), available from PQ Corporation, was added to that solution with agitation. Mole ratios of components in this silicate solution were Na₂OiAI₂O₃ISiO₂IH₂O= 17.0:1:15.0:299.8. The mixture was aged for 1.5 hr to provide an activated silicate solution. A 3399.6 g portion of de-ionized water, 1292.3 g of 50 % caustic and 264.1 g of sodium aluminate were combined, and to this aluminate solution was added the activated silicate solution (after 1.5 hr aging), using a high-sheer "Premier" disperser (10_r000rpm, 10 min). After adding the silicate solution to the aluminate, an additional 190 g of de-ionized water was used to rinse the beaker and was combined with the mixture. The mole ratios in the final gel mixture were Na₂O :AL2O3: SiO₂: H₂O = 15.0:1:2.0:400.1.

The gel mixture was distributed into eight tightly closed Teflon^® bottles. After storage on the bench for 40 hrs, four of the bottles were mounted radially on a vertical rotating metal disk inside an oven preheated to 40⁰C, At certain time intervals, bottles were taken off, opened, the contents dumped into de- ionized water, and the product filtered and washed to a pH about 11.5.

The other four bottles were left on the bench for 66 hrs, and then placed to rotate in the same oven at 100⁰C.

Zeolite A crystallinity was determined to be 23% after 4 hrs at 40⁰C, 82% after 18 hrs, and 86% after 24 hrs. Particle size distribution data for the crystalline products are given in Table 1.

The product resulting from the gel that stayed at room temperature for 66 hrs and was taken from the 100⁰C furnace after one half hour contained a mixture of zeolite X, zeolite A, and amorphous material. Products of 1, 2 and 3 hrs (100⁰C) crystallization revealed (by XRD pattern analysis) the presence of only zeolite A, with a crystallinity of 75% (FWHM = 0.16° 2Θ), 78% and 81%, respectively. Elemental analysis of the 3 hrs (100⁰C) product by XRF showed that the component molar ratios were rather close to ideal NaA: SiO₂ZAI₂O₃ (SAR)= 2.05; Na/AI=0.96. Particle size distribution data are shown in Table 1.

Table 1: Crystallization conditions and PSD (μm) for Crystalline Products of

Example 2.

40⁰C 40⁰C 100⁰C 100⁰C 100⁰C

18 hrs 24 hrs 1 hr 2 hrs 3 hrs

D(V, 0.10) 0.26 0.26 0.25 0.26 0.27 D(v, 0.50) 0.45 0.45 0.46 0.44 0.45

D(v, 0.90) 0.79 0.79 1.04 0.77 0.76

D(v, 0.99) 1.20 1.20 3.10 1.24 1.06

The variation coefficient of PSD for all of these crystalline products was about 40%.

SEM-based PSD data (equivalent spherical volume mean diameter) for product that had been digested at 100°C/3 hrs was 0.20±0.07 μm. The results were indistinguishable from those obtained in Example 1 and were, as in Example 1, close to the corresponding light scattering-based data of 0.49±0.19 μm). The degree of aggregation, DA, was 2.4.

A high external surface area (46 m²/g) indicated a very low estimated spherical particle size on the order of 0.1 μm.

Example 3

Activated silicate solution was prepared by mixing 71.2 g commercial sodium aluminate, 171.7 g of 50% caustic, 445 g of de-ionized water and 631.4 g of JL silicate. Na₂OiAI₂O₃ISiO₂IH₂O ratios of the solution were 17.1:1:15.1:302.2. After 1.5 hr activation, the silicate solution was added with vigorous agitation (10,000 rprn, 10 min) to an aluminate solution having a complementary composition for forming zeolite A. The produced gel had a formula ratio of Na₂OiAI₂O₃ISiO₂IH₂O=S.6:1:2.0:150.2. The gel was distributed into Teflon^® bottles and crystallized with rotation for various time intervals at 95⁰C. Dried products after 2, 3 and 4 hrs crystallization were characterized by XRD as zeolite A with 90, 90 (FWHM = 0.17° 2Θ) and 92 % crystallinities, respectively. Wet cake products were analyzed for PSD. The results are shown in Table 2.

Table 2: Example 3 Particle Size Distributions (μm)

95°C/2 hrs 95°C/3 hrs 95°C/4 hrs

D(V, 0.10) 0.27 0.27 0.27

D(V, 0.50) 0.38 0.37 0.38 D(V, 0.90) 0.58 0.53 0.54

D(v, 0.99) 0.78 0.78 0.78

The PSD curve for the 3 hrs crystallization wet product is shown in FIG. 3 by the plot labeled "Laser Light Scattering." Fig. 3 also shows the particle size distribution obtained by SEM. A comparison of the equivalent spherical mean volume diameters determined from SEM and laser light scattering gives a degree of aggregation of 1.8.

Those skilled in the art having the benefit of the teachings of the present invention as hereinabove set forth, can effect numerous modifications thereto. These modifications are to be construed as being encompassed within the scope of the present invention as set forth in the appended claims. In addition, although the zeolite products have been identified with reference to certain properties and characteristics, the invention is not limited to these characterizations but also includes other properties and characteristics inherent in the zeolite products formed by the processes of the present invention.

Claims

What is Claimed:

1. A composition comprising submicron zeolite A, wherein the zeolite A has a laser light scattering particle size distribution according to the following ranges:

D (V, 0.99) is at most 1.2 μm; D (V, 0.9) is at most 0.8 μm; D (V, 0.5) is at most 0.6 μm; D (V, 0.1) is at most 0.4 μm; and has a particle size variation coefficient of at most 40%, and wherein an X-ray powder diffraction pattern of the zeolite A shows a full width at half maximum of at most 0.17° 2Θ and a crystallinity of at least 80%.

2. The composition of claim 1, wherein the zeolite A has a degree of aggregation less than 3.

3. The composition of claim 1, wherein the zeolite A has an external surface area of at least 30 m²/g.

4. The composition of claim 1, wherein the zeolite A is at least 90% crystalline.

5. The composition of claim 1, wherein the composition is organic- free and the zeolite A is uncalcined zeolite A.

6. The composition of claim 1, wherein the composition comprises at least 90 wt% of zeolite A.

7. The composition of claim 1, wherein the composition comprises at least 95 wt% of zeolite A.

8. The composition of claim 1, wherein the composition is a zeolite synthesis mixture having mole ratios of Na₂O, AI₂O₃, H₂O, and SiO₂ in the following ranges:

Na₂O/AI₂O₃ = 3.5-30 H₂O/AI₂O₃ = 100-600 SiO₂/AI₂O₃ = 1.6-7.5 .

9. The composition of claim 1, wherein the composition is a zeolite synthesis mixture having mole ratios of Na₂O, AI₂O₃, H₂O, and SiO₂ in the following ranges:

Na₂O/AI₂O₃ = 5-10 H₂O/AI₂O₃ = 130-200 SiO₂/AI₂O₃ = 1.8-2.5 .

10. The composition of claim 5, wherein the zeolite A is at least 90% crystalline.

11. A stable water dispersion composition comprising 20% to 70 wt% of the composition of claim 1, and 0 - 5 wt% of a dispersing agent.

12. A detergent composition comprising a detersive surfactant and the composition of claim 1.

13. A method for producing a composition comprising zeolite A, the method comprising performing in sequence the steps of: a) combining water, sodium silicate, sodium aluminate, and sodium hydroxide in amounts according to the following ranges of mole ratios:

Na₂O/AI₂O₃ = 3.5-30 H₂O/AI₂O₃ = 100-600 SiO₂ZAI₂O₃ = 1.6-7.5; and d) maintaining the crystallization mixture for a crystallization time, and at a crystallization temperature, sufficient to form the zeolite A.

14. The method of claim 13, further comprising, between steps c) and d), the step of maintaining the crystallization mixture for an aging time at an aging temperature.

15. The method of claim 14, wherein in step d) the aging time is between six and 24 hours and the aging temperature is between 20 and 40⁰C.

16. The method of claim 13, wherein the aging temperature in step b) is between 15 and 4O⁰C and the aging time is between 0.5 and 8 hours.

17. The method of claim 13, wherein the aging temperature in step b) is between 20 and 35°C and the aging time is between 1 and 3 hours.

18. The method of claim 13, wherein the aging time and the aging temperature in step b) are selected to provide a composition comprising at least 90 wt% of zeolite A.

19. The method of claim 13, wherein the aging time and the aging temperature in step b) are selected to provide a composition comprising at least 95 wt% of zeolite A.

20. The method of claim 13, wherein in step a) the mole ratios are in the following ranges:

Na₂CVAI₂O₃ = 10-30 H₂O/AI₂O₃ = 200-500 SiO₂/AI₂O₃ = 10-25.

21. The method of claim 13, wherein the crystallization mixture has mole ratios in the following ranges:

Na₂O/AI₂O₃ = 5-10 H₂O/AI₂O₃ = 130-200 SiO₂ZAI₂O₃ = 1.8-2.5. .

22. The method of claim 13, wherein the sodium silicate provided in step a) is at least 50% of a total amount of sodium silicate provided to the crystallization mixture in steps a) and c).

23. The method of claim 13, wherein the sodium silicate provided in step a) is at least 75% of a total amount of sodium silicate provided to the crystallization mixture in steps a) and c).

24. The method of claim 13, wherein the sodium silicate provided in step a) is at least 95% of a total amount of sodium silicate provided to the crystallization mixture in steps a) and c).

25. The method of claim 17, wherein in step a) the mole ratios are in the following ranges:

Na₂CVAI₂O₃ = 10-30 H₂CVAI₂O₃ = 200-500 SiO₂/AI₂O₃ = 10-25 and wherein the crystallization mixture has mole ratios in the following ranges:

Na₂O/AI₂O₃ = 5-10 H₂O/AI₂O₃ = 130-200 SiO₂/AI₂O₃ = 1.8-2.5.

26. Zeolite A made by the method of claim 13.