WO2006081333A2

WO2006081333A2 - Kaolins having controlled water absorption, oil absorption, or porosity

Info

Publication number: WO2006081333A2
Application number: PCT/US2006/002719
Authority: WO
Inventors: Edward J. Sare; Tommy L. Adkins
Original assignee: Imerys Kaolin, Inc.
Priority date: 2005-01-27
Filing date: 2006-01-26
Publication date: 2006-08-03

Abstract

Disclosed herein are methods of forming calcined kaolins having controlled properties, such as water absorption, oil absorption, and porosity. Also disclosed is a method for determining water absorption of a mineral, in a manner similar to performing an oil absorption test except by using water. Also disclosed are calcined kaolin slurries and ceramic bodies, comprising the calcined kaolin having controlled properties.

Description

KAOLINS HAVING CONTROLLED WATER ABSORPTION, OIL ABSORPTION, OR POROSITY

[001] This application claims priority to U.S. Provisional Patent Application No. 60/646,979, filed January 27, 2005.

[002] The present invention relates to new methods for controlling properties of minerals, such as kaolins, and the uses of the resulting compositions comprising these minerals, such as ceramic honeycomb automotive substrates, polymers, and rubbers.

[003] Kaolin is a white industrial mineral, which has found use in a wide range of applications. Large deposits of kaolin clay exist in Devon and Cornwall, England, Brazil, China, Australia and in the states of Georgia and South Carolina, United States of America.

[004] Particulate kaolins occur naturally in the hydrous form and exist as crystalline structures containing hydroxyl functionality. Particulate kaolins may be converted to a calcined form by thermal processes. Such processes cause the particulate kaolin to dehydroxylate. During calcination, the hydrous kaolin converts from a crystalline to an amorphous form. Further, during calcination, aggregation typically occurs.

[005] Kaolins are used in many products, such as paints, paper coating compositions, ceramics, rubbers, and polymers. Like many minerals, kaolins are capable of a certain amount of water uptake. Due to the inherent variability of natural kaolin even across a single deposit, there is some unavoidable variability in the final water absorption. This can present a problem for ceramic automotive catalysts comprising kaolin, which require kaolin having a consistent level of water absorption.

[006] Accordingly, there remains a need to provide kaolin having controlled properties, such as water absorption, oil absorption, and porosity.

[007] Generally, the properties of both hydrous and calcined kaolin are dependent on attributes, such as particle size (expressed in terms of particle size distribution, or PSD)₁ shape, and texture of the individual particles and of agglomerates thereof. [008] One aspect of the present disclosure is a method for adjusting at least one property of a composition comprising a calcined kaolin, wherein the method comprises:

(a) measuring the at least one property of a calcined kaolin having a d₅₀ of at least about 1 μm; and

(b) grinding the calcined kaolin to adjust the at least one property, wherein the at least one property is chosen from water absorption, oil absorption, and porosity.

[009] According to the present disclosure, "chosen from" or "selected from" as used herein refers to selection of individual components or the combination of two (or more) components. For example, the at least one property that is adjusted may be any single property of water absorption, oil absorption, or porosity, or a combination of any two properties, or even all three properties.

[010] In one aspect, the calcined kaolin in (a) has a dso of at least about 1 μm, such as a d₅₀ of at least about 1.5 μm such as a dso of at least about 2 μm, at least about 3 μm, or at least about 5 μm. The particle size distribution (psd) may be determined by measuring the sedimentation speeds of the dispersed particles of the particulate product under test through a standard dilute aqueous suspension using a SEDIGRAPH ™, e.g., SEDIGRAPH 5100, obtained from Micromeritics Corporation, USA. The size of a given particle can be expressed in terms of the diameter of a sphere of equivalent diameter (esd), which sediments through the suspension. The SEDIGRAPH graphically records the percentage by weight of particles having an esd less than a particular esd value, versus that esd value.

[011] "Mean particle diameter" is defined as the diameter of a circle that has the same area as the largest face of the particle. The mean particle size, dso value, and other particle size properties referred to in the present application are measured in a well-known manner by sedimentation of the particulate material in a fully dispersed condition in an aqueous medium using a SEDIGRAPH 5100. The mean particle size dso is the value determined in this way of the particle esd at which there are 50% by weight of the particles, which have an esd less than that d₅o value. [012] In one aspect, the calcined kaolin in (a) has a multimodal, such as a bimodal, particle size distribution. For example, the calcined kaolin can comprise coarse calcined kaolin having a mean particle size greater than about 1 μm, greater than about 1.5 μm, or greater than about 2 μm, and a fine kaolin having a mean particle size less than about 1 μm, or less than about 0.5 μm.

[013] In one aspect, the grinding method mentioned in (b) comprises at least one process chosen from ball milling, roller milling, hammer milling, and attrition grinding, and any other method of comminuting a calcined kaolin.

[014] In one aspect, the grinding method mentioned in (b) comprises ball milling, which occurs over a period of time of at least about 30 min., such as a period of time of at least about 45 min., at least about 60 min., at least about 2 h, at least about 3 h, or at least about 4 h.

[015] In one aspect, the mean particle size of the calcined kaolin is reduced in (b) by no more about 15%, or by no more than about 10%. In another aspect, the grinding in (b) causes the 2 μm content of the kaolin to increase by no more about 5%.

[016] "Calcined kaolin" as used herein refers to a kaolin that has been converted from the corresponding (naturally occurring) hydrous kaolin to the dehydroxylated form by thermal methods. Calcination changes, among other properties, the kaolin structure from crystalline to amorphous. Calcination is carried out by heat-treating coarse or fine hydrous kaolin in known manner, e.g., at temperatures ranging from 500⁰C to 1200⁰C, such as temperatures ranging from 800⁰C to 1200⁰C.

[017] The degree to which hydrous kaolin undergoes changes in crystalline form can depend upon the amount of heat to which the hydrous kaolin is subjected. Initially, dehydroxylation of the hydrous kaolin can occur upon exposure to heat. At temperatures below a maximum of about 850 - 900⁰C, the product is often considered to be virtually dehydroxylated, with the resultant amorphous structure commonly referred to as a metakaolin. Frequently, calcination at this temperature is referred to "partial calcination," and the product may also be referred to as "partially calcined kaolin." Further heating to temperatures above about 900 - 95O⁰C can result in further structural changes, such as densification. Calcination at these higher temperatures is commonly referred to as "full calcination," and the product is commonly referred to as 'fully calcined kaolin'. If the calcined kaolin is further heated, a portion of the calcined kaolin may be converted to the mullite phase. Thus, in some cases the calcined kaolin can comprise a high mullite content, such as for example greater than 3% mullite, greater than 5% mullite or greater than 10% mullite.

[018] "Calcined" (or "calcination"), as used in herein, may encompass any degree of calcination, including partial (meta) and/or full and/or flash calcination.

[019] In one aspect, the at least one property is oil absorption. Oil absorption refers to the number of grams of oil absorbed by 100 grams of the pigment (units of g/g, indicated as a %) and is traditionally considered to be an indication of the total resin demand of the pigment. Oil absorption is dependent on particle structure, interparticle packing, and particle size. Higher oil absorption indicates higher resin demand, which can lead to, for example, increased opacity in high PVC paints. One technique to determine oil absorption is the Spatula Rub- out Oil Absorption Test (ASTM D-281. Another technique to determine oil absorption is the Gardner-Coleman method (ASTM D1483-95).

[020] In one aspect, the calcined kaolin can be ground to obtain an oil absorption of at least about 100%, such as an oil absorption of at least about 110%.

[021] In one aspect, the at least one property is porosity. In one aspect, porosity is assessed as relative porosity, which can be determined by a Baroid^® Filter Assay using a Baroid^® High Pressure Filter Press. The Baroid^® High Pressure Filter Press applies nitrogen pressure to the top of a slurry column, which is resting on a filter disk. Application of the pressure forces the filtrate through the filter, which is then collected and measured. The calcined kaolin forms a filter cake on the filter. When temperature and pressure are held constant, the time required for a certain quantity of filtrate to be collected is a good measure of ease of filtration. Relative porosity is generally inversely related to the time to blowout.

[022] Alternatively, porosity can be measured using a porosimeter or by the BET method. In one aspect, the grinding in (b) decreases the porosity by at least about 5%, such as an amount of at least about 10%. [023] One aspect of the present invention is a test for measuring water absorption, also referred to herein as a "Water Rub-Out Test" (WROT). In one aspect, the WROT test is similar to the rub-out oil absorption test (e.g., such as ASTM D-281 , the disclosure of which is herein incorporated by reference), but performed with water instead of oil. Both oil absorption and water absorption can depend on the porosity of the calcined kaolin.

[024] In one aspect, the water absorption of the calcined kaolin in (a) is high, such as an amount of at least about 60%. In another aspect, the grinding in (b) reduces water absorption by at least about 10%, such as an amount of at least about 15%, or an amount of at least about 20%.

[025] Another aspect of the disclosure provides a method for determining water absorption of a mineral, comprising:

(a) measuring an amount of the mineral in a dry form;

(b) adding water dropwise to the dry mineral until the water/mineral mixture forms a single ball; and

(c) determining the amount of water added.

[026] In one aspect, the amount of added water in (b) is determined by weight or by volume. In one aspect, the mineral comprises calcined kaolin. In another aspect, the mineral comprising calcined kaolin further comprises hydrous kaolin, talc, halloysite, calcium carbonate, gypsum, feldspar, silica, and nepheline syenite.

[027] The dropwise addition in (b) initially results in clumping of the mineral. As more water is added, the mineral coalesces. In one aspect the method determines the minimum amount of water needed to coalesce the mineral into a single ball. In another aspect, the adding in (b) is performed with stirring.

[028] Another aspect of the disclosure provides a method of forming a calcined kaolin slurry, comprising:

(a) measuring at least one property of a calcined kaolin having a d₅₀ of at least about 1 μm;

(b) dry milling the calcined kaolin to adjust the at least one property to obtain a desired result;

(c) adding a liquid medium to the dry milled calcined kaolin to form the calcined kaolin slurry. [029] In one aspect, the calcined kaolin slurry further comprises at least one mineral chosen from hydrous kaolin, talc, halloysite, calcium carbonate, gypsum, feldspar, silica, and nepheline syenite.

[030] In one aspect, the method of forming the slurry further comprises adding a biocide to the calcined kaolin slurry.

[031] With the slurry described above, the present disclosure provides a method of forming a ceramic body, comprising:

(a) dewatering the calcined kaolin slurry to obtain a calcined kaolin wet cake; and

(b) forming the calcined kaolin wet cake into a ceramic body. [032] In one aspect, the forming in (a) comprises at least one method chosen from casting, extruding, pressing, and molding the kaolin calcined wet cake.

[033] The calcined kaolin slurry may also be screened by blunging a calcined kaolin clay with water to form an aqueous suspension. In one embodiment, the slurry further comprises at least one dispersant. The at least one dispersant can be present in an amount effective to fluidize the slurry, for example in an amount ranging from about 0.01% to about 2% by weight, relative to the total weight of the slurry, such as an amount ranging from about 0.01% to about 1 % by weight.

[034] In one aspect, a dispersing agent is added to the slurry before flocculation, resulting in a pH that is greater than or equal to about 6.5, such as a pH ranging from 8 to 10. To achieve the desired pH, the composition can further comprise at least one water-soluble pH modifier. Non-limiting examples of suitable pH-modifiers include sodium carbonate, ammonium carbonate, amino-2- methyl-1-propanol, sodium silicate, sodium hydroxide, and ammonium hydroxide.

[035] Dispersants may also be chosen from art recognized organic polymeric dispersants that are traditionally used in kaolin-containing compositions. Appropriate dispersants will be readily apparent to the skilled artisan. For example, dispersants may be chosen from polyelectrolytes such as polyacrylates and copolymers comprising polyacrylate species, for example polyacrylate salts (such as sodium, ammonium and potassium salts), sodium hexametaphosphates, polyphosphoric acid, condensed sodium phosphate, alkanolamines, and other reagents commonly used for this function. Other non-limiting examples of suitable dispersants include 2-amino-2-methyl-1-propanol, tetrasodium pyrophosphate, trisodium phosphate, tetrasodium phosphate, sodium tripolyphosphate, sodium silicate, sodium carbonate, sodium or potassium salts of weak acids, such as condensed naphthalene sulfonic acid and polymeric carboxylic acid, and water- soluble organic polymeric salts, such as sodium or ammonium polyacrylate, and polymethacrylates such as sodium or ammonium polymethacrylate.

[036] As stated, the fluid calcined kaolin slurry is flocculated, typically by lowering the pH of the fluid kaolin slurry to less than or equal to about 5, such as less than or equal to about 4.5. This downward pH adjustment can be accomplished by simply adding an appropriate amount of an acid, such as for example sulfuric acid, alum or other suitable acid.

[037] In one embodiment, the flocced calcined kaolin slurry may be dewatered in one of the ways well known in the art, e.g., filtration such as via rotary filter or filter press, centrifugation, evaporation and the like, provided that the slurry has a moisture content of greater than or equal to 10%, such as 15% and 20%, at all points between the flocculating and forming processes. Dewatering can also be accomplished with a filter press. Whatever the process, it is understood that wherein the kaolin is not dried to a moisture content of less than 10%, less than 15%, or even less than 20%, at any time between screening and forming.

[038] In one aspect, the method allows formation of cast ceramic ware product comprising the ceramic body, or formation of an extruded ceramic body comprising the ceramic body.

[039] Even further disclosed herein are ceramic body filter cakes, greenware products, and catalyst substrates comprising the ceramic bodies as described herein.

[040] Still further disclosed herein are cast ceramic ware products made from the ceramic bodies as described herein.

[041] In one aspect, the ceramic composition can comprise a calcined kaolin blend. For example, the calcined kaolin can be blended with other minerals known in the art such as, hydrous kaolin, talc, halloysite, calcium carbonate, titanium dioxide, gypsum, feldspar, nepheline syenite, silica and the like. [042] In another embodiment, additional components, such as biocides, may be added to the fluid calcined kaolin slurry.

[043] Even further disclosed herein are products formed by casting, rolling, molding, pressing, and extrusion.

[044] Extrusion is a forming method that is commonly used in the production of complex ceramic objects such as the intricate honeycomb ceramics used as substrate supports in automotive catalytic converters. One skilled in the art will recognize that extrusion may be carried out in a number of different ways, such as, for example, the methods disclosed in U.S. Patent No. 3,885,977 to Lachman, U.S. Patent No. 5,332,703 to Hickman et al., or U.S. Patent No. 5,997,984 to Koike et al., the disclosures of which are herein incorporated by reference.

[045] Slip casting is typically used in production of products having complex shapes and where plastic forming or semi-dry pressing are not possible. Thus, slip casting is applicable to the production of, for example, hollow tableware, figures and ornamental ware, and sanitary ware. For whiteware production, 'jiggering¹ can also be used to produce ware. Slip casting involves the use of a mold of appropriate shape into which a fluid suspension of a body can be poured and wherein the mold progressively extracts some of the water until a solid layer is formed.

[046] Two primary methods are typically employed for slip casting: drain casting and solid casting. In drain casting, a mold is filled with slip and casting takes place on one surface only. After a suitable time, during which the desired cast thickness is built up, the excess slip is poured off. The mold and cast are then partially dried, to allow mold release, after which the cast can be trimmed, cut or sponged. In solid casting, which is typically used for products having varying wall thicknesses, the mold is filled with slip and casting takes place on both surfaces. The removal of water generally means that the slip has to be topped up during the casting. For complex shapes, the mold can be constructed in several sections.

[047] The present invention is further illuminated by the following non- limiting examples, which are intended to be purely exemplary of the invention. Example 1

[048] This Example describes one embodiment for measuring water absorption of a mineral, such as calcined kaolin. Water was added dropwise to calcined kaolin having a known amount, such as a known weight. During the dropwise addition, a spatula was applied to the calcined kaolin/water mixture on a non-wetting surface. As more water was added, the calcined kaolin/water mixture coalesced and formed lumps. The end point was reached when the wetted calcined kaolin formed a single ball. The sample was then weighed to determine the amount of water added. Example 2

[049] The water absorption of a commercial calcined kaolin was measured followed by dry ball milling. A one gallon jar mill having inner dimensions of approximately 7.5 inches in depth and approximately 8 inches in diameter was filled with 7500 grams of the ceramic media made of 75% (5625 g ) is 1 in. diameter balls and 25% (1875g) 0.5 in. diameter balls. The sample (600 g) was then added, (no TSPP) and rolled on a "Paul O. Abbe" roller for 45 min., 60 min., and 240 min.

Table I

Summary of Particle Size, Optical, and Water Absor tion Properties

[050] It can be seen that milling affects the water demand of the calcined kaolin, where the demand decreases as the milling time increases.

[051] The dewatering characteristics of the resulting slurries are summarized in Table II. As can be seen, the relative rate of dewatering and the final cake solids were dependent on the degree of water absorption reduction. The experimental procedure for this Baroid Filter assay (300 grams Dry Basis Sample @ 55.0% Solids) was as follows: 75g of nepheline syenite (Flux), 75g flint (crystalline silica), 75g Kaolin(hydrous or calcined kaolin, dry basis) ball clay slurry - 123.2 grams slurry @ 60.9% solids, 197.3g deionized water, and 0.09 g Colloid 211 dispersant (0.05% dosage on clay only) was mixed for 2 minutes in a 1 quart Waring blender and flocced to pH 3.5 with 10% H₂SO₄. 400 grams of this mixture was then used to run the Baroid filtration test @ 50 psi. The filtrate was measured as a function of time, and the time of "blowout" (complete dewatering) was measured, along with the final filtrate volume. ..

Table Il Summary of Dewatering Properties

[052] Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention.

[053] Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims

WHAT IS CLAIMED IS:

1. A method for adjusting at least one property of a composition comprising calcined kaolin, said method comprising:

(a) measuring the at least one property of the calcined kaolin having a dβo of at least about 1 μm; and

(b) grinding the calcined kaolin to an amount sufficient to adjust the at least one property, wherein the at least one property is chosen from water absorption, oil absorption, and porosity.

2. The method according to claim 1 , wherein the calcined kaolin in (a) has a d₅o of at least about 1.5 μm.

3. The method according to claim 1 , wherein the calcined kaolin in (a) has a d₅₀ of at least about 2 μm.

4. The method according to claim 1 , wherein the calcined kaolin in (a) has a d₅₀ of at least about 3 μm.

5. The method according to claim 1 , wherein the calcined kaolin in (a) has a d₅o of at least about 5 μm.

6. The method according to claim 1 , wherein the calcined kaolin in (a) comprises coarse calcined kaolin having a mean particle size greater than about

1 μm, and a fine calcined kaolin having a mean particle size less than about 1 μm.

7. The method according to claim 6, wherein the coarse calcined kaolin has a mean particle size greater than about 1.5 μm.

8. The method according to claim 6, wherein the coarse calcined kaolin has a mean particle size greater than about 2 μm.

9. The method according to claim 6, wherein the fine calcined kaolin has a mean particle size less than about 0.5 μm.

10. The method according to claim 1 , wherein the grinding in (b) comprises at least one process chosen from ball milling, roller milling, hammer milling, and attrition grinding.

11. The method according to claim 10, wherein the grinding of (b) is performed by ball milling.

12. The method according to claim 11 , wherein the grinding in (b) comprises ball milling for a period of time of at least about 30 min.

13. The method according to claim 12, wherein the grinding in (b) comprises ball milling for a period of time of at least about 60 min.

14. The method according to claim 1 , wherein the dso of the calcined kaolin is reduced in (b) by no more than about 15%.

15. The method according to claim 1 , wherein the d₅₀ of the calcined kaolin is reduced in (b) by no more than about 10%.

16. The method according to claim 1 , wherein the grinding in (b) causes the 2 μm content of the kaolin to increase by no more about 5%.

17. The method according to claim 1 , wherein the at least one property is oil absorption, and the grinding in (b) causes the kaolin to achieve an oil absorption of at least about 100%.

18. The method according to claim 17, wherein the grinding in (b) causes the kaolin to achieve an oil absorption of at least about 110%.

19. The method according to claim 1 , wherein the at least one property is porosity, and the grinding in (b) decreases the porosity by at least about 5%.

20. The method according to claim 1 , wherein the at least one property is water absorption, and the water absorption of the kaolin in (a) is at least about 60%.

21. The method according to claim 20, wherein the grinding in (b) reduces water absorption by at least about 10%.

22. The method according to claim 21 , wherein the grinding in (b) reduces water absorption by at least about 15%,

23. The method according to claim 22, wherein the grinding in (b) reduces water absorption by at least about 20%.

24. A method for determining water absorption of a mineral, comprising:

(a) measuring an amount of the mineral in a dry form;

(c) determining the amount of water added.

25. The method according to claim 24, wherein the mineral comprises calcined kaolin.

26. The method according to claim 25, wherein the mineral comprising calcined kaolin further comprises hydrous kaolin, talc, halloysite, calcium carbonate, gypsum, feldspar, silica, and nepheline syenite

27. The method according to claim 24, wherein the adding in (b) is performed with stirring.

28. A method of forming a calcined kaolin slurry, comprising:

(a) measuring at least one property of a calcined kaolin having a dso of at least about 1 μm;

(c) adding a liquid medium to the dry milled calcined kaolin to form the calcined kaolin slurry.

29. The method according to claim 28, wherein the calcined kaolin slurry further comprises at least one mineral component chosen from talc, halloysite, calcium carbonate, gypsum, feldspar, silica, and nepheline syenite.

30. The method according to claim 28, further comprising adding a biocide to the calcined kaolin slurry.

31. A method of forming a ceramic body, comprising:

(a) dewatering the calcined kaolin slurry according to claim 28 to obtain a calcined kaolin wet cake;

(b) forming the calcined kaolin wet cake into a ceramic body.

32. The method according to claim 31 , wherein the forming comprises at least one method chosen from casting, extruding, pressing, and molding the calcined kaolin wet cake.

33. A cast ceramic ware product comprising the ceramic body formed by the method according to claim 31.

34. An extruded ceramic body comprising the ceramic body formed by the method according to claim 31.