Source: https://patents.justia.com/patent/9981855
Timestamp: 2019-07-20 03:42:01
Document Index: 695684792

Matched Legal Cases: ['Application No. 61', 'in fine', 'Application No. 2013235257', 'Application No. 201380015854', 'Application No. 12164041', 'Application No. 10']

US Patent for Process for preparing scalenohedral precipitated calcium carbonate Patent (Patent # 9,981,855 issued May 29, 2018) - Justia Patents Search
Justia Patents Calcium Containing, E.g., Calcite, Dolomite, Chalk, Whiting, Etc.US Patent for Process for preparing scalenohedral precipitated calcium carbonate Patent (Patent # 9,981,855)
Oct 2, 2015 - Omya International AG
The present invention provides a process for preparing a precipitated calcium carbonate product. The process comprises the steps of preparing slaking quick lime to obtain slaked lime; and subjecting the slaked lime, without agitation, without prior cooling in a heat exchanger, and in the absence of any additives, to carbonation with carbon dioxide gas to produce PCC. The newly prepared product develops better performance thanks to improved resistance during processing.
This is a divisional of Ser. No. 14/379,110, filed Aug. 15, 2014, which is a National Phase of PCT Application No. PCT/US2013/032923, filed Mar. 19, 2013 and which claims priority to U.S. Provisional Application No. 61/614,644, filed Mar. 23, 2012 and European Application No. EP12164041.1, filed Apr. 13, 2012, the contents of which are hereby incorporated herein by reference in their entirety.
In recent years calcium carbonate has found a wide array of uses across many fields. For example, calcium carbonate is one of the most widely used minerals in the paper, plastic, paint and coating industries both as a filler and, due to its white color, as a coating pigment. In the paper industry calcium carbonate is valued for its high brightness, opacity and gloss and is commonly used as a filler to make bright opaque paper. In addition, calcium carbonate is frequently used as an extender in paints and is also used as a filler in adhesives, sealants and plastics. High grade calcium carbonate has also found uses in formulations of pharmaceuticals.
“Ground natural calcium carbonate (GNCC)” in the meaning of the present invention is a calcium carbonate obtained from natural sources including marble, chalk or limestone or dolomite. Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate. The other polymorphs of calcium carbonate are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470° C., and vaterite is even less stable. Ground calcium carbonate is processed through a treatment such as grinding, screening and/or fractionizing by wet and/or dry, for example, by a cyclone. It is known to the skilled person that ground calcium carbonate can inherently contain a defined concentration of magnesium, such as it is the case for dolomitic limestone.
“Precipitated calcium carbonate (PCC)” in the meaning of the present invention is a synthesized material, generally obtained by precipitation following the reaction of carbon dioxide and lime in an aqueous environment or by precipitation of a calcium and carbonate source in water or by precipitation of calcium and carbonate ions, for example CaCl2 and Na2CO3, out of solution. Precipitated calcium carbonate exists in three primary crystalline forms: calcite, aragonite and vaterite, and there are many different polymorphs (crystal habits) for each of these crystalline forms. Calcite has a trigonal structure with typical crystal habits such as scalenohedral (S-PCC), rhombohedral (R-PCC), hexagonal prismatic, pinacoidal, colloidal (C-PCC), cubic, and prismatic (P-PCC). Aragonite is an orthorhombic structure with typical crystal habits of twinned hexagonal prismatic crystals, as well as a diverse assortment of thin elongated prismatic, curved bladed, steep pyramidal, chisel shaped crystals, branching tree, and coral or worm-like forms.
Prior art processes for producing scalenohedral PCC product typically rely on the use of additives such as monosaccharides (e.g, simple sugars such as fructose, glucose), disaccharides (e.g., sucrose, maltose, lactose), polysaccharides (e.g, starch, cellulose, glycogen), triethanolamine, mannitol, diethanolamine, bicine, morpholine, tri-isopropanolamine, N-ethyl diethanolamine, N,N-diethylethanolamine, sodium boroheptonate, or reagents including a polyhydric alcohol or a polyhydric phenol, during the slaking of the quick lime or prior to carbonation (see, e.g., U.S. Pat. Nos. 6,294,143, 5,232,678 and 5,558,850).
Conventional processes for preparing scalenohedral PCC also typically cool the slaked lime before carbonation (see, e.g., U.S. Pat. Nos. 3,320,026 and 6,251,356).
In accordance with the present invention, a precipitated calcium carbonate product is prepared in a two-stage process. In the first stage, quick lime (CaO) is slaked in water to obtain a calcium hydroxide (Ca(OH)2) slurry, or milk of lime. This reaction is shown in reaction (1) and preferably takes place in a slaker tank:
The source of quick lime (CaO) used in the slaking reaction is preferably obtained by subjecting crushed limestone to heat (calcination) to form lime (CaO) and carbon dioxide (CO2). The reaction is preferably performed at an initial temperature of about 85° F. to 120° F., and preferably 95° F. to 110° F. Since the reaction is exothermic, the temperature typically raises to 180° F. to 210° F., and preferably to 195° F. to 205° F. The reaction also is desirably performed with mixing or agitation. The duration of the reaction may vary but is typically about 5 to 15 minutes. The solids content of the slurry is typically about 10 to 20 wt.-% solids, and preferably 12 to 18 wt.-% solids. It is within the confines of the present invention that additional water may be introduced during the slaking reaction in order to control and/or maintain and/or achieve the desired solids concentration.
The calcium hydroxide slurry or slaked lime from the slaking reaction may then be screened if desired in order to remove oversize particles. A suitable screen can include, for example, a screen having an about 30-50 mesh screen size. The calcium hydroxide slurry or slaked lime may then be transferred to an intermediate tank if desired. As a result of air cooling, the temperature of the calcium hydroxide slurry or slaked lime is then reduced by about 40° F. to 70° F., and more preferably about 60° F., resulting in slurry temperature of 125° F. to 165° F., and preferably 135° F. to 155° F. However, contrary to conventional processes for preparing PCC, the calcium hydroxide slurry or slaked lime is not subjected to cooling in a heating exchanger prior to carbonation. In this regard, conventional processes for preparing PCC typically cool the calcium hydroxide slurry or slaked lime to 90° F. to 120° F. in a heating exchanger prior to carbonation.
In addition, contrary to methods for preparing PCC in the prior art, the carbonation is conducted in the absence of any additives. As used herein, the “absence of any additives” means the absence of any additives that may be added prior to or during carbonation, including additives that may be added during the slaking of the quick lime or the resulting calcium hydroxide slurry. Such additives include, for example, a carbohydrate, a monosaccharide, a disaccharide, a polysaccharide, triethanolamine, mannitol, diethanolamine, bicine, morpholine, tri-isopropanolamine, N-ethyl diethanolamine, N,N-diethylethanolamine, sodium boroheptonate, or reagents including a polyhydric alcohol or a polyhydric phenol, or any mixture thereof. Preferably, the absence of any additive means the absence of a monosaccharide or a disaccharide, and most preferably, the absence of any additive means the absence of a disaccharide (e.g., sucrose).
In accordance with the present invention, the carbon dioxide (CO2) is selected from gaseous carbon dioxide, liquid carbon dioxide, solid carbon dioxide or a gaseous mixture of carbon dioxide and at least one other gas, and is preferably gaseous carbon dioxide. When the CO2 is a gaseous mixture of carbon dioxide and at least one other gas, then the gaseous mixture is a carbon dioxide containing flue gas exhausted from industrial processes like combustion processes or calcination processed or alike. CO2 can also be produced by reacting an alkali- and/or earth alkali carbonate with acid. Furthermore, it can be produced by the combustion of organics, such as ethyl alcohol, wood and the like, or by fermentation. When a gaseous mixture of carbon dioxide and at least one other gas is used, then the carbon dioxide is present in the range of 8 to about 99% by volume, and preferably in the range of 10 to 25% by volume, for example 20% by volume. Preferably, the CO2 is obtained from an external source, and is more preferably captured from the calcination of the crushed calcium carbonate. The carbonation reaction is preferably conducted at an initial temperature of 130° F. to 160° F., and more preferably at an initial temperature of 135° F. to 145° F. The medium particle size of the calcium carbonate can be controlled by adjusting the starting temperature upwards or downwards 1-2° F. The reaction desirably precedes until all or substantially all of the calcium hydroxide or slaked lime has been converted into calcium carbonate slurry. In the preferred embodiment, the reaction is stopped when the conductivity of the reaction mixture increases.
If the PCC is subjected to dewatering, dispersion and/or grinding steps, these steps may be accomplished by procedures known in the art. With respect to grinding, the PCC product may be dry ground and/or wet ground. Wet grinding refers to grinding the PCC in a liquid medium (e.g., slurry). Wet grinding may be carried out in the absence of a grinding aid or in the presence of a grinding aid. One or more grinding agents can be included, such as, e.g., sodium polyacrylate, a salt of polyacrylate acid, and/or a salt of a copolymer of acrylic acid. Drying may take place using any suitable drying equipment and can, for example, include thermal drying and/or drying at reduced pressure using equipment such as an evaporator, a flash drier, an oven, a spray drier (such as a spray drier sold by Niro and/or Nara), and/or drying in a vacuum chamber. Dispersants also can be included to prepare dispersions if desired.
The PCC or PCC product produced according to the present invention may be used in various materials in which it is desirable to use calcium carbonate as a filler. For example, the scalenohedral PCC or PCC product may be used in the pharmaceutical field with products such as medicines, in human or animal foodstuffs, in the papermaking field as a filler or in the coating of paper, in water-based or non-water-based paints, in plastics, or in printing inks (e.g., offset printing, rotogravure printing). Preferably, the PCC or PCC product is used as a filler in paper, and more preferably as a filler in uncoated woodfree paper. In this regard, the PCC product of the present invention offers an improvement over conventional PCC in uncoated wood free paper, by allowing better bulk (+5-10%), higher opacity and stiffness than conventional PCC.
Particle Size Distribution (Mass % Particles with a Diameter <X) and Weight Medium Diameter (d50) of Mineral Material.
The conventional PCC from Example 1 and the PCC according to the present invention from Example 2 were used to prepare handsheets for further testing. More specifically, the handsheets were prepared by first combining 80% hardwood pulp with 20% softwood pulp to achieve a 100% pulp mix. Hanksheets were then made using 80% of the pulp and 20% of either the conventional PCC or the PCC according to the present invention. The handsheets were then subjected to the following tests.
This test measured the internal fiber bond strength of paper, and gave an indication of expected performance of the strength in the Z direction. This test was performed with the Scott Internal Bond Tester (Model # B, version AV-2)(Huygen Corporation, Illinois) in accordance with Tappi T569.
This test measured the maximum tensile strength developed at rupture, and more specifically, the force per unit width required to break a paper sample. This test used the Instron Testing System (Model #1011)(Instron Corporation, Massachusetts) in accordance with Tappi T-498 om-88.
The results of the testing are presented in Table 1. As can be seen, a handsheet prepared from the PCC according to the present invention had improved stiffness (as determined using the Scott Bond test, the Tabor stiffness test, and tensile strength test) at a higher buck density than handsheets prepared from the conventional PCC products.
PCC according Comparative Comparative to Example 1 Example 1 invention (2.5 mps) (2.9 mps) Example 2
Basis weight Basis weight g/m2 72.0 71.9 72.2 Basis weight lb/3300 ft2 48.8 48.6 48.8 Brightness R457 TAPPI % 88.5 89.5 89.4 Standard 0.2 0.3 0.2 deviation Caliper Thickness Thousandths 5.00 4.70 4.60 of inch Standard 0.20 0.10 0.10 deviation Specific Volume cm3/g 1.76 1.66 1.62 Bulk density g/cm3 0.57 0.60 0.62 Filler Filler content % 21.30 21.50 19.90 Gurley Porosity Porosity s 3.9 5.1 4.7 Standard 0.2 0.6 0.5 deviation Opacity Opacity % 88.3 89.6 88.4 Standard 0.7 0.3 0.3 deviation Corrected opacity % 88.7 90.0 88.8 Scott Bond Scott Bond ft-lb/in2 64 61 78 Standard 5 7 3 deviation Taber Stiffness Bending TU 1.91 2.23 2.33 resist 15° Standard 0.31 0.28 0.26 deviation Tensile strength Tensile strength lbs/in 8.0 8.4 9.8 Standard 0.3 0.2 0.4 deviation Breaking length km 1.98 2.09 2.42 Tensile index Nm/g 19.4 20.5 23.7
The PCC prepared by the conventional process (“old PCC”) and the PCC prepared by the process of the present invention (“new PCC”) were subjected to a resistance test involving centrifugation, which subjects the PCC to stress forces due to centrifugal effect and the shear effect generated by the differential speed of the rotor. The parameters of the testing were as follows:
centrifuge type, model: KHD Humboldt SC01
The particle size distribution was determined for the old PCC and the new PCC, both before and after centrifugation. The results are shown in Table 2 below and in FIG. 1. As shown in Table 2 and FIG. 1, the new PCC generated less fines than the old PCC after being subjected to centrifugation. For example, as a result of centrifugation, the old PCC generated an increase of 56% of particles having a dp<2 μm, while the new PCC generated an increase of 48.9% of particles having a dp<2 μm. For dp<1.5 μm, the old PCC generated an increase of 34.6% of particles having a dp<1.5 μm, while the new PCC generated an increase of 27.8% of particles having a dp<1.5 μm. For dp<1.0 μm, the old PCC generated an increase of 13% of particles having a having a dp<1 μm, while the new PCC generated an increase of 10.1% particles having a dp<1 μm. The reduction in fines for the new PCC in comparison to the old PCC as a result of centrifugation demonstrates that the new PCC has a stronger resistance of the PCC clusters/crystals during processing than the old PCC.
Mass % < dp 0.2 0.3 0.4 0.5 0.6 0.8 1 1.5 2 3 4 5 6 8 10
S270 “old” 0.3 0.1 0.9 4 12.2 24.2 64.4 89.9 97.4 99.1 99.6 99.5 S270 “old” 1.2 1.6 2.6 3.6 7.1 13 34.6 56 88.7 97.4 99.1 99.3 99.4 99.5 (after CF) S270 “new” 0.5 1.6 3.4 4.9 12.2 24.9 69.2 91.9 98 99.3 99.2 99.1 S270 “new” 0.6 1.2 2.5 3.2 4 6.2 10.1 27.8 48.2 85.5 96.6 98.9 99.6 99.8 99.9 (after CF)
All publications mentioned herein above are hereby incorporated in their entirety. While the foregoing invention has been described in detail for the purposed of clarity and understanding, it will be appreciated by one skilled in the art from a reading of the disclosure that various changes in form and detail can be made without departing from the true scope of the invention in the appended claims. All changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
1. A precipitated calcium carbonate (PCC) product produced by the process comprising the steps of:
(c) subjecting the PCC obtained in step (b) to one or more screening, dewatering, dispersion and grinding steps to obtain a PCC product containing 85% or more scalenohedral particles, having a medium particle size (d50) of 2.5 microns, a d75/d25 of 1.5, a BET surface area of 4.7 m2/g, and no additives, wherein the PCC product, when subjected to centrifugation, generates less fines than a PCC product prepared by subjecting slaked lime, with agitation, with prior cooling in a heat exchanger, and in the presence of additives, to carbonation with carbon dioxide gas.
2. The PCC product according to claim 1, wherein step (a) is performed at an initial temperature of 85° F. to 120° F.
3. The PCC product according to claim 1, wherein step (a) is performed at an initial temperature of 95° F. to 110° F.
4. The PCC product according to claim 1, wherein the temperature of the reaction in step (a) raises to 180° F. to 210° F.
5. The PCC product according to claim 1, wherein the temperature of the reaction in step (a) raises to 195° F. to 205° F.
6. The PCC product according to claim 1, wherein step (a) is performed with mixing or agitation.
7. The PCC product according to claim 1, wherein slaked lime obtained in step (a) has a solids content of 10 to 20% solids.
8. The PCC product according to claim 1, wherein slaked lime obtained in step (a) has a solids content of 12 to 18% solids.
9. The PCC product according to claim 1, which further comprises subjecting the slaked lime obtained in step (a) to screening.
10. The PCC product according to claim 1, wherein as a result of air cooling, the temperature of the slaked lime obtained in step (a) is reduced by 40° F. to 70° F., prior to carbonation in step (b).
11. The PCC product according to claim 1, wherein the slaked lime obtained in step (a) is not subjected to cooling in a heating exchanger prior to carbonation in step (b).
12. The PCC product according to claim 1, wherein the carbonation reaction in step (b) is conducted at an initial temperature of 130° F. to 160° F.
13. The PCC product according to claim 1, wherein the carbonation reaction in step (b) is conducted at an initial temperature of 135° F. to 145° F.
14. The PCC product according to claim 1, wherein the PCC obtained in step (b) is isolated.
15. The PCC product according to claim 1, containing 90% or more scalenohedral particles.
16. The PCC product according to claim 1, containing 95% or more scalenohedral particles.
17. A material comprising the PCC product according to claim 1.
18. The material according to claim 17, wherein the material is a paper, a paper coating, a paper product, an ink, a paint, a coating, a plastic, an adhesive, a building product, a foodstuff or a pharmaceutical product.
19. The material according to claim 18, which is paper.
20. The material according to claim 18, which is uncoated woodfree paper.
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Patent Publication Number: 20160023915
Inventors: Joe Wenk (Kingsport, TN), George Saunders (Brandon, VT), Marc Maurer (Village-Neuf), Mathieu Skrzypczak (Terrace Park, OH)
Application Number: 14/873,924
International Classification: C01F 11/18 (20060101); D21H 17/67 (20060101); D21H 19/38 (20060101);