US 4,888,161 AGrant
Method of Forming Dense, Unsintered, Granular Alkaline Earth Metal Carbonates
Issue Date:1989-12-19
•26 Claims
Abstract
A method of converting fine particle size alkaline earth metal carbonate, e.g., barium or strontium carbonate, into a free-flowing granular form with relatively high bulk density, without sintering, grinding, or briquetting, is disclosed. It involves the following steps: The product is especially useful as an additive for glass used to make television face plates. (a) forming a suspension of the carbonate in water with enough deflocculating agent, e.g., sodium polyacrylate or sodium hexametaphosphate, to substantially completely deflocculate the carbonate; (b) drying the resultant suspension at a temperature that is elevated, but without heating the carbonate to its sintering point, for example by spray drying in a spray drier operating at an inlet temperature in the range of about 400.degree. to 600.degree. C., to obtain a granular material primarily passing 10 mesh and held on a 150 mesh screen (Tyler); and (c) heating the granular material to about 600.degree. to 700.degree. C., which causes it to shrink, thereby increasing its bulk density by at least about 5%, preferably at least 10 or 20 percent.
Metadata
Assignee
- Chemical Products Corporation
Inventors
- Charles Adams, Jr.
- Jerry A. Cook
Application Information
Application Number:US 223386&
Filing Date:1988-07-25
Priority Date:1987-01-28
Art Unit:116
Classifications
IPC:
C01F 1118
Field of Search:
42323106501241252430;635;636;637293 R306;463;46527;1116182.32;182.33
Patent Drawings
This patent does not have any drawings.
Description
The invention is further illustrated by the following examples:
EXAMPLE I
(Preparation of Granular Strontium Carbonate)
Freshly precipitated strontium carbonate crystals are dewatered in a continuous pressure filter to yield a 67% by weight strontium carbonate filter cake having the consistency of a crumbly, semi-hard clay. (If this flocculated filter cake is dried at 110.degree. C. and pulverized, the loose bulk density of the dry strontium carbonate will be 37 lb./ft..sup.3, the tapped bulk density about 65 lb/ft..sup.3, and the packed powder will not flow). The wet filter cake is continuously introduced into a 10 HP, 41/2 gallon capacity Kneadermaster mixer, manufactured by Patterson Corp., Toccoa, Georgia, at the rate of 80 pounds of filter cake per minute. Colloid 211 sodium polyacrylate dispersant, manufactured by North Chemical Company, is simultaneously added to the mixer at the rate of 140 ml. per minute. A substantially completely deflocculated fluid suspension flows continuously out of the mixer into an open-throated Moyno pump. The suspension is pumped into a stirred 20,000 gallon tank. Some of the suspension is recycled to the mixer to aid the deflocculation. None of the ingredients or equipment is heated or cooled; the mixing is conducted at room temperature.
The suspension in the stirred tank has a low shear viscosity at 25.degree. C. of approximately 100 centipoises. It is pumped into a spray drier by a Manton-Gaulin pump and atomized by a Spraying Systems T2 nozzle. The inlet temperature of the spray drier is held at approximately 600.degree. C. and the spraying pressure used is approximately 900 pounds per square inch gauge (psig). A substantially dry, bead-like product is obtained leaving the spray dryer at a temperature of about 90.degree. C. and having the following properties: loose bulk density of 62 lb./ft..sup.3 ; 20 wt. % passing 10 mesh and held on a 14 mesh screen, and 99 wt.% held on a 150 mesh screen.
The spray-dried strontium carbonate granules (sometimes referred to as "pellicles" ) are continuously conveyed via a belt conveyor to a gas-fired rotary kiln. The kiln temperature is maintained at 650.degree. C. The rate of feed is approximately 11/2 tons per hour. The residence time while the beads are tumbled in the kiln is approximately 40 minutes. The heat treatment substantially shrinks the strontium carbonate beads without sintering them, leaving them with a loose bulk density of 80 lb./ft..sup.3 and a particle size such that about 95 wt. % passes 14 mesh and is held on 150 mesh.
EXAMPLE II
(Preparation of Sodium-Enriched Strontium Carbonate)
The process of Example I is repeated, except that a source of sodium cations is added to the deflocculated strontium carbonate slurry before it is spray dried. Chem-Silate.RTM.41A, a commercially available aqueous solution of 3.2 ratio sodium silicate (i.e., Na.sub.2 O 3.2 SiO.sub.2) having a concentration of 37 weight percent, is added batchwise to the stirred 20,000 gallon tank at the rate of 4.3 gallons for each 185 gallons of slurry in the tank. This amounts to 2.5% of sodium silicate solution, based on the dry weight of the strontium carbonate. The resultant slurry has a low shear viscosity at 25.degree. C. of approximately 400 centipoises. It is pumped into the spray drier at a nozzle pressure of about 900 psig.
After spray drying, the strontium carbonate beads have a loose bulk density of about 62 lb./ft..sup.3 and a particle size distribution such that about 20 wt. % thereof pass 10 mesh but are held on 14 mesh, and about 99 wt. % are held on 150 mesh.
But whereas the beads in Example I contain only about 0.0034 gram atom of sodium per each mole of SrCO.sub.3, the beads of this example contain about 0.014 gram atom of Na per mole of SrCo.sub.3.
After heating in the rotary dryer, the beads exhibit a loose bulk density of about 70 lb./ft..sup.3 and a particle size distribution such that about 95 wt. % passes 14 mesh and is held on 150 mesh.
EXAMPLE III
(Preparation of Granular Barium Carbonate)
Freshly precipitated barium carbonate crystals are dewatered in a continuous pressure filter to yield a 75% by weight barium carbonate filter cake having the consistency of a crumbly, semi-hard clay. (If this flocculated filter cake is dried at 110.degree. C. and pulverized, the loose bulk density of the dry barium carbonate will be 44 lb./ft..sup.3, the tapped bulk density about 75 lb./ft..sup.3., and the packed powder will not flow.) The wet filter cake is continuously introduced into a 10 HP, 41/2 gallon capacity Kneadermaster mixer at the rate of 80 pounds of filter cake per minute. Colloid 211 polyacrylate dispersant solution is simultaneously added to the mixer at the rate of 65 ml. per minute. A substantially completely deflocculated fluid suspension, having a low shear viscosity at 25.degree. C. of approximately 80 centipoises, flows continuously out of the mixer into an open-throated Moyno pump. The suspension is pumped into a stirred 20,000 gallon tank. Some of the dispersed slurry is recycled to the mixer to aid deflocculation.
The suspension in the stirred 20,000 gallon tank has a low shear viscosity at 25.degree. C. of approximately 80 centipoises. It is pumped into the spray dryer by a Manton-Gaulin pump and atomized through a Spraying Systems T2 nozzle at a pressure of approximately 1000 psig. The inlet temperature of the spray dryer is held at approximately 600.degree. C. A bead-like product is obtained leaving the spray dryer at a temperature of about 90.degree. C. and having the following properties: loose bulk density of 70 lb./ft..sup.3 ; 15 wt. % passing 10 mesh and held on 14 mesh, and 99 wt. % held on 150 mesh.
The spray-dried barium carbonate granules are continuously fed to a rotary dryer as described in Example I. The dryer temperature is maintained at 650.degree. C. The rate of feed is about 11/2 tons per hour. The residence time is approximately 40 minutes. The heat treatment substantially shrinks the barium carbonate beads without sintering them, leaving them with a loose bulk density of 80 lb./ft..sup.3 and a particle size such that 95 wt. % passes 14 mesh and is held on 150 mesh.
EXAMPLE IV
(Preparation of Sodium-Enriched Barium Carbonate)
The process of Example III is repeated, except that a source of sodium cations is added to the deflocculated strontium carbonate slurry before it is spray dried. Chem-Silate 41A is added batchwise to the stirred 20,000 gallon tank at the rate of 5.2 gallons for each 135 gallons of slurry in the tank. This amounts to 3.0% of sodium silicate, based on the dry weight of the barium carbonate. The resultant slurry has a low shear viscosity at 25.degree. C. of approximately 3800 centipoises. It is pumped into the spray dryer at a nozzle pressure of about 1000 psig.
After spray drying, the barium carbonate beads have a loose bulk density of about 70 lb./ft..sup.3 and a particle size distribution such that about 15 wt. % thereof pass 10 mesh but are held on 14 mesh, and about 99 wt. % are held on 150 mesh.
Whereas the beads in Example III contain only about 0.0002 gram atom of Na per each mole of BaCO.sub.3, the beads of this example contain about 0.020 gram atom per mole.
After heating in the rotary dryer, the beads exhibit a loose bulk density of about 75 lb./ft..sup.3 and a particle size distribution such that about 95 wt. % passes 14 mesh and is held on 150 mesh.
EXAMPLE V
(Comparison with Prior Art Bulk Densities)
To illustrate the unique shrinkage that occurs when the alkaline earth metal carbonate granules are prepared by the process of the present invention, the bulk densities of the same strontium carbonate, when dried in different ways, were measured and compared. As reported in the following table, the freshly precipitated filter cake was divided into three portions. One was dried at 110.degree. C. in a laboratory oven and then pulverized using a mortar and pestle. The second portion was deflocculated with sodium polyacrylate, dried at 110.degree. C., and then pulverized. The third portion was deflocculated and then spray dried to form minus 10 mesh, plus 150 mesh beads. All three portions were then heated for approximately 10 minutes at 650.degree. C. The bulk densities of the powdered materials (minus 150 mesh particle size) were measured after tapping. The density of the granular material was measured loose. In our experience with these materials, tapping generally adds about 10 lb./ft..sup.3 to the bulk density.
As reported in the table, the deflocculated granular product is the one that exhibited the greatest shrinkage when subjected to the final heat treatment. It experienced approximately a 43% increase in bulk density. This material's final loose bulk density of 80 lb./ft..sup.3 is much closer to that of sintered strontium carbonate than either of the other two portions is. Sintered strontium carbonate, after grinding and screening to approximately the same particle size, normally has a loose bulk density of about 105 lb./ft..sup.3.
EXAMPLE VI
(Comparison of Different Deflocculants and Sodium Sources)
To illustrate the effect of different deflocculants and sodium cation sources on the final bulk density of granular alkaline earth metal carbonates prepared by the process of the present invention, freshly precipitated strontium carbonate filter cake was divided into five portions and treated as follows. Two portions were deflocculated with sodium polyacrylate and three were deflocculated with sodium hexametaphosphate. Four-tenths (0.4) weight percent sodium carbonate was added to two of the portions, and 0.6% sodium carbamate was added to another portion. All five slurries were spray-dried using an inlet temperature of 600.degree. C. to a minus 10 mesh, plus 140 mesh particle size. Then each sample was heated for about 10 minutes at 650.degree. C. The resultant loose bulk densities are shown in the following table. As seen from the data there, the incorporation of the added alkali metal cation did not appreciably change the bulk density of any of the products.
EXAMPLE VII
(Manufacture of Glass Face Plates for Color TV Sets)
The following ingredients are intimately blended in the stated amounts to form a batch of glass furnace feed:
The blended batch of glass furnace feed is continuously introduced into the glass furnace at the controlled rate of 1/22 of the furnace's glass-holding capacity per hour. The melting zone of the furnace is held at 1350.degree. C., the fining zone at 1450.degree. C., and the conditioning zone at 1200.degree. C. The molten glass flows out of the furnace and is formed into the shape of television face plates in stainless steel molds at about 1000.degree. C.
The face plates are inspected for defects. Tiny "cold glass" defects, which show up as bright spots in the glass when the glass is illuminated, cause a face plate to be rejected and crushed up to be reintroduced to the glass furnace as cullet. When the strontium carbonate ingredient is a sintered product such as Strontium Carbonate, Type C, manufactured by Chemical Products Corporation, and the barium carbonate is a sintered product such as Barium Carbonate, Type CFF, also manufactured by Chemical Products Corporation, the 25-inch color TV face plates rejected because of "stones" and "cold glass defects" are approximately 10% of all these face plates molded. But when the strontium carbonate and barium carbonate ingredients are the unsintered products of Examples I and III herein, the face plates rejected are only about 8% of all those molded. When the sodium-enriched strontium and barium carbonates of Examples II and IV are used, the number of rejected face plates drops even further, to about 7 percent.
EXAMPLE VIII
(Manufacture of Glass Face Plates for Black-And-White TV Sets)
The following ingredients are intimately blended in the stated amounts to form a batch of glass furnace feed:
The blended batch of glass furnace feed is continuously introduced into the glass furnace at the controlled rate of 1/25 of the furnace's glass-holding capacity per hour. The melting zone of the furnace is held at 1300.degree. C., the fining zone at 1400.degree. C., and the conditioning zone at 1200.degree. C. The molten glass flows out of the furnace and is formed into the shape of television face plates in stainless steel molds at about 1000.degree. C.
The face plates are inspected for defects. When the barium carbonate ingredient is a sintered product such as Barium Carbonate, Type CFF, the 19-inch black-and-white television face plates rejected because of "stones" and "cold glass defects" are approximately 12% of all these face plates molded. When the barium carbonate ingredient is the product of Example III herein, only about 10% of the face plates have to be rejected, and when it is the sodium-enriched product of Example IV herein, the number of rejects drops to about 9%.
Claims
We claim:
1. A method of converting precipitated alkaline earth metal carbonate selected from the group consisting of strontium carbonate and barium carbonate into a granular form suitable for use in a feedstock to a glass furnace, comprising the steps of (a) forming a suspension of the precipitated carbonate in water containing a water-soluble deflocculating agent that dissolves in molten glass without causing defects in the glass, said suspension containing at least about 35 volume percent of the carbonate and sufficient deflocculating agent to substantially completely deflocculate the carbonate; (b) drying the resultant suspension at an elevated temperature so as to produce a substantially dry, granular product, at least about 80 weight percent of which has a particle size passing 10 mesh but not 150 mesh (Tyler), said drying being conducted without allowing the product to reach 400.degree. C.; and (c) heating the resultant granular product in a zone maintained at a temperature in the range of about 600.degree. to 700.degree. C. for a time long enough to increase the loose bulk density of the granular product by at least about 5 percent, but not for so long a time as to cause the product to sinter.
2. The method of claim 1 wherein the deflocculating agent is selected from the group consisting of inorganic condensed phosphates and salts containing n organic, polymeric, macromolecular anion having a number average molecular weight in the range of about 500 to 5,000, said salts being selected from the group consisting of alkali metal and ammonium salts of polymers of ethylenically-unsaturated carboxylic acids, sulfonated condensation products of naphthalene and formaldehyde, and lignosulfonic acid.
3. The method of claim 2 wherein, in step (b), the suspension is spray dried using a spray drier operating at an inlet temperature in the range of about 400.degree. to 600.degree. C., to produce a granular product having a loose bulk density below about 65 pounds per cubic foot, the residence time of the suspended solids in the spray drier being short enough that they do not reach a temperature in excess of about 200.degree. C. before leaving the drier.
4. The method of claim 3 wherein the ethylenically-unsaturated carboxylic acid is selected from the group consisting of acrylic acid and methacrylic acid.
5. The method of claim 3 wherein the water-soluble condensed phosphate is an alkali metal salt of a condensed phosphate selected from the group consisting of pyrophosphates, hexametaphosphates, tripolyphosphates, and tetraphosphates.
6. The method of claim 4 wherein the water-soluble condensed phosphate is an alkali metal salt of a condensed phosphate selected from the group consisting of pyrophosphates, hexametaphosphates, tripolyphosphates, and tetraphosphates and, in step (c), the heating is conducted while tumbling the spray dried product.
7. The method of claim 3 wherein, in step (a), the alkaline earth metal carbonate is barium carbonate having a particle size primarily in the range of about 0.7 to 1.1 microns, the granular product of step (b) has a loose bulk density in the range of about 55 to 65 pounds per cubic foot, and the product of step (c) has a loose bulk density of at least about 85 pounds per cubic foot.
8. The method of claim 7 wherein, in step (c), the heating is conducted for about 10 to 20 minutes and wherein at least about 90 weight percent of the product of step (c) has a particle size passing 14 mesh but not 150 mesh (Tyler).
9. The method of claim 8 wherein, between steps (a) and (b), a water-soluble source of alkali metal cations that dissolves in molten glass without causing defects in the glass is added to the suspension in an amount sufficient to shorten the dissolution time in molten glass of the granular barium carbonate product produced in step (c).
10. The method of claim 9 wherein the source of alkali metal cations is selected from the group consisting of sodium and potassium salts of inorganic anions.
11. The method of claim 10 wherein the inorganic anions are selected from the group consisting of carbonate and silicate anions.
12. The method of claim 11 wherein the amount of the source of alkali metal cations used is sufficient to provide at least about 0.01 gram atomic weight of alkali metal per each gram molecular weight of alkaline earth metal carbonate in the suspension.
13. The method of claim 11 wherein the amount of the source of alkali metal cations used is sufficient to provide about 0.015 to 0.03 gram atomic weight of alkali metal per each gram molecular weight of alkaline earth metal carbonate in the suspension.
14. The method of claim 3 wherein, in step (a), the alkaline earth metal carbonate is strontium carbonate having a particle size primarily in the range of about 0.6 to 1.0 micron, the granular product of step (b) has a loose bulk density in the range of about 50 to 60 pounds per cubic foot, and the product of step (c) has a loose bulk density of at least about 75 pounds per cubic foot.
15. The method of claim 14 wherein at least about 90 weight percent of the product of step (c) has a particle size passing 14 mesh but not 150 mesh (Tyler).
16. The method of claim 15 wherein, between steps (a) and (b), a water-soluble source of alkali metal cations that will dissolve in molten glass without causing defects in the glass is added to the suspension in an amount sufficient to shorten the dissolution time in molten glass of the granular strontium carbonate product produced in step (c).
17. The method of claim 16 wherein the source of alkali metal cations is selected from the group consisting of sodium and potassium salts of inorganic anions.
18. The method of claim 17 wherein the inorganic anions are selected from the group consisting of carbonate and silicate anions.
19. The method of claim 18 wherein the amount of the source of alkali metal cations used is sufficient to provide at least about 0.01 gram atomic weight of alkali metal per each gram molecular weight of alkaline earth metal carbonate in the suspension.
20. The method of claim 18 wherein the amount of the source of alkali metal cations used is sufficient to provide about 0.015 to 0.03 gram atomic weight of alkali metal per each gram molecular weight of alkaline earth metal carbonate in the suspension.
21. The method of claim 3 wherein the deflocculating agent is selected from the group consisting of sodium and potassium salts of polymers of acrylic and methacrylic acids having number average molecular weights in the range of about 500 to 5000 and, in step (c), the heating is conducted in an atmosphere that supports combustion.
22. The method of claim 3 wherein the deflocculating agent is sodium polyacrylate, the polyacrylate anion of which has a number average molecular weight of about 1,000 to 3,000, and, in step (c), the heating is conducted while tumbling the spray-dried product in a gas-fired rotary kiln for a time long enough to increase the loose bulk density of the granular product by at least about 10 percent.
23. A method of converting precipitated barium carbonate into granular form for use in a feedstock to a glass furnace, comprising the steps of (a) forming a suspension of the carbonate in water containing a deflocculating agent selected from the group consisting of sodium polyacrylate, potassium polyacrylate, sodium hexametaphosphate, and tetrasodium pyrophosphate, said suspension containing at least about 71 percent of the barium carbonate, based upon the weight of the suspension, and sufficient deflocculating agent to substantially completely deflocculate the barium carbonate; (b) adding sufficient salt selected from the group consisting of sodium and potassium carbonates and silicates to the suspension to increase the low shear viscosity of the suspension (measured in centipoises at 25.degree. C. and 39 volume percent solids) by at least about 100 percent, but not so much that the suspension no longer flows; (c) spray drying the resultant suspension using a spray drier operating at an inlet temperature of about 400.degree. to 600.degree. C. so as to produce a substantially dry, granular product having a loose bulk density in the range of about 55 to 65 pounds per cubic foot, at least about 80 weight percent of which has a particle size passing 10 mesh but not 150 mesh (Tyler), said drying being conducted without allowing the product to reach 400.degree. C.; and (d) heating the resultant granular product in an atmosphere that supports combustion in a zone maintained at a temperature in the range of about 600.degree. to 700.degree. C. for a time long enough to increase the loose bulk density of the product by at least about 10 percent, but not for so long a time as to cause the product to sinter.
24. A method of converting precipitated strontium carbonate into a granular form for use in a feedstock to a glass furnace, comprising the steps of (a) forming a suspension of the carbonate in water containing a deflocculating agent selected from the group consisting of sodium polyacrylate, potassium polyacrylate, sodium hexametaphosphate, and tetrasodium pyrophosphate, said suspension containing at least about 67 percent of the strontium carbonate, based upon the weight of the suspension, and sufficient deflocculating agent to substantially completely deflocculate the strontium carbonate; (b) adding sufficient salt selected from the group consisting of sodium and potassium carbonates and silicates to the suspension to increase the low shear viscosity of the suspension (measured in centipoises at 25.degree. C. and 39 volume percent solids) by at least about 100 percent, but not so much that the suspension no longer flows. (c) spray drying the resultant suspension using a spray drier operating at an inlet temperature of about 400.degree. to 600.degree. C. so as to produce a substantially dry, granular product having a loose bulk density in the range of about 50 to 60 pounds per cubic foot, at least about 80 weight percent of which has a particle size passing 10 mesh but not 150 mesh (Tyler), said drying being conducted without allowing the product to reach, 400.degree. C.; and (d) heating the resultant granular product in an atmosphere that supports combustion in a zone maintained at a temperature in the range of about 600.degree. to 700.degree. C. for a time long enough to increase the tapped bulk density of the product by at least about 20 percent, but not for so long a time as to cause the product to sinter.
25. The method of claim 23 wherein, in step (c), the barium carbonate leaves the spray drier at a temperature of about 70.degree. to 200.degree. C.
26. The method of claim 24 wherein, in step (c), the strontium carbonate leaves the spray drier at a temperature of about 70.degree. to 200.degree. C.
Patent Citations (12)
| Patent | Date | Inventor | Cited By |
|---|---|---|---|
| US3615811 | 1971-10-01 | Barrett et al. | |
| US3661610 | 1972-05-01 | Ferris | |
| US3738938 | 1973-06-01 | Barrett | |
| US3802901 | 1974-04-01 | Robertson et al. | |
| US3883364 | 1975-05-01 | Robertson et al. | |
| US3989195 | 1976-11-01 | Falcon-Steward | |
| US4208388 | 1980-06-01 | Nicholson | |
| US4251351 | 1981-02-01 | Bowman | |
| US4257817 | 1981-03-01 | Mathur et al. | |
| US4421729 | 1983-12-01 | Chiang et al. | |
| US4793985 | 1988-12-01 | Price et al. | |
| US4806331 | 1989-02-01 | Adams, Jr. et al. |