Method for producing precipitated calcium carbonate (PCC) and PCC product

Abstract

A method for producing precipitated calcium carbonate (PCC) is provided. The method includes the step of adding a PCC additive or PCC seed to the process before the carbonation of slaked lime to form precipitated calcium carbonate.

Description

Detailed description of the invention

[0001] [Field] The present invention relates to a method for producing precipitated calcium carbonate (PCC). Furthermore, the present invention relates to an aqueous suspension of PCC, the produced PCC, and products made from the produced PCC. More specifically, the present invention relates to a process for producing PPC with a larger particle size by adding PCC seeds or additives to the process before the carbonation of slaked lime.

[0002] [background] Precipitated calcium carbonate (PCC), with the chemical formula CaCO3, exists in three main crystalline forms: calcite, aragonite, and vaterite. PCC can have many different polymorphs. Crystal habits include triangular, rhombohedral, hexagonal, cubic, and prismatic. PCC is generally prepared by introducing CO2 into an aqueous suspension of calcium hydroxide (Ca(OH)2), commonly known as "lime milk." Ca(OH)2 + CO2 → CaCO3 + H2O

[0003] PCC is widely used in the paper industry. PCC is inexpensive and used as a bulking agent. PCC can improve the whiteness and opacity of paper and add strength to paper products. Therefore, PCC is considered an excellent filler for paper and cardboard. PCC with relatively large particle sizes can provide superior strength and bulking effects, particularly in uncoated wood-free ("UCWF") paper. Current methods for producing larger particle sizes of PCC have been found to be inefficient, costly, and unable to achieve the required particle size growth. Embodiments of the present invention relate to an efficient and cost-effective method for producing large PCC particles.

[0004] [overview] According to one embodiment of the present invention, a method for producing precipitated calcium carbonate (PCC) is provided. The method may include the steps of: mixing components containing calcium oxide and water to prepare a slurry containing calcium hydroxide; adding PCC seeds to the slurry containing calcium hydroxide to form a mixture containing PCC seeds and calcium hydroxide; and carrying out a carbonation process of the mixture containing PCC seeds and calcium hydroxide to form a suspension containing PCC. The total amount of PCC seeds added to the slurry containing calcium hydroxide may be in the range of more than 2.5% by volume and less than 30% by volume. The suspension has a median diameter d of at least 2.0 μm 50 The method includes PCC having [specific characteristics]. The carbonation process includes the step of adding a carbon dioxide generating material to a mixture containing PCC seeds and calcium hydroxide. The method may further include the steps of separating the PCC from the suspension and drying the separated solid to form dried PCC. The dried PCC may be used as PCC seeds. The PCC seeds can be mixed with a slurry containing calcium hydroxide for more than 0 minutes and less than or equal to 60 minutes, after which the carbonation process can be started.

[0005] According to another embodiment, a method for producing large PCC particles is provided. The method includes the steps of: producing generated PCC particles; adding a certain amount of generated PCC particles as an additive to lime milk; and carbonating the lime milk having the PCC additive to produce final PCC particles having a larger size than the generated PCC particles. 2.5% to 30% of the generated PCC particles can be recycled and added to lime milk as a PCC additive. The generated PCC particles added as an additive to lime milk may be in dry particle form. The generated PCC particles added as an additive to lime milk may be in aqueous suspension form. The method may include the step of sieving the generated PCC particles to obtain an additive having particles of a selected size before being added to lime milk. In one variant, the PCC particles are not sieved to obtain an additive having particles of a selected size before being added to lime milk. The total amount of PCC additive added to lime milk is in the range of more than 2.5% to less than 30% by volume relative to the total volume of the composition. The final PCC particles have a median weight diameter d of at least 2.0 μm. 50 The final PCC particles may have a median diameter d of 2.8 μm to 3.1 μm. 50 It may have the following properties. The PCC additive is mixed with the lime milk for 60 minutes or less, and then the carbonation of the lime milk is started.

[0006] Paper products containing PCC can be manufactured through the aforementioned process. [Brief explanation of the drawing]

[0007] [Figure 1] This figure shows a basic flowchart of the process for producing precipitated calcium carbonate (PCC) according to one embodiment of the present invention. [Figure 2] This figure shows the components of a process for producing precipitated calcium carbonate (PCC) according to one embodiment of the present invention. [Figure 3] This graph shows the mass frequency versus PCC particle diameter for Example 1.

[0008] [explanation] In this specification, precipitated calcium carbonate (PCC) is defined by the common chemical definition represented by the chemical formula CaCO3. PCC has three main crystalline forms: calcite, aragonite, and vaterite. Furthermore, each of these crystalline forms may have various different polymorphs or crystal habits. In embodiments of the present invention, the crystal habit may preferably be, for example, a symmetric triangular hedron (S-PCC).

[0009] In this specification, calcium hydroxide is referred to by its common chemical definition represented by the chemical formula Ca(OH)2. Calcium hydroxide has traditionally been called "slaked lime" or "lime milk." Slake, slaked lime, lime milk, and slurry containing calcium hydroxide are interchangeable terms used herein. Slaked lime is produced by mixing, slakening, or hydrating calcium oxide or quicklime with water. Calcium hydroxide has many other names, including hydrated lime, caustic lime, building lime, and pickling lime. Slake can be a calcium hydroxide slurry, such as an aqueous calcium hydroxide suspension, and may have a solid content of less than 40% by weight, for example.

[0010] In this specification, calcium oxide is defined by its usual chemical definition represented by the chemical formula CaO. Calcium oxide is generally known as lime or quicklime and is an alkaline substance.

[0011] In this specification, a calcium oxide-containing compound or material is a material containing at least 40% by weight of calcium oxide relative to the total weight of the material. Preferably, the content is at least 70% by weight, and more preferably at least 90%.

[0012] In this specification, a slurry is a mixture in which a solid is suspended in a liquid, usually water. This suspension may contain an insoluble solid, water, and optionally additives.

[0013] In this specification, carbon dioxide-generating compounds or materials include, but are not limited to, gaseous carbon dioxide, liquid carbon dioxide, solid carbon dioxide, gases or liquids containing carbon dioxide (e.g., Na2CO3, K2CO3, etc.), pure gaseous carbon dioxide, and exhaust gases containing carbon dioxide. The carbon dioxide-generating compound may also be a gaseous mixture of carbon dioxide and air, or carbon dioxide and nitrogen.

[0014] In this specification, the carbonation process (or carbonation) refers to the process of converting calcium hydroxide to PCC. The conversion can be carried out by adding or supplying a certain amount or volume (e.g., kgCO2 / min per 21 kg of dry Ca(OH)) of a carbon dioxide-producing compound to a slake in a reaction vessel or carbonation apparatus. The completion of the carbonation process can be extended after the completion of the addition of the carbon dioxide-producing compound, and the addition of the carbon dioxide-producing compound may be continuous or intermittent.

[0015] In this specification, PCC additive or PPC seed is a term used interchangeably and may include (or be essentially from or consist of) PCC particles produced by a carbonation process. PPC seed / additive may be PCC particles in an aqueous suspension. PCC seed / additive may also be removed or separated from the aqueous suspension and may be in the form of dry particles. PCC particles produced by the carbonation process may also be sieved for size to obtain PPC seed / additive of a selected size. In another embodiment, PCC particles produced by the carbonation process are not sieved for size for use as seed / additive.

[0016] In this specification, an aqueous suspension means a system in which the liquid phase contains water, is essentially water-based, or consists of water. This term may also broadly include water in combination with small amounts of water-miscible organic solvents, such as methanol, ethanol, acetone, acetonitrile, tetrahydrofuran, and combinations thereof.

[0017] In this specification, the term "dried form" means separating the generated PCC particles from the obtained aqueous suspension and drying the PCC particles. The dried PCC may be completely dry or essentially dry, i.e., may contain residual water (e.g., less than 3% by volume, preferably less than 1% by volume).

[0018] In this specification, particle size refers to particle size d x This refers to a distribution based on weight. x The value of x is the amount of particles by weight d x This represents the diameter corresponding to a diameter less than [specified value]. The particle size values ​​disclosed herein are measured by sedigraph particle size analysis, as is well known in the art.

[0019] In this specification, the solid content of a liquid composition refers to the amount, in weight percent or volume percent, of solid material remaining after all of the solvent and / or water has been removed and / or evaporated.

[0020] In this specification, the singular forms “a,” “an,” and “the” are intended to include the plural, and the plural is intended to include the singular unless the context explicitly states otherwise (for example, when using the terms “one” or “plurality”). For example, reaction contents may include multiple contents.

[0021] In this specification, the term "and / or" includes one or more of the related enumerated items or any combination thereof.

[0022] Figure 1 is a basic schematic flow diagram for producing precipitated calcium carbonate (PCC) according to one embodiment. Calcium oxide (lime or quicklime) is mixed or slaked with water, or hydrated, to produce milk of lime. The slurry is carbonated to produce an aqueous suspension of PCC. Before the start of the carbonation process, an amount of the aqueous PCC suspension used as a seed or additive can be added to or recycled into the process continuously or intermittently. Additionally, before the aqueous suspension is added to or recycled into the process, PCC particles suspended in the aqueous solution can be sieved to obtain particles of a selected size.

[0023] The method according to an embodiment of the present invention may also comprise the steps of: removing or filtering (e.g., dewatering) PCC particles from the aqueous suspension; optionally, separating (e.g., sieving) the particles to obtain particles of a selected size; and optionally, drying the PCC particles or the separated PCC particles. The sieving step may be performed before or after the dewatering step. PCC seeds can be formed using the removal, optional separation, and optional drying steps. An amount of the removed, optionally separated, and / or optionally dried PCC seeds can be added to or recycled into the process continuously or intermittently before the start of the carbonation process.

[0024] FIG. 2 illustrates an embodiment of components for producing precipitated calcium carbonate (PCC). A calcium oxide-containing material is hydrated. That is, quicklime and water can be mixed in a slaking apparatus 10 to form a slurry containing slaked lime or calcium hydroxide. The slaked slurry can be sieved through a slaked slurry screen 12 to remove undesired-sized particles. The slaked slurry can be conveyed to a slaked slurry surge tank 14 and pumped to a slaked slurry holding tank 18 by a slaked slurry surge pump 16. A slaked slurry transfer pump 20 can transfer the slaked slurry to a carbonation apparatus 22. A carbon dioxide-generating material is introduced into the carbonation apparatus 22 for the carbonation process. An aqueous suspension of PCC is produced. The aqueous PCC suspension can be transferred to a pre-screen tank 26 via a transfer pump 24. A pre-screen pump 28 can transfer the PCC suspension to a product screen 30, where the PCC is sieved and sorted into particles of a predetermined size. The sieved PCC is stored in a post-screen tank 32, after which a post-screen pump 34 can transfer the PCC suspension to a product storage tank 36.

[0025] Next, the process includes using PCC as an additive or seed by re-adding the produced PCC to the slaking apparatus 10, the slaked slurry holding tank 18, and / or the slaked slurry surge tank 14. That is, before the start of the carbonation process, an amount of PCC seed is added to slaked lime or lime milk. A seed metering pump 38 can re-add PCC to the slaking apparatus 10, the slaked slurry holding tank 18, and / or the slaked slurry surge tank 14. The time for mixing or blending the PCC seed with slaked lime may be more than 0 minutes to 60 minutes, after which the carbonation process is started. In one embodiment, the blending time is less than 60 minutes. In one embodiment, the mixing time is 15 minutes to 50 minutes.

[0026] In one embodiment, PCC seed can be added to the carbonator 22. In this case, the time for mixing or blending the PCC seed with slaked lime may be more than 0 minutes to 60 minutes, after which the carbonation process is started. In one embodiment, the blending time is less than 60 minutes. In one embodiment, the mixing time is 15 minutes to 50 minutes. The PCC seed is mixed or blended with slaked lime before the start of carbonation. In an alternative embodiment, the addition of the PCC seed and the start of carbonation may be simultaneous.

[0027] In another embodiment, PCC particles from the pre-screen tank 26 can be added to slaked lime as an additive. For example, PCC particles from the pre-screen tank can be re-added to the slaking device 10, the slake holding tank 18, the slake surge tank 14, and / or the carbonator 22.

[0028] In one embodiment, more than 0% to 40%, more preferably 2.5% to 30%, of the produced PCC is recycled to slaked lime as an additive (e.g., recycled to the slaking device 10, the slake holding tank 18, the slake surge tank 14, and / or the carbonator 22). In a preferred embodiment, the addition amount may be less than 10%. In one embodiment, the total amount of PCC seed added to slaked lime may be an amount in the range of more than 2.5 vol% to less than 30 vol%, preferably 10 vol% to 15 vol%, based on the total weight of the composition.

[0029] The PCC seed or additive added to slaked lime (e.g., re-added to the slaking device 10, the slake holding tank 18, the slake surge tank 14, and / or the carbonator 22) has a weight median diameter d of at least 1.0 μm 50 . Adding the PCC seed before the carbonation step can produce PCC having a weight median diameter d of 1.0 μm to 3.2 μm, more preferably 1.4 μm to 3.0 μm 50 . In one embodiment, the weight median diameter d 50The particle size is at least 2.0 μm, preferably 2.8 μm or larger, and may be between 2.8 μm and 3.1 μm. Therefore, it is possible to produce PCC particles of a larger size compared to PCC produced without using PCC seeds or additives.

[0030] Next, compared to the case where PCC is not used as an additive, larger PCC particles can be transferred by the product transfer pump 40 toward final use.

[0031] PCC produced by the process of the present invention may be used in paper (intended herein to include cardboard and all paper products). PCC produced by the process of the present invention may also be used in consumer goods including, but not limited to, coatings, paints, rubber, plastics, polymers, building materials, inks, food, cosmetics, agricultural products, drugs, and pharmaceuticals.

[0032] Furthermore, it is understood that various additives can be added before, during, or after the carbonation process. For example, additives can be added to the lime milk. Additives may be, for example, scavenging additives or precipitating additives. Examples of additives include sugars, citric acid, potassium, sodium, and other additives well known in the art. Furthermore, the process of the present invention can be carried out in batch, semi-batch, or continuous mode. Continuous mode can be carried out in a continuous tubular reactor or in a plurality of separate carbonation units (the pH of the suspension gradually decreases from the first carbonation unit to the last carbonation unit).

[0033] Example 1 The completed PCC seeds were added to the slake.

[0034] [Table 1] Figure 3 shows the mass frequency versus particle diameter of the generated PCCs. The sedigraph PSD distribution shows a single peak.

[0035] Example 2 The completed PCC seeds were added to the carbonation device.

[0036] [Table 2] While several specific forms, variations, and embodiments of the present invention have been illustrated and described, it is also evident that various modifications can be made without departing from the scope of the invention. Furthermore, it is intended that various combinations or subcombinations of specific features and aspects of the disclosed embodiments can be combined or substituted with each other to form various forms of the present invention.

Claims

1. A method for producing precipitated calcium carbonate (PCC), (a) A step of mixing components containing calcium oxide and water to prepare a slurry containing calcium hydroxide; (b) Adding PCC seeds to the slurry containing calcium hydroxide to form a mixture containing the PCC seeds and calcium hydroxide; (c) A step of carrying out a carbonation process of the mixture containing the PCC seeds and calcium hydroxide to form a suspension containing PCC, Methods that include...

2. The method according to claim 1, wherein the total amount of PCC seeds added to the slurry containing calcium hydroxide is in the range of more than 2.5% by volume and less than 30% by volume relative to the total volume of the composition.

3. The suspension has a median weight diameter d of at least 2.0 μm. ５０ The method according to claim 1 or 2, comprising a PCC having

4. The suspension has a mid-weight diameter d of 2.8 μm to 3.1 μm. ５０ The method according to claim 1 or 2, comprising a PCC having

5. The method according to any one of claims 1 to 4, wherein the carbonation process includes the step of adding a carbon dioxide generating material to the mixture containing the PCC seeds and the calcium hydroxide.

6. (d) the step of separating the PCC from the suspension; (e) The step of drying the separated solid to form dried PCC The method according to any one of claims 1 to 5, further comprising:

7. The method according to claim 6, wherein the dried PCC is used as the PCC seed.

8. The method according to any one of claims 2 to 7, comprising mixing the PCC seeds with the slurry containing calcium hydroxide for 60 minutes or less, and then starting the carbonation process.

9. A paper product comprising a PCC manufactured by the method described in any one of claims 1 to 8.

10. A method for generating large PCC particles, Steps for producing generated PCC particles; The steps include: adding a certain amount of the generated PCC particles as an additive to the lime milk; The steps include: carbonating the lime milk containing the PCC additive to produce final PCC particles having a larger size than the generated PCC particles; Methods that include...

11. The method according to claim 10, wherein 2.5% to 30% of the generated PCC particles are recycled and added to the lime milk as a PCC additive.

12. The method according to claim 10 or 11, wherein the generated PCC particles added to the lime milk as an additive are in the form of dried particles.

13. The method according to claim 10 or 11, wherein the generated PCC particles added as an additive to the lime milk are an aqueous suspension.

14. The method according to any one of claims 10 to 13, further comprising the step of sieving the generated PCC particles to obtain the additive having particles of a selected size before adding it to the lime milk.

15. The method according to any one of claims 10 to 13, wherein the PCC particles are not sieved to obtain an additive having particles of a selected size before being added to the lime milk.

16. The method according to any one of claims 10 to 15, wherein the total amount of the PCC additive added to the lime milk is in the range of more than 2.5% by volume and less than 30% by volume relative to the total volume of the composition.

17. The final PCC particles have a weight median diameter d of at least 2.0 μm. ５０ The method according to any one of claims 10 to 16, comprising:

18. The aforementioned final PCC particles have a mid-weight diameter d of 2.8 μm to 3.1 μm. ５０ The method according to any one of claims 10 to 17, comprising:

19. The method according to any one of claims 10 to 17, wherein the PCC additive is mixed with lime milk for 60 minutes or less, and then the carbonation of the lime milk is started.

20. A paper product comprising a PCC manufactured by the method described in any one of claims 10 to 19.

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