PROCESS FOR PRODUCING PRECIPITATED CALCIUM CARBONATE IN THE PRESENCE OF NATURAL GROUND CALCIUM CARBONATE
20230357035 · 2023-11-09
Assignee
Inventors
Cpc classification
C01P2004/61
CHEMISTRY; METALLURGY
C01P2006/22
CHEMISTRY; METALLURGY
C01P2004/62
CHEMISTRY; METALLURGY
C01P2004/51
CHEMISTRY; METALLURGY
International classification
Abstract
The present invention relates to a process for producing an aqueous suspension of precipitated calcium carbonate, an aqueous suspension of precipitated calcium carbonate obtainable by the process, a precipitated calcium carbonate obtainable by the process, a product comprising the precipitated calcium carbonate as well as the use of the natural ground calcium carbonate (NGCC) in a process for producing an aqueous suspension of precipitated calcium carbonate.
Claims
1. A process for producing an aqueous suspension of precipitated calcium carbonate, the process comprising the steps of: i) providing a calcium oxide containing material, ii) providing a natural ground calcium carbonate (NGCC) as precipitation additive, wherein the natural ground calcium carbonate (NGCC) has a weight median diameter d.sub.50 of at least 0.3 .Math.m, iii) preparing a milk of lime by mixing water, the calcium oxide containing material of step i), and the natural ground calcium carbonate (NGCC) of step ii), wherein the natural ground calcium carbonate (NGCC) is present in an amount ranging from > 5 to 25 wt.-%, based on the total weight of the calcium oxide containing material, iv) carbonating the milk of lime obtained from step iii) to form an aqueous suspension of precipitated calcium carbonate.
2. The process according to claim 1, wherein step iii) comprises the steps of: a1) mixing the calcium oxide containing material of step i) with water, and a2) adding the natural ground calcium carbonate (NGCC) of step ii) to the mixture of step a1).
3. The process according to claim 1, wherein step iii) comprises the steps of a1) mixing the natural ground calcium carbonate (NGCC) of step ii) with water, and a2) adding the calcium oxide containing material of step i) to the mixture of step a1).
4. The process according to claim 1, wherein the natural ground calcium carbonate (NGCC) a) is selected from marble, limestone, chalk and mixtures thereof, and/or b) has a content of calcium carbonate of > 90 wt.-%, preferably of ≥ 92 wt.-% and most preferably of ≥ 96 wt.-%, based on the total weight of the natural ground calcium carbonate (NGCC), and/or c) has a weight median diameter d.sub.50 in the range from 0.3 to 10 .Math.m, preferably from 0.5 to 8 .Math.m, more preferably from 0.8 to 6 .Math.m and most preferably from 1 to 4 .Math.m.
5. The process according to claim 1, wherein a slaking additive is added before, during or after step iii), preferably the slaking additive is selected from the group consisting of organic acids, organic acid salts, sugar alcohols, monosaccharides, disaccharides, polysaccharides, gluconates, phosphonates, lignosulfonates, and mixtures thereof.
6. The process according to claim 1, wherein the slaking additive is added in an amount of ≤ 2 wt. %, based on the total amount of calcium oxide containing material, preferably from 0.01 to 1 wt.-%, more preferably from 0.01 to 0.5 wt.-%, and most preferably from 0.01 to 0.2 wt.-%.
7. The process according to claim 1, wherein the obtained suspension of precipitated calcium carbonate has a solids content of at least 5 wt. %, preferably from 5 to 50 wt.-%, more preferably from 10 to 45 wt.-%, and most preferably from 12 to 25 wt.-%, based on the total weight of the suspension.
8. The process according to claim 1, wherein the milk of lime is screened after step iii) and before step iv), preferably with a screen having a sieve size from 100 to 300 .Math.m.
9. A process for producing precipitated calcium carbonate comprising the steps i) to iv) of the process according to claim 1, and further a step v) of separating the precipitated calcium carbonate from the aqueous suspension obtained from step iv).
10. The process according to claim 9, wherein the process further comprises a step vi) of drying the separated precipitated calcium carbonate obtained from step v), and optionally a step vii) of contacting at least a part of the surface of the precipitated calcium carbonate with a surface-treatment agent.
11. An aqueous suspension of precipitated calcium carbonate obtainable by a process according to claim 1.
12. Precipitated calcium carbonate obtainable by a process according to claim 9.
13. The precipitated calcium carbonate according to claim 12, wherein the precipitated calcium carbonate is a dried calcium carbonate, optionally comprising a treatment layer on at least a part of the surface of the precipitated calcium carbonate.
14. A product comprising the precipitated calcium carbonate according to claim 12, preferably the product is a paper, a paper product, an ink, a paint, a coating, a plastic, a polymer composition, an adhesive, a building product, a foodstuff, an agricultural product, a cosmetic product or a pharmaceutical product, and more preferably the product is a plastic or a polymer composition.
15. (canceled)
Description
BRIEF DESCRIPTION OF THE FIGURES
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[0238] The scope and interest of the invention will be better understood based on the following examples which are intended to illustrate certain embodiments of the present invention and are non-limitative.
EXAMPLES
1. Measurement Methods
[0239] In the following, measurement methods implemented in the examples are described.
Particle Size Distribution
[0240] The weight median diameter d.sub.50(wt) and weight top cut particle size d.sub.98(wt) is determined by the sedimentation method, which is an analysis of sedimentation behaviour in a gravimetric field. The measurement is made with a Sedigraph™ 5120, Micromeritics Instrument Corporation. The method and the instrument are known to the skilled person and are commonly used to determine the particle size of fillers and pigments. The measurement is carried out in an aqueous solution of 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and sonicated.
[0241] The processes and instruments are known to the skilled person and are commonly used to determine the particle size of fillers and pigments.
BET Specific Surface Area (SSA)
[0242] The specific surface area was measured via the BET method according to ISO 9277:2010 using nitrogen as adsorbing gas on a Micromeritics ASAP 2460 instrument from Micromeritics. The samples were pretreated in vacuum (10.sup.-5 bar) by heating at 300° C. for a period of 30 min prior to measurement.
Solids Content of an Aqueous Suspension
[0243] The suspension solids content (also known as “dry weight”) was determined using a HR73 from Mettler-Toledo (T = 120° C., automatic switch off 3, standard drying) with a sample size of 5 to 20 g.
Scanning Electron Microscope (SEM)
[0244] A doubled-sided conductive adhesive tape was mounted on a SEM stub. 50 mg of dry sample was applied on the adhesive tape. The investigation under the FESEM (Zeiss Sigma VP) was done at 2 kV. Subsequently, the prepared samples were examined by using a Sigma VP field emission scanning electron microscope (Carl Zeiss AG, Germany) and a secondary electron detector (SE2) at high vacuum (< 10.sup.-2 Pa).
Brookfield Viscosity
[0245] The Brookfield viscosity is measured by a Brookfield (type RVT) viscometer at 23° C. ± 1° C. at 100 rpm after 30 seconds using an appropriate spindle and is specified in mPa.Math.s.
D/d
[0246] The term “d/d” refers to the dry amount based on the dry amount of the solid material.
pH of an Aqueous Suspension
[0247] The pH of the aqueous suspension is measured using a standard pH-meter at approximately 22° C.
Brightness and Whiteness R457
[0248] Whiteness R457 was determined according to norm TAPPI T452 / ISO 247. Brightness was measured using an ELREPHO 3000 from the company Datacolor according to ISO 2469:1994 (DIN 53145-2:2000 and DIN 53146:2000)
Conductivity
[0249] Conductivity was measured in the slurry sample at 23° C. using a WTW 3110 conductivity meter equipped with a TetraCon 325 probe.
2. Examples
A) Preparation of Natural Ground Calcium Carbonate (NGCC)
[0250] A slurry of marble having a d.sub.50 of 15 .Math.m and a d.sub.98 of 50 .Math.m was prepared at lab-scale, using only water and marble, without dispersant or any other additive. The solids content of the slurry was 40 wt.-%, based on the total weight of the slurry. Then, the slurry was ground in a 3 L laboratory sandmill using the grinding media Kings Kaolin 0.8-1.0 mm. Multiple grinding batches were made to achieve the necessary quantity of GCC for each carbonation test. Table 1 shows the grinding conditions for the slurry of marble.
TABLE-US-00001 Milling conditions Slurry solids content [wt.-%] 40 Density of the slurry [g/cm.sup.3] 1.34 Total Slurry [cm.sup.3] 656 Beads mass [g] 2300 Stirrer velocity [rpm] 970 Grind Time [min] 6
[0251] The slurry of marble obtained had the characteristics as set out in the following Table 2.
TABLE-US-00002 Characteristics of the slurry of marble Sedigraph d.sub.50 [.Math.m] 1.49 d.sub.98 [.Math.m] 6 < 20 .Math.m [%] 100 < 10 .Math.m [%] 99 < 5 .Math.m [%] 97 < 2 .Math.m [%] 66 < 1 .Math.m [%] 31 < 0.8 .Math.m [%] 23 pH 8.17 Viscosity 100 rpm [mPa.Math.s] 204 Conductivity [.Math.S/cm] 321 Solids content [wt.-%] 41.2 Brightness R457 95.4 L 98.5 a 0.11 b 0.64 y 1.28 BET [m.sup.2/g] 3.92
B) Preparation of an Aqueous Suspension of Precipitated Calcium Carbonate (Comparative Example 1 - CE1)
[0252] A milk of lime was prepared by using lime from Lusical (Portugal) and water with a lime to water ratio of 1:8.5. Sodium citrate was used in an amount of 0.1 wt.-% based on lime.
[0253] Carbonation was carried out in a 10 liter laboratory reactor, equipped with a stirrer rotating at 750 rpm. Gas was 20% CO.sub.2 and 80% N.sub.2 - Aligal 12 from Air Liquid, used at a flowrate of 15 I/min. The carbonation was started at 50° C. and CO.sub.2 injection was made until conductivity reached a minimum value, plus 10 minutes.
C) Preparation of an Aqueous Suspension of Precipitated Calcium Carbonate (Inventive Example 1 - IE1)
[0254] A milk of lime was prepared by using lime from Lusical (Portugal) and water with a lime to water ratio of 1:8.5. Sodium citrate was used in an amount of 0.1 wt.-% based on lime.
[0255] Carbonation was carried out in a 10 liter laboratory reactor, equipped with a stirrer rotating at 750 rpm. Gas was 20% CO.sub.2 and 80% N.sub.2 - Aligal 12 from Air Liquid, used at a flowrate of 15 I/min. The carbonation was started at 50° C. and CO.sub.2 injection was made until conductivity reached a minimum value, plus 10 minutes. At the beginning of the carbonation, 10.6 wt.-% of the natural ground calcium carbonate (NGCC), based on the final total weight of calcium carbonate, (d/d) as obtained under A) in form of a slurry was added to the milk of lime.
D) Preparation of an Aqueous Suspension of Precipitated Calcium Carbonate (Inventive Example 2 - IE2)
[0256] A milk of lime was prepared by using lime from Lusical (Portugal) and water with a lime to water ratio of 1:8.5. Sodium citrate was used in an amount of 0.1 wt.-% based on lime.
[0257] Carbonation was carried out in a 10 liter laboratory reactor, equipped with a stirrer rotating at 750 rpm. Gas was 20% CO.sub.2 and 80% N.sub.2 - Aligal 12 from Air Liquid, used at a flowrate of 15 I/min. The carbonation was started at 50° C. and CO.sub.2 injection was made until conductivity reached a minimum value, plus 10 minutes. At the beginning of the carbonation, 19.5 wt.-% of the natural ground calcium carbonate (NGCC), based on the final total weight of calcium carbonate, (d/d) as obtained under A) in form of a slurry was added to the milk of lime.
E) Preparation of an Aqueous Suspension of Precipitated Calcium Carbonate (Comparative Example 2 - CE2)
[0258] A milk of lime was prepared by using lime from Lusical (Portugal) and water with a lime to water ratio of 1:8.5. Sodium citrate was used in an amount of 0.1 wt.-% based on lime.
[0259] Carbonation was carried out in a 10 liter laboratory reactor, equipped with a stirrer rotating at 750 rpm. Gas was 20% CO.sub.2 and 80% N.sub.2 - Aligal 12 from Air Liquid, used at a flowrate of 15 I/min. The carbonation was started at 50° C. and CO.sub.2 injection was made until conductivity reached a minimum value, plus 10 minutes. At the beginning of the carbonation, 31.4 wt.-% of the natural ground calcium carbonate (NGCC), based on the final total weight of calcium carbonate, (d/d) as obtained under A) in form of a slurry was added to the milk of lime.
F) Preparation of an Aqueous Suspension of Precipitated Calcium Carbonate (Comparative Example 3 - CE3)
[0260] The precipitated calcium carbonate as obtained under A) was simply mixed with the natural ground calcium carbonate (NGCC) (d/d) in form of a slurry as obtained under A) in a weight ratio of about 4:1.
TABLE-US-00003 Characteristics of the precipitated calcium carbonates obtained in CE1, IE1, IE2 and CE2 CE1 IE1 IE2 CE2 CE3 GCC added [wt.-%] 0 10.6 19.5 31.4 20.3 Time of addition [min] -- 0 0 0 100 Viscosity [mPa.Math.s] 23 20.8 20.4 19.6 26.4 Sedigraph d.sub.50 [mm] 2.9 3.0 3.2 3.1 2.6 d.sub.98 [mm] 7 6 6 6 6 < 2 .Math.m [%] 17.3 12.8 8.9 5.9 28.5 d.sub.75/d.sub.25 1.62 1.51 1.45 1.42 1.79 Brightness R457 97.2 96.7 95.6 95.4 96.8 L 99.2 99.1 98.7 98.6 99.1 a 0.12 0.15 0.19 0.15 0.11 b 0.50 0.69 0.78 0.81 0.55 y 1.02 1.39 1.6 1.63 1.11 BET [m.sup.2/g] 3.96 4.31 4.01 3.0 4.75 Solids content [wt.-%] 17.1 17.0 17.8 18.1 20.1 pH 8.2 8.0 7.9 7.8 7.8
[0261] From Table 3, it can be gathered that the precipitated calcium carbonate of inventive examples 1 and 2 have comparable characteristics in terms of d.sub.50, d.sub.98, BET specific surface area as well as brightness compared to the precipitated calcium carbonate of comparative example 1, even though a part of lime has been replaced by natural ground calcium carbonate (NGCC) during the production of the precipitated calcium carbonate. Contrary thereto, the mixture of precipitated calcium carbonate and natural ground calcium carbonate (NGCC) (comparative example 3) provides different characteristics especially in terms of the BET specific surface area and particles of < 2 .Math.m. It is to be noted that the precipitated calcium carbonate of comparative example 2 shows similar characteristics compared to the precipitated calcium carbonates of inventive examples 1 and 2. However, from the SEM result of the precipitated calcium carbonate of comparative example 2 (
G) Preparation of Natural Ground Calcium Carbonate (NGCC)
[0262] A slurry comprising marble from PTOU plant was ground in wet at solids content of about 11 wt.-%, based on the total weight of the slurry, without any additives. The final solids content of the slurry was 11%. Table 4 shows the weight median diameter d.sub.50 and top cut d.sub.98 of the NGCC.
TABLE-US-00004 PSD of the NGCC d.sub.50 d.sub.98 NGCC 0.17 0.25
H) Preparation of an Aqueous Suspension of Precipitated Calcium Carbonate (Comparative Example 4 - CE4)
[0263] A milk of lime was prepared by mixing under mechanical stirring 5 liters water with 1000 g calcium oxide (quicklime raw material from Lusical, Portugal) at an initial temperature of 40° C. The obtained mixture was stirred for 30 min, wherein additional 4 liters of water were added. Subsequently, the mixture was sieved through a 100 .Math.m screen.
[0264] Carbonation trials were made in a 10 liter laboratory reactor. The reactor was equipped with a stirrer that was rotating at 1500 rpm. Lime was from Lusical (Portugal). Sodium citrate was used at 0.1% of the lime. Gas was 20% CO.sub.2 and 80% N.sub.2 - Aligal 12 from Air Liquid, used at a flowrate of 15 I/min. The carbonation started at 50° C. and CO.sub.2 injection was made until conductivity reached a minimum value, plus 10 minutes. At the beginning of the carbonation, 5 wt.-% of the natural ground calcium carbonate (NGCC) (d/d) as obtained under G) was added to the milk of lime.
I) Preparation of an Aqueous Suspension of Precipitated Calcium Carbonate (Comparative Example 5 - CE5)
[0265] A milk of lime was prepared by mixing under mechanical stirring 5 liters water with 1000 g calcium oxide (quicklime raw material from Lusical, Portugal) at an initial temperature of 40° C. The obtained mixture was stirred for 30 min, wherein additional 4 liters of water were added. Subsequently, the mixture was sieved through a 100 .Math.m screen.
[0266] Carbonation trials were made in a 10 liter laboratory reactor. The reactor was equipped with a stirrer that was rotating at 1400 rpm. Lime was from Lusical (Portugal). Sodium citrate was used at 0.1% of the lime. Gas was 20% CO.sub.2 and 80% N.sub.2 - Aligal 12 from Air Liquid, used at a flowrate of 15 I/min. The carbonation started at 50° C. and CO.sub.2 injection was made until conductivity reached a minimum value, plus 10 minutes. At the beginning of the carbonation, 19.9 wt.-% of the natural ground calcium carbonate (NGCC) (d/d) as obtained under G) was added to the milk of lime.
TABLE-US-00005 Characteristics of IE1, IE2, CE4 and CE5 IE1 IE2 CE4 CE5 GCC added [wt.-%] 10.6 19.5 5 19.9 Time of addition [min] 0 0 0 0 Viscosity [mPa.Math.s] 20.8 20.4 24.4 26.8 Sedigraph d.sub.50 [mm] 3.0 3.2 2.8 1.9 d.sub.98 [mm] 6 6 5 4 < 2 .Math.m [%] 12.8 8.9 11.2 54.9 d.sub.75/d.sub.25 1.51 1.45 1.38 1.38 Brightness R457 96.7 95.6 97.3 97.3 L 99.1 98.7 99.2 99.2 a 0.15 0.19 0.14 0.13 b 0.69 0.78 0.55 0.48 y 1.39 1.6 1.13 0.99 BET [m.sup.2/g] 4.31 4.01 3.9 5.2 Solids content [wt.-%] 17.0 17.8 16.0 15.9 pH 8.0 7.9 8.15 8.05
[0267] From Table 5, it can be gathered that the precipitated calcium carbonates of inventive examples 1 and 2 have similar characteristics in terms of d.sub.50, d.sub.98, BET specific surface area as well as brightness compared to the precipitated calcium carbonate of comparative examples 4 and 5. However, from the SEM results of the precipitated calcium carbonates of comparative examples 4 and 5 (