High solids precipitated calcium carbonate with cationic additive

Abstract

The present invention relates to a process for producing an aqueous suspension of precipitated calcium carbonate, an aqueous suspension of precipitated calcium carbonate and a precipitated calcium carbonate obtained by the process, a process comprising the precipitated calcium carbonate and its use.

Claims

1. A process for producing an aqueous suspension of precipitated calcium carbonate comprising the steps of: i) providing a calcium oxide containing material, the calcium oxide containing material having a minimum calcium oxide content of at least 75 wt.-%, based on the total weight of the calcium oxide containing material, ii) providing at least one cationic polymer comprising monomer units, the at least one cationic polymer being a quaternized ammonium compound which consists of monomer units, the monomer units each being a quaternized ammonium compound, iii) preparing a milk of lime by mixing water, the calcium oxide containing material of step i), and the at least one cationic polymer of step ii) to obtain a milk of lime, wherein the calcium oxide containing material and the water are mixed in a weight ratio from 1:1 to 1:5, and wherein the at least one cationic polymer is present in an amount from 0.01 to 0.5 wt.-%, based on the total weight of the calcium oxide containing material, and iv) carbonating the milk of lime obtained in step iii) to form an aqueous suspension of precipitated calcium carbonate.

2. The process of claim 1, wherein step iii) comprises the steps of: a1) mixing the at least one cationic polymer of step ii) with water, and a2) adding the calcium oxide containing material of step i) to the mixture of step a1); or b1) mixing the calcium oxide containing material of step i), and the at least one cationic polymer of step ii), and b2) adding water to the mixture of step b1); or c) mixing the calcium oxide containing material of step i), the at least one cationic polymer of step ii) and water simultaneously.

3. The process of claim 1, wherein the process further comprises step v) of adding at least one slaking additive to process step iii).

4. The process of claim 3, wherein the at least one 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.

5. The process of claim 1, wherein the milk of lime obtained in step iii) has a Brookfield viscosity from 1 to 1,000 mPa.Math.s at 25 C.; and/or the suspension of PCC obtained in step iv) has a Brookfield viscosity of less than or equal to 1,600 mPa.Math.s at 25 C.

6. The process of claim 1, wherein the milk of lime obtained in step iii) has a Brookfield viscosity from 10 to 500 mPa.Math.s at 25 C.; and/or the suspension of PCC obtained in step iv) has a Brookfield viscosity of less than or equal to 1,400 mPa.Math.s at 25 C.

7. The process of claim 1, wherein the milk of lime obtained in step iii) has a solids content from 20 to 38 wt.-%, based on the total weight of the suspension.

8. The process of claim 1, wherein the suspension of PCC obtained in step iv) has a solids content from 24 to 42 wt.-%, based on the total weight of the suspension.

9. The process of claim 1, wherein the temperature of the water, which is used in mixing step iii), is adjusted to be in the range from more than 0 C. and less than 100 C.; and/or the temperature of the milk of lime obtained in step iii), which is employed in step iv), is adjusted to be in the range from 20 C. to 60 C.

10. The process of claim 1, wherein the calcium oxide containing material is calcium oxide.

11. The process of claim 1, wherein the at least one cationic polymer is: a) a homopolymer based on monomer units selected from the group consisting of vinyl-based dialkyl ammonium compounds, allyl-based dialkyl ammonium compounds, diallyldimethyl ammonium chloride (DADMAC), diallyldiethyl ammonium chloride (DADEAC), diallyldimethyl ammonium bromide (DADMAB), diallyldiethyl ammonium bromide (DADEAB); vinyl-based trialkyl ammonium compounds, [2-(acryloyloxy)ethyl]trimethylammonium chloride (AETAC), [2-(acryloyloxy)ethyl]trimethylammonium methosulfate (AETAMS), 3-(acrylamidopropyl)-trimethylammonium chloride (APTAC), 3-(acrylamidopropyl)-trimethylammonium methosulfate (APTAMS); allyl-based trialkyl ammonium compounds, 2-(methacryloyloxy)-ethyltrimethylammonium chloride (MADQUAT), 2-(methacryloyloxy)-ethyltrimethylammonium methosulfate (METAMS), 3-(methacryloyloxy)-propyltrimethylammonium chloride or 3-(methacrylamidopropyl)-trimethylammonium chloride (MAPTAC), 3-(methacrylamidopropyl)-trimethylammonium methosulfate (MAPTAMS), or b) a copolymer based on monomer and comonomer units selected from the group consisting of vinyl-based dialkyl ammonium compounds, allyl-based dialkyl ammonium compounds, diallyldimethyl ammonium chloride (DADMAC), diallyldiethyl ammonium chloride (DADEAC), diallyldimethyl ammonium bromide (DADMAB), diallyldiethyl ammonium bromide (DADEAB); vinyl-based trialkyl ammonium compounds, [2-(acryloyloxy)ethyl]trimethylammonium chloride (AETAC), [2-(acryloyloxy)ethyl]trimethylammonium methosulfate (AETAMS), 3-(acrylamidopropyl)-trimethylammonium chloride (APTAC), 3-(acrylamidopropyl)-trimethylammonium methosulfate (APTAMS); allyl-based trialkyl ammonium compounds, 2-(methacryloyloxy)-ethyltrimethylammonium chloride (MADQUAT), 2-(methacryloyloxy)-ethyltrimethylammonium methosulfate (METAMS), 3-(methacryloyloxy)-propyltrimethylammonium chloride or 3-(methacrylamidopropyl)-trimethylammonium chloride (MAPTAC), 3-(methacrylamidopropyl)-trimethylammonium methosulfate (MAPTAMS).

12. The process of claim 1, wherein the at least one cationic polymer is a homopolymer selected from poly(diallyldimethyl ammonium chloride) (pDADMAC) and poly(2-(methacryloyloxy)-ethyltrimethylammonium chloride) (pMADQUAT), or a copolymer based on monomer units selected from 2-(methacryloyloxy)-ethyltrimethylammonium chloride (MADQUAT) and comonomer units selected from 3-(methacrylamidopropyl)-trimethylammonium chloride (MAPTAC).

13. The process of claim 1, wherein the at least one cationic polymer has a specific viscosity in the range from 1.2 to 15.0; and/or a has a positive charge density in the range of from >0 Val/g to +15 Val/g.

14. The process of claim 1, wherein the process further comprises a step of separating the precipitated calcium carbonate from the aqueous suspension obtained in step iv).

15. The process of claim 1, wherein the calcium oxide containing material has a minimum calcium oxide content of at least 90 wt.-%, based on the total weight of the calcium oxide containing material.

Description

DESCRIPTION OF THE FIGURE

(1) FIG. 1 is a sketch of a continuous slaking process.

EXAMPLES

1. Measurement Methods

(2) In the following, measurement methods implemented in the examples are described.

(3) Brookfield Viscosity

(4) The Brookfield viscosity of the liquid coating compositions was measured after one hour of production and after one minute of stirring at 25 C.1 C. at 100 rpm by the use of a Brookfield viscometer type RVT equipped with an appropriate disc spindle, for example spindle 2 to 5.

(5) pH Value

(6) The pH of a suspension or solution was measured at 25 C. using a Mettler Toledo Seven Easy pH meter and a Mettler Toledo InLab Expert Pro pH electrode. A three point calibration (according to the segment method) of the instrument was first made using commercially available buffer solutions having pH values of 4, 7 and 10 at 20 C. (from Sigma-Aldrich Corp., USA). The reported pH values are the endpoint values detected by the instrument (the endpoint was when the measured signal differed by less than 0.1 mV from the average over the last 6 seconds).

(7) Particle Size Distribution

(8) The particle size distribution of the prepared PCC particles was measured using a Sedigraph 5120 from the company Micromeritics, USA. The method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurement was carried out in an aqueous solution comprising 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and supersonics. For the measurement of dispersed samples, no further dispersing agents were added.

(9) Solids Content of an Aqueous Suspension

(10) The suspension solids content (also known as dry weight) was determined using a Moisture Analyser MJ33 from the company Mettler-Toledo, Switzerland, with the following settings: drying temperature of 160 C., automatic switch off if the mass does not change more than 1 mg over a period of 30 sec, standard drying of 5 to 20 g of suspension.

(11) Specific Surface Area (SSA)

(12) The specific surface area was measured via the BET method according to ISO 9277 using nitrogen, following conditioning of the sample by heating at 250 C. for a period of 30 minutes. Prior to such measurements, the sample is filtered within a Buchner funnel, rinsed with deionised water and dried overnight at 90 to 100 C. in an oven. Subsequently the dry cake is ground thoroughly in a mortar and the resulting powder placed in a moisture balance at 130 C. until a constant weight is reached.

(13) Specific Carbonation Time

(14) The monitoring of the conductivity, which slowly decreases during the carbonation reaction and rapidly decreases to a minimal level, thereby indicating the end of the reaction, was used to assess the time needed to perform the complete precipitation. The specific carbonation time (min/kg Ca(OH).sub.2) was determined by the following formula:

(15) $\mathrm{Specific}\mathrm{carbonation}\mathrm{time}=\frac{{10}^5.Math.\mathrm{Tf}}{M.Math.{\mathrm{SC}}_{\mathrm{MoL}}}$
wherein: Tf (min) is the time needed to complete the carbonation of the milk of lime, as determined by monitoring the conductivity, M (g) is the weight of the milk of lime introduced into the carbonation reactor, and SC.sub.MoL (%) is the weight solids content of the milk of lime.
Specific Viscosity

(16) The term specific viscosity in the meaning of the present invention is defined as the difference of the relative viscosity minus 1:
.sub.sp=.sub.rel1

(17) The relative viscosity as used herein is the quotient of the solution viscosity and the solvent viscosity:

(18) ${}_{\mathrm{rel}}=\frac{}{{}_0}$
wherein the solvent viscosity .sub.0 is defined as the viscosity of the pure solvent and the solution viscosity is defined as the viscosity of the polymer dissolved in the pure solvent.

(19) However, to determine the relative viscosity it is sufficient to measure the elution time t (of the solution) and t.sub.0 (of the solvent) at a given temperature if the boundary conditions are constant. Therefore, the relative viscosity may be defined as

(20) ${}_{\mathrm{rel}}=\frac{t}{t_0}$
and, thus, the specific viscosity may be defined as:

(21) ${}_{\mathrm{sp}}=\frac{t}{t_0}-1$

(22) More precisely, the specific viscosity of the polymer was obtained from an aqueous polymer solution with a polymer concentration of 50 g/L in NaCl solution (120 g/L), the pH of the polymer solution being possibly adjusted with ammonia to be within the range of 6 to 7. The elution time t and t.sub.0 was measured at 25 C.+/0.2, using a viscosimetric tube USA KIMAX (reference: size 100 n 46460 B2).

(23) t.sub.0: In order to determine t.sub.0, an aqueous NaCl solution was prepared by using reverse osmosis water, the NaCl solution having a concentration of 120 g/L.

(24) t: In order to determine t, about 2.5 g of the polymer was combined with 50 g of reverse osmosis water and 6 g of NaCl in order to obtain a solution.

(25) The elution time t and t.sub.0 was measured at 25 C.0.2 C. and .sub.sp was calculated according to the above mentioned formulas.

(26) Charge MeasurementMtek

(27) The charge measurement was carried out using a Mtek PCD 03 device equipped with a Mtek PCD titrator.

(28) About 1 g of the PCC suspension is weighed in the plastic measuring cell and is diluted with 20 mL of deionised water. Put the displacement piston on. While the piston oscillates in the cell, wait until the streaming current between the two electrodes stabilize.

(29) The sign of the measured value shown on the display indicates whether the charge of the sample is positive (cationic) or negative (anionic). An oppositely charged polyelectrolyte of known charge density is added to the sample as a titrant (either sodium polyoxyethylene sulfate 0.001 N or pDADMAC 0.001 N). The titrant charges neutralize existing charges of the sample. Titration is discontinued as soon as the point of zero charge (0 mV) is reached.

(30) Titrant consumption in mL forms the basis for further calculations. The specific charge quantity q [Val/g of sly] is calculated according to the following formula:
q=(Vc)/m
V: consumed titrant volume [l]
c: titrant concentration [Val/l]
m: mass of the weighed slurry [g]
q: specific charge quantity [Val/g of slurry]
Zeta Potential

(31) For measuring the Zeta potential, a few drops of the PCC suspensions are dispersed in a sufficient quantity of serum obtained by mechanical filtration of the said suspension in order to obtain a colloidal suspension which is slightly cloudy.

(32) This suspension is introduced into the measuring cell of the Zetasizer Nano-ZS from Malvern, which directly displays the value of the Zeta potential of the PCC suspension in mV.

2. Polymers and Slaking Additives

(33) The following polymers were used in the processes for producing PCC described in examples 1 and 2:

(34) P1: pMADQUAT; specific viscosity: 2.66

(35) P2: 70% MADQUAT/30% MAPTAC; specific viscosity: 2.19

(36) P3: 70% MADQUAT/30% MAPTAC; specific viscosity: 1.68

(37) P4: pDADMAC; specific viscosity: 9.98

(38) P5: polyacrylic acid with the following formula,

(39) ##STR00008## wherein R.sub.1 is H, X is Na, and m=45; the M.sub.w being 4270 g/mol, and the polydispersity index being 2.3. The molecular weight M.sub.w and the polydispersity index are determined according to the corresponding method described in EP 14 166 751.9.

(40) The following slaking additives were used in the processes for producing PCC described in examples 1 and 2: A1: Sodium citrate (commercially available from Sigma-Aldrich, Germany), A2: Natural sugar (commercially available from any consumer market),

3. Examples

Example 1

(41) A milk of lime was prepared by mixing under mechanical stirring water with dry sodium citrate (A1) or sucrose (A2) as slaking additive (if present) and cationic polymer P1-P4 (if present) (according to the invention) or polymer P5 (comparison) at an initial temperature between 50 and 51 C. (the amounts of slaking additives and polymer are indicated in Table 2 below). Subsequently, calcium oxide (quicklime raw material from Golling, Austria) was added. The obtained mixture was stirred for 25 min and then sieved through a 200 m screen.

(42) The obtained milk of lime was transferred into a stainless steel reactor, wherein the milk of lime was cooled down to 50 C. Then the milk of lime was carbonated by introducing an air/CO.sub.2 mixture (20 vol-% CO.sub.2). During the carbonation step, the reaction mixture was stirred with a speed of 1 400 rpm. The kinetic of the reaction was monitored by online pH and conductivity measurements.

(43) The characteristics of the prepared milks of lime and aqueous PCC suspensions are described in Tables 1 and 2 below.

(44) TABLE-US-00001 TABLE 1 Characteristics of produced milks of lime of Example 1 (comp: comparative example; IN: inventive example). Polymer amount Slaking additive Solids Polymer [wt.-%/wt. Slaking amount content Sample additive CaO] additive [wt.-%/wt. CaO] [wt.-%] 1 No A1 0.1 15.7 (comp) 2 (IN) P1 0.15 A1 0.1 25.2 3 (IN) P1 0.25 A1 0.1 32.9 4 (IN) P1 0.15 A2 0.1 28.6 5 (IN) P2 0.15 A1 0.1 25.0 6 (IN) P3 0.15 A1 0.1 24.9 7 (IN) P4 0.15 A1 0.1 25.5 8 P5 0.15 A1 0.1 25.0 (comp)

(45) TABLE-US-00002 TABLE 2 Characteristics of the obtained aqueous PCC suspensions of Example 1 (comp: comparative example). All samples had a calcite structure. Viscosity Solids Viscosity of the milk content of the Mtek of lime Carbonation of the PCC Zeta charge (mPa .Math. s) time (min/kg PCC (mPa .Math. s) SSA d.sub.50 potential (Val/g Sample 100 rpm Ca(OH).sub.2) (wt.-%) 100 rpm [m.sup.2/g] [m] (mV) of slurry) 1 (comp) 20 52 19.6 20 3.3 2.45 +4.9 0.2 2 (IN) 204 52.7 31.2 202 4.7 1.85 +0.1 +2.3 3 (IN) 440 123 38.7 605 6.1 1.74 +4.2 4 (IN) 450 105 33.2 232 6.0 1.89 +1.5 5 (IN) 83 45.5 32.1 225 5.2 1.38 +8.8 +1.2 6 (IN) 74 45.6 32.3 175 6.3 1.42 +0.2 +1.4 7 (IN) 164 46.8 33.6 1380 4.9 1.41 +30.5 +3.8 8 (comp) 294 46.0 37.2 573 5.0 1.30 10.5 0.9

(46) The results compiled in Table 2 show that the use of a slaking additive alone leads to a suspension having a PCC content of only about 20 wt.-% (comparative sample 1).

(47) In contrast, inventive samples 2 to 7 confirm that the viscosity of the obtained milk of lime and PCC suspension is totally in adequation with the intended use of the PCC so obtained that is to say suspensions of PCC having a Brookfield viscosity of less than or equal to 1 500 mPa.Math.s at 25 C. Additionally, the kinetic of carbonation and the crystallographic structure of the prepared PCC (results not shown) is similar to the one obtained with a process involving the use of an anionic polymer (P8: polyacrylic acid where 100 mole-% of the carboxylic groups have been neutralized by sodium ions, the M.sub.w being 4270 g/mol, and the polydispersity index being 2.3; sample being outside of the invention).

Example 2

(48) A milk of lime was prepared by mixing under mechanical stirring water with dry sodium citrate (A1) as slaking additive and a polymer at an initial temperature between 40 and 41 C. (the amounts of slaking additives and polymer as well as the used polymer type are indicated in Table 4 below). Subsequently, calcium oxide (quicklime raw material from Golling, Austria) was added. The obtained mixture was stirred for 25 min and then sieved through a 200 m screen.

(49) The obtained milk of lime was transferred into a stainless steel reactor, wherein the milk of lime was cooled down to 70 C. Then the milk of lime was carbonated by introducing an air/CO.sub.2 mixture (20 vol-% CO.sub.2). During the carbonation step, the reaction mixture was stirred with a speed of 1 400 rpm. The kinetic of the reaction was monitored by online pH and conductivity measurements.

(50) The characteristics of the prepared milks of lime and aqueous PCC suspensions are described in Tables 3 and 4 below.

(51) TABLE-US-00003 TABLE 3 Characteristics of produced milks of lime of Example 2 (comp: comparative example; IN: inventive example). Polymer amount Slaking additive Solids Polymer [wt.-%/wt. Slaking amount content Sample additive CaO] additive [wt.-%/wt. CaO] [wt.-%] 9 (IN) P1 0.15 No 29.2 10 (IN) P1 0.15 A1 0.1 28.9 11 (IN) P1 0.25 A1 0.1 29.7

(52) TABLE-US-00004 TABLE 4 Characteristics of the obtained aqueous PCC suspensions of Example 2 (comp: comparative example; IN: inventive example). Viscosity Solids Viscosity of the milk content of the Mtek of lime Carbonation of the PCC Zeta charge (mPa .Math. s) time (min/kg PCC (mPa .Math. s) SSA d.sub.50 potential (Val/g Sample 100 rpm Ca(OH).sub.2) (wt.-%) 100 rpm [m.sup.2/g] [m] (mV) of slurry) 9 (IN) 625 114 33.2 250 5.5 1.73 +1.5 10 (IN) 690 97 34.4 143 5.7 1.91 +1.97 11 (IN) 650 112 35.4 207 6.1 1.74 +1.8

(53) The results given in Table 4 show that it is also possible to obtain PCC at high solids content at a reaction temperature of 70 C. The results also show that the PCC can be obtained by the sole use of the cationic polymer without the need of a slaking additive (sample 9).