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PRODUCTION OF AMORPHOUS CALCIUM CARBONATE

20190135649 ยท 2019-05-09

    Inventors

    Cpc classification

    International classification

    Abstract

    The present invention relates to a process for preparing amorphous calcium carbonate, the amorphous calcium carbonate obtainable by the process, its use as well as a product comprising the amorphous calcium carbonate and the use of a spray dryer for the preparation of amorphous calcium carbonate.

    Claims

    1. A process for preparing amorphous calcium carbonate, the process comprising the steps of: a) providing at least one calcium oxide containing material; b) providing at least one gaseous CO.sub.2 source, c) preparing a milk of lime by mixing the at least one calcium oxide containing material of step a) with water to convert the calcium oxide at least partially into dissolved calcium hydroxide, d) separating the dissolved calcium hydroxide in the milk of lime obtained in step c) from undissolved materials such as to obtain a solution of dissolved calcium hydroxide, e) drying the solution of dissolved calcium hydroxide obtained in step d), and f) carbonating the dissolved calcium hydroxide obtained in step d) with the at least one gaseous CO.sub.2 source of step b) to convert the calcium hydroxide at least partially into amorphous calcium carbonate, wherein process steps e) and f) are carried out simultaneously.

    2. The process according to claim 1, wherein the at least one gaseous CO.sub.2 source is a gaseous CO.sub.2 comprising gas, preferably the at least one gaseous CO.sub.2 source contains at least 20 vol.-%, based on the total volume of the gas, of CO.sub.2.

    3. The process according to claim 1, wherein step c) is carried out in that the at least one calcium oxide containing material is mixed with water in a weight ratio from 1:2 to 1:25, preferably from 1:2.5 to 1:20 and most preferably from 1:3 to 1:15 and/or in that the temperature of the water, which is used in step c), is adjusted to be in the range from >0 C. and <100 C., preferably from 1 C. to 70 C., more preferably from 2 C. to 50 C., even more preferably from 30 C. to 50 C., and most preferably from 35 C. to 45 C.

    4. The process according to claim 1, wherein the process further comprises a step of removing particles having an average particle size of >100 m from the milk of lime obtained in step c) before separating step d) is carried out.

    5. The process according to claim 1, wherein the milk of lime obtained in step c) has a Brookfield viscosity from 1 to 1 000 mPa.Math.s at 25 C., more preferably from 5 to 800 mPa.Math.s at 25 C., and most preferably from 10 to 600 mPa.Math.s at 25 C.; and/or solids content in the range from 5.0 to 40.0 wt.-%, preferably from 6.0 to 30.0 wt.-%, and most preferably from 8.0 to 20.0 wt.-%, based on the total weight of the milk of lime.

    6. The process according to claim 1, wherein separating step d) is carried out via mechanical separation techniques, preferably in a vertical plate pressure filter, a tube press or a vacuum filter, more preferably in a vacuum filter such as a vacuum suction filter.

    7. The process according to claim 1, wherein the solution of dissolved calcium hydroxide obtained in step d) is adjusted to a temperature in the range from 10 C. and less than 60 C., preferably from 10 C. to 50 C., more preferably from 12 C. to 40 C., even more preferably from 14 C. to 30 C., and most preferably from 15 C. to 28 C.

    8. The process according to claim 1, wherein drying step e) and carbonating step f) are carried out in a spray drier.

    9. The process according to claim 1, wherein drying step e) and carbonating step f) are carried out at an inlet temperature in the range from 50 C. to 400 C., preferably from 100 C. to 375 C., more preferably from 150 C. to 350 C. and most preferably from 200 C. to 300 C.

    10. The process according to claim 1, wherein the carbonating in step f) is carried out at a gas pressure of 1 to 20 bar, preferably of 1 to 15 bar and most preferably of 2 to 10 bar.

    11. The process according to claim 1, wherein the amorphous calcium carbonate i) has an average particle size of 30 to 150 nm, more preferably from 40 to 120 nm and most preferably from 50 to 100 nm, and/or ii) has a moisture content of 10.0 wt.-%, preferably from 0.1 to 10.0 wt.-%, and most preferably from 0.2 to 8.0 wt.-%, based on the total dry weight of the amorphous calcium carbonate, and/or iii) has a specific BET surface area of 1.0 m.sup.2/g to 60.0 m.sup.2/g, more preferably of 3.0 m.sup.2/g to 50.0 m.sup.2/g and most preferably of 10.0 m.sup.2/g to 40.0 m.sup.2/g, and/or iv) forms aggregates, preferably aggregates having an average particle size in the range from 0.5 to 10 m, preferably in the range from 1 to 8 m and most preferably in the range from 1 to 5 m, and/or v) is present in the form of deagglomerated particles.

    12. Amorphous calcium carbonate obtainable by a process according to claim 1.

    13. A product comprising the amorphous calcium carbonate according to claim 12, preferably the product is a paper, a paper product, a wood product, cellulose composite, protein composite, bone composite, an ink, a paint, a coating, a plastic, a polymer composition, an adhesive, a building product, a foodstuff, an agricultural product, a biomimetic material, a cosmetic product or a pharmaceutical product.

    14. Use of an amorphous calcium carbonate according to claim 12 in paper making, paper coating, food, plastic, agricultural, paint, coatings, adhesives, sealants, pharmaceuticals, agricultural, biomimetic, construction and/or cosmetic applications.

    15. Use of a spray dryer for the preparation of amorphous calcium carbonate, wherein the amorphous calcium carbonate i) has an average particle size of 30 to 150 nm, more preferably from 40 to 120 nm and most preferably from 50 to 100 nm, and/or ii) has a moisture content of 10.0 wt.-%, preferably from 0.1 to 10.0 wt.-%, and most preferably from 0.2 to 8.0 wt.-%, based on the total dry weight of the amorphous calcium carbonate, and/or iii) has a specific BET surface area of 1.0 m.sup.2/g to 60.0 m.sup.2/g, more preferably of 3.0 m.sup.2/g to 50.0 m.sup.2/g and most preferably of 10.0 m.sup.2/g to 40.0 m.sup.2/g, and/or iv) forms aggregates, preferably aggregates having an average particle size in the range from 0.5 to 10 m, preferably in the range from 1 to 8 m and most preferably in the range from 1 to 5 m, and/or v) is present in the form of deagglomerated particles.

    Description

    BRIEF DESCRIPTION OF THE FIGURES

    [0169] FIG. 1 refers to a SEM image of amorphous calcium carbonate aggregates.

    [0170] FIG. 2 refers to a SEM image of an amorphous calcium carbonate aggregate.

    [0171] FIG. 3 refers to a XRD analysis of an ACC sample.

    [0172] The scope and interest of the present invention will be better understood based on the following figures and examples which are intended to illustrate certain embodiments of the present invention and are non-limitative.

    EXAMPLES

    1. Measurement Methods

    [0173] In the following, measurement methods implemented in the examples are described.

    Brookfield Viscosity

    [0174] For the purpose of the present invention, the term viscosity or Brookfield viscosity refers to Brookfield viscosity. The Brookfield viscosity is for this purpose measured by a Brookfield DV-III Ultra viscometer at 24 C.3 C. at 100 rpm using an appropriate spindle of the Brookfield RV-spindle set and is specified in mPa.Math.s. Once the spindle has been inserted into the sample, the measurement is started with a constant rotating speed of 100 rpm. The reported Brookfield viscosity values are the values displayed 60 s after the start of the measurement. Based on his technical knowledge, the skilled person will select a spindle from the Brookfield RV-spindle set which is suitable for the viscosity range to be measured. For example, for a viscosity range between 200 and 800 mPa.Math.s the spindle number 3 may be used, for a viscosity range between 400 and 1 600 mPa.Math.s the spindle number 4 may be used, for a viscosity range between 800 and 3 200 mPa.Math.s the spindle number 5 may be used, for a viscosity range between 1 000 and 2 000 000 mPa.Math.s the spindle number 6 may be used, and for a viscosity range between 4 000 and 8 000 000 mPa.Math.s the spindle number 7 may be used.

    Average Particle Size

    [0175] The average particle size of the amorphous calcium carbonate was determined by SEM. SEM images were obtained by using a Zeiss Gemini DSM 982.

    Specimen Preparation (Powder):

    [0176] Specimen preparation was carried out by spreading the powder material onto an SEM stub using double-sided adhesive tape. In order to accomplish an electrically conductive surface, the specimen was sputter coated with a thin layer of gold/palladium alloy.

    Image Formation in Scanning Electron Microscopy SEM:

    [0177] The electrons originate from cathode are accelerated toward the sample and focused by electromagnetic lenses. When those fast and high-energy primary electrons hit the sample surface, interaction processes take place. Different signals are released: secondary electrons (essentially topographic contrast) and backscattered electrons (essentially compositional contrast: higher mean atomic number 6 higher brightness) are used for imaging the surface, X-rays provide an insight into the chemical composition.

    [0178] For the standard SEM investigation of amorphous calcium carbonate only secondary electrons images were obtained.

    [0179] The average particle size obtained by SEM refers to the average of 300 particles.

    Solids Content of an Aqueous Suspension

    [0180] 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 s, standard drying of 5 to 20 g of suspension.

    Specific Surface Area (SSA)

    [0181] 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 min. 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.

    Powder X-Ray Diffraction (XRD)

    [0182] The dried ACC powder was monitored with a Bruker D8 X-ray diffractometer, equipped with Cu K-alpha radiation and a LynxEye position sensitive device (PSD). XRD measurement conditions were 40 kV, 40 mA, by using a variable 6.00 mm divergence slit width. 2-Theta-angle was 4-70, the step size was 0.009 with 0.2 seconds per step. All samples were prepared according to the top-load technique and measured with sample rotation.

    2. Examples

    Example 1

    [0183] 1 000 g of PCC grade high-purity quicklime CaO from Austria was added to 5 l of 40 C. tap water in a stirred slaking vessel. The quicklime was slaked for 30 min under continuous stirring and the resulting slurry of hydrated calcium oxide (milk of lime) was then screened on a 100 m screen to remove grit.

    [0184] The subsequent separation of the dissolved calcium hydroxide containing supernatant was conducted via a vacuum suction filter (Buchner funnel) using a filter paper with a pore size of 2.0 m. 1.9 g/l dissolved calcium hydroxide was found as per titration method. The calcium hydroxide solution was then adjusted to a temperature of 20 C., prior feeding of said solution into the Mini Spray Dryer B-290 from Buchi. A gas containing 100% by volume of CO.sub.2 was then introduced with 6 bar pressure as spray gas to the spray nozzle. The CaCO.sub.3 synthesis was controlled by adjusting the spray dryer outlet temperature within 85 and 90 C. The product was recovered in a glass vessel as a powder of ACC.

    Example 2

    [0185] 1 000 g of PCC grade high-purity quicklime CaO from Austria was added to 5 l of 40 C. tap water in a stirred slaking vessel. The quicklime was slaked for 30 min under continuous stirring and the resulting slurry of hydrated calcium oxide (milk of lime) was then screened on a 100 m screen to remove grit.

    [0186] The subsequent separation of the dissolved calcium hydroxide containing supernatant was conducted via a vacuum suction filter (Buchner funnel) using a filter paper with a pore size of 2.0 m. 1.9 g/l dissolved calcium hydroxide was found as per titration method. The calcium hydroxide solution was then adjusted to a temperature of 20 C., prior feeding of said solution into the Mini Spray Dryer B-290 from Bachi. A gas containing 100% by volume of CO.sub.2 was then introduced with 2 bar pressure as spray gas to the spray nozzle. The CaCO.sub.3 synthesis was controlled by adjusting the spray dryer outlet temperature within 85 and 90 C. The product was recovered in a glass vessel as a powder of ACC.

    [0187] SEM images of the obtained ACC samples are shown in FIGS. 1 and 2. XRD analysis was carried out for an ACC sample, which is shown in FIG. 3. ACC samples with 70-90 wt.-% ACC were obtained. XRD analysis of the precipitates showed a broad hump and no discrete peaks, indicating that the investigated samples are lacking a structural ordering, confirming the formation of an amorphous product.

    Example 3

    [0188] 1 000 g of PCC grade high-purity quicklime CaO from Austria was added to 5 l of 40 C. tap water in a stirred slaking vessel. The quicklime was slaked for 30 min under continuous stirring and the resulting slurry of hydrated calcium oxide (milk of lime) was then screened on a 100 m screen to remove grit.

    [0189] The subsequent separation of the dissolved calcium hydroxide containing supernatant was conducted via a vacuum suction filter (Bachner funnel) using a filter paper with a pore size of 2.0 m. 1.9 g/l dissolved calcium hydroxide was found as per titration method. The calcium hydroxide solution was then adjusted to a temperature of 20 C., prior feeding of said solution into the Mini Spray Dryer B-290 from Bachi. A gas mixture containing 20% by volume of CO.sub.2 and 80% by volume of air was then introduced with 2 bar pressure as spray gas to the spray nozzle. The CaCO.sub.3 synthesis was controlled by adjusting the spray dryer outlet temperature within 85 and 90 C. The product was recovered in a glass vessel as a powder of ACC.