WO2022220673A1 - System and process for producing aragonite - Google Patents

Abstract

A process and system for producing Aragonite comprising: forming a mixture comprising calcium ions and magnesium ions in water; spraying the mixture into a carbonation reactor pressurised with carbon dioxide to form a seed solution; and injecting carbon dioxide into the seed solution to form Aragonite characterised in that: the ratio of magnesium to calcium ions in the mixture is less than 1.

Description

SYSTEM AND PROCESS FOR PRODUCING ARAGONITE

FIELD OF INVENTION

[0001] The present invention generally relates to a process and system for producing Aragonite.

BACKGROUND

[0002] Precipitated calcium carbonate (PCC) can be used in producing a wide range of consumer products including cosmetics and pharmaceuticals. Current methods for producing precipitated calcium carbonate typically include a carbonation process, in which a solution is reacted or treated with CO2 gas at elevated temperatures. PCC can form in three polymorphs, these are Calcite, Aragonite and Vaterite. Among these polymorphs, Aragonite has been known to have a high aspect ratio, as it is typically synthesized in needle shape form, hence providing stronger practical advantages - and has been regarded as a new functional particle that can alter properties of organic or inorganic compounds and can be efficient carriers for drug delivery. Owing to its application in various industries, the global PCC demand was 125,282 kilo tonnes in 2018, and it expected to increase to 163,000 toward 2027.

[0003] However, despite its growing demand, producing Aragonite using known methods has been challenging as it involves a complex, time-consuming process and requires a high concentration of additives in order to ensure a high yield.

[0004] Accordingly, there is a need to find a more sustainable and time-efficient way of producing Aragonite.

SUMMARY

[0005] In one aspect the present invention provides a process for producing Aragonite comprising: forming a mixture comprising calcium ions and magnesium ions in water; spraying the mixture into a carbonation reactor pressurised with carbon dioxide to form a seed solution; and injecting carbon dioxide into the seed solution to form Aragonite; characterised in that: the ratio of magnesium to calcium ions in the mixture is less than 1.

[0006] In one embodiment, Aragonite is formed within a predetermined residence time in the reactor, typically wherein the residence time is around 10 minutes.

[0007] Advantageously the yield of Aragonite exceeds 90%.

[0008] In on embodiment, the carbon dioxide pressure in the reactor is 5 barg.

[0009] In a further embodiment, the mixture is sprayed into the reactor at a temperature of at least 40°C.

[0010] In a yet further embodiment, the mixture is sprayed into the reactor at a temperature of around 90°C.

[0011] The magnesium to calcium concentration ratio is at least 0.2, preferably around 0.4. Advantageously, the amount of magnesium required in the current invention is much lower compared to the prior art for about the same yield of aragonite.

[0012] In one embodiment the mixture comprises water, calcium oxide and magnesium chloride.

[0013] In a further embodiment the mixture comprises seawater and 1 to 5 grams per litre calcium oxide. Seawater typically comprises 400ppm calcium ions, 1200ppm magnesium ions and 24000ppm sodium ions. Therefore adding 1000 to 5000 ppm calcium ions increases the calcium concentration to 1400 to 5400ppm. This equates to a magnesium: calcium ion ratio of 0.86 to 0.22 respectively.

[0014] Typically, the Aragonite is formed as a slurry which continuously flows out of the bottom of the reactor via an outlet while maintaining a predetermined height of slurry within the reactor.

[0015] In another aspect, the present invention provides a system for production of Aragonite comprising: a carbonation reactor pressurised with carbon dioxide comprising means for introducing/spraying a mixture comprising calcium oxide (CaO) and magnesium chloride (MgCk) in water to form a seed solution within the reactor; a means for injecting carbon dioxide into the seed solution to form Aragonite; characterised in that: the ratio of magnesium to calcium ions in the mixture is less than 1.

[0016] In one embodiment, the reactor further includes a sensor for measuring the level of slurry within the reactor.

[0017] In one embodiment control means in the form of a back pressure regulator or flow control valve is provided to control the length of time that the slurry is retained in reactor.

[0018] Advantageously the slurry forms a barrier to prevent carbon dioxide from leaking from the reactor and ensures that the slurry is retained in the reactor for sufficient time to form aragonite. In addition, the continuous flow ensures that any shutdown time is minimised.

[0019] In a further embodiment, the reactor further includes a pressure regulator to adjust the pressure of the reactor within a predetermined range to facilitate the reaction between the seed solution and injected CO2 to form Aragonite.

[0020] In another embodiment, the system further includes a temperature sensor to measure the temperature of the mixture prior to being introduced/sprayed into the carbonation reactor.

BRIEF DESCRIPTION OF DRAWINGS

[0021] The invention will be more understood by reference to the description below taken in conjunction with the accompanying drawings herein:

[0022] FIG. 1 provides a schematic diagram of the system in accordance with an embodiment of the present invention;

[0023] FIG. 2 shows a flowchart for the process in accordance with an embodiment of the present invention;

[0024] FIG. 3A shows the results obtained based on experiments under varying conditions in accordance with an embodiment of the present invention; [0025] FIG. 3B shows the results obtained based on experiments under varying reaction time, temperature and Mg-to-Ca ratio in accordance with an embodiment of the present invention; [0026] FIG. 4A shows the optimised conditions for high Aragonite yield in accordance with an embodiment of the present invention;

[0027] FIG. 4B shows the Aragonite yield based on continuous pre-production for a total of 54 hours with 966g of Aragonite obtained with quality maintained in the range of 77- 80% in accordance with an embodiment of the present invention;

[0028] FIG. 5A - FIG. 5B show the XRD and ICP results for the tested Aragonite based on experimental examples in accordance with an embodiment of the present invention; and [0029] FIG. 6 shows the PSD results for tested Aragonite based on experimental examples in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION [0030] In line with the above summary, the following description of a number of specific and alternative embodiments is provided to understand the inventive features of the present invention. It shall be apparent to one skilled in the art, however that this invention may be practiced without such specific details. Some of the details may not be described at length so as not to obscure the invention. For ease of reference, common reference numerals will be used throughout the figures when referring to the same or similar features common to the figures.

[0031] Embodiments of the invention are described by way of illustration. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various respects, all without departing from the scope of the present invention. It should be noted that the drawings include schematic description of how the process in accordance with the preferred embodiments can be carried out. There may be other standard equipment or components may have not been illustrated since they are known in the art. [0032] In the process of the present invention, a mixture of calcium oxide (CaO) and magnesium chloride (MgCk) in water and carbon dioxide (CO2) is reacted together under predetermined process conditions, to produce or generate particulate precipitated Aragonite within a short residence time. In one embodiment, the process of the present invention is a continuous process.

[0033] In accordance with one embodiment of the present invention, the concentration of CaO and MgCk may vary, and additives may be added if required. The parameters and conditions of the carbonation process may be calculated using known or conventional methods, to quantify the yield of aragonite.

[0034] Alternatively, instead of calcium oxide and magnesium chloride being added to distilled water, 1-5 grams per litre of calcium oxide can be added to seawater to create the initial mixture. Seawater typically comprises 400ppm calcium ions, 1200ppm magnesium ions and 24000ppm sodium ions. Therefore adding 1-5 grams per litre (i.e. 1000 to 5000 ppm) calcium oxide increases the calcium ion concentration to 1400 to 5400ppm. This equates to a magnesium: calcium ion ratio of 0.86 to 0.22 respectively

[0035] FIG. 2 provides a flow chart for production of Aragonite according to one embodiment of the present invention, the process comprises: adding calcium oxide and magnesium chloride to water (SI 00) to form a mixture, whereby the mixture is prepared such that the ratio of magnesium to calcium ions is less than 1, preferably about 0.4; spraying the mixture (SI 01) into a carbonation reactor pressurised with carbon dioxide to form a seed solution; and injecting carbon dioxide into the seed solution to form Aragonite (S103), the Aragonite being formed within a predetermined residence time in the reactor. Aragonite slurry is recovered, in which the precipitated particles is separated from water using suitable methods.

[0036] In this embodiment, aragonite is formed within a residence time of 10 minutes or below.

[0037] FIG. 1 is an example of the system for producing aragonite in accordance with an embodiment of the present invention. With reference to FIG. 1, the system comprises a feed tank (1) for mixing calcium oxide (CaO) and magnesium chloride (MgCk) in water to form a homogenous mixture to be fed to a pressurised carbonation reactor (3) facilitated by a feed pump (2). The ratio of magnesium to calcium ions in the mixture is within the range of 0.2- 1

[0038] Prior to being fed or directed to the pressurised reactor (3), the temperature of the mixture is adjusted to about 40 to 90°C. In this embodiment, to increase the temperature of the mixture, the feed tank (1) may be provided with a heater (not shown) for heating the mixture. Alternatively, the mixture maybe heated via an independent heating device (3 A) or unit prior to entering the reactor (3). A temperature sensor may be provided to measure the temperature of the mixture prior to being introduced or sprayed into the reactor (3).

[0039] The reactor (3) is pressurised using carbon dioxide (CO2), in the gas which may be introduced via a direct tube or a conduit from a CO2 gas cylinder (4) and is heated at a predetermined temperature, for carbonation reaction. In this embodiment, the CO2 pressure in the reactor is about 5 barg. It is anticipated that the reactor (3) may include a pressure regulator to accordingly adjust the pressure within the reactor (3) if required.

[0040] During carbonation, pressurised CO2 reacts with the heated mixture to form a seed solution containing aragonite precursor. CO2 that is injected at a predetermined flow rate into the seed solution reacts with the aragonite precursor to form aragonite. In the preferred embodiment, CO2 is injected and maintained at 40mL/min.

[0041] The reactor (3) may further include a temperature control means for adjusting or controlling the reaction temperature within the reactor (3). A level sensor may be positioned within the reactor (3) such that it is able to measure the level/height of the solution/slurry within the reactor (3), and an outlet (3B) is provided to allow the slurry to be continuously drawn out or exit from the bottom of the reactor (3) while maintaining/controlling the level of the slurry. The temperature of the reaction mixture may rise and is accordingly controlled or maintained via suitable probes or sensors to maintain the reaction temperature at about 90°C.

[0042] It should further be noted that the reaction products may include contaminants that exit the reactor (3) to be directed to further operations (not shown). The final product precipitated particles containing aragonite is recovered via a product recovery vessel (5) and may be separated from the slurry via a vacuum filter or other suitable means. In this embodiment, the particle size of Aragonite that can be obtained is D50, between 9 - 10 microns, or below 40 microns. Such characteristic is known to be suitable for in the manufacture of, among others, drugs, antacid tablets, calcium supplements and multivitamins.

[0043] The content and characterisation of particles in the slurry formed in accordance with the preferred embodiment of the present invention may be determined by way of ICP, FESEM and XRD.

[0044] Experimental examples of producing Aragonite with the process described herein under varying parameters are shown in the drawings, in particular, FIG. 3A - FIG. 3B, while yield of product based on the varying parameters and optimised parameters projected in FIG. 4A and FIG. 4B respectively. It can be seen that the optimum yield is produced at about 90°C with a residency time of 10 minutes.

[0045] FIG. 5A - FIG.5B show the ICP and XRD analysis results, in which the content of CaCCh in the final product obtained with the process of the present invention was above 94% and the content of Aragonite in the precipitated CaCCE was within the range of 75% - 81%. FIG. 6 provides Particle Size Distribution (PSD) results of the Aragonite.

[0046] Based on the experimental examples, it is observed that the Aragonite yield was highest (96%) at 90°C reaction temperature, 10 minutes residence time and Mg-to-Ca ratio of 0.4. It is further observed that the Aragonite yield increases with increased Mg concentration. As shown in FIG. 4B, when operated continuously for a total of 54 hours, about 966 of Aragonite material was produced with quality maintained in the range of 77 - 80%. The FESEM results show that the morphology of the Aragonite PCC obtained is needle shape, under the operating temperature of 90°C. This shape is known to be used in strengthening structure due to its high bending and impact strength hence may be suitable for developing artificial bones in the future.

[0047] With the present invention, high Aragonite yield can be achieved with lower concentration of Mg ions and shortened residence time, which exceeds the target yield of 80% aragonite, 10% calcite. Under these conditions, the average cost of production can be effectively reduced to about USD232 from USD750-850 per tonne. The magnesium chloride can be recycled at a rate of loss of 20%. [0048] It should be noted that seawater can be used as a component of the initial mixture as it already contains magnesium ions and of course is inexpensive. The morphology of the aragonite PCC obtained with this starting material is cubic. Seawater can be recycled three times at 50% aragonite purity.

[0049] While the invention has been described as required in terms in preferred embodiments and specific operating ranges and conditions, those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described.

Claims

1. A process for producing Aragonite comprising: forming a mixture comprising calcium ions and magnesium chloride ions in water; spraying the mixture into a carbonation reactor pressurised with carbon dioxide to form a seed solution; and injecting carbon dioxide into the seed solution to form Aragonite; characterised in that: - the ratio of magnesium to calcium ions in the mixture is less than 1.

2. The process according to Claim 1, wherein the Aragonite is formed within a predetermined residence time in the reactor.

3. The process according to Claim 2, wherein the residence time is around 10 minutes.

4. The process according to Claim 1, wherein the carbon dioxide pressure in the reactor is around 5 barg.

5. The process according to Claim 1, wherein the mixture is sprayed into the reactor at a temperature of at least 40°C.

6. The process according to Claim 5, wherein the mixture is sprayed into the reactor at a temperature of around 90°C.

7. The process according to Claim 1, wherein the magnesium to calcium concentration ratio is at least 0 2

8. The process according to Claim 7, wherein the magnesium to calcium concentration ratio is around 0.4.

9. The process according to Claim 1, wherein the mixture comprises water, calcium oxide and magnesium chloride.

10. The process according to Claim 1, wherein the mixture comprises seawater and 1 to 5 grams per litre calcium oxide.

11. The process according to Claim 1, wherein the Aragonite is formed as a slurry which continuously flows out of the bottom of the reactor via an outlet while maintaining a predetermined height of slurry within the reactor.

12. A system for production of Aragonite comprising: a carbonation reactor pressurised with carbon dioxide comprising means for introducing/spraying a mixture comprising calcium ions and magnesium ions in water to form a seed solution within the reactor; a means for inj ecting carbon dioxide into the seed solution to form Aragonite; characterised in that:

- the ratio of magnesium to calcium ions in the mixture is less than 1.

13. The system according to Claim 12, wherein Aragonite is formed as a slurry which continuously flows out from an outlet at the bottom of the reactor to maintain the slurry at a predetermined level/height within the reactor.

14. The system according to Claim 12, wherein the reactor further includes a sensor for measuring the level of slurry within the reactor.

15. The system according to Claim 12, wherein the reactor includes control means in the form of a back pressure regulator or flow control valve to control the length of time that the slurry is retained in the reactor.

16. The system according to Claim 12, wherein the reactor further includes a pressure regulator to adjust the pressure of the reactor within a predetermined range to facilitate the reaction between the seed solution and injected CO2 to form Aragonite.

17. The system according to Claim 12, wherein the system further includes a temperature sensor to measure the temperature of the mixture prior to being introduced/sprayed into the carbonation reactor.

18. The system according to Claim 12, wherein the mixture comprises water, calcium oxide and magnesium chloride.

19. The system according to Claim 12, wherein the mixture comprises seawater and 1 to 5 grams per litre calcium oxide.