PROCESS FOR IN-LINE MINERALISATION AND CARBONATION OF DEMINERALISED WATER

Abstract

The invention proposes a process of in-line mineralisation of water according to which demineralised water is circulated in a pipe inside which enzymes are immobilised to catalyse the reaction of carbon dioxide and water to form bicarbonate, carbon dioxide is introduced into the pipe, and a pre-determined quantity of solid minerals, preferably magnesium and/or calcium carbonate, is introduced into the circulating water. The process enables to accelerate the dissolution of carbon dioxide in the water, which optimises the dissolution of minerals for in-line mineralisation of water, i.e. without stopping the circulation of water. The invention also proposes a system for implementing the process.

Claims

1. The process of in-line mineralisation of water according to which: demineralised water is circulated in a pipe (2; 67) inside which enzymes (10, 60) for catalysing the reaction of carbon dioxide and water to form bicarbonate are immobilised, carbon dioxide is introduced into the pipe (2), and a pre-determined quantity of solid minerals is introduced into the circulating water.

2. A process according to claim 1, in which, in order to introduce a quantity of minerals: a mineral powder (7) is injected and/or the water is circulated in the pipe through a mineral column (67).

3. A process according to any of the claims 1 and 2, according to which the nature and the quantity of enzymes as well as the quantity of carbon dioxide introduced is chosen so as to obtain a pre-determined pH value.

4. A process according to any of the claims 1 to 3, in which the pipe (2; 67) is permeable to carbon dioxide over at least a part of its length and in which carbon dioxide is introduced by applying carbon dioxide pressure on the outer wall of the pipe.

5. A process according to any of the claims 1 to 4 in which the enzymes catalysing the reaction of carbon dioxide and water to form bicarbonate are carbonic anhydrase enzymes.

6. A process according to any of the claims 1 to 5, in which the demineralised water is circulated through a mineral column (51) comprising, mineral balls (57) and balls (59) on which enzymes (60) are grafted, mixed together.

7. A process according to any of the claims 1 to 6, according to which carbon dioxide is introduced by bubbling.

8. A process according to claim 7, according to which carbon dioxide is bubbled against the flow of water.

9. A process according to any of the claims 1 to 8, in which the minerals comprise magnesium and/or calcium carbonate.

10. A process according to any of the claims 1 to 8, in which the water is circulated through a filter that selectively retains the organic substances and is placed downstream of the enzymes.

11. A re-mineralisation system (1, 21, 31, 51) for demineralised water, comprising a pipe (2) for circulating water from an inlet (3, 53) to an outlet (4, 54) along which the following are placed: means (25, 56) for introducing carbon dioxide into the pipe; enzymes (10, 60) that are capable of catalysing the reaction of carbon dioxide and water to form bicarbonate, immobilised inside the said pipe, and means (7, 67) for introducing a pre-determined quantity of solid minerals, preferably comprising magnesium and/or calcium carbonate.

12. A system according to claim 11, in which the means for introducing carbon dioxide into the pipe comprise a wall (26, 63) permeable to carbon dioxide over at least a part of the length of the pipe (2, 51) and means (24, 61) for applying carbon dioxide pressure on the outer side of the said wall that is permeable to carbon dioxide.

13. A system according to claim 12, in which the means for applying carbon dioxide pressure on the outer side of the wall that is permeable to carbon dioxide comprise an air-tight chamber (22, 61) connected to an inlet (54, 56) of pressurised carbon dioxide and through which passes at least the part of the pipe, comprising the wall that is permeable to carbon dioxide.

14. A system according to any of the claims 11 to 13, in which the means for introducing a pre-determined quantity of minerals comprise a powder injector (7) and/or a mineral column (47, 67).

15. A system according to any of the claims 11 to 14, placed in the form of a cartridge (51) comprising an inlet (53) for the water to be re-mineralised and an outlet (54) for re-mineralised water and means (56) for introducing carbon dioxide into the cartridge, said cartridge containing a mixture of mineral balls (57) and the balls (59) onto which are grafted the enzymes (60) catalysing the reaction of carbon dioxide (55) and water to form carbonic acid and then bicarbonate.

16. A system according to claim 15, in which the means (56) for introducing carbon dioxide into the cartridge are placed to allow the circulation of carbon dioxide (55) through the bed (67) of mixed balls, preferably against the circulation of water.

17. A system according to any of the claims 11 to 16, in which a filter selectively retaining the organic substances is placed along the pipe, downstream of the enzymes.

Description

[0050] The invention is better understood using the following description of several embodiments of the invention, with reference to the attached drawing, in which:

[0051] FIG. 1 illustrates the first embodiment of the invention;

[0052] FIG. 2 illustrates the second embodiment of the invention,

[0053] FIG. 3 illustrates the third embodiment of the invention,

[0054] FIG. 4 illustrates the fourth embodiment of the invention, and

[0055] FIG. 5 illustrates a cartridge according to the invention.

[0056] With reference to FIG. 1, a system 1 for re-mineralising water that is at least partially demineralised, comprises a pipe 2, for circulating water from an inlet 3 to an outlet 4 between which an inlet 5 of carbon dioxide, a compartment or cartridge 6 containing balls 9 onto which enzymes 10 capable of catalysing the reaction of carbon dioxide, for example carbonic anhydrase, are grafted, a powder injector 7 and a static mixer 8 are placed.

[0057] The inlet 5 of carbon dioxide (CO.sub.2) can be any means of introducing CO.sub.2 into a water flow well known to the persons skilled in the art such as, for example, a tube connected to a source of pressurised carbon dioxide, for example a CO.sub.2 generator or cylinder, and comprising a valve for regulating the flow rate of CO.sub.2. The type of installation for the CO.sub.2 inlet depends mainly on the size of the system, particularly the flow rates and volumes of water to be managed.

[0058] The compartment 6 containing balls 9 onto which enzymes 10 capable of catalysing the reaction of carbon dioxide are grafted, for example carbonic anhydrase, is typically similar in its structure to any column of ion-exchange resins commonly used in water treatment. The balls can be made of polyamide resin, cellulose derivative, polysaccharide derivatives or any other polymer suitable for enzyme grafting, a technique that is well known to the persons skilled in the art.

[0059] The powder injector 7 is a means of injecting a pre-determined quantity of powder. It can, for example, be a micro-dosing device, such as a micro-dosing valve or pump or a micro-dosing device of micronised powder. Such a device can, for example, comprise an ultrasonic system comprising an dosing nozzle, the diameter of which is 100 to 400 microns, or a system similar to those used in 3D printing, such as for example those described by X Lu, S Yang and JRG Evans (Microfeeding with different ultrasonic nozzle designs; —Ultrasonics, 2009; Dry powder microfeeding system for solid freeform fabrication: Solid Freeform Fabrication Symposium, Austin, Tex., 2006; Metering and dispensing of powder: the quest for new solid freeforming techniques, Powder Technology, 178 (1), 56-72. DOI: 10.1016/j.powtec.2007.04.004).

[0060] The powder injected by the injector 7 is preferably calcium carbonate and/or magnesium carbonate.

[0061] For example, synthesis powder or micronised aragonite can be used. Aragonite is the stable polymorphic form of calcium carbonate at high temperature and under high pressure, while the other two polymorphs that are stable under ambient conditions are calcite and vaterite. The marine oolitic aragonite is particularly native to the Bahamas and Florida. Synthesis powders refer to very specific mineral salts, such as calcium carbonate for example, obtained by precipitation under special conditions that give specific properties and dimensions to the particles. For example, the article by Breçević, L. and Kralj, D. (2007; on calcium carbonates: from fundamental research to application. Croatica Chemica Acta, 80(3-4), 467-484) reviews the techniques to obtain polymorphic forms of calcium carbonate. This article describes in particular the formation of amorphous calcium carbonate, which is less stable than the crystalline forms (calcite, vaterite) or hydrated forms, but having a higher dissolution rate that can advantageously be used for implementing the process of the invention. Aragonite can also be obtained by synthesis. Synthesis powders of calcium carbonate and/or magnesium carbonate can, for example, be used, preferably at least partially in amorphous form.

[0062] Depending on the nature or the quantity of minerals to be dissolved in water, several successive powder injectors can be placed along pipe 2.

[0063] The static mixer 8 is for example a helical mixer. It increases the turbidity in the water flow and improves the dissolution of the injected powder.

[0064] In practice, water with low mineral content, for example spring water, demineralised water or desalinated water enters pipe 2 at inlet 3. CO.sub.2 is injected in gaseous form at CO.sub.2 inlet 5. The water is charged with CO.sub.2 that dissolves in small proportion before entering compartment 6.

[0065] In this compartment 6, upon contact with and under the action of enzymes, the dissolved part of CO.sub.2 reacts with water to form carbonic acid and/or bicarbonate according to the equation H.sub.2O+CO.sub.2.Math.H.sub.2CO.sub.3.Math.HCO.sub.3.sup.−+H.sup.+. Bicarbonate is soluble in water in its ionic form and its formation leads to a reduction in the pH value of the water.

[0066] Preferably, the pH attained by the action of carbonic anhydrase is between 4.5 and 5.5, and more preferably between 4.9 and 5.4.

[0067] The action of the enzyme allows to shift the balance of dissolution of CO.sub.2 in water and to attain a concentration of bicarbonate that is not possible to obtain by other in-line techniques, i.e. without stopping the flow of water in compartment 6. The applicant also observed that, contrary to what might have been expected, this balance induced by the enzymes is maintained for several seconds in the water flowing from compartment 6, which gives ample time for the water that is thus acidified to reach the part of the pipe where the re-mineralisation takes place. The “in-line” aspect is therefore particularly advantageous here.

[0068] An activated carbon filter, or any other selective filter of organic substance, can be inserted into the system, for example before or after the powder injector 7. This helps in removing any possible trace of enzyme or enzyme residue from the water, without changing the mineral and/or carbonic acid or bicarbonate composition.

[0069] At the outlet of compartment 6, the water with low mineral content and high bicarbonate content is re-mineralised by injection, at a regular frequency determined by the flow rate of water and the desired mineral content, of a determined quantity of powder 7, typically calcium and/or magnesium carbonate. The powder dissolves in the water circulating at an optimised speed thanks to the pH value of the water, which has been reduced by the dissolution of the CO.sub.2. Carbonic anhydrase is essential so that sufficient dissolution of CO.sub.2 takes place in-line, i.e. without stopping the water in a tank until complete dissolution.

[0070] These two chemical species, magnesium and calcium, are in fact particularly difficult to dissolve in-line, i.e. without having to stir the powder for a long time with the water to be re-mineralised. Concentrations similar to those found in mineral water rich in calcium and magnesium are particularly impossible to attain without the action of the enzyme described above.

[0071] The system of the invention can therefore prove to be particularly advantageous for in-line production systems of mineral water with pre-determined mineral content as described in the PCT/EP2018/057868 application.

[0072] For example, to reproduce a mineral water of the Geroldsteiner® type, the composition of which is described in Table 1 of the aforementioned document, from a previously demineralised water, 1816 mg/L of bicarbonate, 348 mg/L of calcium and 108 mg/L of magnesium must be provided. In view of the results obtained in Desalinisation 396, (2016) 39-47, (table 1, run 6), it would at best be possible to obtain a final pH value of 5.9, but a maximum concentration of 20 mg/L of calcium (0.53 mm Ca.sup.2+) and 8 mg/L of magnesium (0.36 mm Mg.sup.2+) by passing a solution into which CO.sub.2 has been introduced in gaseous form over dolomite for more than 12 minutes. It would therefore be almost impossible to reproduce the composition of the Gerolsteiner® water.

TABLE-US-00001 TABLE 1 Gerolsteiner Mineral element (mg/L) Ca.sup.2+ 348 mg.sup.2+ 108 Na.sup.+ 118 K.sup.+ 10.8 HCO.sub.3.sup.− 1816 SO.sub.4.sup.2− 38.7 Cl.sup.− 39.7 NO.sub.3.sub.− 5.1 Total dissolved solids 2488 pH 5.9

[0073] There are means other than the direct addition of CO.sub.2 in gaseous form to introduce carbon dioxide into the pipe.

[0074] With reference to FIG. 2, a system 21 for re-mineralising water that is at least partially demineralised, comprises, as described in FIG. 1, a pipe 2, for circulating water from an inlet 3 to an outlet 4 between which means 25 of introducing carbon dioxide, a cartridge 6 containing balls 9 onto which enzymes 10 capable of catalysing the reaction of carbon dioxide, for example carbonic anhydrase, are grafted, a powder injector 7 and a static mixer 8 are placed.

[0075] Here, the means 25 for introducing carbon dioxide comprise a chamber 22 equipped with an inlet 23 and an outlet 24 for CO.sub.2. The pipe 2, after the inlet 3, continues into an anastomosis compartment 27 where the pipe is divided into several or a bundle of hollow fibres 26 (four are shown here) extending along the chamber 22 up to a second anastomosis compartment 28 where the hollow fibres 26 meet before the pipe leaves the chamber 25. Here, the hollow fibres 26 are tubes made using a membrane permeable to CO.sub.2. The inlet 23 and outlet 24 for CO.sub.2 are equipped with valves (not shown) that help in adjusting the pressure in the chamber 22. Such a module can, for example, be the MiniModule® of the 3M company comprising forty polypropylene/epoxy hollow fibres running through a cartridge on which the pressure of a gas can be applied.

[0076] As a general rule, the CO.sub.2 pressure applied to the outer wall of the membrane permeable to CO.sub.2 is preferably between 1 and 6 bar, at room temperature.

[0077] In practice, the water circulating in pipe 2 runs through the hollow fibres 26. The anastomosis compartments 27 and 28 help in managing the flow and the pressure of the water during the division of the pipe into bundles and the grouping of the bundles into a single flow. Carbon dioxide is introduced into the chamber 22 by the inlet 23 such that there is a pressure higher than the CO.sub.2 pressure in the circulating water, in order to help the passage of CO.sub.2 in the water circulating in the bundles. The valves placed at the inlet 23 and outlet 24 for CO.sub.2 help in adjusting this pressure according to the amount of CO.sub.2 that should be introduced into the water depending on the desired result, i.e. the amount of CO.sub.2 that may react after coming into contact with the enzymes in the cartridge 6 and the pH value to be attained later for the proper dissolution of the powdered minerals. This type of chamber through which runs a bundle of membranes permeable to carbon dioxide is known and used to extract CO.sub.2 from industrial fumes in order to limit the release of CO.sub.2 into the atmosphere. In general, the CO.sub.2 is adsorbed by an aqueous solution comprising various solvents that improve the dissolution of CO.sub.2. However, these systems do not provide for the removal of a determined quantity of CO.sub.2 as is the case here. Additionally, as part of the water treatment, in view of human consumption, it is not possible to use solvents to improve the removal of CO.sub.2.

[0078] The division of the pipe into a bundle allows a larger contact surface between the circulating water and the CO.sub.2 in the chamber, via the pores of the membrane permeable to CO.sub.2. The optimum contact surface can be calculated according to the applications (industrial or domestic) and the volume of water to be treated.

[0079] The materials that can be used for membranes permeable to CO.sub.2 are, for example, polypropylene, PTFE (Teflon), polyimide, polyolefins, etc. Such membranes are commercial, such as, for example, Superphobic® Contactors by Membrana GmbH or Celgard X40-200 or X30-240.

[0080] As with the bubbling of CO.sub.2, this technique allows the water to be treated continuously, without immobilising the water in a tank.

[0081] The treatment line can be further optimised, particularly by removing the cartridge 6 and by immobilising the enzymes 10 directly inside the bundles of hollow fibres 26, using, for example, the standard techniques of immobilising enzymes on a polymeric material.

[0082] With reference to FIG. 3, where the elements common to the previous figures are numbered in an identical manner, a system 31 for re-mineralising water that is at least partially demineralised, comprises a pipe 2, for circulation of water from an inlet 3 to an outlet 4, between which is placed a chamber 22 similar to that described with reference to FIG. 2, through which runs a bundle of hollow fibres 26. Enzymes 10 that are capable of catalysing the reaction of carbon dioxide, for example carbonic anhydrase, are immobilised inside the hollow fibres, on the inner wall of the membrane.

[0083] Thus, the water passing through the pipe 2 is charged with CO.sub.2 along the bundles of hollow fibres 26. As the CO.sub.2 is being converted into bicarbonate under the action of enzymes 10 as the water flows through the hollow fibre 26, the absorption of CO.sub.2 along the fibre can be optimised and higher quantities of bicarbonates can be produced. By removing the cartridge 6, it is thus possible to limit the length of the pipe and reduce the overall cost of the installation.

[0084] Here, the powder injector 7 and the mixer 8 are installed downstream of the unit 25. The static mixer has been described as being a helical mixer, but could be any other type of mixer known to the persons skilled in the art.

[0085] The powder injector is not the only way to introduce minerals, in solid form, into the water circulating in the pipe.

[0086] The device of FIG. 4 shows a device similar to that of FIG. 3 where the powder injector 7 and the helical insert 8 are replaced by a mineral column 47, here for example an Akdolit® CM (Magno Dol) column, or any other column operating on the same principle. The column is part of pipe 2; it represents a portion of pipe 2.

[0087] The same modification could also be made on the other systems described above.

[0088] The water circulating in pipe 2 passes through the bed of dolomite granules and after coming into contact with them becomes charged with magnesium, calcium and hydrogen carbonates. The dissolution of these species in the water is optimised thanks to the pH value of the water, which has been reduced by the dissolution of the CO.sub.2. Carbonic anhydrase is essential to shift the acidification balance of water long enough so that sufficient dissolution of CO.sub.2 takes place in-line, i.e. without stopping the water in a tank.

[0089] In all the described embodiments, it is possible to have more than one powder injector and/or more than one mineral column or a combination of the two, placed upstream and/or downstream of the means for introducing CO.sub.2 in the pipe. For example, an injector could be placed upstream of the introduction of CO.sub.2 to inject a part of the powders to be dissolved, a mineral column could, for example, be installed downstream to complement the mineral content. The dissolution could thus be carried out in several stages and distributed over a longer part of the system.

[0090] Depending on the nature of the minerals to be dissolved in the water, some could be injected separately, before or after the introduction of CO.sub.2 or the injection of magnesium and/or calcium carbonate powders.

[0091] It is possible, for a domestic installation as described in PCT/EP2018/057868 to provide the unit 25 in the form of a consumable cartridge that must be changed after a few months, when the enzyme activity is reduced.

[0092] For an industrial installation, it is also possible to provide the unit 25 in the form of interchangeable, and possibly, recyclable columns.

[0093] FIG. 5 illustrates another embodiment of the invention, in the form of cartridge 51.

[0094] The cartridge 51 comprising an inlet 53 for water to be re-mineralised, here at the top of the cartridge, and an outlet 54 for re-mineralised water, here at the bottom of the cartridge. The introduction of carbon dioxide 55 into the cartridge takes place via an inlet 56 of carbon dioxide, here in the lower section of the cartridge, via a compartment 61. The compartment 61 has an interface 63 with a bed 67 of mixed balls 59 and 57. The balls 57 are mineral balls, while the balls 59 help enzymes 60 that catalyse the reaction of carbon dioxide and water to form carbonic acid and then bicarbonate. The bed 67 of mixed balls is here a cylinder that occupies most of the cartridge. At the top of the cartridge, the bed 67 of mixed balls has an interface 64 with a compartment 62 connected to a carbon dioxide outlet 58.

[0095] The water entering the cartridge 51 circulates through the bed 67 but does not enter the compartments 61 and 62. The carbon dioxide passes through the compartment 61, and then the bed 67 of mixed balls and lastly the compartment 62. The carbon dioxide inlet 61 and outlet 62 compartments are optional, but can help to regulate the flow rate and pressure of carbon dioxide passing through the bed 67.

[0096] Other systems can be proposed, for example, with a pressure gauge and/or a valve system.

[0097] The interfaces between the bed 67 of mixed balls and the carbon dioxide inlet 61 and outlet 62 compartments can, for example, be membranes allowing bubbling of the carbon dioxide through the bed, but not allowing the passage of water. It could also be a simple tube that may be equipped with a valve.

[0098] It should be noted that here carbon dioxide is introduced against the flow of water. This increases the residence time of carbon dioxide in the bed 67 of mixed balls.

[0099] The cartridge 51 can be provided at the water inlet 53 and the water outlet 54 with easy connection means to a domestic or industrial water system, possibly downstream of other units such as a softening or a demineralisation unit, so that it can be easily replaced. Any suitable means known to the persons skilled in the art can be considered here. The same applies to the inlet and outlet for carbon dioxide.

[0100] The invention is not limited to the production of mineral water, but can also be used to produce mineral concentrates, such as those used, for example, in the method and system of the WO2019020221 application or for pharmaceutical mineral concentrates.