One-step method in an intensified rotating packed bed device with packing material for the production of hydro-magnetite nanoparticles

Abstract

The invention pertains to a method of producing hydromagnesite nanoparticles (Mg5(CO3)(OH)2·4H2O). In its basic embodiment it is carried out in one step by a chemical reaction of magnesium oxide or magnesium hydroxide carbonation in which a) the carbon dioxide carrying stream is directed inside a rotating packed bed reactor (3); b) inside the reactor it is contacted in packing material and reacts with a suspension of magnesium oxide or magnesium hydroxide; c) the packing material rotates and a centrifugal field is developed inside it; d) the streams of carbon dioxide and magnesium oxide or magnesium hydroxide suspension interact either cocurrently or countercurrently. Their contact increases the reaction rate of carbonation of the magnesium oxide or magnesium hydroxide suspension and the nucleation of hydromagnesite, resulting in the crystallization of hydromagnesite.

Description

DESCRIPTIONONE-STEP METHOD IN AN INTENSIFIED ROTATING PACKED BED DEVICE WITH PACKING MATERIAL FOR THE PRODUCTION OF HYDRO-MAGNETITE NANOPARTICLES

[0001] The invention relates to the production of nanoparticle-sized hydromagnesite. Specifically, existing methods involve two-step carbonation (two reactions are required) and the majority of them are done in continuous stirred tank reactors (CSTR) (See "state of the art").Hydromagnesite exists in nature as a mineral, in mixtures with other substances. Its separation requires a large amount of energy consumption, thus synthetic methods of production are preferred, especially when it can be produced directly in nanoparticle form (its extraction from minerals requires significant further processing and becomes even more difficult and expensive to achieve its production in nanoparticle size). Its use in nanoparticle form is desirable in many applications such as its use as a combustion retardant (e.g., in polymers), as an additive in cement, in drug release methods, tissue engineering, etc.

[0002] The production of hydromagnesite from industrial flue gases, e.g., using carbon dioxide (CO2), is a method of using CO2. It allows the conversion of the latter into a useful product that can be profitable and provide incentives for the installation of capture plants in a variety of industrial applications, contributing significantly to the reduction of greenhouse gas emissions.The production of the hydromagnesite by the present invention using a rotating packed bed (RPB) reactor allows for very rapid scale-up of the process, as it is an intensified reactor of small size, easy to build and handle. The RPB reactor significantly increases the mass transfer from the gas to the liquid phase. This is due to the high rotational speed which leads to the formation of a thin liquid film which exerts little resistance to mass transfer in the liquid.The present invention could be applied to the production of all carbonated substances wherein a positively charged ion of the general form M+fM2+, or M3+reacts with CO2lwherein M can be lithium, sodium, potassium, rubidium, caesium, francium, strontium, barium, radium, manganese, iron, aluminium, zinc, copper, nickel, silver, cadmium, platinum, lead, and in general any element belonging to alkalis, alkaline earths, transition elements, posttransition elements and metalloids. It could also be used directly and easily in industries producing oxides of the above substances and also magnesium oxideand / or magnesium hydroxide as they could avail these products as raw materials and combine them with the utilization of the CO2produced by the process. In particular, general applications of hydromagnesite and magnesium carbonate salts include the following, in addition to those previously mentioned:- Feedstock in plastics, polymers, fertilizers and building materials.- Use in magnesium-ion batteries, which are likely to replace lithium-ion batteries as they have much higher energy density, less environmental impact and can withstand much lower temperatures.- Use in alloys in the vehicle and aircraft industry, as the use of magnesium carbonates increases their strength and reduces their weight.- Additional applications are reported in the cosmetics and pharmaceuticals and paper industries.- In general, the commercial price of carbonate salt nanoparticles can be very high, depending on their purity and crystal characteristics, providing a great commercial incentive for their production.State of the art

[0003] There are only two patents (CN110573458A, AU2018222897) which mention few features that are relevant to this invention, and many features that have no similarity, making the technology of this invention unique. The differences that do exist are commented upon and evaluated below based on specific, representative features of the technology to which the specific invention relates.The present invention is implemented based on the following reaction:SMgO + SH2O + SCO2M^5(CO3)4(O / / )2• 4H2O + CO2(1)It is further implemented based on the following reaction when the starting material is an aqueous suspension of magnesium hydroxide (Mg(0H)2), as follows:SMg(0H)2+ H2O + SCO2M^5(CO3)4(O / / )2• 4H2O + CO2+ H2O (2)Patent CN110573458A does not disclose a reaction, however it refers to the production of salts of the type nMgC03■ Mg(0H)2• mH20, where n and m are integers, and that it is a two-step carbonation (see also below for details). Patent AU2018222897 discloses the following reaction:For AU2018222897, it is obvious that it is a different production method compared to the technology of the present invention.

[0004] The present invention is implemented in one carbonation step, without pre-treatment, as the precursor suspension comprises two components (CO2and an aqueous suspension of MgO or Mg 0H')2). The Chinese patent CN110573458A relates to a carbonation process implemented in two stages, while the Australian patent application AU2018222897 relates to a carbonation process implemented in one stage, but with multi-stage pre-treatment and control of specific treatment and pH indicators with additional ion sources. Two-stage carbonation, as in CN110573458A, is obviously quite different from one-step carbonation, as in the former case there is no direct precipitation of hydromagnesite, as in the case of one-step carbonation. In the case of AU2018222897, prior to the hydromagnesite precipitation, pre-treatment steps are included which are required due to the composition of a specific precursor substance called CSG brine, which is neither required nor used in the technology relating to the present invention. In addition, AU2018222897 includes control of the carbonate / carboxylate ratio and pH by controlled addition of HO~ (hydroxyl) sources’ and / or Mg2+sources. None of these are required or used in the technology of the present invention.The present invention is implemented by means of rotating packed bed (RPB) equipment, while the methods disclosed in patent CN110573458A and patent application AU2018222897 are implemented in a vessel with a stirrer. The RPB is an advanced type of equipment containing packing material which is rotated. In contrast, the vessel with a stirrer does not contain packing material, while the RPB does not contain a stirrer. They are therefore two completely different pieces of equipment. The mode and intensity of mass transfer, which is the main reaction mechanism in the two equipment cases, is completely different in the case of using a rotating packing material than in the case of a rotating stirrer. It has been demonstrated in the published literature, for products other than the one to which the present invention relates, that the RPB has significant advantages over vessels with a stirrer, such as lower reaction volume (and thus lower fixed equipment costs) and better control of the product structure, among others.In the present invention the precursor is a suspension of MgO or Mg(0H2in water, in patent CN110573458A the precursors are suspensions of MgO or Mg 0H)2in water, and in patent application AU2018222897 the precursors are sources of HO~ ions, preferably NaOH, but also ultrafine Mg(0H2of size <lpm. The technology of the present invention relates to direct carbonation of a MgO or Mg 0H)2suspension in water (gas-liquid-solid system), whereas AU2018222897 relates to solution carbonation (gas-liquid system) or suspension carbonation (gas-liquid-solid system) where the liquid is of a specific type, called CSG brine, is related to gas production, contains a specific composition and a high initial concentration of undesirable substances, requiring more than one pre-treatment step before the carbonation reaction.The present invention does not require additional raw materials (additives). The process described in patent application AU2018222897 requires a soluble source of Mg2+ions, of MgCl2or MgS04lMg^NO3~)2or MgOH2. The source may be of hydrated or of other form. The absence of additives simplifies the production. It is the result of the combination of the functional capabilities of the RPB that increases the mass transfer and dissolution rate of MgO or Mg 0H)2which is generally the simplest stage of the process. In the case of AU2018222897 the additives lead to by-products that need to be separated, significantly increasing the complexity.

[0005] In addition to the above patents, equipment for the production of hydromagnesite has been reported once in the literature, via gas-liquid carbonation. This approach involves the gas absorption of a NH3 / CO2mixture in an aqueous solution of MgCl2. The reaction of the present invention is much simpler, requires only MgO or Mg(0H2as raw material, it is a reaction in a hydrated suspension and not of a gas in a solution, does not use ammonia or chlorine compounds, and thus does not require additional steps to separate these components from the final product.Carbonation methods have been documented that also include magnesium and its products and have similarities to some of those of the present invention, but also have very important differences.For example, patent application US20220153647A1 relates to the carbonation of reactive magnesia cement using bacteria, and the objective is to strengthen a specific type of cement without requiring the production of nanoparticles. In contrast, the present invention does not use bacteria, does not require magnesium-containing cement but can use any source of magnesium oxide, aims to produce nanoparticles, and does not aim a specific application.Chinese patent CN1341694A relates to the production of magnesium hydroxide nanoparticles using RPB. The final product is different and is implemented in two stages versus one stage of the present invention.The US patent application US2022048784 relates to the production of magnesium carbonate from materials including magnesium hydroxide, and is implemented using an autoclave. The employed equipment is clearly differentand is implemented in two stages compared to one stage of the present invention.Russian patent RU2681622 relates to the production of magnesium bicarbonate. This is a different product.The international patent application WO2018139975A1 relates to reactive magnesia cement carbonation and to the production of cement composite material. Therefore, it is, again, a different product.The revoked European patent applications EP 3 428 129 Al, EP 3 428 128 Al relate to a method of increasing magnesium ions in water. They pertain to a different product and technology purpose.US patent US2016145155 Al relates to the production of a carbonate containing magnesium and calcium. It is a different product and does not use RPB.International patent application WO2015154194 Al relates to a process for the production of hydromagnesite and magnesium oxide. There is no use of RPB or reference to hydromagnesite nanoparticles (the size referred to is much larger and in the range of 20-50 pm), and there is also the use of multiple raw materials (e.g., MgCl2lNa2CO3) unlike the present invention which requires only the two components mentioned above.The US patent US20140004347A1 is directed to the production of hydromagnesite via a nesquehonite method and is implemented in two steps and without the use of RPB.Chinese patent CN102424409A is for the production of light magnesium carbonate. It is not hydromagnesite as in the present invention. It makes use of RPB but with a chlorine-containing feedstock.International patent application W02010097446A1 is for the production of magnesium carbonate. It is not hydromagnesite as in the present invention.

[0006] There is also a number of inventions using RPB, but relating to the production of products other than that of the present invention, such as calcium carbonate (CN110950338A, CN107814404A, CN104946342A, CN 101451087 A, CN101219330A, CN1116185A, CN1461731A, CN2483374Y,W02003055804A1), lithium carbonate (CN104229838A, CN 104211097 A, CN 104211096A, CN102180488B), aluminium carbonate nanoparticles (CN1752006A), production of nanoparticles of metal oxides, aluminas and zinc oxide (CN102030352A, carbonation of cement products (W02022090796A1, WO2020217232A1). Finally, there are inventions that simply report the production of calcium carbonate nanoparticles (CN110950338A, CN2483374Y).

[0007] Summarizing the above, the present invention is completely different from all the above mentioned methods that form the technological basis, and which either involve the production of other substances, or use other types of equipment, or involve the production of hydromagnesite by different, more complex and more expensive methods, or, finally, require the use of additional raw materials leading to the production of by-products. In contrast, the present invention achieves the production of hydromagnesite in one step, using a rotating bed reactor with packing material, with MgO or Mg(0H)2raw material, without pre-treatment and without additional raw materials that lead to the production of by-products.Short presentation of the inventionThe aim is to produce hydromagnesite nanoparticles(C O3)4(OH)2• 4H2O) through a one-step carbonation reaction of magnesium oxide MgO) or magnesium hydroxide (Mg(0H)2) suspension, carried out in intensified rotating packed bed (RPB) equipment.Advantages of the inventionA) Unlike conventional CSTR reactors and / or two-step production methods, the present patent does not require two reactors, does not require additional raw materials and / or other chemicals (e.g., acids, toxic ammonia, etc.), does not create intermediate crystal phases, and avoids the creation of intermediate, different, undesirable crystal structures (e.g., nesquehonite), high temperatures and / or pressures are not required, the reaction time is much shorter (because in CSTR the mass transfer rate is much reduced) leading to higher reaction efficiency and smaller equipment volume.B) The one-step reaction is carried out by directly using magnesium oxide MgO) or magnesium hydroxide (Mg(0H)2) and carbon dioxide (CO2), in a single reactor (reducing the equipment requirements). The CO2can come directly from a CO2capture unit from the flue gases of any industry, but also from any other source. Due to the one-step reaction only the control of the suspension and gas flow rates and the rotation rate are required to produce hydromagnesite, whereas in multi-stage reactions more parameters need to be controlled making it difficult to find and maintain the conditions required to produce the final product.C) The use of a RPB reactor for the one-step reaction leads to a CO2utilization efficiency of 94% (much higher than that with a CSTR), leads to a hydromagnesite production rate much higher than that with a CSTR under the same conditions, allows the production of nanoparticles withan average thickness of 31 - 69 nm without the use of additional chemicals.Disclosure of the invention

[0008] The present invention relates to a novel method for synthesizing hydromagnesite nanoparticles in a single step via a single carbonation reaction of aqueous magnesium oxide (MgO) or magnesium hydroxide (M^(O / / )2) suspensions in a rotating packed bed reactor.This is a method of producing hydromagnetite nanoparticles• 4H20) by a chemical reaction of a magnesium oxide or magnesium hydroxide carbonation step in which a) the carbon dioxide (CO2) carrying stream is directed inside a rotating packed bed reactor; b) inside the reactor it is contacted in packing material and reacts with a suspension of magnesium oxide or magnesium hydroxide; c) the packing material rotates and a centrifugal field is developed inside it; d) the streams of carbon dioxide and magnesium oxide or magnesium hydroxide suspension interact with each other, either cocurrently or countercurrently. The contact of these streams promotes and increases the speed of the chemical reaction of carbonation of the magnesium oxide or magnesium hydroxide suspension and of the nucleation of hydromagnesite, resulting in the crystallization of hydromagnesite.The raw material is a hydrated suspension of magnesium oxide MgO) or magnesium hydroxide (Mg(0H)2) and CO2regardless of its source. The minimum concentration of the aqueous MgO suspension is greater than the solubility limit of pure MgO in water (8.6 mg / l) at 25 °C. Or equivalently, the concentration of Mg(0H)2is greater than the solubility limit of pure Mg(0H)2in water (6.54 mg / l) at 25 °C. The minimum temperature for the reaction is 40 °C. The minimum rotational speed of the RPB is 10 rpm. The minimum suspension volumetric flow rate / CO2volumetric flow rate ratio is 0.01.The method achieves monodispersity, up to 100% purity in a hydromagnesite crystal structure and repeatable and consistently regular nanoparticle thickness distributions with small standard deviations.The method can be performed in batch or continuous mode. The reactor, used to perform the method of the preceding claims, is characterized in that it comprises a rotating bed with packing material. The reaction of the present method may be achieved in multiple reactors arranged either in series or in parallel with multiple combinations.A simplified and illustrative process flow diagram used for the results presented is given in Figure 1. According to a general description of this, the flow of aCO2gas source (1) is regulated by means of a gas flow regulator (2) and directed to the inside of a RPB reactor (3). Inside the RPB reactor, it is contacted and reacted with an aqueous suspension of the raw material MgO or Mg(0H)2) with a variety of initial concentrations, which is fed from the reactant vessel (4) by means of the reactant pump (7) in the center of the RPB reactor. The mode of contact of the two streams (either in cocurrent or countercurrent flow) is shown in more detail in Figures 3 and 4, respectively. The contact of the two streams under the developing centrifugal field of the RPB reactor promotes and increases the speed of the chemical reaction of MgO or Mg(0H2carbonation and hydromagnesite nucleation. The developing centrifugal field allows the crystallization of hydromagnesite to take place under mild operating conditions (atmospheric pressure and low temperature). At the same time, it avoids the use of additives to control pH and particle size growth, which are necessary with conventional equipment. The evolving product stream leaves the reactor shell through a side hole and is temporarily collected in the product vessel (5), from where it is continuously recycled to the reactant vessel by means of the product pump (6). Upon leaving the reactor shell, the gas is subjected to volumetric flow measurement (8) and then released to the atmosphere with down to zero CO2content. The temperature of the experimental set-up is monitored by thermocouples (12 and 13) placed in the respective containers. The experimental results are obtained by sampling from a suitable location (14 or 15 or 16).Description of the designs

[0009] Figure 1 corresponds to batch production of hydromagnesite nanoparticles. However, it does not exclusively and uniquely characterize the invention. The numbering corresponds to the following parts:1) CO2source;2) Gas flow regulator;3) RPB reactor;4) Reactant vessel;5) Product vessel;6) Product vessel outlet pump;7) Reactant vessel outlet pump;8) Gas flow meter;9) Three-way valve at the outlet stream of the RPB reactor;10) Three-way valve at the outlet stream of the product vessel;11) Three-way valve at the outlet stream of the reactant vessel;12) Reactant vessel temperature gauge;13) Product container temperature gauge;14) Sampling point from the outlet stream of the reactant container;15) Sampling point from the outlet stream of the RPB reactor after the three-way valve (arrow direction from the valve to the vessel) or loading of the vessel 5 through the three-way valve with fresh suspension (arrow direction from the vessel to the valve);16) Sampling point from the outlet stream of the product vessel.Alternatively, or according to the needs of production, according to the characteristics of the raw materials, etc., the flow diagram could take a more complex and generalized form, according to Figure 2.

[0010] Figure 2 shows an arrangement involving multiple RPBs, from which many possible combinations of reactors and streams can be derived for continuous or batch production in series or parallel. The numbered triangles in Figure 2 represent a generic vessel / device where streams from any source in the process can be mixed for use in the RPB or output from the system. The numbered semi-circular shapes in Figure 2 represent a generic vessel / device from which streams can be drawn from the RPB and distributed to any part of the process or components can be introduced into the system. Figure 2 clearly illustrates in each case how each stream is routed from a dispensing device to a mixing device.The numbering corresponds to the following parts:17) CO2inlet gas stream;18) Inlet gas stream dispensing device 17;19) Inlet gas stream mixing device 49 and / or 50 and / or 51 and / or 67;20) Inlet gas stream mixing device 45 and / or 52 and / or 53 and / or 64 and / or 65 and / or 66;21) Outlet gas stream dispensing device for the reactor outlet gas stream 26;22) Inlet gas stream mixing device for inlet gas streams 57 and / or 46 and / or 54 and / or 64 and / or 65 and / or 66;23) RPB reactor outlet gas stream dispensing device 27;24) Inlet gas stream mixing device for inlet gas streams 57 and / or 46 and / or 54 and / or 64 and / or 65 and / or 66;25) Outlet gas stream dispensing device from RPB reactor 28;26) RPB reactor;27) RPB reactor;28) RPB reactor;29) RPB reactor;30) Inlet gas stream mixing device 61 and / or 60 and / or 62 and / or 59 and / or 59 and / or 63 and / or 63 and / or 58 and / or 48 and / or 91;31) Outlet gas stream dispensing device from RPB reactor 29;32) Inlet suspension / liquid stream mixing device 68 and / or 71 and / or 69 and / or 86 and / or 87 and / or 88 and / or 88;33) Outlet suspension / liquid stream dispensing device for gas from RPB reactor 26;34) Inlet suspension / liquid stream mixing device 80 and / or 70 and / or 77 and / or 86 and / or 87 and / or 88 and / or 88;35) Device for distributing the outlet stream of suspension / liquid from RPB reactor 27;36) Device for mixing inlet streams of suspension / liquid 81 and / or 90 and / or 78 and / or 86 and / or 87 and / or 88;37) Device for distributing the outlet stream of suspension / liquid from RPB reactor 28;38) Inlet suspension / liquid stream mixing device 83 and / or 84 and / or 85 and / or 79 and / or 90;39) Outlet suspension / liquid stream distribution device from RPB reactor 29;40) Hydrated MgO suspension inlet stream;41) Inlet suspension / liquid stream distributing device 40;42) Inlet suspension / liquid stream mixing device 72 and / or 73 and / or 74 and / or 89;43) Final product stream;44) Outlet gas stream;45) Outlet gas stream from dispensing device 18;46) Outlet gas stream from dispensing device 18;47) Outlet gas stream from dispensing device 18;48) Outlet gas stream from dispensing device 18;49) Outlet gas stream from dispensing device 21;50) Outlet gas stream from dispensing device 23;51) Outlet gas stream from dispensing device 25;52) Outlet gas stream from dispensing device 23;53) Outlet gas stream from dispensing device 25;54) Outlet gas stream from dispensing device 25;55) Outlet gas stream from dispensing device 21;56) Outlet gas stream from dispensing device 23;57) Outlet gas stream from dispensing device 21;58) Outlet gas stream from dispensing device 21;59) Outlet gas stream from dispensing device 21;60) Outlet gas stream from dispensing device 25;61)Inlet gas stream to mixing device 30;62) Inlet gas stream to mixing device 30;63) Inlet gas stream to mixing device 30;64) Outlet gas stream from dispensing device 31;65) Outlet gas stream from dispensing device 31;66) Outlet gas stream from dispensing device 31;67) Outlet gas stream from dispensing device 31;68) Outlet suspension / liquid stream from dispensing device 35;69) Outlet suspension / liquid stream from dispensing device 37;70) Outlet suspension / liquid stream from dispensing device 37;71) Outlet suspension / liquid stream from dispensing device 41;72) Outlet suspension / liquid stream from dispensing device 33;73) Outlet suspension / liquid stream from dispensing device 35;74) Outlet suspension / liquid stream from dispensing device 37;75) Outlet suspension / liquid stream from dispensing device 35;76) Outlet suspension / liquid stream from dispensing device 33;77) Outlet suspension / liquid stream from dispensing device 41;78)Outlet suspension / liquid stream from dispensing device 41;79) Outlet suspension / liquid stream from dispensing device 41;80) Outlet suspension / liquid stream from dispensing device 33;81) Outlet suspension / liquid stream from dispensing device 35;82) Outlet suspension / liquid stream from dispensing device 37;83) Inlet suspension / liquid stream to mixing device 38;84) Inlet suspension / liquid stream to mixing device 38;85) Inlet suspension / liquid stream to mixing device 38;86) Outlet suspension / liquid stream from dispensing device 39;87) Outlet suspension / liquid stream from dispensing device 39;88) Outlet suspension / liquid stream from dispensing device 37;89) Outlet suspension / liquid stream from dispensing device 39;90) Inlet suspension / liquid stream to mixing device 38;91) Inlet gas stream to mixing device 30.In all cases where multiple streams exit from a dispensing device, they may have equal or different flow rates. Streams with a dashed line followed by a dot represent gas or suspension / liquid outlet from reactors 26, 27, 28 and 29 or from mixing devices 19 and 42. Streams with dashed dots represent gas or liquid suspension recycling. The streams with a dotted line represent the inlet of gas or suspension / liquid raw material. Streams with a continuous line represent the streams necessary to achieve operation of one or more reactors in series. The three continuous dots between reactors 28 and 29 and streams 48 to 91, 58 to 63, 59 to 62, 61 to 60, 83 to 82, 84 to 76, 85 to 75, 90 to 79 and after streams 66, 65, 64, 86, 87 and 88 indicate that additional reactors and / or dispenser and mixing devices may be present in between.The black solid lines indicate a minimum number of streams needed to operate such a system in series, where e.g., the outlet of RPB 27 is an inlet to RPB 28. In such a case the same result can be achieved as with a single RPB (e.g., the same characteristics and yields as in the following examples 1 and 2), but using a smaller size RPB. This may be desirable in case the raw material flowrates are very large and it is not technically feasible or advantageous to carry out the reaction in a single RPB. Note that the reaction in this case remains a one- stage reaction as it is completed at the output of the last RPB. It is also possible for the system to work in parallel. This can be achieved by feeding raw materials independently into different RPBs, with the product produced by each RPB being the final product, without it being fed into the next one. Streams with dotted dots represent recycling and can be used to increase the efficiency of the reaction hence reducing the size of the equipment required. Streams with a dotted line followed by a dot represent gas or suspension / liquid extraction from reactors 26, 27, 28 and 29 and can be used to bypass a subsequent reactor, changing the characteristics of the product, providing flexibility in production (e.g., in case of exogenous or endogenous disturbances, changes in demand, etc.). The possibility of exporting product or importing raw materials from intermediate RPBs can allow the production of products of different qualities, also providing great flexibility in production.Figure 2 represents a generalized production structure. As mentioned above, the black continuous lines represent a minimum requirement for the system operation. The remaining material flow streams can be included or ignored, leading to the derivation of a large number of feasible production structures. In this sense, lines consisting of three dots, e.g., between reactors 28 and 29, or the corresponding streams of Figure 2, represent the possibility of introducing other reactors and / or flow streams in between. Note that a production structure can be derived from Figure 2 that has the same operating efficiency as the structure of Figure 1. In particular, the outlet current from the CO2source 1 and its inlet to the device 3 of Figure 1 is equivalent to the sequence of strea ms-devices 17, 18, 45, 26 of Figure 2. The stream exiting the bottom of device 3 and led into and out of vessel 5 and then led into vessel 4 and again into device 3 in Figure 1, is equivalent to the stream exiting reactor 26 in Figure 2 and directed to the stream-device sequence 33, 80, 34, 27, 35, 68, 32, 26, wherein device 27 is not operating, but the stream exiting the mixing device 27 and entering the dispensing device 35 simply passes through device 27. In other words, device 27 simply represents the union of the outlet streams 34 and inlet streams to 35. The stream of Figure 1 that exits device 3, enters device 8 and exits device 8 is equivalent to the stream exiting reactor 26 of Figure 2 and is routed to the sequence of strea ms-devices 21, 49, 19, 44. In Figure 1, the loading with fresh suspension is done through vessel 15and valve 9, leading the stream into vessel 5. Correspondingly, in Figure 2, this can be done through the stream-device sequence 40, 41, 71, 32. In Figure 2 the auxiliary equipment of pumps, valves and gauges is omitted because it is assumed that they will be available and used without changing anything in the final product.Example of a structure with three RPBs and recirculation and bypass streams for operation in seriesSuch a structure may consist of the sequence of stream-devices 17, 18, 45, 20, 26, 21, 57, 22, 27 , 23, 56, 24, 28, 25, 51, 19, 44 for the gas side. Correspondingly for the suspension / liquid side it may consist of stream-device sequence 40, 41, 71, 32, 26, 33, 80, 34, 27, 35, 81, 36, 28, 37, 74, 42, 43. Also, assuming a bypass stream of the reactor for the gas, the sequence of stream-devices 26, 21, 55, 24, 28 is added. Assuming a recycle stream from reactor 28 to 26 for the suspension / liquid, the sequence of stream-devices s 28, 37, 69, 69, 32, 26 is added.Example of a parallel operation structure with two RPBSuch a structure may consist of the sequence of stream-devices 17, 18, 45, 20,26, 21, 49, 19, 44 and 17, 18, 46, 22, 27, 23, 50, 19, 44 for the gas. Similarly, for the suspension / liquid 40, 41, 71, 32, 26, 33, 72, 42, 43 and 40, 41, 77, 34,27, 35, 73, 42, 43.With corresponding combinations, a large number of structures can be obtained. Note that Figure 2 may include either cocurrent or countercurrent flow devices or both at the same time, if desired. The cocurrent and countercurrent flow regimes are determined by the internal arrangement of the RPBs 26, 27, 28, 29 of Figure 2 described in Figures 3 and 4. The case of simultaneous cocurrent- and countercurrent flow refers to the possibility of having at least one or more RPBs in the diagram in Figure 2 operating in cocurrent flow mode and correspondingly one or more RPBs in the same diagram operating in countercurrent flow mode.

[0011] Figure 3 shows the flow pattern that is developed inside the RPB reactor when it is operating in cocurrent flow mode. The term "cocurrent flow" means that both the suspension (S) and gas (G) are fed from the same concentric tube, with the suspension fed through opening (92) toward and through the internal tube (94) of the concentric setup and the gas fed through opening (93) toward and through the annulus of the concentric setup. The suspension and the gas enter and pass through the packing material (96) in the same radial direction towards the RPB shell (97). The raw material suspension is fed through the reactant pump toward the centre of the reactor. Specifically, from the internal tube (94) of the concentric setup, the rawmaterial suspension is distributed through openings toward the packing material (96) radially and towards the shell (97). It is collected at the bottom of the shell, from where it leaves the reactor through an outlet opening (99). At the same time the CO2source gas is fed into the RPB reactor through opening (93) toward and through the annulus of the concentric setup. Through the concentric setup's cross-sectional area (95) it is introduced into the space that is between the packing material and externally of the concentric setup. It permeates the packing material under the influence of a small pressure gradient in the direction of the RPB shell. Finally, the part of the CO2gas source not captured by the reaction in the suspension of raw material leaves the reactor through a side opening of the shell (98). In addition to the above, Figure 3 shows the rotor rotational axis (100). The above description and operation of the entire setup depicted in Figure 3 is also valid even if the setup is rotated by 90° clockwise or 90° counter-clockwise with respect to a vertical axis that starts from point (92) and crosses the setup up to point (100).

[0012] Figure 4 shows the flow pattern that is developed inside the RPB reactor when it is operating in countercurrent flow. The term "countercurrent flow" means that the suspension (S) is fed through opening (101) and then through the internal tube (103) of the concentric setup and flows through the packing material (105) in the direction of the shell (106), while the gas (G) is introduced through the side opening (102) in the shell (106), flows through the packing material toward the concentric setup, passes from the annulus of the concentric setup and exits the assembly through the gas outlet (108). The suspension of the raw material is fed through the reactant pump toward the center of the reactor. In particular, from the inner tube of the concentric setup (103), the suspension of the raw material is distributed through openings toward the packing material (105) radially and towards the shell (106). It is collected at the bottom of the shell, from where the flow leaves the reactor through an outlet opening (107). At the same time the CO2source gas is fed into the RPB reactor through a side opening of the shell (102). After occupying the available volume inside the shell, under the influence of a small pressure gradient it flows through the packing material towards the center, where the concentric setup is located. It enters the annulus of the concentric setup through its cross-sectional area (104), flows through the annulus and leaves the reactor from opening (108). The whole system rotates around the rotor rotational axis (109). The above description and operation of the entire setup depicted in Figure 4 is also valid even if the setup is rotated by 90° clockwise or 90° counter-clockwise with respect to a vertical axis that starts from point (101) and crosses the setup up to point (109).On the surface of the packing material, the suspension of the raw material (magnesium oxide or magnesium hydroxide) and the gaseous source CO2come into contact. Upon contact, the CO2binding reaction takes place, and hydromagnesite is formed. The one-step reaction that occurs when the raw material is an aqueous suspension of magnesium oxide (MgO) is as follows:SMgO + SH2O + SCO2M^5(CO3)4(O / f)2• 4tf2O + CO2(4)Similarly, when the raw meterial is an aqueous suspension of magnesium hydroxide (M#(0H)2) it is:5Mg(OH)2+ H2O + SCO24MgCO2■ Mg(0tf)2• 4tf2O + CO2+ 10tf20 (5)The progress of the reaction is monitored by monitoring and recording the pH and temperature of the reactant stream, by collecting a sample of the suspension at regular intervals. At the same time, the volumetric delivery of CO2to the outlet is monitored and recorded, and the CO2consumption is calculated. The operation of the device shall be stopped (interruption of CO2supply and circulation of the suspension) when it is found that the suspension has been completely neutralized, i.e., when the pH value becomes equal to 7. This means that the raw material has been completely converted into hydromagnesite. A final quantity of sample is collected, from which the solid product of the hydromagnesite is recovered by filtration. The solid product is then dried in an air-drying oven in an air atmosphere. The dried, solid product of hydromagnesite obtained in the form of a paste is then subjected to a structural and property characterization.The following examples of applications of the present invention are given by way of illustration. The invention is not limited to these. The physicochemical properties of the hydromagnesite particles were determined by the methods described below.(1) Compositional identification by X-ray diffraction and fluorescence spectroscopy. Identification of carbonate content by thermostat analysis.(2) Particle morphology by scanning electron microscopy.(3) Particle size by dynamic light scattering and particle thickness analysis with Image J scanning electron microscopy image processing software.(4) Particle size distribution by laser beam diffraction in water.(5) Special surface with nitrogen sorption.(6) Porosity and porosity characteristics (total pore volume, micro-porosity and average pore size) by nitrogen porosimetry.(7) Bulk density of powder (free) by conventional method after partial deagglomeration.

[0013] Figure 5 is a diagram showing the change in pH of the suspension with carbonation time.

[0014] Figure 6 is an X-ray diffraction image that identifies the structure of the hydromagnesite in the product described in Example 2.

[0015] Figure 7 is the negative of a scanning electron microscope photograph of a product resulting from the experimental procedure described in Example 2. Leaf-shaped particles of two dimensions of a few nanometers in thickness can be seen. The data / settings at the time of taking the picture are as follows: SED 20.0 kV, WD: 10.6 mm, Std.-PC: 40.0, HighVAc: x5,000, STD 7156.

[0016] Figure 8 is a diagram showing the particle size distribution with an average thickness of 61 nm for a product synthesized with a combination of functional parameters in the range described in Example 2.

[0017] Figure 9 is a diagram showing the particle size distribution with an average thickness of 44 nm for product synthesized with different combination of functional parameters in the range described in Example 2.Embodiment of the inventionExample 1: Production of hydromagnesite from MgO suspension in one step

[0018] A quantity of 30 L of MgO suspension, at a concentration of 10 - 50 g / L, is introduced into the system. Heating is carried out with simultaneous circulation of the suspension in the apparatus until the minimum desired reaction temperature is reached. A rotational speed in the range 600 - 1800 rpm is applied. A gaseous source of CO2of 5 to 100 % by volume is added. The flow rate of the gas stream carrying CO2is adjusted so that the ratio [volumetric suspension flow rate / volumetric gas flow rate] or [S / G] is in the range 0.57 - 1.58. The pressure inside the rotating packed bed reactor is atmospheric. The change in pH of the suspension at the outlet of the reactor is recorded (the pH follows a decreasing trend from the initial pH value of 9.8 - 10.0). The CO2flow rate at the outlet (corresponding to CO2not reacted) is recorded. The suspension circulation and the gas supply continue until the pH is neutralized and the suspension becomes slightly acidic (pH 6.5<pH<7). The reaction time varies (80 - 250 min) depending on the selected operating conditions. The efficiency of using the CO2also varies depending on the operating conditions, but remains consistently high (92.2 % - 99.5 %) in contrast to the case where the hydromagnesite is produced with conventional equipment (CSTR). At the end, a sample of the suspension is collected fromthe product container and the solid product is removed by filtration. This is followed by drying at a temperature of 105 °C to 120 °C in air.X-ray analysis confirms the chemical composition of hydromagnesite, with a carbonate content of 35.7 - 37.8 %. Scanning electron microscopy shows primary particles of foliated morphology (two-dimensional sheets) organized in secondary spherical clusters (encapsulated structures). The primary particles of hydromagnesite show an average thickness of 31-69 nm, an average width of 2.5-3.0 pm with standard distribution deviations of 6.77-14.62 nm. The thickness dimension varies with the operating conditions, mainly depending on the rotational speed and the [S / G] ratio. In the same range of operating conditions, the product is characterized by a free bulk density of 51 - 173 g / cm3, specific surface area of 19 - 40 m2 / g, average pore volume of 0.08 - 0.17 cm3 / g.Example 2: Different conditions

[0019] A quantity of 30 L of MgO suspension (30 g / L) is introduced into the system. Heating is carried out with simultaneous circulation of the suspension through the apparatus until the desired minimum reaction temperature is reached. A rotational speed in the range 600 - 1800 rpm is applied. A gaseous source of CO2of 100 % by volume composition is added at a flow rate such that the S / G ratio [volumetric suspension flow rate / volumetric gas flow rate] is in the range 0.57 - 1.58, preferably in the range 0.9 - 1.58. The change in pH of the suspension at the outlet of the reactor (the pH follows a decreasing trend from the initial pH value of 9.8 - 10.0) (Figure 5) is recorded. Finally, a sample of suspension is collected and the solid product is removed by filtration. This is followed by rinsing with water and drying at 105 °C- 120 °C, preferably in the range 105 °C-110 °C. X-ray analysis confirms the chemical composition of the hydromagnesite (Figure 6), while scanning electron microscopy shows primary particles of leaf-shaped morphology (two-dimensional sheets) organized in secondary spherical clusters (encapsulated) structures (Figure 7). Below this reaction temperature the primary particles of hydromagnesite exhibit an average thickness of 61 nm (Figure 8), with a size distribution range for the different products in the range 25 - 53 nm, an average width of 2.5 - 3.0 pm and a standard deviation of distribution of 6.77 nm. The utilization efficiency of CO2is in the range 96.2 % - 99.5 %. With different combinations of operating parameters (rotational speed and [S / G] ratio) within the same range, a product with a particle distribution with an average thickness of 44 nm is obtained (Figure 9). Note that for the ranges of conditions mentioned in the two examples, in addition to Figures 8 and 9, consistently and repeatably corresponding normal nanoparticle thickness distributions with small standard deviations have been obtained.

Claims

CLAIMS1. A method of producing hydromagnesite (Mg5(CO3)4(OH)2• 4W20) characterized by a one-step chemical reaction of carbonation of magnesium oxide or magnesium hydroxide whereby: a) a stream carrying carbon dioxide (CO2) is mixed and reacts with a suspension of magnesium oxide or magnesium hydroxide; b) the mixture of the carbon dioxide stream and the magnesium oxide or magnesium hydroxide suspension is in contact with packing material contained in a reactor and is rotated inside the packing material of the said reactor, where a centrifugal field is developed; c) the carbon dioxide and magnesium oxide or magnesium hydroxide suspension streams interact either cocurrently or countercurrently, and their contact promotes and increases the speed of the chemical reaction of carbonation of the magnesium oxide or magnesium hydroxide suspension and the nucleation of hydromagnesite, resulting in the crystallization of hydromagnesite.

2. A method according to claim 1, characterized in that the feedstock is a hydrated suspension of magnesium oxide (MgO) or magnesium hydroxide (M^(0 / f)2) and CO2irrespectively of its source.

3. A method according to the preceding claims, characterized in that the minimum concentration of the aqueous MgO suspension is higher than the solubility limit of pure MgO in water (8.6 mg / l) at 25 °C or, respectively, the concentration of magnesium hydroxide is higher than the solubility limit of pure Mg(0ff)2in water (6.54 mg / l) at 25 °C.

4. A method according to the preceding claims, characterized in that the minimum temperature for the reaction is 40 °C.

5. A method according to the preceding claims, characterized in that the minimum rotational speed of the reactor bed is 10 rpm.

6. A method according to the preceding claims, characterized in that the minimum liquid volumetric flow rate / volumetric CO2flow rate ratio is 0.01.

7. A method according to the preceding claims, characterized in that it results in the attainment of monodispersity, up to 100% purity in the hydromagnesite crystal structure and repeatable and consistently regular nanoparticle thickness distributions with small standard deviations.

8. A method according to the preceding claims, characterized in that the method can be performed in batch or continuous operation.

9. A method according to any of the preceding claims, wherein the reaction can be achieved in multiple reactors arranged either in series or in parallel with multiple combinations.

10. A system, used to perform the method of the preceding claims, comprising a CO2source (1); a gas flow regulator (2); a reactor (3), a reactant vessel (4); a product vessel (5); a product vessel outlet pump (6); a reactant vessel outlet pump (7); a gas flow meter (8); a three-way valve at the outlet stream of the reactor (9); a three-way valve at the outlet stream of the product vessel (10); a three-way valve at the outlet stream of the reactant vessel (11); a reactant vessel temperature gauge (12); a product vessel temperature gauge (13); a sampling point from the outlet stream of the reactant vessel (14); sampling point from the reactor outlet stream (15) after the three-way valve (arrow direction from the valve to the vessel) or loading the vessel 5 through the three-way valve with fresh suspension (arrow direction from the vessel to the valve); a sampling point from the outlet stream of the product vessel (16); and characterized in that the reactor (3) has a rotating bed with packing material (96) or (105).

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