WO2010043730A1

WO2010043730A1 - Silica and larnite powder aerogel composite material and use thereof in the storage and fixing of gases

Info

Publication number: WO2010043730A1
Application number: PCT/ES2009/000308
Authority: WO
Inventors: Alberto SANTOS SÁNCHEZ; Luis María ESQUIVIAS FEDRIANI; Mohamed Ajbari; Manuel PIÑERO DE LOS RÍOS
Original assignee: Universidad De Cádiz
Priority date: 2008-10-16
Filing date: 2009-06-02
Publication date: 2010-04-22
Also published as: ES2336996A1; ES2336996B2

Abstract

A silica and larnite powder aerogel composite material is described, obtainable through mixing larnite powder (the surface whereof is chemically modified by an aminosilane) with a sol obtained through hydrolysis and polycondensation of a silane. Said material may be utilised in the storage and fixing of gases, particularly CO₂.

Description

AEROGEL COMPOSITE MATERIAL OF SILICA AND DUST OF LARNITA AND ITS USE IN THE STORAGE AND FIXATION OF GASES

FIELD OF THE INVENTION The present invention relates to a composite material of silica airgel and larnite powder, a process for obtaining it and its applications; in particular, with its use in the storage and fixation of gases, especially CO ₂ .

BACKGROUND OF THE INVENTION In the storage and fixation of carbon dioxide (CO ₂ ), one of the most promising technologies is related to the fixation of said gas in the form of inorganic and insoluble carbonates. This fixation is achieved through a chemical reaction, known as mineral carbonation.

In carbonation reactions, CO ₂ reacts with materials (mostly silicates) that have metal oxides (typically alkaline earth metals) in their composition, thus forming the corresponding carbonate and silica (SiO ₂ ) as a by-product. However, these reactions are very slow when they occur in natural environments, so that the studies that currently implement these reactions require the addition of an intensive energy (activation), to make the minerals more reactive. Ultimately, adding activation energy pursues this storage technology evolves from a study or development stage to another stage that is intended to fixation of CO ₂ to a massive scale economically feasible.

Within this evolution, certain recently published works stand out (Wu et al. Ind. Eng. Chem. Res. 2001, 40: 3902 and Tai et al. AIChE J. 2005, 52: 292). In them it is possible to highlight, for different experimental protocols, the values obtained in the conversion rate wollastonite (CaSiθ ₃ ) / calcite (CaCO ₃ ), where wollastonite and calcite are mineral phases. These values should be interpreted as a measure of the efficiency in the fixation of CO ₂ by minerals, from the conversion of Ca from silicate to Ca from carbonate, after the carbonation reaction has occurred. Thus, Wu et al. (quoted above), based on a sample of wollastonite ore, pulverized in a reactor at atmospheric pressure and room temperature, have obtained Conversion values (carbonation reaction) of 14% in 22 days of the experiment.

Subsequently, comparative studies have been carried out analyzing different types of samples and experimental conditions (Zevenhoven et al. Catal. Today 2006, 115: 206), obtaining more promising results. Among them, those obtained from magnesium silicate (O 'Connor et al. Proceeding of the 27th Int. Conf. On Coal utilization and Fuel system 2002, 819) with sample also pulverized, and in reactors with high conditions pressure and temperature, reaching 80% values in the conversion reaction for 1 hour of the experiment. The experimental variables that have allowed such protocols to obtain such promising results include the spraying of the sample, the chemical species present in the aqueous solution where the reaction with CO ₂ occurs, as well as the conditions of high pressure and temperature.

Tests have also been carried out with synthesized samples. Previous studies (Ahmed et al App Thermal Eng 1998, 18:.... 787) have demonstrated the usefulness of aerogels in CO ₂ fixation. For this, they have followed the preparation of alcogels (gels whose hydrolysis occurs in alcoholic medium) by sol-gel processing (processing of solutions that involve polymerization through reactions of hydrolysis and polycondensation of silicates), containing CaO ₅ MgO and SiO ₂ , and subsequent supercritical drying (solvent extraction method contained in the pores of the gel, which takes advantage of the supercritical conditions where the gas-liquid interface disappears and the resulting tensions on the pore walls). In that article, reference is only made to the fact that aerogels (generally silica gels dried under the conditions described above) are adsorbents effective in capturing a mixture of gases from a simulated emission flow system.

Subsequently, the inventors' research group (Santos et al. Ind. Eng. Chem. 2007, 46: 103), has synthesized a composite material with a CaO content of 40% by weight, consisting of synthetic wollastonite powders (CaSiO ₃ ) chemically modified with 3-aminopropyltrimethoxysilane (APTMS) encapsulated in a silica airgel matrix. The composite material, introduced in a reactor at atmospheric pressure and temperature, allows to obtain values in the wollastonite / calcite conversion rate greater than 80%, in an approximate period of time 40 minutes of CO ₂ flow. Subsequently, the attacked samples were allowed to stand in the reactor until they were analyzed. The relevant factor in the process was the nanometric grain size of the powder and the reactive surface of the composite material, wollastonite powders acting as the active phase to trigger the reaction. Apart from the results provided and obtained, the difference between the works of

Ahmed et al. 1998 (cited supra) and Santos et al. 2007 (quoted above) is that the material synthesized for the reaction with CO ₂ is different. In the first one, the airgel is synthesized directly, while in the second, synthetic wollastonite powders were used, which were subsequently added to a previously prepared polymerizing silica sol, and, as a final result, a composite material was obtained in which the Powders are encapsulated in a silica airgel matrix. On the other hand, the difference with respect to the first works cited (Wu et al. 2001, Tai et al. 2005, Zevenhoven et al. 2006 and O'Connor et al. 2002, cited above), is that these studies are performed with natural samples sprayed and under conditions of high pressure and temperature. However, in the case of Santos et al. 2007 (cited above), all the components of the samples are synthetic, so that it allows to act on the textural characteristics (porosity, specific surface of the compound and grain size of the ore powders) and the carbonation reaction takes place under pressure atmospheric and ambient temperature. In another work published by the research group of the inventors (Santos et al. J. Sol-Gel Sci. Tech. 2008, 45: 261), whose objective is to optimize costs in the processing of composite material, describes the obtaining of composite materials by adding to a silica sol, Wollastonite powders modified with APTMS. However, in this experimental procedure a double route was followed; in the first, natural Wollastonite powders modified with APTMS were added to the silica sol, obtaining a composite material whose CaO content was 29% by weight; and, in the second, synthetic powders of Wollastonite modified with APTMS were added to said silica sol, obtaining a composite material with a CaO content of 19% by weight. In both cases equivalent results have been obtained in the reaction rate for a CO ₂ flow time of 30 minutes. Samples were also left in the reactor at rest for a few hours until analyzed. Finally, in a post-previous work, and still in digital version (Santos et al. J. Sol-Gel Sci. Tech. 2008, DOI: 10.1007 / sl0971-008-1719-y), some details that complement the previous studies. The samples are equivalent to those already described. Only the variation of the reaction rate during the time that the samples were subjected to a CO ₂ flow of 15, 30 and 40 min is explained. In this study, velocity values comparable to previous studies are obtained, but it is detailed that the highest velocity is obtained in the first 15 minutes of flow, and when the attacked samples remain in the reactor in rest conditions for a few hours (12 hours), before being analyzed. Although the articles published by the inventors' research group mention the by-product obtained in the carbonation reaction, identifying its components, there is no reference to any subsequent treatment applied to said by-product or to the result obtained with that treatment.

On the other hand, the use of dicalcium silicate (Ca ₂ SiO ₄ ), known as larnite or bellite (mineral phase) according to different authors, in the fixation of gases type CO ₂ , is referenced by different authors. Such gas fixation studies (Young et al. J. Am. Ceram. Soc. 1974, 57: 394; Bukowski et al. Cem. Conc. Res. 1979, 9:57; Goodbrake et al. J. Am. Ceram Soc. 1979, 62: 168; Goto et al. J. Am. Ceram. Soc. 1995, 78: 2867; Shtepenko et al. Chem. Eng. J. 2006, 118: 107) were made with that mineral (larnite or bellita), either as a component of cement or as an individual mineral component. In the last article cited, the synthesis is carried out from the reactive grade mixture of silica and carbonate, subsequently sintered to 1,400-1,500 ⁰ C, that is, densified by heat treatment; said mixture, in the presence of water, is placed in a carbonation chamber at a pressure of 2 bar (2x10 ⁵ ^• Pa), and for 60 minutes it is subjected to a flow of CO ₂ . The resulting material is dried and ground. This procedure is repeated 5 times until the entire sample of the entire mixture has reacted.

In addition to this, and in view of an alternative synthesis method to the conventional method of high temperature manufacturing of cement components, there are several references on synthesis of larnite (Hong et al. J. Am. Ceram. Soc. 1999, 82 : 1681; Chrysafi et al. J. Eur. Ceram. Soc. 2007, 27: 1707). In both and in relation to the synthesis, only the experimental procedure and the product obtained are described. In Specifically, in the most recent, the process comprises obtaining a gel from the mixture of different reagents or tetraethoxysilane (TEOS) and calcium nitrate tetrahydrate or a 30% silica sol in water and calcium nitrate tetrahydrate and subsequent heating at 1000 ⁰ C for larnite amorphous gel.

DETAILED DESCRIPTION OF THE INVENTION

1. Definitions

The term "larnite", as used herein, refers to dicalcium silicate (Ca ₂ SiO ₄ ), also known as bellite, a mineral scarce in natural media and, together with tricalcium silicate, the fundamental components of Portland cement.

The term "airgel", as used herein, refers to a mesoporous material obtained by a sol-gel process followed by drying under supercritical conditions. ,

The term "supercritical conditions", as used herein, refers to conditions of pressure and temperature above the critical point of a given substance, such that said substance acquires intermediate properties between a liquid and a gas; Thus, for example, a supercritical fluid has a high diffusivity like gases and a high solvation power like liquids. The supercritical conditions for extracting the ethanol according to the present invention correspond to a temperature greater than 243 ° C and a pressure greater than 63.6 bar (63.6 x ⁵ Pa). In a particular embodiment, the supercritical conditions used to form the composite material of the invention correspond to 255 ⁰ C and 90 bar (9OxIO ⁵ Pa) (Example 2).

The term "sun", as used herein, refers to a colloidal system whose dispersion medium is a liquid or a gas; specifically, in the present invention, the tetraethoxysilane polycondensation and polycondensation product (TEOS) is dispersed in a liquid hydrolysis medium.

2. Composite material of silica airgel v larnite powder

In one aspect, the invention relates to a material composed of silica airgel and larnite powder, hereinafter "composite material of the invention", obtainable by mixing larnite powder whose surface has been chemically modified with an aminosilane selected from (3-aminopropyl) -triethoxysilane (APTES), (3-aminopropyl) -dimethyl-ethoxy silane (APMES), (3-aminopropyl) -trimethoxy-silane (APTMS), (3-aminopropyl) -diethoxymethylsilane (APDEMS) and mixtures thereof, with a sol obtained by hydrolysis and polycondensation of tetraethoxysilane (TEOS).

In a particular embodiment, said aminosilane is selected from APTES, APMES and mixtures thereof; preferably, said aminosilane is APTES.

In a particular embodiment, said composite material of the invention has the following composition:

(1-X) SiO ₂ - X CaO where x is a number between 0.34 and 0.62. The higher value of said range ("x" = 0.62) indicates a chemical composition that is within the range of the natural mineral phase. In this sense, a greater percentage by weight of CaO implies a greater amount of the available divalent cation to react with CO ₂ , and, therefore, a greater consumption (fixation) of said gas per kg of material. In a particular embodiment, the invention provides a composite material of the invention in which "x" is 0.34. In another particular embodiment, the invention provides a composite material of the invention in which "x" is 0.44. In another particular embodiment, the invention provides a composite material of the invention in which "x" is 0.62. Illustrative, non-limiting examples of composite materials of the invention include: a composite of silica airgel and larnite powder whose surface is chemically modified with APTES, and whose chemical composition comprises between 62% and 61% by weight of CaO and between 38% and 39% by weight of SiO ₂ ; a composite of silica airgel and larnite powder whose surface is chemically modified with APTES, and whose chemical composition comprises 44% by weight of CaO and 54.98% by weight of SiO ₂ ; - a composite material of silica airgel and larnite powder whose surface is chemically modified with APTES, and whose Chemical composition comprises 40.48% by weight of CaO and 58.38% by weight of SiO ₂ ; and a composite of silica airgel and larnite powder whose surface is chemically modified with APTES, and whose chemical composition comprises 34.33% by weight of CaO and 64.70% by weight of SiO ₂ .

3. Procedure for obtaining composite material of silica airgel and larnite powder (composite material of the invention) In another aspect, the invention relates to a process for obtaining the composite material of the invention, hereinafter "process of the invention ", which comprises contacting larnite powder, the surface of which is chemically modified with an aminosilane selected from (3-ammopropyl) - triethoxysilane (APTES), (3-aminopropyl) -dimethyl-ethoxy silane (APMES), (3- aminopropyl) -trimethoxysilane (APTMS), (3-aminopropyl) -diethoxymethylsilane (APDEMS) and mixtures thereof, with a sol obtained by hydrolysis and polycondensation of tetraethoxysilane (TEOS).

3.1 Larnite powder In a particular embodiment, the larnite powder used in the implementation of the process of the invention is a synthetic larnite powder, that is, a powder obtained from the synthesis of larnite, since this mineral is Scarce in nature.

Synthetic larnite powder can be obtained by different methods (Hong et al. J. Am. Ceram. Soc. 1999, 82: 1681; Chrysafi et al. J Eur Ceram Soc 2007, 27: 1707). However, in a particular embodiment, the synthetic larnite powder is obtained by a process comprising: a) mixing a source of silicon with a source of calcium, in the presence of a solvent; b) remove the solvent used in step a); c) drying the product obtained in step b); d) crush the product obtained in step c); Y e) subject the product obtained in step d) to a heat treatment to obtain synthetic larnite powder.

In step a) a source of silicon is mixed with a source of calcium, in the presence of a solvent. Virtually any source of suitable silicon can be used to obtain synthetic larnite powder according to the above procedure. In a particular embodiment, said source of silicon is silicon dioxide (silica), typically in the form of a colloidal solution, such as an aqueous colloidal silica solution. The concentration of silica present in said colloidal solution may vary within a wide range, typically between 25% and 40% by weight. In a specific embodiment, a 30% aqueous silica colloidal solution is used (Example

one). Alternatively, the source of silicon is a product resulting from the hydrolysis of an alkoxysilane.

Likewise, any suitable calcium source can be used to obtain synthetic larnite powder according to the above procedure. Illustrative, non-limiting examples of calcium sources include calcium salts, e.g., calcium nitrate, calcium chloride, etc. In a particular embodiment, an aqueous solution of calcium nitrate tetrahydrate is used as the source of calcium.

The sources of silicon and calcium are mixed, in appropriate stoichiometric amounts, depending on the synthetic larnite powder to be obtained, generally choosing molar relationships between said silica and calcium sources that allow obtaining synthetic larnite powders with a chemical composition close to that of the natural phase.

In this sense, although the Si / Ca molar ratio in the synthetic larnite powder can vary over a wide range, in a particular embodiment, the synthetic larnite powder has a Si / Ca molar ratio between 0.5 and 1. Thus, in a particular embodiment, a synthetic larnite powder with a molar ratio is obtained.

Si / Ca of 0.5; In another particular embodiment, a synthetic larnite powder with a Si / Ca molar ratio of 1 is obtained.

The mixing of said sources of silicon and calcium is carried out in the presence of an appropriate solvent, optionally, with the help of ultrasound. Illustrative, non - limiting examples of such solvents include ethylene glycol (EG) ₅ polyvinyl alcohol (PVA), polyethylene glycol (PEG), etc., and mixtures thereof with water, preferably in aqueous solution EG. In a particular embodiment, the mixture of Sources of silica and calcium are carried out in the presence of an aqueous solution of ethylene glycol. In general, the use of such solvents is intended to ensure the presence of hydroxyl groups in order to inhibit contact between cations and prevent agglomeration and precipitation. Optionally, if desired, ultrasound can be used in order to reduce, to some extent, the use of said solvent. The use of EG allows to obtain larnite powders with less amorphous component which is indicative that the reaction between the source of silicon and the source of calcium is more complete.

Once the mixture between the silica source and the calcium source has been carried out, the solvent used is removed [step b)]. The removal of said solvent, which can be carried out by conventional methods, for example, by evaporation under suitable conditions, results in a product that is typically a gel. In a particular embodiment, when the solvent comprises an aqueous solution of EG, solvent removal is conducted by heating at a temperature of 100 ⁰ C, with stirring, to evaporate all the solvent.

Then, in step c), the product (gel) obtained after removal of the solvent in step b) is dried. In general, drying is carried out in conventional equipment under conditions that do not alter the product. In a particular embodiment, said gel is dried in an oven at a temperature of about 100 ⁰ C for about 48 h.

Then, the product obtained after drying the gel is crushed [step d)] to obtain an amorphous powder with a particle size of the order of tens of microns, for example, between 10 and 100 microns, and, finally, said material (amorphous powder) It undergoes a heat treatment to remove organic residues that are present and obtain the crystalline phase of larnite. In a particular embodiment, said heat treatment comprises heating said material (amorphous powder) with a heating rate of 5 ° C / min to a temperature of 600 ⁰ approximately C and hold at that temperature for about 1 hour, thereby a powder is obtained whose characterization both at the level of composition and at the mineralogical level shows that it is synthetic larnite powders (Example 1). 3.2 Chemical modification of the surface of the larnite powder

For use in the process of the invention, the larnite powder is subjected to a treatment intended to chemically modify its surface with a surface modifying agent, such as an aminosilane commonly used in this sector of the art, for example, APTES, APMES, APTMS, APDEMS ₅ etc., or their mixtures in order to stabilize their dispersion on a colloidal scale. In a particular embodiment, said aminosilane is selected from APTES, APMES and mixtures thereof; preferably, said aminosilane is APTES.

To chemically modify the surface of the larnite powder, it is contacted with said aminosilane in the presence of a solvent, such as an alcohol, for example, methanol or ethanol. The mixing of the aminosilane with the larnite powder is carried out under conditions that facilitate their intimate contact, for example, by the use of ultrasound or by the use of a mechanical stirring device, a high speed disperser (10,000 rpm), etc. In a particular embodiment, the mixing of the aminosilane with the larnite powder is carried out by means of the use of ultrasound, for example, providing a power of approximately 0.6 W-cm ^"3 , during a soundproofing time of approximately 10 minutes (Example 2).

The suspension of solid particles (slurry) obtained after mixing the aminosilane with powder larnite centrifuged and dried under suitable conditions, for example, 100 ⁰ C for 48 hours in conventional equipment (eg, wood), conditions they allow to obtain larnite powder whose surface has been chemically modified with a surface modifying agent, such as an aminosilane (eg, APTES, APMES, APTMS, APDEMS, etc., or mixtures thereof), that is, to a reaction between the groups hydroxyl present on the surface of the larnite powder and the alkoxy, eg, ethoxy (APTES, APMES, APDEMS) or methoxy (APTMS) groups to give rise to surface modifications that sterically prevent the approach to other dust particles, stabilizing the colloidal size of this. Said product obtainable by chemical modification of the surface of the larnite powder with an aminosilane selected from APTES, APMES, APTMS, APDEMS and mixtures thereof, constitutes a further aspect of the present invention. In a particular embodiment, said aminosilane is selected from APTES, APMES and mixtures thereof; preferably, said aminosilane is APTES. 3.3 Procedure of the invention

Larnite powder whose surface has been chemically modified with said surface modifying agent, such as an aminosilane commonly used in this sector of the art, for example, APTES, APMES, APTMS, APDEMS, etc., or mixtures thereof, is put in contact with a sun obtained by controlled hydrolysis and polycondensation of TEOS. Hydrolysis consists in the rupture of the TEOS molecule by the action of water, followed by polymerization of resulting units to give rise to a three-dimensional network of silica, the basis of the colloidal particle structure. In a particular embodiment, the hydrolysis and polycondensation of TEOS is carried out in the presence of an acid, such as an inorganic acid, eg, nitric acid (since it acts as a reaction catalyst), etc., and a solvent, such as a alcohol, eg, ethanol (since it favors the mixture between alkoxide and water, initially immiscible), etc., under conditions that allow the formation of said sun, for example, by the use of ultrasound, or, alternatively, in the absence of ultrasound, by mechanical agitation, although in this case the reaction time is usually longer. In a particular embodiment, the hydrolysis and polycondensation of TEOS is carried out with the help of ultrasound, for example, providing a power of approximately 0.6 W-cm ^" , during a soundproofing time of approximately 20 minutes (Example 2).

In a particular embodiment, the hydrolysis and polycondensation of TEOS is carried out in the presence of an aqueous solution of nitric acid and ethanol; In a specific embodiment, a sun is obtained that maintains a stoichiometric ratio TEOSrH ₂ OrHNO ₃ IEtOH = 1: 4: 0.03: 1.6. In another particular embodiment, the hydrolysis and polycondensation of TEOS is carried out in basic medium, in the presence of a solvent, such as an alcohol, eg, methanol.

Alternatively, the hydrolysis and polycondensation of TEOS can be performed using ultrasound, without the need to use any solvent. In a particular and preferred embodiment, the mixture of the larnite powder whose surface is chemically modified with a surface modifying agent, such as an aminosilane commonly used in this sector of the art, for example, APTES ₅ APMES, APTMS, APDEMS, etc., or mixtures thereof, with the sun resulting from the controlled hydrolysis and polycondensation of TEOS is carried out under the action of ultrasound, advantageously, high power ultrasound (ultrasonic radiation in the frequency range of 20 KHz) so that the gelation time is short enough to prevent the decantation of the dispersed solid phase.

After mixing the larnite powder whose surface has been chemically modified with said surface modifying agent, such as an aminosilane commonly used in this sector of the art, for example, APTES, APMES, APTMS, APDEMS, etc., or mixtures thereof With the sun obtained by controlled hydrolysis and polycondensation of TEOS, a wet gel is obtained which is suitably treated to remove the solvent used in the production of the sun in order to obtain the airgel. The removal of said solvent can be carried out by conventional methods depending on the solvent to be removed. In a particular embodiment, solvent removal is carried out in an autoclave under supercritical conditions for solvent extraction. In a specific embodiment, the solvent is ethanol and the supercritical conditions comprise heating at 255 ⁰ C and 90 bar (9OxIO ⁵ Pa).

The material resulting from the removal of the solvent (eg, the material extracted from the autoclave), is subjected to an appropriate heat treatment to obtain the composite material of the invention. In a particular embodiment, said heat treating comprises heating said material resulting from removal of the solvent at a temperature of 600 ⁰ C, with a heating rate of 5 ° C / min and maintaining it at that temperature (600 ⁰ C) for about 1 hour, whereby the composite material of the invention is obtained, that is, a composite of silica airgel and larnite powder.

Depending on the amount of larnite powder with the chemically modified surface with said surface modifying agent, such as an aminosilane commonly used in this sector of the art, for example, APTES, APMES, APTMS, APDEMS, etc., or mixtures thereof , added to the sun resulting from controlled hydrolysis and polycondensation of TEOS, composite materials of the invention of different composition are obtained. In a particular embodiment, different amounts (2.5 g; 5 g and 10 g), respectively, of synthetic larnite powder have been added with a Si / Ca molar ratio of 1, whose surface had been modified with APTES, to said sun obtained by controlled hydrolysis and polycondensation of TEOS (Example 2.1). In another particular embodiment, 15 g of synthetic larnite powder with a Si / Ca molar ratio of 0.5, whose surface had been modified with APTES, has been added to said sol obtained by controlled hydrolysis and polycondensation of TEOS (Example 2.2) .

Synthetic larnite powders and composite materials of the invention thus obtained can be characterized at the textural, compositional and mineralogical level, by using conventional techniques, such as, for example, X-ray Fluorescence (FRX), Ray Diffraction X (DRX), Brunauer-Emmet-Teller (BET) method and X-ray dispersive energy analysis (EDX) coupled to a Scanning Electron Microscope (MEB).

Illustrative, non-limiting examples of composite materials of the invention include: - a composite of silica airgel and larnite powder whose surface is chemically modified with APTES, and whose chemical composition comprises 62-61% by weight of CaO and 38- 39% by weight of SiO ₂ ; a composite of silica airgel and larnite powder whose surface is chemically modified with APTES, and whose chemical composition comprises 44% by weight of CaO and 54.98% by weight of SiO ₂ ; a composite of silica airgel and larnite powder whose surface is chemically modified with APTES, and whose chemical composition comprises 40.48% by weight of CaO and 58.38% by weight of SiO ₂ ; and a composite of silica airgel and larnite powder whose surface is chemically modified with APTES, and whose chemical composition comprises 34.33% by weight of CaO and 64.70% by weight of SiO ₂ . 4. Applications of the composite material of the invention

The composite material of the invention can be obtained to fix, store or remove gases, for example, CO ₂ , by a carbonation reaction. Other types of gases emitted into the atmosphere such as SO ₂ , NOx, CO and H ₂ S could also be fixed, stored or disposed of by said composite material of the invention.

Therefore, in another aspect, the invention relates to a process for the storage of a gas, hereinafter gas storage method (A) of the invention, which comprises the use of the composite material of the invention. More specifically, the gas storage process (A) of the invention comprises contacting a gas stream comprising said gas with the composite material of the invention under conditions that allow said gas to be fixed by the composite material of the invention.

In a particular embodiment, the gas storage process (A) of the invention comprises contacting a stream of said gas with an aqueous suspension (dispersion) of the composite material of the invention under appropriate temperature and pressure conditions.

Illustrative, non-limiting examples of gases that can be stored according to the gas storage method (A) of the invention include gases emitted into the atmosphere such as CO ₂ , SO ₂ , NOx, CO, H ₂ S, etc., as well as their mixtures. Thus, by means of the gas storage method (A) of the invention, gases potentially harmful to the environment can be stored and, consequently, eliminated.

The characteristics of the composite material of the invention have already been previously defined. The temperature and pressure conditions will be chosen from those that are appropriate to facilitate the fixation of the gas by the composite material of the invention; although said temperature and pressure conditions may vary over a wide range, in a particular embodiment, said appropriate temperature and pressure conditions consist of ambient temperature and atmospheric pressure. Advantageously, the gas storage process (A) of the invention is carried out while maintaining the stirring. The gas fixing reaction by the composite material of the invention according to the gas storage method (A) of the invention can be carried out in an appropriate reactor, for example, in a reactor comprising a valve for the inlet of gas and another for the gas outlet, controlling the time and pH of the reaction. If desired, the products resulting from subjecting the composite materials of the invention to said gas fixation reaction can be analyzed immediately after the end of the process, without having to be kept at rest in the reactor for a period of time. The analysis of said products by appropriate techniques, for example, DRX ₅ allows to verify the effectiveness of the gas fixation reaction, that is, of the transformation of larnite (Ca ₂ SiO ₄ ) into the corresponding product as a function of the fixed gas. The product resulting from subjecting a composite material of the invention to a gas fixation reaction, as previously described, constitutes a further aspect of the present invention.

Although the gas storage process (A) of the invention allows to store and, consequently, eliminate, gases emitted into the atmosphere potentially harmful to the environment, such as CO ₂ , SO ₂ , NOx, CO, H ₂ S ₅ etc., in a particular embodiment, the gas to be stored according to the gas storage method (A) of the invention, due to its special relevance, is CO ₂ .

Therefore, in a specific embodiment, the invention provides a process for the storage of CO ₂ (A) comprising the use of the composite material of the invention. More specifically, said method comprises contacting a stream of a gas comprising CO ₂ with the composite material of the invention. To do this, briefly, a stream of a gas comprising CO ₂ is contacted with an aqueous suspension (dispersion) of the composite material of the invention under appropriate temperature and pressure conditions. In a specific embodiment, said gas comprising CO ₂ is a gas composed mostly, that is, almost entirely, of CO ₂ ; In another specific embodiment, said gas comprising CO ₂ is a gas containing CO ₂ together with other gases in different relative proportions. The characteristics of the composite material of the invention have already been previously defined. The temperature and pressure conditions will be chosen from those that are appropriate to facilitate the fixation of CO ₂ by the material compound of the invention; although said temperature and pressure conditions may vary over a wide range, in a particular embodiment, said appropriate temperature and pressure conditions consist of ambient temperature and atmospheric pressure. Advantageously, the CO ₂ (A) storage procedure provided by this invention is carried out while maintaining the stirring.

The carbonation reaction of the CO ₂ storage process (A) provided by this invention can be carried out in an appropriate reactor, for example, in a reactor comprising a valve for the gas inlet and another for the gas outlet, controlling the time and the pH of the reaction. If desired, the carbonated products, that is, the products resulting from subjecting the composite materials of the invention to said carbonation reaction, can be analyzed immediately after the end of the process, without having to keep them at rest in the reactor for A period of time. The analysis of said carbonated products by DRX allows to verify the effectiveness of the carbonation reaction, that is, of the transformation of larnite (Ca ₂ SiO ₄ ) into CaCO ₃ (see Example 3). Using this technique, very high carbonation rates are observed, since in only a period of time of approximately 15 minutes no larnite is detected but only calcium carbonate minerals (eg, vaterite and calcite). The presence of SiO ₂ cannot be determined by DRX due to its amorphous character, so other techniques are used, for example, EDX-MEB; In this sense, the analysis of said carbonated product by EDX-MEB reveals the presence of Si, an element that in the EDX analysis (for any type of material used) is expressed as an oxide, SiO ₂ . The ratio of silica to CaCO ₃ is variable depending on the Si / Ca ratio present in the raw material (larnite powder). Said carbonated product, resulting from subjecting a composite material of the invention to a carbonation reaction, constitutes an additional aspect of the present invention.

In another aspect, the invention relates to a process for recovering larnite (A) from a carbonated product obtainable by the CO ₂ (A) storage method of the invention, which comprises subjecting said carbonated product to an appropriate heat treatment. in order to obtain a material comprising larnite. The carbonated product obtainable by the CO ₂ (A) storage process of the invention can be obtained by subjecting a composite material of the invention to a carbonation reaction, as previously described. The heat treatment to be applied will be chosen based on various factors, including the nature of the product to be treated, although it will be aimed at obtaining a material comprising larnite. Although such heat treatment can vary, in a particular embodiment, said heat treating comprises heating said obtainable carbonated product by the method of storing CO ₂ (A) of the invention, at a temperature of 900 ⁰ C at a rate of heating 5 ° C / min and maintaining it at that temperature (900 ⁰ C) for 1 hour, to obtain a material comprising larnite.

In a particular embodiment, said carbonated product resulting from subjecting a composite material of the invention to a carbonation reaction, is dried and the components of the obtained by-product (eg, calcite and silica) are mixed and the resulting mixture is heat treated in an oven to about 900 ⁰ C, with a heating rate of 5 ° C / minute and held at that temperature for about 1 hour to obtain a material which, analyzed by XRD, mostly results to be constituted by larnite and minor amounts of other minerals, eg, wollastonite (Example 4).

As can be seen, the invention allows a cycle to be closed since starting with larnite as a raw material, a material composed of airgel and larnite powder (whose surface has been chemically modified) is first obtained, which is subsequently subjected to a fixing reaction of a gas (CO ₂ ) (eg, by a carbonation reaction) to give rise to a product (eg, a carbonated product) that, after heat treatment, gives rise to a material comprising mostly larnite, that is, the material initial.

5. Applications of larnite powder Tests carried out by the inventors have shown that larnite powder can also be used to fix, store or remove gases, for example, CO ₂ , by a carbonation reaction (Example 3). Other types of gases emitted to the atmosphere such as SO ₂ , NOx, CO and H ₂ S could also be fixed, stored or disposed of by said larnite powder. Likewise, other tests carried out by the inventors have shown that the carbonated product resulting from subjecting the larnite powder to a carbonation reaction can also be used to recover larnite (Example 4).

Therefore, in another aspect, the invention relates to a process for the storage of a gas, hereinafter gas storage method (B) of the invention, which comprises the use of larnite powder. More specifically, the gas storage process (B) of the invention comprises contacting a gas stream comprising said gas with larnite powder under conditions that allow said gas to be fixed by the larnite powder.

In a particular embodiment, the gas storage process of the invention comprises contacting a stream of said gas with an aqueous suspension (dispersion) of larnite powder under appropriate temperature and pressure conditions.

Illustrative, non-limiting examples of gases that can be stored according to the gas storage method of the invention include gases emitted into the atmosphere such as CO ₂ , SO ₂ , NOx, CO, H ₂ S, etc., as well as their mixtures Thus, by means of the gas storage method (B) of the invention, gases potentially harmful to the environment can be stored and, consequently, eliminated.

The larnite powder to be used can be natural larnite powder or synthetic larnite powder, which can be obtained as previously indicated. Also, the characteristics of the larnite powder have already been previously defined. The temperature and pressure conditions will be chosen among those that are appropriate to facilitate the fixation of the gas by the larnite powder; although said temperature and pressure conditions may vary over a wide range, in a particular embodiment, said appropriate temperature and pressure conditions consist of ambient temperature and atmospheric pressure. Advantageously, the gas storage process (B) of the invention is carried out while maintaining the stirring. The reaction of fixing the gas by the larnite powder according to the gas storage process (B) of the invention can be carried out in an appropriate reactor, for example, in a reactor comprising a valve for the inlet of gas and another for the exit of the gas, controlling the time and the pH of the reaction. If desired, the products resulting from subjecting the larnite powder to said gas fixation reaction can be analyzed immediately after the end of the process, without having to be kept at rest in the reactor for a period of time. The analysis of said products by appropriate techniques, for example, DRX, allows to verify the effectiveness of the gas fixation reaction, that is, of the transformation of larnite (Ca ₂ SiO ₄ ) into the corresponding product as a function of the fixed gas. The product resulting from subjecting larnite powder to a gas fixation reaction, as previously described, constitutes a further aspect of the present invention.

Although the gas storage process (B) of the invention allows storage and, consequently, eliminating, gases emitted into the atmosphere potentially harmful to the environment, such as CO ₂ , SO ₂ , NOx, CO, H ₂ S, etc., in a particular embodiment, the gas to be stored according to the gas storage procedure (B) of the invention, due to its special relevance, is CO ₂ .

Therefore, in a specific embodiment, the invention provides a process for the storage of CO ₂ (B) comprising the use of larnite powder. More specifically, said method comprises contacting a stream of a gas comprising CO ₂ with larnite powder. To do this, briefly, a stream of a gas comprising CO ₂ is contacted with an aqueous suspension (dispersion) of larnite powder under appropriate temperature and pressure conditions. In a specific embodiment, said gas comprising CO ₂ is a gas composed mostly, that is, almost entirely, of CO ₂ ; In another specific embodiment, said gas comprising CO ₂ is a gas containing CO ₂ together with other gases in different relative proportions.

The characteristics of larnite powder have been previously defined. The conditions of temperature and pressure will be chosen among those that are appropriate to facilitate the fixation of CO ₂ by larnite powder; although said temperature and pressure conditions may vary over a wide range, in one embodiment. in particular, said appropriate temperature and pressure conditions consist of ambient temperature and atmospheric pressure. Advantageously, the CO ₂ (B) storage process provided by this invention is carried out while maintaining the stirring. The carbonation reaction of the alternative CO ₂ storage process provided by this invention (based on the use of larnite powder) can be carried out in an appropriate reactor, for example, in a reactor comprising a gas inlet valve. and another for the exit of the gas, controlling the time and the pH of the reaction. If desired, the carbonated products, that is, the products resulting from subjecting the larnite powder to said carbonation reaction, can be analyzed immediately after the end of the process, without having to keep them at rest in the reactor for a period of time. of time. The analysis of said carbonated products by DRX allows to verify the effectiveness of the carbonation reaction, that is, of the transformation of larnite (Ca ₂ SiO ₄ ) into CaCO ₃ (see Example 3). Using this technique, very high carbonation rates are observed, since in only a period of time of approximately 15 minutes no larnite is detected but only calcium carbonate minerals (eg, vaterite and calcite). The presence of SiO ₂ cannot be determined by DRX due to its amorphous character, so other techniques are used, for example, EDX-MEB; In this sense, the analysis of said carbonated product by EDX-MEB reveals the presence of Si, an element that in the EDX analysis (for any type of material used) is expressed as an oxide, SiO ₂ . The ratio of silica to CaCO ₃ is variable depending on the Si / Ca ratio present in the raw material (larnite powder). Said carbonated product, resulting from subjecting larnite powder to a carbonation reaction, constitutes an additional aspect of the present invention.

In another aspect, the invention relates to a process for recovering larnite (B) from a carbonated product obtainable by the CO ₂ (B) storage method of the invention, which comprises subjecting said carbonated product to an appropriate heat treatment. in order to obtain a material comprising larnite. The carbonated product obtainable by the CO ₂ (B) storage process of the invention can be obtained by subjecting larnite powder to a carbonation reaction, as previously described.

The heat treatment to be applied will be chosen based on various factors, including the nature of the product to be treated, although it will be aimed at obtaining a material comprising larnite. Although such heat treatment can vary, in a particular embodiment, said heat treating comprises heating said obtainable carbonated product by the method of storing CO ₂ (B) of the invention, at a temperature of 900 ⁰ C ₃ at a speed of heating 5 ° C / min and maintaining it at that temperature (900 ⁰ C) for 1 hour, to obtain a material comprising larnite.

In a particular embodiment, said carbonated product resulting from subjecting larnite powder to a carbonation reaction is dried and the components of the obtained by-product (eg, calcite and silica) are mixed and the resulting mixture is heat treated in an oven at approximately 900 ⁰ C, with a heating rate of approximately 5 ° C / minute, and is maintained at that temperature for approximately 1 hour, obtaining a material that, analyzed by DRX, turns out to consist mostly of larnite and smaller amounts of other minerals, eg , wollastonite (Example 4). As can be seen, alternatively, the invention allows a cycle to be closed since starting from larnite powder which is subsequently subjected to a gas fixation reaction (CO ₂ ) (eg, by a carbonation reaction) to give rise to a product (eg, a carbonated product) which, after heat treatment, gives rise to a material comprising mostly larnite, that is, the initial material. The following examples illustrate the invention and should not be considered in a limiting sense of the scope thereof. EXAMPLE 1 Production of synthetic larnite powders

Different larnite powders with 2 different Si / Ca molar ratios were synthesized.

1.1 Synthetic larnite powders with a Si / Ca molar ratio of 0.5 A 0.46 M solution of Ludox® [30% aqueous colloidal silica solution] (solution of 6 g of Ludox® in 56 ml of distilled water) is added an aqueous solution of 1M calcium nitrate tetrahydrate (solution of 14,152 g of calcium nitrate tetrahydrate in 60 ml of distilled water). After 10 minutes of stirring, 104 ml of a 5% ethylene glycol aqueous solution was added. Under magnetic stirring, the mixture was heated to 100 ⁰ C until total evaporation of the solvent. This mode of operation involves obtaining a gel with a Si / Ca molar ratio of 0.5 in the product obtained. The gel obtained was dried in an oven at 100 ⁰ C for 48 h, then triturated, and then the powder obtained was heat treated at 600 ⁰ C (heating rate of 5 ° C / min) for 1 h. Once treated, the powder obtained (identified in Table 1 as "Si / Ca larnite powder (molar): 0.5") was characterized both at the level of its composition and at the mineralogical level. The results obtained were the following: composition [determined by X-ray Fluorescence (FRX)]: 65-67% by weight of CaO and 34-32% by weight of SiO ₂ ; and mineralogical characterization [determined by X-ray Diffraction (DRX)]: larnite (dicalcium silicate).

1.2 Synthetic larnite powders with a Si / Ca molar ratio of 1

Operating in a manner similar to that described in Example 1.1 but varying the proportion of calcium nitrate tetrahydrate (dissolution of 7.07 g of calcium nitrate tetrahydrate in 60 ml of distilled water) and of the aqueous solution of ethylene glycol at 5 % (67 ml), a gel was obtained in which the Si / Ca molar ratio is 1. Next, the gel was dried, crushed and the powder obtained was heat treated as indicated in Example 1.1. The characterization both at the level of the composition and Mineralogical of the obtained powder (identified in Table 1 as "Si / Ca larnite powder (molar): 1") provided the following results: composition (by FRX): 55-50% by weight of CaO and 45-50% SiO ₂ weight; and - mineralogical characterization (by DRX): larnite (dicalcium silicate).

EXAMPLE 2 Synthesis of composite material of silica airgel and larnite powder Two types of composite materials of silica airgel and larnite powder were synthesized according to the synthetic larnite powders used as active phase; in particular, said synthetic larnite powders used were (i) "Si / Ca (molar) larnite powder: 0.5" and (ii) "Si / Ca (molar) larnite powder: 1" (Examples 1.1 and 1.2 , respectively).

However, previously, the surface of both types of larnite powders, independently, was modified with 3-aminopropyltriethoxysilane (APTES). The mixture APTES / larnite powder was dispersed in ethanol (EtOH) in a proportion of 17 ml of EtOH and 1 ml of APTES for each gram of synthetic larnite powder with the assistance of ultrasound (the power supplied was 0.6 W -cm ^"3 and time insonation was about 10 min). then we proceeded to centrifugation of the suspension of solid particles (slurry) and then drying at 100 ⁰ C for 48 hours in conventional equipment (oven) .

2.1 Composite material 1 To obtain this "composite material 1" (the number indicates the Si / Ca molar ratio of the synthetic starting larnite powder), the starting point was the "Si / Ca (molar) larnite powder: 1" (Example 1.2). Different composite materials 1 were obtained, depending on the amount of synthetic larnite powder used with a Si / Ca molar ratio of 1, the surface of which had been modified with APTES according to the procedure previously described. For this, being processed separately, 3 different amounts (2.5 g; 5 g and 10 g, respectively) of said synthetic larnite powder with a Si / Ca molar ratio of 1, whose surface had been modified with APTES, and were added under ultrasound conditions (power supplied: 0.6 W-cm ^"3 and time of insolation: approximately 18 minutes) to a sun, which had previously been prepared by acid medium hydrolysis (HNO ₃ ) and tetraethoxysilane polycondensation (TEOS) (1.66 ml of 0.5 N nitric acid and 5 ml of TEOS, in 2 ml of ethanol). The resulting wet gels were placed in an autoclave at 255 ⁰ C and 90 bar (9OxIO ⁵ Pa) to extract the solvent (ethanol) under supercritical conditions. Then, the materials obtained were heated to 600 ⁰ C (with a heating rate of 5 ° C / min) and maintained at this temperature (600 ⁰ C) for 1 h. Three types of composite materials 1 (identified as "composite material", "composite material Ib" and "composite material Ic", in Table 1) were obtained, which were characterized by FRX (chemical composition) and the BET method (surface specific), as shown in Table 1.

2.2 Composite material 0.5 To obtain this "composite material 0.5" (the number indicates the Si / Ca molar ratio of the synthetic starting larnite powder), the starting point was "Si / Ca larnite powder (molar): 0.5 "(Example 1.1). In this case, a single type of 0.5 composite material was obtained by adding 15 g of said synthetic larnite powder with a Si / Ca molar ratio of 0.5, the surface of which had been modified with APTES according to the procedure previously described, to said sun previously prepared by hydrolysis in acid medium and polycondensation of TEOS (1.66 ml of 0.5 N nitric acid and 5 ml of TEOS, in 2 ml of ethanol). The preparation conditions of the composite 0.5 are equal to those previously described in relation to the composite 1. The composite obtained (identified as "composite 0.5" in Table 1), which was characterized by FRX and the BET method, as shown in Table 1.

Table 1

Composition

Textural Characteristics Chemistry

CaO SiO ₂

Sample Specific surface area (m ^z / g)

%%

Larnite powder

65-67 34-32 39

Si / Ca (molar): 0.5

Composite material 0.5 61-62 39-38 40

Larnite powder

50-55 50-45 -

Si / Ca (molar): l

Composite material 44.0 54.98 53

Composite material Ib 40.48 58.38 115

Composite material Ic 34.33 64.7 258

EXAMPLE 3 Carbonation procedure

To monitor the fixation of CO ₂ (carbonation), 2 types of samples were tested: a) synthetic larnite powders (67% by weight of CaO, Si / Ca molar ratio of 0.5); and b) composite material (44% by weight of CaO).

The carbonation procedure was performed in separate experiments for each sample. The description of the procedure and the results obtained that follows is common for the 2 types of samples. Briefly, 0.5 g of each sample was introduced into a reactor containing 25 ml of distilled water. The pH of the dispersion obtained was greater than 10.5. Then, said dispersion was subjected to a flow of CO ₂ for 15 minutes under permanent stirring. In that period of time, the pH dropped to a value of 6.5-7. The product resulting from the reaction in the reactor was analyzed and identified. The identification of carbonates was carried out by DRX, which revealed only the presence of vaterite and calcite, two calcium carbonate minerals (CaCO ₃ ) that belong to the same structural family. Silica (SiO ₂ ) was identified by the detection of Si by EDX-MEB analysis since DRX is not possible due to its amorphous character. No larnite was identified in the samples analyzed. Therefore, the absence (non-presence) of larnite, by DRX, in said samples analyzed after the carbonation procedure leads to the conclusion that the efficiency of the reaction of transformation of silicate into carbonate was 100%, for a period of flow time and reaction with CO ₂ of 15 minutes. These results show the great efficacy of the 2 types of samples tested, with no appreciable differences between them during the period of time studied. Although it is not desired to be linked to any hypothesis, this high efficiency can be justified on the basis that the samples analyzed in these experiments, unlike other protocols already described with materials composed of wollastonite powders, are analyzed immediately after the end of the experiment. , without having to keep them at rest in the reactor.

EXAMPLE 4

Larnite recovery

This heat treatment test was performed separately for each of the experiments described in the carbonation procedure (Example 3), according to the protocol described below. Once dried product obtained components (calcite and silica) in each experiment, mixed and the mixture was heat treated in an oven at 900 ⁰ C (heating rate of 5 ° C / min) for 3 hours. The sample was analyzed by DRX, mostly identifying larnite and smaller amounts of wollastonite.

In this way, the cycle is closed, that is, from a raw material (larnite), whose processing allows obtaining a composite material of airgel and larnite powders, which undergoes a flow of CO ₂ and through a carbonation reaction After 15 minutes, it generates a by-product (calcite and silica) that, heat treated, yields a final material in which the majority part is the initial product (larnite).

Claims

1. A composite material of silica airgel and larnite powder, obtainable by mixing larnite powder whose surface is chemically modified with an aminosilane selected from (3-aminopropyl) -triethoxysilane (APTES), (3- aminopropyl) - dimethyl-ethoxy silane (APMES), (3-aminopropyl) -trimethoxysilane (APTMS), (3-aminopropyl) -diethoxymethylsilane (APDEMS) and mixtures thereof, with a sol obtained by hydrolysis and polycondensation of tetraethoxysilane (TEOS).

2. Composite material according to claim 1, comprising the following composition

(lx) SiO ₂ - x CaO where x is a number between 0.34 and 0.62

3. Composite material according to claim 2, wherein "x" is 0.34, 0.44 or

0.62.

4. Composite material according to claim 1, selected from the group consisting of: - a composite material of silica airgel and larnite powder whose surface is chemically modified with APTES, and whose chemical composition comprises between 62% and 61% by weight of CaO and between 38% and 39% by weight of SiO ₂ ; a composite of silica airgel and larnite powder whose surface is chemically modified with APTES, and whose chemical composition comprises 44% by weight of CaO and 54.98% by weight of SiO ₂ ; a composite of silica airgel and larnite powder whose surface is chemically modified with APTES, and whose chemical composition comprises 40.48% by weight of CaO and 58.38% by weight of SiO ₂ ; a composite of silica airgel and larnite powder whose surface is chemically modified with APTES, and whose chemical composition comprises 34.33% by weight of CaO and 64.70% by weight of SiO ₂ ; and - their mixtures.

5. A process for obtaining a composite of silica and larnite powder airgel according to claim I ₉ comprising contacting larnite powder, the surface of which is chemically modified with an aminosilane selected from (3-aminopropyl) -triethoxysilane (APTES), (3-aminopropyl) -dimethyl-ethoxy silane (APMES), (3-aminopropyl) -trimethoxysilane (APTMS), (3-aminopropyl) - diethoxymethylsilane (APDEMS) and mixtures thereof, with a sol obtained by hydrolysis and polycondensation of tetraethoxysilane (TEOS).

Method according to claim 5, wherein the mixture of said larnite powder whose surface is chemically modified with said sol resulting from the controlled hydrolysis and polycondensation of TEOS is carried out under the action of ultrasound.

7. Method according to claim 5 or 6, further comprising removing the solvent used in the production of the sun.

Method according to claim 7, further comprising subjecting the material resulting from the removal of the solvent to a heat treatment to obtain said composite of silica airgel and larnite powder.

9. Method according to claim 8, wherein said heat treatment comprises heating said material resulting from removal of the solvent at a temperature of 600 ⁰ C, with a heating rate of 5 ° C / min and maintaining it at that temperature for about 1 hour.

10. A process for the storage of a gas comprising contacting a gas stream comprising said gas with a composite material of silica airgel and larnite powder according to claim 1 under conditions that allow said gas to be fixed by said gas. composite material.

11. The method according to claim 10, wherein said gas is selected from the group consisting of CO ₂ , SO ₂ , NOx, CO, H ₂ S, and mixtures thereof.

12. A method according to claim 10, comprising contacting a gaseous stream comprising CO ₂ with an aqueous suspension of said silica airgel composite and larnite powder, at room temperature and atmospheric pressure.

13. A process for recovering larnite from a carbonated product obtainable by carbonation of a composite material of silica airgel and larnite powder according to claim 1, which comprises subjecting said carbonated product to a suitable heat treatment to obtain a material comprising larnite.

14. Method according to claim 13, wherein said heat treatment comprises heating said carbonated product at a temperature of 900 ⁰ C, with a heating rate of 5 ° C / min and maintaining it at that temperature for about 1 hour.

15. Use of a composite material of silica airgel and larnite powder according to claim 1, for the storage of a gas.

16. Use according to claim 15, wherein said gas is selected from the group consisting of CO ₂ , SO ₂ , NOx, CO, H ₂ S, and mixtures thereof.

17. A product obtainable by chemical modification of the surface of the larnite powder with an aminosilane selected from (3-aminopropyl) -triethoxysilane (APTES), (3-aminopropyl) -dimethyl-ethoxy silane (APMES), (3-aminopropyl) - trimethoxysilane (APTMS), (3-aminopropyl) -diethoxymethylsilane (APDEMS) and mixtures thereof.

18. A process for the storage of a gas comprising contacting a gas stream comprising said gas with larnite powder under conditions that allow said gas to be fixed by said larnite powder.

19. The method of claim 18, wherein said gas is selected from the group consisting of CO ₂ , SO ₂ , NOx, CO, H ₂ S, and mixtures thereof.

20. A method according to claim 19, comprising contacting a gas stream comprising CO ₂ with an aqueous suspension of larnite powder, at room temperature and atmospheric pressure.

21. Use of larnite powder for the storage of a gas.

22. Use according to claim 21, wherein said gas is selected from the group consisting of CO ₂ , SO ₂ , NOx, CO, H ₂ S, and mixtures thereof.

23. A process for the recovery of larnite from a carbonated product obtainable by carbonation of larnite powder, which comprises subjecting said carbonated product to a suitable heat treatment to obtain a material comprising larnite.

24. The method of claim 23, wherein said heat treatment comprises heating said carbonated product, at a temperature of 900 ⁰ C, with a heating rate of 5 ° C / min and maintaining it at that temperature for about 1 hour.