PROCESS FOR OBTAINING SYNTHETIC GEOPOLYMERS AND SYNTHETIC GEOPOLYMERS

Abstract

The present invention relates to a geopolymer produced from a synthetic aluminosilicate. The synthetic aluminosilicate was produced by sol gel technology, heat treated and, later, activated using sodium silicate and sodium hydroxide in solution, having as a final product a synthetic geopolymer. The final product was submitted to CO.sub.2 adsorption analysis using thermogravimetry for adsorbed quantification. In addition to the pure geopolymer, it is also possible to produce the synthetic geopolymer with the addition of surfactant, or in the composite form with the addition of zeolite, or heat treated to form a zeolite or functionalized with amine, for example, to increase the adsorption capacity.

Claims

1. A process for producing synthetic geopolymers characterized by comprising the following steps: (a) preparing solutions containing water, silicate and sodium hydroxide and leave to rest at room temperature for at least 10 minutes; (b) calcining the synthetic powder at a temperature between 300° C. and 900° C., followed by basic or acid activation; (e) mixing the solution prepared in step (a) with the synthetic powder to obtain the geopolymer paste; (d) after step (c) waiting for the final cure, from 10 minutes, until the desired final resistance.

2. A process according to claim 1, characterized in that the synthetic powder is a synthetic aluminosilicate obtained by sol gel technology.

3. A process according to claim 1, characterized in that sodium silicate has from 5% to 20% of Na.sub.2O and 5% to 50% of SiO.sub.2, the alkaline activator being sodium hydroxide or potassium hydroxide; or acid activator is phosphoric acid.

4. A process according to claim 1, characterized by including the functionalization of the sample through the impregnation of a component of the amine group after step (d).

5. A process according to claim 4, characterized in that the impregnation consists of preparing a solution between 1% and 50% of an amine in a solvent, leaving it under stirring for 1 minute to 1 hour, adding the geopolymer samples while maintaining stirring from 3 to 24 hours and drying in an oven for 10 minutes to 12 hours at a temperature of 40° C. to 80° C.

6. A process according to claim 5, characterized in that the amine is diethyl triamine and the solvent is ethanol.

7. A process according to claim 1, characterized by incorporating a surfactant during step (c).

8. A process according to claim 1, characterized by using a heat treatment at a temperature above 200° C., after step (d) for the formation of zeolite.

9. A process according to claim 1, characterized by adding a zeolite in step (c) for the formation of a composite.

10. A process according to claim 1, characterized in that the geopolymer is subjected to a washing process to remove excess unreacted sodium during the geopolymerization process.

11. Synthetic geopolymers as obtained in claim 1, characterized by having mechanical resistance to compression from 0 to 40 MPa, surface area from 1 m.sup.2/g to 800 m.sup.2/g, pore structure that can present micro, meso and macropores and CO.sub.2 adsorption capacity from 0 to 100 milligrams of CO.sub.2 per gram of geopolymer.

12. The process of claim 7, wherein the surfactant comprises cetyl trimethylammonium bromide (CTAB).

13. The process of claim 9, wherein the zeolite comprises zeolite Y.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0036] The present invention will be described in more detail below, with reference to the attached figures which, in a schematic and non-limiting manner of the inventive scope, represent examples of its realization. In the drawings, there are:

[0037] FIG. 1 illustrating the CO.sub.2 adsorption curves of the geopolymers with molar ratio Na.sub.2O/SiO.sub.2 = 0.68 after the washing process and without washing;

[0038] FIG. 2 illustrating the CO.sub.2 adsorption curves of geopolymers with molar ratio Na.sub.2O/SiO.sub.2 = 0.68 after the washing process and submitted to 300° C. before CO.sub.2 adsorption;

[0039] FIG. 3 illustrating the adsorption curves of geopolymers with molar ratio Na.sub.2O/SiO.sub.2 = 0.50 after the washing process, without washing and with the addition of diethyl triamine (DT).

DETAILED DESCRIPTION OF THE INVENTION

[0040] The present invention relates to a process of producing a geopolymer from the activation of a synthetic aluminosilicate, with application in the gas adsorption of CO.sub.2. The synthetic aluminosilicate was produced by a sol gel process, as described in Patent Application BR 102018012455, heat treated and, later, synthesized using sodium silicate and sodium hydroxide in solution, having as a final product a synthetic geopolymer. The final product was submitted to CO.sub.2 adsorption analysis using thermogravimetry to quantify the adsorbed CO.sub.2.

[0041] The aluminosilicate obtained by sol gel technology was subjected to calcination temperatures between 300° C. and 900° C., followed by basic activation with sodium silicate and sodium hydroxide, which may also undergo acid activation with phosphoric acid. The sodium silicate used has from 5% to 20% Na.sub.2O and 5% to 50% SiO.sub.2.

[0042] Initially, solutions were prepared containing: water, silicate and sodium hydroxide. The mixtures remained at rest and at room temperature for at least 10 minutes. The ratios were stipulated based on bibliographic reviews, adopting maximum and minimum conditions for the addition of Na.sub.2O.

[0043] For the production of geopolymer pastes, the silicate and sodium hydroxide solution prepared previously was mixed with the synthetic powder in a container kept in an ice bath to minimize the effects of temperature, since the reaction is exothermic. Furthermore, the temperature has a catalytic effect, accelerating the geopolymerization reactions, which would make it difficult to mold the pastes. Optionally, it is possible to add a zeolite to the mixture (water/sodium silicate/sodium hydroxide solution + synthetic powder), such as zeolite Y, for example, to form the composite.

[0044] The geopolymer pastes after one minute of mixing were poured into cylindrical acrylic molds with dimensions of 5 × 10 mm. After the molding process was completed, the mold was sealed and placed in an oven for 24 hours at a temperature of 60° C. Subsequently, the specimens were unmoulded and kept at a temperature of 60° C. until the final curing age, from 10 minutes, until the desired final resistance. The curing temperature adopted, above room temperature, aims to accelerate the geopolymerization reactions, however, it is possible to perform it at room temperature. After the final curing, optionally, a heat treatment at a temperature above 200° C. can be used to form zeolite.

[0045] Furthermore, after the final curing step, optionally a step of functionalization of the sample by means of the impregnation of a component of the group of amines. Impregnation consists of preparing a solution between 1% and 50% of an amine, for example, diethyl triamine in a solvent, for example, ethanol, leaving it under stirring for 1 minute to 1 hour, then adding the geopolymer samples, keeping stirring for 3 to 24 hours. Subsequently, it was dried in an oven for 10 minutes to 12 hours at a temperature of 40° C. to 80° C.

[0046] Optionally, a surfactant may be incorporated during the step of mixing the prepared solution (water/sodium silicate/sodium hydroxide) with the synthetic powder, in which the surfactant cetyl trimethylammonium (CTAB) is moistened so as not to change the initial viscosity of the geopolymer. Then the samples are molded.

[0047] Optionally, the geopolymers obtained can be subjected to a washing process to remove excess unreacted sodium during the geopolymerization process, aiming at the release of pores.

[0048] The adsorption capacity of the samples was determined by thermogravimetric analysis as described in the following examples.

[0049] The thermogravimetric analyzes consisted of the following methodologies: [0050] Condition (1): treating the materials at 100° C. for 30 minutes, cooling to 30° C. and keeping at that temperature for 5 minutes for stabilization, these steps being in a N.sub.2 atmosphere with a gas flow of 50 ml/min. Then, changing the atmosphere to CO.sub.2 (50 ml/min), keeping the temperature at 30° C. for 90 minutes, followed by desorption again in a N.sub.2 atmosphere for 10 minutes. [0051] Condition (2): treating the materials at 300° C. for 30 minutes, cooling up to 30° C. and keeping at that temperature for 30 minutes for stabilization, these steps being in a N.sub.2 atmosphere with a gas flow of 50 ml/min. Then, changing the atmosphere to CO.sub.2 (50 ml/min), keeping the temperature at 30° C. for 90 minutes, followed by desorption again in a N.sub.2 atmosphere for 10 minutes.

[0052] The objective of the heat treatment at a temperature above 200° C. is the transformation of the geopolymer (amorphous structure) into zeolite (crystalline structure), to assess whether this modification would influence the adsorption capacity of the material.

[0053] It is possible to produce geopolymer for adsorption of CO.sub.2 and other adsorbates with other molar ratios, being able to increase the porosity of the final material, allowing a greater adsorption capacity or decreasing the porosity, increasing the mechanical resistance. It is also possible to activate the geopolymer through another alkaline solution such as, for example, potassium silicate, or even acid activation.

[0054] It is also possible, in addition to the value quoted in the text, to add a greater or lesser amount of zeolite for the formation of the geopolymer-zeolite composite. And any other zeolite compatible with the geopolymer can be used instead of zeolite Y. In addition, other adsorbent materials can also be used for this composite to replace zeolite, such as activated carbon, for example.

[0055] Other metals can be introduced in the production phase of the aluminosilicate, aiming to change the adsorption capacity of the geopolymer or for doping effect.

[0056] The effectiveness of the treatment processes and additions made to the mixture, which act by altering some characteristic, is also dependent on the molar relationship between the analyzed geopolymer and components used in the production of the material (productive trait), thus, these factors can increase or decrease the adsorption capacity of the final material.

[0057] The porosity generated in the geopolymer through the use of CTAB can come from other surfactants or porogenic agents according to the order of magnitude of the pore size to be created. Examples of other compounds that can be used for this purpose (non-limiting): surfactant Pluronic P123, Pluronic F127, Brij 58, Brij 30, starch, sucrose, etc.

[0058] It is also possible the functionalization of geopolymer samples with other functional groups besides amines, such as: amide, sultan, thiol, carbonyl, carboxyl, phosphate, among others.

Examples

[0059] The examples presented below are intended to illustrate some forms of embodiment of the invention, as well as to prove the practical feasibility of its application, not constituting any form of limitation of the invention.

[0060] To analyze the adsorption capacity of the geopolymer, different samples were prepared. Different formulations were tested, in addition to functionalization with an amine group, specifically diethyl triamine (DT) in order to increase the active sites. Another modification studied was the addition of a surfactant, cetyl trimethylammonium bromide (CTAB), in the geopolymer paste for incorporation of mesopores. Furthermore, geopolymer-zeolite composites were produced. The adsorption capacity of the zeolite formed from these geopolymers was evaluated. The formation of zeolite occurred due to the heating of the geopolymers, during the thermogravimetric analysis, at 300° C.

Example 1

[0061] A geopolymer was produced as described above, with a molar ratio of Na.sub.2O/SiO.sub.2 of 0.68 to G0.68. Curing was carried out for a period of 72 hours at 60° C. At the end of the curing process, part of the samples was submitted to the washing process, as detailed above. Subsequently, the CO.sub.2 adsorption capacity was evaluated as follows: heating the samples at 100° C. for 30 minutes to remove the adsorbed water; cooling to 30° C. and keeping at that temperature for 5 minutes for stabilization, these steps being in a N.sub.2 atmosphere with a gas flow of 50 ml/min. Then, changing the atmosphere to CO.sub.2 (50 ml/min), keeping the temperature at 30° C. for 90 minutes, followed by desorption again in the N.sub.2 atmosphere for 10 min.

[0062] As shown in FIG. 1, it is noted that the washing process contributed to the increase in adsorption capacity from 0.2%, G0.68 without washing, to 0.4% G0.68 washed.

Example 2

[0063] A geopolymer was produced as described in the detail text, with a molar ratio of Na.sub.2O/SiO.sub.2 of 0.68 to G0.68, however, in the fresh geopolymer paste 25% of Zeolite Y was added, previously moistened. Curing and adsorption analyzes were performed as per Example 1.

[0064] As shown in FIG. 1, it is noted that the washing process also contributed to the increase in adsorption capacity, going from 1.9%, G0.68-25ZY without washing, to 2.3% G0.68-25ZY washed. Furthermore, the incorporation of zeolite in the geopolymer increases the adsorption capacity.

Example 3

[0065] A geopolymer was produced as described in the detail text, with a molar ratio of Na.sub.2O/SiO.sub.2 of 0.68, however, in the fresh geopolymer paste was added 25% of Zeolite Y and 10% of CTAB, previously moistened so as not to disturb paste consistency - G0.68-25ZY-10%. Curing and adsorption analyzes were performed as per Example 1.

[0066] According to FIG. 1, it is noted that the washing process also contributed to the increase in adsorption capacity from 1.0%, G0.68-25ZY-10CTAB without washing, to 1.8% G0.68-25ZY-10CTAB washed. Furthermore, the incorporation of zeolite and CTAB in the geopolymer increases the adsorption capacity compared to the pure material G0.68.

Example 4

[0067] Geopolymers were produced as described in Examples 1, 2 and 3, respectively being G0.68, G0.68-25ZY and G0.68-25ZY-10CTAB and all samples subjected to the washing process to remove excess sodium. Subsequently, the analysis of CO.sub.2 adsorption took place as follows: treating the materials at 300° C. for 30 minutes to transform the geopolymer matrix into zeolite, cooling to 30° C. and maintaining at this temperature for 30 minutes for stabilization, these steps being in an atmosphere of N.sub.2 with a gas flow of 50 ml/min, then changing the atmosphere to CO.sub.2 (50 ml/min), keeping the temperature at 30° C. for 90 minutes, followed by desorption again in the N.sub.2 atmosphere for 10 minutes.

[0068] According to FIG. 2, it is noted that the adsorption capacities of samples G0.68-25ZY, G0.68-25ZY-10CTAB and G0.68 were 2.4%, 2.2% and 0.2%, respectively.

Example 5

[0069] A geopolymer was produced as described in the detail text, with a molar ratio of Na.sub.2O/SiO.sub.2 = 0.5 - G0.50. Curing was carried out for a period of 72 hours at 60° C. At the end of the curing process, part of the samples was submitted to the washing process as detailed above. Subsequently, the CO.sub.2 adsorption capacity was evaluated as follows: heating the samples at 100° C. for 30 minutes to remove the adsorbed water, cooling to 30° C. and maintaining at this temperature for 5 minutes for stabilization, these steps being in a N.sub.2 atmosphere with gas flow of 50 ml/min. Then, changing the atmosphere to CO.sub.2 (50 ml/min), keeping the temperature at 30° C. for 90 minutes, followed by desorption again in the N.sub.2 atmosphere for 10 minutes.

[0070] As shown in FIG. 3, it can be seen that the washing process also contributed to the increase of the adsorption capacity for the molar ratio Na.sub.2O/SiO.sub.2 = 0.5, going from 4.0%, G0.50 without washing, to 4.9%, G0.50 washed.

Example 6

[0071] A geopolymer was produced as described in the detail text, with a molar ratio of Na.sub.2O/SiO.sub.2 = 0.5. Curing was carried out for a period of 72 hours at 60° C. At the end of the curing process, the samples were submitted to the washing process as detailed above. Subsequently, the samples were functionalized with material from the amine group, more specifically diethyl triamine (DT) as follows: preparing a 5% solution of diethyl triamine in ethanol, leaving under stirring for 10 minutes, then adding the geopolymer samples keeping stirring for 12 hours. Then, drying in an oven for 4 h at 60° C. The CO.sub.2 adsorption capacity was evaluated as follows: heating the samples at 100° C. for 30 minutes to remove the adsorbed water, cooling until 30° C. and keeping at that temperature for 5 minutes for stabilization, these steps being in a N.sub.2 atmosphere with a gas flow of 50 ml/min. Then, changing the atmosphere to CO.sub.2 (50 ml/min), keeping the temperature at 30° C. for 90 minutes, followed by desorption again in the N.sub.2 atmosphere for 10 minutes.

[0072] From FIG. 3 it can be seen that the functionalization with DT decreased the CO.sub.2 adsorption rate, according to the slope of the curve.

Example 7

[0073] Geopolymers were produced as mentioned in Examples 5 and 6 and the adsorption curves shown in FIG. 3 were subjected to a kinetic analysis, according to the model suggested by TAN, K. L.; HAMEED, B. H. “Insight into the adsorption kinetics models for the removal of contaminants from aqueous solutions”, Journal of the Taiwan Institute of Chemical Engineers, v. 74, p. 25 to 48, 2017. From this, the maximum adsorption capacity of the samples was estimated and the results shown in Table 1 were obtained. It is noted that, in principle, the highest adsorption capacity, in the exposure period of 90 minutes, was that of Example 6 (sample G0.5 washing). However, through the kinetic analysis, it was concluded that the G0.5 DT sample has a lower adsorption rate, but in longer periods (t, 300 minutes) it has a higher adsorption capacity than the G0.5 washing sample.

TABLE-US-00001 Maximum adsorption capacity of geopolymer samples with Na.sub.2O/SiO.sub.2 ratio = 0.50 Classification y = A + Bx Balance adsorption Adsorption rate -k (%/min) Kinetic model correlation factor A B q.sub.e (%) t (min) for q.sub.e ≥ 94% G0.50 0.01684 0.00948 105.49 310 9.480E-03 0.9999 G0.50 washing 0.02189 0.00936 106.84 325 9.360E-03 0.9998 G0.50 washing DT 0.02949 0.00933 107.18 320 9.33E-03 0.9999

[0074] The synthetic geopolymers as obtained by the present invention have flexibility in their preparation and allow the production of geopolymers and zeolites from synthetic raw materials where possible to control the molar ratios between silica and alumina, generating products with controlled performance, which would be unfeasible from natural raw materials that have a restricted range of molar ratio between silica and alumina, such as those found in metakaolin, ash and slag. It is also possible to insert organic and inorganic additives in order to project their properties, such as the adsorption capacity of CO.sub.2.

[0075] Synthetic geopolymers have a mechanical compressive resistance of 0 to 40 MPa, a surface area of 1 m.sup.2/g to 800 m.sup.2/g, a pore structure that can present micro, meso and macropores and adsorption capacity of CO.sub.2 from 0 to 100 milligrams of CO.sub.2 per gram of geopolymer. These properties of geopolymers vary depending on the production processes used.

[0076] It should be noted that, although the present invention has been described in relation to the attached drawings, it may undergo modifications and adaptations by persons skilled in the art, depending on the specific situation, but provided that it is within the inventive scope defined herein.