LITHIUM SILICATES WITH HIGH CO2 CAPTURE CAPACITY AND REGENERATION AND MANUFACTURING PROCESS.

Abstract

The present invention provides a process for the production of lithium silicates with high CO2 capture and regeneration capacity from metallurgical slags. The process comprises the steps of: a) characterization and conditioning of the metallurgical slags, b) synthesis of the lithium silicates, and c) modification of the silicates. In an additional embodiment, the process also comprises d) characterization of the resulting silicates, e) determination of their CO2 capture capacity, and f) evaluation of their regeneration capacity. The resulting silicates exhibit high capture capacities compared to silicates prepared with pure reagents, and they also allow for the valorization of industrial byproducts as raw materials.

Description

Lithium silicates with high CO2 capture capacity and their regeneration and manufacturing process FIELD OF INVENTION The present invention relates to a process for the production of lithium silicates with high CO2 capture / adsorption capacity and regeneration, using by-products from the iron and steel industry as a source of silicon. BACKGROUND Lithium silicates are expensive materials that have been extensively studied for use as CO2 adsorbents at high temperatures (above 400 °C). Therefore, in recent years, low-cost alternatives for their production have been sought. The use of industrial waste and byproducts as substitutes for reagent-grade silica (SiO2) has recently been studied, including fly ash, rice husk ash, and metallurgical slag, the latter being used in the present invention. The following prior art documents relate to the production of lithium silicates using industrial waste as raw material: trRj / nn / zznz / e / Yi W02014102404 relates to an optimized process for the preparation of calcium silicates with CO2 capture capacity, the silicates thus obtained, and their use. The silicates are produced from agro-industrial by-products, co-products, or waste as sources of calcium and silicon. The process comprises a mixing and homogenization step of a calcium source and a silicon source, followed by heat treatment of the resulting mixture at temperatures between 400°C and 900°C for a period of 3 to 8 hours. The calcium source is portlandite obtained as a residue from the acetylene industry or calcium chloride, and the silicon source is rice husk, a co-product or agro-industrial residue from the rice industry, or silica powder.Preferably, when using portlandite as a source of calcium and powdered silica as a source of silicon, both compounds are mixed to a Ca / Si ratio of 2 or 4 and subjected to heat treatment at 800°C. CN101885490 also provides a method for preparing a lithium silicate material for high-temperature CO2 absorption from microsilicon powder. The method prepares the lithium silicate material for high-temperature CO2 absorption from microsilicon mineral powder recovered from silica fume and a compound called Quilonum Retará, which appears to be a drug comprising lithium carbonate. For the synthesis, the document proposes a high-temperature solid-phase method. The preparation cost is low, the CO2 absorption rate at temperatures between 500 and 7000°C reaches 25 to 40 percent, and the method provides a new route for converting waste into valuable products. US 2011 / 0165400 discusses a method for producing a primarily carbonate-bonded article by carbonation, the method comprising the steps of: providing a granular material having a pH greater than or equal to 8.3, the granular material comprising at least one alkaline earth metal silicate phase; compacting the granular material to obtain a compact of the granular material, wherein the porosity of the compact is less than or equal to 37% by volume and wherein the intrinsic permeability of the compact is at least 1 · 10-12 cm2;and, reacting the granular material in said compact with carbon dioxide in the presence of water to form at least 5% by weight of carbonates (CO32"), thereby transforming the compact into the primarily carbonate-bonded article, wherein in the reaction step the compact, being unsaturated with moisture at the beginning of the reaction step, is placed in an atmosphere comprising said carbon dioxide, wherein said atmosphere is at a temperature of at least 700°C and a pressure of at least 0.5 MPa so that said alkaline earth metal silicate phase contributes to the formation of said carbonates, said pressure being higher than the saturated vapor pressure of water at said temperature. The granular material comprises at most 5% by weight of ground granulated blast furnace slag, preferably at most 2.5% by weight, and more preferably is substantially free from ground granulated blast furnace slag. The method of the invention can be used to sequester CO2 and / or to produce an article having high compressive strength and / or to recycle waste materials. trRj / nn / zznz / e / Yi The aforementioned efforts to provide materials comprising lithium silicates demonstrate the need to provide alternative materials that allow for a reduction in CO2 emissions to the atmosphere and the reuse of industrial waste and by-products as raw materials. OBJECT OF THE INVENTION As a consequence of the foregoing, the object of the present invention is to provide lithium silicates with high CO2 capture and regeneration capacity, using a byproduct of the iron and steel industry as a raw material. The invention described herein has several potential uses, for example, in post-combustion processes or in hydrogen production processes with integrated CO2 capture. BRIEF DESCRIPTION OF THE FIGURES The following figures illustrate one or more embodiments of the invention and should not be considered as limiting it. Figure 1 is a general scheme of the lithium silicate preparation method 5 according to the present invention. Figure 2 is an XRD (X-ray diffraction) pattern showing the crystalline phases present in the slag used in the present invention. Figure 3 shows a scanning electron microscopy (SEM) image of the slag used in the present invention. Figure 4 is an XRD pattern showing the crystalline phases present in the lithium silicate obtained in the present invention. Figure 5 shows a scanning electron microscopy (SEM) image of the lithium silicate obtained in the present invention. Figure 6 shows the CO2 capture isothermal curves in lithium silicate with 10% K2CO3 prepared in accordance with the present invention. Figure 7 shows the isothermal curves of CO2 capture in lithium silicate with 20% K2CO3 prepared in accordance with the present invention. Figure 8 shows the isothermal curves of CO2 capture in lithium silicate with 30% K2CO3 prepared in accordance with the present invention. Figure 9 shows a CO2 capture-desorption cycle in lithium silicate with 10% K2CO3. BRIEF DESCRIPTION OF THE INVENTION The present invention provides lithium silicates and methods for preparing them using iron and steel industry waste as raw material. In one embodiment, the process comprises the steps of: a) characterization and conditioning of metallurgical slags, b) synthesis of lithium silicates, and c) modification of the silicates. In a further embodiment, the method also comprises the steps of: d) characterization of the obtained silicates, e) determination of the CO2 capture capacity of the prepared silicates, and f) evaluation of their regeneration capacity during multiple consecutive CO2 adsorption-desorption cycles. Lithium silicates prepared according to the present invention exhibit high CO2 capture capacities compared to a silicate made from pure reagents; for example, they can capture over 180 milligrams of CO2 per gram of material. Additionally, the invention allows for the valorization of industrial byproducts as raw materials, offering the added advantage of reducing the potential environmental and health impacts associated with their storage. DETAILED DESCRIPTION OF THE INVENTION The use of the term "approximately" throughout this description provides a certain additional range. The term is defined as follows. The additional range provided by the term is ±10%. For example, but not limited to, if "approximately 40 grams" is stated, the range is within ±10% of the standard deviation, and so on for other measurements. Unless otherwise stated, all percentages used throughout the description are mass / mass. The present invention provides lithium silicates (Li4SiO4) and methods for producing them using waste from the iron and steel industry as a source of silicon. In a preferred embodiment, the method comprises the steps of: a) characterization and conditioning of metallurgical slags, b) synthesis of lithium silicates and c) modification of the silicates. trRj / nn / zznz / e / Yi In an additional modality, the process also includes: d) characterization of the silicates obtained, e) determination of the CO2 capture capacity of the prepared silicates and f) evaluation of their regeneration capacity during multiple consecutive CO2 adsorption-desorption cycles. In one embodiment, iron and steel industry waste comprises metallurgical blast furnace slag. Such slag is characterized prior to the silicate synthesis process to determine its chemical composition. In a preferred embodiment of the invention, this characterization is performed using various analytical techniques, for example, X-ray fluorescence, xy-ray diffraction, and the Brunauer, Emmett, and Teller (BET) method to determine its surface area, but those skilled in the art will understand that other techniques known in the art may be used for this purpose. In a further embodiment of the invention, the slags are conditioned before being used in the silicate manufacturing process. Preferably, this conditioning comprises grinding and sieving. In addition to the slags, a lithium source is used, for example, lithium carbonate, lithium oxide, lithium hydroxide, among other compounds known to the person skilled in the art. In a preferred embodiment of the invention, lithium carbonate is used. To modify the lithium silicates and obtain improved properties, an alkali metal carbonate is also used in the synthesis. Preferably, the alkali metal carbonate used is potassium carbonate, but the person skilled in the art will understand that other similar compounds, e.g., sodium carbonate, etc., may be used. The lithium silicates of the present invention are produced by a solid-state reaction, as described below. Preferably, lithium carbonate is used and mixed with blast furnace slag in a lithium:silicon molar ratio in the range of approximately 2.05:1 to 2.2:1, preferably 2.1:1. Subsequently, the mixture is calcined in equipment operating at high temperatures, for example, a muffle furnace, at a temperature in the range of approximately 800 to 900 °C, preferably 850 °C for a time of approximately 4 to 8 hours, preferably 6 hours with temperature increases of approximately 10 °C per minute. Subsequently, when the mixture cools to room temperature, the reaction mixture is ground to facilitate contact between the materials, and potassium carbonate (K2CO3) is added to the mixture to modify the material and increase its CO2 capture capacity. The K2CO3 is added at a percentage within the range of approximately 5 to 40%, preferably 10 to 30%. This percentage must be selected beforehand by the technician to calculate the amount in grams of K2CO3 to add to the mixture based on the percentage of Li4SiO4 obtained, which must be determined beforehand using any analytical technique known to the technician. For illustrative but not limiting purposes, for an amount of 0.94 grams of reaction mixture for which it is determined that there is 60% of L14SiO4 present (0.54 g L14SiO4) and a percentage of 10% of selected K2CO3, 0.06 g the mixture to meet the percentage of 10% K2CO3 with respect to Li4SiO4. In a preferred embodiment of the invention, the grinding of the metallurgical slags in the conditioning step and the grinding of the reaction mixture before the addition of K2CO3 is carried out with an instrument adapted for this purpose, for example, agate mortar, porcelain mortar, high energy ball mill, among others, and the percentage of Li4SiO4 is determined by XRD analysis using the RIR (reference intensity ratio) method. As a result of this process, modified lithium bR / ynn / zznz / e / Yi silicates are obtained. Once these materials are obtained, they are characterized using any analytical technique known in the state of the art. In a preferred embodiment of the invention, the produced silicates are characterized by X-ray diffraction (XRD) to identify the crystalline phases, the Brunauer, Emmett, and Teller (BET) method to determine their surface area, and scanning electron microscopy (SEM) to determine their elemental composition and morphology. Thermogravimetric and temperature-programmed techniques are used to evaluate the CO2 capture capacity of the lithium silicates of the present invention. In a preferred embodiment, the lithium silicate prepared according to the present invention is heated to a temperature in the range of approximately 400 to 600 °C, preferably 450 °C, at a heating rate of approximately 5 to 15 °C per minute, preferably 10 °C per minute, and subsequently contacted with a gas stream of CO2 at a concentration of approximately 5 to 30% v / v, preferably 20% v / v, at a flow rate of approximately 60 to 100 mL / min in the presence of oxygen at a concentration of approximately 5 to 10% v / v and carbon monoxide at a concentration of approximately 2 to 7% v / v. In a preferred embodiment, a flow of N2 in the range of 60 to 100 mL / min is added while the material is heated to 400-600 °C. Once the desired temperature (400 - 600 °C) is reached, it is maintained for a time of approximately 60 to 180 minutes to promote CO2 adsorption. Thermogravimetric analysis determines the CO2 capture capacity of silicates. According to the results obtained, the silicates produced with the present invention have a capture capacity greater than 180 milligrams of CO2 per gram of material. trRj / nn / zznz / e / Yi Finally, the regeneration capacity of lithium silicates was evaluated during multiple consecutive CO2 adsorption-desorption cycles. In one modality, this number of consecutive cycles ranges from 10 to 50, preferably the number of consecutive cycles is 20. The consecutive cycles for evaluating regeneration capacity comprise a preheating stage of the material to a temperature in the range of approximately 450 to 600 °C, preferably approximately 500 °C. This heating can be carried out with an N2 flow in the range of 60 to 100 mL / min. The silicate is then contacted with a CO2 flow in the range of 60 to 100 mL / min at a concentration of 5 or 20% v / v CO2 for approximately 60 to 180 min. For the desorption step, the CO2 flow is stopped and switched to a pure N2 flow in the range of approximately 600–150 mL / min, and the temperature is increased to 700–800 °C, preferably 750 °C, for approximately 40 to 120 min. Some of the experimental results are shown below only as an example of the present invention. EXAMPLES The following examples are offered to illustrate, but not to limit, the claimed invention. Blast furnace slags were used, which were characterized by X-ray diffraction and scanning electron microscopy (Figs. 2 and 3). Their surface area was also calculated using the BET method, resulting in a value of 4.4 m² / g. The slag was conditioned before being used in the methodology of the present invention. For this purpose, it was ground and sieved with a mesh no larger than 325. Table 1 below shows the results of the slag composition. trRj / nn / zznz / e / Yi Table 1. Composition of slags determined by X-ray fluorescence (XRF) P2O5 SiO2 TiO2 F©203 A12O3 MnO MgO CaO Na2O K2O PXCa Slag 0.03 39.08 1.57 1.62 12.00 1.42 10.16 32.88 0.08 0.56 0.60 : Loss on ignition. Analytical grade lithium carbonate was mixed with the conditioned slag in a lithium:silicon molar ratio of 2.1:1. trRj / nn / zznz / e / Yi The mixture was calcined at 850 °C for 6 hours with temperature increases of approximately 10°C per minute, ground, and analytical grade K2CO3 was added at concentrations of 10%, 20%, and 30% for comparative testing. The silicates obtained were also characterized by X-ray diffraction and scanning electron microscopy techniques (Figs. 4 and 5). Their surface area was also calculated using the BET method, yielding a result of 1.0 m² / g. The evaluation of CO2 capture capacity was done with the 3 samples (10%, 20% and 30% K2CO3 added), using the following conditions: • CO2 capture experiments with lithium silicate modified with 10% K2CO3 Capture temperature = tested in the range of 450 to 550 °C. Heating rate: 10 °C per minute N2 flow = 60mL / min Time = 180 min Adsorption gas = 20-30 v / v% CO2 was tested (N2 balance) and 4 v / v% CO was present (He balance) The results of the evaluation of this material are shown in Figure 6. • CO2 capture experiments with lithium silicate containing 20% ​​K2CO3 Capture temperature = tested in the range of 450 to 650 °C. Heating rate: 10 °C per minute N2 flow = 60mL / min Time = 180 min Adsorption gas = 20 v / v% CO2 (N2 balance) in the presence of O2 5 v / v% (N2 balance) The results of the evaluation of this material are shown in Figure 7. • CO2 capture experiments with lithium silicate with 30% K2CO3 Capture temperature = tested in the range of 450 to 550 °C. Heating rate: 10 °C per minute Flow rate = 60mL / min Time = 180 min Adsorption gas = 20 v / v% CO2 (N2 balance) The results of the evaluation of this material are shown in Figure 8. According to previous experiments, the material with the best capture capacity was lithium silicate modified with 10% K2CO3 and adsorption conditions of 450 °C with a flow rate of 60 mL / min of 20 v / v% CO2 (N2 balance) for 3 hours. Its calculated capture capacity was 184 mgCCWg of material. Finally, the regeneration capacity of the materials was evaluated. Figure 9 shows an example of an absorption-desorption cycle with the silicate modified with 10% K2CO3. The experimental conditions are as follows: Capture stage: Temperature = 500 °C. Flow rate = 60mL / min Time = 60 min Gas = 20 v / v% of CO2 (N2 balance) v / v% of CO2 (air balance) v / v% of CO2 (N2 balance) Desorption stage: Temperature = 725-750 °C. Flow = 100mL / min Time = 40 min Gas — N2 From the results of the adsorption-desorption cycles, it was obtained that the materials prepared according to the present invention showed a CO2 capture capacity of 82 mgCCWg material after 20 consecutive CO2 adsorption-desorption cycles, which indicates that the materials have excellent thermal stability and high capture capacity even after 20 absorption / desorption cycles. Alterations to the process described in the present invention may be foreseen by those skilled in the art. However, it should be understood that the present description relates to preferred embodiments of the invention, is for illustrative purposes only, and should not be construed as a limitation of the invention. All obvious modifications to the spirit of the invention, such as changes in the shape, material, and dimensions of the elements comprising the invention, shall be considered within the scope of the appended claims.

Claims

1. A process for manufacturing lithium silicates with CO2 capture and regeneration capabilities using metallurgical slags comprising the steps: a) characterization and conditioning of the metallurgical slags, wherein characterization comprises analytical techniques and conditioning comprises milling and sieving; b) synthesis of the lithium silicates by solid-state reaction of a lithium source with the metallurgical slag from step a); and, c) modification of the silicates to improve their CO2 capture capacity by adding alkali metal carbonate.

2. The process for manufacturing lithium silicates according to claim 1, wherein the analytical techniques for characterizing the metallurgical slags of step a) comprise X-ray fluorescence, xy-ray diffraction, and the Brunauer, Emmett, and Teller (BET) methodology.

3. The process for manufacturing lithium silicates according to claim 1, wherein the solid-state reaction of step b) comprises mixing the lithium source with metallurgical slag in a lithium:silicon molar ratio in the range of approximately 2.05:1 to 2.2:1, preferably 2.1:1, and calcining the mixture, and wherein said lithium source is selected from lithium carbonate, lithium oxide, lithium hydroxide, and similar compounds, preferably lithium carbonate.

4. The process for manufacturing lithium silicates according to claim 3, wherein the calcination of the mixture is carried out at a temperature in the range of approximately 800 to 900 °C, preferably 850 °C for a time of approximately 4 to 8 hours, preferably 6 hours with temperature increases of approximately 10 °C per minute.

5. The process for manufacturing lithium silicates according to claim 1, wherein prior to step c) of modifying the silicates, the reaction mixture of step b) is ground at room temperature to facilitate contact between the materials and wherein the alkali metal carbonate is preferably potassium carbonate.

6. The process for manufacturing lithium silicates according to claims 1 and 5, wherein the grinding of the metallurgical slags in the conditioning step and of the reaction mixture of step b) is carried out with an instrument selected from agate mortar, porcelain mortar, high energy ball mill and the like.

7. The process for manufacturing lithium silicates according to claim 1, wherein the amount of alkali metal carbonate is added based on the percentage of Li4SiO4 obtained, after selecting a percentage of K2CO3 within the range of approximately 5 to 40%, preferably 10 to 30%.

8. The process for manufacturing lithium silicates according to claim 7, wherein the percentage of Li4SiO4 obtained is determined by analytical techniques, preferably by XRD using the RIR method.

9. The process for manufacturing lithium silicates according to the preceding claims, wherein the process further comprises the steps: d) characterization of the lithium silicates obtained in step c) by analytical techniques; e) determination of the CO2 capture capacity of the prepared silicates by thermogravimetric and temperature-programmed techniques; and f) evaluation of the regeneration capacity of the lithium silicates during multiple consecutive CO2 adsorption-desorption cycles.

10. The process for manufacturing lithium silicates according to claim 9, wherein the analytical techniques for characterizing the lithium silicates of step d) comprise X-ray fluorescence, xy-ray diffraction, and the Brunauer, Emmett, and Teller (BET) methodology.

11. The process for manufacturing lithium silicates according to claim 9, wherein the thermogravimetric and temperature programmed techniques of step e) comprise heating the lithium silicate to a temperature in the range of approximately 400 to 600 °C at a heating rate of approximately 5 to 15 °C per minute and subsequently contacting it with a gas stream of CO2 at a concentration of approximately 5 to 30% v / v at a flow rate of approximately 60 to 100 mL / min in the presence of oxygen at a concentration of approximately 5 to 10% v / v and carbon monoxide at a concentration of approximately 2 to 7% v / v.

12. The process for manufacturing lithium silicates according to claim 11, wherein the heating temperature of the lithium silicate is 450 °C, wherein the heating rate is 10 °C per minute, and wherein the concentration of CO2 in the gas stream is 20%v / v.

13. The process for manufacturing lithium silicates according to claim 11, wherein a flow of N2 in the range of 60 to 100 mL / min is added while the silicate is heated to 400-600 °C.

14. The process for manufacturing lithium silicates according to claim 11, wherein the temperature of 400 - 600 °C is maintained for a time of approximately 60 to 180 minutes to favor CO2 adsorption.

15. The process for manufacturing lithium silicates according to claim 9, wherein the multiple CO2 adsorption-desorption cycles of step f) comprise a preheating step of the silicate to a temperature in the range of approximately 450 to 600 °C in an N2 flow in the range of 60 to 100 mL / min; an adsorption step comprising contacting the silicate with a CO2 flow in the range of 60 to 100 mL / min at a concentration of 5 or 20% v / v for a time of approximately 60 to 180 min; and a desorption step wherein the CO2 flow is stopped and changed to a pure N2 flow in the range of approximately 600-150 mL / min while increasing the temperature to 700-800 °C for approximately 40 to 120 min.

16. The process for manufacturing lithium silicates according to claim 15, wherein the number of multiple consecutive CO2 adsorption-desorption cycles ranges from 10 to 50, preferably 20, wherein the preheating temperature is approximately 500 °C and wherein the desorption temperature is 750 °C.

17. The process for the manufacture of lithium silicates according to the preceding claims, wherein the metallurgical slags are from a blast furnace.

18. Lithium silicates prepared in accordance with any of claims 1 to 17.

19. Lithium silicates according to claim 18 for use in post-combustion processes and in hydrogen production processes with integrated CO2 capture.