Hexaaluminates with improved textural properties, their preparation from salt slags from aluminum re

专利摘要:
Hexaaluminates with improved textural properties, their preparation from salt slags from aluminum recycling processes and their use. The invention provides a process for the preparation of hexaaluminates with a reduced number of stages, as it directly uses aluminum extracted from salt slags from aluminum recycling, without additional stages and hot, to be mixed drop by drop with solutions containing metal cations, being able to obtained from the mixture hexaaluminate precursors by coprecipitation, dilution with alcohols or lyophilization. Hexaaluminates are obtained at lower calcination temperatures than usual, and have a perfectly defined crystalline structure and values for specific surfaces and pore volumes, which make them suitable as catalysts, especially for high temperature reactions such as dry reforming of CH4, reaction for which it is preferred that the hexaaluminate contains Ni2+ . Other possible cations present are La3+ and/or Ce3+ . (Machine-translation by Google Translate, not legally binding)
公开号:ES2803955A1
申请号:ES201930694
申请日:2019-07-26
公开日:2021-02-01
发明作者:Bravo Antonio Gil；Sophia A Korili；Ordonez Edwin Gustavo Fuentes；Herrera Jonathan Josué Torrez
申请人:Universidad Publica de Navarra；
IPC主号:

专利说明:

[0002] Hexaaluminates with improved textural properties, their preparation from salt slags from aluminum recycling processes and their use
[0004] Technical field of the invention
[0006] The present invention relates to the obtaining of hexaaluminates and their derivatives, from aluminum residues, for example salt slags from the second melting processes of aluminum. By chemical attack of these residues, it is possible to extract part of the aluminum that is used directly hot and without further treatment steps for the synthesis of hexaaluminates that incorporate cations of other metals, in addition to Al3 +, and products derived from Ni2 +, among others. Hexaaluminates synthesized with the presence of Ni are suitable catalysts to obtain synthesis gas (H ² / CO) from the dry reforming of CH ⁴ .
[0008] Background of the invention
[0010] Aluminum recycling and generation of salt slags:
[0012] Various types of waste are generated in the aluminum recycling process [1], the most important being salt slag. Salt slags are produced by the use of salts that are used to reduce the melting temperature, prevent the oxidation of aluminum and separate impurities from the raw material used [2]. The average composition of salt slags can be summarized as: 3-9% aluminum metal; Various oxides 20-50%, AhO ³ , Na ² O, K ² O, SiO ² and MgO, fraction called non-metallic products; fluxes 50-75%, usually NaCl and KCl; and other compounds to a lesser extent; among them NaI, ALC ³ , AhS ³ , Si ³ P ⁴ , Na ² SO ⁴ , Na ² S and cryolite [3]. The composition of the slag can vary widely depending on the material to be melted, the type of furnace used and its operating mode and the composition of the fluxes used, among others [3-11]. Due to its origin and composition, the salt slags resulting from the aluminum recycling processes are classified as hazardous waste. LER code (European List of Waste) 100308 [12], and they must be deposited in controlled landfills or in security deposits.
[0014] The processes involved in the recovery of this waste are complex. Once the aluminum metal has been separated from the residue by screening, the material produced is treated with water to separate the soluble from the insoluble fraction. In this way, a new residue with lower salt content and a saline solution would be obtained from which the salt should be recovered. The heterogeneous composition of this new waste limits the possible applications and makes it possible to choose its management in controlled discharge. Controlled landfill storage is precisely the other alternative to salt slag management once the aluminum metal fraction has been recovered [3]. This option is not the most desirable, so an attempt has been made to look for alternatives to landfilling that value this type of waste, as well as applications for new materials. The main phase detected in this type of waste is aluminum oxide [13]. Without any additional treatment, it can be used for direct applications such as inert filler for construction, road paving, mortar components, aluminum salts, inert filler in polymeric composites, adsorbents, mineral wool, etc. Aluminum can also be recovered as a high value-added product and used to synthesize materials such as pure alumina, salts and hydroxides [14-16]. Therefore, obtaining aluminum-based materials from this type of waste is one of the objectives set out in this invention.
[0016] Recovery of salt slags:
[0018] There are various processes in which this type of materials have been applied, as well as the new materials that have been synthesized from this waste. Shinzato and Hypolito [17], Miqueleiz et al. [18], Hsieh et al. [19] and Gómez de Salazar et al. [20] have used the non-metallic fraction of salt slags as a substitute material for clay in obtaining blocks with industrial and building applications. López et al. [6] analyze the possibility of producing a mixture of alumina and spinel by sintering the residues produced after the leaching of salt slags. The authors propose that sintered materials can be applied in cement and glass foundries, such as refractory materials, mineral wool, abrasives and ceramic fibers. Yoshimura et al. [21] have proposed to directly use aluminum slag to replace raw material in obtaining refractories. The use of the non-metallic fraction in the production of mineral wool has been reported by O'Driscoll [22].
[0019] The synthesis of calcium aluminate from salt slags or aluminum residues carried out by López-Delgado et al. [23-25] is also an interesting valuation procedure. These types of materials are extremely useful in many fields of metallurgy as additives that reduce the sulfur content of steel and, in general, as refractory materials. Ewais et al. [26] use calcium aluminate made from aluminum slag of 12.50 to 13.75% alumina in mixtures with cement.
[0021] Bajare et al. [27] synthesize lightweight expanded clay aggregates from a clay with a high carbonate content and varying proportions of the non-metallic fraction of salt slags. These aggregates were treated at a temperature of between 1150 and 1270 ° C to remove impurities and to produce a material rich in M ² O ³ and spinel.
[0023] Valorization of aluminum present in salt slags:
[0025] Aluminum present in salt slags can be extracted by treatment with acid or base solutions to be used later in the synthesis of other materials. Thus, for example, aluminum slag treated with H ² SO ⁴ makes it possible to recover a high percentage of aluminum that can be used in the production of y-AhO3 [28]. The authors propose that the synthesized material can be used as an adsorbent or catalytic support, after a treatment at 900 ° C. Pickens and Waite, in US patent US6110434 [29], treat the non-metallic fraction at various pHs to selectively remove alumina and magnesia. At acidic pH, the undissolved magnesium aluminate is filtered off. If the pH of the solution is raised between 9.5 and 12, magnesium oxide precipitates, which can also be removed by filtration. As the pH of the remaining liquid approaches neutrality, alumina trihydrate precipitates, resulting in a pure product. Several authors [30-32] extract the aluminum by means of an acid leaching treatment of the non-metallic fraction at low temperature and synthesize alumina with a high degree of purity (99.28%). Aluminum sulfate can also be used directly as a coagulant for wastewater treatment, as reflected in Spanish Patents ES2176064 and ES2277556 [33,34]. By a procedure similar to that previously described, Park et al. [35] leach a residue with NaOH to extract the aluminum as sodium aluminate and precipitate it as aluminum hydroxide. The oxide, once calcined, is used to manufacture castable refractories by mixing with aggregates and alumina cement. El-Katatny et al. [36] describe a process in the that aluminum is recovered from the slag by precipitation with aluminum hydroxide. The powder obtained is activated at 600 ° C to obtain y-AhO3. A similar procedure is described by Jung and Mishra [37]. Recently Meshram et al. [38] propose the synthesis of tamarugite, an aluminum sulfate (NaAl (SO ⁴ ) - ⁶ H ² O) by adding NaOH and H ² SO ⁴ solutions to the salt slag. This salt can be used as a coagulant. Spinel MgAlO4 is an essential material for various applications where a refractory material is required. With this idea, Zhang et al. [39] synthesize spinel from aluminum slag by physically mixing it with MgO, a pressure of 25 MPa and heat treatment between 1100 and 1500 ° C for 3 h. The authors also study how the density of the material obtained increases by the addition of Eu2O3, La2O3, Y ² O ³ and CeO ² . The results obtained are explained by the formation of oxides of the YAO ³ type, Al2Ca0.5La0.5.
[0027] In Spanish Patent ES2673587 Gil et al. [40] propose the use of the aluminum cation, Al3 +, extracted from salt slags for the synthesis of so-called anionic clays, hydrotalcite-type compounds or mixed metal hydroxides of formula [Me (II) ixMe (III) x (OH) ² ( An-) x / n] .mH ² O (where M (II) is a divalent cation (Me2 +), M (III) is a trivalent cation (Me3 +), A is an anion of charge n, and is a rational number between 0.2 and 4, which determines the charge density in each layer and the ion exchange capacity). Said compounds are laminar double hydroxides that incorporate anions and water in the laminar space. The document shows the obtaining of hydrotalcites of divalent cations such as Co2 +, Mg2 + and Ni2 +, from cationic aluminum (Al3 +) extracted from salt slags, by modified coprecipitation in a single step, which is achieved thanks to the aluminum extracted from salt slag is added dropwise and hot to a solution containing both the precipitating agent and the divalent metal cation and the interlaminar anion. Among others, the method has the advantage that it is not necessary to control the pH of the reaction.
[0029] Hexaaluminates and their synthesis:
[0031] Hexaaluminates are a family of hexagonal aluminate compounds that present a peculiar laminar structure: it consists of a structure of alternating blocks of spinel with closed packets of oxide ions. These materials have a stable phase up to 1600 ° C and exceptional resistance to thermal sintering, the result of their peculiar laminar crystalline structure, which makes them attractive catalysts for applications at high temperatures, such as the combustion and partial oxidation of CH ⁴ , the dry reforming of CH ⁴ to syngas and decomposition of N ² O. The general formula of the compounds can be expressed as ABxAli ² -xOi ⁹ , where A is typically a mono, di, or trivalent cation with a size that allows the formation of this structure (that is, of a size close to that of the Na + ion or greater), generally from the group of alkali, alkaline-earth metals or lanthanides, such as, for example, A = Na +, Ba2 +, La3 +, etc. Component B represents a cation of a transition metal (Mn, Fe, Co, Cu, Ni, etc.), including noble metals (Ir, Ru, Pd, Rh, etc.) that can partially or completely replace the positions of the crystallographic Al .
[0033] The crystalline structure of hexaaluminates was described for the first time in 1958 [41] from a composition LaAl ¹² O ¹⁹ and the first studies in which they were used as catalysts were published by Machida et al. in 1987 [42]. The authors observed that the BaO mixed with AhO3 in the ratio (BaO) ^{0, 14} (A ² O ^{3) 0.86} to the calcining temperature of 1200 ° C, the barium hexaaluminate formed. As the structure was maintained at high temperatures, these materials were considered promising catalysts for catalytic applications at high temperatures.
[0035] Hexaaluminates were first prepared from a solid state reaction. The textural properties exhibited by these solids were low due to their high crystallization temperature. To improve the catalytic applications of these materials, it is necessary for the catalytically active centers to be more accessible, which is why research focused on increasing / improving the textural properties has been necessary. With this idea in mind of the interesting catalytic properties that these materials can present, different synthetic routes have been proposed with the aim of increasing the specific surface of the hexaaluminates, increasing the accessibility to the active centers, and consequently, improving the catalytic behavior. . In general, the synthetic routes developed give rise to the formation of a precursor, which is then heated to a temperature between 1100 and 1600 ° C to generate a material with the structure of hexaaluminates.
[0037] In order to improve the catalytic properties of hexaaluminates, several synthetic ways have been developed to increase the textural properties of these solids. Thus, it is worth mentioning the sol-gel, co-precipitation, inverse microemulsion methods, among others [43]. To carry out these procedures, the characteristics of the aluminum source must be taken into account to increase the textural properties of the solids that are synthesized. The procedure to be followed must also make it possible to obtain a homogeneous solid.
[0038] The most widespread synthesis procedure is that of coprecipitation, also known as the carbonate method, in which the nitrate salts of the metals that are going to form part of the structure and (NH4) 2CO3 are used. By this method, the precursors can be mixed homogeneously as ions and precipitated at the same time. These conditions are favorable for its uniform dispersion in the solution. Heating the material to more than 1200 ° C results in one phase substituted metal hexaaluminates with specific surfaces up to 15 m2 / g. This process for the preparation of hexaaluminates by coprecipitation can be found described, for example, in Example 1 of the application CN1326607, where hexaaluminates of Ba, La and / or Fe are specifically obtained (although it is indicated that Co, Ni, Cu , Mn, Ti or Zr), from a mixed solution of nitrates of said metals and Al, a mixed solution whose pH is adjusted to 1. The mixed nitrate solution is quickly poured onto a saturated solution of (NH4) 2CO3, stirring vigorously for 2 h, and maintaining the temperature at 60 ° C and the pH at 7.5 - 8.0. After filtering, washing and drying at 60 ° C, it is indicated to proceed to calcine at 500, 800, 1100 and 1200 ° C for 3 h. Although, in principle, it might seem that any of the products obtained would serve as a catalyst, Table 1 included in said Example only shows the activity of the hexaaluminates obtained at 1200 ° C, as if it were necessary to subject the precursors to that temperature to obtain hexaaluminates. with catalytic activity. In fact, the description of the figures of said patent application qualifies as samples of typical hexaaluminates of the invention those obtained at 1200 ° C for 4 h, while the "Summary of the Invention", in accordance with claim 1, indicates that, once the precursor is obtained, it is subjected to a calcination process in four stages, at 500 ° C, 800 ° C, 1100 ° C and 1200 ° C, to obtain a hexaaluminate with a high specific surface area. Thus, it seems that all the methods for obtaining precursors described in Chinese patent application CN1326607 require at least one heating phase at a temperature higher than 1000 ° C to obtain hexaaluminates with the desired characteristics.
[0040] Similar is the conclusion reached by reading the article by Ersson et al. of 2006 [50], in which the effectiveness of hexaaluminates of the general formula ^ BAlnO ¹⁹ (specifically, LaMnAlnO ¹ g and LaCoAlnO ^) and perovskites of the general formula ABO ³ (specifically, LaMnO3 and LaCoO3) as catalysts in processes of combustion, particularly in the combustion of methane. As described in experimental section 2.1 of said article, the hexaaluminates whose effectiveness is to be tested are prepared through a co-precipitation process similar to that described in the application for Chinese patent CN1326607, adding a solution containing the nitrates of the metals that are to be part of the hexaaluminate on an aqueous solution with excess ammonium carbonate, with vigorous stirring and maintaining the pH of the carbonate solution at a value of 9. Once the precipitates have been obtained, and after they have been washed and dried, they are calcined at 600, 1000 and 1200 ° C consecutively for 4 h each and then at 1000 ° C for 1 h. As discussed in section 3.1., The materials from which hexaaluminates were to be obtained maintained an amorphous structure after calcination at 600 ° C and only showed a slightly crystalline structure after calcination at 1000 ° C. The final crystalline phase did not form until calcination took place at 1200 ° C. The authors of this article comment that these results are in accordance with previous studies in which it is shown that the hexaaluminate phase is formed at temperatures above 1100 ° C. Regarding the surface area, the hexaaluminates obtained after 4 h at 1200 ° C showed BET surface area values (Brunauer, Emmet and Teller) of 27 m2 / g (LaMnAl ¹¹ Ü ¹ g) and 24 m2 / g (LaCoAlnO ^) and a high activity in the methane combustion reaction (20% conversion at a temperature of 715 ° C in the case of LaMnAlnO ^) and gasified biomass.
[0042] Increasing the surface area of hexaaluminates by new or modified synthetic routes is of great interest for catalytic applications. Zarur and Ying [44] report on a reverse microemulsion sol-gel method to synthesize Ba hexaaluminate nanoparticles with specific surfaces of up to 160 m2 / g. The path is correct but not susceptible to industrial implementation. Metal alkoxides are harmful and expensive, and their hydrolysis must be practiced under extremely controlled conditions. To avoid this limitation, a reverse microemulsion route is proposed by Teng et al. [45] using inorganic salts obtaining hexaaluminates with specific surfaces of up to 70 m2 / g. Alternatively, templates can be used to synthesize high-surface materials by controlling their structure and textural properties [46]. The template methodology was introduced in the field of zeolites and spread in the field of mesoporous materials, where periodic pore systems are created by occlusion of molecular units in the resulting solid. This strategy is called "endotemplar" and is also used in the case of metal oxides. A recent approach is "exotemplary" where extended porous structures provide the space where a divided solid can form. Carbon is the ideal model because of its easy removal by combustion, its versatile porous characteristics, and its relatively low cost. This strategy has been applied to synthesize mesoporous zeolite crystals and nanocrystalline zeolites [47], as high surface oxides [48] (TiO ² , NiAhO4, LaFeO3). The typical preparation of this The type of template oxides involves impregnation of carbon with concentrated solutions of the metal cations, followed by drying and heat treatment. There are no previous studies in which the effectiveness of carbon templates for the synthesis of oxides is presented, mainly in this case where high temperatures of 1200 ° C are required to obtain the hexaaluminate oxide. Under these conditions, the carbon is removed and the formation of hexaaluminate could lead to severe sintering of the intermediate oxidized phase once the carbon is removed.
[0044] US patent US7442669, refers to the synthesis of metal catalysts based on hexaaluminates that are used in the oxidation of methane and natural gas, although it can be extended for the combustion of alkanes and alkenes. This document describes the synthesis of hexaaluminates from an alumoxane precursor. To incorporate the replacement metal they use an acetylacetonate salt of the metal that allows the metal to be incorporated by atomic scale exchange. The authors indicate a series of advantages of this method compared to the traditional coprecipitation or hydrolysis of alkoxides, such as the almost atomic dispersion by ion exchange and the use of water instead of organic solvents. The hexaaluminate structure is obtained after calcination at 1300 ° C. The specific surface area of the material prepared with the formula LaxSryMno, ⁴ A liiO i ⁹ (with x + y = 0.6) is a maximum of 13.5 m2 / g, and can decrease to values close to zero after treatment for 50 h at 1300 ° C.
[0046] The US patent published under the number US 9,566,571 refers to catalysts with hexaaluminate phase containing Co and at least one of the following elements: La, Ba or Sr. The synthesized materials are used for the reforming of hydrocarbons in presence of CO ² at temperatures above 700 ° C and at a pressure greater than 5 bar. The synthesis procedure is based on putting an aluminum source (aluminum oxide, hydrotalcites, etc.) in contact with the salts of Co and one of the elements (La, Ba, Sr). After a time of contact, dry and calcine so that the hexaaluminate-like structure develops. The calcination temperature can be up to 1500 ° C. The specific surfaces that the materials synthesized by this procedure can reach are 15 m2 / g.
[0048] Ferrandon presents in US patent application US 2013/0085062 new formulations of hexaaluminates as reforming catalysts for the production of H ² from organic compounds. In these new formulations, it includes in the hexaaluminates up to four metals with a composition provided by the formula M1aM2bM3cM4dAliiOi9-a, where M1 and M2 can be Be, Mg, Ca, Sr, Ba, La, Ce, Pr, Nd, Pm, Sa and Gd. In the case of M3 and M4 they can be Cr, Mn, Fe, Co, Ni, Cu, Mo, Ru, Rh, Pd, W, Re, Os, Ir, Pt. In addition, the following must be met: 0.010 ^ a + b + c + d ^ 2.0; 0 ^ a <1, and additionally M1 + M2 and M3 + M4. The method used for the preparation of the hexaaluminates is that of coprecipitation from the nitrates of the metals and a solution of ammonium carbonate. The final calcination temperature is 1100 ° C. The author presents specific surfaces for the case of CaAl ¹² O ¹⁹ hexaaluminate of 97 m2 / g, but in no case does he confirm that the oxide phase has developed, so it could be an initial stage of an amorphous phase.
[0050] In European patent application EP 2119671A1, Elm Svensson et al. present a method of preparing hexaaluminates in which they take into account a template material for synthesis. The synthesis begins with a step in which the porous template material, with pore sizes between 5 and 200 nm, is impregnated with a solution containing the metals that constitute the hexaaluminate. The impregnated material is then dried and calcined in an inert atmosphere, obtaining the hexaaluminate by eliminating the mold material. In example 1 of this patent application, they use as template materials a carbon xerogel (CX) synthesized by the authors from the pyrolysis of a resorcyanol formaldehyde gel and a commercial activated carbon (A). The hexaaluminates they intend to prepare are LaAlnO ¹⁹ (LHA), LaMnAlnO ¹⁹ (LMHA) and LaMgAlnO ¹⁹ (LMgHA). The impregnated solids are calcined for 5 h at 1300 ° C in an Ar atmosphere. When commercial activated carbon is used as a mold, the surface areas of the solids are between 55 and 66 m2 / g. They indicate that the amount of hexaaluminate formed is low and that the phase is most abundant in y-AhO3. When they use the carbon xerogel, they obtain a greater amount of hexaaluminate with specific surfaces between 44 and 49 m2 / g. When they replace the Ar atmosphere with air, the specific surfaces decrease to values of 9 to 16 m2 / g.
[0052] For its part, in the family of international patent application WO2013118078, which includes Japanese patent JP6238909B2, Schunk et al. present a process for the preparation of a catalyst for reforming hydrocarbon-containing compounds and the use of said catalyst in reforming hydrocarbons, preferably CH ⁴ , in the presence of CO ² . The catalyst whose preparation is described contains a hexaaluminate phase, which comprises cobalt and at least one additional element from the group of La, Ba and Sr, and may contain a secondary phase of oxides. The method of obtaining the catalyst is based on contacting a suspension that contains cobalt and at least one element from the group of La, Ba and Sr with a source of aluminum oxide, preferably, a boehmite composed of small primary particles, forming a suspension, which is stirred sufficiently before being introduced dropwise in a liquid N ² bath, obtaining frozen particles of 5 mm in diameter with the suspension, particles that are subjected to drying by lyophilization to later, with intermediate grinding, be subjected to a precalcination at 520 ° C followed by another calcination at 1100 ° C.
[0054] In line with the previous patent ES2673587, it is interesting to have processes that facilitate the recovery of salt slags from aluminum second-melting processes and that give rise to products of industrial interest, such as hexaaluminates. Preferably, the designed process should be as simple as possible, reducing if possible the temperature at which the hexaaluminate structure is obtained, and the contact between the metal cations that constitute the oxide, but achieving a product that has high textural properties. , to facilitate its industrial application, particularly as a catalyst. The contribution of new and alternative processes to obtain the precursors of the hexaaluminates could also provide new synthesis routes to explore, on which to make modifications with a view to obtaining improvements.
[0056] The present invention provides a solution to that problem.
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[0156] Patents
[0158] D. Wickham, R. Cook, Oxidation catalysts comprising metal exchanged hexaaluminate wherein the metal is Sr, Pd, La, and / or Mn. US 7,442,669 (2008).
[0160] A. Gil Bravo, S.A. Korili, E. Arrieta Chango, Procedure for the manufacture of anionic aluminum clays and their derivatives from salt slags from aluminum recycling processes. ES 2,673,587 (2018).
[0162] MS Ferrandon, Novel formulation of hexa-aluminates for reforming fuels. US 2013/0085062 A1.
[0163] S. Schunk, A. Milanov, A. Strasser, G. Wasserschaff, T. Roussiere, Hexaaluminatecomprising catalyst for the reforming of hydrocarbons and a reforming process. US 9,566,571 (2017).
[0165] E. Elm Svensson, M. Boutonnet, S. Jaras, Preparation of hexaaluminate. EP 2119671 A1 (2009).
[0167] S. Schunk, A. Milanov, A. Strasser, G. Wasserschaff, T. Roussiere, Hexaaluminathaltiger Katalysator zur Reformierung von Kohlewasserstoffen sowie ein Verfahren zu Reformierung. WO2013118078A1, published August 15, 2013
[0169] Summary of the invention
[0171] The present invention is based on a process for the preparation of hexaaluminates with an ABxAl ¹² -xO ¹⁹ type structure, where A is a cation of a metal from the group of alkaline earth metals or lanthanides, such as La, Ba, Ca , Ce, Sm, Sr; and where B, if present (that is, when x is nonzero), is a cation of a transition metal, such as Mn, Fe, Co, Cu, Ni, with preference for B = Ni2 +, and being possible also one or more noble metal cations, such as Ir, Ru, Pd, Rh, among others, and where the hexaaluminates contain Al3 + from a saline slag, a process in which the preparation of the precursor takes place either by modified coprecipitation procedures or by dilution with alcohols that include the dropwise addition of all the solutions containing the metal cations, both the solution containing Al3 + and the solution containing the remaining metal cations, the latter solution that may have been previously mixed with the solution containing the Al3 + or it can be added simultaneously together with the solution containing Al3 + to the liquid in which the hexaaluminate precursor is produced. Thus, the solution that contains the remaining metal cations and that is added dropwise can be: either a different solution from the one that contains the Al3 +, and that is added at the same time as the Al3 + on a solution that contains a precipitant in the one that is going to form the precursor (coprecipitation process), or it can be a solution that also already contains Al3 +, because it has previously been added dropwise to the solution containing the remaining cations, then adding the combined solution that it already contains Al3 + and the remaining cations on the liquid in which the precursors are formed and from which the precursors of the hexaaluminates are obtained in solid form. Said liquid from which the hexaaluminate precursors are obtained can be a solution with one or more alcohols in the process of formation of dilution precursors with alcohols.
[0172] Surprisingly, the method of the present invention, characterized in that it produces the dropwise addition of each of the solutions containing cations that are to form part of the hexaaluminate, not only has the advantages that no control is required of the pH (simplifying the procedure) and that Al3 + is recovered from an industrial waste such as saline slags that it was unknown that could be used for the synthesis of products with a structure as complicated to obtain as hexaaluminates, valuing them, But, in addition, it is observed that the precursor calcination process can be carried out at temperatures lower than usual or close to the usual lower limit (starting to form the structure with calcination at 800 ° C and having a perfectly defined structure at 1000 ° C ), still obtaining solids with the peculiar structure of hexaaluminates, which, in addition, have a high specific surface and other prop Properties that make them suitable as catalysts for high temperature applications, such as the partial combustion and oxidation of CH ⁴ , the dry reforming of CH ⁴ to synthesis gas and the decomposition of N ² O.
[0174] Thus, it can be said that the object of the present invention refers to a method of preparing hexaaluminates and its derivatives with improved textural properties, from salt slags from aluminum recycling processes, and their application as catalysts, for example in the dry reforming reaction of methane. The general method for preparing hexaaluminates of the present invention encompasses several alternatives for obtaining the hexaaluminate precursor, preferably in solid form, one of which, the dilution procedure with alcohols, had not been proposed until now for this purpose and which It is an alternative with specific advantages (especially with respect to favoring the interaction between cations) and variants with respect to the usual methods on which new modifications can be made to seek additional improvements.
[0176] Therefore, in a first aspect, the present invention relates to a method for the preparation of hexaaluminates with improved textural properties of the general formula
[0178] ABxAli2-xOi9,
[0180] where
[0181] A is a cation of a metal selected from the group of alkaline earth metals with an atomic weight equal to or greater than that of Ca and lanthanides, or a combination of metal cations selected from said group,
[0183] B is a cation of a transition metal or a combination of cations of different transition metals, including the noble metals
[0185] x is a rational number that varies between 0 and 2,
[0187] from salt slags from aluminum recycling processes, comprising the stages of:
[0189] a) Obtain a solution containing Al3 + from the saline slag by means of the sub-stages of
[0191] i) contacting the salt slag with an acidic or basic aqueous solution, ii) allowing the solution to react with the salt slag,
[0192] iii) separating the saline slag from the acusa phase containing Al3 + in solution,
[0194] b) Obtain a hexaaluminate precursor in a liquid by means of a process in which the aqueous solution containing Al3 + is mixed, drop by drop, with another solution containing the metal cations A and, if x is different from 0, it also contains B ;
[0196] c) subjecting the solid precursor obtained in step b) to a calcination heat treatment at a temperature between 800 ° C and 1000 ° C.
[0198] Step b) of obtaining the precursor is carried out by means of a process that, preferably, is selected from the group of:
[0199] i) a coprecipitation procedure, comprising the sub-stages of: a. mix the solution containing the metal cations A and, if x is different from 0, also B, with the solution containing Al3 +, adding both solutions simultaneously, dropwise and hot, on a hot solution containing a precipitating agent, b. allow the mixture obtained in sub-step a to react. at least until the solution containing Al3 + has been added and up to a maximum of 16 h,
[0200] c. optionally, separate the solid formed in sub-step b. of the supernatant; Y
[0201] d. optionally, submit the solid obtained in b or c. to a drying treatment;
[0203] ii) a dilution procedure with alcohols, comprising the sub-steps of:
[0204] to. add the solution containing Al3 +, drop by drop, to the solution containing the metal cations A and, if x is different from 0, also B, b. add the solution with the mixture of metal cations A, B if x is different from 0, and Al3 + obtained in sub-step a., drop by drop, to a solution containing at least one alcohol, which is selected from the group of ethylene glycol , isopropanol, ethanol, methanol, n-hexanol, polyethylene glycol, and polyethylene glycol monolaurate, and mixtures thereof, c. allow the mixture obtained in sub-step b to react. at least until the solution with the mixture of metal cations obtained in sub-step a is finished adding. and up to a maximum of 30 minutes, d. optionally, submit the solution obtained in sub-step c. to a drying treatment until obtaining a solid.
[0206] Following this method, in step b) the hexaaluminate precursors are obtained, preferably in solid form, either due to their precipitation or due to drying (depending on the precursor preparation procedure used). The precursor is preferably subjected to an initial heat treatment that causes it to dry, and is then subsequently subjected to a final heat treatment, which is usually called calcination, at a temperature between 800 and 1000 ° C that produces the hexaaluminates with improved textural properties, useful for use as adsorbents or as catalysts.
[0208] Another aspect of the present invention is the use of the hexaaluminates obtained by the method of the present invention as adsorbents and / or as catalysts. The use as catalysts is preferred, particularly in reactions that take place at elevated temperatures, for which the hexaaluminate preferably has a specific surface area between 1 m2 / g and 60 m2 / g. One possible embodiment is the use as catalysts in synthesis gas formation reactions (production of H ² and CO) from the reforming of CH ⁴ and / or other hydrocarbons in the presence of CO ² , as well as the combustion and partial oxidation of CH ⁴ , and decomposition of N ² O. For the dry reforming of CH ⁴ (conversion of CH ⁴ in the presence of CO ² for the production of H ² and CO), it is preferred that the selected hexaaluminate contain Ni2 + in its structure.
[0210] A further aspect of the present invention are the hexaaluminates obtained by the process of the present invention. Preferably, they are hexaaluminates obtained by the process of the present invention of the general formula
[0212] ABxAl12-xO19,
[0214] where
[0216] A is a cation selected from the group of La3 +, Ce3 +, and combinations thereof,
[0218] B that can partially or completely replace the positions of the crystallographic Al3 + that can be Ni2 + or be absent (that is, x = 0)
[0220] x is a rational number that varies between 0 and 2,
[0222] and that have a specific surface equal to or greater than 1 m2 / g. In particular, those in which x is 0 and A is a cation selected from the group of La3 +, Ce3 +, or combinations thereof, in which the metal cations / Al3 + ratio is 1/12 are included within the present invention. Specifically, such hexaaluminates can be LaAl12O19, CeAl12O19, La0.8Ce0.2Ah2O19, very especially those obtained by the method of the present invention in which the solution containing Al3 + has been obtained by treating a saline slag with an acid, especially HCl.
[0224] Embodiments of the invention are those in which the specific surface area is between 1 m2 / g and 60 m2 / g. Preferably, the specific surface is greater than 10 m2 / g.
[0226] Also embodiments of the invention are those in which the total pore volume is between 0.0001 and 0.4000 cm3 / g.
[0227] Brief description of the figures
[0229] Fig. 1: X-ray diffractograms of La hexaaluminates synthesized by the process of coprecipitation with commercial aluminum precursors and aluminum extracted with an acid solution of salt slags. For comparison, the lower panel includes the diffraction pattern of LaAl ¹² O ¹⁹ powder with its reference number.
[0231] Fig. 2: X-ray diffractograms of La hexaaluminates synthesized by the procedure of dilution with alcohols with aluminum extracted with an acid solution of salt slags. For comparison, the diffraction patterns of the LaAl ¹² O ¹⁹ and LaMgAl ¹² O ¹⁹ powder samples are included.
[0233] Fig. 3: Conversion of CH ⁴ and CO ² and molar ratio H ² / CO, according to time in stream (TOS), in the dry reforming reaction of CH ⁴ . Catalysts: R-NiLaCeAlnO ¹⁹ calcined at 1200 ° C and EA-NiCeAlnO ¹⁹ calcined at 1000 ° C. Reaction conditions: GHSV = 120000 gcat-1-h-1, Reaction temperature = 700 ° C, P = atmospheric, molar composition CH ⁴ : CO ² : He = 10:10:80, catalyst weight = 25 mg.
[0235] Description of the invention
[0237] As mentioned above, the object of the present invention refers to the manufacture of hexaaluminates and their derivatives with improved textural properties from salt slags from aluminum recycling processes, to the hexaaluminates obtained by said process and to use of the same as adsorbents and / or catalysts.
[0239] The synthesis process is carried out using directly and preferably hot, the solution containing Al3 +, without any conditioning step and applying new procedures to obtain the precursors of the hexaaluminates in which it is not necessary to control the pH. These new procedures, specifically, are two alternative methods for obtaining the hexaaluminate precursors, either as a precipitate or in alcoholic solution, with approximately similar results: they are the procedures that are called herein the coprecipitation procedure, and the dilution procedure with alcohols. Next, the hexaaluminate precursors obtained by either of the two processes are preferably subjected to an initial drying treatment, from which the precursors are obtained in solid form and separated from the medium in which they have been formed, and subsequent heat treatment at a temperature between 800 and 1000 ° C, to obtain the hexaaluminates themselves, preferably at a value of 1000 ° C or close to it, in the well defined structures are obtained. In the state of the art, the temperatures necessary to obtain hexaaluminates range between 1100 and 1600 ° C depending on the nature of the cation A or B present in the structure, so that calcination at a lower temperature is an important technical advantage over of commonly known methods. Furthermore, the hexaaluminates object of the present invention have specific surfaces generally comprised between 10 and 60 m2 / g, the range of 1 m2 / g being able to extend to about 160 m2 + / g, that is to say, notably higher than those obtained by many of the methods known in the state of the art and, in any case, suitable for use as catalysts. As used herein, a hexaaluminate is considered to have improved textural properties when its specific surface area is at least 1 m2 / g, which is a suitable value for use as a catalyst, particularly in reactions such as reforming hydrocarbons. (preferably methane) or the oxidation of various components of gasified biomass.
[0241] The synthesized hexaaluminates can be used as catalysts, for example in the dry reforming reaction of methane for the production of synthesis gas, a process for which, as in other documents of the state of the art, hexaaluminates that include Ni2 + in its structure.
[0243] The present invention includes new methods for the synthesis of hexaaluminates that make it possible to use, directly and hot, the aqueous solution from the extraction of Al3 + from a salt slag. For this, the starting material (salt slag) is treated with solutions of acids or bases to extract aluminum, taking into account the treatment time and temperature as variables. This first stage of treatment of the starting material was already described and optimized in a previous patent, specifically Spanish Patent ES2350435 [49], aimed at making use of salt slag once it has been treated for the synthesis of compounds with a structure different from that of hexaaluminates: lamellar double hydroxides known as anionic clays, hydrotalcite-type compounds or mixed metal hydroxides of formula [Me (II) ¹ -xMe (III) x (OH) ² (An-) x / n] .mH ² O ( where M (II) is a divalent cation (Me2 +), M (III) is a trivalent cation (Me3 +), A is an anion of charge n, and is a rational number between 0.2 and 4, which determines the density load in each layer and the capacity of ion exchange). The aluminum extraction procedure described in said Spanish patent consists of putting a saline aluminum slag in contact with an aqueous, acidic or alkaline solution. The conditions under which this step of contact with the slag or extraction of the aluminum is carried out can be any, as long as they give rise to the extraction of aluminum. The contact process temperature is generally room temperature, but may range from 20 ° C to reflux temperature, which will be approximately 100 ° C at a pressure of 101.33 kPa (1 atmosphere). The pressure at which this step is carried out can be atmospheric pressure, but it can also be carried out at higher pressures. The contact time is highly dependent on the reaction temperature, but is generally in the range of 0 to 2 h. Preferably, this extraction step a) is carried out in a stirred vessel although, optionally and / or after a first stirring step, it can be carried out under refluxing conditions.
[0245] In the present invention, the aluminum extracted from saline slag is used following the same method described in Spanish patent ES2350435, also using directly, and adding it drop by drop, the solution obtained as a supernatant in the residue activation process (the saline slag) . But in the present invention, said solution with the extracted aluminum is used for the synthesis of different products, not mentioned in said Spanish patent and that have a different and peculiar structure, often difficult to obtain, and different from the structure of clays. anionic or hydrotalcites: hexaaluminates, also with high values of specific surface. And, surprisingly, the direct use of the solution containing the Al3 + extracted from the saline slag, in combination with the addition of said solution with Al3 + dropwise with the dropwise addition of the solution containing the remaining metal cations that It is intended that they form part of the hexaaluminate structure (either simultaneously with the solution containing Al3 +, or after having incorporated this last cation also to the same solution) in the container in which the precursors are formed, facilitating the obtaining of the precursors by means of any of the two alternative processes compatible with the present invention and that are part of it (coprecipitation and dilution with alcohols), gives rise to the fact that hexaaluminates can be obtained by calcining the precursors at temperatures lower than those required in the state of technique (between 800 ° C and 1000 ° C, compared to the usual 1100 ° C - 1600 ° C, although the temperature range Heating ures can be extended up to, e.g. eg 1200 ° C for added safety, as has been done with a specific hexaaluminate in the Example 2), hexaaluminates that, in addition, have specific surface values that make them suitable for use as catalysts in high temperature reactions.
[0247] As in Spanish patent ES2350435, it is preferred that the saline slag is a slag from a second aluminum melting process, with special preference for slag from a fixed shaft rotary furnace, and very especially when they have a size equal to or less than 1 mm. But the process of the present invention can also be applied to salt slags from other processes related to aluminum, these other alternatives being included within the scope of the invention.
[0249] Regarding the ratio between the reagents, it is considered appropriate to contact, for example, 2 g of salt slag with 0.2 liters of aqueous, acidic or basic solution, as in the Examples of the present application.
[0251] Of all the variables of the aluminum extraction process studied in patent ES2350435, the most important are the pH of the activation solution, the concentration of the chemical agents, the time and the contact temperature.
[0253] It is preferred that the pH of the extraction solution is less than 2 or greater than 10, although it depends on the concentration of the acid or the base. Specifically, the concentration of the acids and bases used in this work varied between 0 and 2 mol / liter, observing that a greater quantity of extracted aluminum is obtained when concentrations of 2 mol / liter are used.
[0255] Regarding the concentration of the acidic or alkaline aqueous solution, concentrations of 2 mol / liter or less are preferred. Thus, in said aqueous solution one or more acidic compounds or one or more basic compounds may be present at concentrations preferably between 0 and 2 mol / liter. Acids can be organic or mineral origin, such as nitric (HNO ³ ), sulfuric (H ² SO ⁴ ) or hydrochloric (HCl) acids. Among the possible basic compounds that can be added to achieve alkaline solutions, sodium hydroxide (NaOH) stands out, but others can also be used, such as sodium bicarbonate (NaHCO3), which leads to alkaline pHs closer to neutrality, of about 8.
[0256] As for the extraction temperature, it can be between room temperature and reflux temperature, but the latter is preferable since the amount of aluminum extracted is greater.
[0258] Once the contact time that has been considered adequate has elapsed, the saline slag is separated from the solution with which the aluminum in the form of Al3 + cations has been extracted. To carry out the salt slag separation step, any separation technique can be used, such as filtration, centrifugation, decanting of the supernatant after leaving the mixture of salt slag and solution and the like. In the present invention, the use of filtration is preferred.
[0260] The sub-stages that have just been described, which give rise to obtaining the solution containing Al3 + from salt slags, are included in the procedure described in the patent publication number ES2673587 B2 and coincide in the way of being carried out with what is described in said patent document, although it did not mention that the use of said solution and, specifically, that the addition of the same dropwise and hot to a container in which it is going to be mixed with other cations metallic, could have some interest or some advantage for the preparation of other solid structures of which the Al3 + cation forms part other than anionic clays, not mentioning in said patent a possible application for the preparation of compounds with a structure as peculiar as that of of hexaaluminates, which are the object of the present invention. The steps detailed below are already specifically intended for the synthesis of hexaaluminates and designed for it.
[0262] The aluminum in cationic form present in the aqueous solution resulting from step a) of the method of the present invention is used for the synthesis of hexaaluminates. Said synthesis is carried out according to this invention, using directly and, if desired, hot, the solution in which the aluminum has been extracted, without any conditioning step, but adding it drop by drop to the container in which it is mixed with the metal cations. A and B, all of which had not been described so far in any of the state-of-the-art methods for the preparation of hexaaluminates. The method of preparing hexaaluminates of the present invention is the main object of the invention, as explained above. The temperature range in which the solution containing Al3 + extracted from the salt slags can be used, without the need for additional heating of said solution containing the extracted Al3 +, would be between 40 and 60 ° C or 70 ° C, if the Precursor is obtained by the coprecipitation method, the temperature is not critical when dilution with alcohols is used. The solution containing Al3 + is reacted with a solution containing the cations of the remaining metals that will form part of the hexaaluminate structure to obtain a hexaaluminate precursor, which can be achieved, according to the method of the present invention, by at least two different procedures, which have been called coprecipitation and dissolution with alcohols, although the method of the present invention is compatible with other procedures for obtaining precursors. Depending on the specific procedure for obtaining the precursor, the mixture of the aluminum cation and that of the remaining metal cations is carried out well by adding the solution containing Al3 + and the solution containing the remaining metal cations at the same time, drop by drop, to the solution containing the precipitating agent (in the case of the coprecipitation process), or because the solution containing Al3 + is previously added to the solution containing the remaining metal cations and the solution formed, with the mixture of all metal cations , is then added to the container in which the precursor is produced (case of the dilution process with alcohols, where no precipitating agent is necessary). In the case of using an extraction temperature lower than 40 ° C, the amount of aluminum extracted will be much less. In this situation, the amount of hexaaluminate that can be synthesized will also be less or it will be necessary to increase the volume of the equipment since the volumes of the solutions to maintain the yields will also be greater. In this second case, the volume of water to be managed will increase. It should also be noted that, if the extraction of aluminum occurs at a lower temperature, an additional step of heating the solution containing Al3 + will be necessary, to at least 40 - 60 ° C or 70 ° C, since the reaction for the Obtaining the hexaaluminate precursors must be done hot, in the case of the coprecipitation process. Therefore, the temperature of the solution containing the divalent metals and the precipitating agent should also be at least 40 - 70 ° C, preferably at least 40 - 60 ° C, when the Al3 + is added and should be kept at least at that temperature during the reaction time between Al3 + and the other reagents that give rise to the hexaaluminate. In the case of the dilution process with alcohols, this heating sub-step is not limiting.
[0264] The preparation of the precursor by the coprecipitation process that is part of the method of the present invention requires the preparation of three solutions. In the first, as already mentioned, the starting point is an aqueous solution containing aluminum that comes from the attack, with acidic or basic solutions, of salt slags generated in the recycling of scrap metal and aluminum by-products. This dissolution is not undergoes no additional intermediate preparation step, unless it is at a lower temperature and requires heating up to 40 ° C - 70 ° C. Additionally, another solution is prepared that contains the other cations that will form part of the hexaaluminate structure. The pH of this solution must be acidic and can be between 0 and 5. These two solutions are added dropwise, and preferably with stirring, to another solution containing the precipitating agent. The precipitating agent is preferably ammonium carbonate, (NH / O ² CO ³ , preferably at a concentration of ¹ mol / dm3, which is what will cause the precipitation. Other precipitating agents can be used, including ammonium and sodium hydroxide.
[0266] The reaction time between the solutions can vary, although it is considered suitable, whatever the precursor preparation procedure used, which is comprised between at least until the solution is added with the aluminum and up to a maximum of 16 h , it being preferred that it be between 1 and ⁶ , as in Example 1 of the present application, in which the coprecipitation procedure is used. The reaction is carried out under stirring, and it is recommended that the stirring speed be in the range between 100 and 700 rpm.
[0268] Preferably, the precursor is separated from the liquid medium in which it has been formed before being subjected to the calcination heat treatment, by a technique that is selected, for example, from the group of filtration (as in Example 1), centrifugation, decantation or direct evaporation of the solvent. It is also preferred that it undergoes a drying heat treatment, optionally (but also preferably) after having been separated from the liquid medium (supernatant) in which it has been formed, a drying treatment that can take place in an oven at atmospheric pressure, or empty. When drying occurs in an oven, it is preferred that it lasts between 4 h and 24 h, and more preferably, that it occurs at 100 ° C for 16 h.
[0270] This method, in addition to serving to value salt slags by obtaining a solution with Al3 + that is used directly to obtain the precursors, has the advantage that it is not necessary to control the pH of the reaction, unlike the reported coprecipitation methods. to date, such as that described in application CN1326607 or in the article by Ersson et al. of 2006 discussed above, in which it was necessary to control the pH of the reaction. In any of these methods, unlike the modified coprecipitation process of the present invention, neither the solution containing the Al3 + nor the solution containing the cations of the other metals are added separately (although simultaneously) drop by drop on the precipitating agent, but in both cases a solution is prepared that contains all the metal cations that will form part of the hexaaluminate and it is poured on the precipitating agent, even indicating that that step must be done quickly, as can be read in application CN1326607.
[0272] Surprisingly, this variation in the coprecipitation process results in the hexaaluminates of the present invention being obtained from their precursors using calcination temperatures preferably between 800 ° C and 1000 ° C, obtaining the hexaaluminates with the highest specific surface area at temperatures from about 800 ° C to 1000 ° C (which is the preferred calcination range) and the hexaaluminate structure being fully formed at 1000 ° C, which is the particularly preferred temperature, with a calcination time of 0.5 h at 4 h, preferably 2 h. In any of the methods of the state of the art in which co-precipitation is used that were discussed above, it is necessary that there be a heating phase at a temperature higher than 1000 ° C to obtain hexaaluminates of the desired characteristics.
[0274] Therefore, the step of obtaining hexaaluminate precursors by the coprecipitation process, by itself, constitutes an alternative to the processes of the state of the art that incorporates variants thereof that had not been described in them and that gives rise , among others, to an unexpected advantage with regard to the calcination temperature ranges that it is valid to use to obtain hexaaluminates with the desired characteristics.
[0276] The method of the present invention for the preparation of hexaaluminates from salt slags from aluminum recycling processes, in which the precursors are obtained by means of the modified coprecipitation process that has just been described, can thus also be defined as a method that comprises the stages of:
[0278] a) contacting the salt slag with an acidic or basic aqueous solution; b) allowing the solution to react with the salt slag;
[0279] c) separating the salt slag from the resulting aqueous solution with Al3 +;
[0280] d) adding the aqueous solution from step c), dropwise, while hot and together with another solution containing metal cations, on a hot solution containing a precipitating agent;
[0281] e) allow to react at least until the solution with aluminum has been added and up to a maximum of 16 h.
[0283] where steps d) and e) would be those of the procedure for obtaining precursors by modified coprecipitation.
[0285] The method of obtaining the hexaaluminates comprises the additional steps of:
[0287] f) separating the solid formed in e) from the supernatant;
[0288] g) subjecting the solid obtained in f) to initial heat treatment (which can be in an oven or under vacuum).
[0289] h) subjecting the solid obtained in g) to final thermal treatment, at a temperature preferably between 800 and 1000 ° C, preferably 1000 ° C.
[0291] In a second procedure for obtaining precursors, the procedure by dilution with alcohols, the aqueous solution containing the aluminum cation is added, drop by drop but without the need for other treatment, on the dilution containing the cations of other metals: the cations metal cations A and, if cations B must be present (that is, if x is different from 0 in the formula of the hexaaluminate to be formed), also metal cations B. Next, the solution formed, with the mixture of all cations Metals are added dropwise and without the need for pH control to a solution containing one or more alcohols, which can be isopropanol and / or ethylene glycol, but also others such as ethanol, methanol and n-hexanol, also including polyethylene glycol and polyethylene glycol monolaurate, or mixtures thereof. The reaction should be allowed to proceed at least until the solution with the metals has been added and up to a maximum of 30 minutes.
[0293] Once the reaction time has elapsed, a precipitate is not obtained, but it is convenient to subject the mixture obtained to a drying treatment (which can be in an oven, under vacuum, or even an additional treatment in an autoclave reactor for a maximum time 24 h) to obtain the precursor in solid form and submit it to the final calcination treatment to obtain the hexaaluminate.
[0295] In carrying out the method of the invention in which the precursors are obtained by this dilution procedure in alcohols, it is not necessary that the solution containing the Al3 + is hot when it is added to the solution containing the metal cations A and (if they have to be present in the hexaaluminate) also B, although it is preferred that it be at a temperature of 40 ° C to 70 ° C for simplicity of the procedure, since it is the temperature range in which it will probably have been obtained from the Al3 + extraction step from salt slag and thus can be used directly. As for the solution containing one or more alcohols, it preferably contains at least ethylene glycol, and optionally also isopropanol. Regardless of the above preferences, it is preferred that the reaction of the alcohol solution with the mixture of metal cations occurs with stirring, and it is also preferred that, after the reaction time has elapsed, the mixture is subjected to a drying treatment at a temperature between 60 ° C and 120 ° C for a time between 4 and 24 h until a solid is obtained, optionally followed by an additional treatment in an autoclave reactor for a maximum time of 24 h. All these preferences on the conditions of formation of the precursor by the process of dilution with alcohols can be chosen independently and can be combined with each other.
[0297] As in the previous case, this method has the advantage that it is not necessary to control the pH of the reaction. As an additional advantage is that, if present, ethylene glycol favors the interaction between the metals that are part of the hexaaluminate structure, without forming the metal alkoxide, so it is preferred that at least ethylene glycol is present in the solution. of one or more alcohols, more preferably mixed with isopropanol, as in Example 2, where a 50% -50% (1: 1 volume: volume) solution of ethylene glycol and isopropanol is used. Likewise, it is intended to avoid the excessive presence of water that can favor the sintering of the hexaaluminate crystals, reducing the textural development of the oxide. Furthermore, again, the temperature necessary for the formation of a hexaaluminate with the desired structure is lower than in the usual methods of the state of the art, and can preferably be between 800 ° C and 1000 ° C, for example during 4 h at 24 h, heating at 1000 ° C for 6 h to 16 h at atmospheric pressure, for example for 6 h, as in Example 2 being particularly preferred.
[0299] It is worth noting that none of the hexaaluminate preparation methods of the state of the art include or propose a step in which the metal cations that must form part of the hexaaluminate structure are mixed with alcohols, nor has any document been found to suggest that Said procedure could be used to prepare hexaaluminates, so the method of the invention in which this procedure of dilution with alcohols is used to obtain the hexaaluminate precursors it constitutes a new and inventive alternative to the usual procedures. Being a new method and the use of which had not been suggested, there was also no reason to expect that obtaining the precursors using this procedure would allow the temperature at which hexaaluminates are formed to decrease.
[0301] Therefore, the stage of obtaining hexaaluminate precursors by the dilution procedure in alcohols of the solution containing the metal cations, especially when it is added dropwise, constitutes by itself an alternative to the procedures of the state of the art. not described so far and that gives rise, among others, to an unexpected advantage in regard to the ranges of calcination temperature that is valid to use to obtain hexaaluminates with the desired characteristics but that also provides another advantage, regardless of whether it achieves or does not reduce the calcination temperature, which is the advantage, as has already been pointed out, of avoiding the excessive presence of water that can favor the sintering of the hexaaluminate crystals, reducing the textural development of the oxide. Furthermore, as demonstrated in Example 2, this process for the preparation of hexaaluminate precursors is perfectly compatible with the use of salt slags as a source from which to extract the aluminum, giving rise to a solution with Al3 + that combines with the solution that It contains other cations and is then added to the solution with alcohols. Thus, carrying out the method of the present invention for the preparation of hexaaluminates from salt slags from aluminum recycling processes, in which the stage of obtaining the precursors includes the dilution procedure with alcohols that has just been described, is a new and inventive embodiment that can also be defined as a method comprising the steps of:
[0303] a) contacting the salt slag with an acidic or basic aqueous solution; b) allowing the solution to react with the salt slag;
[0304] c) separating the salt slag from the resulting aqueous solution with Al3 +;
[0305] d) adding the aqueous solution from step c), dropwise, to another solution containing metal cations;
[0306] e) adding the aqueous solution from step d), dropwise, to a mixture of alcohols, which preferably ethylene glycol and, more preferably, also includes isopropanol;
[0307] f) allow to react at least until the solution with the metals has been added and up to a maximum of 30 minutes.
[0308] The method comprises the additional steps of:
[0310] g) subjecting the solution obtained in f) to a drying treatment, which can be in an oven for 4 h to 24 h (preferably 16), under vacuum, and even be followed by an additional treatment in an autoclave reactor for a maximum time of 24 h, h) subjecting the solid obtained in g) to final heat treatment at a temperature preferably comprised between 800 and 1000 ° C.
[0312] According to the foregoing, it can be seen that in the process for the formation of dilution precursors with alcohols of the present invention, this reaction consists of adding drop by drop, and preferably under stirring, the solution containing Al3 + and the metal cations on a solution of one or more alcohols, preferably a mixture of alcohols. In this procedure, as has been commented, it is not critical that the solution containing Al3 + is hot, although it can thus be added to the solution containing the other metal cations, so as not to have to modify the temperature at which it is obtained in the extraction of aluminum from salt slags and simplify the procedure as much as possible.
[0314] Regarding the cation "A" of the hexaaluminates, whatever the process by which the precursor is prepared, it is a cation of a metal that is preferred because it is selected from the group of cations of alkaline earth metals or lanthanides, such as Ca, Ba, La, Sm, Sr, Pr, Nd, Pm, Gd. The cations Ca2 +, Ba2 +, La3 +, Sm3 +, Sr2 + are preferred, although it can also be Pr2 +, Nd2 +, Pm2 +, Gd2 + or other metal cations, preferably divalent, of large size, that is, the cation of Ca2 + or higher (condition that they fulfill divalent cations with an atomic number equal to or greater than that of Ca2 +). The ABxAli ^{2 -xOi 9} hexaaluminate structure can also incorporate cations of one or more transition metals (B) (Mn, Fe, Co, Cu, Ni, among others), including those considered noble metals (Ir, Ru, Pd, Rh, among others) whose objective is to partially replace Al3 +, and whose charge will depend on its size and that they can comply with the neutrality of the structure, so they can be present in the structure of hexaaluminates with different charges (Mn2 + / 3 +, Fe2 + / 3 +, Co2 + / 3 +, Cu + / 2 +, Ni2 +, Ir3 + / 4 +, Ru2 + / 4 +, Pd2 + / 4 +, Rh2 + / 3 +, among others).
[0316] The solutions containing the metals (and, in the co-precipitation method, the precipitating agent) are preferably prepared once the concentration of aluminum in the extraction solution is known, by choosing the concentrations of the salts of the metals. metal cations in order to obtain solids with the desired Me / Al3 + ratios. Preference is given for the ratio range used in the Examples of the present invention, ie Me / Al3 + 1:12 molar ratios. As for the salts used, preference is given to those customary in the methods of preparing hexaaluminates, particularly nitrates and / or chlorides, and also acetates.
[0318] As a result, a hexaaluminate precursor is generated which will be properly obtained as such once treated at high temperature, after which a solid with the structure of hexaaluminates will be obtained. In order to obtain the dry and separated precursor from the reaction mixture in which it has been formed, it is preferred that the method of the invention includes subsequent steps in which the precursor is separated from the supernatant (coprecipitation method) or from the liquid in which It has been formed and subjected to drying heat treatment. The separation of the precursor from the supernatant or from the liquid medium in which it has formed can be carried out by filtration, centrifugation, decantation or direct evaporation of the solvent, the latter technique being more appropriate for the precursors obtained by dilution in alcohols.
[0320] The subsequent heat treatment of the precursor consists in subjecting it to a temperature between 800 and 1200 ° C, for the purposes of the present invention preferably between 800 ° C and 1000 ° C, more preferably 1000 ° C, for a time preferably between 0 , 5 and 24 h for precursors obtained by either of the two procedures detailed above, a time that will normally range between 4 h and 24 h or between 4 and 16 h, with a time of between 0.5 and 6 h or between 0 being sufficient. 5 and 4 h. In particular, when the coprecipitation process is used to obtain the precursors, a time of 0.5 to 4 h is sufficient and a time of 2 h is preferred. This step is often called calcination and allows to obtain solids with a hexaaluminate structure. .
[0322] In the Examples that follow, the synthesis of hexaaluminates in which La, Ce and Ni have been selected as representative metals is described. The preparation method that allows to increase the texture of the synthesized oxides is also selected. The experiments carried out show that its specific surface varies between 1 and 157 m2 / g, in most cases between 10 and 60 m2 / g, and its total pore volume is between 0.001 and 0.400, being more specifically 0.395 cm3 / g one of the highest values obtained. This degree of porosity makes them suitable for use in catalytic and adsorption processes. The hexaaluminates obtained by The method of the present invention can be considered new and inventive, due to the particularities of its structure, which is why they are also an aspect of the present invention, particularly those whose preparation is described in the Examples herein.
[0324] The tests shown in the Examples section, performed with La3 + and Ce3 +, and additionally with Ni2 + in Example 3, are representative cases of the applicability of the method of the invention. The method is considered applicable and suitable for any other metal cation, especially those that have been previously used or are known to be valid for the preparation of hexaaluminates, under the usual conditions for preparing these compounds, as previously stated. The tests carried out in Example 3 with the hexaaluminates containing Ni2 + also show that the hexaaluminates of the invention can be used as useful catalysts in the synthesis of synthesis gas (H ² / CO) from dry reforming of CH ⁴ , although Other hydrocarbons can also be used. The results show that these catalysts have a stable conversion at 700 ° C, a behavior very similar to that obtained when compared with hexaaluminates obtained using commercial Al precursors. Therefore, one more aspect of the present invention is the use of hexaaluminates obtained by the method of the present invention as catalysts, preferably for their use as catalysts in the synthesis of synthesis gas from the dry reforming of CH ⁴ (preferably) or other hydrocarbons.
[0326] The synthesis method of the hexaaluminates and the properties thereof will now be explained in more detail by means of the Examples and Figures included below.
[0328] Examples
[0330] Example 1.- Obtaining hexaaluminates of La and Ce, method with coprecipitation.
[0332] In the present Example, a salt slag from a rotary kiln with a fixed shaft and a size less than 1 mm was used for the extraction of aluminum by chemical agents.
[0334] Chemical extraction was carried out using aqueous solutions of NaHCO ³ (99.7%, Sigma-Aldrich), HCl (65%, Panreac), H ² SO ⁴ (98%, Panreac) and NaOH (Panreac) in various concentrations . Specifically, concentrations between 0 and 2 mol / liter. The reaction time with each of these solutions was also a parameter studied, being between 0 and 2 h. Briefly, in each activation 2 g of salt slag are contacted with 200 cm3 of chemical reagent solution. The stirring speed of the suspensions was 600 rpm. After the reaction time, the suspensions were filtered to separate the slag from the solution. The amount of aluminum extracted was analyzed by ICP-radial and is between 3 and 1884 mgAl / liter depending on the conditions of reaction time, concentration of the chemical reagent and temperature (see patent ES2673587).
[0336] The hexaaluminatos of La and Ce were prepared from aqueous solutions of LaCl3-9H2O (analysis grade, 99.9%, Sigma) and Ce (NO ^{3) 3 to 6} H ² O (analysis grade, 99.9%, Aldrich ) in order to obtain solids with Me / Al3 + 1:12 molar ratios (see Table 1). The solutions with extracted aluminum and the rest of the metal cations were added dropwise and with stirring at 500 rpm, to the solution resulting from dissolving the ammonium carbonate. A molar ratio (NH ⁴ ) ² CO ³ / metals = 2.6 was sought. The reaction temperature and time were 60 ° C and 1 hr.
[0338] Table 1. Concentrations of the reagents used in the synthesis of hexaaluminates.
[0340] Sample Al3 + * LaCl3-9H2O ** Ce (NO3) 3-6H2O (NH4) 2CO3 **
[0341] **
[0343] EB-LaAl12O19 14.06 6.28 g / liter - 0.55 mol / liter g / liter
[0345] EB-CeAl12O19 14.06 - 7.08 g / liter 0.55 mol / liter g / liter
[0347] E B- La0.8Ce0.2Al12O19 14.06 5.03 g / liter 1.48 g / liter 0.55 mol / liter g / liter
[0349] EA-LaAl12O19 8.96 g / liter 6.28 g / liter - 0.55 mol / liter
[0350] EA-CeAl12O19 7.08 g / liter - 7.08 g / liter 0.55 mol / liter
[0351] EA- La0.8Ce0.2Al12O19 7.08 g / liter 5.03 g / liter 1.48 g / liter 0.55 mol / liter
[0352] * Aluminum extracted from saline slag with NaOH (EB) or HCl (EA).
[0353] ** Concentration in final volume 400 ml.
[0354] After the reaction time, the suspensions were filtered to separate the solid from the solution. To dry the product, it was heated at 80 ° C at atmospheric pressure for 12 h. Calcination was carried out for a period of 0.5 h to 4 h, with 2 h being preferable.
[0356] The textural properties, specific surface and total pore volume, of the solids obtained were determined by adsorption of N ² (Air Liquide, 99.999%) at -196 ° C in a commercial static volumetric equipment (ASAP 2020 Plus from the commercial house Micromeritics ). The solids were previously degassed for 24 h and at a pressure below 0.1 Pa. The amount of solid used in the experiment was 0.2 g.
[0358] The results regarding the textural properties obtained for the hexaaluminates synthesized from the extraction of aluminum with solutions of NaOH and HCl with a concentration of 2 mol / liter are shown below in Table 2. Information is included on the R samples obtained at starting from the same synthesis conditions, but with Al (NOs) 3-9H2O as the source of Al3 + instead of Al3 + extracted from the salt slag.
[0360] These materials were also characterized by X-ray diffraction using a SIEMENS diffractometer, model D5000. A representative example is presented in Fig. 1, where the intensity data is represented, in arbitrary units, as a function of the diffraction angle (20), as usual in X-ray diffractograms. It is also included, for comparison , the diffraction pattern of powder LaAl ¹² O ¹⁹ , according to letter 00-033-0699 of the PDF database ( “powder diffraction file” ), which can be purchased for example from from the ICDD website ( International Center for Diffraction Data: International Center for Diffraction Data , www.icdd.com).
[0362] The X-ray diffraction results included in Fig. 1 confirm the obtaining of La hexaaluminate at a temperature of 1000 ° C when the synthesis procedure followed is from the Al extracted under acidic conditions. In the case of hexaaluminate synthesized from a commercial Al salt (R), the hexaaluminate structure has not yet developed at 1000 ° C: In Fig 1 it can be clearly seen how the hexaaluminate obtained using commercial reagents and calcined at 1000 ° C does not have sharp diffraction lines of the structure that is being sought, which are observed in the case of that obtained by using the Al extracted under acidic conditions. It can be suggested that the solutions obtained with the Al extracted under acidic conditions are very homogeneous, with reduced migration of inorganic species in the solid, allowing the formation of hexaaluminate structures at lower temperatures. Therefore, the method presented in this invention makes it possible to obtain hexaaluminates from aluminum extracted from residues from the aluminum industry at a lower temperature than if commercial starting materials are used. In the case of the textural results included in Table 2, the method presented in this invention also makes it possible to obtain solids with high values of specific surface area and pore volume, solids that will be suitable to be applied as adsorbents and as catalysts. These properties are included in Example 3 of this invention.
[0364] Table 2. Textural properties derived from the adsorption of N ² at -196 ° C.
[0366] Sample T calcination Sa VpTotalb
[0367] (° C) (m2 / gc) (mL / gc)
[0368] EB-LaAli2Oi9 iooo i, oo, oo4 EB-CeAli2Oi9 iooo i, 5 o, oo ² EB-Lao, sCeo, 2Ali2Oi9 iooo i, 6 o, ooi EA-LaAli2Oi9 800 52 o, 395 EA-LaAli2Oi9, o59oo i7 o EA-CeAli2Oi9 iooo io o, o37 EA-Lao, 8Ceo, 2Ali2Oi9 iooo 36 o, 372 R-LaAli2Oi9 8oo 157 o, o79 R-LaAli2Oi9 iooo 5th o, 2i4 R-LaAli2Oi9 i2oo i7 o, i35 a Specific surface area;
[0369] b Total pore volume;
[0370] c grams of degassed sample
[0372] Example 2.- Obtaining hexaaluminates of La, method with dilution with alcohols.
[0374] In the present Example, a salt slag from a rotary kiln with a fixed shaft and a size less than 1 mm was used for the extraction of aluminum by chemical agents.
[0376] The extraction procedure followed was the same as in Example 1, but in this case only HCl was used. The hexaaluminates of La were prepared from solutions LaCI3-9H2O (analysis grade, 99.9%, Sigma) and extracted Al aqueous solutions. (see Table 3). This solution is added dropwise to a mixture of alcohols, isopropanol and 50% ethylene glycol, under stirring at 500 rpm and without pH control. Drying was carried out at 200 ° C for 24 h in an autoclave reactor.
[0378] Table 3. Concentrations of the reagents used in the synthesis of hexaaluminates.
[0380] Sample A ^í 3+ * LaCI3-9H2O ** Isopropanol ** ethylene glycol ** LaAl12O19 90 g / liter 7.6 g / liter 524 g / liter 370 g / liter * Aluminum extracted from saline slag with HCl.
[0381] ** Concentration in final volume 300 ml.
[0383] After the reaction time, the solid obtained was subjected to heating at temperatures between 800 and 1200 ° C at atmospheric pressure for 6 h.
[0385] The textural properties, specific surface and total pore volume, of the solids obtained were determined by adsorption of N ² (Air Liquide, 99.999%) at -196 ° C in a commercial static volumetric equipment (ASAP 2020 Plus from the commercial house Micromeritics ). The solids were previously degassed for 24 h and at a pressure below 0.1 Pa. The amount of solid used in the experiment was 0.2 g. The results are included in Table 4.
[0387] Table 4. Textural properties derived from the adsorption of N ² at -196 ° C.
[0389] Sample Denomination in the T calcination Sa VpTota | b Fig. 2 (° C) (m2 / gc) (mL / gc) LaAÍ12O19 LaHA_600 ° C 600 59 0.216 LaAÍ12O19 LaHA_800 ° C 800 28 0.154 LaAÍ12O19 LaHA_1000 ° C 1000 17 0.056 LaAÍ12O19 LaHA_1200 ° C 1200 1.2 0.003 a Specific surface;
[0390] b Total pore volume;
[0391] c grams of degassed sample
[0393] These materials were also characterized by X-ray diffraction using a SIEMENS diffractometer, model D5000. A representative example is presented in the Fig. 2, in whose lower panel the powder diffraction patterns of LaAl ¹² O ¹⁹ and LaMgAl ¹² O ¹⁹ have been included, for comparison, according to their PDF diffraction data charts (see Example 1).
[0395] The X-ray diffraction results included in Fig. 2 confirm the obtaining of La hexaaluminate at a temperature of 1000 ° C. At this same temperature, but using commercial precursors, this structure did not develop (see Fig. 1): at a lower temperature the y-alumina structure is obtained (graph e) of Fig. 2). Therefore, this second method presented in this invention also makes it possible to obtain hexaaluminates from aluminum extracted from residues from the aluminum industry at a lower temperature than if commercial starting materials are used. In the case of the textural results included in Table 2, the method presented in this invention also makes it possible to obtain solids with high values of specific surface area and pore volume, solids that will be suitable to be applied as adsorbents and as catalysts. These properties are included in Example 3 of this invention.
[0397] Example 3.- Evaluation of the catalytic behavior in the dry reforming of CH ⁴ .
[0399] In the present Example, the synthesis gas obtaining ability was evaluated by dry CH ⁴ reforming of the synthesized Ni hexaaluminates. The preparation method followed is that described in Example 1 to obtain the hexaaluminate of formula CeAli ² Oi ⁹ starting from a solution of Al3 + obtained by extraction with hydrochloric acid (EA), where Ni2 + is also incorporated from Ni (NO ^{3) 2 to 6} H ² O (analysis grade,> 98.5%, Aldrich).
[0401] The catalysts thus synthesized presented a specific surface area of 36 m2 / g after being subjected to a heat treatment of 1000 ° C for 16 hours.
[0403] The reforming experiments were carried out in an automated and controlled Microactivity-reference PID Eng & Tech reaction system, connected in line to an Agilent 6890 gas chromatograph that allows the quantitative analysis of the gases involved in the reaction. The reactivity of the catalysts was evaluated at atmospheric pressure and at a temperature of 700 ° C. The feed stream used was a molar ratio CH ⁴ : CO ² : He = 10:10:80 with a total flow rate of the mixture of 50 ml / min and a space velocity (GHSV, Gas Houríy Space Velocity), referred to the volume total catalytic bed, 120,000 gcat- ¹ -h-1. To check the stability of the catalysts under the reaction conditions, the process (the time maintained in the current or TOS, of the English time on stream) was extended during 6 h.
[0405] As can be seen in the results included in Fig. 3, the catalyst synthesized from the extracted aluminum has high stability, the conversion of reagents and product production does not decline with time, which is comparable to that obtained if Aluminum from commercial salts is used. Therefore, this catalyst obtained from aluminum from an industrial waste could compete in terms of operability with that obtained from commercial reagents.

权利要求:
Claims (30)
[1]
1. A method for the preparation of hexaaluminates with improved textural properties of the general formula
ABxAli2-xOi9,
where
A is a cation of a metal selected from the group of alkaline earth metals with an atomic weight equal to or greater than that of Ca and lanthanides, or a combination of metal cations selected from said group,
B is a cation of a transition metal or a combination of cations of different transition metals,
x is a rational number that varies between 0 and 2,
from salt slags from aluminum recycling processes, comprising the stages of:
a) Obtain a solution containing Al3 + from the saline slag by means of the sub-stages of
i) contacting the salt slag with an acidic or basic aqueous solution, ii) allowing the solution to react with the salt slag,
iii) separating the saline slag from the acusa phase containing Al3 + in solution,
b) Obtain a hexaaluminate precursor in a liquid by means of a process in which the aqueous solution containing Al3 + is mixed, drop by drop, with another solution containing the metal cations A and, if x is different from 0, also B, and wherein the solution containing at least the metal cations A and, if x is different from 0, also B, is also added dropwise, to the liquid in which the precursor is formed;
c) subjecting the solid precursor obtained in step b) to a calcination heat treatment at a temperature between 800 ° C and 1000 ° C.
[2]
The method according to claim 1, wherein
step b) of obtaining the hexaaluminate precursor is carried out by means of a procedure selected from the group of:
i) a coprecipitation procedure, comprising the sub-stages of: a. mix the solution containing the metal cations A and, if x is different from 0, also B, with the solution containing Al3 +, adding both solutions simultaneously, dropwise and hot, on a hot solution containing a precipitating agent,
b. allow the mixture obtained in sub-step a to react. at least until the solution containing Al3 + has been added and up to a maximum of 16 h, with stirring,
c. optionally, separate the solid formed in sub-step b. of the supernatant;
d. optionally, submit the solid obtained in b. or in c. to a drying treatment;
ii) a dilution procedure with alcohols, comprising the sub-steps of:
to. add the solution containing Al3 +, drop by drop, to the solution containing the metal cations A and, if x is different from 0, also B, b. add the solution with the metal cations A, B if x is different from 0 and Al3 + obtained in sub-step a., drop by drop, to a solution containing at least one alcohol, which is selected from the group of ethylene glycol, isopropanol, ethanol , methanol, n-hexanol, polyethylene glycol and polyethylene glycol monolaurate, and mixtures thereof, c. allow the mixture obtained in sub-step b to react. at least until the solution with the metal catons obtained in sub-step a is finished adding. and up to a maximum of 30 minutes, d. optionally, submit the solution obtained in sub-step c. to a drying treatment until obtaining a solid;
and in which
The precursor obtained is subjected in step c) to a heat treatment for calcination at a temperature between 800 ° C and 1000 ° C for a time of 0.5 h to 24 h.
[3]
3. - The method according to claim 2, wherein
step b) of obtaining the precursor is carried out by means of a co-precipitation process, in which.
a.1) the solution containing Al3 + obtained from the saline slag, the solution containing the metal cations A and, if x is different from 0, also B, are mixed by adding them dropwise to the solution containing the agent precipitant being all of them at temperatures of 40 ° C - 70 ° C, and / or a.2) the pH of the solution containing the metal cations A and, if x is different from 0, also B, it is between 0 and 5, and / or
to. 3) the precipitating agent is selected from the group of (NH4) 2CÜ3, (NH ⁴ ) OH, NaOH;
me
b. 1) the mixture obtained in sub-step a is allowed to react. for a reaction time between 1 h and 6 h, and / or
b. 2) the mixture obtained in sub-step a is allowed to react. with stirring at a speed in the range of 100 r.p.m. at 700 r.p.m. , me
c. the solid formed in sub-stage b. the coprecipitation reaction is separated from the supernatant by a technique selected from the group of filtration, centrifugation, decantation or direct evaporation of the solvent; and / or d. the solid obtained in sub-stage b. of the coprecipitation reaction, or optionally in substep c. After being separated from the supernatant, it is subjected to a heat treatment of drying in an oven for 4 h to 24 h and / or to a treatment of vacuum drying;
or combinations of the above,
and in which
The precursor obtained in said stage b) is subjected in stage c) to a calcination heat treatment at a temperature between 800 ° C and 1000 ° C for a time of 0.5 h to 4 h.
[4]
The method according to claim 2 or 3, in which step b) of obtaining the precursor is carried out by means of a co-precipitation process,
and in which
i) the precipitating agent is (NH4) 2CO3 at a concentration of 1 M; me
ii) the solid obtained in the coprecipitation reaction, optionally after having been separated from the supernatant, is subjected to a drying heat treatment at atmospheric pressure, at a temperature of 100 ° C, for 16 h.
[5]
The method according to any one of claims 2, 3 or 4, in which step b) of obtaining the precursor is carried out by means of a coprecipitation process, and in which the precursor obtained in said step b) is subjected in step c) to a calcination heat treatment at a temperature of 1000 ° C for 2 h.
[6]
6. The method according to claim 2, wherein
step b) of obtaining the precursor is carried out by means of a dilution procedure with alcohols, in which.
to. the solution containing Al3 + is at a temperature of 40 ° C to 70 ° C when added to the solution containing the metal cations A, and if x is different from 0, also B, and / or
b. the solution containing one or more alcohols comprises ethylene glycol and optionally also isopropanol, and / or
c. the reaction of the alcohol solution with the mixture of metal cations occurs with stirring, and / or
d. The solution obtained after the reaction time is subjected to a drying treatment at a temperature between 60 ° C and 120 ° C for a time between 4 and 24 h until a solid is obtained, optionally followed by an additional treatment in an autoclave reactor by a maximum time of 24 h,
or combinations of the above,
and in which
The precursor obtained in step b) is subjected in step c) to a calcination heat treatment at a temperature between 800 ° C and 1000 ° C, between 4h and 24h.
[7]
The method according to claim 2 or 6, in which step b) of obtaining the precursor is carried out by means of a dilution process with alcohols and in which said precursor obtained in said step b) is subjected in step c) to a heat treatment of calcination at a temperature between 800 ° C and 1000 ° C, between 6 h and 16 h.
[8]
8. The method according to any one of the preceding claims, wherein the metal cations A of the solution that binds with the solution containing Al3 + are selected from the group of cations of metals Ca, Ba, La, Sm, Sr , Ce, Pr, Nd, Pm, Sa, Gd, and the metal cations B, if present, are selected from the group of the metal cations Mn, Fe, Co, Cu, Ni, Ir, Ru, Pd, Rh.
[9]
9. The method according to claim 8, characterized in that the metal cations A are selected from the group of cations La3 +, Ce3 + or mixtures thereof.
[10]
10. The method according to claim 8 or 9, wherein B cations are present and are Ni2 + cations.
[11]
11. The method according to any one of the preceding claims, characterized in that it includes an additional intermediate stage in which the concentration of Al3 + present in the aqueous solution containing Al3 + in solution is determined, before preparing the solution containing metal cations, which It is prepared so that the metal cation A / Al3 + molar ratio has a value of 1:12.
[12]
12. The method according to any one of claims 1 to 11, wherein the Al3 + -containing solution is prepared in step a) from a salt slag by a process in which
i) salt slag is a slag that comes from a second melting process of aluminum that has taken place in fixed shaft rotary kilns,
ii) the salt slag is brought into contact with an aqueous solution with a pH lower than 2 or higher than 10,
iii) one or more acidic compounds or one or more basic compounds are present in the aqueous solution that is brought into contact with the salt slag at concentrations between 0 and 2 mol / liter,
iv) the extraction temperature is between room temperature and reflux temperature,
v) the contact time between the salt slag and the aqueous solution is in the range of 0 to 2 h, and / or
vi) Once the contact time has elapsed, the saline slag is separated from the solution with which the aluminum has been extracted in the form of Al3 + cations by means of a separation technique selected from filtration, centrifugation or decantation, or combinations of the above.
[13]
The method according to claim 12, wherein
a) the solution containing Al3 + is prepared in step a) from a salt slag by a process in which
i) the metal cations A are La3 +, Ce3 + cations or mixtures thereof and, optionally, Ni 2+ cations are present as metal cations B,
ii) ² g of saline slag from a second aluminum melting process that has taken place in rotary kilns with a fixed shaft, are put in contact with ^{2 0 0} cm3 + of acidic or basic aqueous solution,
iii) the saline slag is brought into contact with an aqueous solution of NaHCO ³ , HCl, H ² SO ⁴ or NaOH, at concentrations between 0 and 2 mol / liter,
iv) the reaction temperature is 60 ° C,
v) the contact time between the salt slag and the aqueous solution is ⁰ to ² h,
vi) the salt slag is separated from the solution with which the aluminum has been extracted in the form of Al3 + cations by filtration,
b) the hexaaluminate precursor is obtained by coprecipitation with (NH ⁴ ) ² CO ³ as precipitating agent at a molar ratio (NH ⁴ ) ² CO ³ / metal cations equal to 2.6, at a temperature of 60 ° C for 1 h, separating the solid precursor from the solution by filtration and heating it at 80 ° C at atmospheric pressure for ¹² h,
c) the hexaaluminate is obtained by calcining the precursors at temperatures of 800 to 1000 ° C for 0.5 to 4 h.
[14]
14. The method according to claim 13, wherein the Al3 + -containing solution is obtained by contacting the salt slag with a solution of HCl or H ² SO ⁴ at a concentration of ² mol / liter.
[15]
15. The method according to any one of claims 13 or 14, wherein the hexaaluminate responds to a formula selected from LaAl ¹² O ¹⁹ , CeAl ¹² O ¹⁹ , La0.8Ce0.2Al12O19 or Ni-CeAlnO19.
[16]
16. The method according to claim 12, wherein
to)
[17]
17. The method according to claim 16, wherein the hexaaluminate is obtained by calcining the precursors at 1000 ° C for 6 h.
[18]
18. A hexaaluminate obtained by the process of any one of the preceding claims.
[19]
19. Hexaaluminate according to claim 18 characterized in that it responds to the formula:
ABxAl12-xO19,
where
A is a cation selected from the group of La3 +, Ce3 +, and combinations thereof B is a cation that can partially or completely replace the positions of the crystallographic Al that can be N¡2 + or be absent
x is a rational number between 0 and 2,
and that has a specific surface equal to or greater than 1 m2 / g.
[20]
20. Hexaaluminate according to claim 18 or 19, characterized in that its specific surface area is between 1 m2 / g and 60 m2 / g.
[21]
21. Hexaaluminate according to any one of claims 18 to 20, in which its specific surface area is greater than 10 m2 / g.
[22]
22. Hexaaluminate according to any one of claims 18 to 21, in which its total pore volume is between 0.001 and 0.400 cm3 / g.
[23]
23. Hexaaluminate according to any one of claims 18 to 22, characterized in that x is 0 and the metal cations A are selected from the group of La3 +, Ce3 +, and combinations thereof and that the metal cations / Al3 + ratio is 1/12 .
[24]
24. Hexaaluminate according to any one of claims 19 to 23, selected from the group of LaAl12Ü19, CeAl12Ü19, La0.8Ce0.2Al12O19.
[25]
25. Hexaaluminate according to any one of claims 19 to 22, characterized in that the metal cations A are selected from the group of La3 +, Ce3 + and combinations thereof and the metal cation B is Ni2 +.
[26]
26. Hexaaluminate according to claim 25, which is Ni-CeAlnO ^.
[27]
27. Use of a hexaaluminate obtained by the method of any one of claims 1 to 17 as a catalyst or as an adsorbent.
[28]
28. Use according to claim 27, in which the hexaaluminate is used as a catalyst and has a specific surface area between 1 m2 / g and 60 m2 / g.
[29]
29. Use according to claim 27 or 28, in which the hexaaluminate is used as a catalyst in CH ⁴ conversion reactions in the presence of CO ² for the production of H ² and CO, combustion and partial oxidation of CH ⁴ or decomposition of N ² O.
[30]
30. Use according to claim 29, in which the hexaaluminate is used as a catalyst for the conversion of CH ⁴ in the presence of CO ² for the production of H ² and CO and the selected hexaaluminate contains Ni2 + in its structure.

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同族专利:

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公开号 | 公开日

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ES2803955B2|2021-12-21|

引用文献:

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公开号 | 申请日 | 公开日 | 申请人 | 专利标题

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CN1680020A|2004-04-05|2005-10-12|中国科学院生态环境研究中心|Preparation of transition metal substituted hexaaluminate as catalyst for natural gas combustion|

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ES2673587A1|2016-12-22|2018-06-22|Universidad Pública de Navarra|Method of manufacturing anionic clays of aluminum and its derivatives from salt slags from aluminum recycling processes |

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ES201930694A|ES2803955B2|2019-07-26|2019-07-26|Hexaaluminates with improved textural properties, their preparation from salt slag from aluminum recycling processes and their use|ES201930694A| ES2803955B2|2019-07-26|2019-07-26|Hexaaluminates with improved textural properties, their preparation from salt slag from aluminum recycling processes and their use|