RU2794972C1 - Magnesium aluminate and method for its production (embodiments) - Google Patents

Abstract

FIELD: chemical; petrochemical industries.

SUBSTANCE: invention can be used in manufacturing of carriers for catalysts for oxidation processes, as well as hydrogenation/dehydrogenation. First, an aqueous suspension of powders of the product of centrifugal thermal activation of hydrargillite (CTA HG) and nitrate or magnesium oxide, taken in a stoichiometric ratio, is prepared. According to another embodiment, a surfactant is added to the suspension, which is polyvinyl alcohol, at a mass ratio of CTA HG:surfactant of at least 25:1. In both embodiments, the resulting suspension is subjected to hydrothermal treatment in a steam chamber at 150°C, producing a highly concentrated suspension moulded by extrusion, belonging to the 0 structural-mechanical type with a predominance of elastic deformations. Then extrusion moulding of the resulting highly concentrated suspension is carried out. The extrudates are dried at 120°C and calcined at a temperature not lower than 550°C, but less than 600°C.

EFFECT: invention enables a simple method for producing high-strength magnesium aluminate MgAl₂O₄ granules with a spinel structure, characterized by a specific surface area of at least 130 m²/g, a pore volume of at least 0.23 cm³/g and a mechanical strength of at least 2.8 MPa for granules with a size of at least 3 mm. Labour-intensive stages of sedimentation and washing are eliminated, the amount of reagents used is reduced, the formation of washing water is reduced or completely eliminated.

7 cl, 2 tbl, 9 ex

Description

The invention relates to carriers for catalysts of various processes, namely to granular magnesium aluminate - MgAl ₂ O ₄ and a method for its preparation. The use of granulated MgAl ₂ O ₄ as a carrier is based on its neutral acid-base characteristics and very high thermal stability, which can be widely used in the chemical and petrochemical industries, for example, for the production of hydrogenation/dehydrogenation catalysts, as well as catalysts for oxidation processes.

There is enough information on the use of magnesium aluminate as a carrier in various catalytic processes [Pankina G.V., Chernavsky P.A., Lunin V.V. Co-Fe/carrier bimetallic catalysts: dynamics of CO hydrogenation // Zh. physical chemistry. 2013. V. 87. No. 10. S. 1647-1652.; Belskaya O.B., Stepanova L.N., Gulyaeva T.I., Golinskiy D.V., Belyi A.S., Likholobov V.A. Investigation of Pt/MgAlO _x catalysts in the reaction of n-decane dehydrogenation // Kinetics and Catalysis. 2015. V. 56. No. 5. S. 663-671], as well as methods for obtaining magnesium aluminate in the form of a powder.

The traditional method for the preparation of aluminum-magnesium spinels, based on the sintering of mechanical mixtures of oxides and/or hydroxides of the corresponding metals at temperatures of 1100-1300°C and above in an oxidizing or inert atmosphere [Ivanova A.S., Skripchenko E.V., Moroz E.M. , Litvak G.S., Kustova G.N., Krivoruchko O.P. Investigation of solid-phase transformations during heat treatment of individual and mixed magnesium and aluminum hydroxides. Izv. Sib. Dep. Academy of Sciences of the USSR. 1989. V. 6. No. 6. S. 116-122], does not allow to prepare fine powders and is energy-intensive.

A common method for preparing dispersed magnesium aluminates is the method of co-precipitation (“sol-gel” technology) of Al ³⁺ and Mg ²⁺ hydroxocomplexes from mixed aqueous solutions of salts of various nature [Evans DG, Slade RCT Structural aspects of layered double hydroxides // Struct. Bond. 2006. V. 119. P. 1-87; Li F., Duan X. Applications of layered double hydroxides // Struct. Bond. 2006. V. 119. P. 193-223 ; Thesis FL, Ayoko GA, Frost RL Synthesis of layered double hydroxides containing Mg ²⁺ , Zn ²⁺ , Ca ²⁺ and Al ³⁺ layer cations by co-precipitation methods - A review // Appl. Surf. sci. 2018. V. 134. P. 1481-1492; Othman MR, Helwani Z., Martunus, Fernando WJN Synthetic hydrotalcites from different routes and their application as catalysts and gas adsorbents: a review // App. Organometal. Chem. 2009. V. 23. P. 335-346]. Precipitates in the form of gels formed as a result of co-precipitation are decanted, filtered, washed to remove anion impurities, dried in the temperature range of 80-110°C and calcined at temperatures of 500-600°C and higher, resulting in the formation of aluminates with a spinel structure. The precipitation method is characterized by multi-stage and the use of a large number of solutions of salts, acids or alkalis. Co-precipitated gels contain high concentrations of anion impurities (nitrates, sulfates, chlorides, carbonates, etc.), which can only be removed using a large volume of washing water. That is, the main disadvantages of the co-precipitation method for obtaining dispersed complex oxides are the high costs of reagents and wastewater that must be disposed of.

There are also known methods for the preparation of aluminum-magnesium spinel, based on the interaction of mechanically activated gibbsite and oxides of divalent metals [Krivoruchko O.P., Buyanov R.A., Paramzin S.M., Zolotovsky B.P. Interaction of mechanochemically activated Al ³⁺ hydroxides with crystalline divalent metal oxides // Kinetics and Catalysis. 1988. V. 29. No. 1. S. 252-253]. The results of obtaining aluminates of alkaline earth metals using hydrothermal treatment have been published [Zhuzhgov A.V., Kruglyakov V.Yu., Suprun E.A., Protsenko R.S., Isupova L.A. Synthesis of highly dispersed aluminum-magnesium oxides based on the product of centrifugal thermal activation of gibbsite // Journal of Applied Chemistry. 2021. V. 94. No. 2. pp. 163-173; RF patent No. 2735668 C1, C01F 7/16, 05.11.2020]. In the above article and RF patent No. 2735668, the authors describe a method for preparing magnesium aluminate, which is closest to the proposed technical solution, but MgAl ₂ O ₄ is obtained in the form of a powder, while granular carriers and catalysts are used in industry.

Data on the preparation (by any molding method) and properties of MgAl ₂ O ₄ granules are practically absent in the literature. For example, in [S. A. Bocanegra, A. Guerto-Ruiz, O. A. Selza, S. R. de Miguel. Spinel MgAl ₂ O ₄ prepared by mechanochemical synthesis as a carrier of polymetallic catalysts for paraffin dehydrogenation // Catalysis in the industry. 2012. No. 5. S. 63-74] describes the preparation of MgAl ₂ O ₄ powder by the mechanochemical method. MgO and γ-Al ₂ O ₃ powders (99.9%) are thoroughly mixed in a 1:1 molar ratio and then ground to a very fine powder (particle diameter < 105 µm) with a mortar. After grinding, distilled water is added to the powder to a content of 45 wt. %. The resulting wet powder or paste is ground again in a ball mill for 24 hours at room temperature, then dried at 100°C for 12 hours and calcined at 900°C for 12 hours in air. The resulting solid, MgAl ₂ O ₄ spinel, is further ground to particle sizes of 177 to 500 µm.

There are also known methods for the preparation of aluminum-magnesium spinel, based on the interaction of mechanically activated gibbsite and oxides of divalent metals [Krivoruchko O.P., Buyanov R.A., Paramzin S.M., Zolotovsky B.P. Interaction of mechanochemically activated Al ³⁺ hydroxides with crystalline divalent metal oxides // Kinetics and Catalysis. 1988. V. 29. No. 1. S. 252-253]. The results of obtaining aluminates of alkaline earth metals using hydrothermal treatment have been published [Zhuzhgov A.V., Kruglyakov V.Yu., Suprun E.A., Protsenko R.S., Isupova L.A. Synthesis of highly dispersed aluminum-magnesium oxides based on the product of centrifugal thermal activation of gibbsite // Journal of Applied Chemistry. 2021. V. 94. No. 2. S. 163-173; RF patent No. 2735668 C1, C01F 7/16, 05.11.2020]. In the above references, the authors describe the preparation of magnesium aluminate in the form of a powder, while granular carriers and catalysts are used in industry.

Data on the preparation (by any molding method) and properties of MgAl ₂ O ₄ granules are practically absent in the literature. For example, in [S. A. Bocanegra, A. Guerto-Ruiz, O. A. Selza, S. R. de Miguel. Spinel MgAl ₂ O ₄ prepared by mechanochemical synthesis as a carrier of polymetallic catalysts for paraffin dehydrogenation // Catalysis in industry. 2012. No. 5. S. 63-74] describes the preparation of MgAl ₂ O ₄ powder by the mechanochemical method. MgO and γ-Al ₂ O ₃ powders (99.9%) are thoroughly mixed in a 1:1 molar ratio and then ground to a very fine powder (particle diameter < 105 µm) with a mortar. After grinding, distilled water is added to the powder to a content of 45 wt. %. The resulting wet powder or paste is ground again in a ball mill for 24 h at room temperature, then dried at 100°C for 12 h and calcined at 900°C for 12 h in air. The resulting solid, MgAl ₂ O4 spinel, is further ground to a particle size of 177 to 500 µm.

The extrusion molding method is the most common and convenient method for producing molded granules of various sizes, including granules of complex shape (rings, rings with partitions, multi-hole granules), as well as blocks of a honeycomb structure. The method consists in preparing a highly concentrated suspension (paste) with the necessary structural and mechanical characteristics, which is forced through dies of various shapes and sizes, followed by heat treatment. However, there is very little information on the extrusion molding of aluminates, and it does not contain quantitative estimates of the molding mass and the properties of the obtained granules.

For example, in [T. Nagaoka, R.Sato, Y.Hotta, K.Watari Extrusion behavior of mono-calcium aluminate (CaAl ₂ O ₄ ) paste // J. Ceram. soc. Japan. 2008. V. 116 P. 239-241] describe the extrusion molding of calcium aluminate CaAl ₂ O ₄ , in which the finished product is obtained in the form of granules. The initial calcium aluminate is prepared by the ceramic method by sintering a mechanical mixture of calcium carbonate and aluminum oxide at 1300°C. The resulting CaAl ₂ O ₄ powder is ground in a planetary mill, then a paste is prepared from the powder and distilled water at a ratio of 1:1.4, which is placed in plastic bags and kept at 25°C and 90% humidity for 1 to 7 days. According to the results of extrusion molding on a plunger (piston) granulator, there is a direct correlation between the quality of the extrudate and the holding time of the paste: the longer the holding time of the paste, the better the quality results of molding. Although the authors do not give quantitative characteristics of the obtained granules, it can be argued that the granules will have a low specific surface area (since the initial CaAl ₂ O ₄ powder was obtained by the ceramic method at a high calcination temperature). Therefore, it is not possible to prepare granules with a high specific surface by the described method.

The invention solves the problem of obtaining an effective carrier based on magnesium aluminate.

EFFECT: strong granules of magnesium aluminate with a spinel structure with a high specific surface area of at least 130 m ² /g and a pore volume of at least 0.23 cm ³ /g, having a mechanical strength of at least 2.8 MPa.

The problem is solved by two possible options for the preparation of magnesium aluminate MgAl ₂ O ₄ with a spinel structure in the form of granules.

In the first variant, magnesium aluminate MgAl ₂ O ₄ with a spinel structure in the form of granules is obtained by a method including hydrothermal treatment of an aqueous suspension of powders of the product of centrifugal thermal activation of hydrargillite CTA GG and magnesium nitrate or magnesium oxide, taken in a stoichiometric ratio, extrusion molding of the resulting highly concentrated suspension with subsequent stages of drying and calcination, resulting in magnesium aluminate MgAl ₂ O ₄ with a spinel structure in the form of granules, characterized by a specific surface area of at least 130 m ² /g, a pore volume of at least 0.23 cm ³ /g and a mechanical strength of not less than 2.8 MPa for granules with a size of at least 3 mm.

In the second variant, magnesium aluminate MgAl₂O₄ with spinel structure in the form of granules is obtained by a method including hydrothermal treatment of an aqueous suspension of powders of the product of centrifugal-thermal activation of hydrargillite CTA GG and magnesium nitrate or magnesium oxide, taken in a stoichiometric ratio, with the addition of a surfactant, and the ratio of CTA GG : surfactant is not less than 25:1, then extrusion molding of the resulting highly concentrated suspension is carried out, followed by drying and calcination stages, resulting in magnesium aluminate MgAl₂O₄with a spinel structure in the form of granules, characterized by a specific surface area of at least 130 m²/g, pore volume not less than 0.23 cm3³/g and mechanical strength of at least 2.8 MPa for granules with a size of at least 3 mm. At the same time, by adding a surfactant at the stage of hydrothermal treatment, for example, polyvinyl alcohol (PVA), it is possible to control the texture characteristics of the granules.

In both cases, hydrothermal treatment of aqueous suspensions is carried out in an autoclave at a temperature of 150°C, obtaining a highly concentrated suspension molded by extrusion, belonging to the 0 structural-mechanical type with a predominance of elastic deformations, and the granules (extrudates) obtained by extrusion are dried at 120°C and then calcined at temperature not lower than 550°C.

At temperatures below 550°C, 100% magnesium aluminate is not formed, and the strength of the granules also decreases; at temperatures above 550°C, the specific surface area of the granules decreases and strength increases. At the optimum temperature of 550°C, aluminate is obtained with a high specific surface area and sufficient strength of the granules. A distinctive feature of this method is that for the preparation of the molding mass, plasticizers and electrolytes are not additionally used, which are added during the preparation of the molding mass in mixing devices, i.e. there is no plasticization stage.

The plastic strength of the resulting molding mass (paste) Pm is determined on a Rebinder design conical plastometer and calculated by the formula P _m =K _α F/h ² , where F is an external load, h is the cone immersion depth, K _α is a dimensionless coefficient depending on the angle at the apex of the cone α.

The constants of the elastic-viscous-plastic properties of the molding paste are determined on the Tolstoy design device according to the method proposed in the works [Nichiporenko S.P. Physical and chemical mechanics of dispersed structures in the technology of building ceramics. Kyiv: Naukova Dumka, 1968. 76 p.; Kruglitsky N.N. Fundamentals of physical and chemical mechanics: Part 1. Kyiv: Vishcha shkola, 1975. 268 s]. To calculate the mass parameters, the Maxwell-Shvedov and Kelvin model (MSK) is used [Kruglitsky N.N. Fundamentals of physical and chemical mechanics: Part 1. Kyiv: Vishcha school, 1975. 268 p.]:

- относительная суммарная деформация; E₁, E₂ - соответственно модули быстрой и медленной эластических деформаций; P - внешняя нагрузка; P₁ - условный статический предел текучести; η₁ - наибольшая пластическая вязкость; η₂ - вязкость упругого последействия; τ - время действия нагрузки.Where

- relative total deformation; E ₁ , E ₂ - respectively, the modules of fast and slow elastic deformations; P - external load; P ₁ - conditional static yield strength; η ₁ - the highest plastic viscosity; η ₂ - the viscosity of the elastic aftereffect; τ is the time of the load.

The textural characteristics of the obtained granular samples of MgAl ₂ O ₄ are determined by the method of low-temperature desorption of nitrogen on an ASAP 2400 instrument (USA). Before analysis, the samples are purged in a stream of N ₂ at a temperature of 200°C for 2 h and then cooled. Methods for measuring and calculating texture parameters comply with ASTM D3663, ASTM D4820, ASTM D1993, UOP425-86 standards. The value of the specific surface area is calculated from the amount of adsorbed nitrogen at relative pressure values of 0.05÷0.30. The pore volume is determined from the amount of adsorbed nitrogen at a relative pressure close to 1 (actually at P/P ⁰ =0.995) in the approximation that all available pores are filled with liquid condensed nitrogen.

The mechanical strength of the granules is determined by measuring the force under which, as a result of coaxial compression between two parallel planes, the granule is completely destroyed. In this case, the strength is characterized by the average value of the mechanical strength calculated from the strength values of 30 granules according to the formula (2):

,

,

where P is the breaking force, N; n is the number of tested granules; 100 - conversion factor from N/cm2 to MPa; F is the cross-sectional area of the granules.

,

,

- приведенные деформации, доли упругих, эластических и пластических деформаций; СМТ - структурно-механический тип. Свойства полученных гранул MgAl₂O₄ приведены в таблице 2.The elastic-viscous-plastic constants of the molding mass, its plastic strength and structural-mechanical type (related to the 0 structural-mechanical type with a predominance of elastic deformations) were determined; textural properties and mechanical strength of finished granules (after heat treatment). The properties of extrusion molding pastes are presented in Table 1, where the characteristics are given: P_m - value of plastic strength, kPa; P_k- value of the limiting shear stress, kPa; E - equilibrium modulus, Pa; ή₁ - value of the highest plastic viscosity, Pa s; E₁ - elastic modulus_, Pa; E₂ - modulus of elasticity, Pa; Ps - value of plasticity, s^-1; λ is the value of elasticity; Θ - relaxation period, s;

,

,

- reduced deformations, shares of elastic, elastic and plastic deformations; SMT - structural-mechanical type. Properties of obtained MgAl granules₂O₄given in table 2.

The phase composition of MgAl ₂ O ₄ samples after heat treatment is confirmed by X-ray phase analysis (XPA). The measurements were carried out using a D-500 diffractometer (Siemens) using CuKα radiation and a reflected beam graphite monochromator. The samples are taken by scanning in the range of angles 2θ=10-70º with a step of 0.05° and an accumulation time of 3 s. Phase identification is carried out by comparing the experimental diffraction patterns with the diffraction patterns collected in the ICDD and PDF 2 databases.

The essence of the claimed method is illustrated by examples 1-9.

The feedstock for the preparation of MgAl ₂ O ₄ is the product of centrifugal thermal activation of hydrargillite (CTA GG) grade IK-02-76 (TU 2175-040-03533913-2007). CTA GG is produced in a drum-type centrifugal flash reactor (CEFLAR™ unit) at a temperature of thermal electric heaters of 615°C, a drum rotation speed of 60 rpm and a hydrargillite flow rate of 30 kg/h [RF patent No. 2264589, F26BB7 / 00, 20.11.2005] . Loss on ignition (LOI) CTA GG at 800°C is 13.7%. The feedstock for obtaining the CTA GG product is hydrargillite produced by CJSC BaselCement-Pikalyovo, Pikalevo (TU 1711-069-00196368-2001). CTA GG is dried in air at 110°C for 6 hours before use to ensure that the surface is clean from possible adsorbed impurities from the atmosphere during storage.

Example 1 - 1st option

50 g of CTA GG are loaded into the autoclave and 122 ml of a magnesium nitrate solution (Mg concentration = 0.080 g/ml) is added, the resulting suspension is stirred with a magnetic stirrer (rotation speed 120 rpm) and heated at 150°C for 4 h (pressure 4 .1-4.6 bar). After the autoclave cools down, the resulting highly concentrated suspension (paste) with a moisture index of about 40% is unloaded and extrusion molded on a laboratory piston extruder to obtain cylindrical extrudates with a diameter of 4 mm. The structural and mechanical properties of the suspension are shown in Table 1. The resulting extrudates are dried at 120°C for 8 hours, then calcined at 550°C for 4 hours. Properties of MgAl granules₂O₄with diameter ~ 3 mm obtained after heat treatment of the extrudates are shown in Table 2.

Example 2 - 2nd option

50 g of CTA GG is loaded into the autoclave and 122 ml of a solution of magnesium nitrate (Mg concentration = 0.080 g/ml) with PVA (1.32 g) is added, the ratio of CTA GG: PVA is ~ 38:1, the resulting suspension is stirred with a magnetic stirrer (rotation speed 120 rpm). /min) and heated at 150°C for 4 hours (pressure 4.1-4.6 bar). After the autoclave cools down, the resulting highly concentrated suspension (paste) with a moisture index of about 40% is unloaded and extrusion molded on a laboratory piston extruder to obtain cylindrical extrudates with a diameter of 4 mm. The resulting extrudates are dried at _a temperature of 120°C for 8 hours, then calcined at 550°C for ₄ hours.

Example 3 - 1st option

60 g of CTA GG, 22 g of MgO are loaded into the autoclave and 90 ml of water are added, stirred with a magnetic stirrer at a speed of 120 rpm at a temperature of 150°C for 4 h (pressure 4.1-4.6 bar). After the autoclave cools down, the resulting highly concentrated suspension (paste) with a moisture content of about 40% is unloaded and extrusion molded on a laboratory piston extruder to obtain cylindrical extrudates with a diameter of 4 mm. The structural and mechanical properties of the suspension are shown in Table 1. The obtained extrudates are dried at a temperature of 120°C for 8 hours, then calcined at 550°C for _{4 hours} . table 2. Example 4 - 2nd option

60 g of CTA GG, 22 g of MgO are loaded into the autoclave and 90 ml of a 2% solution of polyvinyl alcohol (PVA content is 1.58 g, the ratio of CTA GG : PVA is ~ 38:1) is added, stirred with a magnetic stirrer at a speed of 120 rpm at a temperature of 150°C for 4 hours (pressure 4.1-4.6 bar). After the autoclave cools down, the resulting highly concentrated suspension with a moisture content of about 40% is unloaded and extrusion molded on a laboratory piston extruder to obtain cylindrical extrudates with a diameter of 4 mm. The _resulting extrudates are dried at a temperature of 120°C for 8 hours, then calcined at 550°C for ₄ hours. and pore volume of the granules (table 2).

Example 5 - 2nd option

60 g of CTA GG, 22 g of MgO are loaded into the autoclave and 90 ml of a 3% solution of polyvinyl alcohol (PVA content is 2.37 g, the ratio of CTA GG : PVA is ~ 25:1) is added, the mixture is stirred with a magnetic stirrer at a speed of 120 rpm at temperature 150°C for 4 hours (pressure 4.1-4.6 bar). After the autoclave cools down, the resulting highly concentrated suspension with a moisture content of about 40% is unloaded and extrusion molded on a laboratory piston extruder to obtain extrudates with a diameter of 4 mm. The obtained extrudates are dried at a temperature of 120°C for 8 hours, then calcined at 550°C for _{4 hours} . CTA GG: PVA) leads to a decrease in the strength of the granules (table 2).

Example 6

The extrudates obtained according to example 1 are dried at a temperature of 120°C for 8 hours, then calcined at a temperature of 600°C for 4 hours. An increase in the calcination temperature leads to a decrease in the specific surface of the MgAl ₂ O ₄ granules, texture characteristics and a slight increase in the strength of the granules ( table 2).

Example 7

The extrudates obtained according to example 1 are dried at a temperature of 120°C for 8 hours, then calcined _at a temperature of ₅₀₀ °C for _{4 hours} . ² /g.

Example 8 - Comparative

Obtained in example 1 highly concentrated suspension after cooling the autoclave is dried at 110°C for 12 h, then crushed in a ball mill for 1 h and sieved through a sieve with a mesh size of 100 μm. The resulting powder weighing 100 g is loaded into a mixer with Z-shaped blades, 35 ml of 1% nitric acid solution is added and mixed until a plastic paste is obtained. Next, extrusion molding of the paste is carried out on a laboratory piston extruder to obtain extrudates with a diameter of 4 mm. The resulting extrudates are dried at a temperature of 120°C for 8 hours, then calcined at 550°C for 4 hours. The properties of the obtained MgAl ₂ O ₄ granules with a diameter of ~3 mm are shown in Table 2.

Example 9 - Comparative

Obtained in example 2 highly concentrated suspension after cooling the autoclave is dried at 110°C for 12 h, then crushed in a ball mill for 1 h and sieved through a sieve with a mesh size of 100 μm. The resulting powder weighing 100 g is loaded into a mixer with Z-shaped blades, 35 ml of 1% nitric acid solution is added and mixed until a plastic paste is obtained. Next, extrusion molding of the paste is carried out on a laboratory piston extruder to obtain extrudates with a diameter of 4 mm. The resulting extrudates are dried at a temperature of 120°C for 8 hours, then calcined at 550°C for 4 hours. The properties of the obtained MgAl ₂ O ₄ granules with a diameter of ~3 mm are shown in Table 2.

Thus, the proposed method in both versions makes it possible to obtain durable magnesium aluminate granules with a high specific surface area in a fairly simple way - extrusion molding of a paste to obtain products of any shape and size compared to dry pressing and disk (plate) granulation. There are no settling stages in the method, the stages of filtering and washing the suspension sediment, as well as the mixing stages for the preparation of the moldable mass are not required. The formed paste obtained at the stage of hydrothermal treatment belongs to the 0 structural-mechanical type, characterized by the predominance of elastic deformations over plastic and elastic ones. The method allows to significantly reduce the amount of initial reagents, technological stages, as well as to minimize or completely eliminate the formation of wash water. The use of various sources of magnesium at the stage of hydrothermal treatment and PVA as a surfactant allows you to control the pore volume and strength of the granules without changing the average pore size, which may be important in the preparation of supported catalysts by impregnation according to the moisture capacity of the inventive carrier, as well as in determining the parameters of the catalytic process.

Table 1 - Properties of high-concentration suspensions of magnesium aluminate Example Source of magnesium P _k ,
kPa ή ₁ , 10 ^-9
Pass Ps, 10 ⁶ s ^-1 λ E ,
MPa Θ, s E ₁ ,
MPa E ₂ ,
MPa _Pm
kPa

отн. ед. (%)

rel. units (%)

, rel. units
(%)

rel. units (%) SMT Example 1 Mg(NO ₃ ) ₂ 18.5 25.3 0.73 0.35 1.85 13675 2.83 5.36 3.14 0.71
(61.2) 0.37
(31.9) 0.08
(6.9) 0 Example 3 MgO 16.3 21.2 0.77 0.34 1.75 12114 2.67 5.11 2.87 0.75
(61.0) 0.39
(31.7) 0.09
(7.3) 0

Table 2 - Properties of magnesium aluminate granules

Example Source of magnesium BET specific surface, m ² /g Granule strength, MPa V _time ,
cm ³ /g D _then ,
nm Example 1 Mg(NO ₃ ) ₂ 131 3, 8 0.23 3.8 Example 2 Mg(NO ₃ ) ₂ 152 7.2 0.23 3.8 Example 3 MgO 135 2.8 0.25 3.8 Example 4 MgO 200 4, 7 0.52 3.8 Example 5 MgO 213 3.8 0.60 4.0 Example 6 Mg(NO ₃ ) ₂ 120 5.1 0.22 3.7 Example 7 Mg(NO ₃ ) ₂ 135 1.8 0.23 3.8 Example 8 Mg(NO ₃ ) ₂ 121 3.06 0.23 3.8 Example 9 MgO 120 2.1 0.23 3.8

Claims (7)

1. Magnesium aluminate MgAl ₂ O ₄ with a spinel structure in the form of granules, characterized by a specific surface area of at least 130 m ² /g, a pore volume of at least 0.23 cm ³ /g and a mechanical strength of at least 2.8 MPa for granules with a size not less than 3 mm. 2. A method for producing magnesium aluminate MgAl ₂ O ₄ in the form of granules, including hydrothermal treatment of an aqueous suspension of powders of the product of centrifugal thermal activation of hydrargillite (CTA GG) and magnesium nitrate or magnesium oxide, taken in a stoichiometric ratio, extrusion molding of the resulting highly concentrated suspension with subsequent stages drying and calcining the resulting extrudates at a temperature not lower than 550°C, but less than 600°C, resulting in magnesium aluminate MgAl ₂ O ₄ with a spinel structure in the form of granules, characterized by a specific surface area of at least 130 m ² /g, pore volume not less than 0.23 cm ³ /g and mechanical strength not less than 2.8 MPa for granules with a size of not less than 3 mm. 3. The method according to claim 2, characterized in that the hydrothermal treatment of aqueous suspensions is carried out in an autoclave at a temperature of 150 ° C, obtaining a highly concentrated suspension molded by extrusion, belonging to the 0 structural-mechanical type with a predominance of elastic deformations. 4. The method according to p. 2, characterized in that the resulting extrudates are dried at 120°C. 5. A method for producing magnesium aluminate MgAl ₂ O ₄ in the form of granules, including hydrothermal treatment of an aqueous suspension of powders of the product of centrifugal thermal activation of hydrargillite (CTA GG) and magnesium nitrate or magnesium oxide, taken in a stoichiometric ratio, with the addition of a surfactant ), which is used as polyvinyl alcohol, with a mass ratio of CTA GG:surfactant of at least 25:1, extrusion molding of the resulting highly concentrated suspension, followed by drying and calcining the resulting extrudates at a temperature not lower than 550°C, but less than 600°C, in resulting in magnesium aluminate MgAl ₂ O ₄ with a spinel structure in the form of granules, characterized by a specific surface area of at least 130 m ² /g, a pore volume of at least 0.23 cm ³ /g and a mechanical strength of at least 2.8 MPa for granules at least 3 mm in size. 6. The method according to claim 5, characterized in that the hydrothermal treatment of aqueous suspensions is carried out in an autoclave at a temperature of 150 ° C, obtaining a highly concentrated suspension molded by extrusion, belonging to the 0 structural-mechanical type with a predominance of elastic deformations. 7. The method according to p. 5, characterized in that the resulting extrudates are dried at 120°C.