RU2763695C1 - Porous iron-potassium oxide composite with a bidisperse structure and a method for its production - Google Patents

Abstract

FIELD: composite materials production.

SUBSTANCE: invention relates to methods for producing porous composite materials with a bidispersed submicrostructure. It can be used in the medical, chemical and petrochemical industries. Prepare a charge containing crystalline hydrate iron nitrate, crystalline hydrate cerium nitrate, potassium nitrate, molybdenum oxide, titanium oxide, calcium carbonate, tetraethoxysilane, taken in a stoichiometric ratio. A burnout microadditive in the form of birch dioxane lignin in an amount of 0.125-0.250 wt.% is impregnated into the charge with the products of hydrolysis of salts obtained using coprecipitation or sol-gel methods. The composite is molded and firing is carried out in the temperature range 20-700°C at a heating rate of 10°/min and isothermal holding for 3 hours. The composite contains phases of iron oxide α-Fe₂O₃, cerium oxide CeO₂, potassium molybdate K₂MoO₄, potassium ferrites of the composition KFeO₂ and KFe₁₁O₁₇, has a bidisperse structure and is characterized by a total pore volume from 0.006 to 0.013 cm³/g, mesopore diameter in the range from 16 to 40 nm, macropore diameters from 75 to 130 nm with a specific surface area from 2 to 5 m²/g.

EFFECT: increased efficiency of application and expansion of functionality in chemical and physical processes.

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Description

The invention relates to the production of porous composite materials with a bidisperse submicrostructure, which can be used in the medical, chemical and petrochemical industries.

The use of iron oxides as the main components of composite materials is limited by the complexity of obtaining a developed porous structure [Komarov V.S., Besarab S.V. Synthesis of biporous metal silicate adsorbents and catalysts // Vesciyanalnaya academy of sciences of Belarus. Gray chemical sciences. 2013. No. 1. S. 36-39]. The formation of composites with a bidisperse porous structure is a fundamental problem of their synthesis [Komarov V.S., Besarab S.V. Synthesis of biporous metallosilicate adsorbents and catalysts // Vesti natsyyanalnaya akademii navuk Belarusi. Gray chemical sciences. 2013. No. 1. S. 36-39]. The advantages of such a structure compared to a monodisperse one lie in the greatest use of the inner surface of the material [Antsiferov V.N., Porozova S.E. Highly porous aluminosilicate materials: preparation, properties, application. Perm: Publishing House Perm. state tech. un-ta, 1995. 120 p.].

To solve this problem, a method was used to form porous textured structures of ceramic materials by introducing burnable additives into the charge. It is known that the production of such materials occurs mainly by dry mixing methods [Ratko A.I., Ivanets A.I., Azarov S.M. Influence of additives on the porous structure of ceramics based on crystalline SiO ₂ // Neorg. mater. 2008. V. 44. No. 7. S. 883-889. DOI: 10.1134/S0020168508070182], using salt coprecipitation and sol-gel methods [Bugaeva A.Yu., Loukhina I.V., Kazakova E.G., Nazarova L.Yu., Ryabkov Yu.I. Influence of powdered cellulose and the method of obtaining a charge on the phase composition and characteristics of iron-potassium oxide material // ZhPKh. 2019. V. 92. Issue. 10. S. 1271-1282. DOI: 10.1134/S0044461819100062].

The closest analogue of the method for producing a porous iron-potassium oxide composite with a bidisperse structure is a method for producing a composite based on an iron-potassium oxide system [Bugaeva A.Yu., Loukhina I.V., Kazakova E.G., Nazarova L.Yu., Ryabkov Yu .AND. Influence of powdered cellulose and the method of obtaining a charge on the phase composition and characteristics of iron-potassium oxide material // ZhPKh. 2019. V. 92. Issue. 10. S. 1271-1282. DOI: 10.1134/S0044461819100062], in which the composite is obtained using co-precipitation/sol-gel methods and impregnation of a burnable additive (1-3 wt.%), having a homogeneous composition; containing potassium monoferrite as an active phase; having an average pore radius of not more than 50 nm. The additive is used as a burnable cellulose powder having the following characteristics: molar ratio C / O 1.2, specific surface area 6.00 m ² / g, a total pore volume 0.007 cm ³ / g, average pore diameter 4.8 nm, the average particle diameter of 2.5 ~ m.

The disadvantages of the used burnable additive are low values of the C/O molar ratio and texture characteristics, a small amount of potassium monoferrite, and the lack of information about the microstructure of the composite obtained as a result of the use of a burnable additive.

The closest analogue of a composite with a bidisperse structure is porous ceramics based on silicon dioxide with the formation of a polydisperse structure with mesopores up to 30 nm in diameter and macropores 10 μm in diameter and ultramacropores 50 μm in diameter [Ratko A.I., Ivanets A.I., Azarov S. M. Influence of additives on the porous structure of ceramics based on crystalline SiO2 // Neorg. mater. 2008. V. 44. No. 7. pp. 883-889 DOI: 10.1134/S0020168508070182]. The composite was obtained using as burn-out additives: flour (particles 10–20 µm long and 2 µm in diameter) or starch (particles 5–70 µm in diameter) or microcellulose (fibers 10–30 µm long, ~2–5 µm in diameter) or technical soot (particle diameter - 50 nm).

The disadvantage of using these burnable additives is their significant amount (2-25 wt.%), which increases the risk of material destruction due to the large number and size of macropores and ultramacropores.

Known requirements for burnable additives: they must have a plasticizing effect, and the size of their particles must be commensurate with the size of the resulting pores.

The objective of the present invention is the synthesis of a porous multicomponent composite composition: hematite α-Fe ₂ O ₃ , potassium ferrites KFeO ₂ and KFe ₁₁ O ₁₇ , cerianite CeO ₂ , potassium molybdate K ₂ MoO ₄ , obtained using birch dioxane lignin in order to increase the efficiency of using active surfaces in various chemical and physical processes.

The task is solved by developing a technology for preparing the initial composition of the charge: choosing the method of obtaining and burning additive, the amount and method of its introduction, which makes it possible to form an optimal porous structure.

The technical result of the method is that the method with the use of birch dioxane lignin burnable microadditives makes it possible to obtain a composite with an improved active surface, which improves the efficiency of use in various chemical and physical processes.

The structure and characteristics of the obtained composite ensure the efficiency of application and the expansion of functionality in the medical, chemical and petrochemical industries.

The technical result of the method is achieved by the fact that the method of obtaining a porous iron-potassium oxide composite includes the preparation of a charge containing hydrated iron nitrate, crystalline hydrate cerium nitrate, potassium nitrate, molybdenum oxide, titanium oxide, calcium carbonate, tetraethoxysilane, taken in a stoichiometric ratio, impregnation into the mixture of burnable microadditives with products of hydrolysis of salts obtained using coprecipitation or sol-gel methods, molding of composite samples by semi-dry pressing, according to the invention, birch dioxanlignin is used as a burnable additive in an amount of 0.125-0.250 wt. %, firing is carried out in the temperature range of 20-700°C with a heating rate of 10°/min and isothermal exposure for 3 hours, while a bidisperse structure is formed in the resulting composite.

The technical result of the porous iron-potassium oxide composite is achieved by the fact that the composite contains phases of iron oxide α-Fe ₂ O ₃ , cerium oxide CeO ₂ , potassium molybdate K ₂ MoO ₄ , potassium ferrite composition KFeO ₂ and KFe ₁₁ O ₁₇ , has a bidisperse structure, obtained by introducing birch dioxanlignin into the mixture as a burnable additive, and is characterized by: total pore volume from 0.006 to 0.013 cm ³ /g; mesopore diameter in the range from 16 to 40 nm; macropore diameter from 75 to 130 nm with a specific surface area from 2 to 5 m ² /g.

The invention is illustrated by figure 1 and tables. In FIG. Figure 1 shows electron microscopic images of samples obtained using the coprecipitation method with impregnation of the DLB microadditive in wt.%: a - 0, b - 0.125, c - 0.250; using the sol-gel method with impregnation of the DLB microadditive in wt %: d - 0, e - 0.125, f - 0.250.

Table 1 shows the phase composition of porous composites obtained using codeposition/sol-gel methods with DLB microadditive impregnation. Table 2 shows the region of coherent scattering (CSR) of the formed phases of porous composites obtained using coprecipitation/sol-gel methods with impregnation of DLB microadditives. Table 3 presents the characteristics of samples of porous iron-potassium oxide composite.

The method is carried out as follows.

The initial precursors used were hydrated iron (III) nitrate grade “chemically pure”, crystalline hydrated cerium (III) nitrate grade “chemically pure”, potassium nitrate grade “chemically pure”, molybdenum (VI) oxide grade “chemically pure”, titanium oxide (IV) grade "high purity", calcium carbonate grade "h", tetraethoxysilane (TU6-09-11 053-94) and birch dioxane lignin (DLB), taken in a stoichiometric ratio. DLB isolated and purified according to the method [Pepper JM, Siddiqueullah M. The effect of initial acid concentration on the lignin isolated by the acidolysis of aspen wood. Canada. // J. Chem. 1961. 39, P.1454–1461. DOI: 10.1139/v61-185.], has the following characteristics: C/O molar ratio 2.4, specific surface 30.00 m ² /g, total pore volume 0.055 cm ³ /g, average pore diameter 1.8 nm, average particle diameter 3 µm and used as a burnable additive in the amount of 0.125-0.250 wt.%.

The charge was prepared by impregnating the burnable DLB microadditive with the hydrolysis products of salts obtained using co-precipitation or sol-gel methods. Samples of the charge in the form of tablets were molded by semi-dry pressing and fired in air in the temperature range of 20-700°C, with a heating rate ( _Vload ) of 10/min and isothermal exposure for 3 hours.

The phase composition of the composite was determined by X-ray diffraction (XRD-6000 Shimadzu, Cu _Kα radiation). Estimation of the size of coherent scattering regions (CSR) was carried out by broadening of diffraction lines using the Selyakov-Scherrer formula [Egorov-Tismenko Yu.K. Crystallography / edited by Urusov V.S. M.: KDU, 2005, 592 p.]. The morphology, structure of the composite samples, and their elemental composition were studied using scanning electron microscopy (SEM) on a VEGA3 TESCAN 3 LMH instrument with an Oxford Instruments X-Max 50 energy-dispersive spectrometer. Measurement of the specific surface area (S _sp ), total pore volume (V _pore ), average pore diameter (d _pore ) of DLB and composite samples was carried out by low-temperature nitrogen physical sorption on a Quantachrome Nova 1200a instrument. Estimation of the particle size (d _cf ) in the powders is based on the results of determining the value of their specific surface area [Gavrilova N.N. Analysis of the porous structure based on adsorption data. Moscow: RKhTU im. D. I. Mendeleev, 2015, 132 p.].

As parameters characterizing the resulting composite, its phase composition (Table 1), CSR of the particles of the resulting porous composite phases (Table 2), microstructure (Fig. 1), and characteristics (Table 3) are considered.

The invention is illustrated by the following examples.

Example 1

Dissolved the calculated sample of salts in terms of metal oxides. The hydrolysis of salts obtained using the coprecipitation method was carried out with an aqueous solution of ammonia with a concentration of 0.1224÷2.0601 mol/l at 20°C and vigorous stirring until pH=4. Added oxides of molybdenum (VI) and titanium (IV). The mixture obtained was mixed in the temperature range 50÷80°C and dried in air according to the technological regime in the temperature range 50÷300°C. The samples were molded into tablets by semi-dry pressing using a technical PVA binder (1.5%). The firing was carried out at a temperature of 700°C with V _load 10 C/min with an isothermal exposure of 3 hours. The characteristics of composite No. 1 are shown in tables 1-3, fig. 1(a).

Example 2

Preparation of the mixture, as indicated in example 1. Changed the stoichiometric ratio of the mixture [Fe ₂ O ₃ :K ₂ O:MoO ₃ :CeO ₂ :CaO:TiO ₂ :MgO:SiO ₂ ] and DLB in terms of (100-x)[ 56.71:20.88:11.55:6.38:3.68:0.58:0.11:0.11]:x, where x=0.125. The impregnation of birch dioxanlignin with the products of hydrolysis of salts obtained using the coprecipitation method was carried out with constant stirring. The characteristics of composite No. 2 are indicated in tables 1-3, Figs. 1(b).

Example 3

Preparation of the mixture, as indicated in example 1. Changed the stoichiometric ratio of the mixture [Fe ₂ O ₃ :K ₂ O:MoO ₃ :CeO ₂ :CaO:TiO ₂ :MgO:SiO ₂ ] and DLB in terms of (100-x)[ 56.71:20.88:11.55:6.38:3.68:0.58:0.11:0.11]:x, where x=0.250. The impregnation of birch dioxanlignin with the products of hydrolysis of salts obtained using the coprecipitation method was carried out with constant stirring. The characteristics of composite No. 3 are shown in tables 1-3, figure 1 (c).

Example 4

The initial 0.5 M solution of iron nitrate was filtered off. Iron oxide sol (sol I), the particles of which formed the matrix of the composite, was synthesized by controlled hydrolysis of iron nitrate crystalline hydrate with an aqueous solution of ammonia with a concentration of 0.1224÷2.0601 mol/l at 20°C and vigorous stirring to pH=4. The initial 0.5 M solutions of cerium nitrate, potassium nitrate, and magnesium nitrate were filtered off. Sol II was obtained by hydrolysis of a mixed solution of cerium, potassium and magnesium nitrates, taken in amounts corresponding to the required composition, with an aqueous ammonia solution with a concentration range of 0.1224÷2.0601 mol/l at 20°C and vigorous stirring until pH=9.46. The calculated amount of silica sol synthesized by hydrolysis of an alcoholic solution of tetraethoxysilane was added. The mixing of sols I and II and oxides of molybdenum (VI), titanium (IV) and calcium was carried out in a stoichiometric ratio in terms of [Fe ₂ O ₃ :K ₂ O:MoO ₃ :CeO ₂ :CaO:TiO ₂ :MgO:SiO ₂ ]=[56.71:20.88:11.55:6.38:3.68:0.58:0.11:0.11]. The resulting mixture was stirred in the temperature range 50÷80°C and dried in air in the temperature range 50÷300°C. The samples were molded into tablets by semi-dry pressing using a technical PVA binder (1.5%). The firing was carried out at a temperature of 700 ^o C with V _load 10 ^o C/min with isothermal exposure 3 hours Characteristics of composite No. 4 are shown in tables 1-3, figure 1 (d).

Example 5

Preparation of a mixture of sols of oxides and metal oxides, as indicated in example 4. Changed the stoichiometric ratio of the mixture [Fe ₂ O ₃ :K ₂ O:MoO ₃ :CeO ₂ :CaO:TiO ₂ :MgO:SiO ₂ ] and DLB in terms of ( 100-x)[56.71:20.88:11.55:6.38:3.68:0.58:0.11:0.11]:x, where x=0.125. Birch dioxanelignin was impregnated with hydrolysis products of salts obtained using the sol-gel method, was carried out with constant stirring. The characteristics of composite No. 5 are shown in tables 1-3, figure 1 (d).

Example 6

Preparation of a mixture of sols of metal oxides and metal oxides, as indicated in example 4. Changed the stoichiometric ratio of the mixture [Fe ₂ O ₃ :K ₂ O:MoO ₃ :CeO ₂ :CaO:TiO ₂ :MgO:SiO ₂ ] and DLB in terms of (100x)[56.71:20.88:11.55:6.38:3.68:0.58:0.11:0.11]:x, where x=0.250. Birch dioxanelignin was impregnated with hydrolysis products of salts obtained using the sol-gel method, was carried out with constant stirring. The characteristics of Composite No. 6 are shown in Tables 1-3 and Figure 1(e).

Table 1

Composite sample no. How to obtain The amount of burnable additive Phase composition, vol.% Fe ₂ O ₃ CeO ₂ K ₂ MoO ₄ KFeO ₂ KFe ₁₁ O ₁₇ one coprecipitation 0 75.6 11.4 13.0 - - 2 coprecipitation 0.125 51.8 11.2 32.0 1.8 3.2 3 coprecipitation 0.250 40.2 7.2 43.1 9.5 - 4 sol-gel 0 68.0 18.0 14.0 - - 5 sol-gel 0.125 40.7 15.9 43.4 - - 6 sol-gel 0.250 47.1 18.7 24.4 9.8 -

table 2

Composite sample no. How to obtain amount of burning additive OKR, nm Fe ₂ O ₃ CeO ₂ K ₂ MoO ₄ KFeO ₂ KFe ₁₁ O ₁₇ one coprecipitation 0 27 27 49 - - 2 coprecipitation 0.125 33 sixteen 38 150 160 3 coprecipitation 0.250 23 15 14 114 - 4 sol-gel 0 28 25 73 - - 5 sol-gel 0.125 32 26 94 - - 6 sol-gel 0.250 thirty 36 84 200 -

Table 3

Composite Sample No. How to obtain Quantity, DLB, wt.% Specific surface, S _beats , m ² /g Total pore volume, V _pore , cm ³ /g Average mesopore diameter, d _pores , nm Average diameter of macropores, d _pores , nm Average particle diameter, d _cf , µm one coprecipitation 0 5.29±0.04 0.008±0.001 38±1 52±1 1.2±0.1 2 coprecipitation 0.125 1.89±0.04 0.007±0.001 40±1 100±1 1.4±0.1 3 coprecipitation 0.250 2.86±0.04 0.006±0.001 16±1 130±1 2.2±0.1 4 sol-gel 0 7.86±0.04 0.011±0.001 32±1 58±1 0.8±0.1 5 sol-gel 0.125 5.22±0.04 0.013±0.001 36±1 75±1 1.2±0.1 6 sol-gel 0.250 4.24±0.04 0.013±0.001 16±1 80±1 1.8±0.1

In the microstructure of composite samples synthesized using the coprecipitation (Figs. a , b, c ) and sol-gel (Figs. d , e, f ) methods, a high uniformity of distribution of all material components is observed. With the introduction of DLB microadditives into the composition of the mixture, a structure of fine-grained ceramics with a mesh-cellular framework was obtained, similar to the structure of ceramic foam [Gibson LJ, Ashby M F. Cellular solids: structure and properties. Cambridge University Press. 1997. 510 p.]. The results of X-ray phase analysis and scanning electron microscopy confirmed the results of measuring the texture characteristics and calculating the average particle size of the samples obtained using DLB. The samples were found to contain mesopores up to 40 nm in diameter and macropores up to 130 nm in diameter, which corresponds to the bidisperse structure of the composite.

Thus, the resulting composite has an improved structure due to the use of the inner surface and improved performance characteristics (sorption, catalytic, filtering, strength, heat-insulating and sound-absorbing), and it is possible to use the composite as sorbents, catalyst carriers, filtering and heat-shielding materials, flame arresters and sound absorbers.

Claims (2)

1. A method for producing a porous iron-potassium oxide composite, including the preparation of a charge containing hydrated iron nitrate, crystalline hydrate cerium nitrate, potassium nitrate, molybdenum oxide, titanium oxide, calcium carbonate, tetraethoxysilane, taken in a stoichiometric ratio, impregnation of a burnable microadditive into the charge with salt hydrolysis products obtained using co-precipitation or sol-gel methods, molding of composite samples by semi-dry pressing, characterized in that birch dioxane lignin is used as a burnable microadditive in an amount of 0.125-0.250 wt.%, firing is carried out in the temperature range of 20-700 ° C at a speed heating 10°/min and isothermal exposure for 3 hours, while in the resulting composite formed bidisperse structure. 2. Porous iron-potassium oxide composite obtained by the method according to claim 1, containing phases of iron oxide α-Fe₂O₃, cerium oxide CeO₂, potassium molybdate K₂MoO₄, potassium ferrite composition KFeO₂ and KFe_elevenO₁₇, having a bidisperse structure obtained by introducing birch dioxane lignin into the charge as a burnable microadditive, which is characterized by a total pore volume of 0.006 to 0.013 cm 3³/G; mesopore diameter from 16 to 40 nm, macropore diameter from 75 to 130 nm with specific surface area from 2 to 5 m²/G.

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