RU2361814C1 - Method of producing hydrotalcite-like compounds - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: method of producing layered hydroxides of formula Mg(1-X)MexÇè3+(OH)2(CO3)x/2nH2O, where the trivalent metal is scandium Sc3+ or iron and aluminium at the same time in the form FeyAlx-y, where y is less than x and x is not more than 0.4. A solution containing Mg2+ and Sc3+ chlorides or nitrates, or a solution containing Mg2+ and Al3+ chlorides or nitrates and Fe3+ sulphates or chlorides or nitrates is added to a precipitation agent solution, containing sodium hydroxide and sodium carbonate. The ratio of ions Me3+: Mg2+: [OH-] : [CO3Çè2-] in the solution is 1:3:8:1. The precipitate formed is kept in a mother solution at 96-98C for two days. After cooling to room temperature, the mother solution with the precipitate is decanted. The residue is subjected to anion exchange with Na2CO3 three times. After settling, the solution is decanted and the residue is washed with distilled water until negative results of presence of sodium ions are obtained, and then dried at 80-105C. Total concentration of metal salts in the precipitation agent solution is not more than 3 M, and total concentration of the precipitation agent solution is not more than 3 M. ^ EFFECT: obtaining good crystallised, homogeneous samples of hydrotalcite-like compounds, wider field of their use. ^ 4 dwg, 4 ex

Description

The invention relates to methods for the synthesis of hydrotalcite-like substances.

To identify the layered structure of hydroxides using x-ray phase analysis. X-ray diffraction patterns of layered hydroxides have a characteristic appearance: a set of 5 peaks, the distance between which depends on the composition of the layered hydroxide, and the peak intensity decreases with an increase in the diffraction angle by two theta. At large angles (more than 56 °) there is a doublet of the sixth and seventh peak, which is also included in the characteristic diffraction pattern to identify the layered structure.

The degree of crystallization of the substance can be estimated by the width of the peaks. Narrow intense peaks indicate a high degree of crystallinity of the samples, as well as the homogeneity of the samples and, therefore, the isotropy of their physicochemical properties.

A known method for the synthesis of layered hydroxides, for example magnesium-aluminum hydroxosulfate (Krasnobaeva ON, Nosova TA, Elizarova TA, Danilov VP Double magnesium-aluminum hydroxosulfates with a layered structure. // J. Inorganic chemistry , 2001, v. 46, - No. 6, - s. 899-902), including precipitation from 2N solutions of magnesium sulfates and aluminum with a solution of 2N sodium hydroxide at 50-70 ° C to a pH of 7.5-7.8, aging mixtures at 60-75 ° C in an oil bath in closed flasks for 2 weeks, separating the precipitates from the solution by filtration and washing with a 50% aqueous acetone solution.

This method has the following disadvantages: prolonged temperature control, use of acetone for washing, and at the same time, insufficient crystallization of the final product and low ordering of anions in the interlayer space of the finished product.

The closest synthesis is essentially (Eliseev A.A., Lukashin A.V., Vergetel A.A., Tarasov V.P., Tretyakov Yu.D. Investigation of crystallization processes of layered Mg-Al double hydroxides. // Reports Academy of Sciences. - 2002. - vol. 387, - No. 6, - p. 777-781), including the precipitation of hydrotalcite-like compounds from solutions of magnesium and aluminum nitrates (Mg ²⁺ : Al ³⁺ = 3: 1, the total concentration of cations is 1M ), a solution of carbonate and sodium hydroxide ([CO ₃ ^2- ]: [OH ^- ] = 1: 6, the total concentration of 3M anions), at a constant pH value of 10.0 ± 0.1, thermostating at 80 ° C for 5 days.

The disadvantage of this method is the duration of the process, the need to maintain a constant pH, while insufficient crystallization and low ordering of anions in the interlayer space, which may cause the heterogeneity of the physicochemical properties of the finished product.

The objective of the invention is to expand the arsenal of methods for producing synthetic hydrotalcite-like compounds with the General formula

Mg _(1-x) Me _x (OH) ₂ (CO ₃ ) _{x / 2} · nH ₂ O, where scandium Sc ³⁺ or, in any ratio, aluminum Al ³⁺ and iron Fe ³⁺ act as a trivalent metal.

EFFECT: obtaining synthetic hydrotalcite-like layered magnesium-scandium hydroxide and magnesium-iron-aluminum hydroxide with improved characteristics, such as high crystallinity and ordering of anions in the interlayer space.

The proposed invention from the specified method, including the precipitation of hydrotalcite-like compounds from a solution of salts of divalent magnesium and a trivalent metal with a precipitating solution containing carbonate and sodium hydroxide, thermostating the precipitate, is characterized in that:

- the precipitation solution contains chlorides or nitrates of Mg ²⁺ and scandium Sc ³⁺ ;

- the precipitation solution contains chlorides or nitrates of Mg ²⁺ and Al ³⁺ and sulfates or chlorides or nitrates of Fe ³⁺ ;

- the concentration of both the precipitation solution and the precipitating solution should not be more than 3M, because the increase in concentration leads to an increased density of the reaction mixture and the impossibility due to this uniform passage of the reaction throughout the volume, which ultimately prevents the necessary homogeneity of the final product;

- the ratio of ions in the solution for precipitation and in the precipitating solution should correspond to: Me ³⁺ : Me ²⁺ : [CO ₃ ^2- ]: [OH ^- ] = 1: 3: 1: 8;

- thermostating is carried out at 96-98 ° C for 2 days, the precipitate of the hydrotalcite-like compound obtained is subjected to anion exchange with Na ₂ CO ₃ three times, then it is washed with distilled water until a negative quality reaction to the Na ⁺ ion, drying is carried out at 80-105 ° C.

The criteria of "novelty" and "inventive step" of the proposed method for producing the claimed layered hydroxides confirm the following features:

- the revealed possibility in the preparation of a salt solution for the deposition of layered hydroxides to use as anions - chlorides or nitrates Mg ²⁺ and S ³⁺ or chlorides or nitrates Mg ²⁺ and Al ³⁺ and sulfates or chlorides or nitrates Fe ³⁺ ;

- the ratio of ions in the solution for precipitation and in the precipitating solution, corresponding to Me ³⁺ : Me ²⁺ : [CO ₃ ^2- ]: [OH ^- ] = 1: 3: 1: 8;

- carrying out thermostating at 96-98 ° C, which reduces the duration of thermostating to 2 days. Lowering the temperature increases the duration of temperature control and degrades the performance of the finished product, and increasing the temperature of temperature control above 100 ° C requires the use of special equipment, i.e. additional costs. At the indicated temperature, after two days, the characteristics of the finished product obtained on an X-ray diffraction pattern confirm the high quality of the finished product;

- decanting the mother liquors with a precipitate of layered hydroxides after cooling to room temperature, which are then subjected to anion exchange with Na ₂ CO ₃ three times, after settling, the solutions are decanted and washed with distilled water to obtain a negative result for the presence of sodium ion, and drying is carried out at 80-105 ° C.

The method allows to obtain synthetic hydrotalcite-like compounds with improved characteristics, i.e. high crystallinity and ordering of anions in the interlayer space, which is confirmed by the presence of high and narrow characteristic peaks in X-ray diffraction patterns.

The claimed invention is characterized in figures 1-4.

Figure 1 - x-ray diffraction pattern of magnesium-scandium layered hydroxide obtained by the proposed method;

Figure 2 - x-ray diffraction pattern of magnesium-iron-aluminum layered hydroxide obtained by the proposed method with a ratio of A1 ³⁺ : Fe ³⁺ = 9: 1 in a solution for precipitation;

Figure 3 - x-ray diffraction pattern of magnesium-iron-aluminum hydroxide obtained by the proposed method with a ratio of Al ³⁺ : Fe ³⁺ = 99: 1 in a solution for precipitation;

Figure 4 - x-ray diffraction pattern of magnesium-iron-aluminum hydroxide obtained by the proposed method with a ratio of Al ³⁺ : Fe ³⁺ = 9: 1 in a solution for precipitation, but at a temperature of 80 ° C.

Examples of the use of the proposed method for producing synthetic hydrotalcite-like compounds

Example 1

In the synthesis of magnesium-scandium layered hydroxide, a precipitating solution containing sodium hydroxide and sodium carbonate was added dropwise to a mixture of solutions of scandium nitrate and magnesium nitrate at a temperature of 3-5 ml / min at room temperature. The total concentration of metal salts is 2M, and the total concentration of the precipitating solution is 1M. Samples of substances for the preparation of solutions were calculated from the ratio: Sc ³⁺ : Mg ²⁺ : [OH ^- ]: [CO ₃ ^2- ] = 1: 3: 8: 1.

Precipitated samples were thermostated in the mother liquor at 96 ° C for two days.

Then, after cooling to room temperature, the mother liquor was decanted and the layered hydroxide precipitate was subjected to anion exchange with Na ₂ CO ₃ in order to replace the residual NO ₃ ^- anions in the interlayer space with CO ₃ ^2- . The operation was repeated three times. After settling, the solutions were decanted and washed repeatedly with distilled water until a qualitative reaction to sodium yields a negative result. Samples were dried at 99 ° C.

The chemical and thermogravimetric analysis allowed us to calculate the chemical formula of the obtained product: Mg _0.677 Sc _0.323 (OH) ₂ (CO ₃ ) _0.162 · 0.805H ₂ O, which has the characteristic of x-ray diffraction with high and narrow peaks, presented in figure 1

Example 2

In the synthesis of magnesium-iron-aluminum layered hydroxide, a precipitating solution containing sodium hydroxide and sodium carbonate was added dropwise to a mixture of solutions of iron chloride, aluminum nitrate and magnesium nitrate at room temperature. The total concentration of metal salts is 3M, and the total concentration of the precipitating solution is 2M. Samples of substances for the preparation of solutions were calculated from the ratio: Me ³⁺ : Mg ²⁺ : [OH ^- ]: [CO ₃ ^2- ] = 1: 3: 8: 1, where Al ³⁺ and Fe ³ act simultaneously as the trivalent metal ⁺ in a ratio of 9: 1.

The precipitated samples were thermostated in the mother liquor at 97 ° C for two days.

Then, after cooling to room temperature, the mother liquor was decanted and the layered hydroxide precipitate was subjected to anion exchange with Na ₂ CO ₃ . The operation was repeated three times. After settling, the solution was decanted and washed repeatedly with distilled water until a qualitative reaction to sodium yields a negative result. Samples were dried at 99 ° C.

The chemical and thermogravimetric analysis performed allowed us to calculate the chemical formula of the obtained product: Mg _0.764 Al _0.219 Fe _0.017 (OH) ₂ (CO ₃ ) _0.118 · 0.886Н ₂ O. This product has the characteristic of high and narrow peak X-ray diffraction shown in FIG. 2.

Example 3

In the synthesis of magnesium-iron-aluminum layered hydroxide, a precipitating solution containing sodium hydroxide and sodium carbonate was added dropwise to a mixture of solutions of iron sulfate, aluminum chloride and magnesium nitrate at room temperature. The total concentration of metal salts is 3M, and the total concentration of the precipitating solution is 1M. Weighed portions of the substances for the preparation of solutions were calculated from the ratio: Me ³⁺ : Mg ²⁺ : [OH ^- ]: [СО ₃ ^2- ] = 1: 3: 8: 1, where Al ³⁺ : Fe ³ act simultaneously as the trivalent metal ⁺ in a ratio of 99: 1.

The precipitated samples were thermostated in the mother liquor at 98 ° C for two days.

Then, after cooling to room temperature, the mother liquor was decanted and the layered hydroxide precipitate was subjected to anion exchange with Na ₂ CO ₃ . The operation was repeated three times. After settling, the solution was decanted and washed repeatedly with distilled water until a qualitative reaction to sodium yields a negative result. Samples were dried at 105 ° C.

The chemical and thermogravimetric analysis performed allowed us to calculate the chemical formula of the obtained product: Mg _0.714 Al _0.282 Fe _0.004 (OH) ₂ (CO ₃ ) _0.146 · 0.820H ₂ O. This product has the characteristic of high and narrow peak X-ray diffraction shown in FIG. 3.

Example 4

In the synthesis of magnesium-iron-aluminum layered hydroxide, a precipitating solution containing sodium hydroxide and sodium carbonate was added dropwise to a mixture of solutions of iron chloride, aluminum nitrate and magnesium nitrate at room temperature. The total concentration of metal salts is 3M, and the total concentration of the precipitating solution is 2M. Samples of substances for the preparation of solutions are calculated from the ratio: Me ³⁺ : Mg ²⁺ : [OH ^- ]: [CO ₃ ^2- ] = 1: 3: 8: 1, where A1 ³⁺ : Fe ³ simultaneously act as a trivalent metal ⁺ in a ratio of 9: 1.

The precipitated samples were thermostated in the mother liquor at 80 ° C for two days.

Then, after cooling to room temperature, the mother liquor was decanted and the layered hydroxide precipitate was subjected to anion exchange with Na ₂ CO ₃ . The operation was repeated three times. After settling, the solution was decanted and washed repeatedly with distilled water until a qualitative reaction to sodium yields a negative result. Samples were dried at 99 ° C.

This product has an X-ray diffraction characteristic shown in FIG. 4. From the x-ray diffraction pattern it is seen that at this temperature in 2 days it is not possible to achieve the same degree of crystallinity as in example 2 when thermostating at 97 ° C and other conditions being equal.

The above examples 1-3 confirm that the proposed method allows to obtain new synthetic hydrotalcite-like compounds with the General formula Mg _(1-x) Me _x (OH) ₂ (CO ₃ ) _{x / 2} · nH ₂ O, where x is not higher than 0.4 , a Me is a trivalent metal, which is scandium, or iron and aluminum at the same time with any ratios between themselves.

Example 4 shows that a decrease in temperature degrades the characteristics of the obtained product, which is confirmed by peaks in the x-ray diffractogram (figure 4).

Thus, the proposed method allows for a short period of time to obtain well crystallized samples of new hydrotalcite-like compounds with the general formula Mg _(1-x) Me _x (OH) ₂ (CO ₃ ) _{x / 2} · nH ₂ O, where x is not higher than 0, 4a, scandium Sc or iron and aluminum in the form of Fe _y Al _xy acts as a trivalent metal. High and narrow characteristic peaks of X-ray diffraction patterns of these compounds indicate the homogeneity of the samples and, therefore, the isotropy of their physicochemical properties, which will expand their scope.

Claims (2)

The method of obtaining layered hydroxides of the formula
Mg _(1-x) Me _x ³⁺ (OH) ₂ (CO ₃ ) _{x /} 2nH ₂ O,
where the trivalent metal is scandium Sc ³⁺ or at the same time iron and aluminum in the form of Fe _y Al _xy , whereby “y” is less than “x” and “x” is not higher than 0.4, which means that in a solution containing chlorides or Mg ²⁺ and Sc ³⁺ nitrates, or to a solution containing chlorides or Mg ²⁺ and Al ³⁺ nitrates and sulfates or chlorides or Fe ³⁺ nitrates, a precipitating solution containing sodium hydroxide and sodium carbonate is added, the ratio ion Me ^3+: Mg ^2+: [OH ^-]: [CO ₃ ^2-] in the solution is 1: 3: 8: 1, and the deposited precipitate was incubated in the mother liquor at 96-98 ° C for two days, after about room temperature to cool the mother liquors were decanted from the precipitate and then subjected to anion exchange three times with Na ₂ CO ₃ solution was decanted after settling and the precipitate was washed with distilled water until a negative result for the presence of sodium ion, drying is carried out at 80-105 ° C. 2. The method of claim 1, characterized in that the total concentration of metal salts in the precipitating solution is not more than 3 M, and the total concentration of the precipitating solution is not more than 3 M.

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