SK10882001A3 - Process for the preparation of hydrotalcite and hydrotalcite-like compounds - Google Patents

Abstract

Hydrotalcite and hydrotalcite like compounds are prepared by reaction of magnesium hydroxide and aluminium hydroxide in alkaline medium with urea or with a mixture solution of ammonium carbamate with urea, which provides carbonate ion CO3exp(2-). An ammonia solution is used to form the alkaline medium.

Description

Name of the invention: Process for the preparation of hydrotalcite and hydrotalcite-like compounds.

Field of the invention.

The present invention relates to the preparation of hydrotalcite-like compounds of the general formula

Mg ,. _x Al _x (OH) ₂ (CO ₃ ) 1 ₍ / _{2. m} H ₂ O where.

0.1 <x <0.5 0.4 <m <0.8 with virtually no undesirable impurities, such as alkali metals, sulphates, nitrates and chlorides, suitable as additives to macromolecular substances which bind acid radicals produced by the macromolecular substances themselves, or catalyst residues used in the synthesis of macromolecular substances.

BACKGROUND OF THE INVENTION.

There are a large number of crystalline compounds among the basic double salts of divalent and trivalent metals, which Feitknecht described as double-layered in double layers in the article Ueber die Bildung von Doppelhydroxiden zwischen zwei- und dreiwertigen Metallen, Helv.Chim.Acta 25, 555-60, (1942). structure and divided them into three basic types:

1. Sjogrenite and pyroaurite (or hydrotalcite and manasseite) stratified structures

2. Layered structures similar to laminar calcium aluminate.

3. Layered structures with two kinds of ions in the main layer.

From the practical point of view, the most interesting is the existence of type 1 minerals. Their designation is derived from the names of minerals that are most commonly found in nature in two isomorphic modifications - hexagonal and rhombohedral. They consist of so-called. brucite-like layers of Me (OH) ₂ , between which so-called &quot; interlayer.

Allmann in Doppelschichtstrukturen mit brucit-ahnlichen Schichtionen, Chimia 24, 99108, (1970), Brown in Mixed magnesium-aluminum hydroxides Clay.Miner.7, 177-201 (1967) and Miyata in The syntheses of HT-like compounds and their structures and physicochemical properties, Clays & Clay Miner. 23, 369-375 (1975) disclose the general formula of layered compounds, wherein the main layer consists of:

[(Μ ²⁺ ) χ (Μ ³⁺ ) γ (ΟΗ) _{2χ +} 3 _Γηζ ] between which interlayers [(A ⁿ ') _z are inserted. mH ₂ 0]

The figure shows a layered structure of hydrotalcite of the formula Mg 4, Al ₂ (OH) 13 CO 3, 4H ₂ O, taken from the prospectus literature of KYOWA Chemical Industry Co., Ltd.

i / · ~. Γ.

The structure of these compounds allows a wide range of ratio of metal divalent and trivalent ions M ² 'and M ³⁴ . The anions can vary in size from small (OH, F ') to large (I'), with a charge of -1 to -3. They may be Cl ', Br, I', NO3, C1O4, OH, IO3, CO3 ² , SO4 ² , S2O3 ² , WO4 ² ', CrO ₄ ² , (Fe (CN) e) ³ ' and a number of organic anions.

Cations, including Fe ²⁺ , Co ²⁺ , Cu ²⁺ , Ni ²⁺ , Zn ²⁺ , Cr ³⁺ , Fe ³⁺ and others, can be mixed with Mg ² and Al ³ , or alone (e.g. Mg ₃ Zn ₃ Al ₂ (OH) 16 CO ₃ .4H ₂ O, Ni ₆ Al ₂ (OH) 16 CO ₃ .4H ₂ O).

The ratio of M ² : M ³⁺ in the main layer can vary in a relatively wide range from 4: 1 to 3: 2.

Attempts to synthesize layered, hydrotalcite-like compounds have been encountered as early as the 1940s. Many authors have been involved in the preparation of hydrotalcite-like compounds. The synthesis procedure can be summarized as follows:

According to US 3,539,306 an aqueous mineral salt solution containing Mg ²⁺ and Al ^3+, are introduced into a reactor and stirred, the dose of the solution containing CO ₃ ^2- and OH in a molar amount approximately equivalent to the content of Mg ²⁺ and Al ^3+. The precipitated product may be subjected to a hydrothermal treatment or so-called &quot;"Thermalaging" to improve crystalline properties and particle morphology. Crystal formation or growth is possible. by treating the freshly precipitated slurry in an autoclave at temperatures of 100-350 ° C and elevated pressure (up to 300 atm). A disadvantage of this process is the formation of reaction by-products such as sulfates, chlorides, nitrates.

According to U.S. Pat. Nos. 3,650,704 and 4,539,306, the preparation of hydrotalcite-like compounds is based on water-insoluble raw materials. Mg (OH) ₂ , Al (OH) ₃ hydroxides, MgO, Al ₂ O ₃ , or a combination thereof with a CO ₃ ² solution are dispersed in water at elevated temperature and an OH-containing solution is added. The source of carbonate ion CO 3 ² are substances such as Na 2 CO _3, NaHCO _3, (NH _{4) 2} CO _3rd

The object of U.S. Pat. No. 4,656,156 is the preparation of hydrotalcite from an industrial so-called &quot; Bayer solution containing some Na ₂ CO ₃ , which at elevated temperature reacts with activated MgO to hydrotalcite. The choice of reaction temperature, raw material concentrations, raw material ratio, reaction time, dynamic conditions in the reactor has a significant influence on the quality of the final product, its crystallinity, particle distribution, surface area. The reaction can be carried out in a continuous or discontinuous manner. The continuous process is analogous to a flow-through, perfectly stirred reactor with recycle and individual solution feeds.

Martin E S. et al. PCT / US95 / 00166, (1995) describes the preparation of synthetic hydrotalcite by first reacting MgO powder with a transition Al ₂ O ₃ in an aqueous medium having a large specific surface area, in suspension or slurry, to form a meixnerite-like intermediate. Subsequently, the intermediate is contacted with an anion source such as an acid, most preferably CO ₂ , to form a layered double hydroxyl compound which is finally separated from the suspension by filtration, centrifugation, vacuum dehydration, drying or other methods. The powder thus prepared has a specific surface area of about 100 m ² / g or greater. In order to achieve related double hydroxyl structures, other reactants selected from the group consisting of bromides, chlorides, boric acid, phosphates, sulfates may be combined with the meixnerite intermediate, which may replace the CO ₂ supplied to the suspension.

According to Martin ES et al. PCT / US95 / 00166, (1995), 100 g of basic magnesium carbonate hydrate with 31 g of alumina with an average particle size of 2.0 µm were introduced into the reactor. The suspension was stirred at room temperature for 3 hours while sufficient liquid CO ₂ was introduced into the reactor to increase the total pressure in the reactor to 40.1 atm. The whole was then heated to 50 ° C for 2 hours. By means of X-ray diffraction analysis, the majority of hydrotalcite content was determined in the dried filter product from the reactor.

Miyata and Okada in Synthesis of HT-like compounds and their physico-chemical properties, Clays & Clay Miner. 25, 14-18, 1977 disclose a process for preparing compounds of the formula [Mgi. _x Al _x (OH) ₂ ] ^x [A ² x 2.m H ₂ O] ^X 'where A ² ' is SO ^{4 2} 'or CrO? and χξ0.25. They are similar in structure to orthorhombic hydrotalcite.

In a 2 L reactor, a 3.5 M NaOH solution and a solution containing 0.75 mol / l Mg ^2r and 0.25 mol / l Al are continuously mixed. The total volumetric flow rate is 40 ml / min, the temperature is maintained at 30 ° C and the pH is 10 ± 0.2. The precipitate was filtered off and, after washing, dried at 80 ° C for 12 hours. The molar ratio of product X = Mg / Al is 3.01, containing 1.7% CO ₂ coming from ambient air.

According to CS 278 484, hydrotalcite-like compounds are prepared by reacting magnesium hydroxide and aluminum hydroxide in an aqueous medium in the presence of ammonia water. The carbonate ion providing substance is gaseous carbon dioxide. The disadvantage of this procedure is. that by delivering carbon dioxide gas into the reaction system it is not possible to achieve reproducible product quality.

SUMMARY OF THE INVENTION.

It is an object of the present invention to provide an improved process for the production of hydrotalcite which provides a well-crystalline product with no trace impurities (gibbsit, brucite, hydromagnesite, magnesite) without the formation of reaction by-products such as sulphates, chlorides, alkali metal nitrates. According to the preferred embodiments of the synthetic hydrotalcite described herein, the process of their manufacture does not produce any by-products, except for weak ammonia water which can be recycled in the production process.

The present invention provides a process for the preparation of hydrotalcite having a stoichiometric composition

Mg ₁ . _x Al _x (OH) ₂ (CO ₃ ) _{x / 2} · _m H ₂ O where:

0.1 < x < 0.5 0.4 < m < 0.8 from an aqueous suspension of aluminum hydroxide, magnesium hydroxide with separation, surface treatment in an aqueous medium, and drying based on an aqueous suspension of magnesium hydroxide and aluminum hydroxide in a molar ratio of MgO / Al ₂ O _{3 of} 4 to 5, preferably 4.4 to 4.5, is reacted at a pH of 8 to 11, preferably 10.4 to 10.8, with a substance providing a carbonate ion under the reaction conditions at a temperature of 120 to 180 ° C, preferably 150 to 165 ° C for 1 to 5 hours, preferably 2 to 4 hours at a pressure of 0.3 to 1.5 MPa, preferably 0.6 to 0.9 MPa. To obtain a suitable pH, an ammonia solution is used and the substance providing under the reaction conditions the carbonate ion is urea, or a mixed solution of ammonium carbaminate with urea in a molar ratio to magnesium hydroxide: CO ₂ / MgO 0.2 to 1, preferably 0.3 to 0. 5th

The advantage of the process is that it is possible to use amorphous aluminum hydroxide, but also any crystalline modification such as gibbsit, beyerite or hydrargillite. In the preparation of hydrotalcite according to the present process, no by-products such as nitrates, sulfates, chlorides are formed by the reaction process. Sodium, expressed as Na ₂ O derived from aluminum hydroxide, is released into the mother liquor in the hydrotalcite synthesis process, leaving only trace amounts of alkali metals in the insoluble product.

The process of preparation of the hydrotalcite according to the invention is industrially applicable, does not require long reaction times, high pressures, besides leached alkali metal compounds, does not produce any by-products such as nitrates, sulfates, chlorides. After separation of the product, the mother liquor contains a small amount of ammonia which can be recycled. The concentration of alkali metals in the mother liquor may increase, so it is appropriate to replace some of the mother liquor with fresh demineralized water.

DETAILED DESCRIPTION OF THE INVENTION.

1. The following was submitted to a stirred laboratory autoclave with a working volume of 2200 ml:

• suspension containing 68.46 g of crystalline Duhor N-Pl type brucite, 41.35 g of crystalline JHD 17 / S type gibbsite, 1710 ml of demineralised water • 14.6 ml of ammonia water containing 25% ammonia • 23.72 g urea

The mixture was homogenized, heated to 160 ° C with stirring, and allowed to react at this temperature for 3 hours. After the reaction time, a mixture of water vapor and ammonia gas was discharged through an autoclave lid valve. The discharge of the gas mixture was terminated at an equilibrium pressure of 0.6 MPa. Then the reaction mixture was cooled, filtered, washed twice with 500 ml of demineralized water and the filter cake was dried at 110 ° C for 12 hours.

A product having the following composition was obtained:

MgO content (%) 35.96

Al ₂ O ₂ content (%) 20.35.

CO ² content ² % (%) 10.85

The DTA product record contained two endothermic peaks at 270 ° C and 445 ° C.

The product had a specific surface area of 11.33 m ² / g and a mean particle size d 50 of 2.41 µm.

The same paste product was surface-treated with a 3% higher fatty acid-stearin mixture, the resulting product after drying at 110 ° C for 12 hours had a median particle size d 50 of 2.00 µm.

The X-ray powder diffraction pattern of the product contained the following diffraction lines compared to the ASTM standard for individual inter-plane distances h k 1:

HKL d (ASTM) d (product) 003 7,690 7.5576 006 3,880 3.7787 1 1 0 1,530 1.5225 1 1 3 1,500 1.4928

2. The following are dispensed into a stirred laboratory autoclave with a working volume of 2200 ml:

• suspension containing 70.39 g of crystalline Duhor N-Pl type brucite, 42.53 g of crystalline AJcan SF 7 type gibbsite, 1590 ml of demineralized water • 14.9 ml of ammonia water containing 25% ammonia • 24.4 g urea

The mixture was homogenized, heated to 160 ° C with stirring, and allowed to react at this temperature for 3 hours. After the reaction time, a mixture of water vapor and ammonia gas was discharged through an autoclave lid valve. The discharge of the gas mixture was terminated at an equilibrium pressure of 0.6 MPa. Then the reaction mixture was cooled, filtered, washed twice with 500 ml of demineralized water and the filter cake was dried at 110 ° C for 12 hours.

A product having the following composition was obtained:

MgO content (%) 35.66 Contents AJ ₂ O ₃ (%) 21.49 Content CO.? ' (%) 11.04

The DTA product record contained two endothermic peaks at 270 ° C and 445 ° C.

The product had a specific surface area of 10.79 m ² / g and a mean particle size d 50 of 2.1 µηι.

The same paste-like product was surface-treated with a 3% higher fatty acid-stearin mixture, the resulting product after drying at 110 ° C for 12 hours had a mean particle size d _{50 of} 1.6 μην

The X-ray powder diffraction pattern of the product contained the following diffraction lines compared to the ASTM standard for individual inter-plane distances h k 1:

HKL d (ASTM) d (product) 003 7,690 7.5996 006 3,880 3.7946 1 1 0 1,530 1.5237 1 1 3 1,500 1.4955

3. The following is dispensed into a stirred laboratory autoclave with a working volume of 2200 ml:

• suspension containing 70.39 g of crystalline Duhor N-Pl type brucite, 42.53 g of crystalline Alcan SF 7 type, 1590 ml of demineralised water • 50 g of a mixed solution of ammonium carbaminate and urea containing:

24.45% wt. NH ₃

28.94% wt. CO ₂ 9.41 wt. urea

The mixture was homogenized, heated to 160 ° C with stirring, and allowed to react at this temperature for 3 hours. After the reaction time, a mixture of water vapor and ammonia gas was discharged through an autoclave lid valve. The discharge of the gas mixture was terminated at an equilibrium pressure of 0.6 MPa. Then the reaction mixture was cooled, filtered, washed twice with 500 ml of demineralized water and the filter cake was dried at 110 ° C for 12 hours.

A product having the following composition was obtained:

MgO content (%) 35.68 Contents A1 ₂ O ₃ (%) 21.35 Content CO.? ' (%) 9.39

The DTA product record contained two endothermic peaks at 270 ° C and 445 ° C.

The product had a surface area of 12.26 m ² / g and a mean particle size d 50 of 2.0 µm.

The same paste-like product was surface-treated with a 3% higher fatty acid-stearin mixture, the resulting product after drying at 110 ° C for 12 hours had a mean particle size d 50 of 1.6 µm and a BET surface area of 7.63 m ² / g.

The X-ray powder diffraction pattern of the product contained the following diffraction lines compared to the ASTM standard for individual inter-plane distances h k 1:

HKL d (ASTM) d (product) 00 3 7,690 7.6029 006 3,880 3.7978 1 1 0 1,530 1.5246 1 1 3 1,500 1.4952

* * Γ

Claims (6)

Patent claims. A process for the preparation of hydrotalcite-like compounds having a stoichiometric composition Mg ,. _x Al _x (OH) ₂ (CO ₃ ) x / 2. _m H ₂ O where: 0.1 <x <0.5 0.4 <m <0.8 from an aqueous suspension of aluminum hydroxide, magnesium hydroxide with separation, surface treatment in an aqueous medium and drying, characterized in that the aqueous suspension of magnesium hydroxide and aluminum hydroxide in the molar ratio of MgO / Al ₂ O 3 4 to 5, preferably from 4.4 to 4.5 at pH 8 to 11, preferably from 10.4 to 10.8 is reacted with urea or with a solution comprising urea and ammonium carbamate in any ratio at 120 to 180 ° C, preferably 150 to 165 C for 1 to 5 hours, preferably 2 to 4 hours at a pressure of 0.3 to 1.5 MPa, preferably 0.6 to 0.9 MPa. A process for the preparation of hydrotalcite-like compounds having a stoichiometric composition according to claim 1, characterized in that an ammonia solution is used to achieve a suitable pH. Process for the preparation of hydrotalcite-like compounds according to claims 1 and 2, characterized in that the source of carbonate, CO ₃ ² 'ion is urea or a solution containing urea and ammonium carbaminate in any ratio, which hydrolyzes at the reaction temperature to give CO .3 ² 'ion. The urea or solution containing urea and ammonium carbaminate is added to the feedstock suspension in a molar ratio to magnesium hydroxide: CO ₂ / MgO = 0.2 to 1, preferably 0.3 to 0.5. Process for the preparation of hydrotalcite-like compounds according to claims 1, 2 and 3, characterized in that in order to prepare the return ammonia water, a mixture of ammonia gas and water vapor is discharged during the synthesis of hydrotalcite-like compounds, preferably after reaction to equilibrium pressure 0 5 to 0.7 MPa, preferably to 0.6 MPa. A process for the preparation of hydrotalcite-like compounds according to claim 1, 2, 3 and 4, characterized in that the depressurization temperature of the reaction system according to claim 4 is carried out at a temperature of 120 to 180 ° C, preferably 160 to 165 ° C. A process for the preparation of hydrotalcite-like compounds according to claims 1, 2, 3, 4 and 5, obtains a product characterized in that the BET surface area is 10-12 m ² / g, the mean particle size d ₅₀ is 1.5-2 1 µm, MgO content is 35 - 36%, Al ₂ O ₃ content is 20 - 22%, CO ₃ ² 'content is 10 to 12%.