CN1507944A

CN1507944A - Method for clean synthesizing magnesite-alumina hydrotalcite

Info

Publication number: CN1507944A
Application number: CNA021567476A
Authority: CN
Inventors: 蕾李; 李蕾; 罗青松
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2002-12-18
Filing date: 2002-12-18
Publication date: 2004-06-30

Abstract

The present invention relates to a synthesis method of cationic clay, specially it is a synthesis method of magnesium-aluminium hydrotalcite whose chemical composite is Mg1-xAlx(OH)2(CO3)0.5xmH2O, x is greater than or equal to 0.2 or less than or equal to 0.2 or less than or equal to 0.4. Its synthesis process includes the following steps: using MgCo3 or mg(OH)2 as magnesium source, roasting for 3-5 hr. at 400-900 deg.C to obtain active MgO, its specific area is 250-40 sq.m/g, mixing it with sodium aluminate aqueous solution, Mg/Al added mole ratio is 1.0-4.5, adding NaOH and Na2CO3, and the mole ratio of NaOH/NaOH+Na2CO3 is 0.7-0.9, controlling pH value in 10-12, stirring at 60-100 deg.C and making reaction for 4-15 hr., filtering obtained product washing and drying.

Description

Clean synthesis method of magnesium-aluminum hydrotalcite

Technical Field

The invention relates to a synthetic method of anionic clay, in particular to a synthetic method of magnesium-aluminum hydrotalcite.

Background

The chemical composition of magnesium aluminum hydrotalcite is generally: mg (magnesium)_1-xAl_x(OH)₂(CO₃)_0.5xmH₂O and x satisfy that x is more than or equal to 0.2 and less than or equal to 0.4. It has a layered structure, the framework of the laminate has positive charges, and the ions with opposite charges between layers are balanced with the positive charges, so that the whole structure is electrically neutral. The interlayer anions have exchangeability, and the interlayer spacing shows regular change along with the difference of the interlayer ion size. The chemical composition of the laminate, the kind and amount of interlayer ions, the interlayer spacing, etc. may vary depending on the design requirements, and thus do not appear to beThe same and diversified physical and chemical properties can be used as catalytic materials, adsorption and ion exchange materials, infrared absorption materials, ultraviolet barrier materials, flame retardant materials, sterilization materials, medical materials and the like, and can be widely applied to the fields of rubber, plastics, coatings, cosmetics and the like.

The synthesis method described in the current domestic and foreign literature reports and patents is generally a coprecipitation method, for example: U.S. patent No.4,458,026 to Kerchle, discloses the preparation of hydrotalcite by coprecipitation of aqueous solutions of magnesium and aluminum salts under basic conditions:

the reaction is acid-base reaction, which is easy to proceed, but the reaction product is colloidal, which is difficult to wash and filter, and the reaction consumes a large amount of NaOH, which is in addition to Cl in the raw material^-、SO₄ ^2-Reacting to produce low-value NaCl and Na₂SO₄And the discharge is not beneficial to environmental protection on one hand, and the reaction cost is relatively high on the other hand.

Disclosure of Invention

The technical problem to be solved is as follows: a clean synthesis route of magnesium aluminum hydrotalcite is adopted, and the method is to mix MgO and sodium aluminate aqueous solution for reaction to generate hydrotalcite. The reaction product has single phase, is granular and easy to wash, mother liquor after reaction is completely recycled and used for next batch of materials, no high-concentration waste liquid is discharged, and the synthetic route is economical, reasonable and environment-friendly.

The technical scheme is as follows: the chemical composition of magnesium aluminum hydrotalcite is generally: mg (magnesium)_1-xAl_x(OH)₂(CO₃)_0.5xmH₂O and x satisfy that x is more than or equal to 0.2 and less than or equal to 0.4. The synthetic route of the invention is MgCO₃Or Mg (OH)₂As magnesium source, roasting at 400-900 deg.C for 3-5 hr to obtain active MgO, mixing with sodium aluminate solution, adding NaOH and Na₂CO₃At a molar ratio of NaOH/NaOH+Na₂CO₃0.7-0.9, controlling the pH value at 10-12, and reacting for 4-15 hours at the temperature of 60-100 ℃ under stirring to generate the magnalium hydrotalcite with single phase.

The magnesium-aluminum hydrotalcite with single phase can be synthesized by using commercially available MgO through the synthetic route.

The invention has the following effects: the x of the prepared magnesium-aluminum hydrotalcite is not less than 0.25 and not more than 0.35, the reaction product has a single phase and is granular, the washing is easy, the mother liquor after the reaction can be completely recycled and used as the next batch of materials, no high-concentration waste liquid is discharged, the product cost is greatly reduced, and the method belongs to an environment-friendly process.

The specific implementation mode is as follows: the specific synthetic route is shown in the attached figure 1 in the specification.

An embodiment of the invention is MgCO₃Or Mg (OH)₂Is a magnesium source, is roasted for 3 to 5 hours at the temperature of 400-900 ℃ to prepare active MgO, and the specific surface of the active MgO is 250 to 40m²Mixing with sodium aluminate solution at Mg/Al molar ratio of 1.0-4.5, adding NaOH and Na₂CO₃In the molar ratio of NaOH/NaOH + Na₂CO₃The reaction time is 0.7-0.9, the pH value is controlled at 10-12, the reaction is carried out for 4-15 hours under the stirring of 60-100 ℃, and the magnesium-aluminum hydrotalcite with single phase can be obtained after filtering, washing and drying (the X-ray powder diffraction spectrum and the corresponding XRD index of the magnesium-aluminum hydrotalcite and the standard XRD index of the magnesium-aluminum hydrotalcite are shown in the attached figure 2 and the table 1 of the specification), in addition, the filtrate after the reaction can be completely recycled and used as the next batch of materials, no high-concentration waste liquid is discharged, and the method belongs to the environment-friendly process.

The MgO roasting temperature is 500-700 ℃, the roasting time is 3-4 hours, the Mg/Al feeding molar ratio is 1.0-4.0, and the reaction is preferably carried out for 6-10 hours under the conditions of 100 ℃ reflux and stirring.

Examples

Example 1:

with Mg (OH)₂Is used as a magnesium source, is roasted for 4 hours at 400 ℃ at the heating rate of 10 ℃/min to prepare active MgO, and the specific surface area of the active MgO is 220m²(ii) in terms of/g. First Al (OH)₃20.8g、NaOH24.0g、Na₂CO₃8.68g is dissolved in 250 by heatingAdding the prepared MgO11.4g into ml of water, stirring and mixing the mixture, reacting the mixture for 10 hours at 100 ℃ under reflux, and filtering, washing and drying the product. The product is the magnesium-aluminum hydrotalcite with single phase and x being 0.27 (namely the Mg/Al molar ratio is 2.75).

Example 2:

with Mg (OH)₂Is used as a magnesium source, is roasted for 4 hours at 700 ℃ at the heating rate of 10 ℃/min to prepare active MgO, and the specific surface of the active MgO is 80m²(ii) in terms of/g. First Al (OH)₃20.8g、NaOH24.0g、Na₂CO₃8.68g is heated and dissolved in 250ml of water, then MgO11.4g is added, the pH value is about 12, the mixture is stirred and mixed, the reaction is carried out for 6 hours under the reflux at 100 ℃, and the product is filtered, washed and dried. The product is the magnesium-aluminum hydrotalcite with single phase and x being 0.27 (namely the Mg/Al molar ratio being 2.67).

Example 3:

with Mg (OH)₂Is used as a magnesium source, is roasted for 3 hours at 900 ℃ at the heating rate of 10 ℃/min to prepare active MgO, and the specific surface area of the active MgO is 40m²(ii) in terms of/g. First Al (OH)₃5.8g、NaOH6.8g、Na₂CO₃2.4g was dissolved in 125ml of water under heating, and then 7.5g of the prepared MgO7 was added thereto, the pH was about 12, and the mixture was stirred and mixed, reacted at 80 ℃ for 12 hours, and the product was filtered, washed and dried. The product is the magnesium-aluminum hydrotalcite with single phase and x being 0.27 (namely the Mg/Al molar ratio is 2.72).

Example 4:

with MgCO₃Is used as a magnesium source, is roasted for 4 hours at the temperature of 600 ℃ at the temperature rising rate of 10 ℃/min to prepare active MgO, and the specific surface of the active MgO is 250m²(ii) in terms of/g. First Al (OH)₃24.8g、NaOH29.0g、Na₂CO₃10.4g of MgO10.0g of MgO10 was added thereto at a pH of about 11, and the mixture was stirred and mixed, reacted at 100 ℃ under reflux for 8 hours, and the product was filtered, washed and dried. The product is the magnesium-aluminum hydrotalcite with single phase and x being 0.31 (namely the Mg/Al molar ratio is 2.23).

Example 5:

in the form of MgCO₃Is used as a magnesium source, is roasted for 3 hours at 800 ℃ at the temperature rising rate of 10 ℃/minThen, active MgO is prepared, the specific surface area of which is 90m²(ii) in terms of/g. First Al (OH)₃3.2g、NaOH3.6g、Na₂CO₃1.3g was dissolved in 125ml of water under heating, and 6.5g of the prepared MgO6 was added thereto at a pH of about 11, followed by stirring and mixing, reaction at 70 ℃ for 12 hours, filtration, washing and drying of the product. The product is the magnesium-aluminum hydrotalcite with single phase and x being 0.26 (namely the Mg/Al molar ratio being 2.82).

Example 6:

commercially available MgO is used as a magnesium source. First Al (OH)₃20.8g、NaOH24.0g、Na₂CO₃8.68g is heated and dissolved in 250ml of water, then commercial MgO11.4g is added thereto, the pH value is about 12, the mixture is stirred and mixed, the reaction is carried out for 8 hours under reflux at 100 ℃, and the product is filtered, washed and dried. The product is the magnesium-aluminum hydrotalcite with single phase and x being 0.28 (namely the Mg/Al molar ratio is 2.56).

Example 7:

and (5) recycling and synthesizing the filtrate. Taking the filtrate as mother liquor, feeding materials according to the Mg/Al feeding molar ratio of 1.0 if the concentration of magnesium ions in the filtrate is 0.041mol/l and the concentration of aluminum ions in the filtrate is 0.398mol/l, reacting for 6 hours under reflux at 100 ℃, filtering, washing and drying. The product is the magnalium hydrotalcite with single phase, and the example shows that the synthetic route not only can not discharge three wastes in the synthetic process, but also can recycle the mother liquor, and is an environment-friendly process.

Table 1.

	Standard index of hydrotalcite	Product magnesium aluminum hydrotalcite index
	Standard index of hydrotalcite	Product magnesium aluminum hydrotalcite index	hkl	I/I₀ d/nm	I/I₀ d/nm
003	100 0.784	100 0.774	hkl	I/I₀ d/nm	I/I₀ d/nm
003	100 0.784	100 0.774	006	60 0.390	34 0.386
009	40 0.260	21 0.259	006	60 0.390	34 0.386

Claims

1. A method for synthesizing anionic clay, in particular to a method for synthesizing magnesium aluminum hydrotalcite. The chemical composition of magnesium aluminum hydrotalcite is generally: mg (magnesium)_1-xAl_x(OH)₂(CO₃)_0.5xmH₂O and x satisfy that x is more than or equal to 0.2 and less than or equal to 0.4. The synthetic route is MgCO₃Or Mg (OH)₂Is used as a magnesium source and is baked at the temperature of 400 ℃ and 900 DEG CBurning for 3-5 hr to obtain active MgO with specific surface area of 250-40m²Mixing with sodium aluminate solution at Mg/Al molar ratio of 1.0-4.5, adding NaOH and Na₂CO₃In the molar ratio of NaOH/NaOH + Na₂CO₃0.7-0.9, controlling the pH value at 10-12, reacting for 4-15 hours at the temperature of 60-100 ℃ under stirring, filtering, washing and drying to obtain the magnalium hydrotalcite with single phase.

2. The synthesis of the magnesium aluminum hydrotalcite of claim 1, wherein: the magnesium-aluminum hydrotalcite is prepared by reacting MgO prepared by different methods with a sodium aluminate aqueous solution.

3. The synthesis process according to claims 1 and 2, characterized in that: the roasting temperature of MgO is 500-700 ℃, the roasting time is 3-4 hours, the Mg/Al feeding molar ratio is 1.0-4.0, and the reaction is carried out for 6-10 hours at 100 ℃.

4. The synthesis process of claims 1, 2 and 3, wherein the magnesium-aluminum hydrotalcite is prepared with x of 0.25-0.35 (Mg/Al molar ratio of 2-3), is granular and is easy to wash.

5. The process of claim 1, 2, 3, 4, wherein: the mother liquor after reaction can be completely recycled and used as the next batch of materials, no high-concentration waste liquid is discharged, the product cost is greatly reduced, and the method belongs to an environment-friendly process.