JP2002159849A - Laminar double hydroxide-alumina/silica gel composite and method for preparing the same, and adsorbent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminar double hydroxide-alumina/silica gel composite having a high adsorbing ability for both of the acidic and basic substances. SOLUTION: The laminar double hydroxide-alumina/silica gel composite contains the following laminar double hydroxide and alumina/silica gel. The composite is a nonstoichiometric compound of which the general formula is expressed by [M1-x2+Mx3+(OH)2]x+Ax/zz-.mH2O (M2+=Mg2+, Ni2+, Zn2+, Co2+, Mn2+ or the like; M3+=Al3+, Fe3+, Ga3+, Cr3+, In3+ or the like; AZ-=CO3-, NO3-, Cl- or the like; 0<x<=0.33). The alumina/silica gel and SiO2/Al2O3 (mass% ratio) of 96/4 to 10/90.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a layered double hydroxide.
The present invention relates to an alumina silica gel composite and a method for producing the same, and an adsorbent containing a layered double hydroxide-alumina silica gel composite.

[0002]

2. Description of the Related Art An important use of a porous material is an adsorbent. There are various driving forces for this porous body to adsorb ions, gases, fine particles, etc. One of them is a chemical action. From this viewpoint, the adsorbent can be roughly divided into two. For example, alumina-silica gel, zeolite and the like have solid acidity and strongly adsorb basic substances such as ammonia. On the other hand, MgO and CaO have solid basicity and can strongly adsorb acidic substances such as hydrogen sulfide. Thus, in one adsorbent, acidic
In many cases, only one of the basic substances can be adsorbed.

[0003] Among them, porous ceramics are generally excellent in heat resistance, chemical resistance, and weather resistance, and many of them are environmentally friendly. From such a viewpoint, it is suitable as a material for preserving and purifying the atmosphere and water environment. Considering such applications, for example, in the conservation of water quality in lakes and rivers, it is necessary to be able to remove both ammonia and phosphate ions at the same time, and the development of an adsorbent having such amphoteric adsorption capacity is required. ing.

That is, in recent years, H _{2 has been used for} the purpose of environmental purification and deodorization.
Acid gases such as S, CO ₂ and mercaptan, basic gases such as NH ₃ and amines, and NH ₄ ⁺ and PO ₄ ^3- for water purification
There is a demand for the development of adsorbents having multiple adsorption functions such as simultaneous removal of water.

[0005]

However, adsorbents having or being conscious of the composite adsorption function have not been studied much so far, and are not suitable for frying ponite ([Zn _{6 -X} Al _X ] [Si _4-X Al _X ] O ₁₀ [OH]
₈ ) A complex of silica gel and a complex of zeolite and sepiolite is known. In the former, the amphoteric adsorption ability is reported to frypontite, but it does not have such a high double adsorption ability due to the fact that the specific surface area is not so large and the crystallinity is not good. In the latter,
Even lower adsorption capacities were obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a layered double hydroxide-alumina silica gel composite having high adsorption capacity for both an acidic substance and a basic substance, and production thereof. Provide a method,
An object of the present invention is to provide an adsorbent containing the layered double hydroxide-alumina silica gel composite.

[0007]

SUMMARY OF THE INVENTION The layered double hydroxide of the present invention
-Alumina silica gel composite is composed of the following layered double hydroxide
And alumina silica gel. (A) Layered double hydroxylation
The product has the general formula [M_1-x ²⁺ M _x ³⁺ (OH)_Two]^{x +} A_{x / z} ^z- ・ MH_TwoO
(M²⁺= Mg²⁺, Ni²⁺, Zn²⁺, Co²⁺, Mn²⁺Etc; M^{Three +}= Al
³⁺, Fe³⁺, Ga³⁺, Cr³⁺, In³⁺Etc .; A^z-= CO^3-, NO^3-,
Cl^-Etc.) (0 <x ≦
0.33). (B) Alumina silica gel is SiO_Two / Al_TwoO_Three (mass%
Ratio) = 96/4 to 10/90.

The above-mentioned layered double hydroxide-alumina silica gel composite may include the following layered double hydroxide in place of the layered double hydroxide described in (a) above. (A) The layered double hydroxide has the general formula [M _1-x ²⁺ M _x ³⁺ (OH) ₂ ] ^{x +} A
_{x / z} ^z -mH ₂ O (M ²⁺ = Mg ²⁺ , Ni ²⁺ Co ²⁺ , Mn ²⁺ ; M
³⁺ = Al ³⁺ , Fe ³⁺ , Cr ³⁺ , In ³⁺ ; A ^z- = CO ^3- , N
O ³ , Cl ⁻ ) is a non-stoichiometric compound (0 <x ≦
0.33).

The layered double hydroxide-alumina silica gel composite of the present invention contains the following layered double hydroxide and alumina silica gel. (A) The layered double hydroxide has the general formula [M _1-x
²⁺ M _x ³⁺ (OH) ₂ ] ^{x +} A _{x / z} ^z -mH ₂ O (M ²⁺ = M
g ²⁺ ; M ³⁺ = Al ³⁺ ; A ^z− = NO ³⁻ ) (0 <x ≦ 0.33). (B) Alumina silica gel has SiO ₂ / Al ₂ O ₃ (mass% ratio) = 85/15.

The method for producing a layered double hydroxide-alumina silica gel composite of the present invention is a production method comprising the following steps. (A) A step of adding alumina silica gel to water and adjusting it to alkaline. (B) A step of preparing a mixed aqueous solution of a divalent metal salt and a trivalent metal salt. (C) a step of charging the mixed aqueous solution into the water containing alumina silica gel while adjusting the aqueous solution to be alkaline. This method for producing a layered double hydroxide-alumina silica gel composite can produce the above-mentioned layered double hydroxide-alumina silica gel composite.

The adsorbent of the present invention contains the above-mentioned layered double hydroxide-alumina silica gel composite.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the invention relating to a layered double hydroxide-alumina silica gel composite, a method for producing the same, and an adsorbent containing the layered double hydroxide-alumina silica gel composite will be described. .

The present invention develops a composite adsorption functional material having simultaneous adsorption of both acidic and basic components and high adsorption capacity for both components in the technical field of purifiers and deodorants for the atmosphere, water quality and residential environment. Therefore, a composite is prepared by complexing a layered double hydroxide excellent in the ability to adsorb acidic components and alumina silica gel excellent in the ability to adsorb basic components by precipitation in a suspension.

Alumina silica gel having solid acidity and layered double hydroxide having solid basicity have the advantage that they can be synthesized easily and in large quantities from solution at a relatively low temperature of around room temperature.

Here, the characteristics of the layered double hydroxide^1)-12)To
explain about. The layered double hydroxide has the general formula [M_1-x ²⁺ M
_x ³⁺ (OH)_Two]^{x +} A_{x / z} ^z-・ MH_TwoO (M²⁺ = Mg²⁺, Ni
²⁺, Zn²⁺,…; M³⁺ = Al³⁺, Fe³⁺, Ga³⁺,…; A
^z- = CO^3-, NO^3-, Cl^-,…) Nonstoichiometric compound
(0 <x ≦ 0.33). The outline of the crystal structure is bivalent
Metal M²⁺Part of trivalent metal M³⁺Is replaced by
Mg (OH) with ras charge _TwoBasic layer similar to
Layered structure consisting of a negatively charged intermediate layer to maintain its properties
It is. This layered double hydroxide is solid basic and anionic.
Intercalation reaction / regeneration reaction
Such a specific reaction is shown.

Next, preparation methods and characterization of a layered double hydroxide having solid basicity, alumina-silica gel having solid acidity and a composite thereof will be described. First, preparation of a sample will be described. At first,
Preparation of layered double hydroxide ¹⁾ -7 ⁾ will be described. That is, carbonated layered double hydroxide
de; hereinafter abbreviated as LDH). The raw materials used for the preparation are as follows.・ Magnesium nitrate hexahydrate (Mg (NO ₃ ) ₂・ 6H ₂ O) reagent grade, manufactured by Wako Pure Chemical Industries, Ltd. ・ Aluminum nitrate nonahydrate (Al (NO ₃ ) ₃・ 9H ₂ O) reagent grade Manufactured by Wako Pure Chemical Industries, Ltd. ・ Sodium hydroxide (NaOH) reagent special grade Made by Wako Pure Chemical Industries, Ltd. ・ Sodium carbonate (Na ₂ CO ₃ ) reagent special grade Made by Wako Pure Chemical Industries, Ltd.

Add distilled water to a beaker, and add
Sodium carbonate (SC)
Was dissolved. Add distilled water into another beaker,
This is followed by a predetermined amount of magnesium nitrate hexahydrate (magnesium
nitrate hexahydrate; hereinafter abbreviated as MNH) and aluminum nitrate
Aluminum nitrate nonahydrate;
Lower ANN) was added and dissolved. In this case, S
C, the ratio of MNH to ANN is Na _TwoCO_Three / Mg / Al = 1/3/1 (m
ol% ratio). Use these solutions as starting solutions,
Cover the beaker containing the
Stir with a netic stirrer. Stir for 15 minutes
After that, sodium hydroxide solution (sodium hydroxide solution) was added to SC solution.
 solution; hereafter abbreviated as SHS), and a pH of 10
Was adjusted. Further, while adjusting the pH of the SC solution, (MHN
 , ANN) solution was added little by little and coprecipitated. this
After filtration, washing with distilled water, washing with ethanol
went. Next, it was dried in a thermostat at 60 ° C.

Next, preparation of alumina silica gel ¹⁶⁾ will be described. Here, the preparation of alumina silica gel (aluminosilicate gel; hereinafter abbreviated as ASgel) by the RH method (coprecipitation method) will be described. The raw materials used for the preparation are as follows.・ Aluminum nitrate nonahydrate (Al (NO ₃ ) ₃・ 9H ₂ O) reagent grade, manufactured by Wako Pure Chemical Industries, Ltd. ・ tetraethyl orthosilicate (Si (OC ₂ H ₅ ) ₄ ) Wako grade, Wako Pure Chemical Industries Ltd.・ Ethanol (99% or more synthetic undenatured ethanol) Manufactured by Japan Alcohol Sales Co., Ltd.

Ethanol is added to a beaker, and a predetermined amount of ANN and ethyl orthosilicate (tetraethyl orthosi
license; hereinafter abbreviated as TEOS). Thereafter, the two are mixed and a predetermined concentration (total concentration of Si and Al is 1.2 m
ol / l). In this case, TEOS and AN
The ratio of N _{is, SiO 2 / Al 2 O 3} = 85/15 (mass% ratio) = 90.6
/9.4 (mol% ratio). This solution was used as a starting solution, and vigorously stirred at room temperature with a magnetic stirrer while the beaker containing the solution was covered with a plastic wrap. After stirring for 3 hours, 25% aqueous ammonia (25% ammonia solution; hereinafter abbreviated as 25AS) of 1/2 volume of the starting solution was added instantaneously as a precipitant to coprecipitate and gel. After drying this at 60 ° C. for 2 hours using a rotary evaporator, it was left in a thermostat at 110 ° C. for about 15 hours. The resulting dried gel is thermally decomposed to remove the nitrate groups.
It was calcined for hours.

Next, the preparation of the composite will be described.
First, materials having high adsorption capacity for acidic and basic components are selected. In preparing them, a composite having a large specific surface area and a high composite effect is produced by compounding using a precipitation method in suspension, thereby improving the adsorption capacity for both components.

Each of the adsorbing materials has an excellent adsorbing ability,
LDH and alumina silica gel which can be easily synthesized and manufactured at low cost were selected. As a composite technique, first, alumina silica gel is synthesized by a usual method, and a slurry is prepared by dispersing the silica gel in a solution in which each component necessary for LDH synthesis is dissolved. This is adjusted to a pH of about 10 suitable for LDH generation, and aged at room temperature or at a relatively low temperature (about 200 ° C. or less) under hydrothermal conditions to produce a composite, thereby causing excessive growth of LDH particles. And a composite having a high specific surface area and excellent double adsorption ability.

Here, the preparation of the complex by the synthesis of LDH in ASgel injection solution (precipitation in suspension method) will be described. The method for producing a layered double hydroxide-alumina silica gel composite of the present invention generally comprises the following steps. That is, first, alumina silica gel is added to water, and this is adjusted to alkaline. Next, a mixed aqueous solution of a divalent metal salt and a trivalent metal salt is prepared. Next, while adjusting the pH to alkaline, the mixed aqueous solution is poured into water containing alumina silica gel.

The raw materials used for the preparation are as follows.・ Magnesium nitrate hexahydrate (Mg (NO ₃ ) ₂・ 6H ₂ O) Special grade reagent made by Wako Pure Chemical Industries, Ltd. ・ Aluminum nitrate nonahydrate (Al (NO ₃ ) ₃・ 9H ₂ O) Special grade reagent Made by Kojun Pharmaceutical Co., Ltd. ・ Special grade of sodium hydroxide (NaOH) reagent Made by Wako Pure Chemical Industries

[Example 1] Here, a method for preparing a complex by synthesis of LDH in an ASgel injection solution will be described. The raw materials used for preparation were ASgel, MN
H, ANN and SHS. Decarbonated distilled water was added to two beakers to dissolve a predetermined amount of ASgel. Decarbonated distilled water was added to the other beaker to dissolve predetermined amounts of MNH and ANN. In this case, MNH, ANN and LDH components, ASgel
Are Mg / Al = 3/1 (mol% ratio) and LDH component / ASgel = 1/1 (mass% ratio), respectively. With the two beakers covered with plastic wrap, mix well with a magnetic stirrer at room temperature, then use AS
The input solution was adjusted to pH10. Add LDH component solution to this solution
It was added while adjusting the pH to 10, and coprecipitated. This was further stirred for 5 hours to ripen. This was filtered, washed with decarbonated distilled water, and then dried in a thermostat at 60 ° C.

Example 2 The same as Example 1 except that the aging time was 24 hours.

The layered double hydroxide-alumina silica of the present invention
The gel composite was synthesized in Examples 1 and 2 described above.
It is not limited to. Layered double hydroxide of the present invention-
The alumina silica gel composite is composed of the following layered double hydroxide and
And alumina silica gel. That is,
The layered double hydroxide has the general formula [M_1-x ²⁺ M_x ³⁺ (OH)_Two]^{x +} A
_{x / z} ^z- ・ MH_TwoO (M²⁺= Mg²⁺, Ni²⁺, Zn²⁺, Co²⁺, Mn²⁺What
Etc; M³⁺= Al³⁺, Fe³⁺, Ga³⁺, Cr³⁺, In³⁺Etc .; A^z-=
CO^3-, NO^3-, Cl ^-Etc.)
(0 <x ≦ 0.33).

Alumina silica gel is SiO ₂ / Al ₂
It is desirable that O ₃ (mass% ratio) = 96/4 to 10/90. This is because, when it is within this range, there is an advantage that the ability of solid acidity is high.

LDH component / ASgel (mass% ratio) = 1/3
３3/1 is desirable. Within this range,
This is because there is an advantage that the ability to adsorb both acidic and basic components is excellent.

Next, the characterization of the sample will be described. The prepared sample was characterized by the following method as necessary.

-Identification of crystal phase by X-ray powder diffraction and calculation of crystallite size-Investigation of heating change of sample by simultaneous differential thermal analysis and thermogravimetric analysis-Interlayer anion by infrared absorption (IR) spectrum measurement Investigation of impurities

The apparatus used for powder X-ray diffraction was a sample horizontal Geiger flex X-ray diffractometer manufactured by Rigaku Corporation, and the measurement conditions were as follows. Target Cu (monochromated with graphite) Slit 1 °-1 °-0.30 mm 0.8 mm Tube voltage 40 kV Tube current 20 mA Measuring range 2 θ = 2 to 80 ° Step width 0.05 ° (When calculating crystallite diameter, 0.02 ° or less) Constant 1 sec

The apparatus used for the simultaneous analysis of the differential thermal analysis and the thermogravimetric analysis is Thermo plus TG8120 manufactured by Rigaku Corporation, and the measurement conditions are shown below. Atmosphere Air flow Heating rate 10 ° C / min Measurement temperature range RT-1300 ° C Sample amount Approx. 20 mg Reference sample α-Al ₂ O ₃

The apparatus used for the infrared absorption (IR) spectrum measurement is FTIR 8600 manufactured by Shimadzu Corporation, and the measurement conditions are shown below. Measurement KBr method apodization function Happ-Genzel function resolution 2 cm ^-1 cumulative times 50 times measurement range 4000 cm ^-1 to 400 cm ^-1 Amount of sample Sample: KBr = 1: 100

Next, the evaluation ^{1) to 12)} of the layered double hydroxide will be described. First, LDH structural analysis
^{2), 3), 7), 8), 10) and 11)} will be described. In the infrared absorption spectrum of the sample, the absorptions observed at around 3400 and 1650 cm ⁻¹ are due to surface adsorbed water, that is, water that is physically adsorbed. 1390 cm ^-1 absorption and 1470 cm ^-1
The broad absorption near is due to carbonic acid, suggesting that two types of carbonic acid are present in LDH. That is, it is considered that there are two types of carbonic acid associated with the interlayer and the metal cation. 353
The broad absorption seen at 0 cm ^-1 and the shoulder seen at 3100 cm ^-1 are considered to be due to strong ν (OH) absorption. Also, the broad absorption at 1000 cm ^-1 is ν
₁ (CO ₃ ) and the absorption at 880 cm ⁻¹ is ν ₂ (C
It is considered to be absorption by O ₃ ). The absorption at 420 cm ^-1 is believed to be due to the brucite-like structures δ (OH) and γ (OH).

Next, the thermal properties of LDH
^{4), 5), 7), 10) and 12)} will be described. The endothermic reactions at 80 ° C and 190 ° C in carbonated LDH indicate the evaporation of interlayer water and physically adsorbed water, and the endothermic reactions at 400 ° C in carbonated LDH indicate the destruction of LDH structure due to desorption of carbonic acid between layers. ing.

Next, evaluation of the composite will be described.
First, the structure of the composite by the synthesis of LDH in ASgel injection solution (precipitation in suspension method) will be described. From the XRD patterns of the samples, the peak of carbonate type LDH and the overlap due to the halo around 24 ° by ASgel are observed in all samples. Also, as judged from the XRD pattern, it seems that no intercalation reaction of carbonate type LDH has occurred in this method.

Next, the existence state ¹⁷⁾ of LDH in the composite will be described. To investigate how LDH is present in the complex,
From the peak around 11 ° showing diffraction by the (03) plane
The crystallite diameter of LDH was determined. The obtained crystallite diameter is LDH
Since it is the value in the thickness direction of
It is possible to know how much LDH exists in a stacked form. In Example 1, the crystallite diameter was 3.2 nm.
And the number of layers was 4. Further, in Example 2, the crystallite diameter was 4.9 nm, and the number of laminated layers was 6.

Next, the evaluation of pore characteristics ¹⁸⁾ will be described. An important property of the porous body is its pore characteristics. Pore characteristics generally refer to specific surface area, total pore volume, and pore size distribution.
Occupies an important position. Here, the pore properties of LDH, ASgel and their complexes prepared above are clarified.

First, a method for measuring nitrogen adsorption will be described. The specific surface area, total pore volume, and pore size distribution were measured as pore characteristics of LDH, ASgel, and a composite thereof prepared by the above-described method. Both use the nitrogen gas adsorption method,
Measure the adsorption / desorption isotherm of nitrogen gas to the sample at the liquid nitrogen temperature, and calculate the specific surface area from the obtained isotherm by the BET multipoint method and the pore size distribution by the BJH method using the desorption isotherm did. The total pore volume was calculated from the maximum amount of nitrogen adsorbed.

The amount of nitrogen gas adsorbed was measured using a fully automatic gas adsorber AUTOSORB-1 manufactured by QUANTA CHROME. As a pretreatment, AUTOSORB with a rotary pump at 110 ° C overnight.
The sample was degassed by heating while drawing a vacuum at 180 ° C for 2.5 hours by degassing treatment of -1.

The pore characteristics of the layered double hydroxide will be described. The pore radius is 1.9 nm and the specific surface area is 3.8 m
² / g and the total pore volume was 0.021 ml / g.

Next, the pore characteristics of the composite obtained by the synthesis of LDH in ASgel injection solution (precipitation in suspension method) will be described. In Example 1, the pore radius was 6.6 nm, the specific surface area was 460 m ² / g, and the total pore volume was 0.98 ml / g. Example 2
Has a pore radius of 2.0 nm, a specific surface area of 430 m ² / g, and a total pore volume of 0.67 ml / g.
Met.

Next, evaluation of gas adsorption characteristics
^{5), 6), 12), 14), 15), 16)} are explained. In the present invention, ASgel having solid acidity and L having solid basicity
Preparation of DH and their complexes was performed. The ammonia and carbon dioxide thermal desorption spectra were measured in order to investigate the effect of the difference in the preparation method on the amount of adsorption to acidic and basic substances.

The experimental method is as follows. First, measurement of ammonia and carbon dioxide thermal desorption spectra will be described. Ammonia (carbon dioxide) thermal desorption spectrum means that ammonia (carbon dioxide)
After the gas is adsorbed, the temperature of the sample is programmed and the amount of ammonia (carbon dioxide) desorbed as the temperature rises is measured. The amount of acid (base) is determined from the amount of desorbed ammonia (carbon dioxide), and the strength and type of acid (base) point can be determined from the temperature at which desorption occurs. In addition,
Generally, ammonia (carbon dioxide) TPD (Temperatur
e Programmed Desorption) (hereafter NH ₃ -TP
D, CO ₂ -TPD).

For the measurement, a thermal desorption spectrometer TPD-65 manufactured by Bell Japan Co., Ltd. was used. The measurement conditions are as follows. Pretreatment 200 ℃ 1hour (heating rate 10 ℃ / min) Ammonia (carbon dioxide) adsorption 25 ℃ 1hour Vacuum exhaust at the same temperature after adsorption Desorption measurement Temperature rise rate 10 ℃ / min. (Up to 25-800 ℃) ) Carrier gas He sample amount about 50mg

The condition is that the LDH which is a part of the complex is 2
It is set because the pretreatment at 00 ° C. does not cause structural destruction, and the situation where the composite is actually used is room temperature.

Qmass values of 16 and 44 are used for detecting the thermal desorption spectra of ammonia and carbon dioxide, respectively. It should be noted that the Qmass value 16 may detect not only ammonia but also other substances. The pretreatment conditions in this experiment were 500 ° C or less, as recommended by the Catalysis Society of Japan.
This is because it is considered insufficient when considering that it is 1h.

From the results, NH ₃ -TPD measurement was performed for the same sample with and without gas adsorption.
The temperature-programmed desorption spectra were measured for the two species, and by taking the difference between them, the influence of other substances was further reduced and the spectra were made substantial.

The above operation is not performed for the CO ₂ -TPD measurement because it is considered that there is almost no such influence. Instead, in the case of CO ₂ -TPD, the thermal desorption spectrum was measured in a state where the sample was not put into the cell, and this was used as a blank measurement and used as the background. By subtracting this, it was made to be substantial.

To summarize the above, NH ₃ -TPD performs two measurements on the same sample, and determines the CO ₂ -T
In the PD measurement, one measurement was performed. This is the standard measurement method. As a reference, in CO ₂ -TPD, there is a report that LDH causes structural destruction at 500 ° C and then captures carbon dioxide and the like during regeneration. Therefore, pretreatment at 500 ° C will also be performed. In this experiment, the evaluation will be made based on the amount of adsorption rather than the acidity / basicity of the solid.

The following reference samples were used in order to compare and study the amounts of adsorption to acidic substances and basic substances, respectively. MIZUKANITE-HP Zeolite (JRC-Z5-25H) manufactured by Mizusawa Chemical Industry Co., Ltd.

A method for evaluating a thermal desorption spectrum will be described. First, the NH ₃ -TPD measurement will be described. As described above, the NH ₃ -TPD measurement was made substantial by subtracting the thermal desorption spectra when ammonia was adsorbed and when ammonia was not adsorbed. The amount of desorption was determined by calibrating the spectrum area calculated from this. The method is as follows: the area of zeolite (JRC-Z5-25H), which is a reference catalyst of the Japan Society of Catalysis, for which the amount of solid acid is known, is similarly determined from temperature-programmed desorption spectrum measurement and compared with that acid amount. The calibration factor was calculated. By using this factor, the amount of acid can be obtained from the area calculated from the thermal desorption spectrum.

In this experiment, usually, the amount of acid was not determined, but the amount of adsorption calculated from the area determined from the temperature-programmed desorption spectrum was compared and examined to determine the amount of ammonia (basic substance). The adsorption was evaluated.

Next, the CO ₂ -TPD measurement will be described.
In the CO ₂ -TPD measurement, the base amount was determined by pulse measurement because there was no standard sample as in the case of the zeolite in the NH ₃ -TPD measurement. This method uses a certain amount of carbon dioxide,
This is a method in which the amount of base is obtained by pulsing the sample into an empty sample tube and measuring the area of the spectrum appearing therefrom and the number of moles of the injected carbon dioxide.

In this experiment, usually, the amount of base was not determined but the amount of adsorption calculated from the area determined from the temperature-programmed desorption spectrum was compared and examined to determine the amount of carbon dioxide (acidic substance). The adsorption was evaluated.

The results and considerations regarding the layered double hydroxide will be described. The gas adsorption characteristics will be described. In order to investigate the solid basicity of the layered double hydroxide itself, the carbon dioxide LDH sample prepared above was subjected to CO ₂ -TPD measurement, and the thermal desorption spectrum of carbon dioxide was obtained. Was obtained, and the amount of adsorption was calculated.

In this case, the spectrum is divided into a total of five regions, and it is considered that the first peak indicates physical adsorption and the second peak indicates chemical adsorption.
The third and fourth peaks are thought to be due to desorption of carbonic acid between layers due to the thermal decomposition of LDH.

Next, the results and considerations regarding the composite will be described. The gas adsorption characteristics will be described. First,
The ammonia thermal desorption spectrum obtained by NH ₃ -TPD measurement will be described. Constant temperature range of the spectrum (2
5 to 800 ° C)
The adsorption amount was calculated from the value, and the value in each sample is shown in Table 1.

[0059]

[Table 1]

The amount of adsorption was calculated by the above method.
It is difficult to imagine that an evaluation over the entire temperature range of 5 to 800 ° C. is consistent with the use and usage of the adsorbent. Therefore, in this experiment, taking into account the important property of the adsorbent, “easy adsorption, easy release if the situation changes”, the amount of adsorption at the peak (first peak) indicating physical adsorption was considered. Evaluate the adsorption on basic substances.

Next, the thermal desorption spectrum of carbon dioxide obtained by CO ₂ -TPD measurement will be described. The area of each peak in the constant temperature range (25 to 800 ° C.) of the spectrum was obtained, the amount of adsorption was calculated from the value, and the value in each sample was shown in Table 2.

[0062]

[Table 2]

The amount of adsorption was calculated by the above method.
In the entire temperature range of 5 to 800 ° C, taking into account the actual use and usage of the adsorbent,
It is conceivable that if LDH causes structural destruction, it is difficult to repeatedly use it as an adsorbent. Therefore, in this experiment, the adsorption to acidic substances is evaluated based on the amount of adsorption in physical adsorption, taking into account the important property of the adsorbent, “resistant to repeated use”.

Next, the effects of various methods will be described. The adsorption amount for physical adsorption is ASgel for ammonia adsorption and L for carbon dioxide adsorption.
The percentages based on DH are shown in FIG. The diagram on the left shows the ammonia adsorption, and the diagram on the right shows the carbon dioxide adsorption. Since the ratio of LDH to ASgel is LDH / ASgel = 1/1 (mass%) for all samples measured this time, L
LDH / ASgel = DH and ASgel obtained from the adsorption amount of the measured value of ASgel =
The calculated value (cal.) In the case of 1/1 (mass%) (hereinafter abbreviated as calculated value) is also shown.

The adsorption to basic substances is mainly performed by ASg
It is considered that the effect is due to el. This is evident from the fact that LDH alone has little ability to adsorb basic substances. Similarly, the adsorption on acidic substances is thought to be mainly due to LDH.

The samples of Examples 1 and 2 by LDH synthesis (precipitation-in-suspension method) with the ASgel dosing solution show significantly higher adsorption. Compared to the calculated values, the amount of adsorption for basic substances is about twice as much, and for acidic substances, about four times as much. At the same time, the effect of the aging time is also observed. As the aging time increases, both the amount of adsorption to basic and acidic substances increases. From the pore size distribution, pores around 7 nm decrease with aging, and the amount of pores at 2 nm increases. It is suggested that pores around 2 nm show a great effect on adsorption.

As a whole, the ASgel injection solution
LDH synthesis (suspension-in-suspension) is most suitable for providing the most amphoteric adsorption capacity.

From the above, according to the present embodiment,
By using the precipitation method in the suspension, the number of stacked LDH crystals related to the adsorption ability of the acidic component can be clearly reduced as compared with that obtained by the ordinary synthesis method. In addition, by being compounded with alumina silica gel having a large specific surface area, a high specific surface area of 400 to 500 m ² / g and a density of about 0.7 to 500 in LDH / alumina silica gel = 1/1 (weight ratio).
A porous body having a large pore volume of 1.0 ml / g was obtained.

The adsorption capacity of the prepared adsorbent was examined by a temperature-programmed desorption gas analysis method. In this method, first, a gas is adsorbed on a sample under a certain condition, and this is heated at a certain heating rate.
This is a method in which the desorbed adsorbed gas is quantitatively analyzed by a mass spectrometer to evaluate the amount of adsorbed gas and its adsorption strength.
CO ₂ was used as an acid gas, NH ₃ was used as a basic gas, LDH was used as an acid gas adsorption reference sample, and alumina silica gel was used as a basic gas reference sample. As a result, in the composite having the highest adsorption ability, the adsorption ability of CO ₂ was about 1.9 times higher than that of the LDH alone, and N 2
A value almost equivalent to that of alumina silica gel was obtained for the adsorption ability of H ₃ . These adsorption amounts are about 4 times and about 2 times, respectively, compared to the values estimated from the arithmetic average of the values of each individual.
It is twice as large and can be said to be the effect of compounding. Thus, it was confirmed that those containing the layered double hydroxide-alumina silica gel composite were excellent adsorbents.

It should be noted that the present invention is not limited to the above-described embodiment, but can adopt various other configurations without departing from the gist of the present invention.

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(1999) 16) Takahiro Tomita, Master's Thesis, Tokyo Institute of Technology, (1999) 17) BD Cullity, "Essentials of X-ray Diffraction" (1980) Agne 18) Seiichi Kondo et al., "Science of Adsorption" (1991) Maruzen

[0072]

The present invention has the following effects. By using the precipitation method in the suspension, the number of stacked LDH crystals related to the adsorption ability of the acidic component can be clearly reduced as compared with that obtained by the ordinary synthesis method.
Further, by being composited with alumina silica gel having a large specific surface area, a porous body having a high specific surface area and a large pore volume was obtained. As a result, most in it has complex excellent in adsorptivity for the adsorption capacity of CO ₂ LDH about 1.9 times higher than alone, almost the same as the alumina-silica gel for adsorption capacity of the NH ₃ The value was obtained. These adsorption amounts are about 4 times and about 2 times larger, respectively, than the values estimated from the arithmetic average of the values of each individual, which can be said to be the effect of compounding. Thus, it was confirmed that those containing the layered double hydroxide-alumina silica gel composite were excellent adsorbents.

[Brief description of the drawings]

Fig. 1 The adsorption amount in physical adsorption is ASgel for ammonia adsorption and LD for carbon dioxide adsorption.
FIG. 3 is a diagram showing the percentage based on H.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kinichi Kameshima 2-12-1 Ookayama, Meguro-ku, Tokyo Tokyo Institute of Technology (72) Inventor Atsushi Kaneda 2-12-1 Ookayama, Meguro-ku, Tokyo Tokyo Kogyo University F-term (reference) 4G066 AA16B AA18B AA19B AA20B AA25B AA26B AA27B AA30B AE01B AE02B BA36 CA29 CA35 FA03 FA05 FA21 FA36 FA37 4G073 BA02 BA10 BA32 BA36 BA40 BA44 BA52 BA57 BA05 FB01 FB07 GW AA10 AA18 AA19 AB06 AB18 BA26 CA19 CA40 DA25

Claims (6)

[Claims] 1. A layered double hydroxide-alumina silica gel composite comprising the following layered double hydroxide and alumina silica gel. (A) The layered double hydroxide has the general formula [M _1-x ²⁺ M _x ³⁺ (OH) ₂ ]
^{x +} A _{x / z} ^z -mH ₂ O (M ²⁺ = Mg ²⁺ , Ni ²⁺ , Zn ²⁺ , Co ²⁺ , Mn
²⁺ etc .; M ³⁺ = Al ³⁺ , Fe ³⁺ , Ga ³⁺ , Cr ³⁺ , In ³⁺ etc .; A
^{z- = CO 3-, NO 3-,} Cl - is a non-stoichiometric compound represented by like) (0 <x ≦ 0.33) . (B) Alumina silica gel is SiO ₂ / Al ₂ O ₃ (mass%
Ratio) = 96/4 to 10/90. 2. The layered double hydroxide-alumina silica gel composite according to claim 1 includes the following layered double hydroxide in place of the layered double hydroxide according to claim 1 (a). (A) The layered double hydroxide has the general formula [M _1-x ²⁺ M _x ³⁺ (OH)
₂ ] ^{x +} A _{x / z} ^z -mH ₂ O (M ²⁺ = Mg ²⁺ , Ni ²⁺ Co ²⁺ , M
n ²⁺ ; M ³⁺ = Al ³⁺ , Fe ³⁺ , Cr ³⁺ , In ³⁺ ; A ^z- = C
O ^3-, NO ^3-, Cl ^- is a non-stoichiometric compound represented by) (0
<x ≤ 0.33). 3. A layered double hydroxide-alumina silica gel composite comprising the following layered double hydroxide and alumina silica gel. (A) The layered double hydroxide has the general formula [M _1-x ²⁺ M _x ³⁺ (OH)
₂ ] ^{x +} A _{x / z} ^z -mH ₂ O (M ²⁺ = Mg ²⁺ ; M ³⁺ = Al
³⁺ ; A ^z- = NO ^3- ) is a non-stoichiometric compound represented by the formula (0 <x ≦ 0.33). (Ii) alumina-silica _{gel, SiO 2 / Al 2 O 3} (mass% ratio)
= 85/15. 4. A method for producing a layered double hydroxide-alumina silica gel composite comprising the following steps: (a) adding alumina silica gel to water and adjusting the alkalinity to water (b) divalent metal salt and 3 Step of adjusting a mixed aqueous solution of a valent metal salt (c) A step of charging the mixed aqueous solution into the water containing alumina silica gel while adjusting the aqueous solution to be alkaline. 5. The method for producing a layered double hydroxide-alumina silica gel composite according to claim 4 produces the layered double hydroxide-alumina silica gel composite according to claim 1, 2, or 3. 6. An adsorbent comprising the layered double hydroxide-alumina silica gel composite of claim 1, 2, or 3.