JP2011255331A - High performance water vapor adsorbent having alminosilicate compound material as base material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adsorbent not only having high adsorbing performance in a medium humidity region and a high humidity region but also having excellent adsorbing performance in a low humidity region of approximately 10% of a relative humidity in consideration of a support for a particular environment which needs low dew point air such as in a clean room as a dehumidification agent for desiccant air conditioning.SOLUTION: The adsorbent is obtained by impregnating a compound material comprising a low crystallinity laminar clay mineral and amorphous alminosilicate with a magnesium chloride solution, the adsorbent having not less than 40 wt.% of a difference between an adsorbed amount at 60% humidity when adsorbing and an adsorbed amount at 10% humidity when desorbing, and having water vapor adsorbing performance exhibiting an approximately 30 wt.% of an adsorbed amount even in a low humidity region of approximately 10% of a relative humidity. The adsorbent can be used as a dehumidification agent for desiccant air conditioning.

Description

  The present invention, as an important fundamental technology supporting the next generation industry, exhibits excellent characteristics such as adsorption capacity due to the fine structure resulting from its unique shape in the technical field of nanotechnology, which is expected to be put to practical use. , Which relates to a substance expected to be applied as an innovative functional material, and in particular, a composite composed of a low crystalline layered clay mineral and amorphous aluminum silicate having excellent moisture absorption and desorption characteristics Is a water vapor adsorbent in which a hygroscopic salt is supported on the base material.

Porous inorganic materials having sub-nano and nano-sized pores have characteristics that can adsorb various substances on the basis of their unique fine structure, and thus are used in various applications. In addition, since porous inorganic materials have excellent water vapor adsorption performance, applications such as heat pump heat exchange materials, anti-condensation agents, and autonomous humidity control materials are expected.
In particular, because the purpose of desiccant air conditioning is to remove moisture in the air introduced from outside air, not only is it necessary to efficiently remove moisture even from high humidity air in summer, Since it is necessary to remove moisture in the air even in various air conditions, a substance capable of adsorbing water vapor in any humidity region is required.

  On the other hand, in desiccant air conditioning, heated air is sent to desorb the adsorbed water vapor, and regeneration is performed. However, if the temperature of the regeneration air that is fed in is high, the energy required to warm the air is extra. End up. Up to now, the temperature of regeneration air has been required to be 80 ° C. or higher. However, considering the use of unused heat sources and the like, a material that can be regenerated with air at a low temperature of about 60 ° C. is required.

  In the above background, in order to improve the performance as a desiccant air conditioning system, a high-performance water vapor adsorbent capable of low temperature regeneration was developed. Generally, a regeneration temperature of about 60 ° C. is required as a low temperature regeneration performance, and the relative humidity when heated to 60 ° C. at an air temperature of 25 ° C. and a relative humidity of 60% is about 10%. In the adsorption isotherm, an inorganic material having a large difference in adsorption amount between 10% and 60% relative humidity has been demanded. Further, as a substance capable of adsorbing water vapor in any humidity region, an inorganic material having a linear relationship between relative humidity and the amount of water vapor adsorption in a water vapor adsorption isotherm has been demanded.

  Under such circumstances, a substance composed of a composite of a low crystalline lamellar clay mineral and amorphous aluminum silicate was developed, and relative to the adsorption at the water vapor adsorption isotherm that could not be achieved with conventional inorganic materials. The difference in adsorption amount between 60% humidity and 10% relative humidity at the time of desorption has a value of about 30 wt%, and the relative humidity and water vapor adsorption amount have a linear relationship in the water vapor adsorption isotherm. A material was developed (see Patent Document 1).

  In recent years, desiccant air conditioning systems require low dew point air in facilities such as clean rooms, and therefore, a material capable of adsorbing water vapor even in a low humidity region with a relative humidity of about 10% is required. The substance described in Patent Document 1 was very excellent as a conventional desiccant air-conditioning material. However, in a low humidity region with a relative humidity of about 10%, the amount of adsorption is small, so that it is used for facilities such as clean rooms. It had the disadvantage that it could not cope.

  On the other hand, in adsorbents for desiccant air conditioning, it has been studied to increase the amount of adsorption by supporting hygroscopic salts such as lithium chloride and magnesium chloride on porous water adsorbents such as silica gel and mesoporous silica. However, it is known that structural deterioration proceeds when a hygroscopic salt is supported on silica gel or mesoporous silica.

International Publication No. 2009/084632 Japanese Patent Application No. 2009-047914

  The present invention has been made in view of the circumstances as described above, and has an excellent hygroscopic performance not only in a medium humidity and high humidity region but also in a low humidity region of about 10% relative humidity. An object of the present invention is to provide a base material that does not cause structural deterioration even when a salt is supported.

As a result of repeated studies to achieve the above object, the present inventors have found that the Si / Al ratio is 0.7 to 1.0, and the ²⁹ Si solid state NMR spectrum has peaks near −78 ppm and −87 ppm. It has been found that crystalline aluminum silicate is excellent as a substrate for supporting hygroscopic salts, and the amorphous aluminum silicate is made to support hygroscopic salts, and has a relative humidity of 30%, 50% and 90%. In any case, the moisture absorption performance was successfully improved (see Patent Document 2).
However, an amorphous aluminum silicate having a Si / Al ratio of 0.7 to 1.0 and peaks in the vicinity of -78 ppm and -87 ppm in a ²⁹ Si solid state NMR spectrum can be used for a clean room facility. No investigation has been made on a water vapor adsorption mechanism that determines whether or not the adsorption amount is improved in a low humidity region with a relative humidity of about 10% and whether it is suitable for supporting hygroscopic salts.

  Therefore, the present inventors have excellent hygroscopic performance not only in the medium and high humidity regions but also in a low humidity region of about 10% relative humidity, and no structural deterioration occurs even when a hygroscopic salt is supported. As a result of examining the water vapor adsorption mechanism in order to provide a base material, the structural deterioration of the base material that occurs when the hygroscopic salt is supported is not only due to physical adsorption but also to chemical reaction in the water vapor adsorption mechanism of the base material itself. It was found that this is due to the existence of typical adsorption.

As a result of further investigation on the main adsorption mechanism in the water vapor adsorption mechanism, magnesium chloride was supported on an aluminum silicate complex composed of a low crystalline layered clay mineral and amorphous aluminum silicate. The water vapor adsorption performance was successfully improved over the entire range from a low humidity region with a relative humidity of about 10% to a high humidity region.
In addition, in the water vapor adsorption mechanism of the substrate, the water vapor adsorption isotherm obtained by calculation from the Kelvin capillary condensation theory based on the results of the water vapor adsorption isotherm by the actual water vapor adsorption measurement and the pore size distribution obtained from the nitrogen adsorption measurement. The results of the lines are compared, and in the region where the relative humidity is 40% or more, both agree with each other. Therefore, it is clarified that the water vapor adsorption mechanism in the aluminum silicate complex is due to physical adsorption, and the present invention is completed It came to.

That is, the present invention for solving the above-described problems is as follows.
(1) In a powder X-ray diffraction pattern using Cu as an X-ray source, four broad peaks around 2θ = 20, 26, 35, and 39 ° indicate a low crystalline layered clay mineral and amorphous aluminum silicate. A water vapor adsorbent in which an aluminum silicate complex composed of a salt is used as a base material and a hygroscopic salt is supported on the base material.
(2) In the region of relative humidity of 40 to 90% or higher, the measured water vapor adsorption isotherm matches the water vapor adsorption isotherm calculated from the nitrogen adsorption measurement based on the Kelvin capillary aggregation theory. The water vapor adsorbent according to the above (1), which shows that the mechanism is based on physical adsorption.
(3) The above (1) or (1) wherein the proportion of hygroscopic salt is 0.1 to 20% by weight with respect to the aluminum silicate complex comprising the low crystalline layered clay mineral and the amorphous aluminum silicate. 2) Water vapor adsorbent.
(4) A desiccant air-conditioning adsorbent comprising the water vapor adsorbent according to any one of (1) to (3) as a main component.

  A substance in which a hygroscopic salt is supported on a composite of a low crystalline layered clay mineral obtained by the present invention and an amorphous aluminum silicate is from a low humidity region having a relative humidity of about 10% to a high humidity region. As a water vapor adsorbent, especially a desiccant air-conditioning adsorbent, it has excellent water vapor adsorption behavior over all areas and has a stable structure that does not cause structural deterioration even when hygroscopic salts are supported. A special effect is produced.

The figure which shows the powder X-ray-diffraction figure of the base material in an Example. The figure which shows the water vapor | steam adsorption isotherm in a comparative example. The figure which shows the water vapor adsorption result of the measured value and theoretical value in the composite_body | complex which consists of a low crystalline layered clay mineral and an amorphous aluminum silicate in an Example. The figure which shows the water vapor adsorption result of the actual value and theoretical value in a silica gel. The figure which shows the powder X-ray-diffraction figure in the sample after making the base material in an Example impregnate a magnesium chloride.

Next, the present invention will be described in more detail.
In the present invention, an amorphous substance composed of a composite of a low crystalline lamellar clay mineral and an amorphous aluminum silicate as a base material contains silicon (Si), aluminum (Al), and oxygen (O) as constituent elements. And hydrogen (H) and hydrated aluminum silicate assembled with a number of Si-O-Al bonds. The low crystalline lamellar clay mineral is a single crystalline layer or a few layers of gibbsite made of aluminum hydroxide, or a low crystalline lamellar clay mineral showing almost no lamination in the layer direction.

  The composite of this low crystalline layered clay mineral and amorphous aluminum silicate is prepared by mixing an inorganic silicon compound solution and an inorganic aluminum compound solution so that the Si / Al ratio is 0.7 to 1.0, It can be artificially obtained by adding acid or alkali to adjust the pH to 5 to 9, and then heating the salt desalted at 110 ° C. or higher.

In the present invention, magnesium chloride, which is one of hygroscopic salts, is supported on a composite of a low crystalline layered clay mineral and amorphous aluminum silicate, which has been conventionally demanded as an adsorbent for desiccant air conditioning. Further, in the water vapor adsorption isotherm, the difference in adsorption amount between the relative humidity 60% during adsorption and the relative humidity 10% during desorption has a value of 41.8 wt%, and it is obtained as a desiccant adsorbent for clean rooms. It is possible to prepare a substance having an adsorption amount of 29.4 wt% at a relative humidity of 10%.
That is, in an aluminum silicate complex composed of a low crystalline layered clay mineral and an amorphous aluminum silicate, by supporting magnesium chloride, which is one of the hygroscopic salts, it has not been obtained in the past. It has become possible to provide a substance having a water vapor hygroscopic behavior.

In the present invention, an inorganic silicon compound and an inorganic aluminum compound are usually used as raw materials for preparing the composite precursor before heating.
The reagent used as the silicon source may be an aqueous silicic acid solution, and specific examples include sodium orthosilicate, sodium metasilicate, amorphous colloidal silicon dioxide (aerosil, etc.) and the like.
Moreover, the aluminum source couple | bonded with the said silicate molecule | numerator should just be an aluminum ion, Specifically, aluminum compounds, such as aluminum chloride, aluminum nitrate, and sodium aluminate, are mentioned, for example. These silicon sources and aluminum sources are not limited to the above-mentioned compounds, and can be used in the same manner as long as they have the same effect.

  These raw materials are dissolved in an appropriate aqueous solution to prepare a solution having a predetermined concentration. In order to synthesize a composite exhibiting excellent adsorption behavior that satisfies this purpose, it is necessary to mix so that the silicon / aluminum ratio is 0.7 to 1.0. The concentration of the silicon compound in the solution is 1 to 500 mmol / L, and the concentration of the aluminum compound solution is 1 to 1000 mmol / L. The preferred concentration is 1 to 200 mmol / L of the silicon compound solution and 1 to 500 mmol. It is preferable to mix a / L aluminum compound solution. Based on these ratios and concentrations, an aluminum compound solution is mixed with a silicon compound solution, acid or alkali is added to adjust the pH to 6-8, and a precursor is formed, followed by centrifugation, filtration, membrane A complex of low crystalline layered clay mineral and amorphous aluminum silicate is obtained by removing coexisting ions in the solution by separation, etc., and then dispersing the recovered precursor in a weakly acidic to weakly alkaline aqueous solution. Is a suspension containing the precursor material. The suspension containing the precursor substance is heated at 110 ° C. or higher for a predetermined time, and then washed and dried to obtain an aluminum silicate complex as a target carrier.

Although the method for supporting the hygroscopic salt on the obtained aluminum silicate composite is not particularly limited, preferably, the aluminum silicate composite is impregnated with the hygroscopic salt solution. The method is used.
Specifically, the target water vapor adsorption characteristic is obtained by drying the aluminum silicate complex obtained by drying in a solution of a hygroscopic salt such as magnesium chloride, followed by drying at 60 ° C. for 2 days. An excellent adsorbent can be obtained.

  Examples of the hygroscopic salt in the present invention include metal halides such as lithium chloride, sodium chloride, magnesium chloride, and calcium chloride, metal sulfates such as sodium sulfate, calcium sulfate, magnesium sulfate, and zinc sulfate, and metals such as potassium acetate. Amine salts such as acetate, dimethylamine hydrochloride, phosphoric acid compounds such as orthophosphoric acid, guanidine salts such as guanidine hydrochloride, guanidine phosphate, guanidine sulfamate, metal water such as hydrated hydroxide, sodium hydroxide, magnesium hydroxide Although an oxide etc. can be mentioned, Among these, a metal halide salt and a guanidine salt are preferable, magnesium chloride and calcium chloride are more preferable, and magnesium chloride is particularly preferable.

EXAMPLES Next, although this invention is demonstrated concretely based on an Example, this invention is not limited at all by the following Examples.
(Example)
In the present invention, a composite of a low crystalline layered clay mineral and an amorphous aluminum silicate, which is an excellent adsorbent substrate, was synthesized as follows.
100 mL of 0.38 mol / L sodium orthosilicate aqueous solution was used as the Si source, and 100 mL of 0.45 mol / L aluminum chloride aqueous solution was used as the Al source. A sodium orthosilicate aqueous solution was added to the aluminum chloride aqueous solution and stirred for about 10 minutes. The Si / Al ratio at this time is 0.84. After stirring, a 1N aqueous sodium hydroxide solution was added dropwise at a rate of 1 mL / min and added until the pH reached about 6. The dripping amount of the aqueous sodium hydroxide solution was 5.5 mL. The precursor suspension thus generated was subjected to desalting once by centrifugation. The desalting treatment was performed using a centrifuge at a rotational speed of 3000 rpm and a time of 10 minutes. After the desalting treatment, the precursor was dispersed in pure water so as to be 1 L in total, and stirred for 10 minutes to prepare a precursor suspension.
70 mL of the adjusted 1 L precursor suspension was measured in a 100 mL Teflon (registered trademark) container, then placed in a stainless steel rotating reaction container, and heated at 180 ° C. for 6 hours. After the reaction, it was washed twice by centrifugation and dried at 60 ° C. for 1 day.

  The obtained product was subjected to powder X-ray diffraction measurement. FIG. 1 shows a powder X-ray diffraction pattern of the product obtained. As can be seen in FIG. 1, broad peaks are seen in the vicinity of 2θ = 20, 26, 35, 39 °. Among them, the peaks observed at 20 and 35 ° are obtained from the reflection of the hk0 plane of the layered clay mineral, and the 00l reflection generally observed in the layered clay mineral is not observed. It is presumed to be a low crystallinity layered clay mineral. A broad peak around 2θ = 26, 39 ° is a characteristic peak of amorphous aluminum silicate. From the above results, it was confirmed that the substance serving as the excellent adsorbent base material in the examples was composed of a low crystalline layered clay mineral and amorphous aluminum silicate.

  1 g of the base material obtained as described above was impregnated with 10 ml of an 8% by weight magnesium chloride aqueous solution, thoroughly stirred, and then dried at 60 ° C. for 1 day. The target substance was obtained by grinding the dried sample with a mortar.

(Water vapor adsorption evaluation)
Two samples, one obtained by impregnating a magnesium chloride solution with the composite composed of the low crystalline layered clay mineral and amorphous aluminum silicate obtained in the examples and the other not impregnated with magnesium chloride, The water vapor adsorption was evaluated from the water vapor adsorption isotherm measured by Belsorp18 manufactured by the company. FIG. 2 shows the result.
Evaluation was carried out by determining the difference in adsorption amount between 60% relative humidity during adsorption and 10% relative humidity during desorption on the water vapor adsorption isotherm. In the case where the composite composed of the low crystalline lamellar clay mineral and amorphous aluminum silicate obtained in the Examples was impregnated with an aqueous magnesium chloride solution, the water vapor adsorption amount at a relative humidity of 60% during adsorption was 74.8 wt. %, The adsorption amount of water vapor at a relative humidity of 10% at the time of desorption is 33.0 wt%, so the difference between the adsorption amount at a relative humidity of 60% and a relative humidity of 10% at the time of desorption is 41.8 wt%. .
On the other hand, with respect to the untreated base material itself which is not impregnated with a magnesium chloride aqueous solution, a composite composed of a low crystalline layered clay mineral and an amorphous aluminum silicate, water vapor adsorption at a relative humidity of 60% during adsorption. Since the amount of water vapor adsorbed at 45.9 wt% and the relative humidity at desorption of 10% is 15.5 wt%, the difference in adsorption amount between the relative humidity of 60% and the desorption relative humidity of 10% is 30. 4 wt%.
From the above-mentioned adsorption evaluation, the water vapor adsorption performance of the substances obtained in the examples cannot be obtained only with a base material composed of a composite composed of a low crystalline layered clay mineral and amorphous aluminum silicate, It became clear that this was the first property obtained by impregnating a crystalline layered clay mineral and amorphous aluminum silicate in an aqueous magnesium chloride solution.

  In addition, as a result of the present example, a magnesium chloride aqueous solution was impregnated with a complex composed of a low crystalline layered clay mineral and amorphous aluminum silicate in the amount of adsorption in a low humidity region of about 10% relative humidity such as in a clean room. In the case of only the base material composed of the composite composed of the low crystalline layered clay mineral and the amorphous aluminum silicate, the adsorbed amount is about 2 times as high as 12.5 wt%. It became clear that it was a result of improving.

(Substrate and structural stability evaluation after impregnation)
In order to increase the water vapor adsorption amount, impregnation of the substrate with hygroscopic salt has been conventionally performed, but it is known that structural deterioration proceeds when silica gel or mesoporous silica is supported with hygroscopic salt. The reason for this is presumed to be not only physical adsorption but also chemical adsorption in the water vapor adsorption mechanism of the substrate itself.
In determining whether the water vapor adsorption mechanism of the substrate is based on physical adsorption or chemical adsorption, Kelvin is based on the results of the water vapor adsorption isotherm obtained by the actual water vapor adsorption measurement and the pore size distribution obtained from the nitrogen adsorption measurement. The results of the water vapor adsorption isotherm obtained by calculation from the capillary condensation theory of No. 1 were compared, and evaluation was performed by comparing the measured values with the theoretical values in a region where the relative humidity was 40% or more. The reason why the relative humidity is set to 40% or more is that the BJH method is used for the analysis of the pore diameter distribution curve obtained from the nitrogen adsorption data, and information on small pores cannot be analyzed.
FIG. 3 shows the water vapor adsorption results of measured values and theoretical values in a composite composed of a low crystalline layered clay mineral and amorphous aluminum silicate. As shown in FIG. 3, the measured value and the theoretical value almost coincide with each other in the region where the relative humidity is 40% or more, and the water vapor adsorption mechanism in the composite composed of the low crystalline layered clay mineral and the amorphous aluminum silicate. It was revealed that consists of physical adsorption.
As a comparative example, actual water vapor adsorption results of commercially available silica gel are shown in FIG. As shown in FIG. 4, in the region where the relative humidity is 40% or more, the actual measurement value and the theoretical value do not coincide with each other, and it became clear that silica gel is not an adsorption mechanism based on the physical adsorption theory. Thus, it is assumed that water vapor adsorption of silica gel is mainly caused by chemical adsorption because physical adsorption is not mainly used.
From the above, the water vapor adsorption mechanism in the composite composed of low crystalline lamellar clay mineral and amorphous aluminum silicate is mainly physical adsorption, so this substrate has hygroscopicity such as magnesium chloride. It became clear that even when impregnated with salt, no structural deterioration occurred.

  FIG. 5 shows a powder X-ray diffraction pattern of a powder obtained by impregnating a magnesium chloride aqueous solution with a composite composed of a low crystalline layered clay mineral and amorphous aluminum silicate. An X-ray diffraction peak derived from magnesium chloride is observed, but the peak derived from the basic structure is the same as that shown in FIG. 1, and a complex composed of a low crystalline layered clay mineral and amorphous aluminum silicate is chlorinated. It became clear that even when impregnated with a hygroscopic salt such as magnesium, the structure does not deteriorate.

  The present invention is a composite comprising a low crystalline layered clay mineral and an amorphous aluminum silicate having high performance adsorptivity not only in a medium and high humidity region but also in a low humidity region of about 10% relative humidity. Adsorbent obtained by impregnating the body with magnesium chloride aqueous solution, useful not only for general dehumidifiers in desiccant air conditioning, but also for adsorbents for special air conditioning such as clean rooms that require low dew point air It is.

Claims (4)

  In a powder X-ray diffraction pattern using Cu as an X-ray source, from a low crystalline layered clay mineral and amorphous aluminum silicate having four broad peaks around 2θ = 20, 26, 35, 39 ° A water vapor adsorbent comprising an aluminum silicate complex as a base material and a hygroscopic salt supported on the base material.   In the region of relative humidity of 40 to 90% or more, the measured water vapor adsorption isotherm matches the water vapor adsorption isotherm calculated from the nitrogen adsorption measurement based on the Kelvin capillary aggregation theory, and the water vapor adsorption mechanism is physical. The water vapor adsorbent according to claim 1, which indicates that it is due to adsorption.   The water vapor according to claim 1 or 2, wherein the proportion of the hygroscopic salt is 0.1 to 10% by weight with respect to the aluminum silicate complex composed of the low crystalline layered clay mineral and the amorphous aluminum silicate. Adsorbent.   The adsorbent for desiccant air conditioning which has the water vapor adsorbent of any one of Claims 1-3 as a main component.

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