JP2002028482A - Adsorbent for heat pump and heat pump system using the same - Google Patents

Abstract

(57) [Summary] The object of the present invention is to solve the problems of the prior art by adsorbing a larger amount of water when heated at a relatively low temperature than the conventionally known adsorbent. It is an object of the present invention to provide an agent and an efficient heat pump system utilizing the same. The adsorbent has a water desorption amount of 6% by weight or more when heated to 100 ° C from a water-saturated adsorption state at room temperature, and a water desorption amount of 19% by weight when heated to 200 ° C.
And a zeolite adsorbent for a heat pump in which the difference in the amount of desorbed water from 100 to 200 ° C. is 6% by weight or more, and 50% or more of the exchanged ions are protons, divalent and trivalent metal cations. 4. The heat pump adsorbent according to claim 1, which comprises one or more aluminosilicate zeolite which is one or more ions selected from the group, and using the adsorbent. Heat pump system for heating and / or cooling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adsorbent for a heat pump which has a large amount of desorbed water when heated at a relatively low temperature. The present invention also relates to a heat pump using a zeolite adsorbent, which has been difficult to realize with conventional natural or synthetic zeolites and other adsorbents. Heat pumps for heating are used in many applications such as heating of living spaces and working spaces, hot water production, keeping chemicals and preventing cooling, and heat pumps for cooling and heating are used for cooling living and working spaces, producing cold water and ice, and chemicals. It can be used for many purposes such as cooling of food and foodstuffs, refrigeration and freeze-drying.

[0002]

2. Description of the Related Art The idea of a heat pump using an adsorbent has been proposed for a long time. I. Tc
report by Hernev (Natural Zeol)
items, Pergamon Press, pp. 139-143. 47
9-485, 1978 and Proceedings
of 5th International Zeo
light Conference, Heyden, p
p. 788-794, 1980) proposes a system that utilizes the heat of adsorption of water using natural zeolite, and the use of cold heat by the latent heat of vaporization of water upon adsorption of water after dehydration by solar heat. Also, a report by Hiroshi Taoda et al. (Solar Energy, vol. 8, No. 1, pp. 28)
-37 and vol. 8, no. 4, pp. 13-2
According to 2), research on a heat pump system using a synthetic zeolite such as A type or X type is also being conducted. However, none of these studies has been put to practical use. To increase the efficiency of the heat pump using adsorbent,
This is because adsorbents having a large water re-adsorption capacity when heated and regenerated at a relatively low temperature have not been available so far because low-temperature regeneration or utilization of solar heat or low-temperature exhaust heat is premised. In addition, sufficient latent heat of vaporization of water is not available,
Insufficient use of cold heat was also required.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems of the prior art by adsorbing a larger amount of water when heated at a relatively low temperature than a conventionally known adsorbent. It is an object of the present invention to provide an agent and an efficient heat pump system utilizing the same.

[0004]

Means for Solving the Problems In order to solve the problems of the prior art, the present inventors have repeatedly studied the structure and composition of zeolite, the combination with the exchanged ion species, and the chemical treatment of zeolite. As a result, the inventors have found zeolites having an unprecedentedly large amount of water desorption when heated at a relatively low temperature, and have also found that they are suitable for an adsorbent for a heat pump system.

The amount of adsorbent water desorbed when heated from a water-saturated adsorption state at room temperature to 100 ° C. is 6% by weight or more, and the amount of water desorbed when heated to 200 ° C. is 19% by weight or more; and When the difference in the amount of desorbed water from 100 to 200 ° C. is 6% by weight or more, for example, low-temperature regeneration at 200 ° C. or less, or solar heat or low-temperature exhaust heat can be used, and a sufficient amount of heat of adsorption can be recovered. . Further, the latent heat of evaporation at the time of water evaporation can be recovered as a cold heat source. The adsorbent that can realize this is an adsorbent composed of one or more of the zeolite-based aluminosilicate porous materials described below.

[0006] The adsorbent used in the present invention can be used only after the zeolite crystal is synthesized and subjected to an appropriate treatment. Zeolites are porous crystalline aluminosilicates of the general formula _{xM 2 / n O · Al 2} O 3 · ySiO 2 · zH 2 O ( where, n represents the valence of the cation M, x is 0.8 1.
2, y is a number of 2 or more, and z is a number of 0 or more).

Here, the cation M is bound to compensate for the negative charge of the aluminosilicate skeleton. Generally, the cation M is an alkali metal, alkaline earth metal and / or organic cation, but can be easily exchanged for another metal cation. In some cases, an ammonium type which is treated with mineral acids or ion-exchanged with an ammonium salt is heat-treated and used as a proton type. The skeletal structure of zeolite is a three-dimensional regularly bonded tetrahedron in which four oxygen atoms are coordinated around silicon and aluminum, sharing oxygen. Its crystal structure is characterized by an X-ray powder diffractogram, and many types are known. Zeolite has about 3 to about 1 in its structure.
It has pores with a size of 0 ° and its pore size and pore structure are characterized by the type of zeolite.

Preferred among the zeolites used in the present invention are zeolites of BEA and FAU type structures. A zeolite having a BEA type structure is generally synthesized by adding an organic amine, and the organic amine remains in the crystal even after crystallization, and thus needs to be calcined and removed.
Further, the contained cation is exchanged for an appropriate cation before use. In addition, zeolite having a FAU-type structure is generally synthesized without adding an organic amine, and thus the synthesized crystal is exchanged with an appropriate cation and then used as an adsorbent.

The composition SiO ₂ / Al ₂ O _{3 of the} zeolite skeleton having the BEA or FAU type structure depends on the composition of the reaction mixture at the time of crystal synthesis, and it is preferable to use a low value zeolite. As one of the methods for lowering the SiO ₂ / Al ₂ O ₃ ratio of the zeolite skeleton, there is a method in which zeolite is heat-treated in an aqueous alkaline solution, which is effective as a method for preparing the zeolite adsorbent of the present invention. As the alkaline aqueous solution, for example, an aqueous solution of sodium hydroxide or potassium hydroxide is generally used, and the concentration thereof is not particularly limited, but an aqueous solution of about 0.1 to 10% is preferably used. When the concentration of the alkaline aqueous solution is low, the treatment is performed at a relatively high temperature for a long time, and when the concentration of the alkaline aqueous solution is high, the treatment is performed at a relatively low temperature for a short time. A zeolite with a large separation amount is easily obtained. Optimum conditions are determined according to the type of zeolite.

The zeolite thus obtained is then subjected to ion exchange. As the exchange ion, one or more ions selected from the group consisting of protons, divalent and trivalent metal cations are suitably used, and the exchange rate is preferably 50% or more. If the exchange rate is 50% or less, the effect of increasing the water adsorption capacity by ion exchange is not sufficient. In the case of proton ion exchange, a method of removing ammonia by heat treatment after performing ammonium ion exchange may be employed, or exchange may be performed directly using a dilute aqueous solution of mineral acid. In the case of divalent or trivalent metal cations, ion exchange may be performed using an aqueous solution of a salt such as a chloride, a nitric acid compound, or an acetic acid compound.

The zeolite used in the present invention is a crystal which is very stable against heat, and its zeolite structure hardly changes even when a cycle of moisture adsorption and thermal desorption is repeated, and the amount of water desorbed hardly decreases. The major feature is that there is none. The stability of the water desorption characteristics can be evaluated by obtaining the following water desorption retention rate.

On the other hand, since silica-based adsorbents, especially compounds called silica gel or mesoporous silica, are not crystalline compounds, the adsorption and desorption of water are repeated to cause sulfur adsorption.
The i-O-Si bond changes and the water re-adsorption capacity decreases. For more information on these, see X.M. S. Report by Zhao et al. (J. Phys. Chem., B Vol. 10).
2, pp. 4143-4146, 1998) and S.M.
Report by Inagaki et al. (Studies in
Surface Science and Catal
ysis, Vol. 117, MESOPOROUS M
OLECULARSIEVES 1998, pp. 65
-76, 1998).

The form of the adsorbent when the above-mentioned adsorbent is used in a heat pump system is not particularly limited. In the case of a small device, the fine crystal powder may be used as it is, or a method of applying an adsorbent slurry to the heat exchanger surface may be used. In a large-sized apparatus, since the amount of adsorbent charged is large, when the powder is charged, diffusion of water vapor is hindered, and it is difficult to efficiently adsorb moisture to all adsorbents. Therefore, if the adsorbent formed into a granular shape is used, the voids of the molded body serve as a water vapor diffusion path, and can adsorb moisture efficiently and recover heat of adsorption. Further, latent heat of evaporation due to sufficient water evaporation can be recovered. The shape of the granular compact is not particularly limited, and the shape and size are selected in consideration of the size and packing density of the container. The binder and the molding aid for molding are not particularly limited, but it is preferable to devise to increase the thermal conductivity in order to perform heat exchange efficiently.

[0014] The heat pump system using these adsorbents can be used in places where heat and cold are required in all fields of society. Examples of the use of heat include heating for air conditioning, production of hot water, and heat storage. Examples of use of the cold heat include air conditioning cooling, refrigerators, freezers, handy coolers, electronic equipment cooling, computer CPU cooling, and the like. It can also be applied to low-temperature drying. As a heat source for regeneration of the adsorbent, various low-temperature factory exhaust heat and nighttime electric power can be effectively used. In addition to these heat sources, natural energy such as geothermal heat, hot spring heat,
It can also be used in combination with solar heat. In addition, if the exhaust heat of the fuel cell system, which is expected to be widely used in the future, is used, the heat can be easily obtained, so that the efficiency is dramatically increased and the application of the heat pump system is expected to be expanded.

The water desorption amount and the water desorption amount retention rate of the above-mentioned heat pump adsorbent are measured by the following methods, and are obtained by the following equations. However, as long as the accuracy is sufficient, the model of the thermal analyzer does not matter. <Water Desorption Measurement Method> A sample was placed in a vacuum desiccator containing a saturated ammonium chloride aqueous solution and having a relative humidity of 80%.
After deaeration, the mixture is allowed to stand for at least 17 hours to adsorb a saturated amount of water at room temperature. The removed sample is set on a sample dish of a thermal analyzer, and the weight (W _w ) of the sample at that time is read. The temperature is raised at a rate of 3 ° C./minute, and heating is performed to 300 ° C. without flowing an atmosphere gas. The weight (W ₁₀₀ ) when heated from room temperature to 100 ° C. and the weight (W ₂₀₀ ) when heated to 200 ° C. are read. The amount of water desorption is determined by the following equation.

Amount of desorbed water at 100 ° C. (% by weight) = (W _w −W ₁₀₀ ) / (W _w ) × 100 Amount of desorbed water at 200 ° C. (% by weight) = (W _w −W ₂₀₀ ) / ( W _w ) × 100 <Calculation method of retention rate of water desorption amount> The initial water desorption amount obtained by the above method is Q ₁ , and a cycle of water adsorption-300 ° C. heat desorption is repeated 50 times, and then the above method in the obtained water desorption amount and Q _50. The retention rate of the amount of desorbed water is determined by the following equation.

Water desorption amount maintenance rate (%) = (Q ₅₀ / Q ₁ ) × 100 <Synthesis and pretreatment of BEA type zeolite> Sodium hydroxide as an alkali source in sodium aluminosilicate gel slurry, and tetraethylammonium as a template agent Hydroxide was added, and the mixture was heated at 150 ° C. for 48 hours under autogenous pressure to obtain a SiO ₂ / Al ₂ O ₃ ratio = 16.5, 1
7.5 and 27.0 BEA zeolites were synthesized. After washing these zeolites, ammonium ion exchange was performed using an ammonium chloride aqueous solution. After washing, drying and baking at 600 ° C. to remove the template agent,
^{A +} BEA type zeolite was prepared. The ion exchange rate is 9
9%, with the balance being Na ⁺ ions. <Synthesis and Preprocessing of MCM-41> Gruen et al. (Microporous and Mesopor)
ow Materials, Vol. 27, pp. 2
07-216, 1999), MCM-41 was synthesized. N-Hexadecyltrimethylammonium bromide was used as a template agent, and tetraethoxysilane was used as a silica source. This MCM-41 powder was fired at 550 ° C. in air to remove the template agent. The pore size of the obtained MCM-41 was 4 based on the XRD diffraction data.
It was 3Å.

[0018]

The present invention will be described below in detail with reference to examples. However, the present invention is not limited to these examples. <Example _{1~3> SiO 2 / Al 2 O} 3 ratio = 16.5,1
7.5 and 27.0 H ⁺ BEA zeolite
After drying at 00 ° C. for 24 hours, a saturated amount of water was adsorbed according to the method for measuring the amount of desorbed water. This sample was subjected to thermal analysis using a thermal analyzer (TG-DTA2000, a thermal analyzer manufactured by Mac Science). The differences in the amount of desorbed water from room temperature to 100 ° C and 200 ° C and the amount of desorbed water from 100 to 200 ° C were as follows.

[0019]

[Table 1] <Examples 4 to 6> A cycle in which the samples used in Examples 1 to 3 were heated and desorbed at 300 ° C. in air, and then placed again in a vacuum desiccator having a relative humidity of 80% to adsorb a saturated amount of water. Repeated 50 times. Thereafter, the amount of desorbed water was determined by the same operation as in the first time. The results were as follows.
The water desorption amount maintenance rate (Q ₅₀ ) was 90% or more in each case.

[0020]

[Table 2] <Examples 7 and 8> FA having a SiO ₂ / Al ₂ O ₃ ratio = 2.0
Zn ²⁺ and Mn ²⁺ exchangers were prepared from U-type zeolite using an aqueous solution of zinc chloride and an aqueous solution of manganese chloride. The ions other than Zn ²⁺ and Mn ^{2+ in} each sample were N 2
a ⁺ and K ⁺ . The amount of water desorbed from each sample was measured in the same manner as in Example 1. The results were as follows.

[0021]

[Table 3] <Example _{9~11> SiO 2 / Al 2 O} 3 ratio = 2.6 F
Each magnesium chloride AU type zeolite, Mg using aqueous solutions of zinc chloride and manganese chloride ^2+, Zn
²⁺ and Mn ²⁺ exchangers were made. M of each sample
The ^ions other than g ²⁺ , Zn ²⁺ and Mn ²⁺ were Na ⁺ . The amount of water desorbed from each ion exchanger was measured in the same manner as in Example 1. The results were as follows.

[0022]

[Table 4]<Examples 12 to 15> SiO_Two/ Al_TwoO_ThreeRatio = 5.6
Ammonium chloride, chloride
Aqueous solutions of magnesium, zinc chloride and manganese chloride
With NH _Four ⁺, Mg²⁺, Zn²⁺And Mn²⁺Exchanger
Created. NH of each sample_Four ⁺, Mg²⁺, Zn²⁺You
And Mn²⁺Other ions are Na⁺Met. NH_Four ⁺The type is
Baking at 500 ° C⁺Type. Same as in Example 1
The amount of water desorbed from each ion exchanger was measured by the method. as a result
Was as follows.

[0023]

[Table 5] <Example _{16,17> SiO 2 / Al 2 O} 3 ratio = 17.5
BEA type zeolite and SiO ₂ / Al ₂ O ₃ ratio =
A La ³⁺ exchanger was prepared from the 5.6 FAU zeolite using an aqueous lanthanum chloride solution. The ions other than La ^{3+ in} each sample were H ⁺ and Na ⁺ . The amount of water desorbed from each sample was measured in the same manner as in Example 1. The results were as follows.

[0024]

[Table 6] <Example _{18,19> SiO 2 / Al 2 O} 3 ratio = 16.5
BEA type zeolite and SiO ₂ / Al ₂ O ₃ ratio =
The X-type zeolite of 2.6 was treated in a 1% aqueous NaOH solution for 5 hours and a 3% aqueous NaOH solution for 3 hours, 60 hours, respectively.
Treated at ° C. The BEA zeolite is then converted to NH ₄ ⁺
After ion exchange, the mixture was calcined at 500 ° C. to obtain an H ⁺ type. The SiO ₂ / Al ₂ O ₃ ratio of each zeolite after treatment was 11.7 and 2.5. The amount of water desorbed from each sample was measured in the same manner as in Example 1. The results were as follows.

[0025]

[Table 7] <Examples 20 to 24> The samples used in Examples 7, 9, 12, 15 and 18 were dehydrated by heating at 300 ° C. in air, and then placed again in a vacuum desiccator having a relative humidity of 80% to adsorb a saturated amount of water. The cycle was repeated 50 times. afterwards,
The amount of desorbed water was determined by the same operation as in the first time. The results were as follows. The water desorption amount maintenance rate (Q ₅₀ ) was 90% or more in each case.

[0026]

[Table 8] <Comparative Examples 1 to 6> K ⁺ and Ca ²⁺ ion exchangers of NaA-type zeolite were prepared using an aqueous solution of NaA-type zeolite and potassium chloride and a solution of calcium chloride, and the same salt aqueous solution used in Examples was used. And exchanged for divalent metal ions. For these samples, the amount of desorbed water was determined in the same manner as in Example 1. The results were as follows.

[0027]

[Table 9] <Comparative Examples 7 and 8> The amount of water desorbed from Na-type FAU-type zeolites having different SiO ₂ / Al ₂ O ₃ ratios was determined in the same manner as in Example 1. The results were as follows.

[0028]

[Table 10] <Comparative Example 9> The amount of water desorbed from MCM-41 from which the template was removed was determined in the same manner as in Example 1. The results were as follows.

[0029]

[Table 11] This sample was subjected to the water adsorption / desorption cycle three times in the same manner as in Examples 4 to 7, and the water desorption amount retention rate (Q
₃ ), the values at 100 ° C. and 200 ° C. were 71% and 68%.

Claims (6)

[Claims] 1. The adsorbent has a water desorption amount of 6% by weight or more when heated to 100 ° C. from a water-saturated adsorption state at room temperature and 19% by weight when heated to 200 ° C.
A zeolite adsorbent for a heat pump, wherein the difference in the amount of desorbed water from 100 to 200 ° C is 6% by weight or more. 2. The heat pump adsorbent according to claim 1, wherein the adsorbent comprises at least one of aluminosilicate zeolite having a BEA or FAU type structure. 3. The heat pump adsorbent according to claim 1, wherein zeolite heat-treated in an aqueous alkaline solution is used. 4. An aluminosilicate zeolite, wherein at least 50% of the exchanged ions are at least one ion selected from the group consisting of proton, divalent and trivalent metal cations. Item 4. An adsorbent for a heat pump according to item 3. 5. The heat pump according to claim 1, wherein the water desorption amount retention rate after repeating a water adsorption-thermal desorption cycle 50 times is 90% or more. For adsorbent. 6. The first, second, third and fourth aspects of the present invention.
A heat pump system for heating and / or cooling, wherein the adsorbent according to claim 5 is used.