HK1176033B - Activated carbon/silica-gel/cacl2 composite adsorbent material for air-conditioning applications and a method of preparing the same - Google Patents

Abstract

Provided is a composite adsorbent material and a method for preparing the same. The composite adsorbent material comprises a porous host material of activated carbon impregnated with silica-gel and calcium chloride, and is useful for adsorbing high levels of water vapor. The composite adsorbent material is used in low temperature heat driven adsorption cooling and dehumidification systems.

Description

Composite adsorbent material and preparation method and application thereof

Cross reference to related applications

The invention name of New Activate dCarbon/Silica-gel/CaCl submitted in 2011, 4, 18₂Composite Adsorbent for Air-conditioning application (New activated carbon-silica gel for Air-conditioning systems)-calcium chloride complex adsorbent) of U.S. provisional patent application No.61/457,521. The entire disclosure of this provisional patent application is incorporated herein by reference.

Technical Field

The invention relates to a composite adsorbent applicable to an adsorption type refrigeration or dehumidification system, in particular to a composite adsorbent consisting of activated carbon, silica gel and calcium chloride. The invention also relates to a preparation method of the composite adsorbent.

Background

In recent years, with the rapid development of economy, the problems of global warming and energy shortage become more and more serious. Adsorption refrigeration systems driven by solar or waste heat are of interest because such systems do not require chlorofluorocarbons (CFCs) nor Hydrochlorofluorocarbons (HCFCs) as refrigerants for air conditioning. Most importantly, such systems do not require fuel or electric propulsion, but rather only require regenerative or waste heat to drive them. The technology which can make the refrigeration system operate is a green refrigeration technology, and the refrigeration system is a very environment-friendly green refrigeration system. See literature: wang et al, "An Energy responsive Solar powered water heater and absorption maker," Solar Energy, 68(1), 2000, 189-; wang et al, "Adsorption recovery: greenwood drive by low voltage grade thermal energy, "Chinese Science Bulletin, 50 (3); 2005, 193-; zhai et al, "A review for absorption and analysis of related systems in china," Renewable and sustainable energy Reviews, 13(6-7), 2009, 1523-; hamamoto et al, "student addition regeneration activated carbon fibers, part 2: cycle performance evaluation, "International Journal of Refrigeration, 29(2)," 2006, 315- "327.

The working principle of the adsorption refrigeration system is as follows: in a low pressure environment, the adsorbate (e.g., water) stored in the evaporator is constantly evaporating to become water vapor. When a large amount of composite adsorbent in the adsorber adsorbs the continuously evaporated water vapor, the evaporator is in a low-pressure environment for a long time. In this case, the water stored in the evaporator is continuously evaporated, so that cooling water can be manufactured. When hot air blows through the cooling water, cold air is generated. Meanwhile, the heat generated by the adsorption of the composite adsorbent is also taken away by the cooling water in the adsorber. When the adsorption process of the composite adsorbent is finished, the desorption process is started. The hot water or hot oil is usually used for desorbing the water vapor adsorbed before, and because of the high temperature, the water vapor is desorbed from the composite adsorbent, then passes through the condenser and finally returns to the evaporator, and the whole adsorption-desorption thermal cycle is completed. Solar energy or waste heat can be used to heat water or oil, which is a completely free energy source. The two adsorption/desorption chambers of an adsorption refrigeration system work alternately in order to allow the adsorption and desorption processes to be performed at the same time, so that the cooling effect can be constantly produced (see the above-mentioned document: Wang et al, 2000; Zhai et al, 2009).

However, since adsorption refrigeration has many disadvantages to be improved, conventional vapor compression refrigeration systems still occupy the entire market today. The main disadvantages are: 1. longer adsorption and desorption times; 2. too low refrigeration efficiency (COP), thereby increasing energy consumption and cost; 3. the refrigeration power (SCP) is very low, which results in a very large refrigeration system. To overcome these disadvantages, increasing the adsorption capacity (also called adsorption capacity) of the adsorbent is an important factor. The development of new composite adsorbent materials is effective in solving the problem of low adsorbent capacity (see document Y. Li et al, "adsorption removal: a novel of novel technologies," registration Patents on engineering, 1(1), 2007, 1-21). Because of the greater adsorption capacity, higher refrigeration efficiency can be provided. Likewise, a higher adsorption rate (adsorption rate) allows a greater refrigeration power. Therefore, it is an important subject to improve the adsorption performance (i.e., adsorption capacity and adsorption rate) of the composite adsorbent, since this certainly enables to improve the COP and SCP values. Many studies have also been made in this direction in order to improve and develop more complex adsorbents (see the above-mentioned document: Wang et al, 2000).

Silica gel, activated carbon and zeolite 13X are three common adsorbents in adsorption refrigeration systems. Each of these adsorbents has its own strengths and weaknesses in its adsorption capacity. Zeolite 13X has good adsorption capacity under low pressure conditions, but it requires heating to over one hundred degrees celsius for successful desorption (see r.a. shigeishi et al, "Solar storage using chemical porous exchange with drying of zeolites," Solar Energy, 23(6), 1979, 489-channels 495), and it cannot adsorb and desorb large amounts of adsorbate, such as water vapor, within a narrow range of humidity or pressure (see Wang et al, 2009).

Silica gel can adsorb moderate amounts of water vapor at any pressure because it is hydrophilic (see, H. Kakiuchi et al, "Novel zeolite adsorbents and chromatography for AHP and desiccant system," published in the 2004 IEA-Annex 17 conference held in Beijing).

The activated carbon has a large internal surface area (usually 1000-²In the range of/g), because it has high porosity and high surface activity, it can provide a function of adsorbing chemicals in liquid or gas with a large capacity (see literature: swiatkowski, "Industrial carbon absorbers," studios in Surface Science and Catalysis, 120(1), 1999, 69-94). In addition, the activated carbon can adsorb a large amount of water vapor under the environment with high pressure of 1600 Pa; but in a low pressure environment, the water absorption capacity is weak. In this context, the pressure refers to the partial pressure of water vapour, unless otherwise indicated. For adsorption refrigeration systems, the ideal adsorbent isShould exhibit a sigmoidal shape, which represents a large adsorption capacity of the adsorbent in the pressure range of 750Pa to 1100Pa (see Kakiuchi et al, 2004, supra). Activated carbon exhibits an S-type isotherm in this pressure range, but its adsorption capacity is low (see R.A. Shigeishi et al, "Solar Energy storage using chemical porous exchange associated with drying of zeolites," Solar Energy, 23(6), 1979, 489- "495).

One study showed that the activated carbon was impregnated in a sodium silicate solution at an optimum concentration of 0.1 to 10 wt% for forty-eight hours (see, h. huang et al, "Development research on composite adsorbed adsorption heat pump," Applied Thermal Engineering, 30, 2010, 1193-. However, this study did not incorporate any calcium chloride solution and did not investigate the effect of impregnating calcium chloride into the pores of activated carbon. It only investigated the properties between activated carbon and silica gel.

There are many researchers in inventing new adsorbents, including the development of composite materials for adsorbents using silica gel and activated carbon, in order to obtain good performance in terms of adsorption capacity (see the above-mentioned documents: Huang et al, 2010); and a composite adsorbent of calcium chloride and expanded graphite is used in an adsorption type ice maker on a fishing boat (see the above-mentioned document: Wang et al, 2006). A new generation of cooling devices has been developed using a composite adsorbent of calcium chloride and silica gel (see B.B. Saha et al, "A new generation of cooling devices employing CaCl₂In-silica gel-water system, "International Journal of Heat and Mass Transfer, 52, 2009, 516-. In addition, zeolite 13X and calcium chloride have been used as Composite adsorbents in adsorptive refrigeration/heating systems (see J.Li et al, "Composite adsorbed thermal energy storage Material Composite of zeolite 13X and calcium chloride," Material Review, "19 No.8, 2005, 109-. It has been found that most composite adsorbents can be enhancedRefrigeration efficiency and refrigeration power, but the adsorption capacity, COP and SCP are still quite low.

To date, only silica gel has been used in commercial adsorption refrigeration and dehumidification systems because silica gel is hydrophilic and can adsorb moderate amounts of water vapor at any pressure level.

Accordingly, it is desirable to provide better composite sorbent materials for cooling systems and dehumidification systems.

Disclosure of Invention

A good composite adsorbent material can be made by impregnating an inorganic salt (e.g., calcium chloride) and silica gel into the micropores or mesopores of activated carbon. Experiments show that about 0.9 g of water vapor can be adsorbed per gram of calcium chloride under normal temperature and normal pressure. This is why calcium chloride can be one of the adsorbents that are widely used in the humidity extraction cassette. Based on this, if a high-density composite adsorbent can be developed by impregnating silica gel and calcium chloride in the pores of activated carbon, it can improve not only the adsorption capacity under a low pressure environment but also the overall adsorption capacity and adsorption rate. Therefore, the refrigeration efficiency of the adsorption refrigeration system can be improved, and the refrigeration power thereof can be improved.

Based on this principle, composite adsorbent materials comprising activated carbon, silica gel and calcium chloride have been successfully prepared which can adsorb up to 0.23 grams of water vapor per gram of dry adsorbent in a low pressure operating environment of 900Pa, which is an improvement of approximately nine hundred thirty percent over the starting activated carbon. The composite adsorbent material has great potential for being used as an adsorbent in an adsorption refrigeration system. Meanwhile, the difference between the equilibrium water absorption capacity of the composite adsorbent per gram of dry adsorbent at the temperature of 25 ℃ and 115 ℃ under the atmospheric pressure is 0.805 g. The yield is improved by about three hundred twenty four percent compared with the raw material of the active carbon. Thus, the composite adsorbent material also has great potential for use as an adsorbent in a dehumidification system. Overall, the results show that the composite adsorbent material is a good choice for adsorption refrigeration and dehumidification systems.

Accordingly, one aspect of the present invention relates to a composite adsorbent material comprising a porous host or matrix material of activated carbon impregnated with silica gel and calcium chloride. The composite adsorbent preferably has a particle size (diameter) of about twenty mesh (mesh) to about forty mesh (i.e., about 420 to 841 millimeters), and activated carbon as a matrix with an average pore diameter of preferably aboutTo aboutThe total pore volume of the activated carbon as the matrix material is preferably from about 0.4 cubic centimeters per gram to about 1.0 cubic centimeters per gram, while the total surface area is preferably from about 1100 square meters per gram to about 1200 square meters per gram. Herein, data describing the physical properties (e.g., pore size, pore volume, surface area, etc.) of a porous matrix material (e.g., activated carbon) are all physical parameters of the material prior to being impregnated.

Another aspect of the invention relates to a method of making a composite adsorbent material useful in an adsorption refrigeration system or a dehumidification system, the method comprising: activated carbon was prepared as a porous matrix material, and the porous matrix material was impregnated with a sodium silicate solution, followed by a calcium chloride solution. For a composite adsorbent to be used in an adsorption refrigeration system, it may comprise: 60-70 wt% of active carbon, 10-15 wt% of silica gel and 15-30 wt% of calcium chloride; it preferably comprises: about 60% to about 65% by weight of activated carbon, about 10% to about 15% by weight of silica gel, and about 20% to about 30% by weight of calcium chloride. The composite adsorbent used in the dehumidification system may comprise: 30-35 wt% of active carbon, 2-10 wt% of silica gel and 55-68 wt% of calcium chloride; it preferably comprises: about 30% to about 35% by weight of activated carbon, about 5% to about 10% by weight of silica gel, and about 55% to about 65% by weight of calcium chloride.

Yet another aspect of the present invention is directed to a humidity control system that includes a desiccant wheel unit (desiccant wheel dehumidification unit) in which water is used as the target to be adsorbed and the composite adsorbent material provided by the present invention is used as the adsorbent. Further, one aspect of the invention relates to a cooling or temperature control system comprising an adsorption unit; wherein, water, methanol and ammonia can be taken as the absorbed objects, and the composite adsorbent material provided by the invention is used as the adsorbent.

Accordingly, the present invention includes the following:

1) a composite adsorbent material comprises activated carbon as a porous matrix material impregnated with silica gel and calcium chloride.

2) The composite adsorbent material according to 1) above, wherein the porous matrix material has an average pore size of diameterToWithin the range of (1).

3) The composite adsorbent material according to any one of the preceding claims, wherein the porous matrix material contains 0.43 cubic centimeters per gram of micropores.

4) The composite adsorbent material according to any one of the preceding claims, wherein the porous matrix material contains 0.44 cubic centimeters per gram of mesopores.

5) The composite adsorbent material according to any one of the preceding claims, wherein the porous matrix material contains 0.02 cubic centimeters per gram of macropores.

6) The composite adsorbent material according to any one of the preceding claims, wherein the composite adsorbent material has a particle size in the range of twenty to forty mesh in diameter.

7) A composite adsorbent material as claimed in any one of the preceding claims, wherein the porous matrix material is in the form of activated carbon particles.

8) The composite adsorbent material according to any one of the preceding claims, wherein the total pore volume of the porous matrix material is from 0.4 cubic centimeters per gram to 1.0 cubic centimeters per gram.

9) The composite adsorbent material according to item 8) above, wherein the total pore volume is 0.5 cc per gram.

10) The composite adsorbent material according to any one of the preceding claims, wherein the total surface area of the porous matrix material is from 1100 square meters per gram to 1200 square meters per gram.

11) The composite adsorbent material according to item 10) above, wherein the total surface area is 1120 square meters per gram.

12) The composite adsorbent material according to any one of the preceding claims, wherein said composite adsorbent material is capable of adsorbing at least 0.86 grams of water vapor per gram of dry composite adsorbent material under one atmosphere of pressure, the composite adsorbent material being used in an open dehumidification system.

13) The composite adsorbent material according to 1) to 11), wherein the composite adsorbent material is capable of adsorbing at least 0.23 g of water vapor per gram of dry composite adsorbent material under 900Pa of air pressure, and the composite adsorbent material is used in an adsorption-type closed refrigeration system.

14) The composite adsorbent material according to any one of the preceding claims, which is used in an adsorption refrigeration system, wherein a 30 wt% calcium chloride solution is used to provide the composite adsorbent material with the maximum adsorption rate.

15) The composite adsorbent material according to any one of the preceding claims, for use in an adsorption refrigeration and/or dehumidification system, wherein the composite adsorbent material exhibits a sigmoidal adsorption isotherm curve.

16) The composite adsorbent material according to any one of the preceding claims, for use in an adsorption refrigeration system, wherein the theoretical refrigeration efficiency of the composite adsorbent material is 0.7.

17) The composite adsorbent material according to any one of the preceding claims, for use in an adsorption refrigeration system, wherein the composite adsorbent material has an average refrigeration power of 378 watts per kilogram.

18) A composite adsorbent material according to any one of the preceding claims, for use in a dehumidification system, and comprising: 30-35 wt% of active carbon, 2-10 wt% of silica gel and 55-68 wt% of calcium chloride.

19) The composite adsorbent material according to any one of the preceding claims, for use in an adsorption refrigeration system, and comprising: 60-70 wt% of active carbon, 10-15 wt% of silica gel and 15-30 wt% of calcium chloride.

20) The composite adsorbent material according to any one of the preceding claims, further comprising a metal impregnated in the activated carbon.

21) The composite adsorbent material according to item 20) above, wherein the metal is copper or aluminum.

22) Use of a composite adsorbent material according to any one of the preceding claims in a cooling system or a temperature and/or humidity control system.

23) A method of making a composite adsorbent material according to any one of the preceding claims, the method comprising:

preparing activated carbon as a porous matrix material; and

the porous matrix material was immersed in a sodium silicate solution and then in a calcium chloride solution.

24) A method of making a composite adsorbent material according to any one of the preceding claims for use in a dehumidification system, the method comprising:

activated carbon prepared as a porous matrix material, and

the porous matrix material was immersed in a 10 wt% sodium silicate solution for forty-eight hours and then in a 46 wt% calcium chloride solution for seventy-two hours.

25) A method of making a composite adsorbent material according to any one of the preceding claims for use in an adsorption refrigeration system, the method comprising:

preparing a porous activated carbon, and

the porous activated carbon was immersed in a 10 wt% sodium silicate solution for forty-eight hours and then immersed in a 30 wt% calcium chloride solution for forty-eight hours.

26) A humidity control system comprising a desiccant wheel unit in which a composite adsorbent material according to any one of the preceding claims is used as an adsorbent and water is the subject of adsorption.

27) A cooling or temperature control system comprising an adsorption unit in which a composite adsorbent material according to any one of the preceding claims is used as an adsorbent and water, methanol and/or ammonia gas as the subject of adsorption.

Drawings

Various embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

Fig. 1 schematically illustrates the concept of impregnating silica gel and calcium chloride in activated carbon.

Fig. 2A schematically illustrates a process of preparing silica activated carbon (silica activated carbon) by impregnating activated carbon with hydrophilic silica gel.

Fig. 2B schematically illustrates a process of impregnating calcium chloride in silica gel activated carbon to obtain an activated carbon-silica gel-calcium chloride composite.

Fig. 3 shows a Scanning Electron Microscope (SEM) image of the activated carbon before impregnation.

Fig. 4 shows a scanning electron microscope image of the impregnated activated carbon sample.

Figure 5 shows the results of thermogravimetric analysis (TGA) of different composite adsorbent samples at atmospheric pressure.

FIG. 6 shows the water absorption isotherms at 300K for the AC01, AC03, AC07, AC10 and AC12 samples.

FIG. 7 illustrates the water vapor adsorption rates at 300K and 750Pa for the AC01, AC03, AC07, AC10, and AC12 samples.

FIG. 8 illustrates the water vapor adsorption rates at 300K and 900Pa for the AC01, AC03, AC07, AC10, and AC12 samples.

FIG. 9 illustrates the water vapor adsorption rates at 300K and 1000Pa for the AC01, AC03, AC07, AC10, and AC12 samples.

FIG. 10 illustrates the water vapor adsorption rates at 300K and 1100Pa for the AC01, AC03, AC07, AC10, and AC12 samples.

Fig. 11 illustrates the relationship between the adsorption rate and the concentration of calcium chloride solution.

Detailed Description

As used herein, the word "a" or "an" when used in conjunction with a noun includes the singular and plural referents unless the content clearly dictates otherwise. Thus, in this application, "a" or "an" if no number is indicated and "at least one" are used interchangeably.

In this application, the terms "comprising" or "including" are used in describing various embodiments, but those skilled in the art will understand that in certain specific instances, embodiments may alternatively be described using the expression "consisting essentially of … …" or "consisting of … …".

For a better understanding of the invention, and in no way limiting of the scope thereof, all numbers expressing quantities, percentages, parts, and so forth, and other numerical values used in the application, unless otherwise indicated, are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

The meanings of the other terms used herein are the meanings that the corresponding terms known in the art have.

The present invention develops a new hydrophilization method for obtaining high performance adsorbents by impregnating silica gel and calcium chloride in the pores of activated carbon. The composite adsorbent material comprises a combination of three different types of physical adsorbents, which are silica gel, calcium chloride and activated carbon. Wherein the activated carbon is the host material or matrix. The composite adsorbent material can be used in solar adsorption refrigeration systems and dehumidification systems.

The function of the impregnated silica gel is to increase the adsorption capacity in a lower pressure environment, which is a novel, unusual feature. The purpose of calcium chloride impregnation is to further improve the overall adsorption capacity performance over a wide pressure range. The feasibility of this technology has not been described or discussed in advance by any prior art, namely: the feasibility of designing the novel composite adsorbent material by fully utilizing the advantages of the three adsorbents and combining the three adsorbents.

The activated carbon has high thermal conductivity and good adsorption capacity under high pressure. However, at low pressure stripsThe adsorption performance of the activated carbon under the conditions was rather poor. The use of silica gel impregnated in the pores of activated carbon can overcome the drawbacks of silica gel, since silica gel has good adsorption capacity under low pressure conditions. Calcium chloride (CaCl)₂) Is another excellent chemical adsorbent, which has very high adsorption capacity for water vapor, but calcium chloride alone cannot maintain its solid structure because it becomes liquid upon adsorption of water vapor and cannot be recycled. The impregnation of calcium chloride in the pores of the activated carbon not only overcomes the disadvantages of activated carbon, but also serves as a matrix material for the containment of the aqueous calcium chloride, thereby allowing a recycling process to be carried out. The silica gel and calcium chloride are impregnated in the pores of the activated carbon, so that the problem of adsorption capacity in a relatively low pressure range can be solved, and the overall adsorption capacity can be improved. In conclusion, silica gel and calcium chloride can make up for the disadvantages of activated carbon. They are complementary.

The composite adsorbent material comprises active carbon as a main material, and silica gel and calcium chloride are impregnated in pores of the active carbon, so that the adsorption capacity of the composite adsorbent material is remarkably improved, and generally, the adsorption capacity of the composite adsorbent material is at least about fifty percent higher than that of the currently known composite adsorbent. The composite adsorbent has more stable performance, can be used in an adsorption refrigeration and dehumidification system, and can adsorb a large amount of water vapor under the conditions of low pressure and high pressure. In addition, the composite adsorbent material has higher cycle number and can be repeatedly used. The thermal conductivity is also enhanced by the impregnation of a large portion of the pores of the activated carbon with silica gel and calcium chloride. In addition, the composite adsorbent can still maintain its stable structure after being used in an adsorption process, and never become a solution form after adsorption.

One of the main applications of the composite adsorbent material of the present invention is: the method is used for preparing the adsorbent used by the solar adsorption refrigeration air-conditioning system and the dehumidification system. The heating, ventilation, and air conditioning (HVAC) industry, the renewable energy industry, the solar energy industry, other industries that generate waste heat during production, and the home owner can all benefit directly from the technology of the present invention. The solar industry may benefit from more than one application because such sorption refrigeration systems may be driven by solar energy, which means that the industry may have more variations. In addition, the composite adsorbent material is also economical for home use. The air conditioner equipped with the energy efficient adsorption type refrigeration system can reduce electricity charges. Compared with the existing cooling system, the cooling system can save about fifty percent of energy.

In the composite adsorbent material, activated carbon, as a major constituent (matrix or matrix material), is hydrophobic, typically having pores with a radius of from a fraction of three to ten nanometers, and including a large number of micropores and mesopores greater than 1 nanometer. Hydrophilization of activated carbon can be achieved by impregnation of silica gel (which is hydrophilic) and calcium chloride. The concept of impregnating silica gel and calcium chloride into the micropores, mesopores and macropores of activated carbon is depicted in fig. 1.

Any type of activated carbon having a varying pore distribution may be used to prepare the composite adsorbent material of the present invention. Different types of activated carbon, such as chemically activated carbon or steam activated carbon, can be used in the present invention, and these activated carbons are commercially available, for example, from Takeda Pharmaceutical Co., Ltd., Taihei Kagaku Co., Ltd., or Kanebo Co., Ltd. Activated carbon may also be prepared according to methods known in the art. Further, the activated carbon used in the present invention may be granular.

A description of the process of impregnating silica gel with activated carbon is shown in fig. 2A. To obtain silica gel, sodium silicate solution was used as its source. Silica activated carbon was obtained under different experimental conditions. The sodium silicate solution may be prepared at a concentration of one-half to ten percent, preferably ten percent, and the soaking time may be from one to seventy-two hours, preferably forty-eight hours. The temperature may be about 300K to 450K, preferably about 383K to 423K. Further, the impregnation may be performed once, or repeated twice at the same concentration or at different concentrations. In order to prevent the dissolution of silicic acid from the activated carbon,the sodium silicate neutralization process is preferably carried out in two stages: i. the activated carbon is impregnated with sufficient sodium silicate and dried ii. From sodium silicate and sulfuric acid, a silica gel monomer can be prepared, which reacts as follows: na (Na)₂O·3.3SiO₂+H₂SO₄+5.6H₂O→3.3Si(OH)₄+Na₂SO₄. After heating and aging, the following dehydration condensation reaction may occur: 2Si (OH)₄→(OH)₃Si-O-Si(OH)₃+H₂O。

After the preparation of the silica gel activated carbon composite adsorbent is completed, the silica gel activated carbon composite adsorbent is preferably immersed in a calcium chloride solution. The concentration (weight percent) of the calcium chloride solution may be one percent to forty-six percent, preferably ten percent, thirty percent or forty-six percent (i.e., the saturation concentration). The immersion time may be from one to seventy-two hours, preferably twenty-four hours, forty-eight hours or seventy-two hours. The activated carbon before and after impregnation is presented by a scanning electron microscope; as shown in fig. 3 (before impregnation or impregnation) and fig. 4 (after impregnation).

The adsorption performance of the prepared composite material is evaluated through adsorption isotherms, pore size analysis, surface observation and the impregnation amount of silica gel and calcium chloride. For evaluation, brunauer-emmett-teller (BET), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), low-pressure thermogravimetric analysis, theoretical refrigeration efficiency (idealcon), and average refrigeration power (average SCP) analysis tests were performed on the composite adsorbent, and calculation was performed using a method known in the art, and the analysis results thereof will be explained in detail one by one below (tables two to seven and fig. 5 to 11).

According to the data, the pore size of the activated carbon in the composite adsorbent can be aboutToThe capacity of the micropores of the bulk matrix activated carbon in the composite may be about 0.43 cubic centimeters per gram, the mesopores about 0.44 cubic centimeters per gram, and the macropores about 0.02 cubic centimeters per gram. The host matrix may be in the form of activated carbon particles. Further, the size (diameter) of the composite adsorbent may be about twenty to forty mesh. With respect to the pore volume of the activated carbon, the total pore volume of the bulk matrix activated carbon in the composite adsorbent can be about 0.4 cubic centimeters per gram to 1.0 cubic centimeters per gram, preferably about 0.5 cubic centimeters per gram. The total surface area of the activated carbon may be from about 1100 square meters per gram to about 1200 square meters per gram.

When describing a porous substrate (e.g., activated carbon) herein, microporous means having a pore diameter of less than 2 nanometers, mesoporous means having a pore diameter between 2 nanometers and 50 nanometers, and macroporous means having a pore diameter greater than 50 nanometers; the total surface area refers to the sum of the internal surface area and the external surface area of the porous matrix.

In one embodiment, the composite adsorbent used in the dehumidification system comprises (in weight percent): 30-35 wt% of active carbon, 2-10 wt% of silica gel and 55-68 wt% of calcium chloride; preferably, the composite adsorbent comprises: 30 to 35 percent of active carbon, 5 to 10 percent of silica gel and 55 to 65 percent of calcium chloride. The most desirable impregnation formulation for a dehumidification system is to impregnate the activated carbon feedstock in a 10% by weight sodium silicate solution for about forty-eight hours followed by a 46% by weight calcium chloride solution for about seventy-two hours. In another embodiment, a composite adsorbent for use in an adsorption refrigeration system comprises (percent by weight): 60-70 wt% of active carbon, 10-15 wt% of silica gel and 15-30 wt% of calcium chloride; preferably, the composite adsorbent comprises: 60 to 65 percent of active carbon, 10 to 15 percent of silica gel and 20 to 30 percent of calcium chloride. The most desirable impregnation formulation for an adsorption refrigeration system is to impregnate the activated carbon feedstock in a 10% by weight sodium silicate solution for about forty-eight hours followed by a 30% by weight calcium chloride solution for about forty-eight hours.

When used in an open dehumidification system, the composite adsorbent material of the present invention has an adsorption capacity of about at least 0.86 grams of water vapor per gram of adsorbent material at room pressure (i.e., 1 atmosphere). Similarly, when used in an adsorption refrigeration system, the composite adsorbent material of the present invention has an adsorption capacity of about at least 0.23 grams of water vapor at low pressure of 900Pa per gram of adsorbent material.

The composite adsorbent material is particularly useful for adsorbing large quantities of water vapor and in low temperature thermally driven adsorption refrigeration and dehumidification systems. The isothermal adsorption curve of the composite adsorbent used in the adsorption refrigeration and dehumidification system shows an S-shape.

The composite adsorbent applied to the adsorption refrigeration system can improve the theoretical refrigeration efficiency to 0.7 and improve the average refrigeration power to 378W/kg.

Some metals (e.g., copper, aluminum) may also be impregnated into the pores of the activated carbon, and thus the composite adsorbent material may also comprise metals. This is to further increase the thermal conductivity of the composite adsorbent material.

The composite adsorbent material of the present invention can be used in a humidity control system that includes a desiccant wheel dehumidification unit. Likewise, the composite adsorbent material may also be used in cooling or temperature control systems that include an adsorption unit, with water, methanol, and ammonia as adsorbed materials.

Examples of the invention

Various embodiments of the present invention are further described by the following examples, which should not be construed as in any way limiting the scope of the invention.

Sample preparation

Examples one to nine

(sample No.: AC05-AC13)

Nine samples of composite sorbent material were prepared according to the procedure described below, with the main considerations being the impregnation time, the concentration of the sodium silicate solution and the concentration of the calcium chloride solution. The sodium silicate solution was purchased from Sigma-Aldrich (product No. 338443). The calcium chloride solution was prepared as follows: water-soluble anhydrous calcium chloride in powder form, which was purchased from Sigma-Aldrich (product number: C4901), was added to deionized water to form calcium chloride solutions of various concentrations.

Impregnation was performed according to the procedure of fig. 2A using activated carbon as the host material, first silica gel was impregnated into the pores of the activated carbon. Activated carbon was purchased from Sigma-Aldrich, product number: 10275. the ten grams of activated carbon is dried for twenty-four hours at a high temperature of 383K and then is treated with one hundred and fifty milliliters of sodium silicate solution (Na)₂O·3.3SiO₂Sodium silicate concentration of 10 wt%) and then filtered. The resulting product was then oven dried at high temperatures of twenty-four hours and 383K and then impregnated a second time for twenty-four hours with seventy-five milliliters of 3.9 mole per liter sulfuric acid solution. After being filtered again and dried under the same conditions as above, the resultant product was washed with deionized water again in order to remove the sodium sulfate solution. And finally, drying at the high temperature of 423K for twenty-four hours to prepare the silica gel activated carbon composite material.

Next, another process shown in fig. 2B is employed to impregnate the calcium chloride. Samples were prepared under different experimental conditions. Firstly, the concentration of calcium chloride is considered, and the following weight percentage concentrations are adopted: ten percent, thirty percent, forty-six percent (i.e., saturation concentration). In addition, the time of impregnation of calcium chloride plays a very important role, since this affects the weight percentage of calcium chloride in the pores of the composite silica gel activated carbon. Therefore, three different immersion times are also contemplated, twenty-four hours, forty-eight hours and seventy-two hours respectively.

Specifically, 10 g of silica gel activated carbon was contacted with 100 ml of calcium chloride solution. After filtration and drying at 423K for 24 hours, an activated carbon-silica gel-calcium chloride composite adsorbent material was obtained.

As a control group, the raw material, i.e., the non-impregnated activated carbon, was used.

Comparative examples one to three

(sample No.: AC02-AC04)

For comparison, three activated carbon/silica gel composite samples were prepared according to the procedure for producing silica gel activated carbon (FIG. 2A) described above, wherein the immersion time was varied to twenty-four hours, forty-eight hours and seventy-two hours (sample numbers: AC02, AC03 and AC04), respectively.

As shown in table one, a total of thirteen samples were prepared for testing, including untreated activated carbon (control). Comparative examples one to three (AC02-AC04) impregnated only silica gel and corresponded to different silica gel impregnation times. Examples one to nine (AC05-AC13) impregnated silica gel and calcium chloride, and correspond to different calcium chloride impregnation times and calcium chloride concentrations. Fig. 3 and 4 show scanning electron microscope images of the sample.

Watch 1

Experimental examples

To evaluate the properties of all samples, BET, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and low pressure thermogravimetric analysis were performed. The results of the analysis of the composite adsorbent material are set forth in the following table and figures.

Example ten: surface area and pore volume

The surface area and pore volume of the samples were measured by the BET method (see, documents H. Huang et al, "Development research on composite adsorbed Applied adsorption heat pump," Applied Thermal Engineering, 30, (2010)1193-1198), and the results are shown in Table two.

The particle size was almost the same for all thirteen samples, approximately twenty to forty mesh. Table two clearly shows that the length of impregnation time has no significant effect on surface area and pore volume. Comparative examples AC02-AC04 (comparative examples 1-3); AC05-AC07 (examples 1-3); the results were quite similar for AC08-AC10 (examples 4-6) and AC11-AC13 (examples 7-9). However, there are considerable differences from group to group.

Of course, AC01 (control) exhibited the greatest surface area and pore volume due to the many micropores/mesopores in the starting activated carbon. The lowest values of surface area and pore volume were assigned to the AC05-AC07 series (examples 1-3) because the salt concentration of calcium chloride was 46% and the saturation concentration was reached, so the pores of the AC05-AC07 samples were filled with calcium chloride.

TABLE II specific surface area and Total pore volume of the samples

Example eleven: x-ray photoelectron spectroscopy

Analysis by X-ray photoelectron spectroscopy (XPS) to confirm that all compounds were fully impregnated within the pores of the activated carbon is shown in table three.

The experimental result shows that when the composite adsorbent is used for a dehumidification system, the composite adsorbent comprises the following components in percentage by weight: 30-35 wt% of active carbon, 2-10 wt% of silica gel and 55-68 wt% of calcium chloride; preferably, the composite adsorbent comprises: 30-35 wt% of active carbon, 5-10 wt% of silica gel and 55-65 wt% of calcium chloride. When the composite adsorbent is used in an adsorption refrigeration system, the composite adsorbent comprises the following components in percentage by weight: 60-70 wt% of active carbon, 10-15 wt% of silica gel and 15-30 wt% of calcium chloride; preferably, the composite adsorbent comprises: 60-65 wt% of active carbon, 10-15 wt% of silica gel and 20-30 wt% of calcium chloride.

X-ray photoelectron spectroscopy of the three samples in Table (error of. + -. 5%)

Example twelve: analysis of adsorption Capacity

The experimental results show that the more calcium chloride in the pores of the activated carbon, the better the adsorption capacity. It was also found that the optimum formulation was to immerse the activated carbon in a 10 wt% sodium silicate solution for forty-eight hours followed by a 46 wt% calcium chloride solution for seventy-two hours (i.e., case three; sample AC 07); based on TGA analysis, the difference between the equilibrium adsorption capacities of the composite adsorbent in the adsorption stage and the desorption stage can reach a difference of 0.805 g of water vapor adsorbed by each gram of dry composite adsorbent, and the improvement percentage is 324% compared with the raw material activated carbon. The results are shown in table four and fig. 5.

TABLE IV equilibrium water absorption differences at both temperatures of 25 ℃ and 115 ℃ and percent improvement (atmospheric pressure) relative to the starting activated carbon

The adsorption capacity of the samples, as well as the percent improvement over the raw activated carbon (control sample) was determined at different pressures (e.g., 750Pa, 900Pa, 1000Pa, 1100 Pa). The experimental results found that the adsorption capacity of the control sample (AC01) was very low in the pressure range from 200Pa to 1400Pa, but slightly increased after the 1600Pa pressure range. The adsorption performance of comparative example 2(AC03) was quite close to that of example 6(AC10) while reaching 0.13 grams per gram at 900 Pa. However, their compositions were quite different, and comparative example 2(AC03) was a sample that was not soaked in a calcium chloride solution. It follows that soaking with a calcium chloride solution of only 10% by weight does not improve its water absorption capacity at low pressure. Therefore, comparative example 2(AC03) and example 6(AC10) are composite adsorbents that are not suitable for use in adsorption refrigeration systems. Examples 3(AC07) and 8(AC12) showed the best adsorption capacity, which was much better than the control sample, comparative examples 2 and 6. Of these, example 3(AC07) exhibited the highest adsorption capacity, 0.25 grams per gram at 900Pa, and a percent improvement over the starting activated carbon of up to about nine hundred and ninety-two percent, as shown in table five. Example 8(AC12) also had a higher adsorption capacity, about 0.23 grams per gram, which was only slightly lower than the adsorption capacity of example 3(AC 07). However, example 8(AC12) had a much faster adsorption rate than 3(AC07) and a slightly higher adsorption capacity than 3(AC07) at lower pressure conditions (200Pa-750 Pa). This is probably because the silica gel content of example 8(AC12) was higher than that of example 3(AC 07). This result again demonstrates that silica gel can help improve adsorption capacity at lower pressures, while calcium chloride can enhance adsorption capacity at higher pressures. Also, in fig. 6, example 8(AC12) shows an S-shaped isotherm, which further supports the original idea that example 8(AC12) is the best composite adsorbent to be used in adsorption refrigeration systems compared to other compositions. Thus, the optimum formulation was optimized for forty-eight hours of activated carbon immersion in a 10 wt% sodium silicate solution and forty-eight hours of immersion in a 30 wt% calcium chloride solution (i.e., example 8; sample AC 12). Based on low pressure TGA analysis, the adsorption capacity can reach 0.1948 grams per gram, corresponding to a four hundred seventy five percent improvement (at 750 Pa); at 900Pa, an improvement of 0.2335 grams per gram, ninety hundred and thirty three percent, can be achieved; at 1000Pa, an improvement of 0.2485 grams per gram, three hundred and fifty-four percent, can be achieved; at 1100Pa, an improvement of 0.2634 grams per gram, four hundred thirty-two percent, was achieved, all relative to the starting activated carbon. The results are shown in table five and fig. 6.

TABLE V adsorption Capacity of samples at different pressures, and percent improvement over raw activated carbon

Example thirteen: coefficient of adsorption rate

The adsorption isotherm, the adsorption isobaric curve and the adsorption rate can be obtained by an adsorption rate test experiment. Table six shows the adsorption rate coefficients of example 3(AC07), example 6(AC10) and example 8(AC12) compared with the samples of comparative example 2 and the control, and the relationship between the adsorption rate and the concentration of calcium chloride solution is shown in FIG. 11.

The adsorption rate of example 8(AC12) is clearly much higher in any pressure region than that of example 3(AC07) because the specific surface area and total pore volume (also referred to as pore volume) are much larger, as shown in table two. In other words, the adsorbate (water vapor) can be adsorbed quickly due to its rapid diffusion process. This phenomenon is the same for the control (AC01), and at 750Pa and 900Pa, the adsorption rate coefficient of the control (AC01) is much higher than that of example 8(AC12) under the same working conditions. However, as the pressure level increased, the adsorption rate coefficient of the control group (AC01) decreased dramatically. This is because the control group (AC01) can adsorb more water vapor at higher pressure levels. Therefore, it takes a while to reach the saturation state. Although the adsorption rate coefficient of the control group (AC01) was the highest at 750Pa and 900Pa, its adsorption capacity was the worst. Thus, the activated carbon was immersed in a 10 wt% sodium silicate solution for forty-eight hours and a 30 wt% calcium chloride solution for forty-eight hours (i.e., one hour)Example 8, sample AC12) was the optimized combination. It has a fairly good adsorption rate coefficient (at 900Pa, K ═ 1.3X10^-3)。

Table six first sample adsorption rate coefficient comparison at 300K

Example of calculation

Example fourteen: theoretical refrigeration efficiency and average refrigeration power

The theoretical refrigeration efficiency is the ratio of the refrigeration energy To the input energy that can be achieved by the refrigeration system, as shown in equation (1) (see references: Chan, K.C., Chao, C.Y.H., Sze-To G.N., and Hui K.S.2012.Performance compressors for a new zeolite 13X/CaCl)₂composition for the adaptation of the system of systems international journal Heat and Mass Transfer, In press, doi: 10.1016/j.ijheatmasstransferafer.2012.02.054), the greater the ratio, the better the efficiency of the refrigeration system under the same operating conditions. Equation (1) this equation shows that the value of the equilibrium water absorption difference (Δ X) has a positive effect on the efficiency of the adsorption refrigeration system, the larger the value, the better the theoretical refrigeration efficiency. The temperatures involved in Δ X given by the adsorption isotherm are: the operating temperature for adsorption is approximately twenty-seven degrees celsius and the desorption temperature is approximately one hundred and fifteen degrees celsius. The theoretical refrigeration efficiency can be calculated.

Δ X is the difference between the equilibrium water absorption of the adsorption phase and the desorption phase; m is_zIs the mass of the composite adsorbent applied to the adsorption refrigeration system h_{fg, adsorbate}Is the latent heat of vaporization ratio of water (2489 kilojoules per kilogram at 5 ℃), C_acAnd C_adIs the specific heat capacity of the composite adsorbent and the specific heat capacity of the adsorbate (1.09 kilojoules per kilogram per degree and 4.186 kilojoules per kilogram per degree, respectively); t is_H-T_LIs the temperature difference (about 88K) of the adsorption and desorption stages of the composite adsorbent_adIs the amount of heat generated by adsorption of the composite adsorbent, calculated from the equilibrium between the chemical potentials of the gas and the adsorbent (see: Ruthven, d.m., 2008, Fundamental of adsorption equilibrium and kinetics in microporosius disorders.7, 1-43). The balance of chemical potentials was derived Using the Clausius-Clapeyron equation (see Ko, D., Siriwardane, R., Biegler, L.T., 2002.Optimization of a Pressure-swing adsorption Process Using Zeolite 13X for CO2 sequencing, Industrial and Engineering Chemistry research.42, 339-348). The average value of the adsorption heat value of the composite adsorbent is about 2885 kilojoules per kilogram. The theoretical refrigeration efficiency of the control (AC01) was around 0.37, while the composite adsorbent example 8(AC12) achieved 0.70, perhaps an eighty-nine percent improvement, according to equation (1). The details are set forth in table seven.

Refrigeration power (SCP) is proportional to the adsorption rate and is defined as the refrigeration load divided by the mass of adsorbent. The refrigeration load is given by the following formula (see references: Chan, K.C., Chao, C.Y.H., Sze-To G.N. and Hui K.S.2012.Performance compressors for a newzeolite 13X/CaCl)₂ composite adsorbent for adsorption cooling systems.International Journal of Heat and Mass Transfer，In Press.DOI.：10.1016/j.ijheatmasstreansfer.2012.02.054)：

Wherein Q is the refrigeration load in watts; m is_adIs the specific adsorption rate per kilogram of adsorbent in 1 second for the adsorbate (kg), and m_adThe values of (b) were calculated based on the results of the experimental examples of the adsorption rate coefficient (K) shown in table 6; m is_zIs the mass of the adsorbent, in kilograms, h_{fg, adsorbate}Is the latent heat of vaporization ratio of water (2489 kilojoules per kilogram at 5 ℃). The refrigeration power SCP can be expressed as:

the average refrigeration power can also be calculated as:

therefore, in the adsorption refrigeration system, higher refrigeration power can be obtained at higher adsorption rate. All results are shown in table seven. Example 8(AC12) is the sample that achieved the highest refrigeration power, with a value of 378 watts per kilogram, which is approximately a four hundred eighty two percent improvement over the control sample.

TABLE seven comparison of average refrigeration capacity and theoretical refrigeration efficiency for preferred samples (900Pa)

The experimental test results show that the adsorption capacity of the composite adsorbent material provided by the invention is obviously higher than that of other composite adsorbents known in the field by about fifty percent. Currently, only a single silica gel adsorbent is commercially used in adsorption refrigeration and dehumidification systems. The composite adsorbent is used in adsorption refrigerator and dehumidifying system, and can adsorb great amount of water vapor in both the low pressure area and the high pressure area. Each gram of the dry composite adsorbent can adsorb 0.23 g of water vapor under the working environment pressure of 900 Pa. It is higher than 0.2 grams per gram of silica gel and far exceeds 0.02 grams per gram of activated carbon in the same working environment.

Furthermore, the desorption temperature of silica gel is about one hundred degrees celsius. However, according to thermogravimetric analysis experimental results, the desorption temperature of the composite adsorbent material of the present invention is always lower than one hundred degrees celsius.

In addition to the characteristics of adsorption capacity and desorption temperature, the thermal conductivity of the composite adsorbent of the present invention is also higher than that of silica gel. This is because the calcium chloride and silica gel fill the voids between the activated carbon molecules, forming a heat transfer path. This is another advantage of the composite adsorbent of the present invention. The thermal conductivity of the composite adsorbent of the present invention is about 1.5W/mK, which is at least 3 times higher than that of silica gel.

It will be apparent to those skilled in the art from this disclosure that various changes in the precise description of the invention can be made without departing from the spirit and scope of the appended claims. It is to be understood that the scope of the invention is not limited to the procedures, properties or components defined, as these preferred embodiments and other descriptions are intended only to illustrate specific aspects of the invention. Indeed, various modifications of the embodiments of the invention which are obvious to those skilled in the art or related fields are intended to be covered by the scope of the appended claims.

Claims (22)

1. A composite adsorbent material comprising activated carbon which is a porous matrix material impregnated with silica gel and calcium chloride, the composite adsorbent material being for use in an adsorption refrigeration system and comprising: 60-70 wt% of active carbon, 10-15 wt% of silica gel and 15-30 wt% of calcium chloride.

2. The composite adsorbent material of claim 1, wherein the porous matrix material has an average pore size of diameterToWithin the range of (1).

3. The composite adsorbent material of claim 1, wherein said porous matrix material contains 0.43 cubic centimeters per gram of micropores.

4. The composite adsorbent material of claim 1, wherein said porous matrix material contains 0.44 cubic centimeters per gram of mesopores.

5. The composite adsorbent material of claim 1, wherein said porous matrix material contains 0.02 cubic centimeters per gram of macropores.

6. The composite adsorbent material of claim 1, wherein the composite adsorbent material has a particle size in the range of twenty to forty mesh in diameter.

7. The composite adsorbent material of claim 1, wherein the porous matrix material is in the form of activated carbon particles.

8. The composite adsorbent material of claim 1, wherein the porous matrix material has a total pore volume of 0.4 cc per gram to 1.0 cc per gram.

9. The composite adsorbent material of claim 8, wherein said total pore volume is 0.5 cubic centimeters per gram.

10. The composite adsorbent material of claim 1, wherein the porous matrix material has a total surface area of 1100 square meters per gram to 1200 square meters per gram.

11. The composite adsorbent material of claim 10, wherein said total surface area is 1120 square meters per gram.

12. The composite adsorbent material of claim 1, wherein the composite adsorbent material is capable of adsorbing at least 0.23 gram of water vapor per gram of dry composite adsorbent material at 900Pa of pressure, and is used in an adsorption closed refrigeration system.

13. The composite adsorbent material according to claim 1, for use in an adsorption refrigeration system, wherein a 30 wt% calcium chloride solution is used to maximize the adsorption rate of the composite adsorbent material.

14. The composite adsorbent material according to claim 1, for use in adsorption refrigeration, wherein the composite adsorbent material exhibits a sigmoidal adsorption isotherm curve.

15. The composite adsorbent material according to claim 1, for use in an adsorption refrigeration system, wherein the theoretical refrigeration efficiency of the composite adsorbent material is 0.7.

16. The composite adsorbent material of claim 1, for use in an adsorption refrigeration system, wherein the composite adsorbent material has an average refrigeration power of 378 watts per kilogram.

17. The composite adsorbent material of claim 1, further comprising a metal impregnated in the activated carbon.

18. The composite adsorbent material of claim 17, wherein the metal is copper or aluminum.

19. Use of the composite adsorbent material of claim 1 in a cooling system or a temperature control system.

20. A method of making the composite adsorbent material of claim 1, comprising:

preparing activated carbon as a porous matrix material; and

the porous matrix material was immersed in a sodium silicate solution and then in a calcium chloride solution.

21. A method of making the composite adsorbent material of claim 1 for use in an adsorption refrigeration system, the method comprising:

preparing a porous activated carbon, and

the porous activated carbon was immersed in a 10 wt% sodium silicate solution for forty-eight hours and then immersed in a 30 wt% calcium chloride solution for forty-eight hours.

22. A cooling or temperature control system comprising an adsorption unit in which the composite adsorbent material according to claim 1 is used as an adsorbent and water, methanol and/or ammonia gas as an object to be adsorbed.