CN108993414A - Preparation method of MOFs-foam metal composite adsorbent - Google Patents

Abstract

The invention relates to a preparation method of an MOFs-foam metal composite adsorbent, which comprises the following specific steps: mixing MOFs with water, and stirring to obtain a uniform suspension; and filling the suspension into pores of the foam metal by adopting a dip-coating method at normal temperature to prepare the MOFs-foam metal composite adsorbent, wherein the mass fraction of the MOFs in the MOFs-foam metal composite adsorbent is 19-51%. The method has simple preparation process and no need of forming, and the complex three-dimensional compact porous structure of the foam metal improves the heat transfer and mass transfer performance of the material and simultaneously carries out MOF_SThe method has good integration effect, and the physical composition without the addition of the adhesive does not influence the MOFs adsorption performance.

Description

A kind of preparation method of MOFs-metal foam composite adsorbent

technical field

The invention relates to a preparation method of MOFs-metal foam composite adsorbent, which belongs to the preparation technology of new functional materials in the field of chemical industry.

Background technique

Adsorption refrigeration is the use of solid adsorbent to adsorb the adsorbate (refrigerant) to obtain cooling capacity. It can be driven by solar energy or industrial waste heat and other low-grade thermal energy. It is environmentally friendly, low operating cost, simple structure, no noise and wide application range. and many other advantages. Since the 1970s, due to the intensification of the global energy crisis, the adsorption refrigeration technology driven by low-grade heat energy has received extensive attention from scientific and technological workers all over the world.

The commercialization of adsorption refrigeration technology is limited by outstanding problems such as low cooling power per unit of adsorbent mass, large area occupied by adsorption refrigerators, and high cost. Small adsorption capacity, poor thermal conductivity, and long-term cycle structural instability. The adsorbent is usually filled in the adsorption bed with particles, and the contact mode between the adsorbent particles and the surface of the heat exchanger is mainly point-to-surface contact, which leads to a low heat transfer coefficient of the system and affects the cooling power of the system. The development of high-efficiency adsorbents and the enhancement of heat and mass transfer in the adsorption bed are the keys to promote the widespread application of adsorption refrigeration technology.

In order to enhance the heat transfer performance of the adsorption bed for adsorption refrigeration, the adsorbent coating can be formed on the surface of the heat exchanger mainly by in-situ synthesis method or binder at present. The thickness of the adsorbent layer obtained by this method is too thin, and with the As the thickness of the adsorbent layer increases, the thermal conductivity decreases. By in-situ synthesizing composite adsorbents on open-pored and dense metal foams, the thickness of the adsorption layer can be effectively controlled while improving thermal conductivity. In addition, due to its high surface area, metal foam can carry a sufficient amount of adsorbent per unit volume, and due to the strong plasticity of metal foam, it is simple and practical to apply composite adsorbents to adsorption refrigeration systems.

The excellent thermal conductivity of metal foam can greatly enhance the thermal conductivity of the composite adsorbent. On the other hand, due to the complex three-dimensional dense porous structure of metal foam, it can play a good role in integrating the adsorbent without forming, and improve the mass transfer performance of the composite adsorbent. Hyunho Kim et al. simply physically filled MOF-801 powder into metal foam with a porosity of 95% to enhance the thermal conductivity of the adsorbent and applied it to an air water intake device, per kilogram of MOF per day at humidity levels as low as 20%. Can harvest 2.8L of water. HuP et al. prepared molecular sieve/foam aluminum composite adsorbent by percolation method to enhance the heat and mass transfer performance in the adsorption refrigeration process. The thermal conductivity of the material was measured by hot disk method, which can reach 2.89W/mK, which is higher than that of particle accumulation. The thermal conductivity of molecular sieves has increased by about 30 times. Maiti S K et al. directly sintered highly porous copper foam on the outer surface of the copper tube, and wrapped the 4A molecular sieve coating on the surface of the foam copper through in-situ hydrothermal synthesis. The adsorption bed with this structure has a power per unit volume. obvious advantage. Bonaccorsi L et al. synthesized SAPO-34 and SAPO-44 molecular sieves in situ on the surface of foamed aluminum and tested their adsorption properties for water. The results showed that the presence of foamed aluminum carrier had no effect on the adsorption properties of molecular sieves. At present, there are few studies on the application of metal foam in the field of adsorption refrigeration at home and abroad, and most of them combine traditional adsorbents such as molecular sieves with metal foam through in-situ synthesis. The preparation method is complicated and impractical. Preparation of MOFs/metal foam composite adsorbent for adsorption refrigeration by coating method.

Contents of the invention

The purpose of the present invention is to provide a preparation method of MOFs-metal foam composite adsorbent, the preparation method is simple, no binder is added, and the formed adsorbent has good heat transfer performance, good mass transfer performance, water absorption/dehydration cycle Good stability and other characteristics.

The technical scheme of the present invention is as follows: a preparation method of MOFs-metal foam composite adsorbent is provided, the specific steps are as follows: mix MOFs with water, stir to obtain a uniform suspension; use the dip coating method to fill the suspension into the foam at room temperature The MOFs-metal foam composite adsorbent is prepared in the pores of the metal, wherein the mass fraction of MOFs in the MOFs-metal foam composite adsorbent is 19-51%. MOFs are combined with metal foam to prepare composite adsorbents to enhance the thermal conductivity of adsorbents, which can be used in adsorption refrigeration/heat pump processes.

Preferably, the MOFs are any one of MIL-101, MOF-801, UIO-66 or CAU-10.

Preferably, the metal foam is any one of copper foam, aluminum foam, silver foam or nickel foam; the porosity of the foam metal is 90%-98%.

Preferably, MOFs and water are mixed at a mass ratio of 1: (1-5). Preferably, the stirring temperature is 20 to 50°C.

Preferably, the metal foam flakes are pretreated, and the specific steps are: 1) use trichlorethylene to ultrasonically clean the metal foam carrier to remove the oil on the surface of the metal foam; ethylene; 3) wash with deionized water, dry, and weigh the foam metal.

The suspension is filled into the pores of the metal foam by dipping, and the dipping time is preferably 30-180s. Preferably, the composite adsorbent is dried at 50-80°C for 3-8 hours and activated at 100-120°C for 1-4 hours before use.

The invention also provides a method for measuring the thermal conductivity of the composite adsorbent and a method for testing the stability of adsorption/desorption water.

Among them, at a test temperature of 15°C to 150°C, a Hot disk TPS2500S thermal analyzer was used to measure the thermal conductivity of the composite adsorbent prepared with different porosity, and the thermal conductivity of the composite adsorbent can reach 0.28 to 1.16W/(m.K). It is 3 to 20 times the thermal conductivity of MOFs powder under the same test conditions, and the thermal conductivity has been significantly improved. The composite adsorbent is subjected to static aqueous solution adsorption at 25°C to 40°C, and the adsorption/desorption water stability of the composite adsorbent is determined. The composite adsorbent performs 10 times of static aqueous solution adsorption/desorption at 25°C to 40°C, and the static water adsorption capacity remains stable.

The reagents and raw materials used in the present invention are all commercially available.

Beneficial effect:

1. The process of the present invention is simple, does not add binder, does not affect adsorption and saves cost.

2. The composite adsorbent prepared by the present invention has good heat transfer performance and good water absorption/dehydration cycle stability. It can be used in typical closed adsorption air conditioners/heat pumps, and the refrigerants can be water, ethanol, methanol, isobutane, n-butane, propane, etc. It can be regenerated by using medium and low temperature waste heat and solar energy.

Description of drawings

Fig. 1 is the XRD pattern of the composite adsorbent prepared in Example 1.

Fig. 2 is the SEM picture of the composite adsorbent that embodiment 1 makes; Wherein (a) copper foam carrier, (b) MIL-101/copper foam enlarges 50 times, (c) MIL-101/ copper foam enlarges 200 times, (d) 500X magnification of MIL-101/copper foam.

Fig. 3 is the DTA diagram of the composite adsorbent prepared in Example 1.

FIG. 4 is a sample morphology diagram of the composite adsorbent prepared in Example 1.

Fig. 5 is the stability of 10 water absorption/dehydration cycles of the composite adsorbent prepared in Example 7.

Detailed ways

The present invention will be further described below through examples, the purpose of which is only to better understand the content of the present invention, but does not therefore limit the present invention to the scope of the described examples.

SEM instrument model: TM-3000, Hitachi, Japan; TG-DTA thermal analyzer model: JC503-WCT-1D/2D, Baiwan electronic, China; XRD instrument model: Smartlab, Rigaku, Japan, scanning range: 2-20° , step size 0.02, scanning speed: 2°/min, scanning voltage 40kV, current 30Ma; Hot disk thermal constant analyzer model: TPS2500S, Uppsala Hot Disk, Sweden.

Example 1

1. The pretreated copper foam sheet with a porosity of 95% is selected as the metal carrier. Mix MIL-101 and water at a mass ratio of 1:3 and stir at 25°C to obtain a homogeneous suspension. The suspension was filled into the pores of the copper foam by dip coating, the dip coating time was 60 s, and the mass fraction of MIL-101 was 39% (based on the total weight of the composite adsorbent). The composite adsorbent was dried at 60°C for 6h and then activated at 120°C for 2h before use. The XRD spectrum, SEM spectrum, and thermogravimetric analysis diagrams of the composite adsorbent prepared at the mass ratio of suspension MIL-101 to water are 1:3, see Figure 1, Figure 2, and Figure 3, respectively, and Figure 4 shows the composite adsorbent prepared under this condition. Sample topography of the adsorbent. It can be found from Figure 1 that physical recombination does not affect the crystal structure of MIL-101, and the surface of copper foam is not oxidized to copper oxide. Figure 2 shows that MIL-101 and copper foam in the prepared composite adsorbent are closely connected, effectively reducing the contact thermal resistance between the two. Figure 3 shows that the desorption peak temperature of MIL-101 to water is 80°C, the desorption peak temperature of MIL-101/copper foam composite adsorbent to water is 69°C, and the desorption temperature is about 11°C lower.

2. Use the Hot disk TPS2500S thermal analyzer to measure the thermal conductivity of the composite adsorbent. At 25°C and 90°C, the thermal conductivity of the composite adsorbent is 0.87W/(m.K) and 0.95W/(m.K), which are the same Under the conditions, the thermal conductivity of MIL-101 powder is 0.06W/(m.K) and 0.07W/(m.K), respectively, compared with the thermal conductivity of the composite material increased by 15 times and 14 times, respectively. The thermal conductivity of copper is about 400W/(m.K), and the thermal conductivity of the composite adsorbent is greatly improved.

Example 2

1. The pretreated foamed copper sheet with a porosity of 90% is used as the metal carrier. Mix MIL-101 and water at a mass ratio of 1:5, and stir at 50°C to obtain a homogeneous suspension. The suspension was filled into the pores of the copper foam by dip coating, the dip coating time was 180s, and the mass fraction of MIL-101 was 19% (based on the total weight of the composite adsorbent). The composite adsorbent was dried at 80°C for 8h and then activated at 120°C for 4h before use.

2. Use the Hot disk TPS2500S thermal analyzer to measure the thermal conductivity of the composite adsorbent. At 25°C and 90°C, the thermal conductivity of the composite adsorbent is 0.96W/(m.K) and 1.08W/(m.K), which are the same Under the conditions, the thermal conductivity of MIL-101 powder is 0.06W/(m.K) and 0.07W/(m.K), respectively, compared with the thermal conductivity of the composite material increased by 16 times and 15 times, respectively.

Example 3

1. The pretreated foamed copper sheet with a porosity of 98% is used as the metal carrier. Mix MIL-101 and water at a mass ratio of 1:1, and stir at 20°C to obtain a homogeneous suspension. The suspension was filled into the pores of the copper foam by dip coating, the dip coating time was 30s, and the mass fraction of MIL-101 was 51% (based on the total weight of the composite adsorbent). The composite adsorbent was dried at 50°C for 3h and then activated at 100°C for 1h before use.

2. Use the Hot disk TPS2500S thermal analyzer to measure the thermal conductivity of the composite adsorbent. At 25°C and 90°C, the thermal conductivity of the composite adsorbent is 0.36W/(m.K) and 0.45W/(m.K), which are the same Under the conditions, the thermal conductivity of MIL-101 powder is 0.06W/(m.K) and 0.07W/(m.K), respectively, compared with the thermal conductivity of the composite material increased by 6 times and 7 times, respectively.

Example 4

1. The pretreated foamed aluminum sheet with a porosity of 95% is used as the metal carrier. Mix MOF-801 and water at a mass ratio of 1:2.5, and stir at 25°C to obtain a homogeneous suspension. The suspension was filled into the pores of aluminum foam by dip coating, the dip coating time was 60s, and the mass fraction of MOF-801 was 41% (based on the total weight of the composite adsorbent). The composite adsorbent was dried at 60°C for 6h and then activated at 120°C for 2h before use.

2. Use the Hot disk TPS2500S thermal analyzer to measure the thermal conductivity of the composite adsorbent. At 25°C and 90°C, the thermal conductivity of the composite adsorbent is 0.34W/(m.K) and 0.47W/(m.K), which are the same Under the conditions, the thermal conductivity of MOF-801 powder is 0.05W/(m.K) and 0.06W/(m.K), respectively, and the thermal conductivity of the composite material is increased by 7 times and 8 times respectively.

Example 5

1. The pretreated nickel foam sheet with a porosity of 95% is used as the metal carrier. Mix CAU-10 and water at a mass ratio of 1:3, and stir at 25°C to obtain a homogeneous suspension, in which the mass fraction of CAU-10 is 31% (based on the total weight of the composite adsorbent). Fill the suspension into the pores of nickel foam by dipping, and the dipping time is 60s. The composite adsorbent was dried at 60°C for 6h and then activated at 120°C for 2h before use.

2. Use the Hot disk TPS2500S thermal analyzer to measure the thermal conductivity of the composite adsorbent. At 25°C and 90°C, the thermal conductivity of the composite adsorbent is 0.28W/(m.K) and 0.32W/(m.K), which are the same Under the conditions, the thermal conductivity of CAU-10 powder is 0.07W/(m.K) and 0.09W/(m.K), respectively, compared with the thermal conductivity of composite materials increased by 4 times and 3 times respectively.

Example 6

1. Select pretreated foamed silver flakes with a porosity of 95% as the metal carrier. Mix UIO-66 and water at a mass ratio of 1:3, and stir at 25°C to obtain a uniform suspension. The suspension was filled into the pores of aluminum foam by dip coating. The dip coating time was 60 s. Based on the total weight of the composite adsorbent, the mass fraction of the adsorbent MOF-801 was 20%. The composite adsorbent was dried at 60°C for 6h and then activated at 120°C for 2h before use.

2. Use the Hot disk TPS2500S thermal analyzer to measure the thermal conductivity of the composite adsorbent. At 25°C and 90°C, the thermal conductivity of the composite adsorbent is 0.90W/(m.K) and 1.11W/(m.K), which are the same Under the conditions, the thermal conductivity of UIO-66 powder is 0.05W/(m.K) and 0.07W/(m.K), respectively, and the thermal conductivity of the composite material is increased by 18 times and 16 times, respectively.

Example 7

The MIL-101/copper foam composite adsorbent prepared by foam copper with a porosity of 95%, coating suspension MIL-101 and water mass ratios of 1:3 and 1:5 were tested for adsorption/desorption water cycle stability. The change of the static water adsorption of the coating with the number of cycles is shown in Figure 5. From Figure 5, it can be found that when the number of cycles is 10, the coating does not peel off significantly, and the static water adsorption remains stable under different conditions, indicating that it is not necessary to With the addition of a binder, MIL-101 can be well integrated on the copper foam carrier.

Claims (6)

1. a kind of preparation method of MOFs- foam metal compound adsorbent, it is characterised in that: mix MOFs with water, stir To unit for uniform suspension；Suspension filled into the hole of foam metal using dip coating and MOFs- foam metal is prepared answers Adsorbent is closed, wherein the mass fraction of MOFs is 19~51% in MOFs- foam metal compound adsorbent.

2. preparation method according to claim 1, it is characterised in that the MOFs is MIL-101, MOF-801, UIO- Any one in 66 or CAU-10.

3. preparation method according to claim 1, it is characterised in that the foam metal is foam copper, foamed aluminium, bubble Foam silver or nickel foam any one；The porosity of foam metal is 90%~98%.

4. preparation method according to claim 1, it is characterised in that MOFs is with water with mass ratio 1:(1~5) it mixes.

5. preparation method according to claim 1, it is characterised in that whipping temp is 20~50 DEG C.

6. preparation method according to claim 1, it is characterised in that the time of immersion is 30~180s.