Preparation method of chemical heat storage composite material

Abstract

The application discloses a preparation method of a chemical heat storage composite material. The preparation method comprises the following steps: modifying a porous carbon material under a low-temperature plasma in a nitrogen atmosphere, activating the porous carbon material by using nitric acid, adding the obtained nitrogen-doped porous carbon material into a chemical heat storage material solution, performing a hydrothermal reaction, and then performing freeze-drying to obtain the chemical heat storage composite material. The chemical heat storage composite material prepared by the method has the uniform pore structure of the porous carbon material, and can effectively improve the hydration rate of the composite material. In combination with the nitrogen-doping process, the surface hydrophilic property of the porous carbon material is greatly improved. Meanwhile, the porous carbon material has excellent heat conduction performance, and the obtained chemical heat storage composite material also has significantly enhanced heat conduction performance.

Description

Technical Field

[0001] This invention relates to the field of heat storage materials, and more particularly to a method for preparing a chemical heat storage composite material. Background Technology

[0002] With the development of the global economy, energy has become a crucial pillar. Energy conservation and environmental protection have become a focus of attention. Primary energy sources such as coal, oil, and natural gas are consumed rapidly, but their utilization rate is not high. A large amount of medium- and low-temperature waste heat is not effectively utilized. Therefore, effectively utilizing this waste heat, especially in the industrial sector, has become key to energy conservation and emission reduction.

[0003] Chemical thermal energy storage technology, which utilizes reversible chemical reactions to store / release thermal energy, has become a research hotspot in the field of thermal energy storage as an effective means to improve energy utilization and solve the problem of energy supply and demand matching. Compared with traditional sensible and latent heat storage methods, chemical thermal energy storage not only offers an exponential increase in energy density but also avoids problems such as supercooling during material phase changes and phase separation after exothermic cycles. However, current chemical thermal energy storage still suffers from low heat and mass transfer efficiency of the storage material in the reactor, generally slow hydration reaction rates of individual storage components, and easy agglomeration, which seriously restrict the development of chemical thermal energy storage technology.

[0004] Currently, high specific surface area porous carriers are commonly used as the matrix, with chemical heat storage materials loaded onto them. The porous carrier channels disperse the chemical heat storage materials, accelerating the reaction rate of the composite material. Simultaneously, the excellent physical properties of the porous materials enhance the overall heat storage performance of the composite material. Chinese patent application 201811560036.X discloses a composite carbon-based chemical heat storage material, using graphene and / or expanded graphite or expanded graphene-graphene composite carbon materials as the matrix, loaded with chemical heat storage materials such as calcium sulfate, calcium chloride, or magnesium sulfate. Because carbon materials have a high specific surface area, the active components of the chemical heat storage material are dispersed and less prone to agglomeration, which is beneficial to improving the heat storage performance of the material. However, this composite method only utilizes the physical properties of porous carbon materials. Research shows that the adsorption performance of carbon-based materials for water molecules is directly related to the content and distribution of active functional groups on their surface. It is known that surface modification of commercial activated carbon using low-temperature N2 plasma has shown that N2 plasma modification gradually reduces oxygen-containing acidic functional groups and gradually increases nitrogen-containing functional groups, resulting in activated carbon rich in highly hydrophilic groups such as nitro, amine, and amide groups. Therefore, targeting and modifying the surface functional groups of carbon-based materials to enhance their adsorption performance for water molecules is a potentially effective means to improve the hydration performance of composite thermal storage materials. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a method for preparing a chemical thermal storage composite material, which solves the problems of low heat and mass transfer efficiency of thermal storage materials in reactors, generally slow hydration reaction rate of thermal storage components, and easy agglomeration in the prior art.

[0006] To achieve its purpose, the present invention adopts the following technical solution:

[0007] In one aspect of the present invention, a method for preparing a chemically thermally regenerating composite material is provided, comprising the following steps:

[0008] (1) Under a nitrogen atmosphere, porous carbon materials are subjected to low-temperature plasma modification to obtain plasma-modified porous carbon materials.

[0009] (2) The plasma-modified porous carbon material is mixed with nitric acid, and the plasma-modified porous carbon material is activated by nitric acid, filtered, optionally washed with water until neutral and optionally dried to obtain nitrogen-doped porous carbon material.

[0010] (3) The nitrogen-doped porous carbon material is added to a chemical heat storage material solution containing chemical heat storage material to carry out a hydrothermal reaction, and optionally cooled to room temperature;

[0011] (4) The material obtained in step (3) is freeze-dried and then optionally dried under an inert atmosphere to obtain the chemical heat storage composite material.

[0012] In a specific embodiment of the present invention, the specific surface area of ​​the porous carbon material is 250-900 m². 2 / g, preferably 250-300m 2 / g; pore volume is 0.25-0.9cc / g, preferably 0.25-0.29cc / g; average pore size is 3-5nm.

[0013] In a preferred embodiment of the present invention, the porous carbon material is preferably CMK3 (structurally stable) and / or cinder-based carbon fiber (low cost).

[0014] In a specific embodiment of the present invention, the conditions for low-temperature plasma modification in step (1) are as follows: nitrogen flow rate is 10-100 mL / min, for example 20 mL / min, 40 mL / min, 60 mL / min or 80 mL / min, etc.; high-frequency power supply voltage is 35-40V, for example 36V, 37V, 38V or 39V, etc.; modification time is 5-10 min, for example 6 min, 7 min, 8 min or 9 min, etc.

[0015] In a specific embodiment of the present invention, the conditions for the nitric acid activation treatment in step (2) include: a nitric acid concentration of 10%-20% (mass fraction), such as 12%, 14%, 16% or 18%; a volume ratio of porous carbon material to nitric acid of 1:10-20, such as 1:12, 1:14, 1:16 or 1:18; an activation time of 2-4 hours, such as 3 hours; and an activation temperature of 60-80°C, such as 65°C, 70°C or 75°C.

[0016] In a specific embodiment of the present invention, the following steps are included before step (3): adding the chemical heat storage material (preferably vacuum dried first) into water (preferably deionized water) to form the chemical heat storage material solution.

[0017] In a specific embodiment of the present invention, the chemical heat storage material is selected from one or more of LiOH, CaCl2, MgCl2 and MgSO4.

[0018] In a specific embodiment of the present invention, the mass ratio of the nitrogen-doped porous carbon material to the chemical thermal storage material is 0.4:1-4:1, for example, 0.6:1, 0.8:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2:1, 2.5:1, 3:1 or 3.5:1, etc.

[0019] In a specific embodiment of the present invention, the temperature of the hydrothermal reaction in step (3) is 105-120°C, for example 110°C or 115°C; the time is 12-18h, for example 13h, 14h, 15h, 16h or 17h. The hydrothermal reaction is carried out, for example, in a stainless steel high-pressure reactor lined with polytetrafluoroethylene. After thorough mixing, the reactor is heated to the set temperature to start the hydrothermal reaction, and then the reactor is naturally cooled to room temperature.

[0020] In a specific embodiment of the present invention, the freeze-drying temperature in step (4) is -15 to -30°C, for example -20°C or -25°C; the freeze-drying time is 4-20 hours, for example 8 hours, 10 hours, 12 hours, 14 hours, 16 hours or 18 hours; and the drying temperature under an inert atmosphere is 120-150°C, for example 125°C, 130°C, 135°C, 140°C or 145°C. Drying under an inert atmosphere, for example, involves placing the material in a tube furnace and drying it under an argon atmosphere.

[0021] In another aspect of the invention, there is a chemical heat storage composite material obtained by the above preparation method.

[0022] This invention uses porous carbon materials as a matrix, combined with plasma modification and nitric acid activation nitrogen doping processes, to prepare porous carbon materials with a large number of nitrogen-containing functional groups. These materials are then used as a carrier to load chemical heat storage components, forming a nitrogen-doped porous carbon composite chemical heat storage material. The porous carbon materials possess a porous structure and a large specific surface area. The nitrogen doping process employs low-temperature plasma technology (DBD) and nitric acid activation technology to add nitrogen-containing functional groups to the surface of the porous carbon materials through physical and chemical methods, increasing the chemical adsorption of water molecules. Subsequently, a hydrothermal reaction method is used to load the chemical heat storage material into the interior of the nitrogen-doped porous carbon materials.

[0023] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following aspects:

[0024] 1) By using low-temperature plasma technology (DBD) and nitric acid activation technology, nitrogen-containing functional groups are added to the surface of porous carbon materials through physical and chemical methods, which increases the surface hydrophilicity of porous carbon materials and greatly improves the hydration reaction kinetics of chemical composite heat storage materials.

[0025] 2) In a preferred embodiment, a chemical heat storage material is loaded onto a nano-porous carbon material as a matrix. The uniform nanopore structure of the porous carbon material is used to achieve nano-scale dispersion of the chemical heat storage material, thereby improving the hydration rate of the composite material. At the same time, due to the excellent thermal conductivity of the nano-porous carbon material, the thermal conductivity of the composite material is also significantly increased.

[0026] 3) In a preferred embodiment, the preparation method of the present invention can select slag-based carbon fiber as the carbon-based material, which has the characteristics of high specific surface area and abundant pores, and is widely available. Compared with other porous carbon materials, it is inexpensive, which can reduce the overall manufacturing cost of chemical thermal storage materials and help realize the large-scale commercialization of chemical thermal storage technology. Attached Figure Description

[0027] Figure 1 SEM and TEM images of nitrogen-doped CMK3 support, as well as SEM and TEM images of chemical thermal storage composite material prepared with nitrogen-doped CMK3 support and CaCl2 as active component, are presented.

[0028] Figure 2 The comparison of water vapor adsorption performance of CMK3 porous carbon material before and after nitrogen doping is shown;

[0029] Figure 3 The hydration characteristics of the CMK3 porous carbon material itself and the chemical composite heat storage material prepared by using CMK3 porous carbon material as a carrier and CaCl2 as an active component in this invention are shown.

[0030] Figure 4The pore size distribution of the chemical composite thermal storage material prepared by the present invention using slag-based carbon fiber as a carrier and LiOH as an active component is shown.

[0031] Figure 5 The hydration characteristics of pure LiOH material itself and the chemical composite thermal storage material prepared in this invention using slag-based carbon fiber as a carrier and LiOH as an active component are shown. Detailed Implementation

[0032] The method provided by the present invention will be described in further detail below, but the present invention is not limited thereto.

[0033] raw material

[0034] CMK3 porous carbon material / slag-based carbon fiber material: CMK3, Nanjing Jicang Nano; Slag-based carbon fiber material, Beijing Low Carbon Clean Energy Research Institute; Main physical properties: specific surface area of ​​250-900 m² 2 / g, pore volume is 0.25-0.9cc / g, and average pore size is 3-5nm;

[0035] CaCl2 chemical heat storage material: Maclean's Reagent Network; CAS No.: 10043-52-4, solid powder, purity above 99%;

[0036] LiOH chemical heat storage material: Maclean's Reagent Network; CAS No.: 1310-65-2, solid powder, purity above 99%.

[0037] Unless otherwise specified, all other ingredients mentioned in this article are commercially available.

[0038] Test methods

[0039] Adsorption performance and hydration characteristics of water vapor: A thermogravimetric analyzer for water vapor adsorption was used to obtain the amount of water vapor adsorbed by monitoring the mass difference of the material before and after water vapor adsorption in real time. The ratio of mass difference to time is the adsorption rate.

[0040] Pore ​​size distribution: The pore size distribution, pore volume and specific surface area of ​​porous materials were measured using the nitrogen isothermal adsorption-desorption method (BET).

[0041] Unless otherwise specified, other test methods mentioned in this article are conventional methods known in the art.

[0042] Instruments and equipment

[0043] Magnetic stirring device: Shanghai Yangshen Technology Instrument Co., Ltd., Model: DF-101S;

[0044] Vacuum drying oven: Shanghai Shenxian Constant Temperature Equipment Factory, Model: DZF-6050;

[0045] Stainless steel high-pressure reactor: Yanzheng Instruments, Model: YZPR-250;

[0046] Vacuum freeze dryer: Ningbo Xinzhi Biotechnology Co., Ltd., Model: SCIENTZ-12ND.

[0047] Unless otherwise specified, other instruments and equipment mentioned in this article are known in the art or can be reasonably customized by those skilled in the art.

[0048] Example

[0049] Example 1

[0050] 6g of CMK3 porous carbon material was weighed and placed in a low-temperature plasma device. Nitrogen gas was introduced and the flow rate was adjusted to 10mL / min. The high-frequency power supply voltage was adjusted to 35V, and the porous carbon in the reactor was modified for 10min. The plasma-modified CMK3 was mixed with nitric acid (concentration: 10%) at a volume ratio of 1:20 and activated at a set temperature of 80℃ for 2h. After activation, the mixture was filtered, washed with deionized water until neutral, and dried in a vacuum drying oven at 105℃ until completely dry to obtain nitrogen-doped CMK3. 10g of CaCl2 chemical heat storage material was weighed and placed in a vacuum drying oven at 105℃ and -0.1MPa for 4 hours. The dried CaCl2 was then added to 100g of deionized water and stirred thoroughly until homogeneous. 6g of nitrogen-doped CMK3 was weighed and added to the homogeneous CaCl2 solution. The mixture was then placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene and thoroughly mixed. The reactor was heated to 105℃ for a hydrothermal reaction for 12 hours. After the reaction, the reactor was allowed to cool naturally to room temperature. The material was then removed and freeze-dried in a freeze dryer at -30℃ for 10 hours. Finally, the material was dried in a tube furnace at 150℃ under an argon atmosphere for 3 hours to obtain the CMK3-CaCl2 chemical heat storage composite material.

[0051] Figure 1 These are SEM and TEM images of the nitrogen-doped CMK3 support, as well as SEM and TEM images of the chemical thermal storage composite material prepared using nitrogen-doped CMK3 as the support and CaCl2 as the active component. Figure 2 This is a comparison chart of the water vapor adsorption performance of CMK3 before and after nitrogen doping. Figure 3 This is a diagram showing the hydration characteristics of the chemical heat storage composite material prepared according to this invention, using nitrogen-doped CMK3 as a carrier and CaCl2 as the active component. From... Figure 1As can be seen, the composite method provided by this invention can effectively and uniformly load CaCl2 heat storage material onto the surface and pores of nitrogen-doped porous carbon material CMK3, achieving nanoscale dispersion of the chemical heat storage material. Combined with... Figure 2 and Figure 3 It can be seen that the adsorption performance of water vapor by nitrogen-doped CMK3 porous carbon material and the obtained chemical thermal storage composite material is significantly improved.

[0052] Example 2

[0053] 20g of coal slag-based carbon fiber material was weighed and placed in a low-temperature plasma device. An activation atmosphere of nitrogen was introduced, and the nitrogen flow rate was adjusted to 50mL / min. The high-frequency power supply voltage was adjusted to 35V, and the porous carbon in the reactor was modified for 5min. The plasma-modified coal slag-based carbon fiber was mixed with nitric acid (concentration: 20%) at a volume ratio of 1:10 and activated at a set temperature of 60℃ for 4h. After activation, the mixture was filtered, washed with deionized water until neutral, and then placed in a vacuum drying oven and dried at 105℃ until completely dry to obtain nitrogen-doped coal slag-based carbon fiber. 10g of LiOH chemical thermal storage material was weighed and placed in a vacuum drying oven at 105℃ and -0.1MPa for 4 hours. The dried LiOH was then added to 100g of deionized water and stirred thoroughly until homogeneous. 20g of nitrogen-doped coal slag-based carbon fiber was weighed and added to the homogeneous LiOH solution. The mixture was then placed in a stainless steel high-pressure reactor lined with polytetrafluoroethylene and thoroughly mixed. The mixture was heated to 105℃ for a hydrothermal reaction for 18 hours. After the reaction, the reactor was allowed to cool naturally to room temperature. The material was then removed and freeze-dried in a freeze dryer at -30℃ for 10 hours. Finally, the material was dried in a tube furnace at 150℃ under an argon atmosphere for 3 hours to obtain the coal slag-based carbon fiber-LiOH chemical thermal storage composite material.

[0054] Figure 4 This is a pore size distribution diagram of a chemical thermal storage composite material prepared using nitrogen-doped coal slag-based carbon fiber as a carrier and LiOH as the active component. Figure 5 This is a diagram showing the hydration characteristics of a chemical thermal storage composite material prepared using nitrogen-doped coal slag-based carbon fiber as a carrier and LiOH as the active component. From... Figure 4 It can be seen that the nitrogen-doped coal slag-based carbon fiber composite thermal storage material still retains a nanoscale pore size distribution; from Figure 5 It can be seen that the hydration rate of the chemical thermal storage composite material formed by loading LiOH with nitrogen-doped coal slag-based carbon fiber is significantly improved compared with that of pure LiOH material.

[0055] Example 3

[0056] 12g of CMK3 porous carbon material was weighed and placed in a low-temperature plasma device. An activating atmosphere of nitrogen was introduced, and the nitrogen flow rate was adjusted to 100mL / min. The high-frequency power supply voltage was adjusted to 40V, and the porous carbon in the reactor was modified for 5 minutes. The plasma-modified CMK3 porous carbon material was mixed with nitric acid (concentration: 20%) at a volume ratio of 1:15 and activated at a set temperature of 70℃ for 3 hours. After activation, the mixture was filtered, washed with deionized water until neutral, and then placed in a vacuum drying oven and dried at 105℃ until completely dry to obtain nitrogen-doped CMK3 porous carbon material. Weigh 10g of LiOH chemical heat storage material and place it in a vacuum drying oven at 105℃ and -0.1MPa for 4 hours. Then, add the dried LiOH to 100g of deionized water and stir thoroughly until homogeneous. Weigh 12g of nitrogen-doped CMK3 porous carbon material and add it to the homogeneous LiOH solution. Place the solution in a stainless steel high-pressure reactor lined with polytetrafluoroethylene and mix thoroughly. Heat the reactor to 120℃ for a hydrothermal reaction for 12 hours. After the reaction, allow the reactor to cool naturally to room temperature. Remove the material and freeze-dry it in a freeze dryer at -15℃ for 20 hours. Then, place the material in a tube furnace and dry it at 150℃ under an argon atmosphere for 3 hours to obtain the CMK3-LiOH chemical heat storage composite material.

[0057] Although the invention has been described in detail above for illustrative purposes, it should be understood that such detailed description is merely for illustration, and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention, which is defined only by the claims.

Claims

1. A method for preparing a chemical thermal storage composite material, comprising the following steps: (1) Under a nitrogen atmosphere, porous carbon materials are subjected to low-temperature plasma modification to obtain plasma-modified porous carbon materials; (2) The plasma-modified porous carbon material is mixed with nitric acid, and the plasma-modified porous carbon material is activated by nitric acid, filtered, optionally washed with water until neutral and optionally dried to obtain nitrogen-doped porous carbon material. (3) The nitrogen-doped porous carbon material is added to a chemical heat storage material solution containing chemical heat storage material to carry out a hydrothermal reaction, and optionally cooled to room temperature; (4) Freeze-dry the material obtained in step (3), and then optionally dry it under an inert atmosphere to obtain the chemical heat storage composite material; The specific surface area of ​​the porous carbon material is 250-900 m². 2 / g, pore volume is 0.25-0.9 cc / g, and average pore size is 3-5 nm; The conditions for low-temperature plasma modification in step (1) include: nitrogen flow rate of 10-100 mL / min, high-frequency power supply voltage of 35-40 V, and modification time of 5-10 min. The conditions for nitric acid activation treatment in step (2) include: a nitric acid concentration of 10%-20% by mass fraction, a volume ratio of porous carbon material to nitric acid of 1:10-20, an activation time of 2-4 h, and an activation temperature of 60-80℃. The process includes the following steps before step (3): adding the chemical heat storage material to water to form the chemical heat storage material solution; The chemical heat storage material is selected from one or more of LiOH, CaCl2, MgCl2 and MgSO4; The mass ratio of the nitrogen-doped porous carbon material to the chemical thermal storage material is 0.4:1-4:

1. In step (3), the temperature of the hydrothermal reaction is 105-120℃ and the time is 12-18 h.

2. The preparation method according to claim 1, wherein, The porous carbon material is CMK3 and / or cinder-based carbon fiber.

3. The preparation method according to claim 1 or 2, wherein, In step (4), the freeze-drying temperature is -15~-30℃, the freeze-drying time is 4-20 h, and the drying temperature under an inert atmosphere is 120-150℃.

4. A chemically thermally regenerating composite material obtained by the preparation method according to any one of claims 1-3.

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