A molten salt pyrolysis recovery system and method for phenolic resin composite materials

Abstract

The present invention relates to the field of molten salt pyrolysis technology, and in particular to a molten salt pyrolysis recovery system and method for a phenolic resin composite material. Wherein, the system comprises: a first reaction tank for mixing the phenolic resin composite material to be treated with a target molten salt to pyrolyze the phenolic resin composite material under the external action of heating and electrolysis; a mixing device connected to the first reaction tank for mixing the top molten salt and water floating on the target molten salt liquid surface after the pyrolysis reaction is completed to obtain a mixed solution; a second reaction tank connected to the mixing device for passing carbon dioxide gas into the mixed solution until the pH is 7 to 9 and a phenolic substance is precipitated as a black solid; a first recovery device for separating and recovering the fibers in the mixed solution. The above technical solution can realize the molten salt pyrolysis recovery of phenolic resin composite materials.

Description

Technical Field

[0001] The present invention relates to the technical field of molten salt pyrolysis, and in particular to a molten salt pyrolysis recovery system and method for a phenolic resin composite material. Background Art

[0002] Carbon fiber / phenolic resin composite materials are widely used in aerospace, wind power, automobile and other fields due to their excellent properties of light weight and high strength. However, composite materials will face abandonment after their service life expires. If they are not recycled, it will inevitably lead to a huge waste of resources. At present, the key bottleneck problem restricting the high-value recycling of composite materials is that the three-dimensional cross-linked structure of the resin is difficult to break and the decomposition process is difficult to control. First, the three-dimensional cross-linked structure during the thermal decomposition of the resin will make it difficult for the resin to depolymerize and decompose completely, and it is easy to produce residual carbon, which is mixed with the carbon fiber, significantly reducing the quality of the recycled fiber product. On the other hand, the thermal decomposition process of the resin is disordered, resulting in complex components of the resin decomposition products and low quality, making it difficult to recycle the production of phenolic resin.

[0003] Based on this, there is an urgent need for a molten salt pyrolysis recovery system and method for phenolic resin composite materials to solve the above technical problems. Summary of the Invention

[0004] The embodiments of the present invention provide a molten salt pyrolysis and recovery system and method for a phenolic resin composite material, which can realize the molten salt pyrolysis and recovery of the phenolic resin composite material.

[0005] In a first aspect, an embodiment of the present invention provides a molten salt pyrolysis and recovery system for a phenolic resin composite material, comprising a first reaction tank for mixing the phenolic resin composite material to be treated with a target molten salt to pyrolyze the phenolic resin composite material under the external action of heating and electrolysis;

[0006] a mixing device connected to the first reaction tank, for mixing the molten salt floating on the top of the target molten salt liquid surface after the pyrolysis reaction is completed with water to obtain a mixed solution;

[0007] a second reaction tank connected to the mixing device, for introducing carbon dioxide gas into the mixed solution until the pH reaches 7 to 9 and a phenolic substance is precipitated as a black solid;

[0008] The first recovery device is used to separate and recover the fibers in the mixed solution.

[0009] In a second aspect, an embodiment of the present invention provides a method for recovering a phenolic resin composite material by molten salt pyrolysis, comprising:

[0010] mixing the phenolic resin composite material to be treated with a target molten salt to pyrolyze the phenolic resin composite material under the external action of heating and electrolysis;

[0011] Mixing the molten salt floating on the top of the target molten salt liquid surface after the pyrolysis reaction is completed with water to obtain a mixed solution;

[0012] Adding carbon dioxide gas to the mixed solution until the pH reaches 7 to 9 and a phenolic substance is precipitated as a black solid;

[0013] The fibers in the mixed solution are separated and recovered.

[0014] The embodiment of the present invention provides a molten salt pyrolysis recovery system and method for phenolic resin composite materials. By utilizing the target molten salt to pyrolyze the phenolic resin composite material under the external action of heating and electrolysis, the depolymerization of the three-dimensional cross-linked structure of the phenolic resin can be promoted, thereby promoting the cracking of the resin matrix, making the decomposition product components more homogeneous, the molecular weight distribution more uniform, reducing the residual carbon rate of the resin, and improving the quality of the recycled fiber. At the same time, the skeleton structure of the phenolic substance can be effectively retained, and the phenolic substance can be captured in the molten salt system in a timely manner through the replacement reaction, thereby inhibiting its further deep cracking into small molecular gases and increasing the feasibility of reprocessing the resin decomposition products to produce resin. Therefore, the above technical solution can realize the molten salt pyrolysis recovery of phenolic resin composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 1 is a schematic diagram of a molten salt pyrolysis recovery system for a phenolic resin composite material provided by an embodiment of the present invention;

[0017] Figure 2 The figure is a schematic flow chart of a method for recovering a phenolic resin composite material by molten salt pyrolysis according to an embodiment of the present invention.

[0018] Reference numerals:

[0019] 1-first reaction tank; 2-mixing device; 3-second reaction tank; 4-first recovery device; 5-cooling device; 6-second recovery device. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0021] like Figure 1 As shown, an embodiment of the present invention provides a molten salt pyrolysis recovery system for a phenolic resin composite material, comprising a first reaction tank 1, a mixing device 2, a second reaction tank 3 and a first recovery device 4, wherein:

[0022] The first reaction tank 1 is used to mix the phenolic resin composite material to be treated with the target molten salt, so as to pyrolyze the phenolic resin composite material under the external action of heating and electrolysis;

[0023] The mixing device 2 is connected to the first reaction tank 1 and is used to mix the molten salt and water floating on the top of the target molten salt liquid surface after the pyrolysis reaction is completed to obtain a mixed solution;

[0024] The second reaction tank 3 is connected to the mixing device 2 and is used to introduce carbon dioxide gas into the mixed solution until the pH reaches 7-9 and phenolic substances are precipitated as black solids;

[0025] The first recovery device 4 is used to separate and recover the fibers in the mixed solution.

[0026] In the present embodiment, by utilizing the target molten salt to pyrolyze the phenolic resin composite material under the external action of heating and electrolysis, the three-dimensional cross-linked structure depolymerization of the phenolic resin can be promoted, thereby promoting the cracking of the resin matrix, making the decomposed product components more homogeneous, and the molecular weight distribution more uniform, reducing the residual carbon rate of the resin, and improving the quality of the recycled fiber. At the same time, the skeleton structure of the phenolic substance can be effectively retained, and the phenolic substance can be captured in the molten salt system in time through the replacement reaction, which inhibits its further deep cracking into small molecular gases and increases the feasibility of reprocessing the resin decomposition products to produce resin. Therefore, the above technical solution can realize the molten salt pyrolysis recovery of the phenolic resin composite material.

[0027] In addition, electrolysis can further enhance the conversion reaction. The above technical solution can promote the decomposition rate of the resin pyrolysis process through the coupling of thermal field and electric field, and improve the conversion rate of phenolic substances produced by resin decomposition and the reaction of alkaline molten salt to form organic sodium salt. If too much carbon dioxide gas is introduced, aromatic phenolic acid will be generated during the reaction, thereby affecting the purity of phenolic substances. If insufficient carbon dioxide gas is introduced, the phenolic substances will not be completely precipitated, resulting in waste.

[0028] It should be noted that the top fused salt is water-soluble. After being dissolved in water, it passes into carbon dioxide, which not only can separate out phenols, but also can trap carbon dioxide, thereby improving carbon reduction potential. If other acidic gases are passed into mixed solutions, such as sulfur dioxide and hydrogen chloride gas, these acidic gases and sodium phenolate will undergo complex reaction, which will affect the purity of phenols. Therefore, in the present invention, carbon dioxide is selected as the acidic gas for separating out phenols, while carbon dioxide can also be trapped.

[0029] It is understood that the precipitated phenolic substance is pure phenol, which can be dissolved in an organic solvent (such as acetone, dichloromethane, etc.) to obtain a phenolic substance-rich solution, wherein the phenolic substance can be used for recycling to produce phenolic resin.

[0030] In some embodiments, a mixture containing fiber and sodium phenolate is taken out from the top of the first reaction tank, and fiber is fished out from the mixture and subjected to shaking and water washing to recover the fiber.

[0031] In one embodiment of the present invention, the target molten salt is sodium hydroxide and sodium carbonate, the heating temperature of the target molten salt is 350-500°C, and the electrolysis current density of the target molten salt is 150-250 mA / cm 2 , the electrode materials are all made of graphite materials.

[0032] In this example, the depolymerization of the three-dimensional cross-linked structure of the phenolic resin is promoted by the catalytic action of alkali metal cations in a molten salt system. Alkaline sodium salts are used to replace the hydroxyl groups on the phenol with the sodium in the sodium salt to produce sodium phenoxide. The organic component in the top molten salt is sodium phenoxide, which is black in color. Since sodium phenoxide is insoluble in the molten salt and has a lower density than the molten salt, it floats on the upper surface of the molten salt.

[0033] If the electrolysis parameters exceed the given range, carbon deposition may occur (CO3 2- +4e - =C+3O 2- If the electrolysis parameters are below the specified range, the resin decomposition may not be effectively promoted. The molten salt temperature should be controlled between 350°C and 500°C. If the temperature is too high, the organic sodium phenolate may condense and produce carbon. If the temperature is too low, the resin may not be fully cracked and the conversion of the molten salt to sodium phenolate may be limited. The molten salt reaction tank should be controlled to an inert atmosphere; an oxidizing atmosphere may damage the fiber.

[0034] It should be noted that, in the molten salt system of the present invention, with sodium hydroxide as main body, a small amount of sodium carbonate is added to reduce the fusing point of fused salt, by controlling the temperature and molten salt system of the molten salt system, the three-dimensional structure of phenolic resin can be destroyed, and simultaneously, phenolic substance is trapped in the system in time by replacement reaction, namely the skeleton structure of phenolic substance is retained, thus increasing the feasibility of resin decomposition product reprocessing and producing resin. However, conventional pyrolysis technology is usually adopted for the pyrolysis technology of phenolic resin composite material at present, which not only destroys the three-dimensional structure of phenolic resin, but also destroys the skeleton structure of phenolic substance, namely further depth cracking is into small molecule gas.

[0035] In one embodiment of the present invention, a molten salt pump (not shown in the figure) and a cooling device 5 are connected between the first reaction tank 1 and the mixing device 2. The molten salt pump is used to extract the top molten salt into the mixing device 2, and the cooling device 5 is used to cool the extracted top molten salt.

[0036] In this embodiment, the phenolic substances generated by the initial decomposition of the resin react with the alkaline molten salt to form sodium phenolate, which floats on the surface of the molten salt. The top molten salt is then extracted using a molten salt pump. When the molten salt pump extracts the upper liquid surface, the extraction is complete when no visible black material is visible at the upper liquid surface. Because the extracted top molten salt is at a high temperature, directly dissolving it in water would cause the molten salt to splash. Therefore, cooling it to below 100°C prevents the addition of water to the extracted top molten salt, which would cause it to splash.

[0037] In one embodiment of the present invention, an atomizer (not shown) is provided in the second reaction tank 3, which is used to atomize the mixed solution to obtain an atomized liquid, and the flow ratio of the atomized liquid to the carbon dioxide gas is 3:2 to 5:2.

[0038] In this embodiment, the remaining sodium phenolate is dissolved in water and then atomized, and carbon dioxide gas is introduced simultaneously to maintain a certain flow ratio between the atomized liquid and the carbon dioxide gas. On the one hand, the gas-liquid reaction can be changed to a gas-gas reaction, which increases the contact time between the two. While ensuring that the replacement reaction can fully occur, the intake of carbon dioxide gas and solution is controlled, thereby preventing excessive acidification from generating aromatic phenolic acid impurities.

[0039] In one embodiment of the present invention, a second recovery device 6 is further included. The second recovery device 6 is used to sequentially dry, dehydrate, and separate impurities from the gas generated by pyrolysis to obtain high-purity hydrogen.

[0040] In this embodiment, the hydrogen concentration in the gas product generated by resin decomposition is higher than 80%, and high-purity hydrogen can be obtained through further separation.

[0041] In one embodiment of the present invention, a density detector (not shown in the figure) is provided in the first reaction tank 1, and the density detector is used to detect the density of the target molten salt during the pyrolysis reaction;

[0042] When the density of the target molten salt exceeds the preset value, the target molten salt is discharged; the preset value is 1.9 to 2 g / cm 3 The discharged target molten salt is used to react with the introduced carbon dioxide gas to produce sodium carbonate.

[0043] In this embodiment, the density of the molten salt under the initial conditions is ≤1.781g / cm 3 During the reaction, NaOH is continuously consumed to generate sodium carbonate. When the density of the molten salt system is detected to be ≥1.95g / cm 3 When the molar amount of sodium carbonate is greater than or equal to 40%, the molten salt system is not active enough to react, so the waste molten salt is discharged. Carbon dioxide gas is further introduced into the discharged waste molten salt (i.e., sodium hydroxide and sodium carbonate) to convert it all into sodium carbonate, thereby obtaining pure sodium carbonate for utilization, and further capturing carbon dioxide gas.

[0044] It should be pointed out that the specific structures of the above-mentioned entity devices are not shown in the embodiments of the present invention, but those skilled in the art can understand that the structures with the functions of each entity device are within the protection scope of the present invention based on their functions, and the specific structures of each entity device are not described in detail here.

[0045] In addition, if Figure 2 As shown, an embodiment of the present invention further provides a molten salt pyrolysis and recovery method for a phenolic resin composite material, comprising:

[0046] Step S1, mixing the phenolic resin composite material to be treated with a target molten salt, so as to pyrolyze the phenolic resin composite material under the external action of heating and electrolysis;

[0047] Step S2: mixing the top molten salt floating on the target molten salt liquid surface after the pyrolysis reaction is completed with water to obtain a mixed solution;

[0048] Step S3, introducing carbon dioxide gas into the mixed solution until the pH reaches 7-9, and a phenolic substance is precipitated as a black solid;

[0049] Step S4: separating and recovering the fibers in the mixed solution.

[0050] In one embodiment of the present invention, the target molten salt is sodium hydroxide and sodium carbonate, the heating temperature of the target molten salt is 350-500°C, and the electrolysis current density of the target molten salt is 150-250 mA / cm 2 .

[0051] In one embodiment of the present invention, step S2 may specifically include:

[0052] Extract the top molten salt floating on the target molten salt liquid surface after the pyrolysis reaction is completed, until there is no black matter on the upper liquid surface of the target molten salt;

[0053] Cooling the extracted molten salt;

[0054] The cooled molten salt is mixed with water.

[0055] In one embodiment of the present invention, step S3 may specifically include:

[0056] atomizing the mixed solution to obtain an atomized liquid;

[0057] Carbon dioxide gas is introduced into the atomized liquid; wherein the flow ratio of the atomized liquid to the carbon dioxide gas is 3:2 to 5:2.

[0058] In one embodiment of the present invention, the above method further includes:

[0059] The gas produced by pyrolysis is dried, dehydrated and impurities separated in sequence to obtain high-purity hydrogen.

[0060] In one embodiment of the present invention, the above method further includes:

[0061] Detecting the density of the target molten salt during the pyrolysis reaction;

[0062] When the density of the target molten salt exceeds the preset value, the target molten salt is discharged; the preset value is 1.9 to 2 g / cm 3 ;

[0063] Carbon dioxide gas is introduced into the discharged target molten salt to convert all the target molten salt into sodium carbonate.

[0064] It can be understood that the method embodiment and system embodiment provided by the present invention are based on the same inventive concept and have the same beneficial effects. The beneficial effects of the method embodiment will not be described in detail here.

[0065] It should be noted that, in this article, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprising a ..." do not exclude the presence of other identical factors in the process, method, article or device comprising the elements.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A molten salt pyrolysis recovery system for phenolic resin composite materials, characterized in that: A first reaction tank is used to mix the phenolic resin composite material to be treated with a target molten salt, and to pyrolyze the phenolic resin composite material under the external action of heating and electrolysis to promote the depolymerization of the three-dimensional cross-linked structure of the phenolic resin, thereby promoting the cracking of the resin matrix, so that the decomposition product components are homogeneous and the molecular weight distribution is uniform, while retaining the skeleton structure of the phenolic substance, using an alkaline sodium salt to replace the hydroxyl group on the phenol with the sodium in the sodium salt to obtain a sodium phenolate, so that the phenolic substance is trapped in the molten salt system through the replacement reaction, and the phenolic substance is suppressed from further cracking into small molecular gases; a mixing device connected to the first reaction tank, for mixing the molten salt floating on the top of the target molten salt liquid surface after the pyrolysis reaction is completed with water to obtain a mixed solution; a second reaction tank connected to the mixing device, for introducing carbon dioxide gas into the mixed solution until the pH reaches 7 to 9 and a phenolic substance is precipitated as a black solid; a first recovery device, for separating and recovering the fibers in the mixed solution; The target molten salt is sodium hydroxide and sodium carbonate, the heating temperature of the target molten salt is 350-500°C, and the electrolysis current density of the target molten salt is 150-250 mA / cm 2 .

2. The system according to claim 1, wherein: A molten salt pump and a cooling device are connected between the first reaction tank and the mixing device. The molten salt pump is used to extract the top molten salt into the mixing device, and the cooling device is used to cool the extracted top molten salt.

3. The system according to claim 1, wherein: The second reaction tank is provided with an atomizer, and the atomizer is used to atomize the mixed solution to obtain an atomized liquid. The flow ratio of the atomized liquid to the carbon dioxide gas is 3:2 to 5:

2.

4. The system according to any one of claims 1 to 3, characterized in that It also includes a second recovery device, which is used to sequentially dry, dehydrate and separate impurities from the gas generated by pyrolysis to obtain high-purity hydrogen; and / or, A density detector is provided in the first reaction tank, and the density detector is used to detect the density of the target molten salt during the pyrolysis reaction; When the density of the target molten salt exceeds a preset value, the target molten salt is discharged; wherein the preset value is 1.9 to 2 g / cm 3 The discharged target molten salt is used to react with the introduced carbon dioxide gas to generate sodium carbonate.

5. A method for recovering phenolic resin composite materials by molten salt pyrolysis, characterized in that: include: The phenolic resin composite material to be treated is mixed with a target molten salt, and the phenolic resin composite material is pyrolyzed under the external action of heating and electrolysis to promote the depolymerization of the three-dimensional cross-linked structure of the phenolic resin, thereby promoting the cracking of the resin matrix, so that the decomposition product components are homogeneous and the molecular weight distribution is uniform, while retaining the skeleton structure of the phenolic substance, using an alkaline sodium salt to replace the hydroxyl group on the phenol with the sodium in the sodium salt to obtain a sodium phenolate, so that the phenolic substance is trapped in the molten salt system through the replacement reaction, and the phenolic substance is suppressed from further cracking into small molecular gases; Mixing the molten salt floating on the top of the target molten salt liquid surface after the pyrolysis reaction is completed with water to obtain a mixed solution; Adding carbon dioxide gas to the mixed solution until the pH reaches 7 to 9 and a phenolic substance is precipitated as a black solid; separating and recovering the fibers in the mixed solution; The target molten salt is sodium hydroxide and sodium carbonate, the heating temperature of the target molten salt is 350-500°C, and the electrolysis current density of the target molten salt is 150-250 mA / cm 2 .

6. The method according to claim 5, characterized in that The step of mixing the molten salt and water floating on the top of the target molten salt liquid surface after the pyrolysis reaction is completed comprises: extracting the molten salt floating on the top of the target molten salt liquid surface after the pyrolysis reaction is completed, until there is no black matter on the upper liquid surface of the target molten salt; Cooling the extracted molten salt; The cooled molten salt is mixed with water.

7. The method according to claim 5, characterized in that The step of introducing carbon dioxide gas into the mixed solution comprises: atomizing the mixed solution to obtain an atomized liquid; Carbon dioxide gas is introduced into the atomized liquid; wherein the flow ratio of the atomized liquid to the carbon dioxide gas is 3:2 to 5:

2.

8. The method according to any one of claims 5 to 7, characterized in that Also includes: The gas generated by pyrolysis is dried, dehydrated and impurities separated in sequence to obtain high-purity hydrogen; and / or, Also includes: detecting the density of the target molten salt during the pyrolysis reaction; When the density of the target molten salt exceeds a preset value, the target molten salt is discharged; wherein the preset value is 1.9 to 2 g / cm 3 ; Carbon dioxide gas is introduced into the discharged target molten salt to convert all the target molten salt into sodium carbonate.

Images