A method for separating waste photovoltaic module glass and film using a recyclable green solvent

Abstract

The present invention belongs to the field of photovoltaic module recycling technology, and specifically relates to a method for separating the glass and film of waste photovoltaic modules using a recyclable green solvent. The method comprises the following steps: 1) disassembling and cutting the waste photovoltaic modules; 2) washing the modules with an anhydrous ethanol solution; 3) placing the modules in an inner container, pouring in a citric acid aqueous solution, and heating the reaction at 180-200°C for 0.80-1.2 hours to obtain a module consisting of a back EVA film and a backplane, a front EVA film and a silicon wafer, and tempered glass; 4) separating the module from the tempered glass to obtain the glass and the remaining modules. The present invention uses a citric acid aqueous solution, which, by heating at a relatively low temperature, can separate the glass from the front EVA and simultaneously separate the back EVA from the silicon wafer, without swelling the EVA or damaging the silicon wafer or the metal on the silicon wafer surface.

Description

Technical Field

[0001] The invention belongs to the technical field of photovoltaic module recycling, and in particular relates to a method for separating waste photovoltaic module glass and adhesive film using a recyclable green solvent. Background Art

[0002] Photovoltaic modules typically have a lifespan of 20 to 25 years, meaning a significant number of used modules will be scrapped over the next few years. Used modules contain valuable materials such as high-purity silicon, silver, and aluminum. Failure to efficiently recycle these materials will not only result in a waste of resources but also negatively impact the environment. Therefore, developing efficient and environmentally friendly recycling technologies is of great economic and environmental significance.

[0003] Traditional PV module recycling methods primarily include mechanical, thermal, and chemical treatments. Mechanical treatment typically involves crushing and screening, but it cannot efficiently separate high-purity cells. Thermal treatment involves high-temperature incineration, which not only consumes a lot of energy but also produces harmful gases and significant carbon emissions. While chemical treatment methods offer higher recovery rates, they typically require the use of strong acids, bases, or organic solvents, posing environmental and operational safety risks.

[0004] Currently, the recycling and processing methods for photovoltaic modules mainly include physical methods, mechanical methods, and thermal decomposition methods. The physical method effectively recycles glass, aluminum frames, plastics, and silicon materials through mechanical separation, crushing, and screening. Its advantages are simple operation and mature technology, but it has the limitations of dust, noise, and the recovery of high-purity materials. The mechanical method combines crushing, screening, and magnetic separation technologies to process large-scale photovoltaic modules. Although equipment improvements have improved separation efficiency and purity, it is prone to secondary pollution and is not effective in separating composite materials. The thermal decomposition method uses high temperatures to separate organic and inorganic substances and recover high-purity metals and silicon materials. However, high-temperature operation produces harmful gases and exhaust gases, and high energy consumption and equipment costs limit its large-scale application.

[0005] In exploring technologies for recycling and processing photovoltaic modules, efficiency, environmental friendliness, and economic costs must be comprehensively considered to achieve the healthy and sustainable development of the photovoltaic industry. In contrast, citric acid solution offers significant environmental advantages as a green solvent method for processing photovoltaic modules. The citric acid solution separates the EVA on the back and the encapsulated tempered glass, recycling the glass from the module. The process is gentle and produces no harmful gases. Citric acid can be recycled multiple times, reducing processing costs and the environmental burden. The simple operation, high processing efficiency, and no harmful gas emissions make it more environmentally friendly. Overall, compared to traditional methods, the ethanol and sodium carbonate green solvent method offers significant advantages in terms of environmental friendliness, processing efficiency, and cost-effectiveness. Furthermore, citric acid treatment does not cause EVA to swell, allowing for the non-destructive recycling of silicon wafers. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention provides a method for separating waste photovoltaic module glass and adhesive film using a recyclable green solvent. This method utilizes citric acid solution as a green solvent to efficiently separate the EVA and glass from the back of photovoltaic modules, recovering the adhesive film and other valuable materials, thereby achieving environmentally friendly and economical material reuse. This method allows for simple, convenient, and efficient separation of EVA from modules and recovery of the module glass.

[0007] The technical solutions provided by the present invention are as follows:

[0008] A method for separating waste photovoltaic module glass and adhesive film using a recyclable green solvent comprises the following steps:

[0009] 1) Dismantle the waste photovoltaic modules and cut them with an angle grinder;

[0010] 2) washing the assembly obtained in step 1) with an anhydrous ethanol solution to obtain a small photovoltaic assembly without the aluminum frame and the junction box;

[0011] 3) placing the assembly obtained in step 2) in an inner container, pouring a citric acid aqueous solution into it, and heating the reaction at 180-200° C. for 0.80-1.2 hours to obtain an assembly consisting of a back EVA film and a back sheet, an assembly consisting of a front EVA film and a silicon wafer, and tempered glass;

[0012] 4) Separating the components obtained in step 3) from the tempered glass to obtain the glass and the remaining components respectively.

[0013] In the above technical solution:

[0014] By using a citric acid aqueous solution and heating at a relatively low temperature, the glass and the front EVA can be separated, and the back EVA and the silicon wafer can be separated at the same time without swelling the EVA and damaging the silicon wafer or the metal on the surface of the silicon wafer.

[0015] In the above technical solution, after step 3), the bonding between the front EVA film and the tempered glass fails. If the two are not directly separated after the treatment of step 3), they can be separated by a slight separation operation.

[0016] Specifically, in step 3), the concentration of the citric acid aqueous solution is 1.4 mol / L to 1.6 mol / L.

[0017] Specifically, in step 3): pour the citric acid aqueous solution until the component is immersed.

[0018] Specifically, in step 3), heating the reaction at 180° C. for 1 hour.

[0019] Specifically, in step 3), the separated back EVA layer is a complete EVA film.

[0020] Specifically, in step 3), the remaining components are rinsed and the excess water is dried naturally, and then step 4) is performed.

[0021] Specifically, in step 4): the recovered silicon wafer has silver grid lines.

[0022] Specifically, in step 4), the silicon wafers in the remaining components are whole silicon wafers.

[0023] In the above technical solution, during the chemical immersion process, EVA will not swell and the silicon wafer will not be corroded, so the silicon wafer will not be broken.

[0024] In the above technical solution, neither the physical splitting nor the chemical soaking steps will corrode the silver grid lines.

[0025] Furthermore, the method further comprises step 5) which can be repeated multiple times: recovering the citric acid aqueous solution and repeating steps 1) to 4).

[0026] In the above technical solution, the citric acid aqueous solution can be reused. For example, after being reused 10 times, the concentration of the citric acid aqueous solution remains at 80% to 90%, and the volume remains at about 90%.

[0027] The present invention also provides a silicon wafer separated according to the method.

[0028] Beneficial effects of the present invention:

[0029] 1) The chemical solvents used in the present invention are all green and pollution-free solvents, and have little impact on the natural environment;

[0030] 2) The chemical solvent used in the present invention can be recycled repeatedly, greatly reducing the cost of the recycling process;

[0031] 3) The advantage of this invention over existing technologies is that existing methods for separating EVA films mostly remove the film through pyrolysis at around 500°C, which reaches relatively high temperatures during the recycling process and produces some toxic gases. This invention can avoid the excessive energy consumption and environmental pollution problems associated with pyrolysis recovery of battery cells.

[0032] 4) This method uses a wet method to separate EVA from photovoltaic modules and has a good effect in purifying the battery cells. It not only avoids the pollution of the environment caused by pyrolysis of EVA, but also can recycle and reuse silicon wafers, turning waste into treasure, improving economic value, and has strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a structural diagram of the photovoltaic module in Example 1.

[0034] Figure 2 This is a diagram of the remaining components after the back EVA layer is separated in Example 1, wherein the left part is the assembly of the front EVA film and the silicon wafer, and the right part is the assembly of the back EVA film and the backboard.

[0035] Figure 3 This is a picture of the glass recovered in Example 1.

[0036] Figure 4 This is a cross-sectional SEM image of the component before processing.

[0037] Figure 5 This is the cross-sectional EDS diagram of the component before processing. DETAILED DESCRIPTION

[0038] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0039] Unless otherwise specified, the test methods used in the examples of the invention are conventional methods; the materials and reagents used are commercially available reagents and materials unless otherwise specified.

[0040] Example 1

[0041] A method for recycling waste photovoltaic module cells using a green solvent method comprises the following steps:

[0042] 1) Cutting photovoltaic panels

[0043] Remove the aluminum frame and junction box from the retired photovoltaic panels, place the remaining photovoltaic panels on an open space, and use an angle grinder to slowly cut several 2×2cm components.

[0044] 2) Separate the back EVA layer with citric acid

[0045] ① Use a medicine spoon to remove 28.8g of solid from the anhydrous citric acid solid.

[0046] ② Place 28.8 g of anhydrous citric acid solid in a beaker and dilute to volume in a 100 mL volumetric flask.

[0047] ③ Place the 2×2 cm component processed in step 1) into a tetrafluoroethylene liner.

[0048] ④ Pour 25mL of the citric acid liquid adjusted to volume in ② into the inner container.

[0049] ⑤Put the inner container after treatment in ④ into a hydrothermal kettle with a pressure less than 3Mpa.

[0050] ⑥ Preferably, the hydrothermal kettle is placed in an oven and kept at 200° C. for 1 hour.

[0051] ⑦ Take out the hydrothermal reactor after the reaction in step ⑥, open the tetrafluoroethylene liner, and take out the components with tweezers.

[0052] ⑧Step ⑦ Use tweezers to remove and manually separate the EVA on the back to obtain the remaining components and the remaining citric acid liquid in the liner.

[0053] The separated components were washed and placed on a culture dish containing a 2×2 cm component consisting of a back EVA film and a backboard, and a 2×2 cm component consisting of a front EVA film and a silicon wafer.

[0054] 3) Recycling component glass

[0055] ① Pour the liquid in the tetrafluoroethylene liner and the battery cells in step 2) into the beaker.

[0056] ② Use tweezers to pick up the glass on the component.

[0057] The above steps yield a photovoltaic module consisting of a front EVA film and silicon wafer, a back EVA film and backsheet, and tempered glass. The front EVA film and silicon wafer can be further separated using other techniques.

[0058] Figure 1 This is a structural diagram of the photovoltaic module in Example 1.

[0059] Figure 2 This image shows the remaining components after the back EVA layer is removed from Example 1. The left portion shows the front EVA film and silicon wafer assembly, while the right portion shows the back EVA film and backsheet assembly. The cracks are caused by manual peeling or chipping. Other than these cracks, there are no cracks due to EVA swelling.

[0060] Figure 3 This is the glass recovered in Example 1, which is mainly transparent.

[0061] Figure 4 This is a cross-sectional SEM of the component before treatment.

[0062] Figure 5 This is an EDS image of a cross-section of a module before treatment. The sphere in the middle of the image represents aluminum. The mechanism of action of citric acid is to break the chemical bond between the aluminum on the solar cell and the EVA film on the back, causing the back EVA film to separate from the solar cell.

[0063] Example 2

[0064] The method for recycling waste photovoltaic module cells is similar to that of Example 1, except that only anhydrous ethanol is used to separate the EVA layers. The results show that although the silicon wafer and the back EVA layer can be separated, as well as the silicon wafer and the front EVA layer, the ethanol is almost completely consumed after one use.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for separating waste photovoltaic module glass and film using a recyclable green solvent, characterized in that: The following steps are involved: 1) Dismantle the old photovoltaic modules and cut them with an angle grinder; 2) washing the module obtained in step 1) with an anhydrous ethanol solution to obtain a small photovoltaic module without the aluminum frame and the junction box; 3) placing the assembly obtained in step 2) in an inner container, pouring in a citric acid aqueous solution, and heating at 180-200° C. for a reaction for 0.80-1.2 hours to obtain an assembly consisting of a back EVA film and a back sheet, an assembly consisting of a front EVA film and a silicon wafer, and tempered glass; 4) Separating the components obtained in step 3) from the tempered glass to obtain the glass and the remaining components.

2. The method for separating waste photovoltaic module glass and film using a recyclable green solvent according to claim 1, characterized in that: In step 3), the concentration of the citric acid aqueous solution is 1.4 mol / L to 1.6 mol / L.

3. The method for separating waste photovoltaic module glass and film using a recyclable green solvent according to claim 1, characterized in that: Step 3): Pour the citric acid solution into the submerged components.

4. The method for separating waste photovoltaic module glass and film using a recyclable green solvent according to claim 1, characterized in that: In step 3), the reaction was heated at 180° C. for 1 hour.

5. The method for separating waste photovoltaic module glass and film using a recyclable green solvent according to claim 1, characterized in that: In step 3), the separated back EVA film is a complete EVA film.

6. The method for separating waste photovoltaic module glass and film using a recyclable green solvent according to claim 1, characterized in that: In step 3), the components and tempered glass obtained in step 3) are rinsed and the excess water is dried naturally, and then step 4) is performed.

7. The method for separating waste photovoltaic module glass and film using a recyclable green solvent according to claim 1, characterized in that: In step 4): the silicon wafers in the remaining components are whole silicon wafers.

8. The method for separating waste photovoltaic module glass and film using a recyclable green solvent according to claim 1, characterized in that: In step 4), the recovered silicon wafer has silver grid lines.

9. The method for separating waste photovoltaic module glass and film using a recyclable green solvent according to any one of claims 1 to 8, characterized in that: The method further comprises step 5) which can be repeated multiple times): recovering the citric acid aqueous solution and repeating steps 1) to 4).

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