A method for the separation of the eva layer in end-of-life photovoltaic (PV) modules

Abstract

This invention relates to a process for purifying intact glass, which has been separated from PV modules using the hot-knife technique and has EVA residues on its surface, from EVA using an environmentally friendly chemical process.

Description

[0001] A METHOD FOR THE SEPARATION OF THE EVA LAYER IN END-OF-LIFE PHOTOVOLTAIC (PV) MODULES

[0002] TECHNICAL FIELD

[0003] The invention relates to a process for purifying intact glass, which has been separated from end-of-life PV modules using the hot-knife technique and has EVA residues on its surface, from EVA using an environmentally friendly chemical process.

[0004] PRIOR ART

[0005] The recycling of photovoltaic (PV) panels is a critical process for reducing the environmental impact of sustainable energy technologies. PV panels typically have a lifespan of 25-30 years, at the end of which they generate a large amount of waste. Recycling enables this waste to be re-evaluated without harming the environment. The recycling process for PV panels involves separating the panels into their components and converting these components into reusable materials. Furthermore, these recycling processes contribute to the conservation of natural resources and the improvement of waste management. The recycling of photovoltaic panels is a significant example of the application of circular economy principles in the energy sector.

[0006] Various methods for the recovery of components from end-of-life silicon photovoltaic modules are available in the literature. These methods generally include mechanical, thermal, and chemical processes. Mechanical processes include decomposition and separation, crushing, and grinding methods. In these processes, PV modules are dismantled to separate glass, metal frames, and other components, and then the silicon cells and other components are broken into smaller pieces. Thermal processes, on the other hand, encompass thermal separation (pyrolysis) and thermal vacuum processes. In these methods, modules are heated to high temperatures to ensure the combustion of organic components, and organic components are vaporized by applying a thermal process under a vacuum. Chemical processes consist of chemical leaching and electrolytic processes. Silicon cells are cleaned using chemical solutions, and metallic components are dissolved and separated using an electric current. Finally, hybrid methods combine mechanical, thermal, and chemical processes to create efficient recycling processes. All of these methods have been developed with the aim of achieving high-yield recovery from end-of-life PV modules and minimizing environmental impacts.

[0007] A silicon PV module consists of "Glass-EVA-Solar cell-EVA-Backsheet" components, and various methods exist for the disposal and recovery of these components. The glass component is separated from the modules by mechanical crushing and grinding processes to be made reusable or is purified from the coatings on it by heating through a thermal process. EVA (Ethylene-Vinyl Acetate) layers can be separated from other components by being vaporized through thermal separation or dissolved with chemical solvents. Solar cells are cleaned using hydrofluoric acid or nitric acid by the chemical leaching method, or their metal components are dissolved and separated by an electrolytic process. The backsheet, on the other hand, is physically separated from the modules by mechanical separation or can be recovered by being processed with chemical solutions. Thus, the components of solar panels are effectively recovered without harming the environment, and the sustainability and environmental impacts of photovoltaic panels are minimized. New studies are continuously being conducted in the literature to increase the efficiency and reduce the costs of these methods.

[0008] There are several technical difficulties in separating Ethylene-Vinyl Acetate (EVA) layers from solar panels. EVA is a polymer with high thermal stability, and therefore, its separation by thermal processes is difficult as it requires high temperatures, which can damage other components. The EVA layer, being resistant to many chemical solvents due to its chemical resistance, is difficult to separate by chemical methods, and the use of strong chemicals can lead to environmental and safety problems. The tight adhesion of EVA to solar cells and glass surfaces makes its separation by mechanical methods difficult, and the methods applied to remove this adhesion are often time-consuming and require a great deal of energy. The multi-layered and complex structure of the EVA used in solar panels makes its homogeneous separation difficult and requires more processing. The management and disposal of waste products generated during separation is also a significant challenge, as waste from chemical and thermal processes can cause environmental pollution. These technical difficulties complicate the separation of EVA from solar panels and the recycling process, thus requiring the development of efficient and environmentally friendly separation methods.

[0009] The "hot-knife" technique, used for separating Ethylene-Vinyl Acetate (EVA) layers from solar panels, is an effective method developed to facilitate this challenging process. This technique involves cutting and separating the EVA layer using a blade heated to high temperatures. The hot-knife method offers a precise and clean cut despite the adhesive properties of EVA. With this method, the blade is heated to the melting point of EVA and then carefully cut, allowingthe solar cells and other components to be separated without damage. During this process, the heat applied by the hot knife softens the EVA, making it easier to cut, while also preventing the EVA from burning or degrading. The hot-knife technique requires less energy compared to mechanical and chemical methods and is less harmful to the environment. Furthermore, this method ensures the homogeneous and controlled separation of EVA, thereby preservingthe quality of the recycled material. The hot-knife technique is used in the recycling processes of solar panels for separating the glass intact without breaking, thus offering both economically and environmentally sustainable solutions.

[0010] The use of the hot-knife method for separating EVA from solar panels presents some significant disadvantages. Firstly, although the hot-knife method can mechanically separate the glass from other components, it leaves a considerable amount of EVA residue on the glass surface. These residues can remain on the glass surface and may require further chemical or mechanical cleaning. Additionally, vapors and gases that may be released during the application of the hot-knife method can create environmental pollution if not managed properly. Since EVA residues are present on the separated glass surface, if used as a raw material in a furnace, the EVA polymer will burn inside the furnace, changing the furnace's internal atmosphere, which will cause corrosion in the refractories within the furnace and serious quality problems by causing the resulting glass to be out-of-spec. Therefore, since the glass cannot be reused as a whole or as cullet with EVA residues, there is a need to remove the EVA from the surface.

[0011] The fact that EVA cannot be completely separated from the panel with the EVA separation methods used (acid, thermal decomposition), the longtime required for separation, and the persistence of residues on the surface even after separation have necessitated the development of new methods in this direction. For the complete removal of EVA, it can be fully removed from the surface with the help of many secondary processes such as ultrasonic irradiation and thermal separation, after being exposed to acidic chemicals and organic solvents. Furthermore, it is understood that the toxic chemicals used in these studies are applied at high temperatures and irreversibly. The development and optimization of chemical methods aim to minimize harm to the environment by increasingthe sustainability and efficiency of the photovoltaic module recycling process.

[0012] JP2005311178A discloses a method for extracting solar cell material, which includes: immersing the solar cell module in an acid solution, an alkali solution, or an organic solvent solution and extracting the substrate material within the solar cell by burning off the EVA.

[0013] The use of non-ionic surfactants together with alcohol-derivative solvents for the separation of EVA from glass in the recycling of PV modules has not been encountered in the literature. Finding innovative and environmentally friendly solutions is of critical importance both for increasing the efficiency of recycling processes and for minimizing environmental impacts. Therefore, there is a need to develop new methods in this field. The development of new methods will be an important step towards ensuring the sustainable recycling of photovoltaic modules.

[0014] The use of an appropriate amount of non-ionic surfactants in the separation of EVA from photovoltaic modules is extremely important. When an insufficient amount of non-ionic surfactant is used, the interaction of the solution with EVA is inadequate, which reduces the effectiveness of the separation process and leads to an extension of the soaking time. On the other hand, when an excessive amount of surfactant is used, environmental toxic effects can occur. An excess of surfactants can harm water resources and ecosystems, pose a risk of bioaccumulation, and create potential health hazards.

[0015] Given the shortcomings in the literature, it is important to research and develop alternative methods and technologies for separating EVA from solar panels. In particular, there is a need for fast, economical, and environmentally friendly methods.

[0016] BRIEF DESCRIPTION OF THE INVENTION

[0017] The object of the present invention is to ensure the complete and effective removal of EVA (Ethylene Vinyl Acetate) residues remaining on the glass surface separated from photovoltaic (PV) modules using the hot-knife technique.

[0018] Another objective of the invention is to provide for the purification of EVA from the glass surface using environmentally friendly chemical processes.

[0019] A further objective of the invention is to provide a restorative effect on the corroded glass surface, thereby enabling the direct recovery of intact glass.

[0020] A further objective of the invention is to increase the reusability of the glass and to optimize the recycling process.

[0021] A further objective of the invention is to enable the recovery of the used chemical substances and to reduce processing costs.

[0022] A further objective of the invention is to increase energy efficiency with processes that can be carried out at low temperatures and in short durations.

[0023] A further objective of the invention is to improve the recycling processes of photovoltaic modules, offering sustainable solutions that minimize environmental impacts. A further objective of the invention is to provide new, more effective, and environmentally friendly methods that eliminate all the problems mentioned in the prior art and bring additional advantages over the relevant prior art.

[0024] DETAILED DESCRIPTION

[0025] In accordance with the objectives above, the detailed features of the present invention are provided herein.

[0026] Within the scope of the invention, a study was conducted on the separation of EVA (Ethylene Vinyl Acetate) from a photovoltaic panel using non-ionic surfactants together with solvents containing a strong base and alcohol.

[0027] According to one embodiment, a method for purifying EVA (Ethylene Vinyl Acetate) from a photovoltaic (PV) panel, comprising the following steps: i. Preparation of a solution containing a strong base and alcohol ii. Addition of a non-ionic surfactant into the prepared solution iii. Immersion of the glass with EVA residues into the prepared solution iv. Soaking the glass with EVA residues in the solution v. Spontaneous separation of the EVA residues wherein the non-ionic surfactant in the solution is between 0.05-0.5% by weight.

[0028] Accordingto one embodiment, the strong base mentioned in step (i) is selected from the group consisting of Potassium Hydroxide (KOH), Sodium Hydroxide (NaOH), Calcium Hydroxide (Ca(OH)2), Barium Hydroxide (Ba(OH)2), Strontium Hydroxide (Sr(OH)2), Lithium Hydroxide (LiOH), Rubidium Hydroxide (RbOH), Cesium Hydroxide (CsOH), and Francium Hydroxide (FrOH).

[0029] According to one embodiment, the strong base mentioned in step (i) is preferably Potassium Hydroxide (KOH) or Sodium Hydroxide (NaOH). According to one embodiment, the strong base mentioned in step (i) is between 4.5- 7.95% by weight in the solution.

[0030] According to one embodiment, the strong base mentioned in step (i) is preferably 5.94% by weight in the solution.

[0031] According to one embodiment, the alcohol-containing solvent mentioned in step (i) is selected from the group consisting of methanol, ethanol, n-propanol, butanol, isobutanol, pentanol, glycerol, ethylene glycol, butyl glycol, and isopropanol.

[0032] According to one embodiment, the alcohol mentioned in step (i) is between 92-95% by weight in the solution.

[0033] According to one embodiment, the alcohol mentioned in step (i) is 93.74% by weight in the solution.

[0034] Accordingto one embodiment, the alcohol mentioned in step (i) is preferably ethanol.

[0035] The inventors have determined that when a solvent combination containing a strong base and alcohol is used for separating EVA from photovoltaic modules, the strong base (e.g., potassium hydroxide - KOH) effectively weakens the chemical bonds of EVA, facilitating the separation of the polymerfrom the surface, while the use of alcohols (e.g., methanol, ethanol, or isopropanol) increases the penetration of the solution and ensures a faster and more homogeneous dissolution of EVA. This combination and their weight percentages in the solution are effective at low temperatures, thus minimizing energy consumption and reducing processing costs. Furthermore, the synergistic effect of the chemical interactions accelerates the separation process and increases efficiency. Consequently, the solvent combination containing a strong base and alcohol enables the effective, economical, and environmentally friendly separation of EVA, thereby increasing the quality of the recovered materials and optimizing the overall efficiency of the recycling process. Accordingto another preferred embodiment, the non-ionic surfactant mentioned in step (ii) is selected from the group consisting of Octylphenol Ethoxylate, Nonylphenol Ethoxylate (NPE), Alkoxylates, Polyethylene Glycol (PEG), Alkyl Polyglucosides (APG), and Ethylene Oxide-Propylene Oxide Copolymers (EO / PO Block Copolymers).

[0036] Accordingto another preferred embodiment, the non-ionic surfactant mentioned in step (ii) is Octylphenol Ethoxylate.

[0037] The addition of a non-ionic surfactant to a solution prepared using a solvent containing a strong base and alcohol plays a significant role in separating EVA from photovoltaic (PV) modules. Non-ionic surfactants have low toxicity and are environmentally friendly, which makes the recycling process safer and more sustainable. Furthermore, these substances accelerate the separation process by increasing the solubility of EVA and are effective over a wide pH range. Their low-foaming properties prevent the formation of unwanted foam during the process and facilitate the control of the method described in the invention. By reducingthe surface tension, it enhances the interaction of the solvent with the surfactant and facilitates the separation of EVA from the glass surface. The use of octylphenol ethoxylate, in particular, provides extra technical advantages such as strong emulsification properties, high heat and chemical resistance, high surface activity, and easy biodegradability. Octylphenol ethoxylate optimizes the separation of EVA from the glass surface with its low surface tension and helps to achieve a cleaner surface result. These technical advantages increase the effectiveness and sustainability of using non- ionic surfactants, and specifically octylphenol ethoxylate, in the process of separating EVA from PV modules.

[0038] The inventors have determined that using the appropriate amount of non-ionic surfactants in the separation of EVA from photovoltaic modules is extremely important. They have concluded that when an insufficient amount of surfactant is used, the interaction of the solution with EVA is inadequate, which reduces the effectiveness of the separation process and leads to an extension of the soaking time. On the other hand, they foresee that when an excessive amount of surfactant is used, environmentaltoxic effects can occur, it can harm water resources and ecosystems, pose a risk of bioaccumulation, and create potential health hazards. Therefore, the amount of the non-ionic surfactant used in the solution is the most critical point of the invention.

[0039] According to another preferred embodiment, the amount of the non-ionic surfactant mentioned in step (ii) is between 0.05-0.5% by weight.

[0040] According to another preferred embodiment, the amount of the non-ionic surfactant mentioned in step (ii) is 0.3% by weight.

[0041] The use of a surfactant in the separation of EVA from photovoltaic modules significantly increases the effectiveness of the process. Surfactants enable the solvent to interact better with EVA, thereby accelerating the dissolution process and ensuring a more homogeneous separation. These substances reduce the surface tension within the solution, helping EVA to separate evenly and quickly from the surface. As a result, the use of a surfactant shortens the duration of the separation process and increases solubility. This method not only saves time and energy but also enhances the quality of the separated materials, thereby maximizing recycling efficiency. Therefore, the addition of surfactants in the separation of EVA plays a critical role both in increasing process efficiency and in achieving higher quality results.

[0042] According to another preferred embodiment, the application temperature is between 20°C - 25°C. This temperature value is also room temperature. In the present invention, it optimizes the effectiveness of different chemical substances and surfactants. The surfactant and solvents selected within the scope of the invention show maximum performance at room temperature, which allows for faster, more homogeneous, and high-resolution results in the EVA separation process. Therefore, operating in the 20-25°C range increases process efficiency and quality, providing economic and environmental benefits.

[0043] According to another preferred embodiment, the soaking time mentioned in step (iv) is 24-48 hours, preferably 24 hours. The process of separating EVA from photovoltaic modules can take 7-10 days using conventional solvents. However, the inventors have found that the addition of non-ionic surfactants significantly shortens this time. Non-ionic surfactants accelerate the chemical reactions by enabling the solution to interact more effectively with EVA. Thus, the dissolution and separation process of EVA occurs faster and spontaneously in a single piece. The use of a surfactant reduces the surface tension of the solution, allowing for a more homogeneous and rapid separation of EVA. Thanks to these effects, the soaking time is reduced to around 24 hours, thus significantly shortening the processing time and increasing efficiency. The shortened processing time provides energy and cost savings, and also enables the acceleration of production processes and a more environmentally friendly recycling process. Therefore, the use of non-ionic surfactants offers great advantages in terms of both time and resource efficiency in the separation of EVA.

[0044] The method described in the invention ensures that the glass surface is cleaned by completely removingthe EVA residues. This allows the recovered glass to be reused. The clean glass can be used in the production of photovoltaic modules or in the manufacturing of other glass products, thereby reducing the need for raw materials and contributing to the conservation of resources.

[0045] The removal of EVA residues increases the efficiency of the recycling process. The separation of clean glass and other materials becomes easier and more effective, which accelerates the recycling operations. This efficiency reduces recycling costs and increases economic sustainability.

[0046] The use of environmentally friendly chemical methods for the removal of EVA minimizes the environmental impacts of the recycling process. Reducing the use of toxic chemicals and ensuring energy efficiency supports environmental sustainability. This improves waste management and reduces environmental pollution. The quality and purity of the recovered materials are increased by the complete removal of EVA residues. This allows the recycled materials to be used in a wider range of and higher-value applications.

[0047] The high-quality materials obtained by removing EVA residues become more economically valuable. As the efficiency of the recycling process increases, so does the revenue generated from the sale of recycled materials. This economic benefit reduces the operating costs of recycling facilities and increases profitability.

[0048] The effective removal of EVA residues provides energy savings in recycling processes. Operations carried out at low temperatures and in short durations reduce energy consumption. This leads to both a reduction in costs and a decrease in environmental impacts.

[0049] In conclusion, the method described in the invention ensures the complete removal of EVA from the glass surface, thereby increasing the reusability of the glass and making the recycling process more efficient. The environmentally friendly chemical processes used minimize the use of toxic chemicals and do not require high temperatures. Thus, a recycling method that is both economically and environmentally sustainable is provided. These developments will make significant contributions to the growth of the photovoltaic industry and the proliferation of sustainable energy solutions.

Claims

CLAIMS1. A method for purifying EVA (Ethylene Vinyl Acetate) from a photovoltaic panel, comprisin the steps of: i. Preparing a solution containing a strong base and alcohol; ii. Adding a non-ionic surfactant into the prepared solution; iii. Immersingthe glass with EVA residues into the prepared solution; iv. Soaking the glass with EVA residues in the solution; v. Spontaneous separation of the EVA residues; characterized in that the non-ionic surfactant in the solution is between 0.05-0.5% by weight.

2. A method accordingto Claim 1 , wherein the strong base in step (i) is selected from the group consisting of Potassium Hydroxide (KOH), Sodium Hydroxide (NaOH), Calcium Hydroxide (Ca(OH)2), Barium Hydroxide (Ba(OH) 2), Strontium Hydroxide (Sr(OH)2), Lithium Hydroxide (LiOH), Rubidium Hydroxide (RbOH), Cesium Hydroxide (CsOH), and Francium Hydroxide (FrOH).

3. A method according to Claim 2, wherein the strong base in step (i) is Potassium Hydroxide (KOH) or Sodium Hydroxide (NaOH).

4. A method according to Claim 2 or 3, wherein the strong base in step (i) is between 4.5-7.95% by weight in the solution.

5. A method according to Claim 1 , wherein the alcohol-containing solvent in step (i) is selected from the group consisting of methanol, ethanol, n-propanol, butanol, isobutanol, pentanol, glycerol, ethylene glycol, butyl glycol, and isopropanol.

6. A method according to Claim 5, wherein the alcohol in step (i) is between 92-95% by weight in the solution.

7. A method according to Claim 1 , wherein the non-ionic surfactant in step (ii) is selected from the group consisting of Octylphenol Ethoxylate, Nonylphenol Ethoxylate (NPE), Alkoxylates, Polyethylene Glycol (PEG), Alkyl Polyglucosides (APG), and Ethylene Oxide-Propylene Oxide Copolymers (EO / PO Block Copolymers).

8. A method according to Claim 7, wherein the non-ionic surfactant in step (ii) is Octylphenol Ethoxylate.

9. A method according to Claim 1 , wherein the application temperature is between20°C - 25°C.

10. A method according to Claim 1 , wherein the soaking time in step (iv) is 24-48 hours, preferably 24 hours.