Method and apparatus for recycling silicon elements, especially crystalline silicon

Abstract

The invention relates to a method and a device for recycling waste from silicon elements, particularly crystalline silicon, wherein waste without metallic adhering is introduced into a reactor (R) with alkali hydroxide solution or water and is circulated, and wherein hydrogen and alkali silicate solution are simultaneously produced by direct reaction of the silicon with the alkali hydroxide solution, and hydrogen and silica are simultaneously produced with water, and the hydrogen and alkali silicate solution are discharged from the reactor (R) after the required reaction time, or wherein waste containing metals is introduced into a reactor (R) with alkali hydroxide solution and is circulated.and that by direct reaction of the silicon, hydrogen and alkaline water glass solution containing metals are simultaneously produced and, after the required reaction time, are drained from the reactor (R) and the alkaline water glass solution is filtered in a filter and the metals are deposited in the filter, generating heat at the same time.

Description

[0001] The present invention relates to a method and a device for recycling silicon elements, in particular crystalline silicon, according to the preamble of the first and ninth claims.

[0002] In particular, c-Si solar cells are recycled.

[0003] The chemical abbreviation c-Si denotes crystalline silicon.

[0004] The statements, results, and conclusions presented below apply primarily to solar cells made of crystalline silicon. For the sake of simplicity, the following text will not differentiate between these and other types of solar cells, such as dye-sensitized solar cells or compound semiconductor solar cells, but will simply refer to them as "solar cells."

[0005] Solar cells are electronic components that convert light energy into electrical energy. The net current generated by this light absorption can be supplied to a consumer via metallic contacts, for example, silver and / or transparent conductive oxides (TCOs), such as indium tin oxide (ITO). The metallic contacts are usually composed of intricate structures to minimize shading losses. By minimizing this shading, the maximum possible silicon surface area is utilized. Therefore, during manufacturing, very narrow and tall contact fingers are sought, which may taper to a point at the edge of the solar cell. The metallic contacts are applied, for example, by screen printing using a silver paste.

[0006] Currently, neither the contacted c-Si solar cells from production, which become production waste due to breakage or quality defects, nor the material waiting for recycling in discarded photovoltaic modules can be completely and financially responsibly separated into individual fractions.

[0007] In currently produced modern PV modules, following an example of heterojunction technology (HJT), approximately 2.5% silicon but only 0.0003% silver are found. This means that for approximately 0.5 kg of silicon, there are only about 6 g of silver. If one considers the cell debris alone, a considerable 1.2% silver is found in this case. The separation of silver and silicon can be achieved through known reactions, such as those described in German publication DE102008024590B4 using nitric acid or in publication EP000002984192B1 using organosulfonic acids via hydrometallurgical processes. These methods focus on dissolving, for example, silver using nitric acid or organosulfonic acids. The resulting silver-containing solution must, of course, undergo further treatment steps, which is not optimal from an ecological and economic perspective. The reaction with nitric acid also generates NO. x, which are problematic for the environment and require expensive exhaust air treatment.

[0008] The German patent application DE102013112004B4 describes a recycling process for entire solar modules in which silicon is to be electrochemically recrystallized from a solution originating from the recycling process. However, there are considerable doubts about its feasibility. The lack of exemplary embodiments in the document and the fact that there are apparently no references to scientific publications on the recrystallization of silicon from aqueous solutions lead to the conclusion that the described process is not applicable at all.

[0009] The object of the invention is to develop a method and a device for recycling silicon elements, in particular crystalline silicon, especially c-Si solar cells, with which the silicon elements and the metal, e.g., silver and / or copper, adhering to them, can be separated directly or at least in a highly concentrated manner from the contacts of c-Si solar cells and / or other silicon elements, and with which the utilization in the sense of recycling silicon elements, e.g., c-Si solar cells, can be carried out more economically.

[0010] This problem is solved by the features of the first and ninth claims. Advantageous embodiments are described in the dependent claims.

[0011] According to the invention, this can be achieved by reacting the silicon elements, e.g., solar cells, whole or in fragmented form, in a reactor with an alkali hydroxide and / or water. The first main product is either alkaline water glass solution or silicic acid. The second main product is always hydrogen. The hydrogen is collected, dried, and can be used for conventional applications. After the reaction is complete, the reactor contents are filtered. The resulting colorless to pale yellow solution, in the case of alkaline earth hydroxides, is the valuable water glass solution, and the metal, e.g., silver, is found as a residue on the filter and can be directly washed, dried, and utilized.

[0012] The invention offers several advantages: Disposal and processing costs associated with prior art are minimized, and various products can be manufactured from the described waste, preferably alkaline silica solutions, silver, hydrogen, and heat. The process according to the invention also generates heat, which is likewise considered a product. This allows a large portion of the energy previously used for silicon production to be reused, firstly in the form of a new energy carrier, hydrogen, and secondly directly in the form of heat.

[0013] The present invention relates to a versatile method and a plant for the recycling of silver-containing photovoltaic cell waste based on silicon, which follows a zero-waste concept and does not generate any significant residual materials as new waste.

[0014] Silicon cell scrap often consists of contacts; contact metals can currently be silver, silver-coated copper, or just copper.

[0015] In this case, alkali hydroxide solution should be used so that the remaining metals can be filtered out of the clear reaction product, water glass solution.

[0016] Hydrogen is also produced and heat is released.

[0017] If silicon wafer fragments are present without metallic attachments, e.g. contacts, alkali hydroxide can be used: hydrogen, heat and the corresponding alkaline water glass solutions are produced - but no metals are recovered in the filter, because these were not present in the first place.

[0018] Alternatively, you can work with just water if you don't want an alkaline water glass solution, but rather silica, which you separate in the filter. This method would also produce hydrogen and heat as a byproduct.

[0019] The silicon, from which the cells or cell fragments mainly consist, reacts completely with the respective alkali hydroxide or water.

[0020] In the case of alkali hydroxides, the corresponding alkali silicates or water glasses are formed. If water reacts alone, silicic acid or SiO2 is formed from the silicon.

[0021] The invention will be explained in more detail below with reference to an exemplary embodiment and related figures, without being limited to these.

[0022] It shows: Fig. 1 A schematic representation of the device according to the invention.

[0023] The device according to the invention has a reactor R in the form of an autoclave with the following components: - A top-mounted filling port 1 for supplying cell fragments from solar cells. The filling port also serves for adding the respective liquid reaction partner, here in the form of the alkali hydroxide solution or water. Alternatively, a separate filling port (not shown) could be provided for this purpose. - A heat exchanger 2 which, for example, is located in the middle and on the outer circumference of the autoclave. - A stirrer or agitator 3, inside the autoclave / reactor R. - A hydrogen outlet preferably located at the top 4. - A gas drying unit 5 for the extracted hydrogen. - One of the compressors downstream of the gas drying unit 5. - A gas storage tank 7 downstream of the compressor 6 for storing the hydrogen. - A drain valve 8 for the alkali water glass solution or silica, depending on what was supplied to the reactor (alkali hydroxide solution or water). - A filter 9 downstream of the drain valve for filtering the metals (preferably silver and / or copper) from the alkaline water glass solution and with an outlet 10 for the filtered alkaline water glass solution.

[0024] If the silicon cells intended for recycling contain metallic deposits such as silver and / or copper or other metals, they are placed in reactor R / autoclave using an alkali hydroxide solution. The mixture is then circulated, preferably stirred, in the reactor for a defined period (this can be determined through preliminary tests). As the silicon dissolves, hydrogen and a metal-containing alkaline silicate solution are produced. After draining the solution from the reactor, the metals are filtered out.

[0025] If the silicon cells show no metallic adhesions, alkali hydroxide solution or water is used, and hydrogen and alkali water glass solution are produced when alkali hydroxide solution is used.

[0026] When using only water, hydrogen and silica are produced, which are drained from the reactor through the drain valve after the required reaction time.

[0027] In general, the aforementioned processes generate heat, which can be transferred via a heat exchanger and supplied to a consumer.

[0028] According to a process example described below, starting with currently available HJT silicon photovoltaic cells, which had silver deposits, the cell fragments, weighing 7.5 g, were placed in an autoclave / reactor R after a comminution step and covered with 80 g of 13% NaOH (alkali hydroxide solution). The autoclave was closed and the reactants were mixed using a magnetic stirrer with stirrer 3.

[0029] The autoclave was then heated using a heater (not shown). The internal temperature was monitored, and upon reaching 40°C, a rapid increase in temperature and pressure was observed. The reaction was complete after approximately 30 minutes. The exact reaction time can be determined through simple experiments. This was followed by a stirring period, maintaining a temperature of 135°C for a further 30 minutes, preferably. The stirring time required for the complete decomposition / dissolution of the silicon can also be determined through simple preliminary tests.

[0030] The maximum values ​​for this experiment were determined in the autoclave at 236°C and 80 bar. The heating was switched off, and upon reaching 70°C, the pressure was reduced from 59 bar to atmospheric pressure. The escaping gas was collected and identified as 6.7 L of hydrogen. Subsequently, the drain valve 8 of the autoclave / reactor R was opened, and the reactor contents were filtered. The clear and colorless water glass solution had a density of 1.28 d / ml and was chemically characterized. The analysis revealed a SiO₂ content of 3.81 mol and a Na₂O content of 1.72 mol. This ratio of 2.2 to 1 corresponds to that of a commercially available water glass solution (in this case, alkaline water glass solution).

[0031] The residue on the filter material of filter 9 was determined to be 0.11 g, which corresponds to 1.5% of the total weight. This residue is silver.

[0032] A heat exchanger 2, which is located here, for example, in the middle and on the outer circumference of the autoclave / reactor R, allows the resulting process heat to be dissipated and used, for example, for heating purposes or for any consumer or other purpose.

[0033] The silicon elements, preferably crystalline silicon, from which the cells or cell fracture mainly consist, react completely with the respective alkali hydroxide or water.

[0034] In the case of alkali hydroxides, the corresponding alkali silicates or water glasses are formed. If water reacts alone, silicon forms silicic acid or SiO2.

[0035] In particular, crystalline silicon varieties (p- and / or n-conducting and / or amphorae) are processed, possibly with metallic attachments or contacts made of silver and / or silver alloys and / or silver-plated copper and / or copper, but also with aluminum.

[0036] The method and the device are also applicable for the treatment of, in particular, c-Si solar cells or other silicon-based cell types or silicon microchips, or also for perovskites or perovskite solar cells.

[0037] The inventive solution for recycling solar cells provides a very simple and cost-effective method and device that is ideally suited for use as a large-scale industrial solution.

[0038] In large-scale applications, it is also possible to forgo generating pressure in the reactor. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 102008024590B4

[0007] EP 000002984192B1

[0007] DE 102013112004B4

[0008]

Claims

[1] Process for recycling silicon elements, particularly crystalline silicon, characterized by , that A. Waste from silicon elements, which do not have any metallic adhesions, are introduced into a reactor (R) with alkali hydroxide solution or water and circulated, and that by direct conversion of the silicon - hydrogen and alkali water glass solution are produced simultaneously with the alkali hydroxide solution and - hydrogen and silicic acid are produced simultaneously with water, and the hydrogen and the alkali water glass solution are discharged from the reactor (R) after the required reaction time, or B. Waste from silicon elements, which contain metals, is introduced into a reactor (R) with alkali hydroxide solution and this is circulated, and that by direct reaction of the silicon hydrogen and alkali water glass solution with the metals contained therein are produced at the same time and are discharged from the reactor (R) after the required reaction time and the alkali water glass solution is filtered in a filter and the metals settle in the filter and that in A. and B. heat is produced simultaneously. [2] Method according to claim 1, characterized by that the waste, in particular silicon cell scrap, is mixed with a dilute alkali hydroxide solution, in particular lithium, sodium or potassium hydroxides, in a concentration stoichiometrically adapted to the desired end product, preferably 5 to 50%. [3] Method according to claim 1 or 2, characterized bythat the reactants, which are in the form of crushed or uncrushed waste from silicon elements, are reacted by heating the alkali hydride solution, preferably to 30 to 80°C. [4] Method according to one of claims 1 to 3, characterized by that the heat released during the reaction is dissipated and made usable by means of a heat exchanger. [5] Method according to one of claims 1 to 4, characterized by that the hydrogen produced is led out of the reactor (R), dried and collected. [6] Method according to one of claims 1 to 5, characterized by that after completion of the reaction the reactor contents are filtered and thus the silver or other metal remaining in the reactor (R) and the respective water glass solution are separated and used for further purposes. [7] Method according to one of claims 1 to 6, characterized bythat the reaction also takes place only with water instead of alkali hydroxide solution, in the case that cell fragments are processed without contacts and the target product is not water glass but silicic acid and hydrogen. [8] Process for recycling silicon elements, particularly crystalline silicon, characterized by that waste from silicon elements with aluminum contacts for hydrogen production is fed to a reactor (R) with an aqueous alkali hydroxide solution and in this, by direct reaction with the aqueous alkali hydroxide solution, hydrogen, alkali water glass solution, aluminum aluminosilicates and / or zeolites and heat are simultaneously produced and discharged from the reactor. [9] Device for recycling silicon elements, in particular crystalline silicon, characterized by that it comprises a reactor (R), in particular in the form of an autoclave, with the following components: - a filling nozzle (1) for supplying shredded waste (cell breakage) or non-shredded waste, - a heat exchanger (2), - a stirrer or agitator (3), - a hydrogen outlet (4), - a gas drying system (5), - a compressor (6) downstream of the gas drying system - a gas storage device (7) downstream of the compressor, - a drain valve (8), - a filter (9) arranged downstream of the drain valve for filtering silver from the water glass solution and with an outlet (10) for the filtered water glass solution. [10] Device according to claim 9, characterized by that the filler neck (1) and the hydrogen outlet (4) are arranged in the upper area of ​​the reactor (R) and the drain valve (8) in the lower area of ​​the reactor (R). [11] Device according to claim 9 or 10, characterized bythat it has a heater for heating the substances in the reactor (R).

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