Method for reducing carbon dioxide

Abstract

A pulverized solar cell, a fluorine compound, water, and an organic solvent are put into a reaction vessel, the reaction vessel is hermetically sealed and filled with a gas containing carbon dioxide, and the reaction vessel is heated to 95°C to promote a reduction reaction of carbon dioxide.

Description

Carbon dioxide reduction method

[0001] The present disclosure relates to a method for reducing carbon dioxide.

[0002] Solar panels are used all over the world as panels that can convert solar energy into electrical energy. Solar panels are classified into "silicon-based," "compound-based," "organic," and "quantum dot-based" types, with silicon-based solar panels being the most widely used. It is predicted that a large amount of solar panels will be discarded in the future, and if they are not disposed of properly, they will have a negative impact on the environment, including soil and water quality.

[0003] Solar panels are primarily composed of three materials: glass, aluminum frame, and solar cells. While glass and aluminum frames are considered recyclable, sufficient technology has not yet been established for recycling solar cells. Currently, one method for recycling solar cells involves extracting and recovering the precious metals contained in the solar cells at refineries, but this method is one of the factors that increases carbon dioxide emissions. Therefore, there is a need to develop a solar cell recycling technology that places less strain on the environment. Non-Patent Document 1 reports that carbon dioxide is converted into organic compounds by using silicon wafers (metallic silicon) discarded during the solar panel manufacturing process as a reducing agent.

[0004] Ria Ayu Pramudita, et al., "Catalytic reduction and reductive functionalization of carbon dioxide with waste silicon from solar panel as the reducing agent," Energy Advances, 2022, 1, pp. 385-390

[0005] However, Non-Patent Document 1 does not report the use of solar cells contained in solar panels in a carbon dioxide reduction reaction, but rather silicon wafers discarded in the solar panel manufacturing process. Therefore, if discarded solar cells could be recycled and carbon dioxide could be converted into energy substances such as formic acid, a circular economy that is beneficial to the environment would be created.

[0006] The present disclosure has been made in consideration of the above circumstances, and aims to convert carbon dioxide into an energy substance by utilizing solar cells in discarded solar panels.

[0007] In one embodiment of the carbon dioxide reduction method of the present disclosure, crushed solar cells, a fluorine compound, water, and an organic solvent are placed in a reaction vessel, the reaction vessel is sealed and filled with a gas containing carbon dioxide, and the reaction vessel is heated to increase its temperature, thereby causing the carbon dioxide reduction reaction to proceed.

[0008] According to the present disclosure, carbon dioxide can be converted into an energy material by utilizing the solar cells in discarded solar panels.

[0009] Fig. 1 is a flowchart showing an example of the processing flow of the carbon dioxide reduction method of this embodiment. Fig. 2 is a diagram showing the results of particle size distribution of pulverized solar cells. Fig. 3 is a diagram showing the results of elemental analysis of pulverized solar cells by fluorescent X-rays. Fig. 4 is a diagram showing the results of elemental analysis of pulverized solar cells by fluorescent X-rays. Fig. 5 is a diagram showing chromatograms resulting from analysis of the filtrate and a formic acid sample using a liquid chromatography mass spectrometer. Fig. 6 is a diagram showing mass spectra resulting from analysis of the filtrate and a formic acid sample using a liquid chromatography mass spectrometer.

[0010] [Carbon dioxide reduction method] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the embodiments, and various modifications can be made within the scope of the present invention.

[0011] The carbon dioxide reduction method disclosed herein (hereinafter also referred to as the "carbon dioxide reduction reaction") involves adding crushed solar cells, a fluorine compound, water, and an organic solvent to a container filled with carbon dioxide to produce an energy substance such as formic acid. The reason why the method disclosed herein can reduce carbon dioxide is believed to be due to the following reaction formula:

[0012]

[0013] The above reaction formula shows the scheme for reducing carbon dioxide. More specifically, a high-temperature, high-pressure container is filled with carbon dioxide at 1 atm, and a solar cell, water, a fluorine compound, and an organic solvent are added. The reaction takes place at 95°C for 24 hours to produce formic acid.

[0014] An example of the carbon dioxide reduction method of this embodiment will be described with reference to the flowchart of FIG.

[0015] In step S1, the solar cells removed from the waste solar panels are crushed. The solar cells are preferably those from which the encapsulant (ethylene vinyl acetate copolymer (EVA), polyvinyl butyral (PVB), silicone resin, polymethylsiloxane (PDMS), ionomer resin, polyolefin, polyurethane) has been removed, but are not limited to these. Solar cells that have undergone hydrogen reduction treatment may also be used. Silicon-based solar cells are preferred, but compound-based, organic-based, and quantum dot-based solar cells are also acceptable. The maximum particle size of the crushed solar cells is preferably 22 μm or less, but they may be larger than 22 μm.

[0016] In step S2, crushed solar cells, a fluorine compound, water, and an organic solvent are added to a reaction vessel, which is then sealed and filled with carbon dioxide. The reaction vessel is not particularly limited, but a pressure-resistant, high-temperature resistant vessel is preferred. The fluorine compound is preferably tetrabutylammonium fluoride trihydrate (TBAF·3H2O), but is not limited to this as long as it is a fluorine compound. The organic solvent is preferably dimethyl sulfoxide, but is not limited to this as long as it is a polar organic solvent. The pressure at which the carbon dioxide is filled is preferably 1 atm, but can be above or below 1 atm. High-purity carbon dioxide is preferred as the gas to be filled, but exhaust gas or air containing carbon dioxide can also be used.

[0017] In step S3, the reaction vessel is heated to increase the temperature, and the reduction reaction of carbon dioxide proceeds. The temperature is preferably increased to 95°C, but is not limited to this. The reaction time is preferably, but is not limited to, 24 hours. The contents of the reaction vessel may be stirred during the reaction.

[0018] In the method of the present disclosure, after the reaction, the product may be separated by distillation or fractionation. Distillation may be performed, for example, by simple distillation, fractional distillation, reduced pressure (or vacuum) distillation, molecular distillation, or steam distillation. Fractionation may be performed, for example, by high-performance liquid chromatography, ultra-high-performance liquid chromatography, or preparative chromatography. As described above, the method of the present disclosure is simple and can be used to carry out the carbon dioxide reduction reaction in, for example, a chemical plant.

[0019] [Examples] The present disclosure will be described in more detail with reference to the following examples, although the scope of the present disclosure is not limited to the examples.

[0020] First, solar cells were removed from waste solar panels and crushed to a maximum particle size of 22 μm or less using a planetary ball mill (crushing balls: φ5 mm, φ2 mm). A small amount of the crushed solar cells was measured, and the particle size distribution and elemental composition were investigated using X-ray fluorescence spectroscopy (XRF).

[0021] The results of particle size distribution measurements are shown in FIG. 2 and Tables 1 and 2.

[0022]

[0023]

[0024] The arithmetic mean particle size of the crushed solar cells was 4.15 μm, the median was 2.74 μm, and the mode was 6.05 μm. The maximum particle size was 22 μm or less.

[0025] The results of SQX analysis using an XRF device (Rigaku Wavelength Dispersive Fluorescent X-ray ZSX Primus IV) are shown in Figures 3 and 4. As shown in Figures 3 and 4, the composition of the solar cells in the discarded solar panels is found to be 89.8% silicon, 9.5% aluminum, 0.6% silver, and 0.1% bismuth.

[0026] Next, under an argon gas atmosphere, a solar cell (505 mg), distilled water (10 mmol), tetrabutylammonium fluoride trihydrate (0.05 mmol), and dimethyl sulfoxide (28.2 mmol) were placed in a pressure-resistant, high-temperature resistant container. The pressure-resistant, high-temperature resistant container was then sealed, carbon dioxide was added, and the mixture was heated to 95°C and stirred for 24 hours.

[0027] After the reaction, the reaction solution was allowed to cool to room temperature and filtered through a PTFE filter. The filtrate was analyzed by nuclear magnetic resonance spectroscopy ( 1 When measured by HNMR, the following results were obtained:

[0028] < 1 HNMR〉 Measurement equipment: JNM-ECZ400s (JEOL) 1 H NMR (400 MHz, DMSO-d6): δ 8.46 (s, 1H)

[0029] A singlet signal is observed at chemical shift δ = 8.46 ppm, which is within the range of typical values ​​corresponding to the aldehyde protons of formic acid. The multiplicity (singlet) and integral value (1H equivalent) of this signal are consistent with the structure of formic acid.

[0030] The filtrate was analyzed by liquid chromatography-mass spectrometry (LC-MS) under the following experimental conditions.

[0031] <LC> Measurement device: Nexera UC (Shimadzu Corporation) Column: Intrada Organic Acid (2.0 mm × 150 mm, 3.0 μm) Column temperature: 40°C Mobile phase A: 10 mM ammonium bicarbonate aqueous solution Mobile phase B: acetonitrile A:B = 0:100 (0 min) → A:B = 0:100 (1.5 min) → A:B = 65:35 (5 min) → A:B = 65:35 (10 min) Flow rate: 0.2 mL / min Injection volume: 5 μL

[0032] Measurement equipment: LCMS-9050 (Shimadzu Corporation) Ionization method: ESI Interface voltage: 3.0 kV (Negative mode) Mass range: m / z 44.99

[0033] Figure 5(a) shows the LC / MS chromatogram of the filtrate, Figure 5(b) shows the LC / MS chromatogram of the formic acid standard, Figure 6(a) shows the LC / MS mass spectrum of the filtrate, and Figure 6(b) shows the LC / MS mass spectrum of the formic acid standard.

[0034] As shown in Figures 5 and 6, the filtrate contains formic acid, which demonstrates that carbon dioxide can be converted into formic acid by using solar cells crushed to a maximum particle size of 22 μm or less as a catalyst.

[0035] As described above, according to this embodiment, crushed solar cells, a fluorine compound, water, and an organic solvent are placed in a reaction vessel, the reaction vessel is sealed and filled with a gas containing carbon dioxide, and the reaction vessel is heated to 95°C to cause a reduction reaction of the carbon dioxide to proceed, thereby utilizing the solar cells in the discarded solar panels to convert carbon dioxide into an energy substance.

[0036] The disclosed method is based on the novel idea of ​​using solar cells from discarded solar panels as a reducing agent, and can synthesize formic acid from carbon dioxide in a simple manner. In contrast, the method described in Non-Patent Document 1 synthesizes formic acid from carbon dioxide by using silicon wafers (metallic silicon) discarded in the solar panel manufacturing process as a reducing agent, but does not use solar cells from discarded solar panels to reduce carbon dioxide.

Claims

1. A carbon dioxide reduction method comprising placing crushed solar cells, a fluorine compound, water, and an organic solvent in a reaction vessel, sealing the reaction vessel and filling it with a gas containing carbon dioxide, and heating the reaction vessel to increase its temperature, thereby causing a reduction reaction of carbon dioxide to proceed.

2. A carbon dioxide reduction method according to claim 1, wherein the solar cell is one of a silicon-based, compound-based, organic-based, and quantum dot-based solar cell.

3. The carbon dioxide reduction method according to claim 1, wherein the solar cells are crushed to a predetermined size.

4. The carbon dioxide reduction method according to claim 3, wherein the solar cells are pulverized to a particle size of 22 μm or less.

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