A method for preparing photovoltaic-grade potassium hydroxide

Abstract

The application provides a photovoltaic-grade potassium hydroxide preparation method and relates to the technical field of potassium preparation. The application comprises the following steps: rough purification is realized by vacuum gradient crystallization on KOH raw materials; wet crystals generated after rough purification are centrifuged and then dissolved, and then three-stage countercurrent extraction is performed to obtain photovoltaic-grade KOH; the mother liquor generated after rough purification is extracted and then subjected to vacuum gradient crystallization in a cycle; the wet crystals are dissolved in ultrapure water to prepare a KOH solution; the KOH solution is filtered and then enters a three-stage countercurrent extraction tower together with an extractant to perform three-stage countercurrent extraction; photovoltaic-grade KOH products are obtained after nanofiltration and ultrafiltration of the raffinate phase output; and the loaded organic phase output is regenerated to realize cyclic use; a microwave generating device is arranged on the three-stage countercurrent extraction tower, and the microwave generating device applies pulsed microwaves to the mixing area in the tower. The sodium removal rate is improved, the solvent consumption is reduced, and the generation of hazardous waste is reduced.

Description

Technical Field

[0001] This invention relates to the field of potassium preparation technology, and specifically to a method for preparing photovoltaic-grade potassium hydroxide. Background Technology

[0002] Potassium hydroxide, also known as caustic soda, has the chemical formula KOH and is an inorganic compound. Depending on its application, potassium hydroxide can be classified into food-grade, industrial-grade, electronic-grade, and photovoltaic-grade potassium hydroxide. Photovoltaic-grade potassium hydroxide refers to potassium hydroxide specifically used in the photovoltaic industry, possessing advantages such as high purity, good high-temperature stability, and excellent corrosion resistance.

[0003] Purification is a key step in the preparation of photovoltaic-grade potassium hydroxide. Currently, potassium hydroxide purification methods include dissolution-crystallization, solvent extraction, ion exchange, membrane separation, and electrolysis. The sodium removal rate is currently about 70% to 90%, and the removal rate still needs to be improved. The purification process consumes a lot of solvents and generates a lot of hazardous waste. Summary of the Invention

[0004] The purpose of this invention is to develop a method for preparing photovoltaic-grade potassium hydroxide that improves sodium removal rate, reduces solvent consumption, and reduces hazardous waste generation.

[0005] This invention is achieved through the following technical solution:

[0006] A method for preparing photovoltaic-grade potassium hydroxide, comprising:

[0007] Industrial-grade KOH raw material is subjected to vacuum gradient crystallization to achieve crude purification. The wet crystals produced after crude purification are centrifuged and then dissolved, followed by three-stage countercurrent extraction to obtain photovoltaic-grade KOH. The mother liquor produced after crude purification is extracted and then recycled for vacuum gradient crystallization.

[0008] The three-stage countercurrent extraction process includes: dissolving wet crystals in ultrapure water to prepare a KOH solution; filtering the KOH solution and introducing it into a three-stage countercurrent extraction tower for three-stage countercurrent extraction; obtaining photovoltaic-grade KOH product by nanofiltration and ultrafiltration; and regenerating the output loaded organic phase for recycling.

[0009] The three-stage countercurrent extraction tower is equipped with a microwave generator, which applies pulsed microwaves to the mixing zone inside the tower.

[0010] Optionally, the extractant may include a primary extractant, a co-extractant, an ionic liquid modifier, a diluent, and an antiemulsifier.

[0011] Optionally, the main extractant is P204, the co-extractant is 18-crown ether-6, the ionic liquid modifier is 1-butyl-3-methylimidazolium hexafluorophosphate, the diluent is sulfonated kerosene, and the antiemulsifier is perfluoropolyether surfactant.

[0012] Optionally, vacuum gradient crystallization includes primary vacuum crystallization and secondary vacuum crystallization. Primary vacuum crystallization outputs primary crystal slurry and primary mother liquor. The primary mother liquor is subjected to secondary vacuum crystallization to output secondary crystal slurry and secondary mother liquor. The primary and secondary crystal slurries are centrifuged, dehydrated, and washed to obtain wet crystals. The secondary mother liquor is recovered, sodium is removed, and it is reused.

[0013] Optionally, the secondary mother liquor is recovered to a mother liquor storage tank and then extracted to remove sodium. The extractants for the secondary mother liquor extraction include dicyclohexyl-18-crown ether-6, P204, and sulfonated kerosene. The process is a single-stage extraction.

[0014] Optionally, the primary vacuum crystallization pressure is -90 kPa, the temperature is 75 ± 1℃, the primary vacuum crystallization concentration is 40%, the cooling program is from 75℃ to 60℃, and the cooling rate is 3℃ / h.

[0015] Optionally, the secondary vacuum crystallization pressure is -95 kPa and the temperature is 80 ± 0.5℃. The secondary vacuum crystallization concentrates the crystals to 50%. The cooling program is divided into two stages: the first stage is from 80℃ to 50℃ at a cooling rate of 5℃ / h, and the second stage is from 50℃ to 25℃ at a cooling rate of 0.5℃ / h.

[0016] Optionally, the wet crystals are dissolved in a KOH solution prepared with ultrapure water and then filtered in two stages: the first stage is a 5μm sintered titanium filter element, and the second stage is a 0.45μm PTFE filter element.

[0017] Optionally, the microwave generating device includes a microwave generator and a waveguide coupler. A radiating antenna connected to the flange of the waveguide coupler is installed inside the tower. The radiating antenna is located inside the tower, and a quartz window is provided between the radiating antenna and the waveguide coupler.

[0018] Optionally, the regeneration of the supported organic phase includes pretreatment, transition metal back-extraction, and sodium ion electrochemical dissociation. The pretreatment includes dehydration, deacidification, and filtration. The back-extraction solution for the transition metal back-extraction is citric acid with a concentration of 0.5 mol / L. The sodium ion electrochemical dissociation is carried out in an electrolytic cell. The cathode in the electrolytic cell is a platinum-plated titanium mesh, and the anode is an iridium-tantalum oxide-coated titanium electrode. The regenerated organic phase is output from the cathode chamber, and the sodium-containing waste liquid is output from the anode chamber.

[0019] The beneficial effects of this invention are:

[0020] This invention combines vacuum gradient crystallization with extraction to improve sodium removal rate to approximately 98.4%. The mother liquor generated from vacuum gradient crystallization and the loaded organic phase generated from extraction are both regenerated and reused, reducing solvent consumption and hazardous waste generation. During the extraction process, pulsed microwaves are used to break the interfacial membrane resistance and enhance the two-phase mass transfer, thereby improving extraction efficiency. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 Here is a flow chart of the vacuum gradient crystallization process using KOH as a raw material;

[0023] Figure 2 This is a flow chart of the three-stage countercurrent extraction process for KOH. Detailed Implementation

[0024] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0025] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0026] like Figure 1 and Figure 2 As shown, this invention discloses a method for preparing photovoltaic-grade potassium hydroxide, including KOH raw material, which is a 30% concentration industrial-grade KOH solution. The industrial-grade KOH solution is subjected to vacuum gradient crystallization to achieve crude purification. The wet crystals produced after crude purification are centrifuged and then dissolved, and subjected to three-stage countercurrent extraction to obtain photovoltaic-grade KOH. The mother liquor produced after crude purification is subjected to specialized extraction to achieve targeted sodium removal. The generated regenerated KOH is recycled for vacuum gradient crystallization.

[0027] During vacuum gradient crystallization, the first-stage vacuum crystallization (-90kPa, temperature 75±1℃) concentrates the crystals to 40%, and the cooling program is from 75℃ to 60℃ at a rate of 3℃ / h, outputting the first-stage crystal slurry and the first-stage mother liquor.

[0028] The primary mother liquor undergoes secondary vacuum crystallization (-95 kPa, temperature 80 ± 0.5 °C) to concentrate to 50%. The cooling process is divided into two stages: in the first stage, the temperature is reduced from 80 °C to 50 °C at a rate of 5 °C / h; in the second stage, the temperature is reduced from 50 °C to 25 °C at a rate of 0.5 °C / h. The secondary crystal slurry and secondary mother liquor are then output.

[0029] The primary and secondary crystal slurries are centrifuged and dehydrated to a water content of ≤5%. Then, the crystals are washed with ultrapure water spray. The primary and secondary crystal slurries are then dissolved and subjected to tertiary countercurrent extraction. Both the primary and secondary mother liquors are filtered. The secondary mother liquor is recovered to the mother liquor storage tank, then extracted to remove sodium, and then returned for vacuum gradient crystallization.

[0030] For the specialized extraction of the secondary mother liquor, the extractant includes 10% dicyclohexyl-18-crown ether-6 (DCH18C6), 5% P204, and 85% sulfonated kerosene. The process is a single-stage extraction with an organic phase ratio of O to aqueous phase of 1:2, a temperature of 25°C, and a time of 10 min.

[0031] The primary and secondary crystal slurries are dissolved in ultrapure water to prepare a 30% KOH solution, which is then subjected to two-stage filtration. The first stage is a 5μm sintered titanium filter to retain undissolved crystals, and the second stage is a 0.45μm PTFE filter to remove colloidal silica.

[0032] After two-stage filtration, the KOH solution (aqueous phase) and the extractant (organic phase) enter a three-stage countercurrent extraction tower (including a primary tower, a secondary tower, and a tertiary tower). The aqueous phase passes through the tertiary tower, the secondary tower, and the primary tower in sequence and outputs the raffinate phase, while the organic phase passes through the primary tower, the secondary tower, and the tertiary tower in sequence and outputs the loaded organic phase.

[0033] The three-stage countercurrent extraction column is equipped with a microwave generator. This generator applies pulsed microwaves to the mixing zone within the column, breaking down interfacial film resistance and enhancing mass transfer between the two phases, thereby improving extraction efficiency. The microwave generator includes a microwave generator and a waveguide coupler. A radiating antenna, connected to the flange of the waveguide coupler, is located inside the column. A quartz window is positioned between the radiating antenna and the waveguide coupler.

[0034] The extractant includes a main extractant, a co-extractant, an ionic liquid modifier, a diluent, and an antiemulsifier. The main extractant is P204 (di(2-ethylhexyl) phosphate), the co-extractant is 18-crown ether-6, the ionic liquid modifier is 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6), the diluent is sulfonated kerosene, and the antiemulsifier is a perfluoropolyether surfactant.

[0035] The raffinate is subjected to nanofiltration to remove trace organic residues, and then to ultrafiltration to remove particles, yielding photovoltaic-grade KOH product.

[0036] The supported organic phase is regenerated and recycled, and the components in the extractant are replenished in a timely manner. The regeneration of the supported organic phase includes pretreatment, transition metal back-extraction, and electrochemical dissociation of sodium ions. The pretreatment includes dehydration, deacidification, and filtration. The back-extraction solution for transition metal back-extraction is citric acid with a concentration of 0.5 mol / L. Electrochemical dissociation of sodium ions is carried out in an electrolytic cell. The cathode in the electrolytic cell is a platinum-plated titanium mesh, and the anode is an iridium-tantalum oxide-coated titanium electrode. The regenerated organic phase is output from the cathode chamber, and the sodium-containing waste liquid is output from the anode chamber.

[0037] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the technical solutions of the present invention. Any technical solution that can be implemented based on the above embodiments without creative effort should be considered to fall within the scope of protection of the patent of the present invention.

Claims

1. A method for preparing photovoltaic-grade potassium hydroxide, characterized in that, include: Industrial-grade KOH raw material is subjected to vacuum gradient crystallization to achieve crude purification. The wet crystals produced after crude purification are centrifuged and then dissolved, followed by three-stage countercurrent extraction to obtain photovoltaic-grade KOH. The mother liquor produced after crude purification is extracted and then recycled for vacuum gradient crystallization. The three-stage countercurrent extraction process includes: dissolving wet crystals in ultrapure water to prepare a KOH solution; filtering the KOH solution and introducing it into a three-stage countercurrent extraction tower for three-stage countercurrent extraction; obtaining photovoltaic-grade KOH product by nanofiltration and ultrafiltration; and regenerating the output loaded organic phase for recycling. Among them, the three-stage countercurrent extraction tower is equipped with a microwave generator. The microwave generator applies pulsed microwaves to the mixing zone inside the tower to break the interfacial film resistance and enhance the mass transfer between the two phases. The extractant includes a main extractant, a co-extractant, an ionic liquid modifier, a diluent, and an antiemulsifier. The main extractant is P204, the co-extractant is 18-crown ether-6, the ionic liquid modifier is 1-butyl-3-methylimidazolium hexafluorophosphate, the diluent is sulfonated kerosene, and the antiemulsifier is a perfluoropolyether surfactant. The regeneration of the loaded organic phase includes pretreatment, transition metal back-extraction, and sodium ion electrochemical dissociation. The pretreatment includes dehydration, deacidification, and filtration. The back-extraction solution for the transition metal back-extraction is citric acid with a concentration of 0.5 mol / L. The sodium ion electrochemical dissociation is carried out in an electrolytic cell. The cathode in the electrolytic cell is a platinum-plated titanium mesh, and the anode is an iridium-tantalum oxide-coated titanium electrode. The regenerated organic phase is output from the cathode chamber, and the sodium-containing waste liquid is output from the anode chamber.

2. The method for preparing photovoltaic-grade potassium hydroxide according to claim 1, characterized in that, Vacuum gradient crystallization includes primary vacuum crystallization and secondary vacuum crystallization. Primary vacuum crystallization outputs primary crystal slurry and primary mother liquor. The primary mother liquor is subjected to secondary vacuum crystallization to output secondary crystal slurry and secondary mother liquor. The primary and secondary crystal slurries are centrifuged, dehydrated, and washed to obtain wet crystals. The secondary mother liquor is recovered, sodium is removed, and it is reused.

3. The method for preparing photovoltaic-grade potassium hydroxide according to claim 2, characterized in that, The secondary mother liquor is recovered to the mother liquor storage tank and then extracted to remove sodium. The extractants for the secondary mother liquor extraction include dicyclohexyl-18-crown ether-6, P204, and sulfonated kerosene. The process is a single-stage extraction.

4. The method for preparing photovoltaic-grade potassium hydroxide according to claim 2, characterized in that, The primary vacuum crystallization pressure is -90 kPa and the temperature is 75 ± 1℃. The primary vacuum crystallization concentration is 40%, and the cooling program is from 75℃ to 60℃ at a cooling rate of 3℃ / h.

5. The method for preparing photovoltaic-grade potassium hydroxide according to claim 2, characterized in that, The secondary vacuum crystallization pressure is -95 kPa and the temperature is 80 ± 0.5℃. The secondary vacuum crystallization concentrates the crystals to 50%. The cooling process is divided into two stages: the first stage is from 80℃ to 50℃ at a cooling rate of 5℃ / h, and the second stage is from 50℃ to 25℃ at a cooling rate of 0.5℃ / h.

6. The method for preparing photovoltaic-grade potassium hydroxide according to claim 1, characterized in that, The wet crystals were dissolved in a KOH solution prepared with ultrapure water and then filtered in two stages: the first stage was a 5μm sintered titanium filter element, and the second stage was a 0.45μm PTFE filter element.

7. The method for preparing photovoltaic-grade potassium hydroxide according to claim 1, characterized in that, The microwave generating device includes a microwave generator and a waveguide coupler. A radiating antenna connected to the flange of the waveguide coupler is installed inside the tower. The radiating antenna is located inside the tower, and a quartz window is provided between the radiating antenna and the waveguide coupler.

Images