A partition reaction method for preparing sodium hydroxide by sodium sulfate electrolytic conversion and co-producing sulfur

Abstract

The present application relates to a kind of sodium sulfate electrolytic conversion preparation sodium hydroxide and byproduct sulfur partition reaction method, belong to sodium sulfate electrolytic resource conversion technical field, including: sodium sulfate solution is introduced into sodium sulfate supply area, under the action of electric field makes sodium ion migration to sodium hydroxide generation area, and combine to generate sodium hydroxide with the hydroxyl ion generated by electrolysis water;Make sulphate ion migration to sulphate conversion area, and form the intermediate liquid containing reduced state sulphur species by electrochemical reduction;Intermediate liquid is introduced into the sulfur precipitation area isolated from sulphate conversion area, so that reduced state sulphur species is converted into elemental sulfur and precipitates on solid nucleation medium, sulfur is recovered by solid-liquid separation, and the sulfur-containing liquid that does not precipitate elemental sulfur returns to sulphate conversion area or sulfur precipitation area for continuous reaction.The present application realizes the partition coupling of sodium element alkali production process and sulfur element sulfur precipitation process, reduces the interference of product system, improves the stability of sulfur recovery and the resource utilization value of sodium sulfate.

Description

Technical Field

[0001] This invention relates to the field of sodium sulfate electrolytic resource conversion technology, specifically a partitioned reaction method for the electrolytic conversion of sodium sulfate to prepare sodium hydroxide and simultaneously produce sulfur. Background Technology

[0002] In existing technologies, sodium sulfate-type high-salt wastewater, sodium sulfate-containing by-products, and related industrial by-product salt solutions are typically treated using methods such as evaporation crystallization, membrane separation, electrodialysis, bipolar membrane electrodialysis, lime causticization, or electrochemical oxidation. The main technical approaches focus on reducing the salinity of the wastewater, recovering anhydrous sodium sulfate, preparing sulfuric acid or sodium hydroxide, and preparing persulfate. For example, document CN116789236A discloses a method for the electrolytic resource utilization of sodium sulfate-type high-salt wastewater. This method first sends the sodium sulfate-type high-salt wastewater into an electrochemical oxidation system to remove recalcitrant organic matter, then increases the sulfate concentration in an evaporation tank, and finally sends the mother liquor to the anode unit of a multi-stage membrane electrolytic cell. Under the action of a DC electric field, sodium sulfate is selectively electrolyzed in one step to produce sodium persulfate. The anode uses a boron-doped diamond electrode containing a sulfate selective adsorption layer. This type of scheme can improve the oxidation and utilization of sulfate in sodium sulfate-type wastewater, but its products are mainly persulfate or crystalline salt. The reaction system focuses on the anodic oxidation process and does not conduct zoned control of the reduced sulfur-containing species formed by the reduction of sulfate, nor does it establish a synergistic reaction pathway for the generation of sodium hydroxide and the precipitation of elemental sulfur.

[0003] Public document CN117377639A discloses a method for preparing sodium hydroxide from sodium sulfate wastewater generated during lithium battery recycling. The method involves adding calcium oxide powder to the sodium sulfate wastewater for a mixed reaction, followed by steps such as filtration, nanofiltration, reverse osmosis, electrodialysis, and evaporation concentration to obtain a sodium hydroxide solution. This type of scheme aims to convert sodium sulfate wastewater into sodium hydroxide, which can improve the utilization value of sodium sulfate by-product wastewater to some extent. However, because it relies on calcium source reactions and multi-stage membrane separation and concentration, the system is prone to problems such as the formation of solid-phase calcium sulfate, removal of impurities from the reaction mother liquor, concentration of low-concentration alkali solution, and membrane separation load. Furthermore, sulfate anions are mainly treated as objects to be separated or transferred, and are not further converted into sulfur products that are easier to recover through solid-liquid separation.

[0004] Therefore, although existing technologies have proposed technical routes such as sodium sulfate electrolytic resource recovery, sodium sulfate wastewater alkali production, and sulfate oxidation to prepare high-valence sulfur-containing products, a process is still lacking that can, within the same electrochemical conversion system, direct sodium ions into the sodium hydroxide generation zone to form sodium hydroxide, while simultaneously directing sulfate ions into a separate sulfate conversion zone to generate reduced sulfur-containing species that can be further converted. This sulfur-containing intermediate liquid can then be introduced into a relatively isolated sulfur precipitation zone to achieve the recovery of elemental sulfur. Especially when reduced sulfur-containing species and sulfur-oxygen intermediates coexist, the lack of spatial partitioning, liquid flow guidance, nucleation and precipitation control, and sulfur-containing liquid reflux control can easily lead to problems such as sulfur anion migration, reaction path dispersion, low elemental sulfur nucleation efficiency, difficulty in stable separation of precipitated solids, and insufficient utilization of sulfur. This limits the high-value conversion of sodium sulfate into a dual-product of sodium hydroxide and sulfur. Summary of the Invention

[0005] The purpose of this invention is to provide a partitioned reaction method for the electrolytic conversion of sodium sulfate to prepare sodium hydroxide and produce sulfur, thereby solving some of the drawbacks and shortcomings pointed out in the background art.

[0006] The present invention adopts the following technical solution to solve the above-mentioned technical problems:

[0007] Sodium sulfate solution is introduced into the sodium sulfate supply area, and sodium ions migrate to the sodium hydroxide generation area under the action of an electric field, and combine with hydroxide ions generated by the electrolysis of water in the sodium hydroxide generation area to generate sodium hydroxide.

[0008] Sulfate ions migrate to the sulfate conversion zone and are electrochemically reduced within the sulfate conversion zone to form an intermediate liquid containing reduced sulfur species. Sulfate-oxygen intermediate species capable of reacting with the reduced sulfur species are also formed within the sulfate conversion zone.

[0009] The intermediate liquid is introduced into a sulfur precipitation zone isolated from the sulfate conversion zone, so that the reduced sulfur species in the intermediate liquid are converted into elemental sulfur. The elemental sulfur precipitates on the solid nucleation medium in the sulfur precipitation zone and is recovered by solid-liquid separation. The sulfur-containing liquid that does not precipitate elemental sulfur is returned to the sulfate conversion zone or the sulfur precipitation zone to continue the reaction.

[0010] Furthermore, after the intermediate liquid enters the sulfur precipitation zone, it splits into a first liquid stream and a second liquid stream. The first liquid stream forms intermediate-valence sulfur-oxygen species through electrochemical action, while the second liquid stream retains reduced-state sulfur-containing species. The first liquid stream and the second liquid stream merge on the surface of the solid nucleation medium to generate elemental sulfur.

[0011] Furthermore, the solid nucleation medium is a circulating sulfur particle, and a sulfur-containing adsorption layer is retained on the surface of the circulating sulfur particle. The sulfur-containing adsorption layer enriches the reduced sulfur-containing species and induces newly generated elemental sulfur to grow on the surface of the circulating sulfur particle.

[0012] Furthermore, the sulfur-containing liquid returns from the side of the sulfate conversion zone away from the sodium hydroxide generation zone, so that the reduced sulfur-containing species in the sulfur-containing liquid first come into contact with the sulfur-oxygen intermediate species in the sulfate conversion zone, and form an intermediate liquid that can be introduced into the sulfur precipitation zone.

[0013] Furthermore, the circulating sulfur particles are circulated in the sulfur precipitation zone according to particle size classification. Circulating sulfur particles with a particle size lower than the preset classification particle size return to the entry position of the intermediate liquid, while circulating sulfur particles with a particle size higher than the preset classification particle size enter the solid-liquid separation step, so that the sulfur-containing adsorption layer comes into contact with the newly entered intermediate liquid.

[0014] Furthermore, before the circulating sulfur particles enter the sulfur precipitation zone, they first come into contact with the diverted sulfur-containing liquid and are preloaded with reduced sulfur-containing species. The preloaded circulating sulfur particles then come into contact with the intermediate liquid, causing the newly generated elemental sulfur to be deposited on the outside of the sulfur-containing adsorption layer.

[0015] Furthermore, the circulating sulfur particles undergo liquid flow shearing to remove the outer layer of elemental sulfur within the sulfur precipitation zone, while retaining the inner sulfur-containing adsorption layer before returning to the sulfur precipitation zone, thereby maintaining the enrichment and nucleation of reduced sulfur-containing species by the circulating sulfur particles.

[0016] Furthermore, after the sulfur-containing liquid enters the sulfate conversion zone, it flows in the direction away from the sodium hydroxide generation zone, so that the reduced sulfur-containing species consume the sulfur-oxygen intermediate species on the side away from the sodium hydroxide generation zone, and form a reaction buffer section that restricts the migration of sulfur-containing anions to the sodium hydroxide generation zone.

[0017] Furthermore, before returning to the sulfate conversion zone, the sulfur-containing liquid is mixed with the diverted intermediate liquid, so that the reduced sulfur-containing species in the sulfur-containing liquid are converted into polysulfide forms before contacting the sulfur-oxygen intermediate species, thereby increasing the proportion of sulfur-containing species that can be precipitated in the intermediate liquid entering the sulfur precipitation zone.

[0018] Furthermore, within the reaction buffer section, the returned sulfur-containing liquid is brought into countercurrent contact with the newly generated sulfur-oxygen intermediate species in the sulfate conversion zone, forming a zone where reduced sulfur-containing species are preferentially consumed; the sulfur-containing anions migrating toward the sodium hydroxide generation zone are converted into intermediate liquid within the zone where reduced sulfur-containing species are preferentially consumed, and are guided by the liquid flow to the sulfur precipitation zone.

[0019] This invention establishes a sodium sulfate supply zone, a sodium hydroxide generation zone, a sulfate conversion zone, and a sulfur precipitation zone. This allows sodium ions in the sodium sulfate solution to migrate to the sodium hydroxide generation zone under the influence of an electric field, where they combine with hydroxide ions generated from water electrolysis to form sodium hydroxide. Simultaneously, sulfate ions enter the sulfate conversion zone and undergo electrochemical reduction to form an intermediate solution containing reduced sulfur species. This achieves zoned coupling of the sodium alkali production process and the sulfur conversion process, reducing mutual interference between different product systems.

[0020] This invention introduces an intermediate solution containing reduced sulfur-containing species into a sulfur precipitation zone isolated from the sulfate conversion zone. This allows the reduced sulfur-containing species to be further converted into elemental sulfur within this independent zone, and the elemental sulfur is then recovered via solid-liquid separation after precipitation on a solid nucleation medium. This method facilitates the conversion of sulfur-containing species dispersed in solution into easily separable solid-phase sulfur, improves the stability of sulfur precipitation and recovery, and reduces the risk of elemental sulfur depositing, clogging, or interfering with electrode reactions within the electrochemical conversion zone.

[0021] This invention also allows the sulfur-containing liquid that has not precipitated elemental sulfur to return to the sulfate conversion zone or sulfur precipitation zone for continued reaction. This enables the insufficiently converted reduced sulfur-containing species to continue participating in subsequent reactions and entering the sulfur precipitation pathway, thereby improving sulfur utilization and sulfur recovery rates. Through the above-mentioned cyclic reaction, this invention can simultaneously obtain sodium hydroxide and sulfur products during the electrolytic conversion of sodium sulfate, enhancing the resource utilization value of sodium sulfate by-products or sodium sulfate-containing liquids, and providing an feasible zoned reaction scheme for reducing the treatment load of high-salt sulfur-containing systems. Attached Figure Description

[0022] Figure 1 This is a flow chart of the partitioned reaction process for the electrolytic conversion of sodium sulfate to prepare sodium hydroxide and produce sulfur in this invention.

[0023] Figure 2 This is a schematic diagram of the partitioned reaction and intermediate liquid introduction in Example 1 of the present invention.

[0024] Figure 3 This is a flow distribution diagram of the intermediate liquid in Embodiment 1 of the present invention.

[0025] Figure 4 This is a diagram showing the loading and stripping recovery of circulating sulfur particles in Example 1 of the present invention.

[0026] Figure 5 This is a diagram of the return path of the sulfur-containing liquid to the far end and the reaction buffer path in Embodiment 2 of the present invention.

[0027] Figure 6 This is a diagram showing the calculation of the return mixture flow rate and residence time in Embodiment 2 of the present invention.

[0028] Figure 7This is a verification diagram of the reduction in sulfur-containing anion concentration in Example 2 of the present invention. Detailed Implementation

[0029] As attached Figure 1 As shown, in one specific embodiment, a partitioned electrolytic reaction system is used to electrolytically convert sodium sulfate solution. This reaction system includes a sodium sulfate supply zone, a sodium hydroxide generation zone, a sulfate conversion zone, and a sulfur precipitation zone. These reaction zones are functionally separated according to the direction of ion migration and liquid flow. Isolation structures that allow target ion migration and inhibit direct liquid-phase mixing can be provided between the sodium sulfate supply zone and the sodium hydroxide generation zone, as well as between the sodium sulfate supply zone and the sulfate conversion zone, allowing sodium ions and sulfate ions to enter their respective reaction zones. During operation, sodium sulfate solution is continuously or intermittently introduced into the sodium sulfate supply zone. Under the action of an applied electric field, sodium ions in the sodium sulfate solution migrate to the sodium hydroxide generation zone. A water electrolysis reaction occurs in the sodium hydroxide generation zone, producing hydroxide ions. The sodium ions that migrate into this zone combine with the hydroxide ions, thereby generating sodium hydroxide solution within the sodium hydroxide generation zone. Simultaneously, sulfate ions in the sodium sulfate solution migrate to the sulfate conversion zone and undergo electrochemical reduction, gradually forming an intermediate liquid containing reduced sulfur-containing species. Reduced sulfur-containing species include at least one of the following: sulfides, hydrosulfides, or polysulfides formed after sulfate reduction. Sulfo-oxygen intermediates are also formed within the sulfate transformation zone. These intermediate sulfur-containing species still contain sulfur-oxygen bonds during the stepwise sulfate transformation process. These intermediates can undergo subsequent reactions with reduced sulfur-containing species, providing a reaction basis for the formation of elemental sulfur.

[0030] Furthermore, the intermediate liquid formed in the sulfate conversion zone is introduced into the sulfur precipitation zone. The sulfur precipitation zone is isolated from the sulfate conversion zone, allowing the electrochemical reduction process and the elemental sulfur precipitation process to occur in separate areas, thereby reducing the interference of the sulfur precipitation process on the sulfate conversion process. The intermediate liquid entering the sulfur precipitation zone contains reduced sulfur-containing species, which are further converted into elemental sulfur within the zone. A solid nucleation medium is provided in the sulfur precipitation zone, allowing the generated elemental sulfur to precipitate and grow using this medium as an attachment base, preventing disordered dispersion of elemental sulfur in the liquid phase. The solid nucleation medium can be sulfur particles, inert particles resistant to reaction liquid corrosion, or circulating particles with sulfur already attached to their surface, enabling the newly generated elemental sulfur to stably nucleate on its surface. The precipitated elemental sulfur, along with the solid nucleation medium or sulfur particles, enters a solid-liquid separation process, achieving elemental sulfur recovery after solid-liquid separation. The sulfur-containing liquid that still contains unconverted or unprecipitated sulfur species after solid-liquid separation is returned to the sulfate conversion zone or sulfur precipitation zone for further reaction, depending on the degree of conversion of the sulfur species. This allows the sulfur species to be recycled within the system and improves the continuity and stability of sodium hydroxide generation and sulfur co-production during the sodium sulfate electrolytic conversion process.

[0031] Based on the above implementation method, after the intermediate liquid enters the sulfur precipitation zone, it can be divided into a first liquid flow and a second liquid flow through a diversion structure. The diversion structure can be a guide plate, a diversion channel, or a liquid passage with different flow resistance, allowing the intermediate liquid entering the sulfur precipitation zone to enter corresponding positions in different directions. The first liquid flow is guided to a position within the sulfur precipitation zone where electrochemical action occurs. This position can be equipped with an auxiliary electrode or polarization component, causing the sulfur-containing species in the first liquid flow to undergo valence state adjustment and form intermediate valence sulfur-oxygen species. The second liquid flow avoids or weakens the electrochemical action region, allowing the reduced sulfur-containing species in the second liquid flow to be retained. The first and second liquid flows are then guided to the region where the solid nucleation medium is located and converge on the surface of the solid nucleation medium. Since the first liquid flow contains intermediate valence sulfur-oxygen species and the second liquid flow contains reduced sulfur-containing species, the two types of sulfur-containing species react at the surface of the solid nucleation medium, thereby generating elemental sulfur on the surface of the solid nucleation medium. In this way, the formation site of elemental sulfur is confined to the surface of the solid nucleation medium, which is conducive to promoting the nucleation and attachment growth of elemental sulfur and reducing the dispersion of elemental sulfur in the liquid phase of the sulfur precipitation zone.

[0032] Based on the above implementation method, the solid nucleation medium in the sulfur precipitation zone can be recycled sulfur particles. During the reaction, the recycled sulfur particles serve as the substrate for the precipitation of elemental sulfur, and their surface retains a sulfur-containing adsorption layer. This sulfur-containing adsorption layer is formed by reduced sulfur species, polysulfide sulfur species, and fine elemental sulfur adsorbed on the surface of the recycled sulfur particles. It can adsorb and enrich the reduced sulfur species entering the sulfur precipitation zone, causing the reduced sulfur species to concentrate on the surface of the recycled sulfur particles. When the intermediate liquid comes into contact with the recycled sulfur particles, the sulfur-containing adsorption layer provides nucleation sites for newly generated elemental sulfur and induces elemental sulfur to continue depositing and growing along the surface of the recycled sulfur particles, thereby reducing the dispersion of elemental sulfur in the liquid phase and improving the stability of subsequent separation and recovery of elemental sulfur.

[0033] Circulating sulfur particles are graded and circulated according to particle size within the sulfur precipitation zone. The preset grading particle size can be determined based on the separation requirements of the solid-liquid separation equipment, the circulation stability of the circulating sulfur particles, and the required recovery particle size. Circulating sulfur particles with a particle size smaller than the preset grading particle size are guided back to the entry point of the intermediate liquid, allowing their sulfur-containing adsorption layer to first contact the newly entering intermediate liquid and continue to enrich reduced sulfur-containing species. Circulating sulfur particles with a particle size larger than the preset grading particle size enter the solid-liquid separation step to separate particles that have been loaded with or deposited with a large amount of elemental sulfur from the liquid phase. Through this graded circulation method, circulating sulfur particles in the growth phase can repeatedly participate in the nucleation and growth process, and circulating sulfur particles that meet the separation conditions can enter the recovery process in a timely manner, thus balancing the efficiency of elemental sulfur generation and solid-liquid separation.

[0034] Before the circulating sulfur particles enter the sulfur precipitation zone, they can be contacted with the diverted sulfur-containing liquid. This diverted liquid can be taken from the sulfur-containing liquid after solid-liquid separation or from the circulating liquid within the sulfur precipitation zone. The diverted liquid contains reduced sulfur species; upon contact with it, the sulfur-containing adsorption layer on the surface of the circulating sulfur particles is pre-loaded with these reduced sulfur species. The pre-loaded circulating sulfur particles then enter the sulfur precipitation zone and contact the intermediate liquid, causing newly generated elemental sulfur to deposit on the outside of the sulfur-containing adsorption layer. Thus, a particle structure can be formed on the surface of the circulating sulfur particles, with the sulfur-containing adsorption layer as the inner base and the newly deposited elemental sulfur as the outer growth layer. This facilitates the continuous thickening of elemental sulfur and the formation of easily separable sulfur particles.

[0035] Furthermore, within the sulfur precipitation zone, the circulating sulfur particles are subjected to liquid flow scouring and shearing. The weaker-bonded portions of the outer layer of elemental sulfur are stripped away and enter the subsequent solid-liquid separation process, while the inner sulfur-containing adsorbed layer remains on the surface of the circulating sulfur particles. The liquid flow scouring and shearing can be generated by changes in the circulating liquid flow, stirred flow, or flow rate within the guide channel in the sulfur precipitation zone, causing the weakly bonded outer layer of elemental sulfur to detach from the particle surface without damaging the sulfur-containing adsorbed layer on the surface of the circulating sulfur particles. The circulating sulfur particles, retaining the inner sulfur-containing adsorbed layer, return to the sulfur precipitation zone to continue participating in the reaction, allowing the circulating sulfur particles to continuously maintain their ability to enrich and nucleate reduced sulfur species in multiple cycles. Through this operating mode, the active surface of the circulating sulfur particles can be maintained while recovering the outer layer of elemental sulfur, thereby improving the continuity and controllability of the sulfur precipitation process.

[0036] Based on the above implementation method, the sulfur-containing liquid can be returned to the sulfate conversion zone from the side away from the sodium hydroxide generation zone within the sulfate conversion zone. The returned sulfur-containing liquid contains reduced sulfur-containing species, which first come into contact with the sulfur-oxygen intermediate species formed in the sulfate conversion zone and undergo a conversion reaction, thereby forming an intermediate liquid that can be reintroduced into the sulfur precipitation zone. The return inlet of the sulfur-containing liquid can be located at the outer end of the sulfate conversion zone or near the connection point of the sulfur precipitation zone, preventing the returned sulfur-containing liquid from directly entering the side near the sodium hydroxide generation zone. By setting the return location of the sulfur-containing liquid on the side away from the sodium hydroxide generation zone, the reduced sulfur-containing species can participate in the reaction first near the return inlet, reducing the possibility of sulfur-containing species migrating to the sodium hydroxide generation zone and minimizing the impact of sulfur-containing species on the sodium hydroxide generation process.

[0037] After the sulfur-containing liquid enters the sulfate conversion zone, it can flow in a direction away from the sodium hydroxide generation zone. This flow direction can be formed by coordinating the positions of the sulfur-containing liquid return inlet, guide plate, isolation channel, or outlet, so that the returning sulfur-containing liquid first flows away from the sodium hydroxide generation zone within the sulfate conversion zone. This flow direction differs from the direction of sulfur-containing anions migrating towards the sodium hydroxide generation zone, causing reduced sulfur-containing species to preferentially consume sulfur-oxygen intermediates on the side away from the sodium hydroxide generation zone, forming a reaction buffer section in this region. The reaction buffer section provides pre-reaction space for sulfur-containing species within the sulfate conversion zone, intercepting and converting sulfur-containing anions migrating towards the sodium hydroxide generation zone before they enter, thus limiting further migration of sulfur-containing anions into the sodium hydroxide generation zone.

[0038] Before the sulfur-containing solution returns to the sulfate conversion zone, it can be mixed with the intermediate liquid that flows out. The intermediate liquid can be drawn out from the sulfate conversion zone before entering the sulfur precipitation zone or at the inlet of the sulfur precipitation zone. The intermediate liquid contains sulfur-containing species that can participate in the sulfur conversion reaction. The reduced sulfur-containing species in the sulfur-containing solution are converted into polysulfides upon contact with these species. The polysulfide forms of the sulfur-containing species then enter the sulfate conversion zone and come into contact with sulfur-oxygen intermediates, which is conducive to the formation of an intermediate liquid suitable for subsequent sulfur precipitation reactions, thereby increasing the proportion of sulfur-containing species that can be precipitated in the intermediate liquid entering the sulfur precipitation zone.

[0039] Furthermore, within the reaction buffer zone, the returned sulfur-containing liquid can come into counter-current contact with newly generated sulfur-oxygen intermediates in the sulfate conversion zone. This counter-current contact is achieved by aligning the local diffusion direction of the sulfur-oxygen intermediates, formed by their migration along with sulfate, with the flow direction of the returning sulfur-containing liquid. This counter-current contact concentrates the reduced sulfur-containing species within the reaction buffer zone, creating a preferential consumption zone for them. Sulfur-containing anions migrating towards the sodium hydroxide formation zone enter this preferential consumption zone and are transformed into an intermediate liquid by the combined action of the sulfur-oxygen intermediates and the reduced sulfur-containing species. Subsequently, they flow towards the sulfur precipitation zone. Through this process, a directional consumption and directional flow reaction path is formed within the sulfate conversion zone, which improves the efficiency of intermediate liquid formation and reduces the interference of sulfur-containing anions on the sodium hydroxide formation zone.

[0040] Example 1:

[0041] This embodiment provides a partitioned reaction method for the electrolytic conversion of sodium sulfate to prepare sodium hydroxide and simultaneously produce sulfur, implemented by a certain unit using a partitioned electrolytic reaction system. The reaction system includes a sodium sulfate supply zone, a sodium hydroxide generation zone, a sulfate conversion zone, and a sulfur precipitation zone. The sodium sulfate supply zone receives sodium sulfate solution, the sodium hydroxide generation zone generates sodium hydroxide solution, the sulfate conversion zone electrochemically reduces sulfate ions to form an intermediate solution containing reduced sulfur-containing species, and the sulfur precipitation zone converts the sulfur-containing species in the intermediate solution onto the surface of a solid nucleation medium and precipitates them as elemental sulfur.

[0042] In this embodiment, a sodium sulfate solution with a mass concentration of 180 g / L is introduced into the sodium sulfate supply zone at a flow rate of 12 L / h, and the system operates under an electrolysis voltage of 4.8 V and a current of 18 A. Sodium ions in the sodium sulfate solution migrate to the sodium hydroxide generation zone under the influence of the electric field, and combine with hydroxide ions generated from water electrolysis in the sodium hydroxide generation zone to form sodium hydroxide. Sulfate ions migrate to the sulfate conversion zone, where they undergo electrochemical reduction to form an intermediate solution containing reduced sulfur-containing species. Simultaneously, a sulfur-oxygen intermediate species capable of reacting with the reduced sulfur-containing species is formed in the sulfate conversion zone.

[0043] Figure 2 The functional separation relationship between the sodium sulfate supply zone, sodium hydroxide generation zone, sulfate conversion zone, and sulfur precipitation zone in this embodiment is shown. Figure 2 The paths from the sodium sulfate supply zone to the sodium hydroxide generation zone and the sulfate conversion zone respectively are used to illustrate the zoned guidance of sodium ion migration and sulfate migration; the path from the sulfate conversion zone to the sulfur precipitation zone is used to illustrate the sulfur precipitation reaction after the intermediate liquid is introduced into the sulfur precipitation zone; the dashed flow direction from the sulfur precipitation zone back to the sulfate conversion zone is used to illustrate the recycling of sulfur-containing liquid that has not precipitated elemental sulfur. Figure 2 The circulating sulfur particle symbol set in the sulfur precipitation zone is used to correspond to the solid nucleation medium and the growth process of elemental sulfur adhering to its surface, thereby forming a continuous correspondence between zone conversion, liquid phase introduction, sulfur-containing liquid circulation and solid nucleation.

[0044] The intermediate liquid formed in the sulfate conversion zone is introduced into a sulfur precipitation zone isolated from the sulfate conversion zone, allowing the electrochemical reduction process and the elemental sulfur precipitation process to occur in separate regions. After entering the sulfur precipitation zone, the intermediate liquid is divided into a first liquid stream and a second liquid stream by a diversion structure. The first liquid stream is guided to a location within the sulfur precipitation zone where electrochemical activity occurs, causing the sulfur-containing species in the first liquid stream to undergo valence state adjustment and form intermediate valence sulfur-oxygen species. The second liquid stream avoids this electrochemically active location, thus preserving the reduced sulfur-containing species in the second liquid stream. The first and second liquid streams are then directed to the region containing the solid nucleation medium and converge on the surface of the solid nucleation medium.

[0045] In this embodiment, to determine the actual flow rates of the first and second liquid flows, a liquid flow distribution calculation formula is used for calculation:

[0046]

[0047]

[0048] In the formula, Q is the total flow rate of the intermediate liquid entering the sulfur precipitation zone, in L / h; Qa is the flow rate of the first liquid stream, in L / h; Qb is the flow rate of the second liquid stream, in L / h; and α is the first liquid stream distribution coefficient. Since the total flow rate of the intermediate liquid entering the sulfur precipitation zone is divided into the first liquid stream and the second liquid stream by the diversion structure, and the proportion of the first liquid stream to the total flow rate of the intermediate liquid is α, the flow rate of the first liquid stream is the product of the total flow rate of the intermediate liquid and the first liquid stream distribution coefficient. The flow rate of the second liquid stream is the remaining portion of the total flow rate of the intermediate liquid after deducting the first liquid stream.

[0049] In this embodiment, the total flow rate Q of the intermediate liquid entering the sulfur precipitation zone is 12 L / h, and the first liquid distribution coefficient α is 40%. Substituting these values ​​into the above calculation formula yields:

[0050]

[0051]

[0052] Therefore, the first liquid flow rate is 4.8 L / h, and the second liquid flow rate is 7.2 L / h. Figure 3 The above-mentioned flow division calculation results are shown with the column height and total flow baseline as the reference, where the total flow rate of the intermediate liquid is maintained at 12.0 L / h, the first liquid flow corresponds to 4.8 L / h, and the second liquid flow corresponds to 7.2 L / h. Figure 3 The dashed line connecting the first and second liquid streams indicates that the two streams are guided together to the subsequent confluence region after the split. The first liquid stream is used to form intermediate-valence sulfur-oxygen species at the electrochemically active site, while the second liquid stream is used to retain reduced sulfur-containing species. After the two liquid streams converge on the surface of the solid nucleation medium, the intermediate-valence sulfur-oxygen species and the reduced sulfur-containing species react in contact on the surface of the solid nucleation medium, thereby confining the generation site of elemental sulfur to the surface of the solid nucleation medium and reducing the disordered dispersion of elemental sulfur in the liquid phase of the sulfur precipitation zone.

[0053] In this embodiment, the solid nucleation medium is recycled sulfur particles. During the reaction, the recycled sulfur particles serve as the substrate for the precipitation of elemental sulfur. Their surface retains a sulfur-containing adsorption layer, which adsorbs and enriches reduced sulfur-containing species entering the sulfur precipitation zone, resulting in a concentrated distribution of these species on the surface of the recycled sulfur particles. When the first and second liquid flows converge on the surface of the recycled sulfur particles, the sulfur-containing adsorption layer provides nucleation sites for newly generated elemental sulfur and induces its deposition and growth along the surface of the recycled sulfur particles.

[0054] Before entering the sulfur precipitation zone, the circulating sulfur particles first come into contact with the diverted sulfur-containing liquid. This liquid contains reduced sulfur species; upon contact, the circulating sulfur particles preload the sulfur-containing adsorption layer on their surface with these reduced species. The preloaded circulating sulfur particles then enter the sulfur precipitation zone and come into contact with the intermediate liquid, causing newly generated elemental sulfur to deposit on the outer side of the sulfur-containing adsorption layer. This forms a particle structure with the inner sulfur-containing adsorption layer as the base and the newly deposited elemental sulfur on the outer side as the growth layer.

[0055] The circulating sulfur particles are graded and circulated within the sulfur precipitation zone according to particle size. In this embodiment, the initial average particle size of the circulating sulfur particles is 0.45 mm, and the preset grading particle size is 0.80 mm. Circulating sulfur particles with a particle size smaller than 0.80 mm return to the entry point of the intermediate liquid, allowing their sulfur-containing adsorption layer to continue contacting the newly entering intermediate liquid and enriching reduced sulfur-containing species; circulating sulfur particles with a particle size larger than 0.80 mm enter the solid-liquid separation step to separate particles with a large amount of elemental sulfur deposited from the liquid phase.

[0056] During the continuous nucleation and growth of circulating sulfur particles, the increase in solid load can be characterized by the change in the mass of circulating sulfur particles before and after operation, and the particle loading calculation formula is used for calculation:

[0057]

[0058] In the formula, Gm represents the increase in solid load mass of the circulating sulfur particles during the operating cycle, in grams; M1 represents the mass of the circulating sulfur particles before preloading, in grams; and M2 represents the mass of the sulfur particles entering the solid-liquid separation step after operation, in grams. Since the circulating sulfur particles serve as the substrate for the deposition and growth of elemental sulfur in the sulfur precipitation zone, the increase in the mass of the sulfur particles entering the solid-liquid separation step after operation relative to their mass before preloading is the increase in solid load mass of the circulating sulfur particles during that operating cycle.

[0059] In this embodiment, the mass M1 of the circulating sulfur particles before preloading is 120 g, and the mass M2 of the sulfur particles entering the solid-liquid separation step after 6 hours of operation is 154 g. Substituting these values ​​into the above calculation formula yields:

[0060]

[0061] Therefore, the circulating sulfur particles increased their solid load by 34 g during this operating cycle. Of this increased solid load, part is the outer layer of elemental sulfur deposited on the outside and capable of being sheared off by the liquid flow, while the other part remains with the sulfur-containing adsorption layer on the surface of the circulating sulfur particles, maintaining the enrichment and nucleation of reduced sulfur-containing species by the circulating sulfur particles. In this embodiment, the mass of the outer layer of elemental sulfur sheared off and recovered was 28 g. After shearing, the circulating sulfur particles retained the inner sulfur-containing adsorption layer and returned to the sulfur precipitation zone to continue participating in the reaction.

[0062] Figure 4 The mass changes of the circulating sulfur particles before preloading, before solid-liquid separation, after shearing and stripping, and during the outer sulfur recovery process are shown in terms of stacked mass. Figure 4 In the figure, the initial mass of the circulating particles before preloading was 120 g; the total mass before solid-liquid separation was 154 g, an increase of 34 g relative to the initial mass of 120 g; the mass of particles returned after shearing and stripping was 126 g, indicating that the initial mass of 120 g of circulating particles and 6 g of retained load were returned to the sulfur precipitation zone; the outer layer sulfur recovery was 28 g, indicating that the outer layer of elemental sulfur could be stripped and separated from the surface of the circulating particles and entered the recovery process. This figure further illustrates that the stripping and recovery of the outer layer of elemental sulfur does not damage the sulfur-containing adsorption layer on the surface of the circulating sulfur particles, and the retained load can still serve as an active basis for subsequent nucleation and enrichment.

[0063] Through the above operation, intermediate-valence sulfur-oxygen species in the first liquid stream and reduced-valence sulfur-containing species in the second liquid stream are guided to converge on the surface of the circulating sulfur particles. The sulfur-containing adsorption layer on the surface of the circulating sulfur particles enriches the reduced-valence sulfur-containing species and provides nucleation sites, allowing elemental sulfur to preferentially generate and grow on the surface of the circulating sulfur particles. Circulating sulfur particles with a particle size lower than the preset classification particle size continuously return to the intermediate liquid entry position, while circulating sulfur particles with a particle size higher than the preset classification particle size enter the solid-liquid separation step. The outer layer of elemental sulfur is recovered after being sheared and stripped by the liquid flow, while the inner layer of sulfur-containing adsorption layer remains. This improves the controllability of the elemental sulfur precipitation location, the stability of sulfur particle separation and recovery, and the continuity of the sodium hydroxide generation and sulfur co-production process.

[0064] Example 2:

[0065] This embodiment provides a partitioned reaction method for the electrolytic conversion of sodium sulfate to prepare sodium hydroxide and simultaneously produce sulfur, implemented by a certain unit using a partitioned electrolytic reaction system. The reaction system includes a sodium sulfate supply zone, a sodium hydroxide generation zone, a sulfate conversion zone, and a sulfur precipitation zone. The sodium sulfate supply zone is used to introduce sodium sulfate solution; the sodium hydroxide generation zone is used to receive migrating sodium ions and generate sodium hydroxide; the sulfate conversion zone is used to receive migrating sulfate ions and form an intermediate solution containing reduced sulfur-containing species; and the sulfur precipitation zone is used to further convert the sulfur-containing species in the intermediate solution and precipitate elemental sulfur.

[0066] In this embodiment, a sodium sulfate solution with a mass concentration of 160 g / L is introduced into the sodium sulfate supply zone at a flow rate of 10 L / h, and the system operates under an electrolysis voltage of 5.0 V and a current of 16 A. Sodium ions in the sodium sulfate solution migrate to the sodium hydroxide generation zone under the influence of the electric field, and combine with hydroxide ions generated from water electrolysis in the sodium hydroxide generation zone to form sodium hydroxide. Sulfate ions migrate to the sulfate conversion zone, where they undergo electrochemical reduction to form an intermediate solution containing reduced sulfur-containing species. Simultaneously, sulfur-oxygen intermediate species capable of participating in subsequent sulfur conversion reactions are formed in the sulfate conversion zone.

[0067] The sulfur-containing liquid after solid-liquid separation in the sulfur precipitation zone is returned to the sulfate conversion zone at a flow rate of 3.0 L / h. The return inlet is located on the side of the sulfate conversion zone away from the sodium hydroxide generation zone. Before returning, the sulfur-containing liquid is mixed with the intermediate liquid diverted at a flow rate of 0.8 L / h, which converts the reduced sulfur species in the sulfur-containing liquid into polysulfide forms before entering the sulfate conversion zone. After entering the sulfate conversion zone, the returned mixture flows in the direction away from the sodium hydroxide generation zone, allowing the reduced sulfur species to contact the sulfur-oxygen intermediate species first on the side away from the sodium hydroxide generation zone.

[0068] Figure 5 The diagram illustrates the flow path of the sulfur-containing liquid after its return from the far end in this embodiment, using a partitioned path approach. The sodium hydroxide generation zone is positioned on one side of the sulfate conversion zone, and the reaction buffer section is located within the sulfate conversion zone, away from the sodium hydroxide generation zone. A dashed line shows the path of the sulfur-containing liquid returning from the sulfur precipitation zone to the reaction buffer section. Figure 5 The relative positions of the return mixture, the direction of sulfur-oxygen intermediates, the migration trend of sulfur-containing anions, and the reverse contact all indicate that the return mixture does not directly approach the sodium hydroxide generation zone, but rather enters the reaction buffer zone first within the sulfate conversion zone, and then reacts with sulfur-oxygen intermediates in the preferential consumption zone.

[0069] In this embodiment, a reaction buffer section is formed within the sulfate conversion zone, with an effective volume of 1.9 L. This reaction buffer section is located between the sulfur-containing liquid return inlet and the side near the sodium hydroxide generation zone, providing contact reaction space for reduced sulfur-containing species, polysulfide-containing sulfur-containing species in the returned mixture, and newly generated sulfur-oxygen intermediates in the sulfate conversion zone. The returned mixture undergoes counter-current contact with the newly generated sulfur-oxygen intermediates within this region, forming a zone where reduced sulfur-containing species are preferentially consumed.

[0070] To characterize the contact reaction time of the returned mixture within the reaction buffer section, this embodiment uses a formula for calculating the residence time in the reaction buffer. Since the returned mixture is formed by mixing the sulfur-containing liquid and the intermediate liquid diverted from the reaction buffer, the flow rate of the returned mixture is the sum of the return flow rate of the sulfur-containing liquid and the flow rate of the intermediate liquid diverted from the reaction buffer, i.e., 3.0 L / h plus 0.8 L / h equals 3.8 L / h. The ratio of the effective volume of the reaction buffer section to the flow rate of the returned mixture is the theoretical residence time of the returned mixture within the reaction buffer section.

[0071]

[0072] In the formula, Tz is the theoretical residence time of the sulfur-containing liquid in the reaction buffer section, in hours (h); Vz is the effective volume of the reaction buffer section, in liters (L); and Fr is the return mixed liquid flow rate, in liters (L / h). Substituting the effective volume of the reaction buffer section (1.9 L) and the return mixed liquid flow rate (3.8 L / h) into the calculation formula, we obtain:

[0073]

[0074] Therefore, the theoretical residence time of the returned mixture in the reaction buffer section is 0.5 h. Figure 6 The calculation process described above is illustrated by the correspondence between the sulfur-containing liquid return flow rate, the split intermediate liquid flow rate, the return mixed liquid flow rate, and the effective volume of the reaction buffer section. The 3.0 L / h sulfur-containing liquid return flow rate and the 0.8 L / h split intermediate liquid flow rate together form the 3.8 L / h return mixed liquid flow rate. The 1.9 L effective volume of the reaction buffer section on the right corresponds to the 0.5 h residence time. This figure further illustrates that the residence time, derived from the coordination between the return mixed liquid flow rate and the effective volume of the reaction buffer section, is used to ensure that the return mixed liquid completes the pre-contact reaction on the side away from the sodium hydroxide generation zone, and is not used to limit the sole operating parameter of this method.

[0075] Within the reaction buffer zone, the return mixture flows away from the sodium hydroxide generation zone, while newly generated sulfur-oxygen intermediates in the sulfate conversion zone approach the region where the return mixture is located, following local concentration distribution and ion migration trends, thus forming a reverse contact. This reverse contact preferentially allows reduced sulfur-containing species to participate in the reaction and converts sulfur-containing anions migrating towards the sodium hydroxide generation zone into intermediates that can be introduced into the sulfur precipitation zone before entering the sodium hydroxide generation zone.

[0076] To characterize the effect of the reaction buffer section on the migration of sulfur-containing anions, this embodiment uses a formula for calculating the reduction of sulfur-containing anions. The concentration of sulfur-containing anions at the inlet of the reaction buffer section is 2.6 g / L, and the concentration of sulfur-containing anions detected near the sodium hydroxide generation zone is 0.35 g / L. The difference between these two concentrations represents the reduction in sulfur-containing anions after passing through the reaction buffer section.

[0077]

[0078] In the formula, Ds represents the decrease in sulfur-containing anion concentration before and after the reaction buffer section, in g / L; Cp represents the sulfur-containing anion concentration at the inlet of the reaction buffer section, in g / L; and Cn represents the sulfur-containing anion concentration detected near the sodium hydroxide generation zone, in g / L. Substituting Cp (2.6 g / L) and Cn (0.35 g / L) into the calculation formula, we obtain:

[0079]

[0080] Therefore, the concentration of sulfur-containing anions decreased by 2.25 g / L before and after the reaction buffer section. Figure 7 The above concentration changes are shown at three locations: the inlet of the buffer section, the side near the sodium hydroxide generation zone, and the concentration decrease. The concentration at the inlet of the buffer section is 2.60 g / L, and the concentration near the generation zone is 0.35 g / L, resulting in a concentration decrease of 2.25 g / L. Figure 7 The concentration change path points from the high-concentration inlet to the low-concentration detection location, indicating that after the sulfur-containing anions are consumed and transformed in the reaction buffer zone, their tendency to continue migrating to the sodium hydroxide generation zone is limited.

[0081] In this embodiment, the intermediate liquid formed in the sulfate conversion zone is further introduced into the sulfur precipitation zone, where the sulfur-containing species that can be precipitated are converted into elemental sulfur. The sulfur-containing liquid after solid-liquid separation is not directly discharged from the system, but is returned to the sulfate conversion zone according to the conversion state of the reduced sulfur-containing species it contains. The return location is located on the side away from the sodium hydroxide generation zone, so that the returned sulfur-containing liquid first enters the reaction buffer section to participate in the pre-reaction, and then forms an intermediate liquid suitable for the subsequent sulfur precipitation reaction.

[0082] Through the above methods, the sulfur-containing liquid returns from the side away from the sodium hydroxide generation zone, the returned mixed liquid flows in the direction away from the sodium hydroxide generation zone, the sulfur-containing liquid and the diverted intermediate liquid are premixed to form polysulfide forms, and the reverse contact in the reaction buffer zone cooperates with each other, so that the reduced sulfur-containing species preferentially consume sulfur-oxygen intermediate species in the sulfate conversion zone, and form a zone where reduced sulfur-containing species are preferentially consumed. This improves the efficiency of intermediate liquid formation, increases the proportion of sulfur-containing species that can be precipitated in the intermediate liquid entering the sulfur precipitation zone, and reduces the interference of sulfur-containing anions migrating to the sodium hydroxide generation zone on the sodium hydroxide generation process.

Claims

1. A partitioned reaction method for the electrolytic conversion of sodium sulfate to prepare sodium hydroxide and simultaneously produce sulfur, characterized in that: Sodium sulfate solution is introduced into the sodium sulfate supply area, and sodium ions migrate to the sodium hydroxide generation area under the action of an electric field, and combine with hydroxide ions generated by the electrolysis of water in the sodium hydroxide generation area to generate sodium hydroxide. Sulfate ions migrate to the sulfate conversion zone and are electrochemically reduced within the sulfate conversion zone to form an intermediate liquid containing reduced sulfur species. Sulfate-oxygen intermediate species capable of reacting with the reduced sulfur species are also formed within the sulfate conversion zone. The intermediate liquid is introduced into a sulfur precipitation zone isolated from the sulfate conversion zone, so that the reduced sulfur species in the intermediate liquid are converted into elemental sulfur. The elemental sulfur precipitates on the solid nucleation medium in the sulfur precipitation zone and is recovered by solid-liquid separation. The sulfur-containing liquid that does not precipitate elemental sulfur is returned to the sulfate conversion zone or the sulfur precipitation zone to continue the reaction.

2. The partitioned reaction method according to claim 1, characterized in that: After entering the sulfur precipitation zone, the intermediate liquid is divided into a first liquid stream and a second liquid stream. The first liquid stream forms intermediate-valence sulfur-oxygen species through electrochemical action, while the second liquid stream retains reduced sulfur-containing species. The first liquid stream and the second liquid stream merge on the surface of the solid nucleation medium to generate elemental sulfur.

3. The partitioned reaction method according to claim 1, characterized in that: The solid nucleation medium is circulating sulfur particles, and a sulfur-containing adsorption layer is retained on the surface of the circulating sulfur particles. The sulfur-containing adsorption layer enriches the reduced sulfur-containing species and induces newly generated elemental sulfur to grow on the surface of the circulating sulfur particles.

4. The partitioned reaction method according to claim 1, characterized in that: The sulfur-containing liquid returns from the side of the sulfate conversion zone away from the sodium hydroxide generation zone, so that the reduced sulfur-containing species in the sulfur-containing liquid first come into contact with the sulfur-oxygen intermediate species in the sulfate conversion zone, and form an intermediate liquid that can be introduced into the sulfur precipitation zone.

5. The partitioned reaction method according to claim 3, characterized in that: The circulating sulfur particles are circulated in the sulfur precipitation zone according to particle size classification. Circulating sulfur particles with a particle size lower than the preset classification particle size return to the entry position of the intermediate liquid, while circulating sulfur particles with a particle size higher than the preset classification particle size enter the solid-liquid separation step, so that the sulfur-containing adsorption layer comes into contact with the newly entered intermediate liquid.

6. The partitioned reaction method according to claim 3, characterized in that: Before entering the sulfur precipitation zone, the circulating sulfur particles first come into contact with the diverted sulfur-containing liquid and are preloaded with reduced sulfur-containing species. The preloaded circulating sulfur particles then come into contact with the intermediate liquid, causing the newly generated elemental sulfur to be deposited on the outside of the sulfur-containing adsorption layer.

7. The partitioned reaction method according to claim 3, characterized in that: The circulating sulfur particles are sheared and stripped of their outer layer of elemental sulfur within the sulfur precipitation zone by a liquid flow, while retaining the inner sulfur-containing adsorption layer before returning to the sulfur precipitation zone, thereby maintaining the enrichment and nucleation of reduced sulfur-containing species by the circulating sulfur particles.

8. The partitioned reaction method according to claim 4, characterized in that: After the sulfur-containing liquid enters the sulfate conversion zone, it flows in the direction away from the sodium hydroxide generation zone, so that the reduced sulfur-containing species consume the sulfur-oxygen intermediate species on the side away from the sodium hydroxide generation zone, and form a reaction buffer section that restricts the migration of sulfur-containing anions to the sodium hydroxide generation zone.

9. The partitioned reaction method according to claim 4, characterized in that: Before returning to the sulfate conversion zone, the sulfur-containing liquid is mixed with the diverted intermediate liquid, so that the reduced sulfur-containing species in the sulfur-containing liquid are converted into polysulfide forms before contacting the sulfur-oxygen intermediate species, thereby increasing the proportion of sulfur-containing species that can be precipitated in the intermediate liquid entering the sulfur precipitation zone.

10. The partitioned reaction method according to claim 8, characterized in that: Within the reaction buffer zone, the returned sulfur-containing liquid comes into countercurrent contact with the newly generated sulfur-oxygen intermediate species in the sulfate conversion zone, forming a zone where reduced sulfur-containing species are preferentially consumed. The sulfur-containing anions migrating toward the sodium hydroxide generation zone are converted into intermediate liquid within the zone where reduced sulfur-containing species are preferentially consumed and are guided by the liquid flow to the sulfur precipitation zone.

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