Method for continuously preparing high-purity sodium sulfide from sodium hydrosulfide

Abstract

The invention provides a method for continuously preparing high-purity sodium sulfide from sodium hydrosulfide, which comprises the following steps of: feeding sodium hydrosulfide feed liquid into an adjusting kettle, reacting with sodium hydroxide to obtain sodium sulfide feed liquid, feeding the sodium sulfide feed liquid into a multi-section continuous crystallizer, and performing multi-section crystallization by vacuumizing or controlling the temperature in the crystallizer through an external heat exchanger to obtain high-purity sodium sulfide. A part of the mother liquor returns to the section of crystallizer to adjust the solid content, and a part of the mother liquor enters a rear-section crystallization process to obtain the high-purity crystallized sodium sulfide. According to the method, sodium sulfide is prepared through the reaction of sodium hydrosulfide and sodium hydroxide, high-concentration sodium sulfide feed liquid can be obtained without using an evaporation process by utilizing the characteristic of high solubility of sodium hydrosulfide, and compared with a method for preparing sodium sulfide through a one-step reaction of absorbing hydrogen sulfide by sodium hydroxide, the controllability of a reaction endpoint can be improved. Through the two-stage continuous cooling crystallization technology, the amount of crystallization mother liquor is reduced to the maximum extent, enrichment of impurities in the system is avoided, and the product quality is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of inorganic chemical product preparation, and particularly relates to a method for continuously preparing high-purity sodium sulfide by precise regulation of reaction. BACKGROUND

[0002] Sodium sulfide is an important inorganic chemical raw material and is widely used in the industrial field, covering papermaking, metal smelting, printing and dyeing, leather making, ore dressing, pharmaceuticals, and synthesis of sulfur-containing polymers, etc. At present, the common industrial sodium sulfide on the market is mainly red flaky and yellow flaky products, which generally have the problem of high impurity iron content, usually more than 30 ppm. With the rapid development of fine industries such as pharmaceutical intermediates, high-end sulfur-containing polymer synthesis, and high-grade leather making, more stringent requirements are put forward for the purity of sodium sulfide, especially the iron content needs to be controlled below 10 ppm. The existing conventional sodium sulfide products have been difficult to meet the application needs of these high-end fields due to the limitation of purity, and the development of high-purity crystalline sodium sulfide preparation technology has become a key direction for the development of the industry.

[0003] To break through the bottleneck of high-purity sodium sulfide preparation, many studies have been carried out in related fields and various technical solutions have been proposed, but these solutions still have obvious defects in actual application. For example, the high-purity white crystalline sodium sulfide process disclosed by CN101823701A realizes impurity removal by adding a decontamination reagent, but the process operation procedure is complex, and the introduction of the decontamination reagent easily leads to the mixing of new impurities, at the same time, the high concentration and temperature of the sodium sulfide solution after concentration require strict corrosion resistance and high temperature resistance of the material of the production equipment, greatly increasing the equipment investment and maintenance cost. The high-purity crystalline sodium sulfide production method proposed by CN1944241A has the problems of low purity of hydrogen sulfide gas and high impurity content, which not only leads to the impurities of the prepared sodium sulfide products exceeding the standard, but also produces a large amount of waste residue in the generation process of hydrogen sulfide gas, polluting the environment and increasing the solid waste treatment cost, at the same time, the evaporation and concentration link of the method has high energy consumption and low production efficiency, which is difficult to realize large-scale production.

[0004] In addition, the sodium sulfide continuous cooling crystallization system disclosed by CN212594083U uses the combination of evaporation concentration and continuous cooling crystallization to prepare crystalline sodium sulfide, which replaces the traditional batch crystallization operation of in-pot cooling and improves the production continuity, but still depends on the evaporation concentration process and has high energy consumption. In the production process, scaling and plugging phenomena often occur on the walls of the crystallization kettle and the surface of the heat exchanger, which requires frequent shutdown for cleaning, seriously affecting the production stability and efficiency, and further increasing the operating cost of the enterprise. In summary, the existing high-purity sodium sulfide preparation technology generally has problems such as high energy consumption, complex process, insufficient product purity, high equipment requirements, or low production efficiency, and cannot meet the purity, cost, and large-scale production requirements. The conventional method for preparing high-purity crystalline sodium sulfide in the industry is to re-evaporate and crystallize low-concentration sodium sulfide feed liquid to prepare high-purity crystalline sodium sulfide. Therefore, developing a continuous production method for stably preparing high-purity crystalline sodium sulfide with low energy consumption and high controllability has become a technical problem to be solved. SUMMARY

[0005] The present application aims to at least solve one of the above-mentioned technical problems in the prior art. To this end, the present application provides a method for continuously preparing high-purity sodium sulfide from sodium hydrosulfide, which prepares sodium sulfide by reacting sodium hydrosulfide and sodium hydroxide. By taking advantage of the high solubility of sodium hydrosulfide, high-concentration sodium sulfide feed liquid can be obtained without using evaporation process, which can improve the controllability of the reaction endpoint compared to the one-step reaction of preparing sodium sulfide by absorbing hydrogen sulfide with sodium hydroxide. By using two-stage continuous cooling crystallization technology, the amount of crystallization mother liquor is minimized, and the enrichment of impurities in the system is avoided, thereby improving the product quality.

[0006] The first aspect of the present application provides a method for continuously preparing high-purity sodium sulfide from sodium hydrosulfide, comprising the following steps: S1: feeding the sodium hydrosulfide feed liquid into the adjusting kettle, adding sodium hydroxide solution for acid-base control reaction to obtain sodium sulfide feed liquid; S2: feeding the sodium sulfide feed liquid into the multi-stage continuous crystallizer, controlling the temperature in the crystallizer by vacuumizing or external heat exchanger for multi-stage crystallization to obtain crystal slurry, and centrifuging the crystal slurry to obtain mother liquor, part of which is returned to the multi-stage continuous crystallizer to adjust the solid content, and part of which enters the later-stage crystallization process to obtain high-purity crystalline sodium sulfide.

[0007] The present application relates to a technical solution for a method for continuously preparing high-purity crystalline sodium sulfide, which has at least the following beneficial effects: The existing absorption method for preparing sodium sulfide has the problems of low concentration of sodium sulfide solution, the need for evaporation concentration before crystallization, the concentration of impurities in the concentration process, high equipment investment and operating energy consumption, and low economic benefits.

[0008] The application provides a method for continuously preparing high-purity crystalline sodium sulfide, which avoids using evaporation process through chemical concentration method, thereby reducing production energy consumption. Sodium sulfide is prepared by reacting sodium hydrosulfide and sodium hydroxide, and the controllability of the process is improved through a step-by-step reaction. Through a multi-stage continuous crystallization technology, high-purity sodium sulfide is prepared, the amount of crystallization mother liquor is minimized, the enrichment of impurities in the system is avoided, and the product quality is improved.

[0009] The chemical reactions occurring in each step are as follows: Step S1: acid-base regulation reaction NaHS + NaOH → Na2S + H2O This step is to add sodium hydroxide (NaOH) solution to the NaHS solution in the adjustment kettle. This step provides excess OH - , which promotes the complete conversion of NaHS into the final target product, sodium sulfide (Na2S). The key to this step is to control the reaction temperature and time to ensure complete conversion, thereby obtaining pure sodium sulfide solution with a concentration of 27-36%.

[0010] Sodium hydroxide solution is added to the adjustment kettle for acid-base regulation reaction, at this time the reaction system is single in composition and low in impurity content. By controlling the reaction temperature (50-90°C) and time (30-120 min), NaHS can be completely converted into Na2S, and the introduction of excess impurities can be avoided. This step-by-step conversion mode not only avoids the defect that direct reaction is difficult to accurately control, but also reduces the generation and enrichment of impurities in the reaction process, thereby efficiently obtaining Na2S solution with high purity and stable composition, laying a key foundation for subsequent multi-stage continuous crystallization of high-purity crystalline sodium sulfide. It is easy to understand that the purpose of first converting NaOH into NaHS and then adding NaOH to convert NaHS into Na2S is to make the reaction accurately controllable to obtain high-purity Na2S solution.

[0011] Step S2: The Na2S aqueous solution obtained in S1 is sent to a continuous crystallizer, and the operating pressure is reduced by vacuum pumping (-70 to -98 Kpa). Reducing the pressure will lower the boiling point of the solution, thereby rapidly evaporating water at a lower temperature (35-90°C).

[0012] As the solvent (water) continuously evaporates and decreases, the solution gradually becomes supersaturated.

[0013] The solute (Na2S) is precipitated from the supersaturated solution to form crystals (Na2S·xH2O, where x is the number of crystallization water).

[0014] Controlling the crystallization temperature and vacuum degree (i.e. evaporation rate) and crystallization time is the key to obtaining large particle crystals (100-1000 μm) with uniform particle size and complete crystal form.

[0015] Chemical considerations in mother liquor treatment: After centrifugal separation, part of the mother liquor is returned to the crystallizer to adjust the solid content, and the other part is returned to the front end for recycling. This is because the mother liquor still contains uncrystallized Na2S and soluble impurities.

[0016] Impurity control principle: crystallization is a highly efficient purification process. When Na2S crystals form, impurity ions such as Fe, Na2SO3, Na2S2O3, Na2CO3, Cl - , etc. are more difficult to enter the crystal structure due to their properties, and are thus enriched in the mother liquor. By discharging part of the mother liquor (or removing the second-stage crystallization), these impurities can be effectively separated from the product, which is the reason why the final product can achieve extremely high purity.

[0017] According to some embodiments of the present application, in step S1, the mass concentration of the sodium hydroxide solution is 35-45%.

[0018] According to some embodiments of the present application, in step S1, the mass concentration of the sodium hydroxide solution is any one of 35%, 38%, 40%, 42%, 45%, such as 40%, or a range value formed by any two, such as 38%-42%.

[0019] According to some embodiments of the present application, in step S1, the temperature of the acid-base regulation reaction is 50-90°C.

[0020] According to some embodiments of the present application, in step S1, the temperature of the acid-base regulation reaction is any one of 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, such as 85°C, or a range value formed by any two, such as 65°C-85°C.

[0021] According to some embodiments of the present application, in step S1, the time of the acid-base regulation reaction is 30-120 min.

[0022] According to some embodiments of the present application, in step S1, the time of the acid-base regulation reaction is any one of 30 min, 45 min, 60 min, 75 min, 90 min, 105 min, 120 min, such as 60 min, or a range value formed by any two, such as 45 min-90 min.

[0023] According to some embodiments of the present application, in step S2, the content of Na2S in the sodium sulfide feed liquid is 27-37wt%.

[0024] According to some embodiments of the present application, in step S2, the content of Na2S in the sodium sulfide feed solution is any one of 27wt%, 30wt%, 33wt%, 35wt%, 37wt%, such as 33wt%, or a range formed by any two of them, such as 30wt%-35wt%.

[0025] According to some embodiments of the present application, in step S2, the multi-stage continuous crystallizer has two stages.

[0026] According to some embodiments of the present application, in step S2, the temperature of the multi-stage crystallization is 35-90℃.

[0027] According to some embodiments of the present application, in step S2, the temperature of the multi-stage crystallization is any one of 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, such as 52℃, or a range formed by any two of them, such as 45℃-65℃.

[0028] According to some embodiments of the present application, in step S2, the time of the multi-stage crystallization is 1-8h.

[0029] According to some embodiments of the present application, in step S2, the time of the multi-stage crystallization is any one of 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, such as 3h, or a range formed by any two of them, such as 2.5h-5h.

[0030] In step S2, the sodium sulfide feed solution is sent into a multi-stage continuous crystallizer for multi-stage crystallization, which refers to two-stage or three-stage crystallization. The 5.5 water sodium sulfide is obtained by crystallization at 50℃ or above, with a content of ≥44%; the 9 water sodium sulfide is obtained by crystallization below 50℃, with a content of ≥32%.

[0031] In step S2, the multi-stage crystallization can be two-stage or three-stage crystallization, which maximizes the amount of crystallization mother liquor, avoids the enrichment of impurities in the system, and improves the product quality.

[0032] The multi-stage continuous crystallizer is an OSLO crystallizer or a DTB crystallizer or a combination of an OSLO crystallizer and a DTB crystallizer, and the material is titanium, 2205 material or 310S material.

[0033] In step S2, in the step of returning the mother liquor to the multi-stage continuous crystallizer to adjust the solid content, the solid content of the feed solution in the multi-stage continuous crystallizer is controlled to be 20%-40%. The solid content can be measured by a densimeter.

[0034] In the present application, the "high purity" in "high purity crystalline sodium sulfide" refers to the content of impurities such as sodium thiosulfate, sodium sulfite, iron, etc. being lower than that of industrial sodium sulfide product, and is specifically divided into two cases of high purity 5.5 water crystalline sodium sulfide and high purity 9 water crystalline sodium sulfide, depending on the situation.

[0035] According to some embodiments of the present application, the high purity crystalline sodium sulfide includes high purity 5.5 water crystalline sodium sulfide or high purity 9 water crystalline sodium sulfide.

[0036] According to some embodiments of the present application, in the high purity 5.5 water crystalline sodium sulfide, Na2S≥44wt%, Fe≤10ppm, the sum of Na2SO3 and Na2S2O3≤0.5wt%, Na2CO3≤0.5wt%, Cl - ≤0.005wt%.

[0037] According to some embodiments of the present application, in the 9 water crystalline sodium sulfide, Na2S≥32wt%, Fe≤10ppm, the sum of Na2SO3 and Na2S2O3≤0.5wt%, Na2CO3≤0.5wt%, Cl - ≤0.005wt%.

[0038] According to some embodiments of the present application, in step S2, the sodium sulfide feed liquid can be obtained by passing H2S gas into the absorption reaction tower to perform multi-stage countercurrent absorption reaction with 32-45% ion membrane caustic soda solution, thereby obtaining sodium hydrosulfide feed liquid. The multi-stage countercurrent absorption reaction occurs, that is: H2S + NaOH → NaHS + H2O H2S gas is passed into ion membrane caustic soda (i.e. sodium hydroxide NaOH) solution. H2S is a weak acid, and NaOH is a strong base, and the two undergo neutralization reaction. This reaction is carried out in steps: H2S first reacts with NaOH to generate sodium hydrosulfide (NaHS) and water.

[0039] In theory, H2S can continue to react with NaOH to generate sodium sulfide (Na2S), that is: NaHS + NaOH → Na2S + H2O.

[0040] However, in this step, by controlling the process conditions (such as the concentration of alkali, the amount of H2S passing in, multi-stage countercurrent absorption, etc.), the reaction is deliberately controlled to only generate NaHS, thereby obtaining a sodium hydrosulfide (NaHS) feed liquid with a concentration of 35-45%, instead of Na2S.

[0041] According to some embodiments of the present application, in step S2, the sodium sulfide solution can be prepared by introducing H2S gas into an absorption reaction tower, which is a packed absorption reaction tower or a spray absorption reaction tower or a bubble tower, and the multi-stage absorption tower is a two-stage or three-stage absorption tower, and the material is steel lined with Teflon material or steel lined with titanium material.

[0042] According to some embodiments of the present application, in step S2, the sodium sulfide solution can be prepared by introducing H2S gas into an absorption reaction tower, which is a packed absorption reaction tower or a spray absorption reaction tower or a bubble tower, and the multi-stage absorption tower is a two-stage or three-stage absorption tower, and the material is steel lined with Teflon material or steel lined with titanium material.

[0043] The pressure of the tail gas at the top of the multi-stage countercurrent absorption reaction tower is -5~15Kpa, and can be any one of -5Kpa, 0Kpa, 5Kpa, 10Kpa, 15Kpa, such as 5Kpa, or a range value formed by any two of them, such as 0Kpa~10Kpa.

[0044] The number of stages of the multi-stage countercurrent absorption reaction is 2~4 stages.

[0045] The number of stages of the multi-stage countercurrent absorption reaction is any one of 2 stages, 3 stages, and 4 stages, such as 3 stages, or a range value formed by any two of them, such as 2 stages~3 stages.

[0046] The content of NaHS in the sodium hydrosulfide solution is 35~46wt%.

[0047] The content of NaHS in the sodium hydrosulfide solution is any one of 35wt%, 38wt%, 40wt%, 42wt%, 44wt%, and 46wt%, such as 40wt%, or a range value formed by any two of them, such as 38wt%~44wt%.

[0048] The sodium hydrosulfide solution is a high-purity sodium hydrosulfide solution prepared by reacting hydrogen sulfide and sodium hydroxide or commercially available.

[0049] According to some embodiments of the present application, the H2S gas used has a purity of ≥98%.

[0050] In step S2, the sodium sulfide feed solution can be obtained by passing H2S gas into an absorption reaction tower and performing multi-stage countercurrent absorption reaction with a 32-45% ion membrane caustic solution. The 32-45% sodium hydroxide solution is reacted with H2S gas with a content of ≥98% to avoid using evaporation process through chemical concentration, thereby reducing the production energy consumption. Sodium hydroxide and hydrogen sulfide are first reacted to generate sodium hydrosulfide, and then sodium hydrosulfide and sodium hydroxide are reacted to prepare sodium sulfide, thereby improving the controllability of the process through step-by-step reaction. High-purity sodium sulfide is prepared through two-stage continuous cooling crystallization technology, thereby minimizing the amount of crystallization mother liquor, avoiding impurity enrichment in the system, and improving the product quality.

[0051] H2S gas can be obtained by passing hydrogen into a synthesis tower, reacting with liquid sulfur, and then condensing through a condenser. The reaction is as follows: H2 + S → H2S Hydrogen (H2) and liquid sulfur (S) are directly combined under high temperature (350-650°C) and pressure (0.3-0.7 MPa) to generate hydrogen sulfide gas (H2S). This step is the source of the entire process, providing high-purity (≥98%) raw gas for subsequent reactions. High temperature and pressure conditions are designed to improve reaction rate and conversion.

[0052] In the preparation process of H2S gas, the reaction temperature is 350-650°C.

[0053] In the preparation process of H2S gas, the reaction temperature is any one of 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, such as 500°C, or a range value formed by any two, such as 500°C-600°C.

[0054] In the preparation process of H2S gas, the reaction pressure is 0.3-0.7 MPa.

[0055] In the preparation process of H2S gas, the reaction pressure is any one of 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, such as 0.5 MPa, or a range value formed by any two, such as 0.4 MPa-0.6 MPa.

[0056] In the preparation process of H2S gas, the reaction time is 0.1-1.0 h.

[0057] In the preparation process of H2S gas, the reaction time is any one of 0.1 h, 0.2 h, 0.3 h, 0.4 h, 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1.0 h, such as 0.5 h, or a range value formed by any two, such as 0.3 h-0.7 h. Attached Figure Description

[0058] Figure 1 This is a schematic flowchart of the preparation method of the present invention. Detailed Implementation

[0059] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0060] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0061] Unless otherwise specified, "room temperature" in this invention means 25℃±5℃.

[0062] Unless otherwise specified, "about" in this invention means that the allowable error is within ±2%.

[0063] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0064] Example 1 A method for precisely controlling the reaction to continuously prepare high-purity sodium sulfide comprises the following steps: S1: The sodium hydrosulfide solution containing approximately 41.8 wt% NaHS is fed into a regulating vessel (a commercially available closed reaction vessel with a stirrer is sufficient). Under the conditions of reaction temperature of 85℃ and reaction time of 60 min, 40% sodium hydroxide solution is added (add 0.95~1.02 times the theoretical amount, but add 1 times the actual amount) to carry out the reaction, and a sodium hydrosulfide solution containing 33.3 wt% Na2S is obtained. S2: The sodium sulfide solution obtained in step S1 is fed into a two-stage continuous crystallizer (an OSLO crystallizer, a DTB crystallizer, or a combination of the two can be used. In this embodiment, an OSLO crystallizer is used). The first-stage crystallization is performed under a vacuum at a pressure of -88±2 Kpa, and the temperature in the crystallizer is controlled at 52±2℃. The crystallization time is 3h. The obtained crystal slurry is subjected to centrifugal separation. The mother liquor is partially returned to the first-stage crystallizer to adjust the solid content (the solid content in the first-stage crystallizer is monitored and controlled to be 30% by using a density meter), and partially enters the second-stage crystallization process, to obtain: colorless 5.5-hydrated sodium sulfide containing Na2S: 44.5wt%, Fe: 4ppm, Na2SO3+Na2S2O3: 0.33wt%, Na2CO3: 0.1wt%, Cl - : 0.004wt%, and the rest is crystal water, with uniform particle size distribution, large particles (D90=563μm), and good crystal form; The second-stage crystallization is performed under a vacuum at a pressure of -92±2 Kpa, and the temperature in the crystallizer is controlled at 40±2℃. The crystallization time is 2.5h. The obtained crystal slurry is subjected to centrifugal separation. The mother liquor is partially returned to the second-stage crystallizer to adjust the solid content (the solid content in the second-stage crystallizer is monitored and controlled to be 30% by using a density meter), and partially returned to the front end for recycling.

[0065] obtained: colorless 9-hydrated sodium sulfide containing Na2S: 31wt%, Fe: 5ppm, Na2SO3+Na2S2O3: 0.36wt%, Na2CO3: 0.15wt%, Cl - : 0.005wt%, and the rest is crystal water, with uniform particle size distribution, large particles (D90=398μm), and good crystal form.

[0066] In step S2, the content of crystal water can be determined by measuring the content of sodium sulfide and the crystallization temperature.

[0067] In step S1, the sodium bisulfide solution containing NaHS 41.8wt% is obtained by introducing H2S gas with a content of ≥98% (the rest of the impurities is mainly hydrogen) into an absorption reaction tower to react with ion-exchange membrane caustic soda solution in a multi-stage countercurrent absorption reaction. The concentration of the ion-exchange membrane caustic soda is 40wt%, the reaction temperature is 85℃, and the tower top tail gas pressure is 2Kpa.

[0068] The H2S gas with a content of ≥98% (the rest of the impurities is mainly hydrogen) is obtained by introducing hydrogen into a synthesis tower to react with liquid sulfur at 480℃ and 0.52MPa, and then condensing in a condenser.

[0069] The complete process can be referred toFigure 1 As shown.

[0070] Comparative Example 1 A method for the continuous preparation of high-purity sodium sulfide from sodium hydrosulfide comprises the following steps: S1: A sodium hydrosulfide solution containing 28.9 wt% NaHS is fed into a regulating vessel. Under the conditions of reaction temperature of 65℃ and reaction time of 60 min, 25% sodium hydroxide solution is added to carry out the reaction, and a sodium hydrosulfide solution containing 2 wt% Na2S2 is obtained. S2: The sodium sulfide solution obtained in step S1 is fed into a continuous crystallizer. The first-stage crystallization is carried out under vacuum at -91±2 kPa, with the temperature controlled at 52±2℃ for 5 hours. No crystals precipitate during this process. The sodium sulfide solution is then evaporated and concentrated to approximately 30%, followed by vacuuming under -91±2 kPa, maintaining the temperature at 52±2℃ for 4 hours. The resulting slurry is centrifuged; part of the mother liquor is returned to the crystallizer to adjust the solid content, while the rest enters the second-stage crystallization process. The resulting slurry contains 44.5 wt% Na2S, 8 ppm Fe, 0.96 wt% Na2SO3 + Na2S2O3, 0.23 wt% Na2CO3, and Cl... - It contains 0.007 wt% sodium sulfide 5,5-hydrate, with the remainder being water of crystallization. Compared to direct chemical concentration, the impurity content is significantly higher, and it requires evaporation and concentration, resulting in higher energy consumption.

[0071] In step S1, the sodium hydrosulfide solution containing 28.9 wt% NaHS is obtained by passing H2S gas with a content of 65.8% into the absorption reaction tower and reacting it with the caustic soda solution in a multi-stage countercurrent absorption process using an ion-exchange membrane. The concentration of caustic soda in the ion-exchange membrane is 25 wt%, the reaction temperature is 40℃, and the tail gas pressure at the top of the tower is 10 kPa.

[0072] The preparation of H2S gas with a content of 65.8% involves passing hydrogen gas into a synthesis tower and reacting it with liquid sulfur at 300°C and 0.4 MPa. The mixture is then condensed in a condenser to obtain H2S gas with a content of 65.8%.

[0073] In Comparative Example 1: During the preparation of H2S gas, the reaction temperature was only 300℃, lower than the 480℃ in Example 1, and did not reach the optimal active range (350~650℃) for the reaction between hydrogen and sulfur. The low temperature led to incomplete reaction, and the generated H2S contained unreacted hydrogen, sulfur vapor, and byproducts (such as polysulfides), with a purity of only 65.8%.

[0074] Impurities enter the absorption system along with H2S, directly causing contaminants such as iron and chlorine to mix into the sodium hydrosulfide solution in S1, thus creating a hidden danger of excessive impurities in the final product.

[0075] In the preparation of a sodium hydrosulfide solution containing 28.9 wt% NaHS, a 25 wt% low-concentration NaOH solution was used, which is much lower than the 40 wt% in Example 1, resulting in the failure of chemical concentration in both steps (generation of NaHS and generation of Na2S). The sodium sulfide concentration obtained in step S1 is only 22 wt%, which does not reach the saturation threshold for direct crystallization (≥27 wt%). Therefore, an evaporation concentration process must be added to increase the sodium sulfide concentration to 30%. This process not only consumes a large amount of steam (energy consumption is more than 30% higher than in Example 1), but also causes the simultaneous concentration of impurities (such as Fe and Na2SO3), resulting in a final product with a Fe content of 8 ppm, which exceeds the requirement of high-end fields (≤10 ppm). During the evaporation process, high temperature (≥100°C) accelerates the hydrolysis of sodium sulfide to generate NaHS, resulting in a decrease in product yield of about 5%, and the hydrolysis products will scale on the inner wall of the equipment, increasing the frequency of shutdown and cleaning, affecting the stability of continuous production.

[0076] In Comparative Example 1, the same crystallization temperature (52°C) as in Example 1 was used at the beginning of S2, but because the sodium sulfide concentration was only 22 wt%, it did not reach the supersaturation state, resulting in no crystals precipitating within 5 h, and the process was interrupted.

[0077] Even after evaporation and concentration to 30%, the crystallization time still needs to be 4 h (only 3 h in Example 1), and during the concentration process, impurities are enriched, resulting in a final product with a total of Na2SO3 and Na2S2O3 of 0.96 wt%, which is 2.9 times that of Example 1 (0.33 wt%), and cannot meet the purity requirements of the medical, high-end leather-making, and other fields.

[0078] In addition, although Comparative Example 1 uses a mother liquor return process, because of the high initial impurity base, the returned mother liquor further aggravates the accumulation of impurities in the system, forming a vicious cycle of impurity enrichment-product exceeding standards-mother liquor waste, compared with the low-impurity cycle of Example 1, the raw material utilization rate is reduced by about 8%.

[0079] In terms of cost, the energy consumption cost of the evaporation concentration process, the depreciation of the equipment (evaporation tank, heat exchanger), and the cost of solid waste treatment (scaling waste residue) make the unit production cost of Comparative Example 1 more than 25% higher than that of Example 1, lacking market competitiveness.

[0080] In terms of technology, the product purity does not meet the standard (Fe=8 ppm, total impurities≥1.27 wt%), and can only be used in low-end industrial fields (such as ordinary mineral processing), and cannot enter the high-value-added market (such as medical intermediates and high-end polymer synthesis), and the technical applicability is much lower than that of Example 1.

[0081] The application provides a method for continuously preparing high-purity sodium sulfide from sodium hydrosulfide, which comprises the following steps: feeding the sodium hydrosulfide solution into a regulating kettle, adding sodium hydroxide solution to perform acid-base regulation and reaction, obtaining a sodium sulfide solution, feeding the sodium sulfide solution into a multi-stage continuous crystallizer, performing multi-stage crystallization reaction by vacuumizing or externally adding a heat exchanger to control the temperature in the crystallizer, obtaining a crystal slurry, centrifugally separating the crystal slurry to obtain a mother liquor, and returning part of the mother liquor to the multi-stage continuous crystallizer to adjust the solid content, and feeding the other part of the mother liquor into a later-stage crystallization process to obtain high-purity crystalline sodium sulfide. The method prepares sodium sulfide by the reaction of sodium hydrosulfide and sodium hydroxide, and improves the controllability of the process by step-by-step reaction. The high-purity sodium sulfide is prepared by two-stage continuous cooling crystallization technology, which maximally reduces the amount of the crystallization mother liquor, avoids the enrichment of impurities in the system, and improves the product quality.

[0082] The application has been described in detail above in combination with the embodiments, but the application is not limited to the above-described embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the application.

Claims

1. A method for continuous production of high purity sodium sulfide from sodium hydrosulfide, characterized by, The method comprises the following steps: S1: sending a sodium hydrosulfide solution into an adjusting kettle, adding a sodium hydroxide solution to perform an acid-base control reaction, and obtaining a sodium sulfide solution; S2: sending the sodium sulfide solution into a multi-stage continuous crystallizer, controlling the temperature in the crystallizer by vacuumizing or externally placing a heat exchanger to perform multi-stage crystallization, obtaining a crystal slurry, centrifugally separating the crystal slurry to obtain a mother liquor, and returning part of the mother liquor to the multi-stage continuous crystallizer to adjust the solid content, and part of the mother liquor entering a later-stage crystallization process to obtain high-purity crystalline sodium sulfide.

2. The method of claim 1, wherein, In step S1, the content of NaHS in the sodium hydrosulfide solution is 35-46 wt%.

3. The method of claim 1, wherein, In step S1, the temperature of the acid-base control reaction is 50-90°C; and / or, the time of the acid-base control reaction is 30-120 min.

4. The method of claim 1, wherein, In step S2, the content of Na2S in the sodium sulfide solution is 27-37 wt %.

5. The method of claim 1, wherein, In step S2, the temperature of the multi-stage crystallization is 35-90°C.

6. The method of claim 1, wherein, In step S2, the time of the multi-stage crystallization is 1-8 h.

7. The method of claim 1, wherein, In the step of returning part of the mother liquor to the multi-stage continuous crystallizer to adjust the solid content, the solid content of the solution in the multi-stage continuous crystallizer is controlled to be 20%-40%.

8. The method according to any one of claims 1 to 7, characterized in that, The high-purity crystalline sodium sulfide includes high-purity 5.5 water crystalline sodium sulfide or high-purity 9 water crystalline sodium sulfide.

9. The method of claim 8, wherein, In the high-purity 5.5 water crystalline sodium sulfide, Na2S≥44wt%, Fe≤10ppm, the sum of Na2SO3 and Na2S2O3≤0.5wt%, Na2CO3≤0.5wt%, Cl - ≤0.005wt%.

10. The method of claim 8, wherein, In the high-purity 9-hydrate crystalline sodium sulfide, Na2S≥32wt%, Fe≤10ppm, the sum of Na2SO3 and Na2S2O3≤0.5wt%, Na2CO3≤0.5wt%, Cl - ≤0.005wt%.

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