A process for the production of sodium carbonate and sulphur from sodium sulphate and carbon

Abstract

The application discloses a method for producing sodium carbonate and sulfur by using sodium sulfate and carbon, and belongs to the technical field of regenerating reaction agents and preparing chemicals. The method uses industrial waste sodium sulfate and common charcoal which is easy to obtain as raw materials, and uses the oxidation-reduction mechanism and the instability of the intermediate product sodium sulfide to produce the highly demanded soda ash. The raw materials used in the method are rich in sources and low in price, and the method has a cost advantage. In the process, ammonia gas is not needed, the preparation process has the characteristics of low carbon dioxide emission and no solid waste emission, and the risk of environmental pollution can be reduced. In addition, the process of the application is simple, the preparation efficiency is high, the process is suitable for scale-up production, and has large-scale production potential.

Description

Technical Field

[0001] This invention relates to the fields of reactant regeneration and chemical preparation technology, and more particularly to a method for producing sodium carbonate and sulfur using sodium sulfate and carbon. Background Technology

[0002] Sulfuric acid and sodium carbonate are widely used in metallurgy, chemicals, and pharmaceuticals. With the rapid development of the lithium battery industry in recent years, the lithium extraction process involves the reaction of lithium sulfate (Li₂SO₄) and sodium carbonate (Na₂CO₃), generating large quantities of mirabilite (sodium sulfate decahydrate, Na₂SO₄·10H₂O) that urgently needs treatment. Statistics show that the annual production of waste sodium sulfate has exceeded 10 million tons in recent years, but less than 5% of this waste sodium sulfate is reused. This is because sodium sulfate has limited applications, low demand, low economic value, and is difficult to process, resulting in large-scale stockpiling and hindering the formation of a complete sodium sulfate treatment chain for resource recovery.

[0003] Currently, there are roughly two methods for treating wastewater containing sodium sulfate: one is to add lime water to convert it into a calcium sulfate and sodium hydroxide solution; the other is to concentrate and crystallize it, extract sodium sulfate, and then solidify and pile it up. The lime water conversion method has been gradually abandoned, but the high calcium and magnesium content in the sodium hydroxide solution makes it unsuitable for the production of high-purity products. Furthermore, the calcium sulfate generated in this process is also difficult to dispose of due to accumulation. Crystallization and concentration is a common industrial treatment method, yielding mirabilite after evaporation and concentration, which is then solidified and piled up to prevent environmental discharge. While this method currently does not cause environmental pollution, the carrying capacity of factories and the environment is limited, and this problem will inevitably be faced in the future. Currently, no mainstream solution has been proposed in this field for waste sodium sulfate; only a small amount is purified and used as a chemical in glass manufacturing, desiccants, and animal feed.

[0004] On the other hand, the chemical industry has a huge demand for sodium carbonate, and how to convert sodium sulfate into sodium carbonate has attracted widespread attention. For example, Chinese invention patent CN115193252A discloses a method for regenerating and recycling sodium sulfate from desulfurization solid waste. The method involves placing the sodium sulfate waste in a reaction apparatus, introducing a gaseous reducing agent, and carrying out a reduction reaction at 500–750°C. Iron-containing compounds can be added as catalysts. After reduction, a mixture of carbon dioxide and water is introduced to obtain sodium carbonate and sodium bicarbonate. The obtained sodium bicarbonate is then used for desulfurization. However, this method requires the introduction of additional reducing gas or the use of a catalyst, increasing application costs. Furthermore, its target product is sodium bicarbonate, while sodium carbonate has low yield and purity. Additionally, sodium carbonate and sodium bicarbonate have similar properties, making separation difficult. This technical solution is insufficient to meet the production demand for converting sodium sulfate into sodium carbonate.

[0005] Currently, some scholars have studied the co-production of sodium carbonate and ammonium sulfate from sodium sulfate and ammonium carbonate, but these methods also suffer from limited annual processing capacity and low sodium carbonate purity. Additionally, there have been studies on the co-production of ammonium sulfate, hydrochloric acid, and sodium hydroxide from sodium sulfate and ammonium chloride via electrochemical membrane filtration; however, the processing rate is slow, and the prospects for large-scale production are bleak.

[0006] Therefore, developing a low-cost, low-carbon dioxide (CO2) emission, and environmentally friendly sodium sulfate to sodium carbonate conversion technology to alleviate the environmental pressure caused by sodium sulfate is of great significance and promise. Summary of the Invention

[0007] In view of the above-mentioned deficiencies of the prior art, in a first aspect of the present invention, a method for producing sodium carbonate and sulfur using sodium sulfate and carbon is provided, comprising the following steps:

[0008] (1) Using sodium sulfate as a substrate and char as an excess reactant, sodium sulfate and char are mixed to form a mixed precursor;

[0009] (2) The mixed precursor is calcined in an inert atmosphere to convert sodium sulfate into sodium sulfide, and a solid crude product containing sodium sulfide is obtained. The carbon monoxide and carbon dioxide product gases produced by the reaction are collected.

[0010] (3) The solid crude product is subjected to a second stage of roasting under the condition of circulating the product gas, so that sodium sulfide reacts to generate sodium carbonate and sulfur, and the roasted crude product is obtained.

[0011] (4) Separate the sulfur from the roasted crude product to obtain the desulfurized crude product;

[0012] (5) Dissolve the sodium carbonate in the crude desulfurization product with a solvent, filter out the insoluble carbon and collect the filtrate, separate the solvent and sodium carbonate in the filtrate, and obtain sodium carbonate.

[0013] In this invention, the source of sodium sulfate is not particularly limited, and waste sodium sulfate obtained from industrial purification and impurity removal is applicable. During the mixing process of sodium sulfate and charcoal, processing the charcoal into fine particles or powder (e.g., pulverizing to a particle size of about 0.1 mm) helps to achieve uniform mixing and increase the reaction contact area. This step can be performed according to the actual process conditions.

[0014] In actual production, due to the limitations of reaction kinetics, a relatively excessive amount of carbon needs to be added to ensure that the sodium sulfate reacts more fully.

[0015] Preferably, in step (1), the molar ratio of sodium sulfate to carbon is 1:4.5 to 6.

[0016] Preferably, in step (2), the roasting temperature of the first stage is 750-800℃ and the roasting time is 2-4h.

[0017] The sulfur generated during the second-stage roasting process may come into contact with air and generate sulfur dioxide, a polluting gas, if the seal is not tight. This will not only reduce the sulfur yield but also cause harm to the environment and operators.

[0018] Preferably, in step (3), during the second stage of roasting, the sulfur generated by the reaction must be controlled to prevent it from coming into contact with air.

[0019] Preferably, in step (3), the second stage roasting temperature is 300-400℃ and the roasting time is 2-8h.

[0020] By changing the physical state of the target product sulfur under temperature-driven conditions, sulfur can be converted from a solid state to a gaseous state. The collected sulfur vapor can then be condensed to obtain solid sulfur again, thus easily completing the separation of sulfur. Among these methods, vacuum distillation is simple to operate and is very suitable for the separation and recovery of sulfur in this process.

[0021] Preferably, in step (4), sulfur is separated by vacuum distillation.

[0022] More preferably, the vacuum distillation is carried out at a pressure of 1–100 Pa, a working temperature of 200–300 °C, and a processing time of 3–5 h.

[0023] Sodium carbonate is readily soluble in water, and water, as a low-cost, environmentally friendly solvent, is non-polluting. There are various methods for separating sodium carbonate from the solvent, including distillation and crystallization. Among these, collecting sodium carbonate by cooling and crystallizing from the filtrate, based on the temperature-dependent solubility of sodium carbonate in solution, is particularly suitable for this step.

[0024] Preferably, in step (5), the solvent is water, and sodium carbonate is collected by cooling crystallization.

[0025] In a further preferred embodiment, in the cooling crystallization method, the crude desulfurization product and deionized water are mixed at 40-60°C to dissolve and form a saturated sodium carbonate solution. The insoluble carbon is removed by filtration, and the saturated sodium carbonate solution is cooled to below 20°C but not lower than 0°C to precipitate sodium carbonate crystals. Sodium carbonate is obtained after vacuum filtration and drying.

[0026] Some of the raw materials used in this invention can be recycled in the process, which improves the efficiency of raw material use and reduces process costs.

[0027] Preferably, in step (5), the carbon obtained from filtration can be recycled and reused.

[0028] Preferably, in step (5), the solvent obtained from the separated filtrate can be recycled for dissolving sodium carbonate.

[0029] Based on the above technical solutions, the inventive concept of this invention lies in using industrially produced waste sodium sulfate and readily available ordinary charcoal as raw materials, and utilizing the redox mechanism and the instability of the intermediate product sodium sulfide to produce the highly sought-after soda ash. The essence of this process is an improvement on the second stage of the Lubrizol soda ash production process through a second-stage roasting process.

[0030] The second-stage reaction formula for the Lubrizol alkali production process:

[0031] Na₂S + CaCO₃ = Na₂CO₃ + CaS;

[0032] The second-stage calcination reaction formula of this invention is as follows:

[0033] Na2S+2CO2(g)=Na2CO3+S+CO(g);

[0034] Na2S+CO2(g)+CO(g)=Na2CO3+S+C;

[0035] Compared with the Lubrizol process, this process has the following advantages: (1) no calcium sulfide (CaS) is generated, and there are no sulfur impurities in the soda ash; (2) the temperature is milder; (3) it can effectively absorb carbon dioxide and has carbon capture potential.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] This invention provides a method for producing sodium carbonate and sulfur using sodium sulfate and carbon. The raw materials used in this method are abundant and inexpensive, giving it a cost advantage. The process does not require the use of ammonia, and the preparation process features low carbon dioxide emissions and no solid waste emissions, which can reduce the risk of environmental pollution. In addition, the process of this invention is simple, has high preparation efficiency, is suitable for scale-up production, and has the potential for large-scale production. Attached Figure Description

[0038] Figure 1 This is a process flow diagram for producing sodium carbonate and sulfur using sodium sulfate and carbon. Detailed Implementation

[0039] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0040] Example 1

[0041] The process flow for producing sodium carbonate and sulfur using sodium sulfate and carbon is as follows: Figure 1 As shown, the steps are as follows:

[0042] (1) Powder 100g of sodium sulfate and 38.05g of charcoal in a crusher to about 0.1mm, and mix for 1 hour to ensure uniform mixing to form a mixed precursor;

[0043] (2) The mixed precursors were placed in a tube furnace and heated to 750°C. The first stage of roasting was carried out at a constant temperature for 2 hours to obtain a crude product containing solids and collect the product gas.

[0044] (3) After the first stage of roasting is completed, the temperature is reduced to 300℃. At this temperature, the product gas is circulated and the solid crude product is roasted in the second stage. After 2 hours of treatment, the tube furnace is cooled to room temperature to obtain the roasted crude product.

[0045] (4) Transfer the calcined crude product to a vacuum distillation apparatus, control the pressure below 100 Pa, the operating temperature at 200 °C, distill for 3 hours, and collect the separated sulfur product (S). x And obtain the crude desulfurized product;

[0046] (5) Using the cooling crystallization method, the sodium carbonate in the crude desulfurization product is dissolved in deionized water and then filtered to separate the residual charcoal powder. The saturated sodium carbonate solution obtained by filtration is cooled to precipitate sodium carbonate crystals, which are then dried by filtration to obtain soda ash product (Na2CO3). The recovered charcoal powder and deionized water can be recycled.

[0047] The products of this embodiment are shown in Table 1.

[0048] Table 1:

[0049]

[0050] In the table, “—” indicates no filling, and the resulting product is a mixture mainly composed of Na2CO3.

[0051] Example 2

[0052] The method for producing sodium carbonate and sulfur using sodium sulfate and carbon involves the following steps:

[0053] (1) Powder 100g of sodium sulfate and 38.05g of charcoal in a crusher to about 0.1mm, and mix for 1 hour to ensure uniform mixing to form a mixed precursor;

[0054] (2) The mixed precursors were placed in a tube furnace and heated to 750°C. The first stage of roasting was carried out at a constant temperature for 2 hours to obtain a crude product containing solids and collect the product gas.

[0055] (3) After the first stage of roasting is completed, the temperature is reduced to 300℃. At this temperature, the product gas is circulated and the solid crude product is roasted in the second stage. After 4 hours of treatment, the tube furnace is cooled to room temperature to obtain the roasted crude product.

[0056] (4) Transfer the calcined crude product to a vacuum distillation apparatus, control the pressure below 100 Pa, the operating temperature at 200 °C, distill for 3 hours, and collect the separated sulfur product (S). x And obtain the crude desulfurized product;

[0057] (5) Using the cooling crystallization method, the sodium carbonate in the crude desulfurization product is dissolved in deionized water and then filtered to separate the residual charcoal powder. The saturated sodium carbonate solution obtained by filtration is cooled to precipitate sodium carbonate crystals, which are then dried by filtration to obtain soda ash product (Na2CO3). The recovered charcoal powder and deionized water can be recycled.

[0058] The products of this embodiment are shown in Table 2.

[0059] Table 2:

[0060] category Vacuum distillation products Filtration and separation products final product Element sulfur carbon <![CDATA[Na2SO4、Na2CO3]]> content 98.53％ Consistent with the initial charcoal —

[0061] In the table, “—” indicates no filling, and the resulting product is a mixture mainly composed of Na2CO3.

[0062] Example 3

[0063] The method for producing sodium carbonate and sulfur using sodium sulfate and carbon involves the following steps:

[0064] (1) Powder 100g of sodium sulfate and 38.05g of charcoal in a crusher to about 0.1mm, and mix for 1 hour to ensure uniform mixing to form a mixed precursor;

[0065] (2) The mixed precursors were placed in a tube furnace and heated to 800°C. The first stage of roasting was carried out at a constant temperature for 2 hours to obtain a crude product containing solids and collect the product gas.

[0066] (3) After the first stage of roasting is completed, the temperature is reduced to 300℃. At this temperature, the product gas is circulated and the solid crude product is roasted in the second stage. After 4 hours of treatment, the tube furnace is cooled to room temperature to obtain the roasted crude product.

[0067] (4) Transfer the calcined crude product to a vacuum distillation apparatus, control the pressure below 100 Pa, the operating temperature at 200 °C, distill for 3 hours, and collect the separated sulfur product (S). x And obtain the crude desulfurized product;

[0068] (5) Using the cooling crystallization method, the sodium carbonate in the crude desulfurization product is dissolved in deionized water and then filtered to separate the residual charcoal powder. The saturated sodium carbonate solution obtained by filtration is cooled to precipitate sodium carbonate crystals, which are then dried by filtration to obtain soda ash product (Na2CO3). The recovered charcoal powder and deionized water can be recycled.

[0069] The products of this embodiment are shown in Table 3.

[0070] Table 3:

[0071] category Vacuum distillation products Filtration and separation products final product Element sulfur carbon <![CDATA[NaOH、Na2CO3]]> content 98.76％ Consistent with the initial charcoal —

[0072] In the table, “—” indicates no filling, and the resulting product is a mixture mainly composed of Na2CO3.

[0073] Example 4

[0074] The method for producing sodium carbonate and sulfur using sodium sulfate and carbon involves the following steps:

[0075] (1) Powder 100g of sodium sulfate and 38.05g of charcoal in a crusher to about 0.1mm, and mix for 1 hour to ensure uniform mixing to form a mixed precursor;

[0076] (2) The mixed precursors were placed in a tube furnace and heated to 800°C. The first stage of roasting was carried out at a constant temperature for 2 hours to obtain a crude product containing solids and collect the product gas.

[0077] (3) After the first stage of roasting is completed, the temperature is reduced to 350℃. At this temperature, the product gas is circulated and the solid crude product is roasted in the second stage. After 4 hours of treatment, the tube furnace is cooled to room temperature to obtain the roasted crude product.

[0078] (4) Transfer the calcined crude product to a vacuum distillation apparatus, control the pressure below 50 Pa, operate at 200 °C, distill for 3 hours, and collect the separated sulfur product (S). x And obtain the crude desulfurized product;

[0079] (5) Using the cooling crystallization method, the sodium carbonate in the crude desulfurization product is dissolved in deionized water and then filtered to separate the residual charcoal powder. The saturated sodium carbonate solution obtained by filtration is cooled to precipitate sodium carbonate crystals, which are then dried by filtration to obtain soda ash product (Na2CO3). The recovered charcoal powder and deionized water can be recycled.

[0080] The products of this embodiment are shown in Table 4.

[0081] Table 4:

[0082] category Vacuum distillation products Filtration and separation products final product Element sulfur carbon <![CDATA[NaOH、Na2CO3]]> content 99.15％ Consistent with the initial charcoal —

[0083] In the table, “—” indicates no filling, and the resulting product is a mixture mainly composed of Na2CO3.

[0084] Example 5

[0085] The method for producing sodium carbonate and sulfur using sodium sulfate and carbon involves the following steps:

[0086] (1) Powder 100g of sodium sulfate and 38.05g of charcoal in a crusher to about 0.1mm, and mix for 1 hour to ensure uniform mixing to form a mixed precursor;

[0087] (2) The mixed precursors were placed in a tube furnace and heated to 800°C. The first stage of roasting was carried out at a constant temperature for 2 hours to obtain a crude product containing solids and collect the product gas.

[0088] (3) After the first stage of roasting is completed, the temperature is reduced to 400℃. At this temperature, the product gas is circulated and the solid crude product is roasted in the second stage. After 4 hours of treatment, the tube furnace is cooled to room temperature to obtain the roasted crude product.

[0089] (4) Transfer the calcined crude product to a vacuum distillation apparatus, control the pressure below 50 Pa, operate at 200 °C, distill for 3 hours, and collect the separated sulfur product (S). x And obtain the crude desulfurized product;

[0090] (5) Using the cooling crystallization method, the sodium carbonate in the crude desulfurization product is dissolved in deionized water and then filtered to separate the residual charcoal powder. The saturated sodium carbonate solution obtained by filtration is cooled to precipitate sodium carbonate crystals, which are then dried by filtration to obtain soda ash product (Na2CO3). The recovered charcoal powder and deionized water can be recycled.

[0091] The products of this embodiment are shown in Table 5.

[0092] Table 5:

[0093] category Vacuum distillation products Filtration and separation products final product Element sulfur carbon <![CDATA[NaOH、Na2CO3]]> content 99.36％ Consistent with the initial charcoal —

[0094] In the table, “—” indicates no filling, and the resulting product is a mixture mainly composed of Na2CO3.

[0095] Example 6

[0096] The method for producing sodium carbonate and sulfur using sodium sulfate and carbon involves the following steps:

[0097] (1) Powder 100g of sodium sulfate and 38.05g of charcoal in a crusher to about 0.1mm, and mix for 1 hour to ensure uniform mixing to form a mixed precursor;

[0098] (2) The mixed precursors were placed in a tube furnace and heated to 800°C. The first stage of roasting was carried out at a constant temperature for 2 hours to obtain a crude product containing solids and collect the product gas.

[0099] (3) After the first stage of roasting is completed, the temperature is reduced to 400℃. At this temperature, the product gas is circulated and the solid crude product is roasted in the second stage. After 8 hours of treatment, the tube furnace is cooled to room temperature to obtain the roasted crude product.

[0100] (4) Transfer the calcined crude product to a vacuum distillation apparatus, control the pressure below 50 Pa, operate at 200 °C, distill for 3 hours, and collect the separated sulfur product (S). x And obtain the crude desulfurized product;

[0101] (5) Using the cooling crystallization method, the sodium carbonate in the crude desulfurization product is dissolved in deionized water and then filtered to separate the residual charcoal powder. The saturated sodium carbonate solution obtained by filtration is cooled to precipitate sodium carbonate crystals, which are then dried by filtration to obtain soda ash product (Na2CO3). The recovered charcoal powder and deionized water can be recycled.

[0102] The products of this embodiment are shown in Table 6.

[0103] Table 6:

[0104] category Vacuum distillation products Filtration and separation products final product Element sulfur carbon <![CDATA[Na2CO3]]> content 99.73％ Consistent with the initial charcoal 99.67％

[0105] In summary, based on the parameters of the examples and the results in Tables 1-6, it can be seen that at lower temperatures and shorter calcination times, the conversion of sodium sulfate to sodium sulfide or the conversion of sodium sulfide to sodium carbonate is easily incomplete. In Examples 1-5, the purity of sulfur was mainly affected by the incomplete conversion of sodium sulfide. After adjusting the parameters, the purity of sulfur was finally achieved at 99.73%, and the purity of sodium carbonate at 99.67%, meeting industrial-grade standards.

[0106] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for producing sodium carbonate and sulfur using sodium sulfate and carbon, characterized in that, Includes the following steps: (1) Using sodium sulfate as a substrate and char as an excess reactant, sodium sulfate and char are mixed to form a mixed precursor; The molar ratio of sodium sulfate to carbon is 1:4.5~6; (2) The mixed precursor is calcined in an inert atmosphere to convert sodium sulfate into sodium sulfide, and a solid crude product containing sodium sulfide is obtained. The carbon monoxide and carbon dioxide product gases produced by the reaction are collected. The first stage of roasting is carried out at a temperature of 750~800 ℃ for 2~4 h. (3) The solid crude product is subjected to a second stage of roasting under the condition of circulating the product gas, so that sodium sulfide reacts to generate sodium carbonate and sulfur, and the roasted crude product is obtained. During the second stage of roasting, it is necessary to control the sulfur generated by the reaction to prevent it from coming into contact with air; The second stage of roasting is carried out at a temperature of 300~400 ℃ for 2~8 h. (4) Separate the sulfur from the roasted crude product to obtain the desulfurized crude product; (5) Dissolve the sodium carbonate in the crude desulfurization product with a solvent, filter out the insoluble carbon and collect the filtrate, separate the solvent and sodium carbonate in the filtrate, and obtain sodium carbonate.

2. The method according to claim 1, characterized in that: In step (4), sulfur is separated by vacuum distillation.

3. The method according to claim 2, characterized in that: The vacuum distillation process involves a pressure of 1-100 Pa, an operating temperature of 200-300 ℃, and a processing time of 3-5 h.

4. The method according to claim 1, characterized in that: In step (5), the solvent is water, and sodium carbonate is collected by cooling crystallization.

5. The method according to claim 4, characterized in that: In the cooling crystallization method, the crude desulfurization product and deionized water are mixed at 40~60 ℃ to dissolve and form a saturated sodium carbonate solution. The insoluble carbon is removed by filtration. The saturated sodium carbonate solution is cooled to below 20 ℃ and not lower than 0 ℃ to precipitate sodium carbonate crystals. Sodium carbonate is obtained after vacuum filtration and drying.

6. The method according to claim 1, characterized in that: In step (5), the carbon obtained from filtration can be recycled and reused; the solvent obtained from the separated filtrate can be recycled to dissolve sodium carbonate.

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