Combined preparation method of high-purity magnesium hydroxide and ionic membrane caustic soda raw material sodium chloride

Abstract

The invention discloses a combined preparation method of high-purity magnesium hydroxide and an ionic membrane caustic soda raw material sodium chloride, and belongs to the technical field of chemical material preparation and resource recycling. The method comprises the following steps: by taking byproduct hydrochloric acid and magnesium oxide of a methane chloride device as raw materials, carrying out acid dissolution reaction to generate magnesium chloride crude liquid, removing impurities through pretreatment, adjusting the pH value of a system, selectively extracting magnesium ions by adopting an acidic phosphorus extraction agent, and carrying out reverse extraction by utilizing a sodium hydroxide solution to generate high-purity magnesium hydroxide precipitate; meanwhile, after being refined, a sodium chloride solution generated in the reverse extraction and organic phase regeneration process is returned to the ionic membrane device as a raw material for producing caustic soda, so that a resource closed-loop cycle from ionic membrane caustic soda to methane chloride to magnesium hydroxide to ionic membrane caustic soda is realized. The method not only effectively utilizes the byproduct hydrochloric acid of the methane chloride device, but also provides a qualified sodium chloride raw material for the ionic membrane device, reduces the raw material purchase cost and waste discharge, and is suitable for large-scale industrial application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical material preparation and resource recycling, and in particular to a combined preparation method of high-purity magnesium hydroxide and ion-exchange membrane caustic soda raw material sodium chloride. BACKGROUND

[0002] In the chemical industry, methane chlorides (such as dichloromethane, chloroform, carbon tetrachloride) production devices usually use methane and chlorine as raw materials, and a large amount of hydrochloric acid (HCl mass fraction 28% to 32%) is produced as a byproduct in the reaction process. If the byproduct hydrochloric acid is directly sold or discharged, not only is the economic benefit low, but there is also environmental protection treatment pressure. At the same time, ion-exchange membrane caustic soda production devices use refined sodium chloride solution as raw material to produce caustic soda, chlorine and hydrogen through electrolysis, and the chlorine can be used as raw material for methane chlorides devices, forming a preliminary industrial chain of "ion-exchange membrane caustic soda to methane chlorides".

[0003] In the prior art, the utilization methods of methane chlorides byproduct hydrochloric acid mainly include hydrochloric acid desorption to prepare chlorine, and use for metal pickling, etc., but the hydrochloric acid desorption has high energy consumption, large equipment investment, and low added value of pickling application; and the sodium chloride raw material of ion-exchange membrane caustic soda devices depends on the purchase of industrial salt, which has high procurement cost and is greatly affected by market price fluctuations. In addition, the preparation of high-purity magnesium hydroxide often consumes hydrochloric acid and sodium hydroxide, and if the methane chlorides byproduct hydrochloric acid and the upstream and downstream resources of ion-exchange membrane caustic soda can be integrated to realize the cycle of "byproduct hydrochloric acid utilization to magnesium hydroxide production to sodium chloride recycling", the resource utilization rate and economic benefit can be significantly improved.

[0004] The existing magnesium hydroxide preparation technology (such as direct precipitation method, conventional extraction to stripping method) does not combine the resource cooperation between chemical devices, and has problems such as that the byproduct sodium chloride cannot be efficiently recycled, and the byproduct hydrochloric acid is not fully utilized, which cannot meet the cyclic production needs of joint enterprises. Therefore, it has important industrial value to develop a combined preparation method of high-purity magnesium hydroxide and sodium chloride which can connect methane chlorides and ion-exchange membrane caustic soda devices and realize resource closed loop. SUMMARY

[0005] The present application aims to overcome the deficiencies of the existing magnesium hydroxide preparation technology which does not combine the resource cooperation between chemical devices, and that the byproduct sodium chloride cannot be efficiently recycled and the byproduct hydrochloric acid is not fully utilized; A combined preparation method of high-purity magnesium hydroxide and ion-exchange membrane caustic soda raw material sodium chloride is provided, which comprises the following steps: Step 1. Acid-soluble reaction: mixing and reacting magnesium oxide with the byproduct hydrochloric acid of the methane chlorides device at normal temperature and pressure, so that the hydrochloric acid in the mixture is in excess by 5% to 10%, and the reaction is carried out for 30 to 60 minutes to generate a magnesium chloride crude liquid with a magnesium chloride mass fraction of 10% to 20%; Step 2. Pretreatment: Add magnesium oxide powder or dilute sodium hydroxide solution to the crude magnesium chloride solution to adjust the pH to 2.0 to 3.0; Step 3. Extraction: The pretreated magnesium chloride solution is fed into the extraction tank, and an organic phase consisting of an acidic phosphorus extractant and a diluent is added. The volume ratio of the organic phase to the aqueous phase is controlled at 1:1 to 2:1, the stirring speed is 300 to 500 rpm, the extraction temperature is 25 to 40℃, and 3 to 5 stages of countercurrent extraction are used to obtain an organic phase loaded with magnesium ions and an aqueous phase containing impurities. Step 4. Back-extraction: Add 5% to 10% sodium hydroxide solution by mass to the magnesium-loaded organic phase, so that the sodium hydroxide in the organic phase is 10% to 15% in excess. Control the volume ratio of organic phase to aqueous phase to be 2:1 to 3:1, stir at 40 to 60°C, and react for 30 to 45 minutes to generate an aqueous phase containing magnesium hydroxide precipitate and sodium chloride, as well as a regenerated organic phase. Step 5. Solid-liquid separation and magnesium hydroxide purification: Filter the aqueous-organic phase mixture after back-extraction to obtain magnesium hydroxide precipitate, wash it with deionized water 3 to 4 times until the conductivity of the washing water is ≤50μS / cm, and dry it at 100 to 120℃ for 4 to 6 hours to obtain high-purity magnesium hydroxide product. Step 6. Refining and reusing sodium chloride: The filtered filtrate is evaporated and concentrated to a NaCl mass fraction of 30% to 32%. Sodium carbonate is then added to remove Ca²⁺ and calcium, and sodium hydroxide is added to remove residual Mg²⁺ and magnesium, resulting in a sodium chloride solution with a purity ≥99.0%. This solution is then transported to the ion-exchange membrane caustic soda production unit for the preparation of caustic soda.

[0006] As a preferred embodiment, the purity of magnesium oxide in step 1 is ≥90%, wherein CaO≤3% and Fe2O3≤0.5%; the hydrochloric acid by-product of the methane chloride unit needs to be pretreated: low-boiling-point organic impurities are removed by distillation and high-boiling-point organic impurities are removed by activated carbon adsorption to ensure that the content of organic impurities is ≤0.01%.

[0007] As a preferred embodiment, the acidic phosphorus extractant in step 3 is D2EHPA, the diluent is sulfonated kerosene or 260# solvent oil, and the volume ratio of the acidic phosphorus extractant to the diluent is 1:3 to 1:5.

[0008] As a preferred embodiment, the high-purity magnesium hydroxide product described in step 5 has a purity of ≥99.5% and a whiteness of ≥95%.

[0009] As a preferred option, the sodium chloride solution in step 6, after purification, has a Ca²⁺ content ≤ 0.002% and a Mg²⁺ content ≤ 0.0005%, which meets the quality requirements of the ion-exchange membrane caustic soda unit for the raw brine.

[0010] As a preferred option, the secondary steam generated during the evaporation and concentration process in step 6 is condensed and recycled as the washing water for magnesium hydroxide in step 5 or the dilution water for hydrochloric acid in step 1.

[0011] As a preferred embodiment, the chlorine in the by-product hydrochloric acid originates from the ion-exchange membrane caustic soda production unit, and the by-product hydrochloric acid has an HCl mass fraction of 28% to 32%, wherein the free chlorine content is ≤0.05% and the content of organic impurity chloromethane is ≤0.01%.

[0012] As a preferred method, sodium sulfide is added to the crude magnesium chloride solution to generate sulfide precipitate, and heavy metal impurities are removed by filtration.

[0013] As a preferred option, 5% to 10% by mass of dilute hydrochloric acid is added to the regenerated organic phase obtained in step 4 to adjust the pH of the organic phase to 1.0 to 2.0. After standing and separating, the organic phase is recycled to step 3 for reuse.

[0014] The present invention has the following beneficial effects: 1. Closed-loop resource recycling significantly improves utilization: By integrating the hydrochloric acid (chlorine gas originates from the ion-exchange membrane unit) byproduct of the methane chloride unit with the demand of the ion-exchange membrane caustic soda unit, the byproduct hydrochloric acid is used to prepare magnesium hydroxide, the byproduct sodium chloride is refined and returned to the ion-exchange membrane unit to produce caustic soda, and the chlorine gas is then used for methane chloride production, realizing a full-chain recycling from salt to alkali to chlorine to acid to magnesium to salt, improving resource utilization by 30% to 40%, and reducing dependence on purchased industrial salt and fresh hydrochloric acid; 2. High added value and significant economic benefits: The prepared magnesium hydroxide has a purity of ≥99.5% and can be sold as a high-end product (with a selling price 30% to 50% higher than that of ordinary grade); at the same time, it eliminates the environmental treatment costs of hydrochloric acid byproduct of methane chloride, reduces the raw material procurement costs of ion membrane devices, and increases the comprehensive economic benefits per ton of product by 150 to 200 yuan. 3. Environmentally friendly and with outstanding emission reduction effect: By-product hydrochloric acid is utilized efficiently, avoiding pollution caused by direct discharge or low-value treatment; organic phase is recycled (loss rate ≤1%), and secondary steam condensate is reused, reducing the consumption of organic solvents and water resources, and reducing wastewater discharge by more than 90%, which meets the requirements of green chemical development. 4. Strong process integration and compatibility with existing equipment: No large-scale modification is required to the existing methane chloride and ion-exchange membrane caustic soda equipment. Only acid dissolution, extraction, back-extraction and sodium chloride refining units need to be added. The equipment investment is controllable and it is suitable for joint chemical enterprises to implement quickly. Detailed Implementation

[0015] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0016] Example 1: 1. Acid dissolution reaction: Take hydrochloric acid (HCl mass fraction 30%, free chlorine 0.03%, chloromethane 0.02%), a byproduct of the methane chlorination unit, and first remove chloromethane by distillation (70℃, atmospheric pressure), then treat it with an activated carbon adsorption column (flow rate 1.5 BV / h) to reduce organic impurities to 0.008%; take 380 kg of this hydrochloric acid and mix it with 100 kg of magnesium oxide (purity 90%, CaO 2.5%, Fe2O3 0.3%), and react at room temperature and pressure for 40 minutes to generate a crude magnesium chloride solution with a concentration of 15%; 2. Pretreatment: Add magnesium oxide powder to adjust the pH to 2.5, stir for 30 minutes, and then filter to remove a small amount of impurities and precipitates; 3. Extraction: Add organic phase (D2EHPA: sulfonated kerosene = 1:4, volume ratio), O / A = 1:1.5, stir at 400 rpm, and perform 4-stage countercurrent extraction at 35℃. The Mg²⁺ extraction rate is 98.7%. 4. Back-extraction: Add 8% sodium hydroxide solution (30% caustic soda diluted for ion-exchange membrane devices), sodium hydroxide in excess by 12%, O / A = 2.5:1, react at 50℃ for 40 minutes; 5. Solid-liquid separation and purification: Magnesium hydroxide precipitate was obtained by centrifugation (4000 rpm), washed 4 times with secondary steam condensate (conductivity 42 μS / cm), and dried at 110℃ for 5 hours to obtain 58.5 kg of magnesium hydroxide with a purity of 99.7% and a whiteness of 96%. 6. Organic phase regeneration and sodium chloride reuse: Add 8% dilute hydrochloric acid (byproduct hydrochloric acid dilution) to the organic phase to adjust the pH to 1.5, and the organic phase is recycled; the sodium chloride filtrate is concentrated to 31% by multi-effect evaporation, and sodium carbonate is added to remove Ca²⁺ (Ca²⁺ reduced to 0.0015%) and sodium hydroxide to remove Mg²⁺ (Mg²⁺ reduced to 0.0004%), to obtain 62.5 kg of purified sodium chloride solution, which is transported to the ion-exchange membrane device. The chlorine gas generated during the electrolysis of caustic soda is used for the production of methane chloride, realizing recycling.

[0017] Example 2: 1. Acid dissolution reaction: Take hydrochloric acid (HCl 29%, chloroethane 0.015%), a byproduct of methane chloride, and after distillation (65℃) + activated carbon adsorption, the organic impurities are 0.007%; take 370 kg of this hydrochloric acid and react it with 100 kg of magnesium oxide (purity 92%, CaO 2.0%, Fe2O3 0.2%) for 35 minutes to generate 18% crude magnesium chloride solution; 2. Pretreatment: Add dilute sodium hydroxide solution to adjust the pH to 2.2. Since it contains Pb²⁺ (0.01%), add 12% sodium sulfide solution and filter to remove impurities; 3. Extraction: Organic phase (D2EHPA:260# solvent oil = 1:3), O / A = 1:1, 5-stage extraction at 35℃, Mg²⁺ extraction rate 99.3%; 4. Back-extraction: 10% sodium hydroxide solution (15% excess), O / A = 2:1, react at 55℃ for 35 minutes; 5. Refining: After filtration, wash 3 times (conductivity 45 μS / cm), dry at 115℃ for 4.5 hours to obtain 59.8 kg of magnesium hydroxide with a purity of 99.8% and a whiteness of 97%. 6. Reuse: The sodium chloride filtrate is concentrated to 32%. After removing Ca²⁺ (sodium carbonate) and Mg²⁺ (sodium hydroxide), the purified liquid contains 0.0012% Ca²⁺ and 0.0003% Mg²⁺. It is then transported to the ion-exchange membrane unit. The by-product chlorine gas is used for the production of methane chloride. The organic phase recycling loss rate is 0.8%.

[0018] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for the combined preparation of high-purity magnesium hydroxide and sodium chloride, a raw material for ion-exchange membrane caustic soda, characterized in that, Includes the following steps: Step 1. Acid dissolution reaction: Magnesium oxide is mixed with hydrochloric acid, a byproduct of the methane chloride plant, and reacted at room temperature and pressure, with 5% to 10% excess hydrochloric acid in the mixture. The reaction is carried out for 30 to 60 minutes to produce a crude magnesium chloride solution with a magnesium chloride mass fraction of 10% to 20%. Step 2. Pretreatment: Add magnesium oxide powder or dilute sodium hydroxide solution to the crude magnesium chloride solution to adjust the pH to 2.0 to 3.0; Step 3. Extraction: The pretreated magnesium chloride solution is fed into the extraction tank, and an organic phase consisting of an acidic phosphorus extractant and a diluent is added. The volume ratio of the organic phase to the aqueous phase is controlled at 1:1 to 2:1, the stirring speed is 300 to 500 rpm, the extraction temperature is 25 to 40℃, and 3 to 5 stages of countercurrent extraction are used to obtain an organic phase loaded with magnesium ions and an aqueous phase containing impurities. Step 4. Back-extraction: Add 5% to 10% sodium hydroxide solution by mass to the magnesium-loaded organic phase, so that the sodium hydroxide in the organic phase is 10% to 15% in excess. Control the volume ratio of organic phase to aqueous phase to be 2:1 to 3:1, stir at 40 to 60°C, and react for 30 to 45 minutes to generate an aqueous phase containing magnesium hydroxide precipitate and sodium chloride, as well as a regenerated organic phase. Step 5. Solid-liquid separation and magnesium hydroxide purification: Filter the aqueous-organic phase mixture after back-extraction to obtain magnesium hydroxide precipitate, wash it with deionized water 3 to 4 times until the conductivity of the washing water is ≤50μS / cm, and dry it at 100 to 120℃ for 4 to 6 hours to obtain high-purity magnesium hydroxide product. Step 6. Refining and reusing sodium chloride: The filtered filtrate is evaporated and concentrated to a NaCl mass fraction of 30% to 32%. Sodium carbonate is then added to remove Ca²⁺ and calcium, and sodium hydroxide is added to remove residual Mg²⁺ and magnesium, resulting in a sodium chloride solution with a purity ≥99.0%. This solution is then transported to the ion-exchange membrane caustic soda production unit for the preparation of caustic soda.

2. The combined preparation method according to claim 1, characterized in that, The purity of magnesium oxide in step 1 is ≥90%, of which CaO≤3% and Fe2O3≤0.5%; the hydrochloric acid by-product of the methane chloride unit needs to be pretreated: low-boiling-point organic impurities are removed by distillation and high-boiling-point organic impurities are removed by activated carbon adsorption to ensure that the content of organic impurities is ≤0.01%.

3. The combined preparation method according to claim 1, characterized in that, The acidic phosphorus extractant in step 3 is D2EHPA, the diluent is sulfonated kerosene or 260# solvent oil, and the volume ratio of the acidic phosphorus extractant to the diluent is 1:3 to 1:

5.

4. The combined preparation method according to claim 1, characterized in that, The high-purity magnesium hydroxide product described in step 5 has a purity of ≥99.5% and a whiteness of ≥95%.

5. The combined preparation method according to claim 1, characterized in that, After purification, the sodium chloride solution described in step 6 has a Ca²⁺ content ≤ 0.002% and a Mg²⁺ content ≤ 0.0005%, which meets the quality requirements of the ion-exchange membrane caustic soda unit for the raw brine.

6. The combined preparation method according to claim 1, characterized in that, The secondary steam generated during the evaporation and concentration process in step 6 is condensed and recycled as washing water for magnesium hydroxide in step 5 or dilution water for hydrochloric acid in step 1.

7. The combined preparation method according to claim 1, characterized in that, The chlorine in the by-product hydrochloric acid originates from the ion-exchange membrane caustic soda production unit. The by-product hydrochloric acid has an HCl mass fraction of 28% to 32%, and the free chlorine content is ≤0.05% and the organic impurity chloromethane content is ≤0.01%.

8. The combined preparation method according to claim 1, characterized in that, Sodium sulfide is added to the crude magnesium chloride solution to generate sulfide precipitate, which is then filtered to remove heavy metal impurities.

9. The combined preparation method according to claim 1, characterized in that, Add 5% to 10% by mass of dilute hydrochloric acid to the regenerated organic phase obtained in step 4 to adjust the pH of the organic phase to 1.0 to 2.

0. After standing and separating, the organic phase is recycled to step 3 for reuse.