Novel method for efficiently removing sulfate radicals in sodium chloride system

Abstract

The invention is applicable to the technical field of removal of sodium sulfate in saline water, and provides a novel method for efficiently removing sulfate radicals in a sodium chloride system, which specifically comprises the following steps: firstly, taking the saline water with the sodium chloride concentration of 200-220g / L and the sodium sulfate concentration of 30-80g / L, then adding pure water, diluting the saline water until the sodium chloride concentration is 100-110g / L and the sodium sulfate concentration is 15-40g / L, and then adding the pure water into the saline water until the sodium chloride concentration is 100-110g / L and the sodium sulfate concentration is 15-40g / L; then the diluted saline water is fed into a nanofiltration membrane set, penetrating fluid and concentrated liquid are separated out through the nanofiltration membrane set, the penetrating fluid is fed into the next procedure, the concentration of sodium chloride in the produced concentrated liquid is 100-110 g / L, and the concentration of sodium sulfate in the produced concentrated liquid is 100-200 g / L. On the basis of an existing technology for removing sulfate radicals from chlor-alkali through a saline water membrane separation method, secondary treatment of the concentrated solution through the membrane separation method is achieved through the advanced concept technology, the recycling rate of sodium chloride in light salt brine after electrolysis is increased, the concentration of the sulfate radicals in the concentrated solution is increased, the treatment cost of the concentrated solution is reduced, and the purposes of reducing cost and improving efficiency are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium sulfate removal from brine, and particularly to a new method for efficiently removing sulfate radicals in a sodium chloride system. Background Art

[0002] Brine refining is the process source of chlor-alkali enterprises. Ensuring the quality of brine is a prerequisite for the normal operation of electrolytic cells. In the process of chlor-alkali production, sulfate radicals are the main impurities in brine. Due to the reuse of the dechlorinated brine after electrolysis, sulfate ions gradually accumulate. When the concentration of sulfate ions reaches a certain level, it will damage the ion-exchange membrane, shorten the service life of the ion-exchange membrane, and also hinder the discharge of chloride ions, promote the discharge of hydroxide ions, generate oxygen, resulting in a decrease in chlorine purity, a decrease in current efficiency, and an increase in power consumption; at the same time, as the sulfate concentration increases, the solubility of sodium chloride decreases, making the brine index fail to meet the requirements.

[0003] Currently, the relatively mature processes for removing sulfate radicals in the sodium chloride system in chlor-alkali enterprises include the BaCl₂ method, the CaCl₂ method, the freezing method, the BaCO₃ method, the ion exchange method, the thermal method for nitrate extraction, and the membrane separation method, all of which have different drawbacks. For example, the membrane separation method is difficult to increase the concentration of removed sulfate radicals, resulting in a decrease in the water recovery rate.

[0004] Therefore, in view of the above current situation, there is an urgent need to develop a new method for efficiently removing sulfate radicals in the sodium chloride system to overcome the deficiencies in current practical applications. Summary of the Invention

[0005] The purpose of the embodiments of the present invention is to provide a new method for efficiently removing sulfate radicals in a sodium chloride system, aiming to solve the problems raised in the above background art.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] A new method for efficiently removing sulfate radicals in a sodium chloride system specifically includes the following steps:

[0008] S100: Take brine with a sodium chloride concentration of 200 - 220 g / L and a sodium sulfate concentration of 30 - 80 g / L;

[0009] S200: Add pure water to dilute the brine solution to a sodium chloride concentration of 100 - 110 g / L and a sodium sulfate concentration of 15 - 40 g / L;

[0010] S300: Feed the diluted brine into a nanofiltration membrane module;

[0011] S400: The nanofiltration membrane module separates the permeate and the concentrate, and the permeate is sent to the next process.

[0012] Further technical solution: the sodium chloride concentration of the concentrated liquid produced in S400 is 100 - 110 g / L, and the sodium sulfate concentration is 100 - 200 g / L.

[0013] Further technical solution: the brine treatment temperature ≤ 80 °C, and the brine pH is 1 - 12.

[0014] Further technical solution: 60% - 80% of sodium chloride can be recycled.

[0015] In summary, compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0016] 1. The present invention is based on the existing brine membrane separation process for removing sulfate radicals in chlor-alkali, realizes the secondary treatment of the concentrated liquid by the membrane separation method, improves the recovery rate of sodium chloride in the dechlorinated brine after electrolysis, increases the sulfate radical concentration in the concentrated liquid, reduces the treatment cost of the concentrated liquid, and achieves the purpose of cost reduction and efficiency improvement;

[0017] 2. There are no processes such as freezing, crystallization, separation, and preparation of chilled brine, which simplifies the process flow and reduces energy consumption and material consumption;

[0018] 3. 60% - 80% of sodium chloride can be recycled, improving the utilization efficiency of resources;

[0019] 4. The transformation on the existing old process is simple, without the need to stop production for transformation, and can be carried out online, reducing the difficulty and cost of transformation.

[0020] In order to more clearly illustrate the structural features and functions of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the process flow diagram of the membrane separation method for removing sulfate radicals in Comparative Example 1 of the present invention;

[0022] Figure 2 It is the process flow diagram of the new method for removing sulfate radicals in the sodium chloride removal system in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] The following describes the specific implementation of the present invention in detail with reference to specific embodiments.

[0025] Comparative Example 1

[0026] Such as Figure 1As shown, this embodiment is an existing membrane separation process, belonging to the prior art, and specifically includes the following steps:

[0027] S1: Cache the brine after electrolysis. At this time, the brine index is approximately 200 g / L sodium chloride and 9 g / L sulfate;

[0028] S2: Add sodium sulfite to the brine for reaction, and adjust the pH with hydrochloric acid;

[0029] S3: Feed the solution after adjusting the pH into a heat exchanger for heat exchange;

[0030] S4: Filter the solution after heat exchange successively through activated carbon and a security filter;

[0031] S5: Enter the nanofiltration membrane module to produce permeate and concentrate;

[0032] S6: Send the permeate to the next process to extract sodium chloride, and discharge or produce nitrate from the concentrate.

[0033] Specifically, the index of the concentrate at this time is 200 - 220 g / L sodium chloride and 20 - 55 g / L sulfate

[0034] Example 1

[0035] As Figure 2 shown, the embodiment of the present invention provides a new method for efficiently removing sulfate in a sodium chloride system. This embodiment is based on the membrane separation process for removing sulfate in Comparative Example 1, adding a new process to remove sulfate in the brine again, and specifically includes the following steps:

[0036] S100: Take brine with a high sulfate concentration, with a sodium chloride concentration of approximately 200 - 220 g / L and a sulfate concentration of approximately 30 - 80 g / L;

[0037] It can be understood that the sulfate concentration in Comparative Example 1 is 20 - 55 g / L, and after conversion, the sodium sulfate concentration is approximately 30 - 80 g / L; the brine with a high sulfate concentration is the concentrate in Comparative Example 1.

[0038] S200: Add pure water to dilute the brine with a high sulfate concentration to a sodium chloride concentration of approximately 100 - 110 g / L and a sodium sulfate concentration of approximately 15 - 40 g / L;

[0039] S300: Feed the diluted brine into the nanofiltration membrane module;

[0040] S400: Filter and separate through the nanofiltration membrane module to produce permeate and concentrate. The permeate is sent to the next process to extract sodium chloride, and the concentrate is discharged or used to produce nitrate.

[0041] Specifically, the sodium chloride concentration of the produced concentrated liquid is about 100-110 g / L, and the sodium sulfate concentration is about 100-200 g / L.

[0042] The present invention is based on the existing brine membrane separation process for removing sulfate radicals in chlor-alkali, realizing the secondary treatment of the concentrated liquid by the membrane separation method, improving the recovery rate of sodium chloride in the dechlorinated brine after electrolysis, increasing the sulfate radical concentration in the concentrated liquid, resulting in a reduction in the treatment cost of the concentrated liquid, achieving the purpose of cost reduction and efficiency improvement; stable operation, reliable output, suitable for brine with a pH of 1-12 and a temperature ≤ 80°C, and a sodium sulfate concentration of 30-80 g / ; no processes such as freezing, crystallization, separation, and preparation of chilled brine, simplifying the process flow, reducing energy consumption and material consumption; the new process only requires two levels of power and has no circulation process, saving a large amount of electricity costs. At the same time, there is no need to prepare chilled brine, reducing the process links and improving the operation safety; 60%-80% of sodium chloride can be recycled, improving the utilization efficiency of resources; the transformation on the existing old process is simple, without the need to stop production for transformation, and can be transformed online, reducing the difficulty and cost of transformation.

[0043] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A new method for efficiently removing sulfate from a sodium chloride system, characterized in that: The specific steps include: S100: taking brine with a sodium chloride concentration of 200-220 g / L and a sodium sulfate concentration of 30-80 g / L; S200: Add pure water to dilute the saline solution to a sodium chloride concentration of 100-110 g / L and a sodium sulfate concentration of 15-40 g / L; S300: sending the diluted brine into the nanofiltration membrane group; S400: The nanofiltration membrane group separates the permeate and the concentrate, and the permeate is sent to the next process.

2. The novel method for efficiently removing sulfate radical from a sodium chloride system according to claim 1, wherein: The concentrated liquid produced in S400 has a sodium chloride concentration of 100-110 g / L and a sodium sulfate concentration of 100-200 g / L.

3. The novel method for efficiently removing sulfate radical from a sodium chloride system according to claim 1, wherein: The brine treatment temperature is ≤80℃, and the brine PH is 1-12.

4. The novel method for efficiently removing sulfate radical from a sodium chloride system according to claim 2, wherein: 60%-80% of the sodium chloride can be recycled.

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