Soluble polymer composite adsorption aid for high-salinity raw water, method for refining high-salinity raw water to be treated and application of soluble polymer composite adsorption aid

Abstract

The invention discloses a soluble polymer composite adsorption auxiliary agent for high-salinity raw water, a method for refining high-salinity raw water to be treated and application of the soluble polymer composite adsorption auxiliary agent, the composite adsorption auxiliary agent is formed by compounding chitosan or water-soluble derivatives thereof and soluble adsorption polymers according to a specific proportion, and the composite adsorption auxiliary agent keeps a dissolved state in the high-salinity raw water; the total organic carbon can be synchronously adsorbed, Fe < 3 + > ions are used as representative polyvalent metal ions, and the removal mechanism is suitable for other heavy metal ion impurities. The method solves the problems of difficult synergistic removal of various impurities, generation of chemical sludge and difficult recovery of an adsorbent in the traditional process, and is suitable for high-salinity raw water refining scenes in chlor-alkali industry, lithium salt purification and the like.

Description

Technical Field

[0001] This invention belongs to the field of water treatment and membrane separation technology, specifically relating to a soluble polymeric composite adsorbent for high-salinity raw water, a method for purifying high-salinity raw water to be treated, and its application. It is suitable for the purification of high-purity sodium chloride brine in the chlor-alkali industry, and is particularly useful for the simultaneous removal of total organic carbon (TOC) and Fe. 3+ The ions are representative multivalent metal ions, and nanofiltration (NF) is used to achieve efficient separation and recycling of the adsorbent and the purification liquid. Background Technology

[0002] In industries such as chlor-alkali, raw industrial brine must meet extremely high purity standards, such as TOC ≤ 10 mg / L and Fe ≤ 10 mg / L. 3+ The purity requirement is ≤20 ppb for ions, while for refined brine from by-product salts, the TOC is generally required to be ≤2 mg / L. To meet this purity requirement, the industry has developed a variety of traditional refining processes, including chemical precipitation, membrane separation, activated carbon adsorption, ion exchange resin, and advanced oxidation methods, but all of these processes have their drawbacks.

[0003] CN116553580A provides a brine purification scheme integrating high-temperature nanofiltration and catalytic oxidation. While it can reduce TOC, it suffers from inherent drawbacks such as a lengthy process route, high energy consumption, and reliance on strong oxidation reactions. This is particularly problematic for trace metal ions (such as ppb-level Fe). 3+ This technology does not offer an effective solution for the deep removal of ions and the avoidance of secondary pollution.

[0004] CN114849659B demonstrates the adsorption and regeneration capabilities of chitosan-based materials, but the target is to remove specific pollutants from the solid phase, which involves heterogeneous adsorption, slow mass transfer, additional separation steps, and a complex regeneration process. It is mainly used in low-salt or freshwater environments (such as lake pollution) and does not involve high-salt complex systems.

[0005] Therefore, a novel solution is urgently needed: the development of a soluble composite polymer adsorption aid. This aid should be able to efficiently capture various impurities in a homogeneous system, and, due to its molecular size and properties, be precisely retained by a subsequent nanofiltration membrane, achieving separation of the adsorbent and the purified brine. The adsorbent concentrate can be recycled after simple desorption and regeneration, thereby minimizing operating costs and solid waste generation while ensuring the highest possible effluent quality. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to provide an environmentally friendly, easy-to-operate brine purification technology that can be integrated into existing production lines. This technology solves the problems of difficulty in the synergistic removal of total organic carbon (TOC) and polyvalent metal ions, the generation of solid waste, and the difficulty in recovering adsorbents in traditional methods, thereby meeting the demand for high-purity brine in industries such as chlor-alkali.

[0007] Based on this, the present invention provides a soluble polymeric composite adsorbent for high-salinity raw water, which is composed of component A and component B in a mass ratio of 1:(0.3~1.2); component A is chitosan or its water-soluble derivative, and component B is a soluble adsorbent polymer; the composite adsorbent remains dissolved in high-salinity raw water containing 1~6wt% NaCl, and can simultaneously adsorb TOC and Fe from the high-salinity raw water. 3+ The ions are representative multivalent metal ions. This invention focuses on Fe. 3+ The efficient ion removal mechanism can be extended to Cu 2+ Ni 2+ Zn 2+ Other multivalent metal ions rely on the chelation effect of amino / carboxyl groups.

[0008] Furthermore, the chitosan water-soluble derivative is selected from at least one of carboxymethyl chitosan, quaternized chitosan, and hydroxypropyl chitosan; the molecular weight of component A is 10,000~50,000 Da, wherein the degree of substitution of carboxymethyl chitosan is ≥0.6 and the degree of deacetylation is ≥85%.

[0009] Further, component B is selected from at least one of polyethyleneimine, carboxymethyl cellulose, polyacrylic acid, and polyaspartic acid; the molecular weight of component B is 50,000 to 100,000 Da.

[0010] A method for purifying high-salinity raw water to be treated using the aforementioned soluble polymeric composite adsorbent in conjunction with membrane separation includes the following steps: (1) Preparation of mother liquor: Dissolve component A and component B in deionized water in proportion to prepare a 1~5g / L polymer composite adsorption aid mother liquor; (2) Addition and adsorption: Add the mother liquor to the high-salt raw water to be treated, so that the final concentration of the polymer composite adsorption aid is 100~300mg / L, adjust the pH of the system to 5.5~7.0, and stir for 20~40min for adsorption; (3) Membrane separation: a tangential flow nanofiltration device is used for separation. The nanofiltration membrane has a molecular weight cutoff of 200~300 Da, an operating pressure of 0.8~1.2 MPa, a temperature of 20~30℃, and the permeate is refined brine. (4) Regeneration and reuse: The concentrated liquid is adjusted to pH 2.5~3.5 with hydrochloric acid, desorbed at ≥60℃, and then separated by high temperature resistant nanofiltration membrane. Small molecule impurities are discharged out of the system through nanofiltration membrane, while the polymer composite adsorption aid is intercepted and returned for addition and adsorption, thus realizing regeneration and reuse.

[0011] Furthermore, the high-salinity raw water to be treated is sodium chloride, potassium chloride, or lithium chloride brine, with a TOC content of 5-15 mg / L and an Fe content of 10 mg / L. 3+ The ion content is 0.5~2ppm.

[0012] Furthermore, the nanofiltration membrane exhibits a salt permeability ≥95%; after the composite adsorption aid is recycled ≥5 times, the TOC removal rate remains ≥80%, and the Fe removal rate remains ≥95%. 3+ The ion removal rate is still ≥99%.

[0013] Furthermore, the nanofiltration membrane is selected as a high-temperature resistant (80°C) nanofiltration membrane.

[0014] The application of the soluble polymeric composite adsorbent in the purification of brine in the chlor-alkali industry is used to simultaneously remove TOC and Fe from the raw brine of the chlor-alkali industry. 3+ Ions, after purification, the brine has a TOC ≤ 2 mg / L and Fe ≤ 2 mg / L. 3+ Ions ≤20 ppb.

[0015] In this invention, the amino groups (-NH2) in chitosan (CS) form hydrogen bonds / hydrophobic interactions with TOC, exhibiting broad-spectrum adsorption. Furthermore, the amino groups in CS are protonated (-NH3). + It undergoes a chelation reaction with metal ions. CS has the advantages of being natural, environmentally friendly, low-cost, and having readily available raw materials, making it suitable for the pretreatment of low-pollution brine.

[0016] The quaternary ammonium salt groups (strong cations) in quaternized chitosan (HTCC) exhibit electrostatic attraction with anionic TOC, resulting in a rapid adsorption rate. The quaternary ammonium salt group cation sites in HTCC chelate with metal ions and undergo electrostatic adsorption, thus enhancing the capacity. HTCC exhibits strong salt resistance, is suitable for high-TOC brine, and demonstrates outstanding simultaneous impurity removal capabilities.

[0017] The hydroxypropyl groups in hydroxypropyl chitosan (HPCS) enhance hydrophilicity and form hydrogen bonds with polar TOC, making it easy to desorb after adsorption. The amino groups in HPCS chelate metal ions, and the hydroxypropyl groups improve the compatibility with the membrane. It is free of precipitation and has scale inhibition properties, making it suitable for brine systems such as lithium salts that require scale prevention. It also has good regenerability.

[0018] The carboxyl groups (-COOH) in carboxymethyl chitosan (CMCS) interact hydrophobically with nonpolar TOC, while the amino groups in CMCS interact with polar TOC through hydrogen bonding, resulting in synergistic adsorption. - It chelates with metal ions and has a high adsorption capacity at two sites. CMCS is water-soluble at all pH levels, does not produce flocculent precipitates, and is suitable for deep treatment of high-salt, high-impurity brine.

[0019] Polyethyleneimine (PEI) contains numerous amino groups (primary / secondary / tertiary amines) that form multi-point hydrogen bonds and electrostatic adsorption with TOC, resulting in deep removal of recalcitrant TOC. The high cation density in PEI allows amino groups to form stable chelates with metal ions, achieving a removal rate exceeding 99%. PEI exhibits strong adsorption activity, and when combined with chitosan, the adsorption capacity of the composite adjuvant is enhanced.

[0020] The beneficial effects of this invention are as follows: It pioneers a "soluble chitosan-based composite adsorbent" formulation system, possessing both broad-spectrum adsorption and high salt stability, breaking through the traditional application limitations of chitosan; it adopts an integrated adsorption-separation design, utilizing membrane technology to achieve physical separation of the adsorbent and the product brine, generating no solid waste and producing no chemical sludge throughout the process, meeting green manufacturing and environmental protection requirements; the process is simple and easy to integrate: requiring only two core operations—mixing and membrane filtration—without large-scale equipment modifications; it is economical: the adsorbent can be recycled ≥5 times, with an adsorption efficiency ≥85% after recycling, significantly reducing operating costs; it is suitable for high-concentration brine systems of 1~6wt% NaCl, and breaks through the pH limitations of traditional chitosan applications, with a wide range of applications, suitable for various brine systems such as NaCl, KCl, and LiCl, adapting to the brine purification needs of different industrial scenarios. Attached Figure Description

[0021] Figure 1 This is a process flow diagram for using soluble polymeric composite adsorption aids in brine purification. Detailed Implementation

[0022] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by this invention.

[0023] The soluble polymeric composite adsorbent of this invention remains dissolved in 1-6 wt% high-salt raw water and can efficiently adsorb TOC and Fe. 3+ The ions are representative multivalent metal ions; the molecular weight of the complex formed after adsorption is significantly larger than the nanofiltration membrane cutoff threshold (200~300 Da), and separation can be achieved through membrane filtration: the permeate is high-purity brine that meets the requirements of high-end processes such as chlor-alkali, and the concentrate is an adsorbent solution enriched with pollutants. This solution is desorbed under high temperature and acidic conditions. The synergistic effect of high temperature and acidic conditions greatly changes the chemical environment on the surface of the adsorbent, weakens its binding force with impurity ions, and enables the captured impurities to be efficiently desorbed. It efficiently and synergistically removes multiple impurities, and can simultaneously achieve the removal of TOC and Fe. 3+The treatment involves the deep removal of representative polyvalent metal ions, resulting in water quality that fully meets standards. Furthermore, the polymer composite adsorption agent can be regenerated and reused through simple membrane separation.

[0024] Example 1 The formulation of a soluble polymeric composite adsorbent for high-salinity raw water is shown in the table below:

[0025] Example 2: Method for refining high-salinity raw water to be treated A method for purifying high-salinity raw water to be treated using the aforementioned soluble polymeric composite adsorbent in conjunction with membrane separation includes the following steps: (1) Preparation of mother liquor: Dissolve component A and component B in deionized water in proportion to prepare a 1~5g / L polymer composite adsorption aid mother liquor; (2) Addition and adsorption: Add the mother liquor to the high-salt raw water to be treated, so that the final concentration of the polymer composite adsorption aid is 100~300mg / L, adjust the pH of the system to 5.5~7.0, and stir for 20~40min for adsorption; (3) Membrane separation: a tangential flow nanofiltration device is used for separation. The nanofiltration membrane has a molecular weight cutoff of 200~300 Da, an operating pressure of 0.8~2.0 MPa, a temperature of 20~35℃, and the permeate is refined brine. (4) Regeneration and reuse: The concentrated liquid is adjusted to pH 2.5~3.5 with hydrochloric acid, desorbed at a high temperature of 60~80℃, and then separated by a high temperature resistant nanofiltration membrane. Small molecule impurities are discharged out of the system through the nanofiltration membrane, while the polymer composite adsorption aid is intercepted and returned for addition and adsorption, thus realizing regeneration and reuse.

[0026] Preferably, the nanofiltration membrane is a high-temperature resistant (80°C) nanofiltration membrane.

[0027] like Figure 1 As shown, a polymer composite adsorption aid is added to the high-salt raw water to be treated, and after mixing and reaction (pH 5.5~7.0, stirring for 20~40 min), it is separated by a nanofiltration membrane module. The permeate that passes through the nanofiltration membrane (purified brine, which meets the standards for reuse) + concentrate (the part that does not pass through the nanofiltration membrane and remains in the system as the adsorbent solution) → high temperature (60~80℃) acid desorption (pH 2.5~3.5) → high temperature nanofiltration membrane filtration → permeate (containing impurities, discharged from the system) + concentrate is returned to the addition and adsorption steps for recycling (adsorbent regeneration and reuse).

[0028] Example 3: Treatment of high-TOC saline solution with low-concentration additives

[0029] High-salinity raw water to be treated: NaCl 3wt%, TOC 15 mg / L, Fe 3+Ions 1.5 ppm. The formulation of the soluble polymeric composite adsorbent is F2 from Example 1. The high-salinity raw water to be treated was purified according to the method in Example 2.

[0030] A soluble polymeric composite adsorption aid was added to a final concentration of 100 mg / L. The pH during addition and adsorption was 6.0, and the mixture was stirred for 30 min. For membrane separation, a high-temperature nanofiltration membrane was used, operating at a pressure of 1.0 MPa and a temperature of 25℃. Treatment results: TOC removal rate 91%, Fe 3+ Ion removal rate: 99.2%; Salt permeability: 96.1%.

[0031] Example 4: Treatment of low-TOC saline solution with high-concentration additives

[0032] High-salinity raw water to be treated: NaCl 5 wt%, TOC 10 mg / L, Fe 3+ Ions 0.5 ppm. The formulation of the soluble polymeric composite adsorbent is F4 from Example 1. The high-salt raw water to be treated is purified according to the method in Example 2.

[0033] A soluble polymeric composite adsorption aid was added to a final concentration of 300 mg / L. The pH during addition and adsorption was 5.5, and the mixture was stirred for 20 min. For membrane separation, a high-temperature nanofiltration membrane was used, operating at a pressure of 1.2 MPa and a temperature of 30℃. Treatment results: TOC removal rate 90%, Fe 3+ Ion removal rate: 99.5%; Salt permeability: 95.0%.

[0034] Example 5: Validation of F5 Formulation Recycling

[0035] High-salinity raw water to be treated: NaCl 4 wt%, TOC 8 mg / L, Fe 3+ Ions 0.8 ppm. The formulation of the soluble polymeric composite adsorbent is F5 from Example 1. The high-salinity raw water to be treated was purified according to the method in Example 2.

[0036] A soluble polymeric composite adsorbent was added to a final concentration of 200 mg / L, with 5 cycles. The pH during addition and adsorption was 6, and the mixture was stirred for 30 min. For membrane separation, a high-temperature nanofiltration membrane was used, operating at a pressure of 1.5 MPa and a temperature of 60 °C.

[0037] Treatment results: TOC removal rate was 82%~90%, Fe... 3+ The ion removal rate remains above 99%.

[0038] Example 6: Adaptability verification to different salt species

[0039] High-salinity raw water to be treated: KCl 2 wt%, TOC 10 mg / L, Fe 3+ Ions 1 ppm. The formulation of the soluble polymeric composite adsorbent is F3 from Example 1. The high-salinity raw water to be treated was purified according to the method in Example 2.

[0040] A soluble polymeric composite adsorbent was added to a final concentration of 150 mg / L. The pH during addition and adsorption was 6.5, and the mixture was stirred for 40 min. For membrane separation, a high-temperature nanofiltration membrane was used, with an operating pressure of 1.8 MPa and a temperature of 70 °C.

[0041] Treatment results: TOC removal rate 90%, Fe 3+ Ion removal rate: 99.3%; Salt permeability: 95.8%.

[0042] Example 7: pH Adaptability Range Verification

[0043] High-salinity raw water to be treated: NaCl 6 wt%, TOC 10 mg / L, Fe 3+ Ions 1 ppm. The formulation of the soluble polymeric composite adsorbent is F1 from Example 1. The high-salt raw water to be treated was purified according to the method in Example 2.

[0044] A soluble polymeric composite adsorbent was added to a final concentration of 250 mg / L. The pH during addition and adsorption was 7.0, and the mixture was stirred for 25 min. For membrane separation, a high-temperature nanofiltration membrane was used, with an operating pressure of 2 MPa and a temperature of 75 °C.

[0045] Treatment results: TOC removal rate 83%, Fe 3+ Ion removal rate: 98.8%; Salt permeability: 96.2%.

[0046] Example 8: Comparison of Experimental Results

[0047] The following comparison of the treatment effects of the present invention and existing technologies is presented using specific experimental data. The high-salinity raw water used in the experiment had the following parameters: TOC: 8.2 mg / L, Fe... 3+ Ions: 800 ppb.

[0048]

[0049] The data above shows that the technology of this invention can achieve a TOC removal rate of over 80%, and a Fe removal rate of over 80%. 3+ The ion removal rate can reach over 99%, and the purified brine has TOC ≤ 2 mg / L and Fe ≤ 2 mg / L. 3+ With ions ≤20ppb, it meets the high purity requirements of industries such as chlor-alkali and generates no solid waste, which is significantly better than existing processes.

Claims

1. A soluble polymeric composite adsorbent for high-salinity raw water, characterized in that, It is a compound composed of component A and component B in a mass ratio of 1:(0.3~1.2); component A is a water-soluble derivative of chitosan, and component B is a soluble adsorbent polymer; the composite adsorbent remains dissolved in high-salt raw water containing 1~6wt% NaCl, and can simultaneously adsorb total organic carbon and Fe from the high-salt raw water. 3+ The ions are representative multivalent metal ions.

2. The soluble polymeric composite adsorbent according to claim 1, characterized in that, The chitosan water-soluble derivative is selected from at least one of carboxymethyl chitosan, quaternized chitosan, and hydroxypropyl chitosan; the molecular weight of component A is 10,000~50,000 Da, wherein the degree of substitution of carboxymethyl chitosan is ≥0.6 and the degree of deacetylation is ≥85%.

3. The soluble polymeric composite adsorbent according to claim 1, characterized in that, Component B is selected from at least one of polyethyleneimine, carboxymethyl cellulose, polyacrylic acid, and polyaspartic acid; the molecular weight of component B is 50,000 to 100,000 Da.

4. A method for purifying high-salinity raw water to be treated using a soluble polymeric composite adsorbent as described in any one of claims 1 to 3 in conjunction with membrane separation, characterized in that, Includes the following steps: (1) Preparation of mother liquor: Dissolve component A and component B in deionized water in proportion to prepare a 1~5g / L polymer composite adsorption aid mother liquor; (2) Addition and adsorption: Add the mother liquor to the high-salt raw water to be treated, so that the final concentration of the polymer composite adsorption aid is 100~300mg / L, adjust the pH of the system to 5.5~7.0, and stir for 20~40min for adsorption; (3) Nanofiltration membrane separation: a tangential flow nanofiltration device is used for separation. The nanofiltration membrane has a molecular weight cutoff of 200~300 Da, an operating pressure of 0.8~2.0 MPa, a temperature of 20~35℃, and the permeate is refined brine. (4) Regeneration and reuse: The concentrated liquid is adjusted to pH 2.5~3.5 with hydrochloric acid, desorbed at 60~80℃, and then separated again through nanofiltration membrane. Small molecule impurities are discharged out of the system through nanofiltration membrane, while the polymer composite adsorption aid is intercepted and returned to be added and adsorbed, thus realizing regeneration and reuse.

5. The application method according to claim 4, characterized in that, The high-salinity raw water to be treated is sodium chloride, potassium chloride, or lithium chloride brine, with a total organic carbon content of 5-15 mg / L and Fe... 3+ The ion content is 0.5~2ppm.

6. The application method according to claim 4, characterized in that, The nanofiltration membrane has a salt permeability of ≥95%; after the composite adsorption aid is recycled ≥5 times, the total organic carbon removal rate is still ≥80%, and the Fe... 3+ The ion removal rate is still ≥99%.

7. The application method according to claim 4, characterized in that, The nanofiltration membrane is selected from high temperature resistant (80℃) nanofiltration membranes.

8. The application of a soluble polymeric composite adsorbent as described in any one of claims 1 to 3 in the purification of brine in the chlor-alkali industry, characterized in that, Used for simultaneous removal of total organic carbon and Fe from brine in chlor-alkali industrial feedstock. 3+ Ions, after purification, the total organic carbon in the brine is ≤2 mg / L, Fe 3+ Ions ≤20 ppb.

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