A method for preparing a polymer for assisting a reaction in a seawater desalination reaction

Abstract

The application relates to a high-molecule preparation method for assisting reaction in a seawater desalination reaction, which can be used as an auxiliary reactant, applied to a film-coated material and a filling material of a seawater desalination reaction kettle and belongs to the technical field of seawater desalination. The method comprises the following steps: furfuryl alcohol resin synthesis, polyacrylic acid synthesis and polyacrylic acid-polyfurfuryl alcohol network structure synthesis. The application has the beneficial effect that the film-coated material is bonded with effective chemical functional groups to assist the treatment of concentrated seawater, and effectively replaces the use of solubility complexing agents such as EDTA and citric acid in EWT reagents.

Description

Technical Field

[0001] This invention belongs to the field of seawater desalination technology, specifically relating to a method for preparing a polymer material that can be used as a packing material for reaction-packed columns in the struvite extraction process. Background Technology

[0002] Magnesium ammonium phosphate, commonly known as struvite, has the molecular formula MgNH4PO4·6H2O. It is an amorphous precipitate that is only slightly soluble in water. Its nutrients are released more slowly than those of other soluble fertilizers, making it suitable as a slow-release fertilizer.

[0003] Concentrated seawater is one of the raw materials required for the production of high-quality struvite. Utilizing concentrated seawater from seawater desalination and ammonium phosphate solution as the main raw materials, and adding chemical reagents, to produce magnesium ammonium phosphate slow-release fertilizer has high market potential and economic benefits. This process requires that the brine used as raw material contains as many divalent ions as possible, especially magnesium ions. 2+ At the same time, it retains the necessary trace elements in seawater.

[0004] Existing technologies provide three intervention schemes for magnesium ammonium sulfate extraction: magnesium ammonium phosphate extraction with intervention at the front end of the seawater desalination process; magnesium ammonium phosphate extraction with intervention in the middle of the seawater desalination process; and magnesium ammonium phosphate extraction with intervention at the end of the seawater desalination process. The biggest problem with the front-end intervention process is that pumping concentrated seawater into the reactor can easily damage the reactor. Furthermore, the complexing agent added in traditional electromagnetic ionic liquids has disadvantages such as being single-use, non-recyclable, and requiring sealed storage to avoid direct sunlight.

[0005] To meet the process water requirements of struvite production and soda ash industry, to share the cost of seawater desalination, and to reduce the energy consumption and chemical costs of seawater desalination systems, there is an urgent need to adopt new low-cost, low-pollution materials. Summary of the Invention

[0006] This invention provides a reversible polymeric material for complexing metal ions, which intervenes in the reaction to replace soluble complexing agents such as EDTA and citric acid in EWT reagents. Specifically, it includes the following steps:

[0007] A. Synthesis of furfuryl alcohol resin (PFA): 100g of furfuryl alcohol and 20ml of deionized water were added to a round-bottom flask. The mixture was heated and stirred under a nitrogen atmosphere at 60℃ for 30 minutes. Subsequently, 5ml of concentrated sulfuric acid was diluted to 30ml and gradually added dropwise to the flask, maintaining the temperature at 70-80℃ for 2 hours. The mixture was cooled to room temperature, and ammonia was added to adjust the pH to neutral. After centrifugation, the product was vacuum dried overnight.

[0008] B. Synthesis of polyacrylic acid (PAA): 1g of acrylic acid and 100ml of deionized water were added to a round-bottom flask. The mixture was heated and stirred under a nitrogen atmosphere at 75℃ for 30 minutes. 20g of acrylic acid and an equivalent amount of ammonium persulfate were then added dropwise to the reaction system over 1 hour. After the addition was complete, the mixture was stirred at a constant temperature for 2 hours. After the reaction was completed, the solvent was removed, and the mixture was dried under vacuum overnight.

[0009] C. Synthesis of polyacrylic acid-polyfurfuryl alcohol (PAA-PFA) network structure: PFA and PAA in a mass ratio of 1.5:1 were weighed and dissolved in anhydrous ethanol. The mixture was stirred and refluxed at 80°C. 10% N-hydroxymethylacrylamide was added and reacted at a constant temperature for 2 hours. After removing the solvent from the product, it was dried overnight to obtain the polypropylene-polyfurfuryl alcohol interpenetrating network structure (PAA-PFA).

[0010] Specifically, the benefits of the present invention are as follows:

[0011] 1. A novel polymer interpenetrating network structure is used to assist in the treatment of concentrated seawater, effectively replacing the use of solubilizing complexing agents such as EDTA and citric acid in EWT reagents, simplifying the process and reducing the use of reagents.

[0012] 2. By bonding polymers containing functional groups such as hydroxyl (-OH) and carboxyl (-COOH) to the inner walls of pipes and reactors, the metal inner walls of the reactors are protected from electrochemical corrosion, eliminating the need for electromagnetic complexing agents and avoiding environmental pollution. Attached Figure Description

[0013] Figure 1 A schematic diagram of the reversible process of polyacrylic acid-polyfurfuryl alcohol network in the production of magnesium ammonium phosphate. Detailed Implementation

[0014] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solution of the present invention more clearly, and should not be used to limit the scope of protection of the present invention.

[0015] Example 1

[0016] Preparation of a polymer-filled column with reversible complexed metal ions:

[0017] A. Synthesis of furfuryl alcohol resin (PFA): 100g of furfuryl alcohol and 20ml of deionized water were added to a round-bottom flask. The mixture was heated and stirred under a nitrogen atmosphere at 60℃ for 30 minutes. Subsequently, 5ml of concentrated sulfuric acid was diluted to 30ml and gradually added dropwise to the flask, maintaining the temperature at 70-80℃ for 2 hours. The mixture was cooled to room temperature, and ammonia was added to adjust the pH to neutral. After centrifugation, the product was vacuum dried overnight.

[0018] B. Synthesis of polyacrylic acid (PAA): 1g of acrylic acid and 100ml of deionized water were added to a round-bottom flask. The mixture was heated and stirred under a nitrogen atmosphere at 75℃ for 30 minutes. 20g of acrylic acid and an equivalent amount of ammonium persulfate were then added dropwise to the reaction system over 1 hour. After the addition was complete, the mixture was stirred at a constant temperature for 2 hours. After the reaction was completed, the solvent was removed, and the mixture was dried under vacuum overnight.

[0019] C. Synthesis of polyacrylic acid-polyfurfuryl alcohol (PAA-PFA) network structure: PFA and PAA in a mass ratio of 1.5:1 were weighed and dissolved in anhydrous ethanol. The mixture was stirred and refluxed at 80°C. 10% N-hydroxymethylacrylamide was added and reacted at a constant temperature for 2 hours. After removing the solvent from the product, it was dried overnight to obtain the polypropylene-polyfurfuryl alcohol interpenetrating network structure (PAA-PFA).

[0020] A column-filled coating was prepared using PAA-PFA. The coating components were in the following proportions by mass: 12 parts water; 40 parts PAA-PFA; 2 parts defoamer; 2 parts dispersant; 10 parts titanium dioxide; 0.2 parts thickener; 3 parts film-forming aid; 10 parts barium sulfate; and 20 parts waterborne epoxy resin.

[0021] Add deionized water and the above-mentioned proportions of raw materials to the dispersion tank, mix and disperse evenly, and then grind on a machine until the particle size is less than 30μm.

[0022] The prepared coating is sprayed onto SiO2 particles with a diameter of 1-3 mm, a speed of 0.3 ml / s, and a wet film thickness of ~75 μm. The mixture is then dried. The prepared packing material is added into a stainless steel chromatography column with a diameter of 5 cm and a length of 8 cm to obtain a packed column.

[0023] The concentrated seawater was evaporated and concentrated to 1 / 10 of its original volume using a rotary evaporator. An appropriate amount of the concentrated solution was taken as a sample, and elemental analysis or titration was performed using atomic spectroscopy to determine the Mg content. 2+ The concentration. The concentrate was added to a stirred reaction metal container with an interior coated with PAA-PFA. Based on Mg... 2+ After adding an equal amount of H3PO4, ammonia was added to adjust the pH to 7.5–8.5 until a white precipitate of struvite was formed. The resulting struvite powder was ground and subjected to X-ray powder diffraction. The diffraction angle was measured in the range of 5–60°. The degree of crystallinity of the resulting struvite was determined based on the half-width at half-maximum (WHM) of the diffraction peaks. It was found that the resulting struvite had a good degree of crystallinity.

[0024] Example 2

[0025] The effects of concentrated seawater quality on the removal rate of high-valence cations such as calcium and magnesium were further analyzed; the effects of supersaturation and pH value on the crystal morphology, formation rate, yield, and purity of magnesium ammonium phosphate were also analyzed.

[0026] A. Supersaturation: When the supersaturation of the reaction is between 1 and 5, the phosphate removal rate and the formation of magnesium ammonium phosphate crystals can reach the best.

[0027] B. pH value: Experimental results and theoretical analysis show that a large amount of struvite is formed when the pH value is between 8.0 and 10.0, and the purity is relatively high.

[0028] C. Ratio of constituent ions: Mg 2+ NH4 + PO4 3- The stoichiometric ratio of the three substances reacting to form struvite is 1:1:1, NH4 + The highest purity is achieved when the residual mass concentration is between 30 and 80 mg / L. Mg 2+ PO4 3- When the molar ratio is greater than 1, struvite forms rapidly, and the amount of phosphorus removed increases with the increase of the ratio, but n(Mg) 2+ ) / n(PO4 3- When the concentration is greater than 1.05, there is no significant effect on the phosphorus removal rate;

[0029] D. Calcium ion coprecipitation: Ca 2+ Increased concentration will reduce the size of struvite crystals, inhibit struvite growth, and may even replace struvite to form amorphous calcium phosphate;

[0030] E. Reaction Time: The reaction is kinetically driven, and extending the reaction time will not increase the phosphorus removal rate. However, extending the reaction time can increase the particle size of struvite crystals. A particle size of 2–4 mm is beneficial for industrial processing and production and better utilizes the slow-release effect of struvite.

[0031] Example 3

[0032] The coating produced in Example 1 was applied to the sample plates using the following method: after the cold-rolled steel plate was sanded and degreased, the coating was sprayed onto the sample plate at a speed of 0.3 ml / s, with a wet film thickness of ~75 μm, and dried in a 50°C oven. The steel plate with the PAA-PFA coating and the control steel plate were placed in beakers containing 10 times their volume of concentrated seawater for aging tests. After 30 days, the results showed that the coated steel plate exhibited no significant changes and better stability.

Claims

1. A method for preparing a polyacrylic acid-polyfurfuryl alcohol interpenetrating network polymer packed column for concentrated seawater treatment, characterized in that, Includes the following steps: A. Synthesis of furfuryl alcohol resin (PFA): 100 g of furfuryl alcohol and 20 ml of deionized water were added to a round-bottom flask. The mixture was heated and stirred under a nitrogen atmosphere at 60°C for 30 minutes. Subsequently, 5 ml of concentrated sulfuric acid was diluted to 30 ml and added dropwise to the flask. The temperature was maintained at 70–80°C for 2 hours. The mixture was cooled to room temperature, and ammonia was added to adjust the pH to neutral. After centrifugation, the product was vacuum dried overnight. B. Synthesis of polyacrylic acid (PAA): 1 g of acrylic acid and 100 ml of deionized water were added to a round-bottom flask. The mixture was heated and stirred under a nitrogen atmosphere at 75°C for 30 minutes. 20 g of acrylic acid and an equivalent amount of ammonium persulfate were added dropwise to the reaction system over 1 hour. After the addition was complete, the mixture was stirred at a constant temperature for 2 hours. After the reaction was completed, the solvent was removed and the mixture was dried under vacuum overnight. C. Synthesis of polyacrylic acid-polyfurfuryl alcohol (PAA-PFA) network structure: PFA and PAA in a mass ratio of 1.5:1 were weighed and dissolved in anhydrous ethanol. The mixture was stirred and refluxed at 80°C. 10% mass equivalent of N-hydroxymethylacrylamide was added and reacted at a constant temperature for 2 hours. After removing the solvent from the product, it was dried overnight to obtain the polyacrylic acid-polyfurfuryl alcohol (PAA-PFA) interpenetrating network structure. D. Preparation of PAA-PFA coating: According to the mass ratio, add 12 parts water, 40 parts PAA-PFA, 2 parts defoamer, 2 parts dispersant, 10 parts titanium dioxide, 0.2 parts thickener, 3 parts film-forming aid, 10 parts barium sulfate, and 20 parts waterborne epoxy resin to a dispersion tank, mix and disperse evenly, and then grind until the particle size is less than 30 μm to obtain PAA-PFA coating; E. Filler preparation: The prepared PAA-PFA coating is sprayed onto SiO2 particles with a diameter of 1 to 3 mm at a spraying speed of 0.3 ml / s and a wet film thickness of 75 μm. The mixture is mixed evenly and dried to obtain SiO2 particle fillers with a PAA-PFA coating on the surface. F. Preparation of packed column: The prepared SiO2 particle packing is packed into a stainless steel chromatography column with a diameter of 5 cm and a length of 8 cm to obtain a PAA-PFA interpenetrating network polymer packed column for concentrated seawater treatment.

2. The preparation method according to claim 1, characterized in that: The PAA-PFA interpenetrating network structure contains hydroxyl (-OH) and carboxyl (-COOH) functional groups, which are used to reversibly complex with Ca²⁺ and Mg²⁺ in concentrated seawater.

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