A method for preparing and using a coating material for a seawater desalination reactor

Abstract

The present invention relates to a method for preparing and using a coating material for a seawater desalination reactor, in particular to a coating material for a seawater desalination reactor, belonging to the technical field of seawater desalination. It includes the following steps: synthesizing a polyacrylic acid-polyfurfuryl alcohol interpenetrating network and preparing a coating. The beneficial effects of the present invention are as follows: The coating material bonds effective functional groups to assist in the treatment of concentrated seawater, effectively replacing the use of non-recyclable EWT reagents, simplifying the process flow and reducing the use of drugs; protecting the metal inner wall of the reactor from electrochemical corrosion, making the production of struvite easy to promote.

Description

Technical Field

[0001] The present invention belongs to the technical field of seawater desalination, and particularly relates to a manufacturing method of a polymer coating material, which can be applied to the lining coating of a reaction kettle in the process of extracting struvite from seawater desalination and the filling material of a reaction filling column. Background Art

[0002] Ammonium magnesium phosphate, commonly known as struvite, has the molecular formula of MgNH4PO4·6H2O and belongs to amorphous precipitation. It is only slightly soluble in water. Its nutrient release rate is slower than that of other soluble fertilizers, and it can be used as a slow-release fertilizer.

[0003] Concentrated seawater is one of the raw materials required for the production of high-quality struvite. Using desalinated seawater concentrated seawater and ammonium phosphate solution as the main raw materials and adding chemical reagents to produce ammonium magnesium phosphate slow-release fertilizer has high market prospects and economic benefits. The production requirements of this process are that the salt water used as the raw material should contain as many divalent ions as possible, especially Mg 2+ , while retaining the necessary trace elements in seawater.

[0004] Three intervention schemes for the extraction of ammonium magnesium sulfate are provided in the prior art, including: intervening in the seawater desalination process flow at the front end of ammonium magnesium phosphate extraction; intervening in the seawater desalination process flow in the middle of ammonium magnesium phosphate extraction; intervening in the seawater desalination process flow at the end of ammonium magnesium phosphate extraction. The biggest problem faced in the process flow of front-end intervention is that when concentrated seawater is pumped into the reaction kettle, it is extremely easy to cause damage to the reaction kettle. At the same time, in traditional electromagnetic ionic liquids, the added complexing agent has the disadvantages of being used once, not recyclable, and requiring sealed storage to avoid direct sunlight.

[0005] To meet the requirements of process water for the production of struvite and soda ash industries, etc., share the cost of seawater desalination, and at the same time reduce the operating energy consumption and drug cost of the seawater desalination system, it is urgently necessary to adopt new low-cost and low-pollution materials for intervention. Summary of the Invention

[0006] The purpose of the present invention is to provide an insoluble and recyclable polymer material that can participate in the synthesis of struvite repeatedly to replace the non-recyclable EWT reagent during the process of intervening in the production of struvite at the front end of ammonium magnesium phosphate extraction.

[0007] Due to the existence of concentrated salt water electrolyte, electrochemical corrosion is extremely easy to occur in the reaction kettle cavity and pipelines. The reaction equation is as follows:

[0008] Anode: 2Fe–4e - ==2Fe 2+

[0009] Cathode: O2+2H2O+4e-==4OH -

[0010] The present invention provides a polymer material for reversibly complexing metal ions, which protects the reaction kettle and intervenes in the reaction regulation while replacing the EWT reaction solvent:

[0011] I. Synthesis of polyacrylic acid-polyfurfuryl alcohol interpenetrating network

[0012] A. Synthesis of furfuryl alcohol resin (PFA): Add 100 g of furfuryl alcohol to a round-bottom flask, add 20 ml of deionized water, heat and stir under a nitrogen atmosphere, control the temperature at 60 °C, and react for 30 minutes. Subsequently, dilute 5 ml of concentrated sulfuric acid to 30 ml and gradually add it dropwise to the flask, control the temperature at 70 - 80 °C, and react for 2 hours; cool down to room temperature, add ammonia water to adjust the pH to neutral, after centrifuging the product, dry it overnight under vacuum;

[0013] B. Synthesis of polyacrylic acid (PAA): Add 1 g of acrylic acid to a round-bottom flask, add 100 ml of deionized water, heat and stir under a nitrogen atmosphere, control the temperature at 75 °C, and react for 30 minutes. Then, add 20 g of acrylic acid and an equivalent amount of ammonium persulfate dropwise into the reaction system for 1 hour. After dropping, stir at a constant temperature for 2 hours. After the reaction is completed, remove the solvent and dry it overnight under vacuum;

[0014] C. Synthesis of polyacrylic acid-polyfurfuryl alcohol (PAA-PFA) network structure: Weigh PFA and PAA with a mass ratio of 1.5:1 and dissolve them in anhydrous ethanol, stir and reflux at 80 °C, add 10% mass equivalent of N-methylolacrylamide, after reacting at a constant temperature for 2 hours, remove the solvent from the product and dry it overnight to obtain the polypropylene-polyfurfuryl alcohol interpenetrating network structure (PAA-PFA).

[0015] II. Coating formulation:

[0016] Number Raw material Ratio / parts 1 Water 12 2 PAA - PFA 40 3 Defoamer 1-3 4 Dispersant 1-3 5 Titanium dioxide 10 6 Thickener 0.2 7 Film - forming aid 3 8 Barium sulfate 10 9 Water - based epoxy resin 20

[0017] Add deionized water and the raw materials in the above proportion in the dispersion tank. After dispersing evenly, grind it on the machine until the particle size is less than 30 μm.

[0018] The defoamer is polymonomethyldioxethyl diethylene glycol methylene silane;

[0019] Its synthesis method is as follows:

[0020] 1. Slowly add 1.10 g of monomethyldioxethyl silane to a mixture system of 11.2 g of diethylene glycol mono vinyl ether and 0.1 ml of Karstedt's catalyst [Pt2[Me2SiCH=CH2]2O]3, control the reaction temperature at 40 °C, and then raise the temperature of the reaction system to 90 °C and stir for 40 hours. The volatile substances are removed by vacuum distillation to obtain the product monomethyldioxethyl diethylene glycol dimethylene silane.

[0021] 1 g of monomethyldioxylethyldiethylene glycol dimethylene silane was dissolved in 20 ml of diethyl carbonate, and 0.68 ml of deionized water was added to the reaction system. The mixture was stirred at room temperature for 6 hours. A catalytic amount of tetrabutylammonium fluoride was added to the reaction, and the reaction temperature was raised to 80 °C. The reaction solution gradually became clear and transparent. After reacting for 48 hours, the solvent was removed by distillation under reduced pressure. Tetrabutylammonium fluoride was removed using neutral alumina. The product was washed with ethyl acetate and then dried under vacuum overnight. The defoamer polymonomethyldioxylethylene glycol dimethylene silane (PMDOEtMG) was obtained; for the preparation of the defoamer, polydimethylsiloxane (PDMS) and PMDOEtMG were mixed at a mass ratio of 10:1 to obtain the defoamer. The inventors found that polysiloxanes bonded with diethylene glycol can improve the hydrophilicity and solubility of polysiloxanes. Polysiloxanes bonded with diethylene glycol have a certain thickening ability.

[0022] Specifically, the benefits of the present invention are as follows:

[0023] 1. A new polymer interpenetrating network structure that assists in the treatment of concentrated seawater, effectively replaces the use of EWT reagents, simplifies the process flow, and reduces the use of chemicals;

[0024] 2. Polymers containing hydroxyl (-OH) and carboxyl (-COOH) functional groups are bonded to the inner walls of pipelines and reaction vessels to protect the metal inner walls of the reaction vessels from electrochemical corrosion, eliminating the use of electromagnetic liquid complexing agents and avoiding environmental pollution. 3.

[0025] 3. Utilize the defoaming effect of polysiloxane compounds, which are safe and non-toxic. Description of the Drawings

[0026] Figure 1 Schematic diagram of the reversible conversion process of coating during the production of ammonium magnesium phosphate. Detailed Embodiments

[0027] The present invention will be further described below with reference to the drawings. The following examples are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0028] Example 1

[0029] Synthesis of a polymer material that reversibly complexes metal ions, polyacrylic acid - polyfurfuryl alcohol interpenetrating network:

[0030] A. Synthesis of furfuryl alcohol resin (PFA): 100 g of furfuryl alcohol was added to a round-bottom flask, 20 ml of deionized water was added, and the mixture was heated and stirred under a nitrogen atmosphere, controlling the temperature at 60 °C and reacting for 30 minutes. Subsequently, 5 ml of concentrated sulfuric acid was diluted to 30 ml and gradually added dropwise to the flask, controlling the temperature at 70 - 80 °C and reacting for 2 hours. The temperature was lowered to room temperature, and ammonia water was added to adjust the pH to neutral. After centrifugation of the product, it was dried under vacuum overnight.

[0031] B. Synthesis of polyacrylic acid (PAA): 1 g of acrylic acid was added to a round-bottom flask, followed by 100 ml of deionized water. The mixture was heated and stirred under a nitrogen atmosphere, with the temperature controlled at 75 °C for 30 minutes. Then, 20 g of acrylic acid and an equivalent amount of ammonium persulfate were respectively dropped into the reaction system over 1 hour. After dropping, the mixture was stirred at a constant temperature for 2 hours. After the reaction ended, the solvent was removed and the product was dried under vacuum overnight.

[0032] C. Synthesis of polyacrylic acid - polyfurfuryl alcohol (PAA - PFA) network structure: PFA and PAA with a mass ratio of 1.5:1 were respectively weighed and dissolved in anhydrous ethanol. The solution was stirred and refluxed at 80 °C, and 10% mass equivalent of N - hydroxymethylacrylamide was added. After reacting at a constant temperature for 2 hours, the solvent of the product was removed and then dried overnight to obtain the polyacrylic - polyfurfuryl alcohol interpenetrating network structure (PAA - PFA).

[0033] 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 atomic spectrometry was used to analyze the elements to determine the content of Mg 2+ . To improve the reaction efficiency, the concentrated seawater was passed through a silica gel column attached with PAA - PACA - PFA once and then added to the reaction system. The concentrated solution was added to a stirred reaction metal container internally coated with PAA - PACA - PFA coating. After adding H3PO4 in an equimolar amount according to Mg 2+ and then adding ammonia water to adjust the pH to 7.5 - 8.5, white precipitate struvite was produced. After grinding the produced struvite powder, X - ray powder diffraction was performed. The X - ray dose was 40 keV, and the diffraction angle measurement range was 5 - 60°. According to the full width at half maximum of the diffraction peak, the crystallization degree of the produced struvite was determined. It can be seen that the produced struvite has good crystallization degree.

[0034] Example 2

[0035] The influence of the quality of concentrated seawater on the removal rate of divalent cations such as calcium and magnesium was further analyzed; the influence of supersaturation, pH value, etc. on the crystal morphology, formation rate, yield and purity of magnesium ammonium phosphate was analyzed:

[0036] A. Supersaturation: When the supersaturation of the reaction is between 1 and 5, the removal rate of phosphate and the formation of magnesium ammonium phosphate crystals can reach the best.

[0037] B. pH value: From the experimental results and theoretical analysis, a large amount of struvite is generated when the pH value is between 8.0 and 10.0, and the purity is relatively high.

[0038] C. Ratio of crystal - forming ions: Mg 2+ , NH4 + , PO4 3-The stoichiometric ratio for the three substances to react to form struvite is 1:1:1, NH4 + When the remaining mass concentration is between 30 and 80 mg / L, the purity is the highest. Mg 2+ PO4 3- When the molar ratio of the substances is greater than 1, struvite forms rapidly, and the removal amount of phosphorus increases with the increase of the ratio of the two. However, when n(Mg 2+ ) / n(PO4 3- ) > 1.05, there is no significant effect on the phosphorus removal rate;

[0039] D. Calcium ion coprecipitation: When the concentration of Ca 2+ increases, it will reduce the size of struvite crystals, inhibit the growth of struvite, and even replace struvite to form amorphous calcium phosphate;

[0040] E. Reaction time: The reaction is a reaction driven by kinetics. Prolonging the time will not increase the phosphorus removal rate. However, prolonging the reaction time can increase the particle size of struvite crystals. A particle size of 2 - 4 mm is beneficial for industrial processing and better utilization of the slow-release effect of struvite.

[0041] Example 3

[0042] The coating sample plates produced in Examples 1 and 2 and the comparison steel plates were placed in a beaker containing concentrated seawater with 10 times the volume of seawater for an aging test. After 30 days, the results showed that the steel plates coated with the coating had no obvious change and had better stability.

Claims

1. A preparation method of a coating material for a seawater desalination reactor, characterized in that: The coating material components include the following: Water: 12 parts; Polypropylene-furfuryl alcohol interpenetrating network structure: 40 parts; Defoamer: 1 - 3 parts; Dispersant: 1 - 3 parts; Titanium dioxide: 10 parts; Thickener: 0.2 part; Film-forming aid: 3 parts; Barium sulfate: 10 parts; Waterborne epoxy resin: 30 parts; Add deionized water and the raw materials in the above proportions into a dispersion tank. After dispersing evenly, grind on a machine until the particle size is lower than 30 μm; After grinding and degreasing cold-rolled steel plates, spray the coating onto the sample plates at a speed of 0.3 ml / s, with a wet film thickness of ~75 μm, and dry in an oven at 50 °C. The polypropylene-furfuryl alcohol interpenetrating network structure is prepared by the following method: Synthesis of furfuryl alcohol resin: Add 100 g of furfuryl alcohol and 20 ml of deionized water into a round-bottom flask, heat and stir under a nitrogen atmosphere, control the temperature at 60 °C for 30 minutes. Then, dilute 5 ml of concentrated sulfuric acid to 30 ml and gradually add it dropwise to the flask, control the temperature at 70 - 80 °C, cool down to room temperature, add ammonia water to adjust the pH to neutral. After centrifuging the product, dry it under vacuum overnight. Synthesis of polyacrylic acid: Add 1 g of acrylic acid and 100 ml of deionized water into a round-bottom flask, heat and stir under a nitrogen atmosphere, control the temperature at 75 °C and react for 30 minutes. Then, drop 20 g of acrylic acid and an equivalent amount of ammonium persulfate into the reaction system respectively, continue for 1 hour. After dropping, stir at a constant temperature for 2 hours. After the reaction is completed, remove the solvent and dry it under vacuum overnight. Synthesis of polyacrylic acid-furfuryl alcohol interpenetrating network structure: Weigh furfuryl alcohol resin and polyacrylic acid with a mass ratio of 1.5:1 and dissolve them in absolute ethanol, stir and reflux at 80 °C. Add 10% mass equivalent of N-methylolacrylamide, react at a constant temperature for 2 hours. After removing the solvent from the product, dry it overnight to obtain the polypropylene-furfuryl alcohol interpenetrating network structure.

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