Environment-friendly phosphorus-free scale inhibitor and preparation method thereof

Abstract

The present application relates to the technical field of water treatment, and particularly relates to an environment-friendly phosphorus-free scale inhibitor and a preparation method thereof. The scale inhibitor is an aqueous solution, and its effective component is a phosphorus-free copolymer composed of maleic acid, acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid units and a partial sodium salt thereof. A step-by-step polymerization process is adopted: firstly, hydrolyzed maleic anhydride and partially unneutralized acrylic acid are used to initiate polymerization to form a front-stage carboxyl-rich segment; then, a pre-neutralized acrylic acid / sodium acrylate mixed feed liquid is added dropwise; meanwhile, pre-neutralized 2-acrylamido-2-methylpropane sulfonic acid is added in batches within a specific time period in the dropwise adding process to realize the concentrated introduction of sulfonic acid groups; and after the polymerization is completed, post-neutralization is performed. The scale inhibitor prepared by the method has a functional gradient distribution of molecular chains, and still exhibits excellent scale inhibition rate, microcrystal dispersion stability and reverse osmosis system operation stability under harsh conditions such as low dosage, high hardness and high alkalinity.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to an environmentally friendly, phosphorus-free scale inhibitor and its preparation method. Background Technology

[0002] In water treatment systems such as circulating cooling water and reverse osmosis, scale inhibitors are typically added to prevent scaling. Phosphorus-containing scale inhibitors (such as organophosphonic acids and phosphonic acids) were once widely used due to their significant effects, but their environmental risks, such as eutrophication, are increasingly being restricted. The development of environmentally friendly, phosphorus-free scale inhibitors has become an important direction for the industry.

[0003] Currently, common phosphorus-free scale inhibitors are mainly obtained by binary or ternary copolymerization of monomers such as acrylic acid (AA), maleic anhydride (MA), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS). These technologies aim to utilize the synergistic effect of different functional groups (such as carboxyl groups and sulfonic acid groups). However, most existing technologies focus on the simple optimization of monomer types and ratios. The polymerization process usually adopts conventional processes of continuously adding each monomer (or its pre-neutralized product) dropwise or adding it all at once. The resulting polymer molecular chains have a random or simple mixed distribution of functional groups.

[0004] Scale inhibitors produced by this type of process often exhibit acceptable scale inhibition rates under standard, mild water quality conditions. However, in practical applications, especially when facing enhanced water quality conditions with high hardness and high alkalinity, or when low dosages are used to reduce operating costs, their performance significantly declines. This is mainly due to the fact that their molecular structure is not finely designed for different stages of the scale inhibition process: initially, a high density of carboxyl groups is needed to rapidly anchor calcium ions and inhibit crystal growth; in the middle stage, sulfonic acid groups need to be introduced into the carboxyl chain segments in a timely and concentrated manner to stabilize the formed microcrystals and prevent their aggregation and growth; in the later stage, moderately ionized carboxyl chain segments are needed to maintain overall solubility and dispersibility. Existing one-pot or simple drop-feeding processes are difficult to effectively control the spatiotemporal distribution of functional groups on polymer single chains.

[0005] Furthermore, in pursuit of high solids content or simplified processes, some solutions sacrifice precise control over the pH of the finished product, resulting in excessively acidic or viscous products. The former affects the product's storage stability and safety, while the latter creates difficulties for pumping and precise dosing. Simultaneously, scale inhibitors that fail to achieve optimal functional group distribution have limited ability to disperse and stabilize calcium carbonate microcrystals. In the cyclic concentration and circulation of membrane water treatment systems such as reverse osmosis, microcrystal deposition easily leads to rapid decline in membrane flux, making it difficult to improve the system's ultimate recovery rate. Therefore, developing an environmentally friendly, phosphorus-free scale inhibitor that can precisely control the chain structure through the polymerization process, thereby maintaining high efficiency, stability, and ease of use under harsh conditions, has become a pressing technical challenge in this field. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose an environmentally friendly phosphorus-free scale inhibitor and its preparation method, so as to solve a series of interrelated technical defects of existing phosphorus-free scale inhibitors under harsh conditions such as high hardness, high alkalinity, and low dosage, such as scale inhibition rate decay, poor microcrystalline dispersion stability, low ultimate recovery rate of reverse osmosis system, and poor stability of finished product storage and pumping, without introducing phosphorus-containing components.

[0007] Based on the above objectives, the present invention provides an environmentally friendly phosphorus-free scale inhibitor, wherein the environmentally friendly phosphorus-free scale inhibitor is an aqueous solution, and the effective component in the aqueous solution is a phosphorus-free copolymer composed of maleic acid unit, acrylic acid unit and 2-acrylamido-2-methylpropanesulfonic acid unit and a portion thereof as sodium salt. The raw materials for preparing the phosphorus-free copolymer and its sodium salt, by mass parts, include: 7-10 parts maleic anhydride, 40-51 parts acrylic acid, 26-35 parts 2-acrylamido-2-methylpropanesulfonic acid and 25-32.2 parts sodium hydroxide. In this process, the maleic anhydride, after hydrolysis, is co-initiated with 14-20 parts of unneutralized acrylic acid to begin polymerization; the remaining 26-31 parts of acrylic acid, after pre-neutralization, form an acrylic acid / sodium acrylate mixed feed solution, which is added dropwise within 65-80 minutes after the initial polymerization; the 2-acrylamido-2-methylpropanesulfonic acid, after pre-neutralization, forms a feed solution, which is added in 4-6 batches starting 15-20 minutes after the addition of the acrylic acid / sodium acrylate mixed feed solution, with an initial time interval of 10-15 minutes between two consecutive additions, and the last addition starting 10-20 minutes before the end of the addition of the acrylic acid / sodium acrylate mixed feed solution, with each addition time controlled within 3 minutes; after polymerization is completed, post-neutralization is performed.

[0008] Preferably, the maleic anhydride is hydrolyzed in 28-34 parts of deionized water at 52-60°C for 25-40 minutes; the hydrolyzed maleic anhydride is then mixed with 14-20 parts of acrylic acid and 9-12 parts of isopropanol at 33-38°C and stirred for 8-12 minutes to form a starting monomer solution.

[0009] Preferably, the total amount of the acrylic acid / sodium acrylate mixed feed solution is 60-72 parts, which is prepared by adding 26-31 parts of acrylic acid dropwise to an alkaline solution prepared by 10.8-13.2 parts of sodium hydroxide and 23.2-27.8 parts of deionized water within 15 minutes, and the temperature of the feed solution is not higher than 25°C.

[0010] Preferably, the total amount of the 2-acrylamido-2-methylpropanesulfonic acid feed solution is 80-100 parts. The 2-acrylamido-2-methylpropanesulfonic acid feed solution is prepared by dissolving 26-35 parts of 2-acrylamido-2-methylpropanesulfonic acid in 30-36 parts of deionized water, and then adding an alkaline solution prepared by 5.2-7.0 parts of sodium hydroxide and 18.4-23.0 parts of deionized water. When the 2-acrylamido-2-methylpropanesulfonic acid feed solution is added in 4-6 times, the amount added in each time is 16-21 parts, the time interval between two adjacent additions is 10-15 minutes, and the time of each addition is controlled within 3 minutes.

[0011] Preferably, the pH of the environmentally friendly phosphorus-free scale inhibitor, when prepared into an aqueous solution at a mass fraction of 1.0%, is 6.5-7.0 as measured at 25°C.

[0012] Furthermore, the present invention also provides a method for preparing an environmentally friendly, phosphorus-free scale inhibitor, comprising the following steps: (1) After hydrolyzing maleic anhydride in deionized water, acrylic acid and isopropanol are added to obtain the starting monomer solution; (2) Prepare pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution, pre-neutralized acrylic acid / sodium acrylate mixed feed solution, ammonium persulfate initiator solution and sodium metabisulfite initiator solution respectively; (3) Add deionized water to the starting monomer solution, heat up and then introduce nitrogen gas, and add part of the ammonium persulfate initiator and part of the sodium metabisulfite initiator to start polymerization; (4) The pre-neutralized acrylic acid / sodium acrylate mixed feed solution is added dropwise, and the remaining ammonium persulfate initiating solution and the remaining sodium metabisulfite initiating solution are added simultaneously; starting from 15-20 minutes after the addition of the pre-neutralized acrylic acid / sodium acrylate mixed feed solution and ending from 45-68 minutes, the pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution is added in 4-6 portions; (5) After the feeding is completed, keep the temperature, then raise the temperature and keep it at that temperature, then lower the temperature, add sodium hydroxide alkaline solution for post-neutralization, and filter to obtain an environmentally friendly phosphorus-free scale inhibitor.

[0013] Preferably, in step (2), based on 26-35 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid, the ammonium persulfate initiating solution is prepared from 3.6-5.0 parts by mass of ammonium persulfate and 18.4-21.2 parts by mass of deionized water; the sodium metabisulfite initiating solution is prepared from 2.6-3.5 parts by mass of sodium metabisulfite and 15.0-16.8 parts by mass of deionized water.

[0014] Preferably, in step (3), the initial polymerization temperature is 64-66°C.

[0015] Preferably, in step (5), after the feeding is completed, the temperature is kept at 69-71℃ for 55-70 minutes, then raised to 76-80℃ and kept for 25-35 minutes, and then cooled to 43-46℃.

[0016] Preferably, in step (5), the filter is passed through a 100-mesh filter.

[0017] The beneficial effects of this invention are: (1) This invention achieves a functional gradient distribution of carboxyl and sulfonic acid groups on a single polymer molecular chain through a sequential control strategy: establishing an unneutralized carboxyl group segment in the front, constructing a sulfonic acid group enrichment window in the middle, adding an ionized carboxyl group segment in the back, and overall neutralization after polymerization. This unique structure enables the product to maintain a high scale inhibition rate (88.7% in Example 1) even at a low dosage (2.0 mg / L), solving the problem of sharp performance reduction of conventional phosphorus-free scale inhibitors at low dosages.

[0018] (2) The scale inhibitor prepared by the present invention exhibits excellent stability under enhanced conditions of high hardness and high alkalinity. For example, the scale inhibition rate of Example 3 under these conditions is as high as 94.2%, and the average particle size of the formed calcium carbonate microcrystals Z is only 412 nm, with a polydispersity index as low as 0.20, indicating that it can induce the formation of smaller and more uniformly distributed distorted crystal forms, which greatly improves the dispersion stability of the microcrystals and effectively prevents deposition.

[0019] (3) The special chain structure of the present invention significantly improves the long-term operating performance in the reverse osmosis system. The reverse osmosis cycle concentration test in Example 3 shows that the system's ultimate recovery rate can reach 80%, the cumulative operating time is 5.8 hours, and the permeate flux decline rate is only 5.4%. This proves that the scale inhibitor can effectively delay membrane fouling, ensure the stable operation of the system under high recovery rate, and has significant energy and water saving benefits.

[0020] (4) Through the overall post-neutralization step after polymerization, the pH of the product is precisely controlled within the near-neutral range of 6.5-7.0, and the product is given a suitable viscosity (142-198 mPa·s). This makes the product not only have good storage stability and no risk of acid corrosion, but also has good fluidity, which is convenient for industrial pumping and precise dosing, thus improving the practicality and safety of the product. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0022] Example 1: Step 1: Add 30g of deionized water and 8g of maleic anhydride to a four-necked flask, turn on the mechanical stirrer, control the stirring speed at 250r / min, heat to 55℃ and keep warm for 30min, cool down to 35℃, add 16g of acrylic acid and 10g of isopropanol, continue stirring for 10min to obtain the carboxyl-rich starting monomer solution. Step 2: Add 35g of deionized water and 30g of 2-acrylamido-2-methylpropanesulfonic acid to a beaker and stir at room temperature until completely dissolved; separately dissolve 6g of sodium hydroxide in 19g of deionized water and cool to below 30°C, then add it to the aforementioned 2-acrylamido-2-methylpropanesulfonic acid solution to obtain 90g of pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution; in another beaker, dissolve 12g of sodium hydroxide in 24g of deionized water and cool to below 25°C, then add 28g of acrylic acid dropwise to this alkaline solution over 15 minutes, keeping the temperature of the feed solution below 25°C, to obtain 64g of pre-neutralized acrylic acid / sodium acrylate mixed feed solution; then dissolve 4g of ammonium persulfate in 20g of deionized water to obtain 24g of ammonium persulfate initiating solution; dissolve 3g of sodium metabisulfite in 15g of deionized water to obtain 18g of sodium metabisulfite initiating solution; Step 3: Add 40g of deionized water to the carboxyl-rich starting monomer solution obtained in Step 1, increase the stirring speed to 300r / min, raise the temperature to 65℃, and then purge with nitrogen for 10min. Subsequently, add 6g of ammonium persulfate initiating solution and 6g of sodium metabisulfite initiating solution within 10min, and continue the reaction at 65℃ for 20min. Step 4: After the reaction in step 3 is completed, stabilize the system temperature at 70℃, and then add 64g of pre-neutralized acrylic acid / sodium acrylate mixed feed solution dropwise over 70min at a uniform rate; at the same time, add the remaining 18g of ammonium persulfate initiator solution and 12g of sodium metabisulfite initiator solution dropwise simultaneously over 80min. Starting from the dropwise addition of acrylic acid / sodium acrylate mixed feed solution, add 18g of pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution at 15min, 25min, 35min, 45min and 55min respectively, with each addition time controlled within 2min. Step 5: After the addition of materials in step 4, continue to keep the temperature at 70℃ for 60 minutes, then raise the temperature to 78℃ and keep it at 78℃ for 30 minutes. Then lower the temperature to 45℃, dissolve 10g of sodium hydroxide in 20g of deionized water to prepare a pH-adjusting alkaline solution, add it to the reaction system and adjust the pH of the system to 6.8, then add 56g of deionized water, continue stirring for 30 minutes, and filter through a 100-mesh filter to obtain an environmentally friendly phosphorus-free scale inhibitor.

[0023] Example 2: Step 1: Add 28g of deionized water and 7g of maleic anhydride to a four-necked flask, turn on mechanical stirring at a speed of 250r / min, heat to 52℃ and hold for 25min to allow the maleic anhydride to hydrolyze completely; after cooling to 33℃, add 14g of acrylic acid and 9g of isopropanol, and continue stirring for 10min to obtain the carboxyl-rich starting monomer solution. Step 2: Add 30g of deionized water and 26g of 2-acrylamido-2-methylpropanesulfonic acid to a beaker and stir at room temperature until completely dissolved; separately dissolve 5.2g of sodium hydroxide in 18.8g of deionized water and cool to below 30°C, then add it to the aforementioned 2-acrylamido-2-methylpropanesulfonic acid solution to obtain 80g of pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution; in another beaker, dissolve 10.8g of sodium hydroxide in 23.2g of deionized water and cool to below 25°C, then add 26g of acrylic acid dropwise to this alkaline solution over 15 minutes, keeping the temperature of the feed solution below 25°C to obtain 60g of pre-neutralized acrylic acid / sodium acrylate mixed feed solution; then dissolve 3.6g of ammonium persulfate in 18.4g of deionized water to obtain 22g of ammonium persulfate initiating solution; dissolve 2.6g of sodium metabisulfite in 15.4g of deionized water to obtain 18g of sodium metabisulfite initiating solution; Step 3: Add 38g of deionized water to the carboxyl-rich starting monomer solution obtained in Step 1, increase the stirring speed to 290r / min, raise the temperature to 64℃, and then purge with nitrogen for 8min. Subsequently, add 5.5g of ammonium persulfate initiator and 5.5g of sodium metabisulfite initiator within 10min, and continue the reaction at 64℃ for 18min. Step 4: After the reaction in step 3 is completed, stabilize the system temperature at 69℃, and then add 60g of the pre-neutralized acrylic acid / sodium acrylate mixed feed solution dropwise over 65min at a uniform rate; at the same time, add the remaining 16.5g of ammonium persulfate initiator solution and 12.5g of sodium metabisulfite initiator solution dropwise simultaneously over 75min; starting from the dropwise addition of the acrylic acid / sodium acrylate mixed feed solution, add 20g of the pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution at 15min, 25min, 35min and 45min respectively, with each addition time controlled within 2min; Step 5: After the addition of materials in step 4, continue to keep the temperature at 69℃ for 55 minutes, then raise the temperature to 76℃ and keep it at 76℃ for 25 minutes. Then lower the temperature to 43℃, dissolve 9g of sodium hydroxide in 18g of deionized water to prepare a pH-adjusting alkaline solution, add it to the reaction system and adjust the pH of the system to 6.5, then add 50g of deionized water, continue stirring for 25 minutes, and filter through a 100-mesh filter to obtain an environmentally friendly phosphorus-free scale inhibitor.

[0024] Example 3: Step 1: Add 32g of deionized water and 9g of maleic anhydride to a four-necked flask, turn on the mechanical stirrer, control the stirring speed at 280r / min, heat to 58℃ and keep at that temperature for 35min to allow the maleic anhydride to complete hydrolysis; after cooling to 37℃, add 18g of acrylic acid and 11g of isopropanol, and continue stirring for 10min to obtain the carboxyl-rich starting monomer solution. Step 2: Add 36g of deionized water and 32g of 2-acrylamido-2-methylpropanesulfonic acid to a beaker and stir at room temperature until completely dissolved; separately dissolve 6.4g of sodium hydroxide in 21.6g of deionized water and cool to below 30°C, then add it to the aforementioned 2-acrylamido-2-methylpropanesulfonic acid solution to obtain 96g of pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution; in another beaker, dissolve 13.2g of sodium hydroxide in 27.8g of deionized water and cool to below 25°C, then add 31g of acrylic acid dropwise to this alkaline solution over 15 minutes, keeping the feed solution temperature below 25°C to obtain 72g of pre-neutralized acrylic acid / sodium acrylate mixed feed solution; then dissolve 4.8g of ammonium persulfate in 21.2g of deionized water to obtain 26g of ammonium persulfate initiating solution; dissolve 3.2g of sodium metabisulfite in 16.8g of deionized water to obtain 20g of sodium metabisulfite initiating solution; Step 3: Add 42g of deionized water to the carboxyl-rich starting monomer solution obtained in Step 1, increase the stirring speed to 310r / min, raise the temperature to 66℃, and then purge with nitrogen for 12min. Subsequently, add 6.5g of ammonium persulfate initiating solution and 6g of sodium metabisulfite initiating solution within 10min, and continue the reaction at 66℃ for 22min. Step 4: After the reaction in step 3 is completed, stabilize the system temperature at 71℃, and then add 72g of pre-neutralized acrylic acid / sodium acrylate mixed feed solution dropwise over 75min at a uniform rate; at the same time, add the remaining 19.5g of ammonium persulfate initiator solution and 14g of sodium metabisulfite initiator solution dropwise over 85min simultaneously; starting from the dropwise addition of acrylic acid / sodium acrylate mixed feed solution, add 16g of pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution at 15min, 25min, 35min, 45min, 55min and 65min respectively, with each addition time controlled within 2min; Step 5: After the addition of materials in step 4, continue to keep the temperature at 71℃ for 65 minutes, then raise the temperature to 79℃ and keep it at 79℃ for 30 minutes. Then lower the temperature to 46℃, dissolve 11g of sodium hydroxide in 22g of deionized water to prepare a pH-adjusting alkaline solution, add it to the reaction system and adjust the pH of the system to 6.9, then add 60g of deionized water, continue stirring for 30 minutes, and filter through a 100-mesh filter to obtain an environmentally friendly phosphorus-free scale inhibitor.

[0025] Example 4: Step 1: Add 30g of deionized water and 8.5g of maleic anhydride to a four-necked flask, turn on the mechanical stirrer, control the stirring speed at 260r / min, heat to 56℃ and keep at that temperature for 30min to allow the maleic anhydride to complete hydrolysis; after cooling to 35℃, add 15g of acrylic acid and 10g of isopropanol, and continue stirring for 10min to obtain the carboxyl-rich starting monomer solution. Step 2: Add 32g of deionized water and 28g of 2-acrylamido-2-methylpropanesulfonic acid to a beaker and stir at room temperature until completely dissolved; separately dissolve 5.6g of sodium hydroxide in 18.4g of deionized water and cool to below 30°C, then add it to the aforementioned 2-acrylamido-2-methylpropanesulfonic acid solution to obtain 84g of pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution; in another beaker, dissolve 12.4g of sodium hydroxide in 25.6g of deionized water and cool to below 25°C, then add 29g of acrylic acid dropwise to this alkaline solution over 15 minutes, keeping the temperature of the feed solution below 25°C, to obtain 67g of pre-neutralized acrylic acid / sodium acrylate mixed feed solution; then dissolve 4.2g of ammonium persulfate in 19.8g of deionized water to obtain 24g of ammonium persulfate initiating solution; dissolve 3.0g of sodium metabisulfite in 15g of deionized water to obtain 18g of sodium metabisulfite initiating solution; Step 3: Add 40g of deionized water to the carboxyl-rich starting monomer solution obtained in Step 1, increase the stirring speed to 300r / min, raise the temperature to 65℃, and then purge with nitrogen for 10min. Subsequently, add 6g of ammonium persulfate initiating solution and 6g of sodium metabisulfite initiating solution within 10min, and continue the reaction at 65℃ for 20min. Step 4: After the reaction in step 3 is completed, stabilize the system temperature at 70℃, and then add 67g of pre-neutralized acrylic acid / sodium acrylate mixed feed solution dropwise over 72min at a uniform rate; at the same time, add the remaining 18g of ammonium persulfate initiator solution and 12g of sodium metabisulfite initiator solution dropwise simultaneously over 82min; starting from the dropwise addition of acrylic acid / sodium acrylate mixed feed solution, add 21g of pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution at 18min, 30min, 42min and 54min respectively, with each addition time controlled within 2min; Step 5: After the addition of materials in step 4, continue to keep the temperature at 70℃ for 60 minutes, then raise the temperature to 78℃ and keep it at 78℃ for 30 minutes. Then lower the temperature to 45℃, dissolve 10g of sodium hydroxide in 20g of deionized water to prepare a pH-adjusting alkaline solution, add it to the reaction system and adjust the pH of the system to 6.6, then add 54g of deionized water, continue stirring for 30 minutes, and filter through a 100-mesh filter to obtain an environmentally friendly phosphorus-free scale inhibitor.

[0026] Example 5: Step 1: Add 34g of deionized water and 10g of maleic anhydride to a four-necked flask, turn on the mechanical stirrer, control the stirring speed at 300r / min, heat to 60℃ and keep at this temperature for 40min to allow the maleic anhydride to complete hydrolysis; after cooling to 38℃, add 20g of acrylic acid and 12g of isopropanol, and continue stirring for 10min to obtain the carboxyl-rich starting monomer solution. Step 2: Add 35g of deionized water and 35g of 2-acrylamido-2-methylpropanesulfonic acid to a beaker and stir at room temperature until completely dissolved; separately dissolve 7g of sodium hydroxide in 23g of deionized water and cool to below 30°C, then add it to the aforementioned 2-acrylamido-2-methylpropanesulfonic acid solution to obtain 100g of pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution; in another beaker, dissolve 13.2g of sodium hydroxide in 27.8g of deionized water and cool to below 25°C, then add 31g of acrylic acid dropwise to this alkaline solution over 15 minutes, keeping the temperature of the feed solution below 25°C, to obtain 72g of pre-neutralized acrylic acid / sodium acrylate mixed feed solution; then dissolve 5.0g of ammonium persulfate in 21.0g of deionized water to obtain 26g of ammonium persulfate initiating solution; dissolve 3.5g of sodium metabisulfite in 16.5g of deionized water to obtain 20g of sodium metabisulfite initiating solution; Step 3: Add 45g of deionized water to the carboxyl-rich starting monomer solution obtained in Step 1, increase the stirring speed to 320r / min, raise the temperature to 66℃, and then purge with nitrogen for 12min. Subsequently, add 7g of ammonium persulfate initiating solution and 6g of sodium metabisulfite initiating solution within 12min, and continue the reaction at 66℃ for 25min. Step 4: After the reaction in step 3 is completed, stabilize the system temperature at 71℃, and then add 72g of pre-neutralized acrylic acid / sodium acrylate mixed feed solution dropwise at a uniform rate over 80min; at the same time, add the remaining 19g of ammonium persulfate initiator solution and 14g of sodium metabisulfite initiator solution dropwise simultaneously over 90min; starting from the dropwise addition of acrylic acid / sodium acrylate mixed feed solution, add 20g of pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution at 20min, 32min, 44min, 56min and 68min respectively, with each addition time controlled within 2min; Step 5: After the addition of materials in step 4, continue to keep the temperature at 71℃ for 70 minutes, then raise the temperature to 80℃ and keep it at 80℃ for 35 minutes, then lower the temperature to 45℃. Dissolve 12g of sodium hydroxide in 20g of deionized water to prepare a pH-adjusting alkaline solution, add it to the reaction system and adjust the pH of the system to 7.0, then add 62g of deionized water, continue stirring for 30 minutes, and filter through a 100-mesh filter to obtain an environmentally friendly phosphorus-free scale inhibitor.

[0027] Comparative Example 1: The difference from Example 1 is that in the first step, after adding 8g of maleic anhydride to 30g of deionized water, hydrolysis treatment at 55°C for 30min is not performed. Instead, after stirring at 25°C for 10min, 16g of acrylic acid and 10g of isopropanol are directly added and stirred for another 10min to obtain the carboxyl-rich starting monomer solution. The other conditions are the same as in Example 1.

[0028] Comparative Example 2: The difference from Example 1 is as follows: 16g of acrylic acid is not added in the first step; in the second step, the 16g of acrylic acid is incorporated into the pre-neutralized acrylic acid / sodium acrylate mixed feed solution described in the second step of Example 1, so that all acrylic acid is added in the latter stage in a pre-neutralized acrylic acid / sodium acrylate mixed state; to ensure that the degree of neutralization of the mixed feed solution is consistent with that of the pre-neutralized acrylic acid / sodium acrylate mixed feed solution described in the second step of Example 1, the sodium hydroxide used in the mixed feed solution in the second step is adjusted to 18.8g, and the deionized water used in the mixed feed solution is adjusted to 37.2g, resulting in 100g of pre-neutralized acrylic acid / sodium acrylate mixed feed solution; in the fourth step, the 100g of pre-neutralized acrylic acid / sodium acrylate mixed feed solution is added dropwise within 70min, and the remaining conditions are the same as in Example 1.

[0029] Comparative Example 3: The difference from Example 1 is that in the fourth step, instead of adding the pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution in five separate additions at 15 min, 25 min, 35 min, 45 min, and 55 min, the same total amount of 90 g of pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution is added dropwise continuously from 15 min to 55 min, and the remaining conditions are the same as in Example 1.

[0030] Comparative Example 4: The difference from Example 1 is that, although 90g of pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution is still added in 5 portions in the fourth step, it is changed to add 18g each at 0min, 18min, 35min, 53min and 70min respectively, and the other conditions are the same as in Example 1.

[0031] Comparative Example 5: The difference from Example 1 is that in step 5, the pH-adjusting alkaline solution prepared with 10g of sodium hydroxide and 20g of deionized water is not added, and the pH of the system is not adjusted. The other conditions are the same as in Example 1.

[0032] The test samples were taken from the environmentally friendly phosphorus-free scale inhibitors prepared in Examples 1-5 and Comparative Examples 1-5, respectively. Samples from the same batch were filtered through a 100-mesh filter and allowed to stand at 25°C for 24 hours. The effective components were first calculated based on the solid content, and then a stock solution with a mass concentration of 10.0 g / L was prepared for later use. For samples used in dynamic light scattering particle size analysis, the middle layer of the suspension formed during the static scale inhibition performance test of calcium carbonate under high hardness and high alkalinity enhanced conditions was used for testing.

[0033] Solid content, pH value, and viscosity. Solid content was determined according to GB / T 1725-2007. 2.0000 g of sample was accurately weighed into a pre-weighed aluminum dish, heated in a 105℃ forced-air drying oven for 2 hours, cooled in a desiccator for 30 minutes, and then weighed. This process was repeated until the difference between two consecutive weighings was no greater than 0.002 g. pH value was determined according to GB / T 22592-2008. The sample was prepared into an aqueous solution at a mass fraction of 1.0%, and measured at 25.0℃ using a calibrated pH meter. Viscosity was determined according to GB / T 22235-2008. A rotational viscometer was used at 25.0℃ with a No. 2 rotor and a speed of 60 r / min, and the stable reading was measured for 60 seconds.

[0034] Static scale inhibition performance of calcium carbonate under standard conditions: The static scale inhibition performance of calcium carbonate was determined according to the calcium carbonate deposition method in GB / T 16632-2019. The dosage of scale inhibitor was 6.0 mg / L based on the effective ingredient. The simulated water used in the experiment was prepared with a total hardness of 350±20 mg / L (calculated as CaCO3) and a total alkalinity of 220±20 mg / L (calculated as CaCO3). 250 mL of simulated water was taken into a 500 mL ground glass conical flask, the corresponding sample was added, and the mixture was thoroughly mixed. The flask was placed in an 80℃ constant temperature water bath for 10 h, then filtered while hot. After the filtrate cooled to room temperature, 25.00 mL was accurately transferred and diluted with deionized water to approximately 80 mL. 5 mL of 200 g / L potassium hydroxide solution and an appropriate amount of calcium indicator were added. The residual calcium ion content was titrated with 0.0100 mol / L disodium ethylenediaminetetraacetate standard titration solution, and the scale inhibition rate was calculated according to the standard.

[0035] Static scale inhibition performance of calcium carbonate at low dosage: Except for adjusting the scale inhibitor dosage to 2.0 mg / L based on the effective ingredient, the other simulated water composition, constant temperature conditions, reaction time, filtration method, titration method and calculation method are the same as those for the static scale inhibition performance test of calcium carbonate under standard conditions.

[0036] Static scale inhibition performance of calcium carbonate under enhanced conditions of high hardness and high alkalinity: This project is still conducted in accordance with GB / T 16632-2019, but the simulated water conditions are enhanced to a total hardness of 450±20 mg / L (calculated as CaCO3), a total alkalinity of 300±20 mg / L (calculated as CaCO3), and a scale inhibitor dosage of 4.0 mg / L (calculated as effective ingredient). Other operations are the same as the static scale inhibition test items of calcium carbonate under standard conditions.

[0037] Reverse osmosis cycle concentration and circulation scale inhibition performance: Refer to GB / T 39221-2020. The scale inhibitor dosage is 3.0 mg / L based on the effective component, and an effective membrane area of ​​7.2 m² is used. 2 The periodic concentration and circulation device of the aromatic polyamide composite reverse osmosis membrane element uses artificially prepared high-scaling-prone simulated brine as the feed water, in which Ca... 2+ The mass concentration is 420 mg / L, Mg 2+ The mass concentration is 1320 mg / L, HCO3- 3- The mass concentration of SO4 is 140 mg / L. 2- The mass concentration was 2700 mg / L, the influent pH was adjusted to 8.2, and the total dissolved solids mass concentration was controlled at 32.0 g / L. The experimental temperature was 25.0℃, the operating pressure was 5.5 MPa, the circulation flow rate was 180 L / h, and the initial recovery rate was set at 25.0%. Thereafter, the recovery rate was increased by 5.0 percentage points every 30 min until the standardized permeate flux decayed to 10.0% or the transmembrane pressure difference increased by 0.05 MPa and remained at that level for 30 min. The experiment was then stopped, and the limiting recovery rate, cumulative operating time, and standardized permeate flux decay rate for each sample were recorded.

[0038] Analysis of the particle size distribution of calcium carbonate microcrystals: 5.0 mL of the middle layer sample of the suspension before filtration after the static scale inhibition performance test of calcium carbonate under high hardness and high alkalinity enhancement conditions was taken and immediately diluted 10 times with deionized water that had been treated to remove carbon dioxide. After slight sonication for 30 s, it was allowed to stand for 60 s. The Z-mean particle size and polydispersity index of the suspended microcrystals were determined by dynamic light scattering method according to GB / T 29022-2021. The test temperature was 25.0℃, and each sample was measured 3 times.

[0039] The test results are shown in Table 1.

[0040] Table 1 Performance Test Results

[0041] As shown in Table 1, the solid content of Examples 1-5 of this application remained at 29.7%-31.8%, the pH was controlled at 6.5-7.0, and the viscosity was 142.0-198.0 mPa·s. This indicates that the finished product after neutralization has both a high effective solid content and good storage stability and pumpability. Comparative Example 5, omitting neutralization, had a pH that dropped to 2.9 and a viscosity that dropped to 94.0 mPa·s. Although it still maintained an 89.1% calcium carbonate scale inhibition rate under standard conditions, the scale inhibition rates under low dosage and high hardness / high alkalinity conditions were only 71.7% and 76.9%, respectively, with a limiting recovery rate of only 60.0%. The average particle size of the microcrystals increased to 918.0 nm, indicating that neutralization plays an important role in the dispersion stability of the finished product and the sustained scale inhibition ability under enhanced operating conditions.

[0042] Compared to Comparative Example 1, the scale inhibition rates of Example 1 under standard conditions, low dosage, and high hardness / high alkali conditions increased from 91.8%, 79.6%, and 82.9% to 95.6%, 88.7%, and 90.8%, respectively, indicating that pre-hydrolysis of maleic anhydride is beneficial for forming a more effective front-end carboxyl-rich segment. Compared to Comparative Example 2, the scale inhibition rate of Example 1 under low dosage increased from 74.8% to 88.7%, the scale inhibition rate under high hardness / high alkali conditions increased from 78.6% to 90.8%, the reverse osmosis limiting recovery rate increased from 60.0% to 75.0%, and the average particle size of microcrystals decreased from 864.0 nm to 468.0 nm, indicating that introducing some acrylic acid in the unneutralized front-end state and adding the remaining acrylic acid in the pre-neutralized rear-end state can simultaneously enhance the calcium content of the carbon dioxide. 2+ Complexation, threshold scale inhibition, and stabilizing effect of distorted microcrystal dispersion. Comparative Examples 3 and 4 changed the addition of 2-acrylamido-2-methylpropanesulfonic acid to continuous addition or staggered pulse addition outside the window, respectively. The scale inhibition rate of the low dosage was only 81.9% and 80.5%, and the scale inhibition rate of the high hardness and high alkali was only 84.7% and 83.5%, respectively, which were significantly lower than those of Example 1. This shows that the addition method of 2-acrylamido-2-methylpropanesulfonic acid is not that the more the better or that it is enough to just add it. Instead, it needs to be matched with the intermediate time window and the interval of entry in the later stage to fully reflect the synergistic effect of carboxyl anchoring and sulfonic acid hydration stabilization.

[0043] Among the various embodiments, Example 3 exhibits the best overall performance. Its scale inhibition rates under standard conditions, low dosage, and high hardness / high alkalinity conditions reach 97.4%, 92.6%, and 94.2%, respectively, with a maximum recovery rate of 80.0%. The cumulative operating time is 5.8 h, and the standardized permeate flux decline rate is only 5.4%. Furthermore, the average Z-particle size and polydispersity index of the microcrystals decrease to 412.0 nm and 0.20, respectively. This indicates that the combined effects of the following four processes—carboxyl-rich initiation, pre-neutralization with acrylic acid / sodium acrylate addition, mid-stage enrichment with 2-acrylamido-2-methylpropanesulfonic acid, and post-polymerization neutralization—can simultaneously improve static scale inhibition capacity, enhance dispersion stability under operating conditions, and improve reverse osmosis operational stability. Although Example 5 also achieves a scale inhibition rate of 96.3% under standard conditions, its high hardness / high alkalinity scale inhibition rate, maximum recovery rate, and particle size control are slightly inferior to Example 3 due to the further increase in system solids content and viscosity.

[0044] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. An environmentally friendly, phosphorus-free scale inhibitor, characterized in that, The environmentally friendly phosphorus-free scale inhibitor is an aqueous solution, and the effective component in the aqueous solution is a phosphorus-free copolymer composed of maleic acid units, acrylic acid units and 2-acrylamido-2-methylpropanesulfonic acid units and its partial sodium salt. The raw materials for preparing the phosphorus-free copolymer and its sodium salt, by mass parts, include: 7-10 parts maleic anhydride, 40-51 parts acrylic acid, 26-35 parts 2-acrylamido-2-methylpropanesulfonic acid and 25-32.2 parts sodium hydroxide. The method for preparing the phosphorus-free copolymer and its partial sodium salt includes: maleic anhydride is hydrolyzed and then co-polymerized with 14-20 parts of unneutralized acrylic acid; the remaining 26-31 parts of acrylic acid are pre-neutralized to form an acrylic acid / sodium acrylate mixed feed solution, which is added dropwise within 65-80 minutes after the initial polymerization; the 2-acrylamido-2-methylpropanesulfonic acid is pre-neutralized to form a feed solution, which is added in 4-6 batches starting 15-20 minutes after the start of the addition of the acrylic acid / sodium acrylate mixed feed solution, with an initial time interval of 10-15 minutes between two adjacent additions, and the start time of the last addition is 10-20 minutes before the end of the addition of the acrylic acid / sodium acrylate mixed feed solution, with each addition time controlled within 3 minutes; after polymerization is completed, post-neutralization is performed.

2. The environmentally friendly phosphorus-free scale inhibitor according to claim 1, characterized in that, The maleic anhydride is hydrolyzed in 28-34 parts of deionized water at 52-60°C for 25-40 minutes; the hydrolyzed maleic anhydride is mixed with 14-20 parts of acrylic acid and 9-12 parts of isopropanol at 33-38°C and stirred for 8-12 minutes to form the starting monomer solution.

3. The environmentally friendly phosphorus-free scale inhibitor according to claim 1, characterized in that, The total amount of the acrylic acid / sodium acrylate mixed feed solution is 60-72 parts. The acrylic acid / sodium acrylate mixed feed solution is prepared by adding 26-31 parts of acrylic acid dropwise to an alkaline solution prepared by 10.8-13.2 parts of sodium hydroxide and 23.2-27.8 parts of deionized water within 15 minutes, and the temperature of the feed solution is not higher than 25°C.

4. The environmentally friendly phosphorus-free scale inhibitor according to claim 1, characterized in that, The total amount of the 2-acrylamido-2-methylpropanesulfonic acid feed solution is 80-100 parts. The 2-acrylamido-2-methylpropanesulfonic acid feed solution is prepared by dissolving 26-35 parts of 2-acrylamido-2-methylpropanesulfonic acid in 30-36 parts of deionized water, and then adding an alkaline solution prepared by 5.2-7.0 parts of sodium hydroxide and 18.4-23.0 parts of deionized water. When the 2-acrylamido-2-methylpropanesulfonic acid feed solution is added in 4-6 times, the amount added in each time is 16-21 parts, the time interval between two adjacent additions is 10-15 minutes, and the time of each addition is controlled within 3 minutes.

5. The environmentally friendly phosphorus-free scale inhibitor according to claim 1, characterized in that, The environmentally friendly, phosphorus-free scale inhibitor, when prepared into an aqueous solution at a mass fraction of 1.0%, has a pH of 6.5-7.0 measured at 25°C.

6. A method for preparing an environmentally friendly, phosphorus-free scale inhibitor according to any one of claims 1-5, characterized in that, Includes the following steps: (1) After hydrolyzing maleic anhydride in deionized water, acrylic acid and isopropanol are added to obtain the starting monomer solution; (2) Prepare pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution, pre-neutralized acrylic acid / sodium acrylate mixed feed solution, ammonium persulfate initiator solution and sodium metabisulfite initiator solution respectively; (3) Add deionized water to the starting monomer solution, heat up and then introduce nitrogen gas, and add part of the ammonium persulfate initiator and part of the sodium metabisulfite initiator to start polymerization; (4) The pre-neutralized acrylic acid / sodium acrylate mixed feed solution is added dropwise, and the remaining ammonium persulfate initiating solution and the remaining sodium metabisulfite initiating solution are added simultaneously; starting from 15-20 minutes after the addition of the pre-neutralized acrylic acid / sodium acrylate mixed feed solution and ending from 45-68 minutes, the pre-neutralized 2-acrylamido-2-methylpropanesulfonic acid feed solution is added in 4-6 portions; (5) After the feeding is completed, keep the temperature, then raise the temperature and keep it at that temperature, then lower the temperature, add sodium hydroxide alkaline solution for post-neutralization, and filter to obtain an environmentally friendly phosphorus-free scale inhibitor.

7. The method for preparing the environmentally friendly phosphorus-free scale inhibitor according to claim 6, characterized in that, In step (2), based on 26-35 parts by mass of 2-acrylamido-2-methylpropanesulfonic acid, the ammonium persulfate initiating solution is prepared by 3.6-5.0 parts by mass of ammonium persulfate and 18.4-21.2 parts by mass of deionized water; the sodium metabisulfite initiating solution is prepared by 2.6-3.5 parts by mass of sodium metabisulfite and 15.0-16.8 parts by mass of deionized water.

8. The method for preparing the environmentally friendly phosphorus-free scale inhibitor according to claim 6, characterized in that, In step (3), the initial polymerization temperature is 64-66℃.

9. The method for preparing the environmentally friendly phosphorus-free scale inhibitor according to claim 6, characterized in that, In step (5), after the material is added, keep the temperature at 69-71℃ for 55-70 minutes, then raise the temperature to 76-80℃ and keep it at 25-35 minutes, and then lower the temperature to 43-46℃.

10. The method for preparing the environmentally friendly phosphorus-free scale inhibitor according to claim 6, characterized in that, In step (5), the filter passes through a 100-mesh filter.

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