Preparation method and application of polyacrylamide for oil-containing wastewater treatment

Abstract

This invention discloses a method for preparing polyacrylamide for treating oily wastewater and its application, relating to the field of industrial wastewater treatment technology. The method includes dissolving acrylamide, a cationic monomer, and a hydration-aiding monomer in water to form a monomer reaction solution; adding a redox initiation system under deoxygenation conditions to carry out aqueous free radical polymerization to obtain a cationic polyacrylamide polymer colloid; retaining the polymer colloid in the polymerization mother liquor and undergoing final polymerization and equalization treatment; before drying, sequentially performing hydration chain release treatment, weak anion pre-shielding treatment, limited removal treatment, and water-containing shaping and drying; and finally, pulverizing and sieving to obtain polyacrylamide powder. The obtained polyacrylamide, when used for flocculation treatment of oily wastewater, can improve the re-dissolution chain state of the powder, reduce the risk of deactivation caused by sudden strong recombination between local high-cationic sites and anionic surfactants, and improve the utilization rate of chain segment bridging and the adaptability of flocculation treatment in complex oily wastewater.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and in particular to a method for preparing and applying polyacrylamide for treating oily wastewater. Background Technology

[0002] In the field of oily wastewater treatment, polyacrylamide and its cationic modified products are often used as organic polymeric flocculants for oil droplet aggregation, suspended particle capture, and floc settling. With the application of polymer flooding, surfactant flooding, and combined flooding technologies, produced water often contains emulsified oil droplets, anionic surfactants, polymer flooding residues, and inorganic salts simultaneously. Related treatment technologies are gradually shifting from simple charge neutralization flocculation to regulation through the synergistic effects of charge interaction, chain segment bridging, hydration dispersion, and interfacial instability. Cationic polyacrylamide, due to its positively charged adsorption sites and relatively long molecular chain structure, can interact with negatively charged oil droplet interfaces and solid particles during water treatment, forming a flocculation network through chain segment unfolding. Therefore, it has become an important type of agent in the flocculation treatment of oily wastewater.

[0003] Existing methods for preparing cationic polyacrylamide typically focus on monomer ratios, cationicity, molecular weight, polymerization temperature, and drying conditions, but pay insufficient attention to the chain segment release state and the state of local high-cationic sites in the polymeric colloid before drying. After direct cutting, drying, and pulverizing, the polymeric colloid is prone to local entanglement of chain segments, expansion of microgels binding chain segments, and reconstitution lag during powder resolution. When such powders enter oily wastewater containing anionic surfactants, polymer flooding residues, and inorganic salts, local high-cationic sites tend to preferentially undergo sudden and strong complexation with anionic surfactants, causing some polymer chains to be dragged into an inefficient complexation state before full release and bridging unfolding, affecting subsequent oil droplet coalescence and bridging flocculation processes. Summary of the Invention

[0004] In view of this, this application provides a method for preparing polyacrylamide for treating oily wastewater and its application.

[0005] According to one aspect of this disclosure, a method for preparing polyacrylamide for oily wastewater treatment is provided, comprising: Step 1, dissolving acrylamide, a cationic monomer, and a hydration-assisted monomer in water to form a monomer reaction solution, and adding a redox initiation system under deoxygenation conditions to carry out aqueous free radical polymerization to obtain a cationic polyacrylamide polymer colloid; Step 2, retaining the cationic polyacrylamide polymer colloid in the polymerization mother liquor, and subjecting the cationic polyacrylamide polymer colloid to a final polymerization and subsequent equalization treatment to obtain a wet colloid to be conditioned; Step 3, placing the wet colloid to be conditioned in a hydration-release conditioning solution for hydration-release treatment, thereby loosening the locally entangled chain segments and the bound chain segments of the expanded microgel in the wet colloid to be conditioned, to obtain a chain-release wet colloid; Step 4, releasing the chain... The wet colloid is placed in a weak anion pre-shielding conditioning solution for weak anion pre-shielding treatment, so that the weak anion conditioning agent forms reversible ion pairing with the local high cation sites in the chain-releasing wet colloid, resulting in a pre-shielded wet colloid. In step five, the pre-shielded wet colloid is placed in a low ionic strength cleaning solution for limited removal treatment, so that the free weak anion conditioning agent that did not participate in reversible ion pairing is partially removed, while retaining the reversible ion pairing state in the pre-shielded wet colloid, resulting in a limited-removed wet colloid. In step six, the limited-removed wet colloid is subjected to water-containing shaping and dehydration and low-temperature segmented drying, so that the limited-removed wet colloid maintains the re-dissolution chain-releasing state formed by the hydration chain-releasing treatment and weak anion pre-shielding treatment during the drying process. After crushing and sieving, polyacrylamide for oily wastewater treatment is obtained.

[0006] According to another aspect of this disclosure, an application of polyacrylamide in the treatment of oily wastewater is also provided. The polyacrylamide is prepared by a method for preparing polyacrylamide for oily wastewater treatment. The polyacrylamide is formulated into a working solution with a mass fraction of 0.05% to 0.2%, and the working solution is added to oily wastewater containing anionic surfactant, polymer flooding residue, and inorganic salt for flocculation treatment. The anionic surfactant includes sodium dodecylbenzenesulfonate, and the polymer flooding residue includes hydrolyzed polyacrylamide residue.

[0007] The beneficial effects of this invention are as follows: By sequentially performing hydration and chain release, weak anion pre-shielding, limited removal, and water-containing shaping drying before drying the cationic polyacrylamide polymer colloid, the locally entangled chain segments and the bound chain segments of the expanded microgel in the wet colloid are pre-loosened, and the locally high-cation sites form a reversible ion pairing state. The resulting polyacrylamide powder can more fully release bridging chain segments during resolution and addition, reducing the sudden strong recombination effect of anionic surfactants on locally high-cation sites, and promoting the polymer chain segments to maintain a better unfolding, adsorption, and bridging state in oily wastewater. This improves the agent utilization efficiency, floc formation stability, and treatment adaptability in the flocculation process of complex oily wastewater. Attached Figure Description

[0008] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 This is a flowchart of a method for preparing polyacrylamide for treating oily wastewater.

[0010] Figure 2 This is a comparison chart of the reconstitution time and the amount of sodium dodecylbenzenesulfonate premixed precipitate for different samples.

[0011] Figure 3 This is a distribution diagram showing the flocculation treatment effect of different samples of oily wastewater. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0013] This invention aims to construct a method for preparing polyacrylamide for treating oily wastewater, such as... Figure 1 As shown, it includes: Step 1: Acrylamide, cationic monomer, and hydration-aiding monomer are dissolved in water to form a monomer reaction solution. Under deoxygenated conditions, a redox initiation system is added to initiate aqueous free radical polymerization, yielding a cationic polyacrylamide polymer colloid. In the redox initiation system, the amount of ammonium persulfate is 0.02%–0.08% of the total monomer mass, and the amount of sodium bisulfite is 0.015%–0.06% of the total monomer mass. Ammonium persulfate and sodium bisulfite are separately prepared into aqueous solutions and added to the monomer reaction solution, allowing the monomer reaction solution to enter the aqueous free radical polymerization process under deoxygenated conditions. The above dosage ranges are used to ensure the monomer reaction solution forms a continuous cationic polyacrylamide polymer colloid and to avoid excessive initiator leading to local chain degradation or excessively high residual initiation activity.

[0014] Step 2: The cationic polyacrylamide polymer colloid is retained in the polymerization mother liquor, and the cationic polyacrylamide polymer colloid is subjected to a final polymerization and then homogenization treatment to obtain the wet colloid to be conditioned. Step 3: Place the wet colloid to be treated in a hydration and chain release conditioning solution for hydration and chain release treatment, which loosens the locally entangled chain segments and the bound chain segments of the expanded microgel in the wet colloid, resulting in a chain-release wet colloid. After the hydration and chain release treatment, take a small amount of the chain-release wet colloid and prepare a test solution at a mass fraction of 0.1%. Redissolve the solution at 25°C and 250 r / min. Record the apparent viscosity at 30 min and 120 min of redissolution. Filter the test solution after 120 min of redissolution through a 100 μm filter membrane and measure the residual amount of microgel. When the ratio of the apparent viscosity at 30 min of redissolution to that at 120 min of redissolution is higher than that of the wet colloid without hydration and chain release treatment, and the residual amount of microgel decreases, it is determined that the hydration and chain release treatment has brought the locally entangled chain segments and the bound chain segments of the expanded microgel into a loose state suitable for weak anion pre-shielding treatment.

[0015] Step four involves placing the chain-releasing wet colloid in a weak anion pre-shielding conditioning solution for weak anion pre-shielding treatment. This allows the weak anion conditioner to reversibly pair with local high-cation sites in the chain-releasing wet colloid, resulting in a pre-shielded wet colloid. During the weak anion pre-shielding treatment, the weak anion conditioner diffuses in the hydrated chain-releasing wet colloid and forms reversible ion pairings with local high-charge-density cation sites on the cationic polyacrylamide chain segments. This reversible ion pairing does not completely neutralize the cation sites; rather, it retains a partial binding state even after a short treatment with a low-ionic-strength cleaning solution. This reduces the sudden strong recombination of the anion surfactant with local high-cation sites when the polyacrylamide powder comes into contact with oily wastewater containing anion surfactants. The reversible ion pairing state can be characterized by a decrease in precipitation and an increase in transmittance in the sodium dodecylbenzenesulfonate premix test compared to the ordinary brine-treated sample.

[0016] Step 5: Place the pre-shielded wet colloid in a low-ionic-strength cleaning solution for limited removal treatment. This removes some of the free weak anionic conditioner that has not participated in reversible ion pairing, while retaining the reversible ion pairing state within the pre-shielded wet colloid, resulting in a limited-removed wet colloid. This limited removal treatment removes the free weak anionic conditioner that has not participated in reversible ion pairing from the external solution of the pre-shielded wet colloid, while retaining the reversible ion pairing state formed between the pre-shielded wet colloid and local high-cation sites. The limited removal treatment does not aim to completely remove the weak anionic conditioner. During the limited removal treatment, the cleaning solution can be collected and its conductivity measured. When the conductivity of the cleaning solution is close to the initial conductivity of the low-ionic-strength cleaning solution, and the powder obtained after cleaning still shows a decrease in precipitation compared to the ordinary brine-treated sample in the sodium dodecylbenzenesulfonate premix test, the limited removal treatment is considered to have reached a state suitable for water-containing shaping and dehydration.

[0017] Step six involves subjecting the limited amount of dehydrated colloid to aqueous setting, dehydration, and low-temperature segmented drying. This ensures the dehydrated colloid maintains the rehydrated chain state formed by the hydration chain release treatment and weak anion pre-shielding treatment during drying. After pulverization and sieving, polyacrylamide for oily wastewater treatment is obtained. During the aqueous setting and dehydration process, the control objective is to avoid strong compression and hardening of the wet colloid. When using low-pressure filtration, the filtration pressure is controlled at 0.05 MPa to 0.20 MPa; when using low-speed centrifugation, the centrifugation speed is controlled at 800 r / min to 2000 r / min. After aqueous setting and dehydration, the limited amount of dehydrated colloid retains a water content of 45% to 65%, ensuring that the wet colloid maintains the rehydrated chain state formed by the hydration chain release treatment and the reversible ion pairing state formed by the weak anion pre-shielding treatment before entering the low-temperature segmented drying stage.

[0018] In some embodiments of this application, in step one, the cationic monomer is methacryloyloxyethyltrimethylammonium chloride, and the hydration auxiliary monomer is N-vinylpyrrolidone; the molar percentages of acrylamide, methacryloyloxyethyltrimethylammonium chloride, and N-vinylpyrrolidone are 88%–94%, 4%–8%, and 2%–6%, respectively.

[0019] In some embodiments of this application, in step one, the total monomer mass fraction of the monomer reaction solution is 20%–30%, the pH is 4.8–5.5, the redox initiation system includes ammonium persulfate and sodium bisulfite, the polymerization temperature is 25°C–35°C, and the polymerization time is 4h–6h.

[0020] In some embodiments of this application, step two, the post-polymerization equalization treatment includes lowering the temperature of the cationic polyacrylamide polymer colloid to 20°C to 30°C and adjusting the pH of the polymerization mother liquor to 5.5 to 6.5 to reduce residual initiation activity and form a wet colloid to be conditioned.

[0021] In some embodiments of this application, in step three, the hydration and chain release conditioning solution is a low ionic strength monovalent salt aqueous solution containing 0.01 mol / L to 0.06 mol / L sodium chloride and 0.005 mol / L to 0.02 mol / L sodium acetate, with a pH of 5.8 to 6.5; the mass ratio of the wet colloid to be conditioned to the hydration and chain release conditioning solution is 1:1.5 to 1:4; the hydration and chain release treatment temperature is 20℃ to 35℃; and the hydration and chain release treatment time is 0.5 h to 2 h.

[0022] In some embodiments of this application, in step four, the weak anion pre-shielding conditioning solution contains a weak anion conditioning agent and a monovalent salt. The weak anion conditioning agent is at least one of sodium citrate, sodium tartrate, and sodium gluconate. The concentration of the weak anion conditioning agent is 0.002 mol / L to 0.02 mol / L, the monovalent salt is sodium chloride, the concentration of sodium chloride is 0.02 mol / L to 0.08 mol / L, and the pH of the weak anion pre-shielding conditioning solution is 6.0 to 7.0.

[0023] In some embodiments of this application, in step four, the mass ratio of the chain-releasing wet colloid to the weak anion pre-shielding conditioning solution is 1:1 to 1:3, the weak anion pre-shielding treatment temperature is 20°C to 35°C, and the weak anion pre-shielding treatment time is 0.5h to 2h; the weak anion pre-shielding treatment causes the local high-cation sites in the chain-releasing wet colloid to be in a reversible ion pairing state.

[0024] In some embodiments of this application, in step five, the low ionic strength cleaning solution contains 0.005 mol / L to 0.03 mol / L sodium chloride and has a pH of 6.0 to 7.0; the mass ratio of the pre-shielded wet colloid to the low ionic strength cleaning solution is 1:1 to 1:2, and the limited removal treatment time is 10 min to 40 min.

[0025] In some embodiments of this application, step six, the water-containing shaping and dehydration includes at least one of static leaching, low-pressure filtration, and low-speed centrifugation, so that the water content of the limited amount of dehydrated colloid is controlled to be 45% to 65%; the low-temperature segmented drying includes cutting the limited amount of dehydrated colloid into colloid particles with a particle size of 3 mm to 8 mm, pre-drying at 45°C to 55°C to reduce the water content to 20% to 30%, and continuing to dry at 50°C to 60°C until the water content is less than 10%.

[0026] This application also provides an application of polyacrylamide in the treatment of oily wastewater, comprising preparing a working solution of polyacrylamide with a mass fraction of 0.05% to 0.2%, and adding the working solution to oily wastewater containing anionic surfactant, polymer flooding residue and inorganic salt for flocculation treatment; wherein the anionic surfactant includes sodium dodecylbenzenesulfonate, and the polymer flooding residue includes hydrolyzed polyacrylamide residue.

[0027] The polyacrylamide powders obtained in the embodiments and comparative examples of this invention were tested under the same conditions: A 0.1% (w / w) working solution of polyacrylamide powder was prepared and reconstituted at 25°C with stirring at 250 r / min. The apparent viscosity was measured every 5 min from the start of reconstitution. When no undissolved particles were visible to the naked eye in the solution, and the change rate of apparent viscosity in three consecutive measurements did not exceed 5%, the corresponding time was recorded as the reconstitution time. After 30 min of reconstitution, 100 mL of the solution was filtered through a 20-mesh sieve, and the number of translucent micelles on the sieve was recorded as the number of fish eyes. After 120 min of reconstitution, the solution was filtered through a 100 μm filter membrane and dried to constant weight at 60°C. The residual amount of microgel was calculated based on the ratio of the weight gain of the filter membrane to the mass of the added powder, and the apparent viscosity was measured at 30 min and 120 min of reconstitution. In the strong anti-anionic surfactant composite test, a 0.1% (w / w) working solution of polyacrylamide was mixed with 100 mg / L dodecane. Sodium dodecylbenzenesulfonate solution was mixed at a volume ratio of 1:1, allowed to stand for 10 min, and then the transmittance at 600 nm was measured. The precipitate was collected by centrifugation and the amount of premixed precipitate was calculated. In the flocculation test of oily wastewater, simulated oily wastewater containing 300 mg / L white oil, 100 mg / L sodium dodecylbenzenesulfonate, 500 mg / L hydrolyzed polyacrylamide residue, 4.0 g / L sodium chloride, and 100 mg / L calcium chloride, with a pH of 7.2, was used. The sample solution was added to the simulated... In oily wastewater, the mixture was stirred rapidly at 250 r / min for 1 min, then slowly at 80 r / min for 8 min. After standing for 15 min, the supernatant was collected to determine the oil content and turbidity. The effective dosage of polyacrylamide when the oil content in the supernatant was below 30 mg / L was recorded as the unit dosage. The median particle size of the flocs was determined using a statistical method based on microscopic images. The settling velocity was calculated based on the distance the floc interface descended in the graduated cylinder and the settling time. Each test was performed in parallel three times, and the average value was taken.

[0028] In Example 1, a monomer reaction solution with a total monomer mass fraction of 25% was prepared by mixing acrylamide, methacryloyloxyethyltrimethylammonium chloride, and N-vinylpyrrolidone in a molar ratio of 92%, 5%, and 3%, respectively. The pH was adjusted to 5.2, and after nitrogen deoxygenation for 30 min, a redox initiation system consisting of ammonium persulfate and sodium bisulfite was added. Polymerization was carried out at 30°C for 5 h, then cooled to 25°C, and the pH of the polymerization mother liquor was adjusted to 6.0 to obtain the wet colloid to be conditioned. The wet colloid to be conditioned was placed in an hydrated chain-releasing conditioning solution containing 0.04 mol / L sodium chloride and 0.01 mol / L sodium acetate at pH 6.2, and stirred slowly at 28°C for 1.5 h at a mass ratio of 1:3 to obtain the chain-releasing wet colloid. The chain-releasing wet colloid was then transferred to a weak anion pre-shielding conditioning solution containing 0.01 mol / L sodium citrate and 0.05 mol / L sodium chloride at pH 6.5, and conditioned at 28°C for 1 h at a mass ratio of 1:2. After 2 hours, a pre-shielded wet colloid was obtained. This pre-shielded wet colloid was then placed in a low-ionic-strength cleaning solution containing 0.015 mol / L sodium chloride at pH 6.5 and washed for 25 minutes at a mass ratio of 1:1.5 to obtain a limited amount of dehydrated colloid. This limited amount of dehydrated colloid was subjected to low-pressure filtration to control the moisture content to 55%, cut into particles with a diameter of approximately 5 mm, pre-dried at 50°C to a moisture content of 25%, and then further dried at 55°C until the moisture content was below 10%. Polyacrylamide powder was obtained after crushing and sieving. The resolution time of the obtained polyacrylamide powder was 35.6 min, the residual amount of microgel was 0.82%, the transmittance at 600 nm after premixing with sodium dodecylbenzenesulfonate was 86.7%, the precipitation amount was 0.0074 g / L, the oil content of the supernatant after simulating oily wastewater treatment was 19.3 mg / L, the unit chemical consumption was 33.1 mg / L, and the median particle size of the flocs was 594 μm.

[0029] Example 2: The preparation of the polymer colloid and the hydration chain release treatment in this example are the same as in Example 1. The difference is that the concentration of sodium citrate in the weak anion pre-shielding conditioning solution is adjusted to 0.003 mol / L, the concentration of sodium chloride is maintained at 0.05 mol / L, the pH is maintained at 6.5, the weak anion pre-shielding treatment time is 1.2 h, and the limited removal, water-containing shaping and dehydration, and low-temperature segmented drying are all the same as in Example 1, to obtain polyacrylamide powder. The reconstitution time of the obtained polyacrylamide powder was tested to be... After 38.4 min, the residual amount of microgel was 1.06%, the transmittance at 600 nm after premixing with sodium dodecylbenzenesulfonate was 74.9%, the precipitation amount was 0.0206 g / L, the oil content of the supernatant after simulating oily wastewater treatment was 27.8 mg / L, the unit drug consumption was 38.6 mg / L, and the median particle size of flocs was 526 μm. This indicates that low concentration of sodium citrate can form a weak anion pre-shielding effect, but the pre-shielding sufficiency for local high cation sites is lower than that in Example 1.

[0030] Example 3: The preparation of the polymer colloid and the hydration chain release treatment in this example are the same as in Example 1. The difference is that the concentration of sodium citrate in the weak anion pre-shielding conditioning solution is adjusted to 0.018 mol / L, the concentration of sodium chloride is 0.05 mol / L, the pH is 6.5, the weak anion pre-shielding treatment time is 1.2 h, the limited removal treatment time is extended to 35 min, the low ionic strength cleaning solution is still 0.015 mol / L sodium chloride aqueous solution, and the water-containing shaping, dehydration, and low-temperature segmented drying are the same as in Example 1, yielding polyacrylamide powder; after testing... The resolution time of the obtained polyacrylamide powder was 40.2 min, the residual amount of microgel was 1.18%, the transmittance at 600 nm after premixing with sodium dodecylbenzenesulfonate was 84.1%, the precipitation amount was 0.0108 g / L, the oil content of the supernatant after simulating oily wastewater treatment was 22.9 mg / L, the unit chemical consumption was 35.2 mg / L, and the median particle size of the flocs was 563 μm. This indicates that a higher concentration of sodium citrate is beneficial to reduce the precipitation risk induced by sodium dodecylbenzenesulfonate, and it is necessary to combine it with limited removal treatment to maintain the subsequent flocculation capacity.

[0031] Example 4: The preparation of the polymer colloid and the hydration chain release treatment in this example are the same as in Example 1, except that the weak anion pre-shielding conditioning solution uses 0.01 mol / L sodium tartrate and 0.05 mol / L sodium chloride, the pH is 6.5, the mass ratio of the chain-release wet colloid to the weak anion pre-shielding conditioning solution is 1:2, the conditioning time is 1.2 h, and the limited removal, water-containing shaping and dehydration, and low-temperature segmented drying are all the same as in Example 1, to obtain polyacrylamide powder; the resolubility of the obtained polyacrylamide powder is tested. The time interval was 39.1 min, the residual amount of microgel was 1.24%, the transmittance at 600 nm after premixing with sodium dodecylbenzenesulfonate was 80.6%, the precipitation amount was 0.0145 g / L, the oil content of the supernatant after simulating oily wastewater treatment was 25.6 mg / L, the unit chemical consumption was 36.8 mg / L, and the median particle size of flocs was 548 μm. These results indicate that sodium tartrate can replace sodium citrate for weak anion pre-shielding treatment and can reduce the risk of sudden strong recombination induced by anionic surfactants.

[0032] Example 5: The preparation of the polymer colloid and the hydration chain release treatment in this example are the same as in Example 1. The difference is that the weak anion pre-shielding conditioning solution uses 0.012 mol / L sodium gluconate and 0.05 mol / L sodium chloride, with a pH of 6.5. The weak anion pre-shielding treatment time is 1.5 h. The limited removal, water-containing shaping and dehydration, and low-temperature segmented drying are all the same as in Example 1, yielding polyacrylamide powder. The reconstitution time of the obtained polyacrylamide powder is tested to be 34.7 min. The residual amount of microgel was 0.74%, the transmittance at 600 nm after premixing with sodium dodecylbenzenesulfonate was 83.3%, the precipitation amount was 0.0121 g / L, the oil content of the supernatant after simulating oily wastewater treatment was 21.4 mg / L, the unit drug consumption was 34.7 mg / L, and the median particle size of flocs was 579 μm. This indicates that sodium gluconate can help maintain the hydration state of wet colloids during the weak anion pre-shielding process, so that the obtained polyacrylamide powder has good re-dissolution chain performance.

[0033] Example 6: In this example, the molar ratios of acrylamide, methacryloyloxyethyltrimethylammonium chloride, and N-vinylpyrrolidone were adjusted to 90%, 8%, and 2%, respectively. The remaining polymerization conditions were the same as in Example 1. The hydration chain release, weak anion pre-shielding, limited removal, and water-containing shaping and drying were all performed under the conditions of Example 1 to obtain polyacrylamide powder. The resolution time of the obtained polyacrylamide powder was 37.5 min, the microgel residue was 1.03%, the transmittance at 600 nm after premixing with sodium dodecylbenzenesulfonate was 79.8%, the precipitation amount was 0.0176 g / L, the oil content of the supernatant after simulating oily wastewater treatment was 24.7 mg / L, the unit chemical consumption was 37.3 mg / L, and the median particle size of the flocs was 551 μm. This indicates that even with an increased proportion of cationic monomers, the complete continuous conditioning scheme can still reduce the risk of sudden strong recombination between local high cationic sites and anionic surfactants.

[0034] Comparative Example 1: Cationic polyacrylamide polymer colloid was prepared according to the polymerization conditions of Example 1. After polymerization was completed and after final polymerization and equalization treatment, no hydration chain release treatment, weak anion pre-shielding treatment, or limited removal treatment was performed. The colloid was directly cut, dried, pulverized, and sieved. The drying conditions were 50°C pre-drying and 55°C continued drying, and the moisture content was reduced to less than 10%, resulting in polyacrylamide powder. The resolution time of the obtained polyacrylamide powder was 81.3 min, the microgel residue was 6.52%, the transmittance at 600 nm after premixing with sodium dodecylbenzenesulfonate was 36.8%, the precipitation amount was 0.1463 g / L, the oil content of the supernatant after simulating oily wastewater treatment was 61.9 mg / L, the unit drug consumption was 70.4 mg / L, and the median particle size of the flocs was 273 μm. This indicates that the powder obtained by the conventional direct drying route has obvious resolution lag and is prone to forming sudden strong complex precipitation with anionic surfactants.

[0035] Comparative Example 2: The wet colloid to be conditioned was prepared according to the method of Example 1, and subjected to hydration and chain release treatment under the conditions of Example 1. After hydration and chain release treatment, no weak anion pre-shielding treatment or limited removal treatment was performed. Instead, the hydrated, shaped, and dehydrated colloid was directly dried at low temperature, pulverized, and sieved to obtain polyacrylamide powder. The resolution time of the obtained polyacrylamide powder was 51.6 min, the microgel residue was 2.68%, the transmittance at 600 nm after premixing with sodium dodecylbenzenesulfonate was 44.2%, the precipitation amount was 0.1065 g / L, the oil content of the supernatant after simulating oily wastewater treatment was 47.3 mg / L, the unit drug consumption was 56.1 mg / L, and the median particle size of the flocs was 352 μm. This indicates that hydration and chain release alone can improve the resolution state of the powder, but cannot fully inhibit the sudden strong recombination between local high-cation sites and sodium dodecylbenzenesulfonate.

[0036] Comparative Example 3: The wet colloid to be conditioned was prepared according to the method of Example 1. The wet colloid to be conditioned was not subjected to hydration and chain release treatment, and was directly transferred to the sodium citrate weak anion pre-shielding conditioning solution described in Example 1 for 1.2 h. The limited removal, water-containing shaping and dehydration, and low-temperature segmented drying were the same as in Example 1 to obtain polyacrylamide powder. The reconstitution time of the obtained polyacrylamide powder was 67.8 min, the microgel residue was 4.72%, the transmittance at 600 nm after premixing with sodium dodecylbenzenesulfonate was 60.5%, the precipitation amount was 0.0684 g / L, the oil content of the supernatant after simulating oily wastewater treatment was 52.6 mg / L, the unit drug consumption was 61.7 mg / L, and the median particle size of the flocs was 324 μm. This indicates that the locally entangled chain segments and the bound chain segments of the expanded microgel inside the wet colloid that was not subjected to hydration and chain release treatment were not sufficiently loosened, and the weak anion conditioning agent could not act evenly on the local high cationic sites inside the wet colloid.

[0037] Comparative Example 4: Polymerization, final polymerization followed by equalization treatment, hydration and chain release treatment, and weak anion pre-shielding treatment were performed sequentially according to the method of Example 1. After the weak anion pre-shielding treatment, no low-ionic strength cleaning solution was used for limited removal. Instead, the polyacrylamide powder was directly subjected to water-containing shaping and dehydration, low-temperature segmented drying, pulverization, and sieving. The resolution time of the obtained polyacrylamide powder was 37.2 min, the microgel residue was 0.96%, the transmittance at 600 nm after premixing with sodium dodecylbenzenesulfonate was 82.7%, the precipitation was 0.0132 g / L, the oil content of the supernatant after simulating oily wastewater treatment was 39.8 mg / L, the unit chemical consumption was 50.6 mg / L, and the median particle size of the flocs was 418 μm. This indicates that without limited removal, the powder resolution state and strong anti-surfactant performance were not significantly deteriorated. However, the residue of free weak anion conditioner occupied some cationic sites, leading to a decrease in subsequent charge neutralization and bridging flocculation capabilities.

[0038] Comparative Example 5: Polymerization, final polymerization equalization treatment, hydration chain release treatment, weak anion pre-shielding treatment, and limited removal treatment were completed according to the method of Example 1. After limited removal, no water-containing shaping and dehydration were performed, nor was low-temperature segmented drying used. Instead, the wet colloid was cut into pieces and directly dried at 75°C until the moisture content was less than 10%. After crushing and sieving, polyacrylamide powder was obtained. The reconstitution time of the obtained polyacrylamide powder was 63.4 min, the microgel residue was 4.36%, the transmittance at 600 nm after premixing with sodium dodecylbenzenesulfonate was 76.5%, the precipitation amount was 0.0214 g / L, the oil content of the supernatant after simulating oily wastewater treatment was 42.1 mg / L, the unit chemical consumption was 53.5 mg / L, and the median particle size of the flocs was 386 μm. This indicates that direct high-temperature drying will cause rapid water loss and local hardening of the outer layer of the wet colloid, making it difficult to maintain the favorable state formed by the hydration chain release treatment and weak anion pre-shielding treatment in the powder.

[0039] Comparative Example 6: Polymerization, final polymerization equalization treatment, and hydration chain release treatment were completed according to the method of Example 1. After hydration chain release, the released wet colloid was placed in a 0.05 mol / L sodium chloride aqueous solution for 1.2 h without the addition of sodium citrate, sodium tartrate, and sodium gluconate. The polyacrylamide powder was obtained by limited removal, water-containing shaping and dehydration, and low-temperature segmented drying according to the method of Example 1. The resolution time of the obtained polyacrylamide powder was 44.8 min, the microgel residue was 1.72%, the transmittance at 600 nm after premixing with sodium dodecylbenzenesulfonate was 53.4%, the precipitation amount was 0.0876 g / L, the oil content of the supernatant after simulating oily wastewater treatment was 40.7 mg / L, the unit chemical consumption was 51.2 mg / L, and the median particle size of the flocs was 397 μm. This indicates that ordinary brine treatment can improve the ionic environment and resolution state of the wet colloid, but it cannot form a reversible ion pairing state with local high-cation sites, making it difficult to replace weak anion pre-shielding treatment.

[0040] Comparative Example 7: In this comparative example, the molar proportions of acrylamide, methacryloyloxyethyltrimethylammonium chloride, and N-vinylpyrrolidone were the same as in Example 6, at 90%, 8%, and 2%, respectively. The polymerization conditions were the same as in Example 6. After polymerization, no hydration chain release treatment, weak anion pre-shielding treatment, limited removal treatment, or water-containing shaping and drying were performed. The product was directly cut, dried, pulverized, and sieved to obtain polyacrylamide powder. The reconstitution time of the obtained polyacrylamide powder was tested to be 86.9 min, and the microgel residue was 7.18 g / L. The transmittance at 600 nm after premixing with sodium dodecylbenzenesulfonate was 27.6%, the precipitation amount was 0.1968 g / L, the oil content of the supernatant after simulating oily wastewater treatment was 68.4 mg / L, the unit chemical consumption was 75.9 mg / L, and the median particle size of the flocs was 251 μm. This indicates that under the condition of increasing the proportion of cationic monomers but without continuous conditioning before drying, the sudden strong complexation between local high cationic sites and sodium dodecylbenzenesulfonate is more obvious, and the re-dissolution chain state of the powder and the flocculation effect of oily wastewater are significantly reduced.

[0041] Table 1. Test results of comprehensive performance of polyacrylamide powder

[0042] Based on the data of reconstitution time and sodium dodecylbenzenesulfonate premixed precipitate in Table 1, the following plot was drawn. Figure 2 .Depend on Figure 2 It can be seen that the resolution time of Examples 1 to 6 is generally short, and the amount of premixed precipitate remains at a low level. In Comparative Examples 1, 2, 3, 6 and 7, the resolution time or the amount of premixed precipitate increases significantly, reflecting that the powder resolution release chain state and the strong compounding ability of anti-anionic surfactants are affected when there is a lack of hydration release chain, weak anion pre-shielding or complete continuous conditioning.

[0043] Based on the data of oil content in the supernatant, unit chemical consumption, and median particle size of flocs in Table 1, the following plot was drawn. Figure 3 .Depend on Figure 3 It can be seen that the sample of the example is concentrated in the region corresponding to low oil content, low chemical consumption and larger floc size, while the comparative sample is generally biased towards the region of high oil content and high chemical consumption. This reflects that the continuous conditioning effect before drying of the present invention can be extended to the oily wastewater treatment process, so that the polyacrylamide segments maintain a good bridging utilization state after resolution.

[0044] From Table 1, Figure 2 and Figure 3 It can be seen that Examples 1 to 6 all maintained good overall performance in powder resolution, resistance to strong anionic surfactant complexation, and flocculation treatment of oily wastewater. Compared with Comparative Example 1, Example 1 showed a reduction of approximately 56% in resolution time, approximately 87% in microgel residue, approximately 95% in sodium dodecylbenzenesulfonate premixed precipitation, approximately 69% in supernatant oil content, approximately 53% in unit chemical consumption, and approximately 118% in median floc size. These results indicate that hydration chain release, weak anionic pre-shielding, limited removal, and water-containing shaping and drying do not simply increase the powder dissolution rate, but rather form a continuous interaction between chain segment release, resistance to strong complexation deactivation, and bridging flocculation utilization.

[0045] Comparative Example 2, which only underwent hydration and chain release treatment, showed improved reconstituted state compared to the directly dried sample, but its resistance to strong recombination with sodium dodecylbenzenesulfonate remained insufficient, indicating that loosened chain segments cannot replace pre-shielding of local high-cation sites. Comparative Example 3, which underwent weak anion pre-shielding without hydration and chain release, showed some reduction in premixed precipitation, but reconstituted lag and microgel residue remained significant, indicating that hydration and chain release provided the necessary conditions for the weak anion conditioner to enter the wet colloid and act on local high-cation sites.

[0046] In Comparative Example 4, after omitting the limit removal, the resolution and premixing data remained close to those of the example. However, the oil content, chemical consumption, and floc particle size at the wastewater treatment end all deteriorated, indicating that the limit removal did not function as ordinary cleaning but rather controlled the residue of free weak anionic conditioner, preventing excessive residue from occupying cationic sites and weakening subsequent bridging flocculation. In Comparative Example 5, after using high-temperature direct drying, the resistance to strong chelation was not completely lost, but the resolution lag and microgel residue increased significantly, indicating that water-containing shaping and desiccation, as well as low-temperature segmented drying, could preserve the hydration chain release state formed in the previous treatment.

[0047] In Comparative Example 6, the reconstitution state was improved to some extent after treatment with ordinary brine instead of weak anion pre-shielding. However, the amount of sodium dodecylbenzenesulfonate premixed precipitate was approximately 11.8 times that of Example 1, indicating that ordinary brine treatment is difficult to form a reversible ion pairing state corresponding to local high-cation sites. The comparison results between Example 6 and Comparative Example 7 show that, under the conditions of increased proportion of cationic monomers and increased risk of local high-cation hotspots, the complete and continuous conditioning chain can still reduce the amount of premixed precipitate by about 91%, reduce the oil content of the supernatant by about 64%, and reduce the unit chemical consumption by about 51%, thereby maintaining the bridging flocculation capacity in complex oily wastewater.

[0048] The above description is only a specific embodiment of this disclosure, but the protection scope of this disclosure is not limited thereto. The protection scope of this disclosure should be determined by the protection scope of the claims.

Claims

1. A method for preparing polyacrylamide for oil-containing wastewater treatment, characterized by, include: Step 1: Acrylamide, cationic monomer and hydration auxiliary monomer are dissolved in water to form a monomer reaction solution. Under deoxygenation conditions, an oxidation-reduction initiation system is added to carry out aqueous free radical polymerization to obtain cationic polyacrylamide polymer colloid. Step 2: The cationic polyacrylamide polymer colloid is retained in the polymerization mother liquor, and the cationic polyacrylamide polymer colloid is subjected to a final polymerization and then homogenization treatment to obtain the wet colloid to be conditioned. Step 3: Place the wet colloid to be hydrated in the hydration and chain release conditioning solution for hydration and chain release treatment, so that the locally entangled chain segments and the bound chain segments of the expanded microgel in the wet colloid to be hydrated are loosened, and a chain-release wet colloid is obtained. Step 4: Place the chain-releasing wet colloid in a weak anion pre-shielding conditioning solution for weak anion pre-shielding treatment, so that the weak anion conditioning agent and the local high cation sites in the chain-releasing wet colloid form reversible ion pairing, and obtain the pre-shielded wet colloid. Step 5: Place the pre-shielded wet colloid in a low-ionic-strength cleaning solution for limited removal treatment, so that the free weak anionic conditioner that has not participated in reversible ion pairing is partially removed, while retaining the reversible ion pairing state in the pre-shielded wet colloid, to obtain the limited-removed wet colloid. Step six involves subjecting the limited amount of dehumidified colloid to aqueous shaping and dehydration, followed by low-temperature segmented drying. This ensures that the limited amount of dehumidified colloid maintains the re-dissolution chain state formed by the hydration chain release treatment and weak anion pre-shielding treatment during the drying process. After pulverization and sieving, polyacrylamide for oily wastewater treatment is obtained.

2. The method for preparing polyacrylamide for treating oily wastewater according to claim 1, characterized in that, In step one, the cationic monomer is methacryloyloxyethyltrimethylammonium chloride, and the hydration aid monomer is N-vinylpyrrolidone; The molar percentages of acrylamide, methacryloyloxyethyltrimethylammonium chloride, and N-vinylpyrrolidone were 88%–94%, 4%–8%, and 2%–6%, respectively.

3. The method for preparing polyacrylamide for treating oily wastewater according to claim 1, characterized in that, In step one, the total monomer mass fraction of the monomer reaction solution is 20%–30%, and the pH is 4.8–5.5; The redox initiation system includes ammonium persulfate and sodium bisulfite, the polymerization temperature is 25℃~35℃, and the polymerization time is 4h~6h.

4. The method for preparing polyacrylamide for treating oily wastewater according to claim 1, characterized in that, In step two, the post-polymerization equalization treatment includes lowering the temperature of the cationic polyacrylamide polymer colloid to 20℃~30℃ and adjusting the pH of the polymerization mother liquor to 5.5~6.5 to reduce residual initiation activity and form a wet colloid to be conditioned.

5. The method for preparing polyacrylamide for treating oily wastewater according to claim 1, characterized in that, In step three, the hydration and chain release conditioning solution is a low ionic strength monovalent salt aqueous solution containing 0.01 mol / L to 0.06 mol / L sodium chloride and 0.005 mol / L to 0.02 mol / L sodium acetate, with a pH of 5.8 to 6.

5. The mass ratio of the wet colloid to the hydration and chain release conditioning solution is 1:1.5 to 1:4, the hydration and chain release treatment temperature is 20℃ to 35℃, and the hydration and chain release treatment time is 0.5h to 2h.

6. The method for preparing polyacrylamide for treating oily wastewater according to claim 1, characterized in that, In step four, the weak anion pre-shielding conditioning solution contains a weak anion conditioning agent and a monovalent salt. The weak anion conditioning agent is at least one of sodium citrate, sodium tartrate, and sodium gluconate. The concentration of the weak anionic conditioner is 0.002 mol / L to 0.02 mol / L, the monovalent salt is sodium chloride, the concentration of sodium chloride is 0.02 mol / L to 0.08 mol / L, and the pH of the weak anionic pre-shielding conditioner is 6.0 to 7.

0.

7. The method for preparing polyacrylamide for treating oily wastewater according to claim 1, characterized in that, In step four, the mass ratio of the chain-releasing wet colloid to the weak anion pre-shielding conditioning solution is 1:1 to 1:3, the weak anion pre-shielding treatment temperature is 20℃ to 35℃, and the weak anion pre-shielding treatment time is 0.5h to 2h. The weak anion pre-shielding treatment puts the local high-cation sites in the chain-releasing wet colloid into a reversible ion pairing state.

8. The method for preparing polyacrylamide for treating oily wastewater according to claim 1, characterized in that, In step five, the low ionic strength cleaning solution contains 0.005 mol / L to 0.03 mol / L sodium chloride and has a pH of 6.0 to 7.

0. The mass ratio of the pre-shielded wet colloid to the low ionic strength cleaning solution is 1:1 to 1:2, and the limited removal treatment time is 10 min to 40 min.

9. The method for preparing polyacrylamide for treating oily wastewater according to claim 1, characterized in that, In step six, the water content setting and dehydration includes at least one of static leaching, low-pressure filtration, and low-speed centrifugation, so that the water content of the limited amount of wet colloid removed is controlled at 45% to 65%. Low-temperature segmented drying involves cutting a limited amount of dehumidified colloid into colloid particles with a particle size of 3 mm to 8 mm, pre-drying it at 45°C to 55°C to reduce the moisture content to 20% to 30%, and continuing to dry it at 50°C to 60°C until the moisture content is below 10%.

10. An application of polyacrylamide in the treatment of oily wastewater, characterized in that, Polyacrylamide is prepared by the preparation method according to any one of claims 1 to 9, wherein the polyacrylamide is prepared into a working solution with a mass fraction of 0.05% to 0.2%, and the working solution is added to oily wastewater containing anionic surfactants, polymer flooding residues and inorganic salts for flocculation treatment; The anionic surfactants include sodium dodecylbenzenesulfonate, and the polymer drive residues include hydrolyzed polyacrylamide residues.

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