Process for preparing polyacrylamide by emulsion polymerization method with low residual monomer content and high cationic degree

Abstract

The invention discloses a process for preparing polyacrylamide by an emulsion polymerization method with low residual monomer content and high cationic degree, and belongs to the technical field of polyacrylamide preparation processes. Comprising the following steps: T1, preparing an oil phase; t2, preparing a water phase; t3, carrying out pre-emulsification; t4, deoxidizing and initiating; t5, carrying out polymerization reaction; and T6, carrying out post-treatment. Through the optimized inverse emulsion polymerization process and composite initiation strategy, the problem that high cationic degree and low residual monomer are difficult to consider at the same time is successfully solved, and synchronous improvement of product performance and process controllability is realized. Specifically, the process can be used for stably preparing polyacrylamide with high cation degree (40-60%), large molecular weight and extremely low residual monomer content (less than or equal to 0.02%) under mild conditions, and meanwhile, the stability and batch consistency of the production process are ensured.

Description

Technical Field

[0001] This invention provides a process for preparing polyacrylamide by emulsion polymerization with low residual monomer and high cationicity, belonging to the technical field of polyacrylamide preparation process. Background Technology

[0002] Polyacrylamide (PAM) and its derivatives are among the most widely used water-soluble polymers in the world today, playing an irreplaceable role in oil extraction, wastewater treatment, papermaking, and mineral processing. Cationic polyacrylamide (CPAM), in particular, is especially effective in treating negatively charged suspended particles, organic matter, and dewatering sludge due to its excellent charge neutralization and adsorption bridging capabilities. The core performance indicators of CPAM include molecular weight, cationicity, and residual monomer content. High molecular weight endows it with good flocculation and bridging capabilities, high cationicity ensures its strong neutralization effect on negatively charged colloids, and low residual monomer content is a fundamental guarantee for the product's environmental and usage safety.

[0003] In existing technologies, the main processes for preparing high-cationic CPAM include aqueous solution polymerization and reverse emulsion polymerization. Aqueous solution polymerization is simple and low-cost, but it faces significant challenges in preparing products with high cationicity (typically >30%). As the proportion of cationic monomers (such as DMC) increases, issues such as pH value of the monomer mixture, differences in polymerization reactivity, and intense exothermic polymerization become extremely acute, easily leading to runaway polymerization or the generation of large amounts of insoluble substances, resulting in low molecular weight and poor solubility. More critically, the reactivity of acrylamide (AM) monomers is inhibited at high cationicity, making it difficult to improve reaction conversion rates. The residual acrylamide monomer content in the product often exceeds the standard (>0.05%), posing toxicity and environmental risks. Furthermore, the subsequent drying of the colloid obtained by the aqueous solution method is energy-intensive and easily leads to product degradation.

[0004] While reverse emulsion polymerization (CPAM) can yield high molecular weight products with rapid dissolution and achieve a certain degree of cationicity, its inherent drawbacks are also significant. This process requires large amounts of organic solvents as the oil phase and emulsifier, increasing production costs and process complexity (related to emulsion stabilization and demulsification), and introducing safety and environmental risks such as volatile organic compound (VOC) emissions and flammability / explosiveness. Residual oil phase and surfactants in the final product may also affect its application in certain sensitive fields. Therefore, developing a new process that circumvents the shortcomings of existing technologies and achieves efficient and green synthesis of CPAM with low residual monomers and high cationicity without relying on complex reverse emulsion systems has significant industrial value. Summary of the Invention

[0005] The technical problem to be solved by this invention is that existing technologies cannot simultaneously achieve the contradiction between high cationicity and low residual monomer content in polyacrylamide products without using complex reverse emulsion systems or facing the risk of reaction runaway.

[0006] To address the aforementioned problems, the present invention proposes a process for preparing polyacrylamide via emulsion polymerization with low residual monomer and high cationicity, comprising the following steps: T1. Oil phase preparation: The composite emulsifier is dissolved in white oil to form a homogeneous oil phase; the composite emulsifier is a compound of sorbitan monooleate (Span-80) and polyoxyethylene sorbitan monooleate (Tween-80); T2. Aqueous phase preparation: Mix acrylamide monomer, cationic monomer, complexing agent, and deionized water, stir to dissolve, and adjust the pH value to 3.0-5.5 with acid solution to form an aqueous phase; the cationic monomer is methacryloyloxyethyltrimethylammonium chloride (DMC). T3. Pre-emulsification: Under high-speed shearing, the aqueous phase obtained in step T2 is slowly added to the oil phase obtained in step T1. The shearing speed is not less than 3000 rpm, and the shearing is continued for 20-40 minutes to obtain a stable W / O type pre-emulsion. T4. Deoxygenation and Initiation: Nitrogen gas is introduced into the pre-emulsion for 20-30 minutes to remove oxygen, and then the redox initiator system is added. T5. Polymerization reaction: Heat the reaction system to 30-45℃ and carry out the polymerization reaction for 4-8 hours under inert gas protection; T6. Post-processing: After the reaction is complete, a demulsifier is added to demulsify and separate the cationic polyacrylamide colloid, which is then granulated and dried to obtain the powder product.

[0007] As an improvement, in step T1, the mass ratio of Span-80 to Tween-80 in the composite emulsifier is (1.5:1) to (2.5:1); the total amount of the composite emulsifier accounts for 3%-6% of the total mass of the entire reverse emulsion, and the mass ratio of the oil phase to the water phase, i.e., the oil-water ratio, is (1:1) to (1:1.5).

[0008] As an improvement, in step T2, the mass ratio of the acrylamide monomer to the cationic monomer is (50:50) to (70:30) so that the cationicity of the final product reaches 40%-60%; the total mass fraction of the monomer in the aqueous phase is 40%-55%.

[0009] As an improvement, in step T2, the complexing agent is disodium ethylenediaminetetraacetate (EDTA-2Na), and its amount is 0.02%-0.08% of the total mass of monomers in the aqueous phase; the acid used to adjust the pH is phosphoric acid or citric acid.

[0010] As an improvement, in step T4, the redox initiator system consists of a water-soluble oxidant and a reducing agent; the oxidant is ammonium persulfate or potassium persulfate, and its amount is 0.1%-0.4% of the total mass of the monomers in the aqueous phase; the reducing agent is sodium bisulfite or ferrous sulfate, and its amount is 0.05%-0.2% of the total mass of the monomers in the aqueous phase.

[0011] As an improvement, the redox initiator is added by dropping, with the dropping time controlled within 30-60 minutes.

[0012] As an improvement, in step T5, an azo initiator is added in the later stage of the polymerization reaction. The azo initiator is azobisisobutyramidine hydrochloride (V-50), and the amount added is 0.01%-0.05% of the total mass of the monomer in the aqueous phase. The reaction temperature is maintained at 40-50℃ and the reaction continues for 1-2 hours.

[0013] As an improvement, in step T6, the demulsifier is acetone or ethanol; the drying is spray drying, with an inlet temperature of 120-150℃ and an outlet temperature of 60-80℃.

[0014] The beneficial effects of this invention are: 1. Through optimized reverse emulsion polymerization process, especially precise control of oil-water ratio, composite emulsifier ratio, and acidic polymerization pH environment, a stable and thorough polymerization reaction was successfully achieved at a high cationic monomer feed ratio (50%-60%). The resulting product not only has high cationicity (40%-60%) and a large molecular weight (intrinsic viscosity ≥12 dL / g), but more importantly, the content of toxic acrylamide residual monomer is stably controlled at an extremely low level (≤0.02%), significantly improving product safety and efficacy.

[0015] 2. A combined initiation strategy, employing both dropwise addition of an oxidation-reduction initiator and subsequent supplementation with an azo initiator, effectively avoids the risk of explosive polymerization during the polymerization of highly reactive monomers, ensuring a mild and controllable reaction process and good batch-to-batch product quality stability. Simultaneously, through optimization of the emulsification system, the overall amount of emulsifier used is reduced while maintaining emulsion stability. Combined with efficient demulsification and drying technologies, the final product exhibits higher purity and superior application performance. Attached Figure Description

[0016] Figure 1 This is a flowchart of the process for preparing polyacrylamide by emulsion polymerization with low residual monomer and high cationicity according to the present invention. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to the embodiments described.

[0018] All raw materials used in this invention are commercially available chemically pure or industrial-grade products. The polymerization reaction is carried out in a reactor equipped with stirring, temperature control, and nitrogen protection devices. Example

[0019] Oil phase preparation: Add 150g white oil, 6g Span-80 and 3g Tween-80 to the reaction vessel (the total amount of composite emulsifier accounts for 4.5% of the expected total mass of the emulsion, and the mass ratio of Span-80 to Tween-80 is 2:1), and stir until dissolved.

[0020] Aqueous phase preparation: In another container, dissolve 105g of acrylamide (AM) monomer, 145g of methacryloyloxyethyltrimethylammonium chloride (DMC) monomer (AM to DMC mass ratio approximately 42:58, target cationicity approximately 55%), and 0.075g of EDTA-2Na in 250g of deionized water (total monomer concentration in aqueous phase 50%). Adjust the pH of the aqueous phase to 4.0 with dilute phosphoric acid solution.

[0021] Pre-emulsification: The aqueous phase was slowly added to the oil phase under high-speed shearing at 4000 rpm, and shearing was continued for 30 minutes after the addition was complete to obtain a stable W / O type pre-emulsion.

[0022] Deoxygenation and initiation: Nitrogen gas was bubbled into the emulsion for 25 minutes to remove oxygen. Then, a redox initiator solution consisting of 0.5 g ammonium persulfate (dissolved in 10 g water) and 0.2 g sodium bisulfite (dissolved in 10 g water) was added dropwise over 45 minutes.

[0023] Polymerization reaction: The reaction system temperature was raised to 35°C and the reaction was carried out for 6 hours under nitrogen protection. In the later stage of the reaction, 0.05 g of azobisisobutyramidine hydrochloride (V-50) was added, and the temperature was raised to 45°C to continue the reaction for 1.5 hours.

[0024] Post-processing: After the reaction was completed, 50 mL of acetone was added to break the emulsion, and the colloid was separated. After granulation, it was spray-dried (inlet temperature 135℃, outlet temperature 70℃) to obtain a white powder product. The product's intrinsic viscosity was tested to be 13.5 dL / g, its cationicity was 56%, and its residual AM monomer content was 0.018%. Example

[0025] Oil phase preparation: Add 160g white oil, 6.4g Span-80 and 3.2g Tween-80 (total percentage of composite emulsifier is 4.8%, mass ratio is 2:1) and dissolve.

[0026] Aqueous phase preparation: Dissolve 125g AM monomer, 100g DMC monomer (AM to DMC mass ratio of 55.6:44.4, target cationicity of approximately 42%), and 0.09g EDTA-2Na in 225g deionized water (total monomer concentration in aqueous phase is 50%). Adjust the pH to 4.5 with citric acid.

[0027] Pre-emulsification: The aqueous phase was added to the oil phase under shear at 3500 rpm and sheared for 25 minutes to obtain a pre-emulsion.

[0028] Deoxygenation and initiation: Deoxygenate with nitrogen for 30 minutes. Add an initiator consisting of 0.3g potassium persulfate and 0.15g ferrous sulfate (both prepared as dilute solutions) dropwise over 60 minutes.

[0029] Polymerization reaction: The reaction was carried out at 40°C for 5 hours. 0.03 g of V-50 was added later, and the reaction was continued at 45°C for 1 hour.

[0030] Post-processing: Demulsification with ethanol, followed by spray drying (inlet temperature 140℃, outlet temperature 65℃) to obtain the product. Testing showed the product had an intrinsic viscosity of 14.2 dL / g, a cationicity of 44%, and a residual AM monomer content of 0.015%.

[0031] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A process for preparing polyacrylamide via emulsion polymerization with low residual monomer and high cationicity, characterized in that, Includes the following steps: T1. Oil phase preparation: The composite emulsifier is dissolved in white oil to form a homogeneous oil phase; the composite emulsifier is a compound of sorbitan monooleate (Span-80) and polyoxyethylene sorbitan monooleate (Tween-80); T2. Aqueous phase preparation: Mix acrylamide monomer, cationic monomer, complexing agent, and deionized water, stir to dissolve, and adjust the pH value to 3.0-5.5 with acid solution to form an aqueous phase; the cationic monomer is methacryloyloxyethyltrimethylammonium chloride (DMC). T3. Pre-emulsification: Under high-speed shearing, the aqueous phase obtained in step T2 is slowly added to the oil phase obtained in step T1. The shearing speed is not less than 3000 rpm, and the shearing is continued for 20-40 minutes to obtain a stable W / O type pre-emulsion. T4. Deoxygenation and Initiation: Nitrogen gas is introduced into the pre-emulsion for 20-30 minutes to remove oxygen, and then the redox initiator system is added. T5. Polymerization reaction: Heat the reaction system to 30-45℃ and carry out the polymerization reaction for 4-8 hours under inert gas protection; T6. Post-processing: After the reaction is complete, a demulsifier is added to demulsify and separate the cationic polyacrylamide colloid, which is then granulated and dried to obtain the powder product.

2. The process according to claim 1, characterized in that, In step T1, the mass ratio of Span-80 to Tween-80 in the composite emulsifier is (1.5:1) to (2.5:1); the total amount of the composite emulsifier accounts for 3%-6% of the total mass of the entire reverse emulsion; and the mass ratio of the oil phase to the water phase, i.e., the oil-water ratio, is (1:1) to (1:1.5).

3. The process according to claim 1, characterized in that, In step T2, the mass ratio of acrylamide monomer to cationic monomer is (50:50) to (70:30) so that the cationicity of the final product reaches 40%-60%; the total mass fraction of monomer in the aqueous phase is 40%-55%.

4. The process according to claim 1, characterized in that, In step T2, the complexing agent is disodium ethylenediaminetetraacetate (EDTA-2Na), and its dosage is 0.02%-0.08% of the total mass of monomers in the aqueous phase; the acid used to adjust the pH is phosphoric acid or citric acid.

5. The process according to claim 1, characterized in that, In step T4, the redox initiator system consists of a water-soluble oxidant and a reducing agent; the oxidant is ammonium persulfate or potassium persulfate, and its dosage is 0.1%-0.4% of the total mass of the monomers in the aqueous phase; the reducing agent is sodium bisulfite or ferrous sulfate, and its dosage is 0.05%-0.2% of the total mass of the monomers in the aqueous phase.

6. The process according to claim 5, characterized in that, The redox initiator is added dropwise over a period of 30-60 minutes.

7. The process according to claim 1, characterized in that, In step T5, an azo initiator is added in the later stage of the polymerization reaction. The azo initiator is azobisisobutyramidine hydrochloride (V-50). The amount added is 0.01%-0.05% of the total mass of the monomer in the aqueous phase. The reaction temperature is maintained at 40-50℃ and the reaction continues for 1-2 hours.

8. The process according to claim 1, characterized in that, In step T6, the demulsifier is acetone or ethanol; the drying is spray drying, with an inlet temperature of 120-150℃ and an outlet temperature of 60-80℃.

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