A membrane separation-based method for purifying alpha-olefin sulfonate (AOS) slurry

Abstract

The application provides a kind of alpha-olefin sulfonate (AOS) slurry purification method based on membrane separation, comprising the following steps: (1) crude slurry pretreatment and foam precontrol;(2) first ultrafiltration pre-clearing and deoiling;(3) secondary nanofiltration rejection concentration and desalination;(4) post-treatment and membrane cleaning;(5) intelligent membrane fouling early warning;(6) dialysis permeate fractionation reuse.Improve the operation stability of membrane separation system, improve the desalination rate and active matter recovery rate, and the product active matter purity is also obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of surfactant analysis and detection technology, specifically relating to a membrane separation-based method for purifying α-olefin sulfonate (AOS) slurry. Background Technology

[0002] Alpha-olefin sulfonates (AOS) are complex surfactant systems produced from long-chain α-olefins through processes such as sulfonation, neutralization, and hydrolysis. Their main active components are olefin sulfonates, hydroxyalkane sulfonates, and disulfonates. AOS possesses advantages such as good biodegradability, insensitivity to hard water, and strong detergency, and is widely used in detergents, shampoos, and other daily chemical products, as well as in industrial cleaning applications.

[0003] Industrial AOS crude slurry is typically supplied in sodium salt form, as a liquid with 35%–40% active ingredient content or a powder product with over 90% active ingredient content. It contains a large amount of inorganic salts (such as Na₂SO₄ and NaCl), unreacted oil, and colored byproducts, requiring desalination and purification. Existing purification technologies mainly include solvent extraction, single-stage nanofiltration desalination, and ion exchange. Among these, single-stage nanofiltration direct concentration suffers from severe membrane fouling, difficulty in controlling foam, and low desalination efficiency; solvent extraction uses large amounts of organic solvents, resulting in high costs and significant environmental risks; and ion exchange involves frequent resin regeneration and complex operation, making it unsuitable for large-scale industrial production.

[0004] Nanofiltration is a membrane separation technology that lies between ultrafiltration and reverse osmosis. It has a molecular weight cutoff of 80-1000 and a pore size of a few nanometers, and is widely used in pharmaceuticals, food, and water treatment. Ultrafiltration, on the other hand, is suitable for the separation of large molecules, including the separation, concentration, and purification of enzymes and proteins, as well as desalination and pyrogen removal. Currently, there are no publicly reported technical solutions in the literature for combining ultrafiltration and nanofiltration for the purification of α-olefin sulfonates, particularly regarding foam control, low-temperature and mild operation, and intelligent pollution early warning in membrane separation processes involving surfactant systems. Summary of the Invention

[0005] The present invention aims to solve the following technical problems in the existing α-olefin sulfonate purification technology: (1) Foam control is difficult in the single nanofiltration direct concentration process. Surfactants are prone to generating stable foam during stirring, pumping and membrane filtration, which seriously affects the gas-liquid separation of membrane modules and the stability of system operation; (2) High temperature operation leads to the deepening of AOS color and degradation of active substances, which affects product quality; (3) The membrane fouling rate is fast, the chemical cleaning frequency is high, and the membrane life is short; (4) The desalination efficiency is low and the product purity is difficult to meet the needs of high-end applications; (5) The wastewater discharge is large and the resource utilization rate is low.

[0006] This invention provides a membrane separation-based method for purifying α-olefin sulfonate (AOS) slurry, comprising the following steps:

[0007] (1) Pretreatment and foam control of coarse slurry: The coarse slurry after AOS sulfonation and neutralization is subjected to static stratification or centrifugation to recover the unreacted oil phase. The aqueous phase layer is taken and the solid content is adjusted to 10-15% (based on active matter). The solid content is heated to 50-60℃ and a three-in-one foam control integrated strategy is adopted to suppress foam generation.

[0008] (2) First-stage ultrafiltration pre-clarification and deoiling: MWCO 100 kDa surfactant-resistant ultrafiltration membrane is used. Circulating cross-flow filtration is carried out under the conditions of operating pressure 0.2-0.4 MPa, temperature 50-60℃, and cross-flow velocity 3-5 m / s. AOS active substances permeate into the permeate.

[0009] (3) Secondary nanofiltration retention concentration and desalination: Using a MWCO 150-300 Da nanofiltration membrane, the active matter content is concentrated to 20-25% under the conditions of operating pressure 0.8-1.5 MPa and temperature 45-55℃. Then, a constant volume dialysis filtration mode is adopted, and 2-3 times the volume of deionized water is added to maintain a constant liquid level and reduce the inorganic salt content to below 0.5%.

[0010] (4) Post-treatment and membrane cleaning: The nanofiltration concentrate is heated to 75-80℃ and kept at that temperature for 20 minutes for mild heat treatment. After filtration, alkaline cleaning and acid cleaning are performed.

[0011] (5) Intelligent membrane fouling early warning: Real-time recording of transmembrane pressure difference (TMP) changes; when the TMP rise rate exceeds the set value, the operating pressure is automatically reduced and the cleaning mode is started.

[0012] (6) Classification and reuse of dialysis permeate: Part of the nanofiltration dialysis permeate is reused in the pretreatment stage, and the rest is concentrated to recover salts.

[0013] Preferably, the three-in-one foam control integrated strategy in step (1) includes: an online pipeline defoamer set between the outlet of the pretreatment tank and the membrane feed pump, a hollow fiber membrane module, and a baffle buffer structure set on the nanofiltration concentrate return pipeline.

[0014] Preferably, the ultrafiltration membrane in step (2) is a ceramic membrane or a hollow fiber organic membrane.

[0015] Preferably, the nanofiltration membrane in step (3) is a polyamide composite membrane, which achieves the retention of AOS active substances and the permeation of inorganic salts based on the dual mechanism of size sieving and Donnan charge repulsion.

[0016] Preferably, the alkaline cleaning in step (4) uses a mixed solution of 0.5-1.0% NaOH and 150-200 ppm NaClO, and is circulated at 45-50°C for 30-60 minutes; the acidic cleaning uses a 1% citric acid solution, and is circulated at 40°C for 20 minutes.

[0017] Preferably, the setting value in step (5) is that the regulation is automatically started when the TMP rises by more than 3% of the initial value within 10 minutes.

[0018] Preferably, the graded reuse in step (6) specifically involves: directly reusing 30% of the clear permeate to the dilution replenishment in the pretreatment stage, and further concentrating and recovering sodium sulfate by nanofiltration or reverse osmosis of the remaining 70%.

[0019] Preferably, all dilution and dialysis water used in step (1) is deionized water or softened water.

[0020] Preferably, the method has an active ingredient recovery rate of ≥85%, a desalination rate of ≥95%, and a product active ingredient purity of ≥92%.

[0021] The beneficial effects of this invention are as follows:

[0022] 1. By adopting a three-in-one foam control integrated strategy, the foam layer thickness at the membrane module inlet was reduced from >20cm in the control group to <4cm, and the system operating pressure drop fluctuation range was narrowed from ±22% to ±6%, which significantly improved the operating stability of the membrane separation system.

[0023] 2. The entire process is carried out at low temperatures (ultrafiltration section 50-60℃, nanofiltration section 45-55℃, post-treatment 75-80℃ / 20 min gentle heat treatment) to avoid the color of AOS darkening and active ingredient degradation at high temperatures.

[0024] 3. Through deep dialysis filtration, the inorganic salt content is reduced from the initial 5-8% to below 0.5%, improving the desalination rate and active ingredient recovery rate, and the purity of the product's active ingredients is also significantly improved.

[0025] 4. The intelligent membrane fouling early warning system enables dynamic monitoring and adaptive control of TMP, extending the membrane chemical cleaning cycle and improving the membrane flux recovery rate.

[0026] 5. The nanofiltration dialysis permeate recycling scheme significantly reduces the consumption of fresh deionized water. Detailed Implementation

[0027] To further understand the features, technical means, and specific objectives and functions achieved by the present invention, the present invention will be described in further detail below with reference to specific embodiments.

[0028] Example 1: This example provides the purification of α-olefin sulfonate (AOS) slurry using the method of the present invention. The specific operation is as follows:

[0029] (1) Pretreatment of coarse slurry and pre-control of foam

[0030] Take the crude slurry after AOS sulfonation and neutralization (solids content 35%, active matter approximately 30%, containing approximately 6% Na2SO4, unsulfonated oil, and colored byproducts), and allow it to stand for separation to recover the unreacted oil phase. Take the aqueous phase layer, adjust the solids content to 12% (based on active matter), and heat to 55°C. Use deionized water for all dilutions and dialysis.

[0031] An online in-line defoamer based on mechanical impact and vacuum degassing is installed between the pretreatment tank outlet and the membrane feed pump. Both ultrafiltration and nanofiltration membrane modules utilize hollow fiber construction. A baffle buffer structure is installed on the nanofiltration concentrate return line. After the above integrated foam control strategy, the foam layer thickness at the membrane module inlet is controlled within the range of 3-4 cm, and the system operating pressure drop fluctuation is controlled within ±6%, ensuring stable operation.

[0032] (2) First-stage ultrafiltration pre-clarification and oil removal

[0033] The pretreated feed solution was fed into an ultrafiltration system using a MWCO 100 kDa ceramic ultrafiltration membrane. The operating pressure was 0.3 MPa, the temperature was 55°C, and the cross-flow velocity was 4 m / s, with circulating cross-flow filtration. AOS active ingredients completely permeated into the permeate. The concentrate was discharged every 2.5 hours, with a discharge rate of approximately 8%, and some unreacted oil was recovered after collection. The AOS permeation rate in the ultrafiltration section was >98%.

[0034] (3) Two-stage nanofiltration retention concentration and desalination

[0035] The ultrafiltration permeate was transferred to a nanofiltration system using a MWCO 200 Da polyamide composite nanofiltration membrane, operating at a pressure of 1.0 MPa and a temperature of 50°C, and concentrated to an active ingredient content of 22%.

[0036] After concentration, a constant-volume dialysis filtration mode was used: 2.5 times the volume of deionized water was continuously added to the concentrate to maintain a constant liquid level for deep desalination. In this step, the AOS rejection rate was >90%, and the permeability of Na2SO4 and NaCl was >95%. Ultimately, the inorganic salt content in the concentrate decreased from approximately 6% initially to below 0.3%, with a desalination rate >95%.

[0037] (4) Post-treatment and membrane cleaning

[0038] The AOS concentrate retained by nanofiltration was collected and subjected to mild heat treatment at 78°C for 20 minutes. Results showed that the Klett color (1% aqueous solution) increased from 25 to 29 (16% increase), the active ingredient content decreased from 26.8% to 26.4% (98.5% retention), and the foaming power (Ross-Miles method) decreased from 185 mm to 180 mm (2.7% decrease), indicating that overall heat damage was controllable.

[0039] After filtration, rinse the system with deionized water until colorless. Alkaline cleaning: use a mixed solution of 0.8% NaOH and 180 ppm NaClO, circulating at 48°C for 45 minutes; acidic cleaning: use a 1% citric acid solution, circulating at 40°C for 20 minutes. Rinse with pure water until neutral pH is achieved, with membrane flux recovery >95%.

[0040] (5) Intelligent membrane pollution early warning

[0041] During operation, the system records TMP changes in real time. When TMP rises by more than 3% of its initial value within 10 minutes, the system automatically reduces the operating pressure and initiates backwashing. Filtration automatically resumes once TMP returns to within ±2% of its initial value. The number of chemical cleaning operations is reduced by 40% compared to conventional processes throughout the entire operating cycle.

[0042] (6) Recycling of dialysis permeate

[0043] In the permeate produced by nanofiltration dialysis, approximately 30% of the clear portion is directly reused as dilution makeup water in the pretreatment stage, while the remaining 70% is concentrated and Na2SO4 is recovered via reverse osmosis. Based on a daily processing capacity of 10 tons of coarse slurry, this saves 3.2 tons of deionized water per day.

[0044] Summary of process parameters: Active substance recovery rate 86% (ultrafiltration section permeability 98% × nanofiltration section retention rate 92% × operation loss); desalination rate > 95%; product active substance purity 93%; all the above parameters meet the expected control standards.

[0045] Example 2: The difference from Example 1 lies in the following parameters:

[0046] (1) Pretreatment: Adjust the solid content to 15% and heat to 60°C.

[0047] (2) Primary ultrafiltration: A hollow fiber organic ultrafiltration membrane (PVDF material) with a MWCO 100 kDa is used. The operating pressure is 0.4 MPa, the temperature is 60℃, and the cross-flow velocity is 3 m / s. The concentrate is discharged once every 2 hours, with a discharge rate of 10%.

[0048] (3) Secondary nanofiltration: A MWCO 150 Da polyamide nanofiltration membrane (wound coil configuration) was used, with an operating pressure of 1.2 MPa and a temperature of 55°C, to concentrate the active matter content to 25%. Dialysis filtration used 3 times the volume of deionized water. The final inorganic salt content was reduced from the initial 5% to below 0.4%.

[0049] (4) Post-treatment: Gentle heat treatment at 80℃ for 20 minutes. Test results: Klett color increased from 25 to 30 (increase of 20%), and the active ingredient retention rate was 98.0%.

[0050] (5) Intelligent early warning system: The TMP rise rate threshold is set to exceed 5% of the initial value within 15 minutes, and the control response mechanism is the same as in Example 1.

[0051] Process parameters: Active substance recovery rate 85%; desalination rate >95%; product active substance purity 92.5%.

[0052] Example 3: The difference from Example 1 lies in the nanofiltration cleaning and dialysate reuse scheme:

[0053] (1) Membrane cleaning: The alkaline cleaning solution formula was adjusted to 0.5% NaOH + 150 ppm NaClO, and the solution was circulated at 45℃ for 60 minutes; the acidic cleaning solution formula remained unchanged.

[0054] (2) Dialysis fluid reuse: The proportion of the clear permeate reused is adjusted to 25%, and the remaining 75% is concentrated by primary nanofiltration (MWCO300 Da) and used for pre-cleaning of the equipment exterior.

[0055] (3) Nanofiltration and ultrafiltration operation: Nanofiltration operation pressure 1.5 MPa, temperature 45℃; concentration to 23% active matter; dialysis filtration using 2 times the volume of deionized water.

[0056] Process parameters: Active substance recovery rate 86%; desalination rate >95%; product active substance purity 92.8%.

[0057] Comparative Example 1

[0058] The conventional single nanofiltration direct concentration process was used without ultrafiltration pretreatment, and the three-in-one foam control strategy and intelligent membrane fouling early warning system of this invention were not adopted.

[0059] Operation: After the AOS coarse slurry is allowed to stand and separate to recover unreacted oil, it is directly fed into a MWCO 200 Da nanofiltration membrane system. The operating pressure is 1.0 MPa and the temperature is 50℃. The concentration is carried out to 22% of the active matter, without dialysis filtration.

[0060] Results: The foam layer thickness at the membrane module inlet was >20 cm. After 30 minutes of system operation, pump cavitation caused by the foam forced a shutdown. Membrane flux decayed rapidly, dropping to 40% of its initial value within 120 minutes. The product desalination rate was only 60% (Na2SO4 content decreased from 6% to 2.4%), and the purity of the active ingredient was less than 75%.

[0061] Compared with Example 1 of the present invention, Comparative Example 1 shows significant differences in foam control, system operation stability, desalination efficiency and product purity.

[0062] Comparative Example 2

[0063] The process employs a "microfiltration pretreatment (MWCO 0.1 μm) + single nanofiltration concentration" process, without dialysis filtration steps, using conventional spiral wound nanofiltration membrane modules, and without foam control strategies.

[0064] Procedure: After microfiltration pretreatment, the AOS coarse slurry was directly fed into a MWCO 200 Da nanofiltration membrane system at an operating pressure of 1.0 MPa and a temperature of 50°C, and concentrated to 22% active matter. Dialysis filtration was not used.

[0065] Results: Microfiltration removed some suspended particles, but the foaming problem of AOS caused severe gas-liquid interference in both the microfiltration and nanofiltration sections, resulting in large fluctuations in membrane flux (±25%). The desalination rate of the nanofiltration section was only 70%, the Na2SO4 content in the product was above 2%, and the purity of the active ingredient was less than 80%. Without low-temperature dialysis, the Klett color of the product increased from 25 to 55 (an increase of 120%), and the color became significantly darker.

[0066] The embodiments described above merely illustrate the optimal implementation of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A membrane separation-based method for purifying α-olefin sulfonate (AOS) slurry, characterized in that, Includes the following steps: (1) Pretreatment and foam control of coarse slurry: The coarse slurry after AOS sulfonation and neutralization is subjected to static stratification or centrifugation to recover the unreacted oil phase. The aqueous phase layer is taken and the solid content is adjusted to 10-15% (based on active matter). The solid content is heated to 50-60℃ and a three-in-one foam control integrated strategy is adopted to suppress foam generation. (2) First-stage ultrafiltration pre-clarification and deoiling: MWCO 100 kDa surfactant-resistant ultrafiltration membrane is used. Circulating cross-flow filtration is carried out under the conditions of operating pressure 0.2-0.4 MPa, temperature 50-60℃, and cross-flow velocity 3-5 m / s. AOS active substances permeate into the permeate. (3) Secondary nanofiltration retention concentration and desalination: Using a MWCO 150-300 Da nanofiltration membrane, the active matter content is concentrated to 20-25% under the conditions of operating pressure 0.8-1.5MPa and temperature 45-55℃. Then, a constant volume dialysis filtration mode is used, adding 2-3 times the volume of deionized water to maintain a constant liquid level and reduce the inorganic salt content to below 0.5%. (4) Post-treatment and membrane cleaning: The nanofiltration concentrate is heated to 75-80℃ and kept at that temperature for 20 minutes for mild heat treatment. After filtration, alkaline cleaning and acid cleaning are performed. (5) Intelligent membrane fouling early warning: Real-time recording of transmembrane pressure difference (TMP) changes; when the TMP rise rate exceeds the set value, the operating pressure is automatically reduced and the cleaning mode is started. (6) Classification and reuse of dialysis permeate: Part of the nanofiltration dialysis permeate is reused in the pretreatment stage, and the rest is concentrated to recover salts.

2. The method for purifying α-olefin sulfonate (AOS) slurry based on membrane separation according to claim 1, characterized in that, The three-in-one foam control integrated strategy in step (1) includes: an online pipeline defoamer set between the pretreatment tank outlet and the membrane feed pump, a hollow fiber membrane module, and a baffle buffer structure set on the nanofiltration concentrate return pipeline.

3. The method for purifying α-olefin sulfonate (AOS) slurry based on membrane separation according to claim 1, characterized in that, The ultrafiltration membrane mentioned in step (2) is a ceramic membrane or a hollow fiber organic membrane.

4. The method for purifying α-olefin sulfonate (AOS) slurry based on membrane separation according to claim 1, characterized in that, The nanofiltration membrane mentioned in step (3) is a polyamide composite membrane, which achieves the retention of AOS active substances and the permeation of inorganic salts based on the dual mechanism of size sieving and Donnan charge repulsion.

5. The method for purifying α-olefin sulfonate (AOS) slurry based on membrane separation according to claim 1, characterized in that, The alkaline cleaning in step (4) uses a mixed solution of 0.5-1.0% NaOH and 150-200 ppm NaClO, and is circulated at 45-50℃ for 30-60 minutes; the acidic cleaning uses a 1% citric acid solution, and is circulated at 40℃ for 20 minutes.

6. The method for purifying α-olefin sulfonate (AOS) slurry based on membrane separation according to claim 1, characterized in that, The setting in step (5) is that the regulation will be automatically started when the TMP rises by more than 3% of the initial value within 10 minutes.

7. The method for purifying α-olefin sulfonate (AOS) slurry based on membrane separation according to claim 1, characterized in that, The graded reuse described in step (6) is as follows: 30% of the clear permeate is directly reused in the dilution replenishment of the pretreatment stage, and the remaining 70% is further concentrated and recovered as sodium sulfate by nanofiltration or reverse osmosis.

8. The method for purifying α-olefin sulfonate (AOS) slurry based on membrane separation according to claim 1, characterized in that, In step (1), all dilution and dialysis water should be deionized water or softened water.

9. The method for purifying α-olefin sulfonate (AOS) slurry based on membrane separation according to claim 1, characterized in that, The method has an active ingredient recovery rate of ≥85%, a desalination rate of ≥95%, and a product active ingredient purity of ≥92%.