A high efficiency seawater desalination system and method based on a multi-stage membrane set

Abstract

The application provides a high-efficiency seawater desalination system and method based on a multistage membrane group, which comprises a pretreatment unit, at least two membrane treatment units with different desalination rates, and a control unit; the control unit is used for adjusting the operation parameters of the membrane treatment units; the membrane treatment units are prepared by the following method: (1) a porous support membrane is immersed in an aqueous solution containing an amine monomer to obtain an immersed porous support membrane; and the aqueous solution is prepared by using a multivariate organic carboxylic acid buffer solution; (2) the immersed porous support membrane is placed in an organic phase solution containing an acid chloride monomer, then taken out and subjected to heat treatment to obtain the membrane treatment unit; wherein the pH values of the aqueous solutions used by different membrane treatment units are different. The scheme can dynamically adjust the combination and operation parameters of the membrane group, significantly improve the energy efficiency and reduce the cost, realize flexible treatment of complex water quality, and is suitable for various seawater desalination scenes.

Description

Technical Field

[0001] This invention relates to the field of seawater desalination technology, and in particular to a high-efficiency seawater desalination system and method based on multi-stage membrane modules. Background Technology

[0002] With the increasing severity of the global freshwater shortage, desalinated seawater is receiving more and more attention as a new type of freshwater resource. Currently, reverse osmosis is the mainstream technology in the global seawater desalination industry, accounting for over 60%. However, existing technologies suffer from the following core problems:

[0003] 1) Fixed membrane module configuration: Traditional devices use a single desalination rate membrane module (usually 98%~99.8%), which cannot be dynamically adjusted according to the salinity of the raw water and the water use standards, resulting in energy waste in high-salinity seawater treatment or redundant cost in low-salinity seawater treatment.

[0004] 2) Inefficient system control: It relies on manual setting of operating parameters and lacks real-time response to the degree of membrane fouling and fluctuations in permeate water quality. The desalination rate often decreases by 10% to 15% due to membrane scaling, requiring frequent chemical cleaning and shortening the membrane life by more than 30%.

[0005] Current reverse osmosis membranes are primarily prepared using interfacial polymerization technology, but this process is extremely complex, making it difficult to customize membrane performance to specific needs. Furthermore, traditional preparation processes often involve adding alkaline substances such as sodium hydroxide or triethylamine to the aqueous phase, mainly to neutralize the reaction byproduct HCl and prevent pH drops that could inhibit the reaction. However, this approach has significant drawbacks: because HCl production is continuous, simply adding alkaline substances cannot maintain a constant pH throughout the polymerization process, leading to dynamic pH changes in the reaction environment. This results in an uneven polyamide layer structure, making customization difficult.

[0006] Therefore, there is an urgent need for a high-efficiency seawater desalination system and method based on multi-stage membrane modules that combines flexibility, high efficiency, and intelligence. Summary of the Invention

[0007] This invention provides a high-efficiency seawater desalination system and method based on multi-stage membrane modules, which dynamically adjusts the membrane module combination and operating parameters, significantly improves energy efficiency and reduces costs, and enables flexible treatment of complex water quality, applicable to various seawater desalination scenarios.

[0008] In a first aspect, a high-efficiency seawater desalination system based on a multi-stage membrane module includes: a pretreatment unit, at least two membrane treatment units with different desalination rates, and a control unit; the control unit is used to adjust the operating parameters of the membrane treatment units.

[0009] The membrane treatment unit is prepared by the following method:

[0010] (1) The porous support membrane is immersed in an aqueous solution containing amine monomers to obtain the immersed porous support membrane; wherein the aqueous solution is prepared using a polycarboxylic acid buffer solution;

[0011] (2) The impregnated porous support membrane is placed in an organic phase solution containing acyl chloride monomer, and then taken out for heat treatment to obtain the membrane treatment unit; wherein the pH value of the aqueous phase solution used in different membrane treatment units is different.

[0012] Secondly, the present invention provides a highly efficient seawater desalination method based on a multi-stage membrane module, comprising:

[0013] The seawater passing through the pretreatment unit is tested to determine the content of the first salt.

[0014] Based on the first salt content and the conductivity of the target water quality, at least two stages of membrane treatment units are determined from the membrane module configuration rule base;

[0015] The operating parameters of each membrane treatment unit are dynamically adjusted to ensure that the freshwater reaches the conductivity required for the target water quality.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects:

[0017] This invention stabilizes interfacial polymerization reaction conditions by constructing a pH buffer system and utilizes the controlled dissociation state of amine monomers to achieve graded membrane rejection, resulting in membrane treatment units with different desalination rates. This replaces traditional fixed membrane module combinations. By configuring multi-stage desalination rate membrane modules and combining them with intelligent control algorithms, flexible treatment of complex water qualities can be achieved. Thus, the system can dynamically adjust the membrane module combination and operating parameters, significantly improving energy efficiency and reducing costs, making it suitable for various seawater desalination scenarios. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of a high-efficiency seawater desalination system based on a multi-stage membrane module provided in an embodiment of the present invention;

[0020] Figure 2 This is a flowchart of an efficient seawater desalination method based on a multi-stage membrane module provided in an embodiment of the present invention;

[0021] Reference numerals: 10-Pretreatment unit; 20-Membrane treatment unit; 30-Control unit. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] The following describes the specific implementation of the concept in this application.

[0024] Please refer to Figure 1 This invention provides a high-efficiency seawater desalination system based on a multi-stage membrane module. The system includes: a pretreatment unit 10, at least two membrane treatment units 20 with different desalination rates, and a control unit 30; the control unit 30 is used to adjust the operating parameters of the membrane treatment units 20.

[0025] The membrane treatment unit was prepared by the following method:

[0026] (1) The porous support membrane is immersed in an aqueous solution containing amine monomers to obtain the immersed porous support membrane; wherein the aqueous solution is prepared using a polycarboxylic acid buffer solution;

[0027] (2) The impregnated porous support membrane is placed in an organic phase solution containing acyl chloride monomer, and then taken out for heat treatment to obtain a membrane treatment unit; wherein the pH value of the aqueous phase solution used in different membrane treatment units is different.

[0028] In this invention, a pH buffer system is constructed to stabilize the interfacial polymerization reaction conditions. The dissociation state of amine monomers is controlled to achieve graded membrane rejection, resulting in membrane treatment units with different desalination rates. This replaces traditional fixed membrane modules. By configuring multi-stage desalination rate membrane modules and combining them with intelligent control algorithms, flexible treatment of complex water qualities is achieved. Thus, the system can dynamically adjust the membrane module combination and operating parameters, significantly improving energy efficiency and reducing costs, making it suitable for various seawater desalination scenarios.

[0029] In a preferred embodiment, the pretreatment unit uses an ultrafiltration membrane to remove suspended solids, and the desalination rate of the pretreatment unit is lower than that of any membrane treatment unit.

[0030] In a preferred embodiment, the amine monomer includes one or more of m-phenylenediamine and piperazine.

[0031] It should be noted that "multiple" refers to any number of mixtures in any proportion.

[0032] In a preferred embodiment, the aqueous solution comprises a polycarboxylic acid buffer solution, an amine monomer, and a surfactant;

[0033] The buffer solution for polycarboxylic acids is sodium ethylenediaminetetraacetate buffer or sodium citrate buffer;

[0034] The mass fraction of amine monomers in the aqueous solution is 0.05 wt% to 5 wt%.

[0035] The mass fraction of the surfactant in the aqueous solution is 0.05 wt% to 5 wt%.

[0036] It should be noted that the molar concentration of the solute in the polycarboxylic acid buffer solution is preferably 0.01~1 mol / L (e.g., 0.01 mol / L, 0.02 mol / L, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, or 1 mol / L). The range of 0.05wt%~5wt% refers to any value from 0.05wt% to 5wt%, for example, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.1wt%, 0.2wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, or 5wt%.

[0037] In this invention, unlike the traditional method of adding a strong alkali, a pH buffer solution of polycarboxylic acids is introduced into the aqueous solution of amine monomers. This buffer solution effectively counteracts the pH impact of HCl generated during the reaction, ensuring the entire interfacial polymerization process proceeds stably in a predetermined pH environment. By precisely controlling the pH of the aqueous solution, the concentration of reactive free amines can be controlled, thereby regulating the degree of polymerization and the final membrane performance. Simultaneously, the polycarboxylic acid system rich in carboxyl groups (-COOH) acts as a buffer system, significantly inhibiting the diffusion rate of amine monomers through hydrogen bonding and other interactions, forming a more uniform polyamide surface and greatly improving the reproducibility and uniformity of membrane treatment unit preparation. Furthermore, m-phenylenediamine is easily oxidized by oxygen in an alkaline environment, generating quinones, azobenzenes, or complex polymerization byproducts. If m-phenylenediamine is partially oxidized before coating, it can lead to incomplete or uneven interfacial polymerization, potentially resulting in loose regions in the formed polyamide separation layer and reducing the desalination rate.

[0038] In a more preferred embodiment, the surfactant is one or more of sodium dodecyl sulfate, sodium hexadecylbenzenesulfonate, Tween, and polyoxyethylene alkylphenol ether.

[0039] In a preferred embodiment, the aqueous solution used to prepare the first-stage membrane treatment unit has a pH value of 8 to 9.5 (e.g., 8, 8.2, 8.5, 8.6, 8.8, 9, 9.2, or 9.5); the aqueous solution used to prepare the second-stage membrane treatment unit has a pH value of 6 to 7.5 (e.g., 6, 6.2, 6.5, 6.6, 6.8, 7, 7.2, or 7.5); and the aqueous solution used to prepare the third-stage membrane treatment unit has a pH value of 10 to 11.5 (e.g., 10, 10.2, 10.5, 10.6, 11, 11.2, or 11.5).

[0040] In a more preferred embodiment, an alkaline reagent is used to adjust the pH value of the aqueous solution, the alkaline reagent including one or more of ammonia water and ammonium chloride solution.

[0041] In this invention, by adjusting the pH value of the aqueous phase solution using ammonia and / or ammonium chloride solution, a first-stage membrane treatment unit with high desalination rate and low flux can be obtained when the pH value is adjusted to 8-9.5; a second-stage membrane treatment unit with medium desalination rate and high flux can be obtained when the pH value is adjusted to 6-7.5; and a third-stage membrane treatment unit with low desalination rate and high flux can be obtained when the pH value is adjusted to 10-11.5.

[0042] In a preferred embodiment, the acyl chloride monomer includes one of phthaloyl chloride or trimesoyl chloride.

[0043] In a more preferred embodiment, the mass fraction of the acyl chloride monomer in the organic phase solution is 0.1 wt% to 2 wt% (e.g., it can be 0.1 wt%, 0.2 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 1.5 wt% or 2 wt%).

[0044] In a preferred embodiment, the solvent used for the organic phase solution is a n-alkanes or isoalkanes.

[0045] In a preferred embodiment, the porous support membrane is an ultrafiltration membrane with a molecular weight cutoff of 20,000 to 100,000 Da (e.g., 20,000 Da, 30,000 Da, 40,000 Da, 50,000 Da, 60,000 Da, 70,000 Da, 80,000 Da, 90,000 Da, or 100,000 Da).

[0046] In a more preferred embodiment, the ultrafiltration membrane is prepared from one or more combinations of polysulfone, polyethersulfone, sulfonated polyethersulfone, polyimide, polypropylene, polyacrylonitrile, and polyetheretherketone.

[0047] In a preferred embodiment, in step (1), the soaking time is 1 to 30 minutes (for example, it can be 1 minute, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes).

[0048] In a preferred embodiment, in step (2), the time for which the impregnated porous support membrane is immersed in the organic phase solution containing acyl chloride monomer is 20 to 300 s (e.g., 20 s, 50 s, 100 s, 150 s, 200 s, 250 s or 300 s).

[0049] The heat treatment temperature is 40~110℃ (e.g., 40℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃ or 110℃), and the time is 3~40min (e.g., 3min, 5min, 10min, 15min, 20min, 25min, 30min, 35min or 40min).

[0050] The present invention also provides a highly efficient seawater desalination method based on the above system, comprising:

[0051] S1, The seawater after the pretreatment unit is tested to determine the content of the first salt;

[0052] S2, Based on the first salt content and the conductivity of the target water quality, determine at least two stages of membrane treatment units from the membrane module configuration rule base;

[0053] S3 dynamically adjusts the operating parameters of each membrane treatment unit to ensure that the freshwater reaches the target water quality conductivity.

[0054] Specifically, in the membrane module configuration rule base, for cases where the first salt content is greater than 35‰ and the target water conductivity is less than 300 μS / cm, a first-stage membrane treatment unit (desalination rate of 99.5%) and a second-stage membrane treatment unit (desalination rate of 98.5%) with a split ratio of 8:2 are selected, with an operating pressure of 5.5~6.5 MPa. For cases where the second salt content is 20‰~30‰ and the target water conductivity is 500~1000 μS / cm, a third-stage membrane treatment unit (desalination rate of 95.05%) and a second-stage membrane treatment unit (desalination rate of 98.5%) with a split ratio of 5:5 are selected, with an operating pressure of 3.5~4.0 MPa.

[0055] In a preferred embodiment, the membrane module configuration rule base includes several membrane treatment unit combinations and the first salt content applicable to each membrane treatment unit combination, the conductivity of the target water quality, and the diversion ratio of the at least two parallel membrane treatment units included.

[0056] In step S2, when determining the three-stage membrane treatment unit from the membrane module configuration rule base, step S3 dynamically adjusts the operating parameters of each stage of membrane treatment unit to ensure that the freshwater reaches the target water quality conductivity, including:

[0057] The seawater after the pretreatment unit is tested to determine the current primary salinity, temperature, and turbidity.

[0058] The inlet and outlet ends of each membrane treatment unit are tested to obtain the second salt content, inlet pressure and turbidity at the corresponding inlet end, and the third salt content and outlet pressure at the corresponding outlet end.

[0059] The current conductivity is calculated based on the diversion ratio and the third salt content of each membrane treatment unit. It is then determined whether the difference between the current conductivity and the conductivity of the target water quality is greater than a preset difference threshold.

[0060] When the judgment result is yes, for each membrane treatment unit, the feed water ratio is dynamically adjusted based on the second salt content, third salt content, inlet pressure and turbidity of that membrane treatment unit, so that the fresh water reaches the conductivity of the target water quality.

[0061] Specifically, when the judgment result is "yes," meaning the difference is greater than a preset difference threshold, it indicates that the current conductivity is too high, i.e., the salinity is too high. In this case, it is necessary to increase the diversion ratio of the first-stage membrane treatment unit and decrease the diversion ratio of the third-stage membrane treatment unit. Based on the adjustment results of these two adjustments, it is then determined whether to increase or decrease the diversion ratio of the second-stage membrane treatment unit. At this point, for the first-stage membrane treatment unit where the diversion ratio needs to be increased, the opening of its inlet valve is adjusted. It can be obtained through the following formula:

[0062] (1)

[0063] (2)

[0064] in, The real-time desalination rate of the i-th stage membrane treatment unit is dimensionless and reflects the single-stage desalination effect; the higher the value, the greater the contribution. The second salt content of the i-th stage membrane treatment unit. The third salt content of the i-th stage membrane treatment unit; This is the turbidity correction factor. If the turbidity at the inlet end... Exceeding the preset turbidity value , Conversely This can prevent turbidity from causing an artificially high desalination rate. This is a pressure correction factor; if the inlet pressure is less than the preset inlet pressure threshold, then... ;on the contrary ; The inlet pressure of the i-th stage membrane treatment unit is... The inlet pressure threshold is preset. Since too low a pressure will lead to a decrease in throughput and a reduction in desalination rate, the real-time desalination rate can be corrected by a pressure correction coefficient. Electrolysis rate for the target water quality This is the difference between the current conductivity output at the outlet of the third-stage membrane treatment unit and the conductivity of the target water quality. k For calibration coefficients;

[0065] At this point, for the third-stage membrane treatment unit where the diversion ratio needs to be reduced, the opening degree of its inlet valve is adjusted. It can be obtained through the following formula:

[0066] (3)

[0067] In formula (3), the meanings of each parameter are the same as in formula (2). k =0.6. It should be noted that the opening degree of the inlet valve is 0~100%. In this way, by using the above formulas (2) and (3), the flow rate can be avoided from changing suddenly.

[0068] In a preferred embodiment, the method further includes: predicting the pressure difference growth rate for each membrane treatment unit based on the pressure difference between the inlet pressure and the outlet pressure of that membrane treatment unit.

[0069] Predict membrane fouling levels based on differential pressure growth rate;

[0070] When the membrane fouling level is "membrane fouling present", the operating parameters of the membrane treatment unit at that level are dynamically adjusted.

[0071] More specifically, when the pressure difference between the inlet and outlet pressures exceeds a preset pressure, the rate of increase in the pressure difference is predicted. r i for:

[0072] (4)

[0073] in, for t The difference between import pressure and export pressure at any given moment; d The interval between detection cycles, i.e., the step size; for td The difference between import pressure and export pressure at any given moment;

[0074] Based on the rate of pressure differential growth, the predicted pressure differential of this membrane treatment unit is calculated after the prediction time. P y ;

[0075] (5)

[0076] in, For the predicted duration; This represents the pressure difference of the membrane treatment unit at the current moment.

[0077] The membrane fouling level is determined based on predicted pressure difference and preset rules; the preset rules include the membrane fouling level corresponding to the predicted pressure difference. This allows for timely and dynamic adjustment of the operating parameters of the membrane treatment unit at that level when membrane fouling is present, thereby extending the service life of the membrane treatment unit and delaying the chemical cleaning cycle caused by membrane fouling. t , d , The units are all the same.

[0078] In this invention, precise control of the target water conductivity is achieved through desalination rate correction and flow diversion ratio coupling, rather than simply adjusting the flow rate. Simultaneously, differential pressure monitoring is combined with flow and pressure pre-adjustment to predict the fouling level of the membrane treatment unit. This allows for timely adjustment of the unit's operating parameters when membrane fouling is predicted, extending the chemical cleaning cycle and breaking through the traditional logic of cleaning simply because fouling occurs, thus extending the membrane treatment unit's lifespan. More specifically, the aforementioned intelligent control method can also be implemented through real-time water quality feedback and neural network algorithms to achieve membrane fouling early warning, effectively alleviating membrane fouling, reducing the amount of membrane cleaning chemicals used, and extending the membrane module's lifespan.

[0079] This invention also provides a computing device, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, it implements the above-described efficient seawater desalination method based on a multi-stage membrane module.

[0080] This invention also provides a computer-readable storage medium storing a computer program that, when executed in a computer, causes the computer to perform the above-described efficient seawater desalination method based on a multi-stage membrane module.

[0081] This invention can treat complex water qualities with salinity ranging from 10 to 45‰, and the conductivity of the produced water can be adjusted within the range of 10 to 2000 μS / cm, meeting diverse needs from industrial cooling water to electronic-grade high-purity water. Compared to traditional single-membrane systems, the high-efficiency seawater desalination system of this invention reduces energy consumption by 30% when treating low-salinity seawater; and reduces desalination energy consumption by 5 to 10% compared to high-salinity seawater, significantly reducing costs.

[0082] To more clearly illustrate the technical solution and advantages of the present invention, the following describes in detail the application method of a high-efficiency seawater desalination system based on a multi-stage membrane module through several embodiments.

[0083] Example 1

[0084] A high-efficiency seawater desalination system based on multi-stage membrane modules includes:

[0085] The pretreatment unit includes, in sequence, a high-efficiency sedimentation tank, a disc filter (50μm precision), and a sand filter to remove suspended solids, colloids, and microorganisms from seawater, so that SDI < 3.

[0086] First-stage membrane treatment unit: Equipped with spiral wound reverse osmosis membranes, each membrane has a desalination rate of 99.5% and a permeate flow rate of 26 m³ / h. 3 / d, the corresponding membrane permeate flux is 29.28 LMH, and multiple pressure vessels are connected in parallel according to the water volume;

[0087] Second-stage membrane treatment unit: Equipped with spiral wound reverse osmosis membranes, each membrane has a desalination rate of 98.5% and a permeate flow rate of 36 m³ / h. 3 / d, the corresponding membrane permeate flux is 40.54 LMH, and multiple pressure vessels are connected in parallel according to the water volume;

[0088] The third-stage membrane treatment unit is equipped with spiral wound reverse osmosis membranes, with a single membrane achieving a desalination rate of 95.05% and a permeate flow rate of 45 m³ / h. 3 / d, corresponding to a membrane permeate flux of 50.68 LMH, with multiple pressure vessels connected in parallel according to the water volume; the reverse osmosis membrane test standard is as follows: under test conditions of 25℃ and 5.5±0.05MPa, with a sodium chloride aqueous solution of 32000ppm±500ppm and a pH of 7.5, the recovery rate is 8%;

[0089] The control unit is used to adjust the operating parameters of the membrane treatment unit.

[0090] The first-stage membrane treatment unit was prepared by the following method:

[0091] A 0.5 mol / L sodium ethylenediaminetetraacetic acid buffer solution, m-phenylenediamine, and sodium dodecyl sulfate were mixed at a mass ratio of 96:2:2 to prepare an aqueous solution. The pH of the aqueous solution was adjusted to 8.17 using ammonia. A polysulfone-based membrane with a molecular weight cutoff of 50,000 Da was then immersed in the aqueous solution at pH 8.17 for 15 min to obtain an impregnated porous support membrane. The impregnated porous support membrane was placed in an organic phase solution (composed of phthaloyl chloride and n-hexane at a mass ratio of 1:99) for 100 s, then removed and heat-treated at 90 °C for 10 min to obtain the first-stage membrane treatment unit.

[0092] The second-stage membrane treatment unit was prepared by the following method:

[0093] A 0.5 mol / L sodium ethylenediaminetetraacetic acid buffer solution, m-phenylenediamine, and sodium dodecyl sulfate were mixed at a mass ratio of 96:2:2 to prepare an aqueous solution. The pH of the aqueous solution was adjusted to 7.17 using ammonia. A polysulfone-based membrane with a molecular weight cutoff of 50,000 Da was then immersed in the aqueous solution at pH 7.17 for 15 min to obtain an impregnated porous support membrane. The impregnated porous support membrane was placed in an organic phase solution (composed of phthaloyl chloride and n-hexane at a mass ratio of 1:99) for 100 s, then removed and heat-treated at 90 °C for 10 min to obtain the second-stage membrane treatment unit.

[0094] The third-stage membrane treatment unit was prepared by the following method:

[0095] An aqueous solution was prepared by mixing sodium ethylenediaminetetraacetate buffer (0.5 mol / L), m-phenylenediamine, and sodium dodecyl sulfate in a mass ratio of 96:2:2. The pH of the aqueous solution was adjusted to 11.17 using ammonia and NaOH solution. A polysulfone-based membrane with a molecular weight cutoff of 50,000 Da was then immersed in the aqueous solution at pH 11.17 for 15 min to obtain an impregnated porous support membrane. The impregnated porous support membrane was placed in an organic phase solution (composed of phthaloyl chloride and n-hexane in a mass ratio of 1:99) for 100 s, then removed and heat-treated at 90 °C for 10 min to obtain the third-stage membrane treatment unit.

[0096] Example 2

[0097] Example 2 is basically the same as Example 1, except that the preparation method of the first-stage membrane treatment unit is different.

[0098] The first-stage membrane treatment unit was prepared by the following method:

[0099] Sodium citrate buffer (0.5 mol / L), piperazine, and sodium hexadecylbenzenesulfonate were mixed at a mass ratio of 95:3:2 to prepare an aqueous solution. The pH of the aqueous solution was adjusted to 8.17 using ammonia. A polysulfone membrane with a molecular weight cutoff of 50,000 Da was then immersed in the aqueous solution at pH 8.17 for 15 min to obtain an impregnated porous support membrane. The impregnated porous support membrane was placed in an organic phase solution (composed of phthaloyl chloride and n-hexane at a mass ratio of 2:98) for 100 s, then removed and heat-treated at 90 °C for 10 min to obtain the first-stage membrane treatment unit.

[0100] Example 3

[0101] Example 3 is basically the same as Example 1, except that the pH of the aqueous solution was adjusted to 9.17 during the preparation of the first-stage membrane treatment unit. The membrane sheet prepared for the first-stage membrane treatment unit has a desalination rate of 99.1% and a permeate flux of 28.65 LMH.

[0102] Example 4

[0103] Example 4 is essentially the same as Example 1, except that the pH of the aqueous solution was adjusted to 6.17 during the preparation of the second-stage membrane treatment unit. The membrane sheet prepared for the second-stage membrane treatment unit had a desalination rate of 97.7% and a permeate flux of 35.4 LMH.

[0104] Comparative Example 1

[0105] Comparative Example 1 is basically the same as Example 3, except that the preparation method of the first-stage membrane treatment unit is different and no sodium ethylenediaminetetraacetate buffer solution is added.

[0106] Deionized water, m-phenylenediamine, and sodium dodecyl sulfate were mixed in a mass ratio of 96:2:2 to prepare an aqueous solution. The pH of the aqueous solution was adjusted to 9.17 using ammonia. A polysulfone-based membrane with a molecular weight cutoff of 50,000 Da was then immersed in the aqueous solution at pH 9.17 for 15 min to obtain an impregnated porous support membrane. The impregnated porous support membrane was placed in an organic phase solution (composed of phthaloyl chloride and n-hexane in a mass ratio of 1:99) for 100 s, then removed and heat-treated at 90 °C for 10 min to obtain the first-stage membrane treatment unit.

[0107] During the preparation of the first-stage membrane treatment unit, the pH of the aqueous solution was adjusted to 9.17. The membrane sheet prepared for the first-stage membrane treatment unit had a desalination rate of 97.6% and a permeate flux of 41.85 LMH.

[0108] The membranes prepared in the embodiments and comparative examples of this invention were used as samples. Under test conditions of 25°C and 5.5±0.05MPa, a sodium chloride aqueous solution of 32000ppm±500ppm with a pH of 7.5 was used as the feed liquid. After pre-pressurizing the prepared samples for 60 minutes, the volume of permeate passing through the effective area of ​​the sample within a certain time was collected. The conductivity of the feed water and permeate was tested using a digital conductivity meter, and the desalination rate and permeate flux were calculated. It should be noted that the unit of permeate flux is LMH, specifically L / (m²). 2 ·h).

[0109] It is understood that the structures illustrated in the embodiments of the present invention do not constitute a specific limitation on a high-efficiency seawater desalination system based on multi-stage membrane modules. In other embodiments of the present invention, a high-efficiency seawater desalination system based on multi-stage membrane modules may include more or fewer components than illustrated, or combine some components, or split some components, or have different component arrangements. The illustrated components may be implemented in hardware, software, or a combination of software and hardware.

[0110] The information interaction and execution process between the devices in the above system are based on the same concept as the method embodiment of the present invention, and the specific details can be found in the description in the method embodiment of the present invention, and will not be repeated here.

[0111] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A highly efficient seawater desalination method based on a multi-stage membrane module-based high-efficiency seawater desalination system, characterized in that, The system includes: a pretreatment unit, three-stage membrane treatment units with different desalination rates, and a control unit; the control unit is used to adjust the operating parameters of the membrane treatment units. The membrane treatment unit is prepared by the following method: (1) The porous support membrane is immersed in an aqueous solution containing amine monomers to obtain the immersed porous support membrane; wherein the aqueous solution is prepared using a polycarboxylic acid buffer solution; the polycarboxylic acid buffer solution is ethylenediaminetetraacetic acid sodium salt buffer solution or sodium citrate buffer solution. (2) The impregnated porous support membrane is placed in an organic phase solution containing acyl chloride monomer, and then taken out for heat treatment to obtain the membrane treatment unit; wherein, the pH value of the aqueous phase solution used in different membrane treatment units is different; the pH value of the aqueous phase solution used in the preparation of the first-stage membrane treatment unit is 8~9.5; the pH value of the aqueous phase solution used in the preparation of the second-stage membrane treatment unit is 6~7.5; and the pH value of the aqueous phase solution used in the preparation of the third-stage membrane treatment unit is 10~11.

5. The efficient seawater desalination method includes: The three-level membrane treatment unit is determined from the membrane module configuration rule base, which includes several combinations of membrane treatment units and the applicable first salt content, target water conductivity, and diversion ratio of at least two parallel membrane treatment units for each combination of membrane treatment units. The seawater passing through the pretreatment unit is tested to determine the current seawater's primary salinity, temperature, and turbidity. The inlet and outlet ends of each membrane treatment unit are tested to obtain the second salt content, inlet pressure and turbidity at the corresponding inlet end, and the third salt content and outlet pressure at the corresponding outlet end. The current conductivity is calculated based on the diversion ratio and the third salt content of each membrane treatment unit. It is then determined whether the difference between the current conductivity and the conductivity of the target water quality is greater than a preset difference threshold. When the judgment result is yes, for each stage of the membrane treatment unit, the diversion ratio is dynamically adjusted based on the second salt content, third salt content, inlet pressure and turbidity of that stage of membrane treatment unit, so that the freshwater reaches the conductivity of the target water quality.

2. The method according to claim 1, characterized in that, The pretreatment unit uses an ultrafiltration membrane to remove suspended solids, and the desalination rate of the pretreatment unit is lower than that of any of the membrane treatment units.

3. The method according to claim 1, characterized in that, The amine monomers include one or more of m-phenylenediamine and piperazine.

4. The method according to claim 1, characterized in that, The aqueous solution includes the polycarboxylic acid buffer solution, the amine monomer, and the surfactant. The amine monomer has a mass fraction of 0.05 wt% to 5 wt% in the aqueous solution; The surfactant has a mass fraction of 0.05 wt% to 5 wt% in the aqueous solution.

5. The method according to claim 4, characterized in that, The surfactant is one or more of sodium dodecyl sulfate, sodium hexadecylbenzenesulfonate, Tween, and polyoxyethylene alkylphenol ether.

6. The method according to claim 4, characterized in that, The pH value of the aqueous solution is adjusted using an alkaline reagent, which includes one or more of ammonia water and ammonium chloride solution.

7. The method according to claim 1, characterized in that, The acyl chloride monomer includes one of phthaloyl chloride or trimesoyl chloride.

8. The method according to claim 1, characterized in that, The mass fraction of the acyl chloride monomer in the organic phase solution is 0.1 wt% to 2 wt%.

9. The method according to claim 1, characterized in that, The solvent used in the organic phase solution is a n-alkanes or isoalkanes.

10. The method according to claim 1, characterized in that, The porous support membrane is an ultrafiltration membrane with a molecular weight cutoff of 20,000 to 100,000 Da.

11. The method according to claim 10, characterized in that, The ultrafiltration membrane is prepared from one or more of polysulfone, polyethersulfone, polyimide, polypropylene, polyacrylonitrile, and polyetheretherketone.

12. The method according to any one of claims 1 to 11, characterized in that, In step (1), the soaking time is 1 to 30 minutes.

13. The method according to any one of claims 1 to 11, characterized in that, In step (2), the time for the impregnated porous support membrane to be immersed in the organic phase solution containing acyl chloride monomer is 20~300s; The heat treatment temperature is 40~110℃ and the time is 3~40min.

14. The method according to claim 1, characterized in that, Also includes: For each stage of the membrane treatment unit, the pressure difference growth rate is predicted based on the pressure difference between the inlet pressure and the outlet pressure of that stage of the membrane treatment unit. Based on the pressure difference growth rate, the membrane fouling level is predicted; When the membrane fouling level is defined as "membrane fouling exists", the operating parameters of the membrane treatment unit at that level are dynamically adjusted.

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