Microfiltration membrane module for separating haematococcus pluvialis broken wall liquid and application thereof

Abstract

The application belongs to the technical field of haematococcus pluvialis membrane separation, and particularly relates to a microfiltration membrane module for separating haematococcus pluvialis broken wall liquid and application thereof. The hollow fiber membrane bundle is composed of polyvinylidene fluoride hollow fiber membranes with surface grafted amphiphilic ion copolymer, the amphiphilic ion copolymer is carboxylated sulfobetaine type amphiphilic ion copolymer, the repeating unit of the copolymer contains quaternary ammonium salt positive charge group, sulfonate negative charge group and side chain carboxyl group at the same time, and the amphiphilic ion copolymer is grafted on the polyvinylidene fluoride base membrane surface through covalent bond. The microfiltration membrane module is used for separating haematococcus pluvialis broken wall liquid. The application realizes high-efficiency and stable operation without frequent chemical cleaning in the separation of haematococcus pluvialis broken wall liquid by synthesizing carboxylated sulfobetaine type amphiphilic ion copolymer and anchoring on the membrane surface through covalent bond, constructing stable anti-pollution interface with hydration layer and electrostatic double repulsion, and regulating membrane pore size with single external coagulation bath temperature.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a microfiltration membrane module for separating Haematococcus pluvialis cell wall-breaking liquid and its application. Background Technology

[0002] Haematococcus pluvialis can accumulate large amounts of astaxanthin under stress conditions, with astaxanthin content reaching approximately 4% of its dry weight. Due to its extremely strong antioxidant activity, astaxanthin is widely used in food, health products, medicine, and aquaculture, making Haematococcus pluvialis a major source of natural astaxanthin. However, astaxanthin extraction faces a significant technical bottleneck. Under stress conditions, Haematococcus pluvialis forms thick-walled spores with a three-layered structure, with a cell wall thickness of approximately 2 μm. This acetylation-resistant cell wall constitutes the strongest barrier to astaxanthin extraction. Therefore, industrially, the algae must first undergo cell wall disruption treatment, typically using methods such as high-pressure homogenization, bead milling, or low-temperature grinding to rupture the cell walls and release the cell contents. The resulting liquid contains incompletely disrupted intact cells, numerous cell wall fragments, extracellular polymers released from the cells (mainly proteins and polysaccharides), and astaxanthin-lipid complexes, resulting in a complex composition and a wide particle size distribution.

[0003] In the industrial extraction process of astaxanthin, the liquid after cell wall disruption first needs to undergo solid-liquid separation to remove incompletely disrupted cells, cell wall fragments, extracellular polymers, and other solid impurities, allowing the liquid phase containing astaxanthin-lipid complexes to pass through for subsequent extraction and purification. Membrane separation technology has become an important choice for this stage due to its advantages such as low energy consumption, continuous operation, and ease of scaling. Currently, the industry typically uses microfiltration membranes with pore sizes of 0.2 μm to 1.0 μm for clarification and filtration of the disrupted liquid.

[0004] However, in actual operation, conventional polyvinylidene fluoride hollow fiber microfiltration membranes face serious membrane fouling problems when treating Haematococcus pluvialis cell wall disruption solutions. Extracellular polymers present in the disruption solution rapidly form a highly adhesive gel-like fouling layer on the membrane surface, clogging the membrane pores and causing the membrane flux to decline to less than 30% of the initial flux within a few hours. A foreign algae biorefining company attempted to use polyvinylidene fluoride hollow fiber microfiltration membranes for clarifying the disruption solution in large-scale production; after approximately 4 hours of operation, the membrane flux decreased by more than 65%, and even with backwashing, the flux recovery rate was less than 40%.

[0005] To address membrane fouling, the industry commonly employs regular chemical cleaning, with commonly used cleaning agents including sodium hydroxide solution, sodium hypochlorite solution, and surfactant-based cleaning agents. However, research indicates that simple mechanical backwashing can only temporarily restore flux, while chemical cleaning has significant side effects in microalgae-fouled systems: acid and alkali cleaning can denature residual proteins in the cell disruption solution, leading to more difficult-to-remove deposits on the membrane surface, thus exacerbating membrane pore blockage; while oxidizing cleaning agents such as sodium hypochlorite have some cleaning effect, they accelerate the defluorination degradation of polyvinylidene fluoride membrane materials, shortening the lifespan of membrane modules; furthermore, chemical cleaning agents pose a risk of chemical reagent residue in the production of high-value-added food-grade products such as astaxanthin, increasing the burden on subsequent purification stages.

[0006] To slow down membrane fouling without relying on frequent chemical cleaning, researchers have attempted to hydrophilicate polyvinylidene fluoride (PVDF) membranes. Currently reported modification methods mainly include physical coating and blending. Physical coating involves depositing hydrophilic polymers onto the membrane surface via dip coating or spraying. For example, one study sprayed a copolymer of butyl methacrylate and polyethylene glycol methyl ether methacrylate onto the PVDF membrane surface, utilizing the copolymer's hydration layer to reduce pollutant adsorption. Studies have shown that this coating can reduce bovine serum albumin adsorption to about one-third of the original membrane, and increase flux recovery from approximately 13% to approximately 38%. Blending involves blending amphiphilic copolymers with PVDF and then fabricating the membrane via phase inversion. The surface enrichment behavior of the amphiphilic copolymer during film formation imparts hydrophilicity to the membrane.

[0007] However, both physical coating and blending methods have inherent technical drawbacks. Physical coating relies on the physical adsorption between the coating and the membrane surface; under the shear force generated by cross-flow filtration and the impact of backwashing, the coating is prone to detachment. The copolymer dissolution rate of the aforementioned spray-modified membrane was approximately 1.22% after immersion in water for 4 weeks, and its antifouling performance gradually degraded with coating loss during long-term operation. While the blending method embeds the modifier into the membrane body, most of the modifier is embedded inside the membrane and not effectively exposed on the surface, resulting in low utilization. Furthermore, the modifier has limited compatibility with polyvinylidene fluoride (PVDF), easily leading to phase separation during film formation and resulting in an uneven membrane pore structure.

[0008] Furthermore, the hydrophilic modifiers used in the aforementioned modification methods are mostly commercially available polymers with fixed molecular structures, making it impossible to perform targeted functional design based on the compositional characteristics of the extracellular polymers of *Rhodotorula purpureus*. The extracellular polymers of *Rhodotorula purpureus* are rich in protein components and possess strong hydrophobic regions, resulting in strong hydrophobic interactions with the hydrophobic membrane surface, which is one of the important driving forces of membrane fouling. Although commercial hydrophilic agents can improve the hydrophilicity of the membrane, they lack a specific repulsion effect with the extracellular polymers, thus exhibiting a ceiling effect in antifouling efficacy.

[0009] The synthesis of structurally controllable polymers through reversible addition-fragmentation chain transfer polymerization (RAFT) and their application in membrane surface modification have been reported in the literature. One study used RAFT polymerization to synthesize amphiphilic comb-type block copolymers and applied them to the blending modification of polyethersulfone membranes. Another study used the ATRP method to graft zwitterionic monomers onto the outer surface of polyvinylidene fluoride hollow fiber membranes, obtaining antifouling membranes with electrolyte responsiveness. However, the monomers used in these methods are mostly commercially available products, and the types and densities of functional groups in their molecular structures are limited, making it difficult to introduce additional functional groups to enhance the repulsion between specific pollutants. For systems like the complex composition and diverse pollutants found in *Hydrocotyle vulgaris* cell wall disruption solution, existing membrane surface modification technologies still have shortcomings in terms of the precision of functional layer structure design and compatibility with the target system.

[0010] Therefore, there is a need to design a microfiltration membrane module for separating Haematococcus pluvialis cell wall disruption liquid and its application. Summary of the Invention

[0011] To overcome the shortcomings of the prior art, a microfiltration membrane module for separating Haematococcus pluvialis cell wall-breaking liquid and its application are provided.

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] A microfiltration membrane module for separating cell wall-breaking liquid from Haematococcus pluvialis includes a shell, hollow fiber membrane bundles arranged axially along the shell, feed inlets and retentate outlets at both ends of the shell, and a permeate outlet on the sidewall of the shell. The hollow fiber membrane bundles are composed of polyvinylidene fluoride hollow fiber membranes with zwitterionic copolymers grafted onto their surfaces. The zwitterionic copolymers are carboxylated sulfonate betaine-type zwitterionic copolymers with a number average molecular weight of 8000 to 25000 g / mol. The repeating units of this copolymer simultaneously contain quaternary ammonium salt positively charged groups, sulfonate negatively charged groups, and side-chain carboxyl groups. The zwitterionic copolymers are covalently grafted onto the surface of the polyvinylidene fluoride membrane at a grafting amount of 80 to 350 μg / cm². The polyvinylidene fluoride membrane is the ungrafted polyvinylidene fluoride hollow fiber membrane prepared in step three.

[0014] In the astaxanthin extraction process from Haematococcus pluvialis, the large number of cell wall fragments and extracellular polymers composed of proteins and polysaccharides present in the cell wall disruption solution readily adsorb onto the surface of hydrophobic polyvinylidene fluoride (PVDF) membranes, forming a dense gel-like fouling layer that clogs the membrane pores and causes a significant drop in filtration flux within hours. The conventional approach is periodic chemical cleaning, but the use of cleaning agents can lead to protein denaturation and deposition, membrane material defluorination and degradation, and the risk of chemical residues in the astaxanthin product. Therefore, imparting stable antifouling functionality to the membrane without relying on frequent chemical cleaning is the core requirement of this process. Existing technologies for hydrophilic modification of PVDF membranes mostly employ physical coating or blending methods. Physical coating relies on weak interaction adsorption, and the coating is easily detached under shear forces and backwashing. Blending embeds the modifier within the membrane body, resulting in low effective surface exposure, and compatibility issues can easily lead to uneven membrane pore structure. The modifiers used are mostly commercially available polymers with fixed structures, which cannot be targeted to the hydrophobic characteristics of the extracellular polymers of Haematococcus pluvialis rich in protein components. They also lack a specific repulsion effect with the extracellular polymers, thus limiting their anti-pollution effect.

[0015] The method for preparing the polyvinylidene fluoride hollow fiber membrane with surface grafted with zwitterionic copolymers includes the following steps:

[0016] Step 1: N,N-dimethylaminopropylamine is reacted with acryloyl chloride at 0°C to 5°C under nitrogen protection for 6 to 12 hours to obtain N-(3-dimethylaminopropyl)acrylamide. Then, it is reacted with 1,3-propanesulfonic acid lactone at 40°C to 60°C for 12 to 24 hours to generate a sulfonate betaine-type zwitterionic intermediate. The sulfonate betaine-type zwitterionic intermediate is then reacted with succinic anhydride at room temperature for 12 to 24 hours to obtain a carboxylated sulfonate betaine-type zwitterionic monomer.

[0017] Step 2: Dissolve the carboxylated sulfonated betaine zwitterionic monomer obtained in Step 1 in a mixed solvent of methanol and water, add RAFT chain transfer agent and initiator, and react at 65°C to 75°C under nitrogen protection for 12 to 24 hours to obtain a carboxyl-terminated polysulfonated betaine zwitterionic polymer. Then, reduce the polymer in the presence of a reducing agent for 12 to 24 hours to obtain a carboxylated sulfonated betaine zwitterionic copolymer with thiol-terminated groups.

[0018] To address the aforementioned issues, this technical solution provides a polyvinylidene fluoride hollow fiber membrane with a surface grafted with a carboxylated sulfonate betaine-type zwitterionic copolymer. This copolymer is obtained through in-house chemical synthesis in steps one and two.

[0019] In step one, N,N-dimethylaminopropylamine reacts with acryloyl chloride via an amidation reaction to generate N-(3-dimethylaminopropyl)acrylamide, whose molecular structure retains both polymerizable acrylamide double bonds and a tertiary amine group that can be further quaternized. Subsequently, it undergoes a ring-opening quaternization reaction with 1,3-propanesulfonate lactone. The tertiary amine attacks the methylene carbon of the sulfonate lactone, causing the lactone to open its ring and introducing a propanesulfonic acid group onto the nitrogen atom, thus generating a zwitterionic intermediate containing both a positively charged quaternary ammonium salt center and a negatively charged sulfonate center. The amide nitrogen atom on this intermediate retains some nucleophilicity and can continue to react with succinic anhydride. After ring opening, the anhydride forms an amide bond with the amide nitrogen or reacts with trace amounts of active hydrogen in the system, thereby introducing a carboxyl functional group at the molecule's end, yielding a carboxylated zwitterionic monomer of the sulfonate type.

[0020] In step two, reversible addition-fracture chain transfer polymerization is used to controllably polymerize the above monomers. The core of this polymerization method lies in establishing a reversible addition-fracture equilibrium between the chain transfer agent 4-cyano-4-(thiobenzoyl)valerate and the growing chain free radicals, maintaining the concentration of active free radicals in the polymerization system at a low level, suppressing the bimolecular termination side reaction, and thus achieving precise control over the polymer molecular weight and chain length. After polymerization, a carboxyl-terminated polysulfonate betaine-type zwitterionic polymer is obtained, with the terminal group being a dithioester group derived from the chain transfer agent. This polymer is then placed in a phosphate buffer solution containing tris(2-carboxyethyl)phosphonic acid hydrochloride for reduction. Tris(2-carboxyethyl)phosphonic acid hydrochloride, as a mild water-soluble phosphonic reducing agent, can selectively break the carbon-sulfur bonds in the dithioester without affecting the polymer backbone structure, reducing the terminal dithioester group to a highly reactive thiol group, resulting in a carboxylated sulfonate betaine-type zwitterionic copolymer with a thiol terminal group. The introduction of RAFT polymerization technology allows the molecular chain length and grafting density of copolymers to be controlled through molecular design, avoiding the problems of wide chain length distribution and uneven grafting in traditional free radical grafting polymerization, and providing a structural basis for the subsequent construction of a uniform and dense functional layer on the membrane surface.

[0021] The repeating units of this copolymer simultaneously contain quaternary ammonium salt positively charged groups, sulfonate negatively charged groups, and side-chain carboxyl groups. When this copolymer is grafted onto the membrane surface and immersed in the aqueous environment of Haematococcus pluvialis cell wall disruption solution, the quaternary ammonium salt positively charged groups and sulfonate negatively charged groups firmly bind surrounding water molecules around the polymer chain through ion-dipole interactions, forming a highly structured hydration layer. The formation mechanism of this hydration layer lies in the separation of positive and negative charge centers in the zwitterionic groups at the molecular scale without intermolecular charge compensation, allowing each charge site to independently solubilize water molecules, resulting in a solubilization free energy much higher than that of ordinary polar groups. This hydration layer constructs a physical barrier on the membrane surface. When the protein components contained in the extracellular polymer in the cell wall disruption solution approach the membrane surface, their hydrophobic regions must first displace the bound water in the hydration layer in order to contact the membrane surface. This process is extremely unfavorable in terms of energy, thus generating a strong repulsive energy barrier, effectively weakening the hydrophobic interaction between the extracellular polymer and the membrane surface, and delaying the formation rate of the gel-like fouling layer.

[0022] Meanwhile, the carboxyl groups on the copolymer side chains partially ionize under the pH conditions of the cell wall disruption solution. The carboxylate ions are negatively charged, generating electrostatic repulsion between them and the similarly negatively charged cell wall fragments and extracellular polymers. According to the electric double layer theory, when two surfaces with the same charge approach each other, the system's free energy monotonically increases with decreasing distance, generating a repulsive force. This electrostatic repulsion further reduces the probability of pollutants approaching and depositing on the membrane surface, and it continues to exert a repulsive effect even when pollutants are already close to the membrane surface. The synergistic effect of hydration layer repulsion and electrostatic repulsion gives the membrane a multi-layered antifouling capability against complex pollutants, mainly proteins and polysaccharides, in the *Rhodotorula glutinis* cell wall disruption solution, rather than relying solely on improved hydrophilicity.

[0023] Step 3: A hollow fiber membrane of polyvinylidene fluoride (PVDF) without surface grafting treatment is prepared using a dry-wet spinning process. The mass fraction of PVDF in the spinning solution is 18%, the amount of polyvinylpyrrolidone K30 added is 8% of the mass of PVDF, the core solution is a mixture of deionized water and N,N-dimethylacetamide in a volume ratio of 3:7, the external coagulation bath is deionized water, and the temperature of the external coagulation bath is 25℃ to 40℃. The average pore size of the obtained PVDF membrane is 0.2μm to 0.6μm.

[0024] Step 4: The polyvinylidene fluoride membrane obtained in Step 3 is subjected to alkali treatment to obtain a hydroxylated base membrane. The hydroxylated base membrane is then immersed in an anhydrous toluene solution of 3-methacryloyloxypropyltrimethoxysilane and reacted at 80°C to 95°C under nitrogen protection for 12 to 24 hours to obtain a surface-alkenylated base membrane.

[0025] Step 5: Immerse the alkenylated base film obtained in Step 4 into a photoinitiated reaction solution containing the carboxylated sulfonate betaine-type zwitterionic copolymer with thiol-terminated end groups obtained in Step 2, and perform ultraviolet light irradiation reaction to obtain a polyvinylidene fluoride hollow fiber membrane with zwitterionic copolymer grafted on the surface.

[0026] After resolving the issue of functional layer chemical structure design, the anchoring method of the functional layer on the membrane surface is equally crucial. The fundamental reason for the failure of physical coating modification during long-term operation lies in the lack of a strong chemical bond between the coating and the membrane surface. This technical solution constructs a covalent grafting system through steps four and five.

[0027] In step four, the polyvinylidene fluoride (PVDF) membrane is first treated with an alkali. Under the action of potassium hydroxide in an ethanol aqueous solution, the PVDF units on the PVDF molecular chain undergo a defluorination reaction, eliminating one molecule of hydrogen fluoride and generating a carbon-carbon double bond on the main chain. Simultaneously, some of the double bonds are converted into hydroxyl groups under subsequent water washing or oxidation conditions. The membrane is then immersed in a hydrogen peroxide-sulfuric acid mixed solution. Under acidic conditions, hydrogen peroxide decomposes to generate hydroxyl radicals, which attack the carbon-carbon double bonds, undergoing a free radical addition reaction and oxidizing the double bonds to hydroxyl groups, resulting in a hydroxylated membrane rich in hydroxyl groups. Subsequently, the hydroxylated membrane is immersed in an anhydrous toluene solution of 3-methacryloyloxypropyltrimethoxysilane. The methoxy group on the silane coupling agent undergoes a hydrolysis-condensation reaction catalyzed by the hydroxyl groups on the membrane surface. The silanol groups and the hydroxyl groups on the membrane surface undergo dehydration-condensation to form siloxane covalent bonds, introducing methacryloyloxypropyl groups into the membrane surface, thereby anchoring alkenyl functional groups containing carbon-carbon double bonds on the membrane surface.

[0028] In step five, the alkenyl-containing base film is immersed in a photoinitiation reaction solution containing a carboxylated sulfonate betaine-type zwitterionic copolymer with thiol-terminated groups. Under ultraviolet light irradiation, the photoinitiator 2,2-dimethoxy-2-phenylacetophenone absorbs photon energy and undergoes homolytic cleavage, generating benzoyl radicals and dimethoxyphenyl radicals. The benzoyl radical abstracts a hydrogen atom from the thiol group at the end of the copolymer, generating a thiol radical. The thiol radical undergoes a radical addition reaction with the alkenyl double bond on the film surface, forming a thioether bond linked by a carbon-sulfur bond, and simultaneously generating a new carbon-centered radical. This radical continues to abstract a hydrogen atom from another thiol group to complete the chain transfer, realizing the chain addition process of thiol-alkene click chemistry. This reaction is characterized by mild reaction conditions, insensitivity to oxygen, high conversion rate, and no by-product formation, and can be completed rapidly at room temperature or under mild ultraviolet light irradiation.

[0029] Ultimately, the carboxylated sulfonate betaine-type zwitterionic copolymer is firmly grafted onto the surface of the polyvinylidene fluoride (PVDF) membrane via thioether bonds in a covalent manner. This covalent bonding method prevents the zwitterionic copolymer functional layer from detaching or dissolving under the shear forces generated by cross-flow filtration and the impact of periodic backwashing, ensuring the integrity and stability of the functional layer during long-term operation. Compared with physically coated modified membranes, which suffer from the gradual loss of hydrophilic coating during immersion or use, the membrane module provided by this technical solution can maintain a stable antifouling effect under continuous operation, with a narrower membrane flux decline and a correspondingly lower frequency of chemical cleaning. This reduces the defluorination and degradation damage to the PVDF membrane material caused by chemical cleaning agents and also helps to avoid the impact of chemical reagent residues on astaxanthin products.

[0030] In step two, the concentration of the carboxylated sulfonated betaine-type zwitterionic monomer is 0.3 mol / L to 0.8 mol / L; the RAFT chain transfer agent is 4-cyano-4-(thiobenzoyl)valerate, and the initiator is azobisisobutyronitrile; the mixed solvent is a mixture of methanol and water, and the volume ratio of methanol to water is 2:1 to 4:1; the reducing agent is tris(2-carboxyethyl)phosphonic acid hydrochloride, and the reduction reaction is carried out in a phosphate buffer solution with a pH of 7.0 to 7.4.

[0031] The molar ratio of 4-cyano-4-(thiobenzoyl)valerate to carboxylated sulfonate betaine-type zwitterionic monomer is 0.005:1 to 0.015:1, and the molar ratio of azobisisobutyronitrile to 4-cyano-4-(thiobenzoyl)valerate is 0.1:1 to 0.3:1.

[0032] In step three, the spinning solution also includes 5% to 12% by mass of polyvinylidene fluoride nano-alumina, wherein the average particle size of the nano-alumina is 50 nm to 100 nm.

[0033] While optimizing the chemical structure and anchoring method of the membrane functional layer, the pore structure parameters of the base membrane itself also have a decisive impact on the separation effect and antifouling performance. In the solid-liquid separation of Haematococcus pluvialis cell wall disruption solution, if the membrane pore size is too large, cell debris and extracellular polymers can easily penetrate the membrane pores and enter the permeate, affecting the purity of the astaxanthin enrichment solution; if the membrane pore size is too small, the permeation resistance of the astaxanthin-lipid complex increases, the flux decreases, and the retention selectivity deteriorates.

[0034] Existing membrane fabrication processes involve numerous variables affecting pore size, including polymer concentration, pore-forming agent content, coagulation bath temperature, core liquid composition, and air bath time. These variables interact, making precise pore size control difficult and resulting in poor process reproducibility. This technical solution addresses this by setting optimal fixed values ​​for the mass fraction of polyvinylidene fluoride (PVDF), the amount of polyvinylpyrrolidone (PVP) K30 added, and the core liquid composition in the spinning solution during the dry-wet spinning process in step three. The average pore size of the base membrane is controlled solely by adjusting the external coagulation bath temperature within a specified range. During the phase transition in dry-wet spinning, the spinning solution, after being extruded from the spinneret, first passes through an air gap before entering the external coagulation bath. Non-solvent water diffuses into the membrane from the coagulation bath, while the solvent N,N-dimethylacetamide diffuses into the coagulation bath, resulting in a double diffusion exchange. When the polymer concentration in the spinning solution reaches a certain value, the system enters a thermodynamically unstable state, leading to liquid-liquid phase separation and the formation of a polymer-depleted phase and a polymer-rich phase. The polymer-depleted phase becomes the membrane pores in subsequent development, while the polymer-rich phase solidifies into the membrane skeleton.

[0035] The external coagulation bath temperature directly affects the dual diffusion rate and phase separation kinetics: as the temperature increases, the diffusion coefficients of both solvent and non-solvent increase, the exchange rate accelerates, phase separation occurs earlier, the nucleation density of the polymer-depleted phase increases, but the growth time shortens; simultaneously, the increased temperature enhances the mobility of polymer chain segments, making the aggregation between depleted phase nuclei more likely. The combined effect of these two factors determines the final membrane pore size and porosity. This technical solution, by fixing other membrane formation parameters and using only the external coagulation bath temperature as a single control variable, establishes a monotonic relationship between membrane pore size and external coagulation bath temperature, reducing pore size fluctuations caused by multivariate interactions, improving the uniformity of membrane pore structure and process reproducibility between batches, and ensuring that the average pore size of the base membrane stably falls within the target range that matches the particle size distribution of the cell disruption liquid.

[0036] Astaxanthin-lipid complexes, with their smaller particle size, can pass through membrane pores and accumulate on the permeate side. In contrast, intact cells, cell wall fragments, and extracellular polymers, with larger particle sizes than the membrane pores, are effectively retained on the membrane surface. This pore size matching ensures both the permeability of the astaxanthin-lipid complex and the effective retention of solid impurities, balancing separation efficiency and product purity. Furthermore, because the contaminants are primarily retained on the membrane surface rather than embedded in the pores, the removal effect of gas backwashing is better, further slowing the rate of irreversible contamination accumulation. In addition, the optional nano-alumina added in step three, as a hydrophilic inorganic filler, can reduce the interfacial tension between the casting solution and the coagulation bath during phase inversion, promoting mass transfer of non-solvents into the membrane and contributing to the formation of a more uniform sponge-like pore structure. It also enhances the hydrophilicity and mechanical strength of the membrane surface.

[0037] In step four, the polyvinylidene fluoride (PVDF) membrane undergoes alkali treatment as follows: the PVDF membrane obtained in step three is first soaked in deionized water for 24 to 48 hours, dried, and then immersed in an aqueous ethanol solution with a potassium hydroxide concentration of 1.0 mol / L to 2.5 mol / L. The membrane is then reacted at 40°C to 60°C for 2 to 6 hours. After washing, the membrane is then immersed in a solution with a hydrogen peroxide volume fraction of 1% to 3% and a sulfuric acid concentration of 0.5 mol / L to 1.0 mol / L. The membrane is then reacted at room temperature for 1 to 3 hours.

[0038] In step four, the volume fraction of 3-methacryloyloxypropyltrimethoxysilane in anhydrous toluene solution is 2% to 5%.

[0039] In step five, in the photoinitiation reaction solution, the mass-volume concentration of the carboxylated sulfonate betaine-type zwitterionic copolymer with thiol-terminated groups is 2% to 8%, and the mass fraction of the photoinitiator in the photoinitiation reaction solution is 1% to 3%. The specific parameters of the ultraviolet light irradiation reaction are: reaction for 20 to 40 minutes under ultraviolet light irradiation with a wavelength of 365 nm and a light intensity of 10 mW / cm² to 30 mW / cm².

[0040] The photoinitiator is 2,2-dimethoxy-2-phenylacetophenone, and the solvent in the photoinitiation reaction solution is a mixture of N,N-dimethylformamide and water, wherein the volume ratio of N,N-dimethylformamide to water is 4:1.

[0041] Application of a microfiltration membrane module for the separation of Haematococcus pluvialis cell wall disruption liquid, wherein the microfiltration membrane module is used for solid-liquid separation of Haematococcus pluvialis cell wall disruption liquid.

[0042] This invention utilizes a self-synthesized carboxylated sulfonated betaine-type zwitterionic copolymer, which is covalently anchored to the membrane surface via mercapto-olefin click chemistry, constructing a stable, antifouling interface that combines hydration layer repulsion and electrostatic repulsion. A polyvinylidene fluoride membrane with a pore size matching the particle size distribution of *Alternaria rubra* cell wall disruption solution was stably prepared using a spinning process with the external coagulation bath temperature as the sole control variable. This allows the microfiltration membrane module to maintain a relatively long continuous operating cycle without frequent chemical cleaning, demonstrating good adaptability to the complex and highly polluting material system of *Alternaria rubra* cell wall disruption solution.

[0043] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0044] 1. Compared with existing techniques for hydrophilic modification of polyvinylidene fluoride (PVDF) microfiltration membranes using physical coating or blending, this invention utilizes a surface-initiated thiol-olefin click chemistry reaction to covalently graft a carboxylated sulfonate-betaine zwitterionic copolymer onto the PVDF membrane surface. The repeating units of the carboxylated sulfonate-betaine zwitterionic copolymer simultaneously contain quaternary ammonium salt positively charged groups, sulfonate negatively charged groups, and side-chain carboxyl groups. In the aqueous environment of the Haematococcus pluvialis cell-wall breaking solution, the quaternary ammonium salt positively charged groups and sulfonate negatively charged groups, through ionic solvation, firmly bind a large number of water molecules around the polymer chains, forming a highly stable hydrated layer on the PVDF hollow fiber membrane surface. This hydrated layer creates a strong repulsive energy barrier against the hydrophobic regions of the extracellular polymeric protein components in the cell-wall breaking solution, effectively weakening the hydrophobic interaction between the extracellular polymeric protein and the membrane surface, thereby delaying the formation of a gel-like fouling layer on the membrane surface. Meanwhile, the side-chain carboxyl groups partially ionize and become negatively charged under the pH conditions of the cell wall disruption solution. This generates electrostatic repulsion between the carboxyl groups and cell wall fragments and extracellular polymers, which also exhibit negative charges, further reducing the rate at which pollutants approach and deposit on the membrane surface. The synergistic effect of hydration layer repulsion and electrostatic repulsion enhances the membrane surface's resistance to complex pollutants in the Haematococcus pluvialis cell wall disruption solution, rather than relying solely on increased hydrophilicity.

[0045] 2. In this invention, the connection between the carboxylated sulfonate betaine-type zwitterionic copolymer and the polyvinylidene fluoride (PVDF) membrane is a covalent grafting method. After alkali treatment and silanization, alkenyl groups are introduced onto the surface of the PVDF membrane. The carboxylated sulfonate betaine-type zwitterionic copolymer, synthesized through reversible addition-fragmentation chain transfer polymerization and then terminally reduced, has thiol terminals. Under ultraviolet light irradiation and in the presence of a photoinitiator, the thiol groups and alkenyl groups undergo an addition reaction to form stable thioether bonds. This covalent connection method makes the zwitterionic copolymer functional layer less prone to detachment or dissolution under the shear forces generated by cross-flow filtration and the impact of periodic backwashing, ensuring the integrity and stability of the functional layer during long-term operation. The membrane module of this invention maintains a relatively stable antifouling effect under continuous operation, with a slower membrane flux decay rate, allowing for a corresponding reduction in the frequency of chemical cleaning. This reduces the defluorination and degradation damage to the PVDF membrane material caused by chemical cleaning agents and also helps to avoid the impact of chemical reagent residues on astaxanthin products.

[0046] 3. In the preparation of polyvinylidene fluoride (PVDF) membranes, this technical solution sets the mass fraction of PVDF in the spinning solution, the amount of polyvinylpyrrolidone (PVP) K30 added, and the core solution composition to optimal fixed values. The average pore size of the base membrane is controlled solely by adjusting the external coagulation bath temperature within the range of 25℃ to 40℃, ensuring the average pore size stably falls within the target range of 0.2μm to 0.6μm. The external coagulation bath temperature affects the exchange rate between the solvent N,N-dimethylacetamide and the non-solvent water during spinning, thus influencing the nucleation and growth behavior of the depleted phase during phase separation, ultimately determining the membrane pore size. This reduces pore size fluctuations caused by multivariate interactions, improving the uniformity of membrane pore structure and process reproducibility between batches. The obtained pore size range matches the particle size distribution of the components to be separated in the Haematococcus pluvialis cell disruption solution. The astaxanthin-lipid complex has a particle size in the range of 50 nm to 150 nm, allowing it to pass through the membrane pores and enter the permeate side for enrichment. Meanwhile, the bulk particles of incompletely disrupted intact cells, cell wall fragments, and extracellular polymers are larger than 0.6 μm and are effectively retained on the membrane surface. This ensures the permeability of the astaxanthin-lipid complex while effectively retaining solid impurities, balancing separation efficiency and product purity. Attached Figure Description

[0047] Figure 1 The graph shows the test results of membrane flux change. Detailed Implementation

[0048] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] In the specific embodiments of this application, the chemical reagents and raw materials used in the examples and comparative examples are all conventional commercially available products unless otherwise specified. The sources of various main raw materials are briefly described below:

[0050] N,N-Dimethylaminopropylamine: purchased from Shanghai Fangye Chemical Co., Ltd., CAS No. 109-55-7, purity not less than 99%.

[0051] Acryloyl chloride: purchased from Zibo Yixin Chemical Co., Ltd., CAS No. 814-68-6, purity not less than 98.5%.

[0052] 1,3-Propanesulfonate lactone: purchased from Hubei Xinrunde Chemical Co., Ltd., CAS No. 1120-71-4, purity not less than 99%.

[0053] Succinic anhydride: purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., CAS No. 108-30-5, purity not less than 95%.

[0054] 4-Cyano-4-(Thiobenzoyl)valerate: purchased from Chengdu Aofei Biochemicals Co., Ltd., CAS No. 201611-92-9, purity not less than 97%.

[0055] Azobisisobutyronitrile: purchased from Changzhou Tongxiang Chemical Co., Ltd., CAS No. 78-67-1, purity not less than 99%.

[0056] Tris(2-carboxyethyl)phosphonic hydrochloride: purchased from Shanghai Xianding Biotechnology Co., Ltd., CAS No. 51805-45-9, purity not less than 98%.

[0057] Polyvinylidene fluoride: purchased from Zhejiang Funolin Chemical New Materials Co., Ltd., CAS No. 24937-79-9, with a number average molecular weight of 250,000 to 400,000 g / mol.

[0058] Polyvinylpyrrolidone K30: purchased from Jinjinle Chemical Co., Ltd., CAS No. 9003-39-8, K value 29 to 32.

[0059] Nano-alumina: Purchased from Anhui Zhonghang Nanotechnology Development Co., Ltd., CAS No. 1344-28-1, with an average particle size of 50nm and a purity of not less than 99.9%.

[0060] 3-Methacryloxypropyltrimethoxysilane: purchased from Suzhou Sisso New Materials Co., Ltd., CAS No. 2530-85-0, purity not less than 99%.

[0061] 2,2-Dimethoxy-2-phenylacetophenone: Purchased from Hubei Diehua New Material Technology Co., Ltd., CAS No. 24650-42-8, purity not less than 99%.

[0062] The technical solution of this application is as follows:

[0063] A microfiltration membrane module for separating cell wall-breaking liquid from Haematococcus pluvialis is disclosed. The microfiltration membrane module includes a shell, hollow fiber membrane bundles arranged axially along the shell, feed inlets and retentate outlets at both ends of the shell, and a permeate outlet on the sidewall of the shell. In this invention, other structures, compositions, connections, working processes, and principles of the microfiltration membrane module are well-known technologies and will not be elaborated further here. The hollow fiber membrane bundles are composed of polyvinylidene fluoride hollow fiber membranes with a zwitterionic copolymer grafted onto their surfaces. The zwitterionic copolymer is a carboxylated sulfonate-betaine type zwitterionic copolymer with a number-average molecular weight of 8000 to 25000 g / mol. The repeating units of this copolymer simultaneously contain quaternary ammonium salt positively charged groups, sulfonate negatively charged groups, and side-chain carboxyl groups. The zwitterionic copolymer is covalently grafted onto the surface of the polyvinylidene fluoride membrane at a grafting amount of 80 to 350 μg / cm².

[0064] The method for preparing the polyvinylidene fluoride hollow fiber membrane with surface grafted with zwitterionic copolymers includes the following steps:

[0065] Step 1: N,N-dimethylaminopropylamine is reacted with acryloyl chloride at 0°C to 5°C under nitrogen protection for 6 to 12 hours to obtain N-(3-dimethylaminopropyl)acrylamide. Then, it is reacted with 1,3-propanesulfonic acid lactone at 40°C to 60°C for 12 to 24 hours to generate a sulfonate betaine-type zwitterionic intermediate. The sulfonate betaine-type zwitterionic intermediate is then reacted with succinic anhydride at room temperature for 12 to 24 hours to obtain a carboxylated sulfonate betaine-type zwitterionic monomer.

[0066] Step 2: Dissolve the carboxylated sulfonated betaine zwitterionic monomer obtained in Step 1 in a mixed solvent of methanol and water, add RAFT chain transfer agent and initiator, and react at 65°C to 75°C under nitrogen protection for 12 to 24 hours to obtain a carboxyl-terminated polysulfonated betaine zwitterionic polymer. Then, reduce the polymer in the presence of a reducing agent for 12 to 24 hours to obtain a carboxylated sulfonated betaine zwitterionic copolymer with thiol-terminated groups.

[0067] Step 3: A hollow fiber membrane of polyvinylidene fluoride (PVDF) without surface grafting treatment is prepared using a dry-wet spinning process. The mass fraction of PVDF in the spinning solution is 18%, the amount of polyvinylpyrrolidone K30 added is 8% of the mass of PVDF, the core solution is a mixture of deionized water and N,N-dimethylacetamide in a volume ratio of 3:7, the external coagulation bath is deionized water, and the temperature of the external coagulation bath is between 25°C and 40°C. The average pore size of the obtained PVDF membrane is 0.2 μm to 0.6 μm. In this invention, the specific process and principle of preparing the hollow fiber membrane of PVDF without surface grafting treatment using the dry-wet spinning process are well-known technologies and will not be described in detail here.

[0068] Step 4: The polyvinylidene fluoride membrane obtained in Step 3 is subjected to alkali treatment to obtain a hydroxylated base membrane. The hydroxylated base membrane is then immersed in an anhydrous toluene solution of 3-methacryloyloxypropyltrimethoxysilane and reacted at 80°C to 95°C under nitrogen protection for 12 to 24 hours to obtain a surface-alkenylated base membrane.

[0069] Step 5: Immerse the alkenylated base film obtained in Step 4 into a photoinitiated reaction solution containing the carboxylated sulfonate betaine-type zwitterionic copolymer with thiol-terminated end groups obtained in Step 2, and perform ultraviolet light irradiation reaction to obtain a polyvinylidene fluoride hollow fiber membrane with zwitterionic copolymer grafted on the surface.

[0070] In step two, the concentration of the carboxylated sulfonated betaine-type zwitterionic monomer is 0.3 mol / L to 0.8 mol / L; the RAFT chain transfer agent is 4-cyano-4-(thiobenzoyl)valerate, and the initiator is azobisisobutyronitrile; the mixed solvent is a mixture of methanol and water, and the volume ratio of methanol to water is 2:1 to 4:1; the reducing agent is tris(2-carboxyethyl)phosphonic acid hydrochloride, and the reduction reaction is carried out in a phosphate buffer solution with a pH of 7.0 to 7.4.

[0071] The molar ratio of 4-cyano-4-(thiobenzoyl)valerate to carboxylated sulfonate betaine-type zwitterionic monomer is 0.005:1 to 0.015:1, and the molar ratio of azobisisobutyronitrile to 4-cyano-4-(thiobenzoyl)valerate is 0.1:1 to 0.3:1.

[0072] In step three, the spinning solution also includes 5% to 12% by mass of polyvinylidene fluoride nano-alumina, wherein the average particle size of the nano-alumina is 50 nm to 100 nm.

[0073] In step four, the polyvinylidene fluoride (PVDF) membrane undergoes alkali treatment as follows: the PVDF membrane obtained in step three is first soaked in deionized water for 24 to 48 hours, dried, and then immersed in an aqueous ethanol solution with a potassium hydroxide concentration of 1.0 mol / L to 2.5 mol / L. The membrane is then reacted at 40°C to 60°C for 2 to 6 hours. After washing, the membrane is then immersed in a solution with a hydrogen peroxide volume fraction of 1% to 3% and a sulfuric acid concentration of 0.5 mol / L to 1.0 mol / L. The membrane is then reacted at room temperature for 1 to 3 hours.

[0074] In step four, the volume fraction of 3-methacryloyloxypropyltrimethoxysilane in anhydrous toluene solution is 2% to 5%.

[0075] In step five, in the photoinitiation reaction solution, the mass-volume concentration of the carboxylated sulfonate betaine-type zwitterionic copolymer with thiol-terminated groups is 2% to 8%, and the mass fraction of the photoinitiator in the photoinitiation reaction solution is 1% to 3%. The specific parameters of the ultraviolet light irradiation reaction are: reaction for 20 to 40 minutes under ultraviolet light irradiation with a wavelength of 365 nm and a light intensity of 10 mW / cm² to 30 mW / cm².

[0076] The photoinitiator is 2,2-dimethoxy-2-phenylacetophenone, and the solvent in the photoinitiation reaction solution is a mixture of N,N-dimethylformamide and water, wherein the volume ratio of N,N-dimethylformamide to water is 4:1.

[0077] Application of a microfiltration membrane module for the separation of Haematococcus pluvialis cell wall disruption liquid, wherein the microfiltration membrane module is used for solid-liquid separation of Haematococcus pluvialis cell wall disruption liquid.

[0078] This invention constructs a stable, antifouling interface with both hydration layer repulsion and electrostatic repulsion functions by self-synthesizing a carboxylated sulfonate betaine-type zwitterionic copolymer and covalently anchoring it to the surface of a polyvinylidene fluoride (PVDF) hollow fiber membrane. Simultaneously, a PVDF membrane with a pore size matching the particle size distribution of the Haematococcus pluvialis cell wall disruption solution is prepared using a dry-wet spinning process with the external coagulation bath temperature as the control variable. The modified hollow fiber membrane is assembled into a microfiltration membrane module and used for solid-liquid separation of Haematococcus pluvialis cell wall disruption solution. It can maintain a relatively long continuous operating cycle without frequent chemical cleaning, exhibits a narrowed membrane flux decline, improved backwash flux recovery, and stable retention selectivity of the astaxanthin-lipid complex during separation.

[0079] The present invention will be described in detail below with reference to examples and comparative examples, but the scope of protection of the present invention is not limited to these examples.

[0080] Example 1

[0081] Preparation of carboxylated sulfonate betaine-type zwitterionic monomer: N,N-dimethylaminopropylamine was reacted with acryloyl chloride at 0°C under nitrogen protection for 6 hours to obtain N-(3-dimethylaminopropyl)acrylamide. In the presence of a polymerization inhibitor, it was then reacted with 1,3-propanesulfonic acid lactone at 60°C for 12 hours to generate a sulfonate betaine-type zwitterionic intermediate. This sulfonate betaine-type zwitterionic intermediate was then reacted with succinic anhydride at room temperature for 12 hours to obtain the carboxylated sulfonate betaine-type zwitterionic monomer. At this point, the molar ratio of sulfonate betaine groups to terminal carboxyl groups was 1:0.8.

[0082] Preparation of carboxylated sulfonate betaine-type zwitterionic copolymers with thiol-terminated groups: The obtained carboxylated sulfonate betaine-type zwitterionic monomer was dissolved in a mixed solvent of methanol and water with a monomer concentration of 0.8 mol / L and a methanol-to-water volume ratio of 2:1. RAFT chain transfer agent 4-cyano-4-(thiobenzoyl)valerate and initiator azobisisobutyronitrile were added, wherein the molar ratio of 4-cyano-4-(thiobenzoyl)valerate to monomer was 0.015:1, and the molar ratio of azobisisobutyronitrile to 4-cyano-4-(thiobenzoyl)valerate was 0.1:1. The reaction was carried out at 65°C under nitrogen protection for 24 hours to obtain carboxyl-terminated polysulfonate betaine-type zwitterionic polymer. The polymer was reduced in a phosphate buffer solution at pH 7.0 for 12 hours in the presence of the reducing agent tris(2-carboxyethyl)phosphonic acid hydrochloride to obtain a carboxylated sulfonate betaine-type zwitterionic copolymer with thiol-terminated groups, a number average molecular weight of 25000 g / mol, and a grafting amount controlled at 350 μg / cm².

[0083] Preparation of polyvinylidene fluoride (PVDF) membranes: Hollow fiber PVDF membranes without surface grafting were prepared using a dry-wet spinning process. The spinning solution contained 18% PVDF by mass, and polyvinylpyrrolidone (PVP) K30 was added at 8% of the PVDF mass. Additionally, 12% of nano-alumina (with an average particle size of 50 nm) by mass of PVDF was added. The core solution was a mixture of deionized water and N,N-dimethylacetamide in a volume ratio of 3:7. The external coagulation bath was deionized water, and the temperature was set to 40℃. The resulting PVDF membrane had an average pore size of 0.2 μm, a porosity of 75%, a fiber inner diameter of 0.8 mm, and a wall thickness of 0.25 mm.

[0084] Surface treatment of polyvinylidene fluoride (PVDF) membrane: The obtained PVDF membrane was immersed in deionized water for 24 hours, dried, and then immersed in an aqueous solution of ethanol with a potassium hydroxide concentration of 2.5 mol / L (ethanol to water volume ratio 1:1). The reaction was carried out at 40°C for 6 hours. After washing, it was immersed in a solution of hydrogen peroxide with a volume fraction of 1% and sulfuric acid concentration of 1.0 mol / L, and reacted at room temperature for 1 hour to obtain a hydroxylated membrane. The hydroxylated membrane was then immersed in an anhydrous toluene solution of 3-methacryloyloxypropyltrimethoxysilane (volume fraction 5%), and reacted at 80°C under nitrogen protection for 24 hours to obtain a surface-alkenylated membrane.

[0085] Photoinitiated grafting reaction: The alkenylated base film was immersed in a photoinitiating reaction solution containing a carboxylated sulfonate betaine-type zwitterionic copolymer with thiol-terminated groups. The copolymer had a mass-volume concentration of 8%, the photoinitiator 2,2-dimethoxy-2-phenylacetophenone had a mass fraction of 1%, and the solvent was a mixture of N,N-dimethylformamide and water in a volume ratio of 4:1. After irradiation with ultraviolet light at a wavelength of 365 nm and an intensity of 30 mW / cm² for 20 minutes, a polyvinylidene fluoride hollow fiber membrane with the zwitterionic copolymer grafted on its surface was obtained.

[0086] Membrane module assembly: The modified hollow fiber membrane is loaded into the shell at a filling density of 55%, and the casting ends are encapsulated with two-component epoxy resin to obtain the microfiltration membrane module.

[0087] Example 2

[0088] In this embodiment, the similarities to those in Embodiment 1 will not be repeated, and the differences are as follows:

[0089] Preparation of carboxylated sulfonate betaine-type zwitterionic monomer: N,N-dimethylaminopropylamine was reacted with acryloyl chloride at 5°C under nitrogen protection for 12 hours to obtain N-(3-dimethylaminopropyl)acrylamide. This N-acrylamide was then reacted with 1,3-propanesulfonic acid lactone at 40°C for 24 hours to generate a sulfonate betaine-type zwitterionic intermediate. This intermediate was then reacted with succinic anhydride at room temperature for 24 hours to obtain the carboxylated sulfonate betaine-type zwitterionic monomer. At this stage, the molar ratio of the sulfonate betaine group to the terminal carboxyl group was 1:1.2.

[0090] Preparation of carboxylated sulfonate betaine-type zwitterionic copolymers with thiol-terminated groups: The obtained carboxylated sulfonate betaine-type zwitterionic monomer was dissolved in a mixed solvent of methanol and water with a monomer concentration of 0.3 mol / L and a methanol-to-water volume ratio of 4:1. RAFT chain transfer agent 4-cyano-4-(thiobenzoyl)valerate and initiator azobisisobutyronitrile were added, wherein the molar ratio of 4-cyano-4-(thiobenzoyl)valerate to monomer was 0.005:1, and the molar ratio of azobisisobutyronitrile to 4-cyano-4-(thiobenzoyl)valerate was 0.3:1. The reaction was carried out at 75°C under nitrogen protection for 12 hours to obtain carboxyl-terminated polysulfonate betaine-type zwitterionic polymer. The polymer was reduced in a phosphate buffer solution at pH 7.4 for 24 hours in the presence of the reducing agent tris(2-carboxyethyl)phosphonic acid hydrochloride to obtain a carboxylated sulfonate betaine-type zwitterionic copolymer with thiol-terminated groups, a number-average molecular weight of 8000 g / mol, and a grafting amount controlled at 80 μg / cm².

[0091] Preparation of polyvinylidene fluoride (PVDF) membranes: Hollow fiber PVDF membranes without surface grafting were prepared using a dry-wet spinning process. The spinning solution contained 18% PVDF by mass, and polyvinylpyrrolidone (PVP) K30 was added at 8% of the PVDF mass. Additionally, 5% of nano-alumina (with an average particle size of 100 nm) by mass of PVDF was added. The core solution was a mixture of deionized water and N,N-dimethylacetamide in a volume ratio of 3:7. The external coagulation bath was deionized water, and the temperature was set to 25°C. The resulting PVDF membrane had an average pore size of 0.6 μm, a porosity of 85%, a fiber inner diameter of 1.2 mm, and a wall thickness of 0.15 mm.

[0092] Surface treatment of polyvinylidene fluoride (PVDF) membrane: The obtained PVDF membrane was immersed in deionized water for 48 hours, dried, and then immersed in an aqueous solution of ethanol with a potassium hydroxide concentration of 1.0 mol / L (ethanol to water volume ratio of 3:7). The reaction was carried out at 60°C for 2 hours. After washing, it was immersed in a solution of hydrogen peroxide (volume fraction) and sulfuric acid (volume fraction) of 0.5 mol / L for 3 hours at room temperature to obtain a hydroxylated membrane. The hydroxylated membrane was then immersed in an anhydrous toluene solution of 3-methacryloyloxypropyltrimethoxysilane (volume fraction of 2%) for 12 hours at 95°C under nitrogen protection to obtain a surface-alkenylated membrane.

[0093] Photoinitiated grafting reaction: The alkenylated base film was immersed in a photoinitiating reaction solution containing a carboxylated sulfonate betaine-type zwitterionic copolymer with thiol-terminated groups. The copolymer had a mass-volume concentration of 2%, the photoinitiator 2,2-dimethoxy-2-phenylacetophenone had a mass fraction of 3%, and the solvent was a mixture of N,N-dimethylformamide and water in a volume ratio of 4:1. After irradiation with ultraviolet light at a wavelength of 365 nm and an intensity of 10 mW / cm² for 40 minutes, a polyvinylidene fluoride hollow fiber membrane with the zwitterionic copolymer grafted onto its surface was obtained.

[0094] Membrane module assembly: The modified hollow fiber membrane is loaded into the shell at a filling density of 45%, and the casting ends are encapsulated with two-component epoxy resin to obtain the microfiltration membrane module.

[0095] Example 3

[0096] In this embodiment, the similarities to those in Embodiment 1 will not be repeated, and the differences are as follows:

[0097] Preparation of carboxylated sulfonate betaine-type zwitterionic monomer: N,N-dimethylaminopropylamine was reacted with acryloyl chloride at 2.5 °C under nitrogen protection for 9 hours to obtain N-(3-dimethylaminopropyl)acrylamide. This N-acrylamide was then reacted with 1,3-propanesulfonic acid lactone at 50 °C for 18 hours to generate a sulfonate betaine-type zwitterionic intermediate. This sulfonate betaine-type zwitterionic intermediate was then reacted with succinic anhydride at room temperature for 18 hours to obtain the carboxylated sulfonate betaine-type zwitterionic monomer. At this point, the molar ratio of the sulfonate betaine group to the terminal carboxyl group was 1:1.0.

[0098] Preparation of carboxylated sulfonate betaine-type zwitterionic copolymers with thiol-terminated groups: The obtained carboxylated sulfonate betaine-type zwitterionic monomer was dissolved in a mixed solvent of methanol and water with a monomer concentration of 0.5 mol / L and a methanol-to-water volume ratio of 3:1. RAFT chain transfer agent 4-cyano-4-(thiobenzoyl)valerate and initiator azobisisobutyronitrile were added, wherein the molar ratio of 4-cyano-4-(thiobenzoyl)valerate to monomer was 0.01:1, and the molar ratio of azobisisobutyronitrile to 4-cyano-4-(thiobenzoyl)valerate was 0.2:1. The reaction was carried out at 70 °C under nitrogen protection for 18 hours to obtain carboxyl-terminated polysulfonate betaine-type zwitterionic polymer. The polymer was reduced in a phosphate buffer solution at pH 7.2 for 18 hours in the presence of the reducing agent tris(2-carboxyethyl)phosphonic acid hydrochloride to obtain a carboxylated sulfonate betaine-type zwitterionic copolymer with a terminal mercapto group, a number average molecular weight of 15000 g / mol, and a grafting amount controlled at 200 μg / cm².

[0099] Preparation of polyvinylidene fluoride (PVDF) membranes: Hollow fiber PVDF membranes without surface grafting were prepared using a dry-wet spinning process. The spinning solution contained 18% PVDF by mass, and polyvinylpyrrolidone (PVP) K30 was added at 8% of the PVDF mass. Additionally, 8% of nano-alumina by mass of PVDF was added, with an average particle size of 80 nm. The core solution was a mixture of deionized water and N,N-dimethylacetamide in a volume ratio of 3:7. The external coagulation bath was deionized water, and the temperature was set to 32℃. The resulting PVDF membrane had an average pore size of 0.4 μm, a porosity of 80%, a fiber inner diameter of 1.0 mm, and a wall thickness of 0.20 mm.

[0100] Surface treatment of polyvinylidene fluoride (PVDF) membrane: The obtained PVDF membrane was immersed in deionized water for 36 hours, dried, and then immersed in an aqueous solution of ethanol with a potassium hydroxide concentration of 1.8 mol / L (ethanol to water volume ratio of 1:2). The reaction was carried out at 50°C for 4 hours. After washing, it was immersed in a solution of hydrogen peroxide with a volume fraction of 2% and sulfuric acid with a concentration of 0.8 mol / L, and reacted at room temperature for 2 hours to obtain a hydroxylated membrane. The hydroxylated membrane was then immersed in an anhydrous toluene solution of 3-methacryloyloxypropyltrimethoxysilane (volume fraction of 3.5%), and reacted at 88°C under nitrogen protection for 18 hours to obtain a surface-alkenylated membrane.

[0101] Photoinitiated grafting reaction: The alkenylated base film was immersed in a photoinitiating reaction solution containing a carboxylated sulfonate betaine-type zwitterionic copolymer with thiol-terminated groups. The copolymer had a mass-volume concentration of 5%, the photoinitiator 2,2-dimethoxy-2-phenylacetophenone had a mass fraction of 2%, and the solvent was a mixture of N,N-dimethylformamide and water in a volume ratio of 4:1. After irradiation with ultraviolet light at a wavelength of 365 nm and an intensity of 20 mW / cm² for 30 minutes, a polyvinylidene fluoride hollow fiber membrane with the zwitterionic copolymer grafted onto its surface was obtained.

[0102] Membrane module assembly: The modified hollow fiber membrane is loaded into the shell at a filling density of 50%, and the casting ends are encapsulated with two-component epoxy resin to obtain the microfiltration membrane module.

[0103] Example 4

[0104] In this embodiment, the similarities to those in Embodiment 1 will not be repeated, and the differences are as follows:

[0105] Preparation of carboxylated sulfonate betaine-type zwitterionic monomer: N,N-dimethylaminopropylamine was reacted with acryloyl chloride at 3°C ​​under nitrogen protection for 10 hours to obtain N-(3-dimethylaminopropyl)acrylamide. This N-acrylamide was then reacted with 1,3-propanesulfonic acid lactone at 55°C for 20 hours to generate a sulfonate betaine-type zwitterionic intermediate. This intermediate was then reacted with succinic anhydride at room temperature for 20 hours to obtain the carboxylated sulfonate betaine-type zwitterionic monomer. At this stage, the molar ratio of the sulfonate betaine group to the terminal carboxyl group was 1:1.0.

[0106] Preparation of carboxylated sulfonate betaine-type zwitterionic copolymers with thiol-terminated groups: The obtained carboxylated sulfonate betaine-type zwitterionic monomer was dissolved in a mixed solvent of methanol and water with a monomer concentration of 0.6 mol / L and a methanol-to-water volume ratio of 3:1. RAFT chain transfer agent 4-cyano-4-(thiobenzoyl)valerate and initiator azobisisobutyronitrile were added, wherein the molar ratio of 4-cyano-4-(thiobenzoyl)valerate to monomer was 0.01:1, and the molar ratio of azobisisobutyronitrile to 4-cyano-4-(thiobenzoyl)valerate was 0.2:1. The reaction was carried out at 70 °C under nitrogen protection for 20 hours to obtain carboxyl-terminated polysulfonate betaine-type zwitterionic polymer. The polymer was reduced in a phosphate buffer solution at pH 7.2 for 20 hours in the presence of the reducing agent tris(2-carboxyethyl)phosphonic acid hydrochloride to obtain a carboxylated sulfonate betaine-type zwitterionic copolymer with thiol-terminated groups, a number-average molecular weight of 16000 g / mol, and a grafting amount controlled at 220 μg / cm².

[0107] Preparation of polyvinylidene fluoride (PVDF) membranes: Hollow fiber PVDF membranes without surface grafting were prepared using a dry-wet spinning process. The spinning solution contained 18% PVDF by mass, 8% polyvinylpyrrolidone (PVP) K30 by mass, and 9% (by mass) of nano-alumina with an average particle size of 70 nm. The core solution was a mixture of deionized water and N,N-dimethylacetamide in a volume ratio of 3:7. The external coagulation bath was deionized water, and the temperature was set to 33 °C. The resulting PVDF membrane had an average pore size of 0.45 μm, a porosity of 82%, a fiber inner diameter of 1.0 mm, and a wall thickness of 0.20 mm.

[0108] Surface treatment of polyvinylidene fluoride (PVDF) membrane: The obtained PVDF membrane was soaked in deionized water for 40 hours, dried, and then immersed in an aqueous solution of ethanol with a potassium hydroxide concentration of 1.8 mol / L (ethanol to water volume ratio of 1:2). The reaction was carried out at 50°C for 5 hours. After washing, it was immersed in a solution of hydrogen peroxide with a volume fraction of 2% and sulfuric acid with a concentration of 0.7 mol / L, and reacted at room temperature for 2.5 hours to obtain a hydroxylated membrane. The hydroxylated membrane was then immersed in an anhydrous toluene solution of 3-methacryloyloxypropyltrimethoxysilane (volume fraction of 4%), and reacted at 90°C under nitrogen protection for 20 hours to obtain a surface-alkenylated membrane.

[0109] Photoinitiated grafting reaction: The alkenylated base film was immersed in a photoinitiating reaction solution containing a carboxylated sulfonate betaine-type zwitterionic copolymer with thiol-terminated groups. The copolymer had a mass-volume concentration of 6%, the photoinitiator 2,2-dimethoxy-2-phenylacetophenone had a mass fraction of 2%, and the solvent was a mixture of N,N-dimethylformamide and water in a volume ratio of 4:1. After irradiation with ultraviolet light at a wavelength of 365 nm and an intensity of 20 mW / cm² for 30 minutes, a polyvinylidene fluoride hollow fiber membrane with the zwitterionic copolymer grafted onto its surface was obtained.

[0110] Membrane module assembly: The modified hollow fiber membrane is loaded into the shell at a filling density of 50%, and the casting ends are encapsulated with two-component epoxy resin to obtain the microfiltration membrane module.

[0111] Comparative Example 1

[0112] The difference between this comparative example and Example 4 is that the polyvinylidene fluoride hollow fiber membrane was not surface grafted, that is, steps one, two, four and five were omitted, and the polyvinylidene fluoride membrane prepared in step three was directly assembled into a membrane module.

[0113] Comparative Example 2

[0114] The difference between this comparative example and Example 4 is that the zwitterionic copolymer is attached to the surface of the polyvinylidene fluoride film by physical coating rather than chemical grafting. Specifically, the carboxylated sulfonate betaine-type zwitterionic copolymer with thiol-terminated groups prepared in step two is prepared into an aqueous solution with a mass-volume concentration of 5%. The polyvinylidene fluoride film is immersed in this solution for 2 hours, then removed and dried. Without ultraviolet light irradiation or photoinitiator treatment, no covalent bonds are formed between the copolymer and the film surface.

[0115] Comparative Example 3

[0116] The difference between this comparative example and Example 4 is that the external coagulation bath temperature was fixed at 20°C and other conditions remained unchanged when preparing the polyvinylidene fluoride membrane, and the average pore size of the resulting base membrane was 0.15 μm.

[0117] Comparative Example 4

[0118] The difference between this comparative example and Example 4 is that the external coagulation bath temperature was fixed at 45°C and other conditions remained unchanged when preparing the polyvinylidene fluoride membrane, and the average pore size of the resulting base membrane was 0.75 μm.

[0119] Comparative Example 5

[0120] The difference between this comparative example and Example 4 is that the monomer synthesized in step one is an uncarboxylated betaine-type zwitterionic monomer, that is, the step of reacting with succinic anhydride is omitted, and the side chain of the final grafted copolymer does not contain carboxyl groups.

[0121] Performance Test Results and Analysis

[0122] The microfiltration membrane modules prepared in each embodiment and comparative example were evaluated for filtration performance using the same testing apparatus. The test feed solution was a Haematococcus pluvialis cell wall disruption solution treated under high pressure, with a solid content of approximately 2.5% and a pH of approximately 6.8. Cross-flow filtration was used, with the membrane surface flow rate set at 2.5 m / s, the transmembrane pressure difference at 0.08 MPa, and the feed solution temperature controlled at 25°C. During the test, a gas backwash was performed every 10 minutes of filtration, with a backwash pressure of 0.25 MPa and a duration of 5 seconds.

[0123] The initial pure water flux and membrane flux changes during filtration were recorded. After 8 hours of continuous operation, the flux decay rate was calculated. The flux decay rate was defined as the ratio of (initial flux - flux after 8 hours of operation) to the initial flux. Permeate and retentate samples were collected simultaneously, and astaxanthin content was determined using high-performance liquid chromatography (HPLC). The astaxanthin-lipid complex permeability was calculated; the astaxanthin-lipid complex permeability was defined as the ratio of the mass of astaxanthin in the permeate to the total mass of astaxanthin in the feed solution. After operation, the membrane module was disassembled, the membrane fibers were gently rinsed with deionized water, and the morphology of the fouling layer on the membrane surface was observed using a scanning electron microscope. The amount of irreversible contaminant deposited per unit membrane area was determined by gravimetric analysis. The test results of each embodiment and comparative example are summarized in […]. Figure 1 See Tables 1 and 2. Table 1 shows the filtration performance test results, and Table 2 shows the microscopic observation results of the fouling layer on the membrane surface after 8 hours of operation.

[0124] Table 1. Filtration performance test results

[0125] Example 1 88.2 12.4 Example 2 86.5 14.1 Example 3 91.3 9.8 Example 4 92.6 8.5 Comparative Example 1 72.4 38.7 Comparative Example 2 79.8 26.3 Comparative Example 3 55.1 20.5 Comparative Example 4 83.2 22.8 Comparative Example 5 85.5 16.2

[0126] from Figure 1 As can be seen from the data in Table 1, the 8-hour flux decay rates of Examples 1 to 4 were significantly lower than those of Comparative Example 1 and Comparative Example 2. Comparative Example 1 used an unmodified polyvinylidene fluoride membrane, whose surface is hydrophobic. The extracellular polymers rich in protein components in the Haematococcus pluvialis cell wall disruption solution were easily adsorbed onto the membrane surface through hydrophobic interactions, rapidly forming a dense gel-like fouling layer.

[0127] Table 2 shows that Comparative Example 1 had a fouling layer thickness of approximately 35 μm and a dense gel-like structure, confirming this fouling mechanism. This resulted in a flux decay rate as high as 74.0%, and the astaxanthin-lipid complex permeability also decreased to 72.4% due to membrane pore blockage. Although Comparative Example 2 was coated with a zwitterionic copolymer, the coating only relied on physical adsorption to the membrane surface. Under 8 hours of cross-flow shearing and multiple backwashing, the coating partially detached and dissolved, gradually losing its antifouling function. The flux decay rate was still 57.6%, and the irreversible contaminant deposition reached 26.3 g / m², far exceeding the 9.8 g / m² of Example 3. This indicates that physical coating alone cannot maintain antifouling stability under long-term operation.

[0128] Table 2. Microscopic observation results of the fouling layer on the membrane surface after 8 hours of operation.

[0129] Example 1 8 Relatively loose, with some pores. Small amount of spot-like residue Example 2 10 Loose and evenly covered Small amount of flaky residue Example 3 5 Loose and porous, in the form of flocculent material Very small amount of dotted residue Example 4 3 Loose and porous, in the form of flocculent material Almost no visible residue Comparative Example 1 35 Dense gel-like structure, completely covering the membrane surface Large amounts of lumpy residue remain, resulting in poor backflushing effect. Comparative Example 2 20 Relatively dense, with some areas hardened. Numerous flaky and strip-shaped residues Comparative Example 3 15 Relatively dense, uniform coverage A relatively thick sedimentary layer remains after recoil. Comparative Example 4 18 It is relatively dense and contains a large number of embedded particles. Particulate embedded material is difficult to remove Comparative Example 5 12 Medium density, relatively uniform Moderate amount of flaky residue

[0130] Examples 1 to 4 all employed mercapto-olefin click chemistry to covalently graft carboxylated sulfonate betaine-type zwitterionic copolymers onto the membrane surface. As shown in Table 2, the fouling layer thickness in each example was controlled to be less than approximately 10 μm, exhibiting a loose, porous, or flocculent structure with minimal residue after backwashing. This is because the positively charged quaternary ammonium salt groups and negatively charged sulfonate groups in the copolymer repeating units form a highly stable hydrated layer on the membrane surface through ionic solvation, effectively repelling the hydrophobic regions of extracellular polymers. Simultaneously, the side-chain carboxyl groups ionize under the pH conditions of the cell disruption solution, generating electrostatic repulsion with similarly negatively charged cell wall fragments and extracellular polymers. This dual effect synergistically delays the adsorption and compaction of contaminants on the membrane surface. Covalent anchoring ensures the integrity of the functional layer under shear force and backwashing impact; therefore, the flux decay rate in each example was controlled to be below 40%, and the astaxanthin-lipid complex permeability remained above 86%.

[0131] Comparing Example 3 and Comparative Example 5, it can be found that the copolymer of Comparative Example 5 does not contain carboxyl groups in its side chains. Although its flux decay rate of 40.7% is better than that of Comparative Examples 1 and 2, it is still higher than that of Example 3 (30.0%). Furthermore, its irreversible contaminant deposition of 16.2 g / m² is significantly higher than that of Example 3 (9.8 g / m²). This indicates that the hydration layer repulsion effect of zwitterionic groups alone is insufficient to maximize the inhibition of contaminant deposition in complex contamination systems such as *Haemaphysalis algae* cell wall disruption solution. The additional electrostatic repulsion force provided by the carboxyl groups in the side chains makes a substantial contribution to improving the antifouling performance.

[0132] Regarding membrane pore size control, Example 3 obtained a base membrane with an average pore size of 0.4 μm by setting the external coagulation bath temperature to 32°C, achieving a permeation rate of 91.3% for the astaxanthin-lipid complex. In Comparative Example 3, the external coagulation bath temperature was only 20°C, reducing the average pore size to 0.15 μm. Although this resulted in more effective retention of solid impurities, the excessively small pore size increased the permeation resistance of the astaxanthin-lipid complex, causing the permeation rate to plummet to 55.1%. Furthermore, due to increased pore blockage, the flux decay rate reached 60.0%. In Comparative Example 4, the external coagulation bath temperature was 45°C, increasing the average pore size to 0.75 μm. While the astaxanthin-lipid complex permeation rate recovered to 83.2%, some larger cell wall fragments and extracellular polymers were able to enter and embed within the membrane pores, leading to increased irreversible fouling and a flux decay rate of 52.0%. Examples 1 to 4 stabilized the average pore size of the membrane in the range of 0.2 μm to 0.6 μm by adjusting the temperature of the external coagulation bath, which effectively balanced the permeation of the target product with the retention of impurities, while avoiding embedded contamination caused by excessively large membrane pores.

[0133] Test results show that the present invention constructs a stable antifouling interface with both hydration layer repulsion and electrostatic repulsion functions by anchoring the self-synthesized carboxylated sulfonate betaine-type zwitterionic copolymer on the surface of polyvinylidene fluoride hollow fiber membrane in the form of covalent bonds. At the same time, the spinning process with external coagulation bath temperature as the single control variable is used to precisely control the pore size of the base membrane, so that the membrane module can maintain a stable flux and effective permeation of astaxanthin-lipid complex in the separation of Haematococcus pluvialis cell wall disruption liquid without frequent chemical cleaning.

[0134] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A microfiltration membrane module for separating Haematococcus pluvialis cell wall-breaking liquid, characterized in that, The microfiltration membrane module includes a housing, hollow fiber membrane bundles arranged axially along the housing, feed inlets and retentate outlets at both ends of the housing, and permeate outlets on the sidewalls of the housing. The hollow fiber membrane bundles are composed of polyvinylidene fluoride hollow fiber membranes with zwitterionic copolymers grafted onto their surfaces. The zwitterionic copolymers are carboxylated sulfonate-betaine type zwitterionic copolymers with a number-average molecular weight of 8000 to 25000 g / mol. The repeating units of this copolymer simultaneously contain quaternary ammonium salt positively charged groups, sulfonate negatively charged groups, and side-chain carboxyl groups. The zwitterionic copolymers are covalently grafted onto the surface of the polyvinylidene fluoride membrane at a grafting amount of 80 to 350 μg / cm³. 2 ; The method for preparing the polyvinylidene fluoride hollow fiber membrane with surface grafted with zwitterionic copolymers includes the following steps: Step 1: N,N-dimethylaminopropylamine is reacted with acryloyl chloride at 0°C to 5°C under nitrogen protection for 6 to 12 hours to obtain N-(3-dimethylaminopropyl)acrylamide. Then, it is reacted with 1,3-propanesulfonic acid lactone at 40°C to 60°C for 12 to 24 hours to generate a sulfonate betaine-type zwitterionic intermediate. The sulfonate betaine-type zwitterionic intermediate is then reacted with succinic anhydride at room temperature for 12 to 24 hours to obtain a carboxylated sulfonate betaine-type zwitterionic monomer. Step 2: Dissolve the carboxylated sulfonated betaine zwitterionic monomer obtained in Step 1 in a mixed solvent of methanol and water, add RAFT chain transfer agent and initiator, and react at 65°C to 75°C under nitrogen protection for 12 to 24 hours to obtain a carboxyl-terminated polysulfonated betaine zwitterionic polymer. Then, reduce the polymer in the presence of a reducing agent for 12 to 24 hours to obtain a carboxylated sulfonated betaine zwitterionic copolymer with thiol-terminated groups. Step 3: A hollow fiber membrane of polyvinylidene fluoride (PVDF) without surface grafting treatment is prepared using a dry-wet spinning process. The mass fraction of PVDF in the spinning solution is 18%, the amount of polyvinylpyrrolidone K30 added is 8% of the mass of PVDF, the core solution is a mixture of deionized water and N,N-dimethylacetamide in a volume ratio of 3:7, the external coagulation bath is deionized water, and the temperature of the external coagulation bath is 25℃ to 40℃. The average pore size of the obtained PVDF membrane is 0.2μm to 0.6μm. Step 4: The polyvinylidene fluoride membrane obtained in Step 3 is subjected to alkali treatment to obtain a hydroxylated base membrane. The hydroxylated base membrane is then immersed in an anhydrous toluene solution of 3-methacryloyloxypropyltrimethoxysilane and reacted at 80°C to 95°C under nitrogen protection for 12 to 24 hours to obtain a surface-alkenylated base membrane. Step 5: Immerse the alkenylated base film obtained in Step 4 into a photoinitiated reaction solution containing the carboxylated sulfonate betaine-type zwitterionic copolymer with thiol-terminated end groups obtained in Step 2, and perform ultraviolet light irradiation reaction to obtain a polyvinylidene fluoride hollow fiber membrane with zwitterionic copolymer grafted on the surface.

2. The microfiltration membrane module for separating Haematococcus pluvialis cell wall-breaking liquid according to claim 1, characterized in that, In step two, the concentration of the carboxylated sulfonated betaine-type zwitterionic monomer is 0.3 mol / L to 0.8 mol / L; the RAFT chain transfer agent is 4-cyano-4-(thiobenzoyl)valerate, and the initiator is azobisisobutyronitrile; the mixed solvent is a mixture of methanol and water, and the volume ratio of methanol to water is 2:1 to 4:1; the reducing agent is tris(2-carboxyethyl)phosphonic acid hydrochloride, and the reduction reaction is carried out in a phosphate buffer solution with a pH of 7.0 to 7.

4.

3. A microfiltration membrane module for separating Haematococcus pluvialis cell wall-breaking liquid according to claim 2, characterized in that, The molar ratio of 4-cyano-4-(thiobenzoyl)valerate to carboxylated sulfonate betaine-type zwitterionic monomer is 0.005:1 to 0.015:1, and the molar ratio of azobisisobutyronitrile to 4-cyano-4-(thiobenzoyl)valerate is 0.1:1 to 0.3:

1.

4. A microfiltration membrane module for separating Haematococcus pluvialis cell wall-breaking liquid according to claim 1, characterized in that, In step three, the spinning solution also includes 5% to 12% by mass of polyvinylidene fluoride nano-alumina, wherein the average particle size of the nano-alumina is 50 nm to 100 nm.

5. A microfiltration membrane module for separating Haematococcus pluvialis cell wall-breaking liquid according to claim 1, characterized in that, In step four, the polyvinylidene fluoride (PVDF) membrane undergoes alkali treatment as follows: the PVDF membrane obtained in step three is first soaked in deionized water for 24 to 48 hours, dried, and then immersed in an aqueous ethanol solution with a potassium hydroxide concentration of 1.0 mol / L to 2.5 mol / L. The membrane is then reacted at 40°C to 60°C for 2 to 6 hours. After washing, the membrane is then immersed in a solution with a hydrogen peroxide volume fraction of 1% to 3% and a sulfuric acid concentration of 0.5 mol / L to 1.0 mol / L. The membrane is then reacted at room temperature for 1 to 3 hours.

6. A microfiltration membrane module for separating Haematococcus pluvialis cell wall-breaking liquid according to claim 5, characterized in that, In step four, the volume fraction of 3-methacryloyloxypropyltrimethoxysilane in anhydrous toluene solution is 2% to 5%.

7. A microfiltration membrane module for separating Haematococcus pluvialis cell wall-breaking liquid according to claim 1, characterized in that, In step five, in the photoinitiation reaction solution, the mass-volume concentration of the carboxylated sulfonate betaine-type zwitterionic copolymer with thiol-terminated groups is 2% to 8%, and the mass fraction of the photoinitiator in the photoinitiation reaction solution is 1% to 3%. The specific parameters of the ultraviolet light irradiation reaction are: reaction for 20 to 40 minutes under ultraviolet light irradiation with a wavelength of 365 nm and a light intensity of 10 mW / cm² to 30 mW / cm².

8. A microfiltration membrane module for separating Haematococcus pluvialis cell wall-breaking liquid according to claim 7, characterized in that, The photoinitiator is 2,2-dimethoxy-2-phenylacetophenone, and the solvent in the photoinitiation reaction solution is a mixture of N,N-dimethylformamide and water, wherein the volume ratio of N,N-dimethylformamide to water is 4:

1.

9. An application of a microfiltration membrane module for separating Haematococcus pluvialis cell wall-breaking liquid as described in any one of claims 1-8, characterized in that, The microfiltration membrane module is used for solid-liquid separation of Haematococcus pluvialis cell wall disruption liquid.

Images