Silk fibroin high-salt solution hollow fiber membrane coupling electrodialysis desalination process

Abstract

The invention belongs to the field of regenerated silk fibroin purification, and provides a silk fibroin high-salt solution hollow fiber membrane coupling electrodialysis desalination process, which comprises a hollow fiber membrane system and an electrodialysis system, and comprises the following steps: S1, adding a silk fibroin solution to be desalted into the inner side of membrane silk of the hollow fiber membrane system, pure water is arranged on the outer side of a membrane wire of the hollow fiber membrane system, and the membrane wire is a large-aperture membrane wire; s2, after pure water in the hollow fiber membrane system receives salt, hollow fiber membrane saline water is formed; s3, introducing the hollow fiber membrane saline water into an electrodialysis system, and desalting in an electrodialysis membrane stack to form fresh water; s4, introducing fresh water to the outer side of membrane filaments of the hollow fiber membrane system, and circularly carrying out the steps S1 to S4; and S5, concentrating until the concentration of the silk fibroin solution reaches 2-5%. The method has the advantages of reasonable design, continuous filtration production of regenerated silk fibroin, suitability for industrial production, high treatment capacity, capability of realizing efficient desalination, environmental protection and suitability for large-scale popularization.

Description

Technical Field

[0001] The invention belongs to the technical field of regenerated silk fibroin purification, and in particular relates to a hollow fiber membrane coupled electrodialysis desalination process for a silk fibroin high-salt solution. Background Art

[0002] Silk protein mainly includes sericin and fibroin. Regenerated silk fibroin derived from silk can be reprocessed, modified, and regulated to prepare various types of scaffold materials, which can then be used in many fields such as tissue engineering, drug delivery, 3D printing, cell coating, microfluidics, and biosensors. Natural silk fibroin is insoluble in water, but soluble in strong acids, strong bases, and some neutral salt solutions. The preparation process of regenerated silk fibroin mainly includes alkaline degumming, high-concentration salt dissolution, ultrafiltration desalination, and freeze-drying.

[0003] In order to obtain high-purity soluble silk fibroin, a high-concentration lithium bromide solution or calcium chloride solution is usually used for dissolution, and the lithium bromide or calcium chloride in the silk fibroin solution is removed to obtain a regenerated silk fibroin solution. In the subsequent removal step, in order to remove the lithium bromide with a concentration of up to 80% to remove the bromide ion content ≤80mg / g and the lithium ion <2mg / g, dialysis bag dialysis, hollow fiber membrane ultrafiltration, electrodialysis, diffusion dialysis and the like are usually used. However, these different methods are applied to the purification process of regenerated silk fibroin, and there are also some practical problems, such as the dialysis bag dialysis process, which has a long dialysis time, a large amount of water, and a small processing volume, and cannot be used for industrial large-scale production; the hollow fiber membrane desalination process, which requires an increase in the membrane surface flow rate to prevent concentration polarization and membrane surface fouling. Silk fibroin is very susceptible to shear denaturation under low salt conditions, forming precipitation, resulting in membrane blockage and protein yield loss; the electrodialysis process is affected by the membrane stack flow channel structure. , which is very easy to form protein precipitation and block the flow channel, easily leading to electrodialysis membrane current overload and burning, and it is difficult to clean after the flow channel is blocked, and it cannot be applied to industrial production; the diffusion dialysis process cannot achieve desalination of the feed solution to a conductivity of <200μs / cm (5% protein concentration); another example is the diffusion dialysis-electrodialysis coupling process, which uses diffusion dialysis for desalination in high salt conditions and electrodialysis for continued desalination in low salt conditions, but the low salt environment cannot avoid the precipitation of silk fibroin and the blockage of the electrodialysis flow channel. Summary of the invention

[0004] The present invention aims at the fact that regenerated silk fibroin must go through the stage of high-salt dissolution and then desalination, while silk fibroin has the characteristics of being extremely easy to be denatured and precipitated under shear in a low-salt environment. The present invention proposes a silk fibroin high-salt solution hollow fiber membrane coupled electrodialysis desalination process with reasonable design, suitability for industrial production, large processing capacity and the ability to achieve efficient desalination.

[0005] In order to achieve the above-mentioned object, the technical solution adopted by the present invention is a hollow fiber membrane coupled electrodialysis desalination process for a high-salt solution of silk fibroin provided by the present invention, comprising a hollow fiber membrane system and an electrodialysis system, wherein the electrodialysis system comprises an electrodialysis membrane stack, pure water, a cathode and an anode, and the electrodialysis membrane stack comprises an anion exchange homogeneous membrane and a cation exchange homogeneous membrane, and the specific steps are as follows:

[0006] S1, adding the silk fibroin solution to be desalted to the inner side of the membrane filament of the hollow fiber membrane system, the outer side of the membrane filament of the hollow fiber membrane system is pure water, the membrane filament is a coarse-pore membrane filament, the pore size of the membrane filament is 0.5mm-1.2mm, reducing the circulation resistance and reducing the drastic shearing of the membrane filament on the protein;

[0007] S2, the hollow fiber membrane system uses an internal pressure cross-flow filtration method to make pure water absorb salt to form hollow fiber membrane brine, and the hollow fiber membrane system adopts a low membrane surface flow rate and a low transmembrane pressure difference to prevent the silk fibroin from being subjected to severe shearing;

[0008] S3, introducing the hollow fiber membrane brine produced in step S2 into the electrodialysis system, the hollow fiber membrane brine does not contain silk fibroin, the hollow fiber membrane brine is desalted in the electrodialysis membrane stack, the pure water in the electrodialysis system receives the salt to form concentrated brine, and the desalted hollow fiber membrane brine is converted into fresh water;

[0009] S4, introducing fresh water in the electrodialysis system into the outer side of the membrane fibers of the hollow fiber membrane system, and cyclically performing steps S1 to S4;

[0010] S5, concentration stage, pressurizing the hollow fiber membrane system, maintaining a low membrane surface flow rate, and concentrating until the concentration of the silk fibroin solution reaches 2-5%.

[0011] Preferably, the low membrane surface flow rate in steps S2 and S5 is 0.05 m / s to 0.5 m / s.

[0012] Preferably, the low membrane surface flow rate in step S5 is 5-10% smaller than the low membrane surface flow rate in step S2.

[0013] Preferably, the transmembrane pressure difference in step S2 is less than 0.1 MPa, and the transmembrane pressure difference in step S5 is 0.1 MPa.

[0014] Preferably, the membrane fibers in the hollow fiber membrane system are made of hydrophilic membrane materials.

[0015] Preferably, the membrane fibers in the hollow fiber membrane system are ultrafiltration membranes with a molecular weight cutoff of 2KD to 50KD.

[0016] Preferably, the electrodialysis uses a DC power supply to form a DC electric field, and adopts an automatic switching mode between constant current and constant voltage.

[0017] Compared with the prior art, the advantages and positive effects of the present invention are:

[0018] 1. The present invention provides a hollow fiber membrane-coupled electrodialysis desalination process for a high-salt solution of silk fibroin. The hollow fiber membrane system processes the silk fibroin solution to be desalted. Large-pore membrane fibers and low flow rates are used to avoid the shearing and precipitation of silk fibroin, thereby ensuring the production quality of regenerated silk fibroin and preventing frequent fouling and clogging of the electrodialysis membrane stack of the electrodialysis system, thereby forming continuous filtration production. In addition, the hollow fiber membrane system adopts a method of desalting first and then concentrating, and the ultrafiltration and concentration time is extremely short, thereby preventing shearing and precipitation of silk fibroin and achieving high-fold concentration of the protein solution after desalting.

[0019] 2. The present invention provides a hollow fiber membrane-coupled electrodialysis desalination process for high-salt solution of silk fibroin. The electrodialysis system coupled with the hollow fiber membrane system adopts an ion exchange membrane to achieve continuous desalination of the brine of the hollow fiber membrane, thereby ensuring the salt concentration difference inside and outside the hollow fiber membrane and realizing continuous and rapid transfer of salt ions. Under the premise of ensuring continuous filtration production of silk fibroin, the use of pure water is effectively reduced, and salt recovery is achieved, thereby reducing waste and environmental pollution.

[0020] 3. The hollow fiber membrane coupled electrodialysis desalination process for high-salt solution of silk fibroin provided by the present invention has a reasonable design, and the regenerated silk fibroin can be continuously filtered and produced. It is suitable for industrial production, has a large processing capacity, can achieve efficient desalination, and is suitable for large-scale promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 A schematic diagram of a silk fibroin high-salt solution hollow fiber membrane coupled electrodialysis desalination process provided in Examples 1 to 4;

[0023] In the above figures, 1. hollow fiber membrane system; 2. electrodialysis system. DETAILED DESCRIPTION

[0024] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict. For the convenience of description, if the words "upper", "lower", "left" and "right" appear below, they only indicate that the upper, lower, left and right directions are consistent with the accompanying drawings themselves, and do not limit the structure.

[0025] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments of the following disclosure.

[0026] like Figure 1 As shown, the present invention provides a hollow fiber membrane coupled electrodialysis desalination process for silk fibroin high-salt solution, comprising a hollow fiber membrane system 1 and an electrodialysis system 2, wherein the electrodialysis system 2 comprises an electrodialysis membrane stack, pure water, a cathode and an anode, and the electrodialysis membrane stack comprises an anion exchange homogeneous membrane and a cation exchange homogeneous membrane, and the specific steps are as follows:

[0027] S1, adding the silk fibroin solution to be desalted to the inner side of the membrane filament of the hollow fiber membrane system 1, the outer side of the membrane filament of the hollow fiber membrane system 1 is pure water, the membrane filament is a coarse-pore membrane filament, the pore size of the membrane filament is 0.5mm-1.2mm, and the use of coarse-pore membrane filament can effectively reduce the circulation resistance and reduce the severe shearing of the membrane filament on the protein;

[0028] S2, the hollow fiber membrane system 1 uses an internal pressure cross-flow filtration method to make pure water receive salt to form hollow fiber membrane brine, and the hollow fiber membrane system 1 adopts a low membrane surface flow rate and a low transmembrane pressure difference, the membrane surface flow rate is 0.05m / s to 0.5m / s, and the transmembrane pressure difference is less than 0.1MPa, so as to avoid severe shearing of silk fibroin;

[0029] S3, introducing the hollow fiber membrane brine produced in step S2 into the electrodialysis system, the hollow fiber membrane brine does not contain silk fibroin, the hollow fiber membrane brine is desalted in the electrodialysis membrane stack, the pure water in the electrodialysis system 2 receives the salt to form concentrated brine, and the desalted hollow fiber membrane brine is formed into fresh water;

[0030] S4, introducing the fresh water in the electrodialysis system 2 to the outside of the membrane fibers of the hollow fiber membrane system 1, and cyclically performing steps S1 to S4;

[0031] S5, concentration stage, the pressure of the hollow fiber membrane system 1 is increased, the transmembrane pressure difference is 0.1 MPa, the membrane surface flow rate is maintained at a low level, and the silk fibroin solution is concentrated until the concentration reaches 2-5%.

[0032] Example 1: Lithium bromide solution of silk fibroin, protein concentration 3%, conductivity 62 ms / cm.

[0033] The hollow fiber membrane has a molecular weight cutoff of 10KD and an area of ​​0.3㎡. The internal circulating liquid of the hollow fiber membrane is 1L of silk protein solution, with a flow rate of 0.3m / s and a temperature control of 5-15℃; the initial external circulation of the hollow fiber membrane is 2L of pure water, with a flow rate of 0.5m / s. The electrodialysis membrane stack is 0.15㎡, with a maximum voltage of 12V and a maximum current of 4A. The electrodialysis polar water is a 3% sodium sulfate aqueous solution; concentrated water: initially 1L of pure water, and new water is replaced when the salt concentration reaches 20%; fresh water: 2L of external circulating water connected to the hollow fiber membrane through a pipe, with a flow rate of 0.5m / s. After continuous operation for 7h, the silk protein solution concentration is 3%, the conductivity is 90μs / cm, and there is no gelation phenomenon.

[0034] Example 2: Lithium bromide solution of silk fibroin, protein concentration 2%, conductivity 43.2 ms / cm.

[0035] The hollow fiber membrane has a molecular weight cutoff of 2KD and an area of ​​0.3㎡. The internal circulating liquid of the hollow fiber membrane is 1L of silk protein solution, with a flow rate of 0.3m / s and a temperature control of 10-20℃; the initial external circulation of the hollow fiber membrane is 2L of pure water, with a flow rate of 0.5m / s. The electrodialysis membrane stack is 0.15㎡, with a maximum voltage of 12V and a maximum current of 4A. The electrodialysis polar water is a 3% sodium sulfate aqueous solution; concentrated water: 1L of initial pure water, and new water is replaced when the salt concentration reaches 20%; fresh water: 2L of external circulating water connected to the hollow fiber membrane through a pipe, with a flow rate of 0.5m / s. After continuous operation for 6h, the silk protein solution concentration is 3%, the conductivity is 98μs / cm, and there is no gelation phenomenon.

[0036] Example 3: Calcium chloride solution of silk fibroin, protein concentration 2%, conductivity 35ms / cm. Hollow fiber membrane cutoff molecular weight 10KD, area 0.3㎡, hollow fiber membrane internal circulation liquid is 1L silk fibroin solution, flow rate 0.3m / s, temperature control 10-15℃; hollow fiber membrane external circulation initially 2L pure water, flow rate 0.5m / s. Electrodialysis membrane stack 0.15㎡, set maximum voltage 12V, set maximum current 4A. Electrodialysis polar water is 3% sodium sulfate aqueous solution (sulfuric acid adjusts pH 3); concentrated water: 1L pure water, replace with new water when salt concentration reaches 15%; fresh water: connect 2L of hollow fiber membrane external circulation water through a pipe, flow rate 0.5m / s. Continuous operation for 5h, silk fibroin solution concentration 2%, conductivity 45μs / cm, no gelation phenomenon.

[0037] Example 4: Calcium chloride solution of silk fibroin, protein concentration 3%, conductivity 45ms / cm. Hollow fiber membrane cutoff molecular weight 20KD, area 0.3㎡, hollow fiber membrane internal circulation liquid is 1L silk fibroin solution, flow rate 0.3m / s, temperature control 5-10℃; hollow fiber membrane external circulation initially 2L pure water, flow rate 0.5m / s. Electrodialysis membrane stack 0.15㎡, set maximum voltage 12V, set maximum current 4A. Electrodialysis polar water is 3% sodium sulfate aqueous solution (sulfuric acid adjusts pH 3); concentrated water: 1L pure water, replace with new water when salt concentration reaches 15%; fresh water: connect 2L of hollow fiber membrane external circulation water through a pipe, flow rate 0.5m / s. Continuous operation for 6h, silk fibroin solution concentration 5%, conductivity 140μs / cm, no gelation phenomenon.

[0038] In Examples 1 to 4, the process provided by the present invention is used to purify lithium bromide solutions and calcium chloride solutions of silk fibroin of different concentrations, effectively avoiding the gelation of silk fibroin; at the same time, for salt solutions with higher protein concentrations, a longer continuous operation time is required, but the overall time required is within an acceptable range for industrial production.

[0039] Specifically, the hollow fiber membrane system 1 adopts large-pore membrane filaments and low flow rate to avoid the problem of shearing and precipitation of silk fibroin, which not only ensures the production quality of regenerated silk fibroin, but also does not cause frequent fouling and clogging of the electrodialysis membrane stack of the electrodialysis system 2, and can form continuous filtration production to meet the needs of industrial production; in addition, the hollow fiber membrane system 1 adopts the method of desalting first and then concentrating, and the ultrafiltration concentration time is extremely short, which does not cause shearing and precipitation of silk fibroin, and realizes high concentration of protein solution after desalination. Further, the electrodialysis system 2 coupled with the hollow fiber membrane system 1 adopts ion exchange membrane, i.e., anion exchange homogeneous membrane and cation exchange homogeneous membrane, to realize continuous desalination of hollow fiber membrane brine, ensure the salt concentration difference inside and outside the hollow fiber membrane, realize continuous and rapid transfer of salt ions, and effectively reduce the use of pure water under the premise of ensuring continuous filtration and production of silk fibroin, and realize salt recovery, reduce waste, and reduce pollution to the environment. In the electrodialysis system 2, Examples 1 to 4 adopt the method of replacing new water when the salt concentration of the concentrated brine reaches 15%, which further ensures the required pure water in the system, has a relatively high water utilization rate, can effectively reduce the industrial production cost of regenerated silk fibroin, and is conducive to the industrialization of regenerated silk fibroin.

[0040] Considering the increase in the transmembrane pressure difference in step S5, in order to ensure the filtering effect inside and outside the membrane fibers, the present invention adopts a membrane surface flow rate in step S5 that is 5 to 10% smaller than the membrane surface flow rate in step S2, thereby avoiding denaturation and precipitation of silk fibroin under the premise of increasing the transmembrane pressure difference.

[0041] In order to improve the processing quality of silk fibroin in the hollow fiber membrane system 1, the membrane fibers provided by the present invention adopt hydrophilic membrane materials, such as PES (polyethersulfone resin), hydrophilic modified PES, PVDF (polyvinylidene fluoride), hydrophilic modified PVDF, modified PP (polypropylene), modified PTFE (polytetrafluoroethylene), modified polysulfone, etc. In this way, the membrane fibers have high permeability, high selectivity and high chemical stability, and can efficiently separate the salt solution in the silk fibroin, so that the transmembrane pressure difference of the operating chamber is lower, and the damage to the silk fibroin molecules is reduced.

[0042] Furthermore, the membrane fibers in the hollow fiber membrane system 1 of the present invention are ultrafiltration membranes, which have more stable water permeability, lower transmembrane pressure difference, lower frequency of chemical cleaning, and can retain molecular weight of 2KD to 50KD, thereby ensuring the processing efficiency of regenerated silk fibroin.

[0043] In order to ensure the filtering stability of the electrodialysis system 2, the electrodialysis provided by the present invention adopts a DC power supply to form a DC electric field, and adopts a constant current and constant voltage automatic switching mode, which is implemented by a power management chip, thereby ensuring that the electrodialysis system 2 can maintain stable filtering performance under the influence of external floating factors.

[0044] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A process for desalination of silk fibroin high-salt solution by hollow fiber membrane coupled electrodialysis, characterized in that: It includes a hollow fiber membrane system and an electrodialysis system, wherein the electrodialysis system includes an electrodialysis membrane stack, pure water, a cathode and an anode, and the electrodialysis membrane stack includes an anion exchange homogeneous membrane and a cation exchange homogeneous membrane. The specific steps are as follows: S1, adding the silk fibroin solution to be desalted to the inner side of the membrane filament of the hollow fiber membrane system, the outer side of the membrane filament of the hollow fiber membrane system is pure water, the membrane filament is a coarse pore membrane filament, and the pore size of the membrane filament is 0.5mm-1.2mm; S2, the hollow fiber membrane system uses an internal pressure cross-flow filtration method to make pure water absorb salt to form hollow fiber membrane brine, and the hollow fiber membrane system adopts low membrane surface flow rate and low transmembrane pressure difference; S3, introducing the hollow fiber membrane brine produced in step S2 into the electrodialysis system, the hollow fiber membrane brine does not contain silk fibroin, the hollow fiber membrane brine is desalted in the electrodialysis membrane stack, the pure water in the electrodialysis system receives the salt to form concentrated brine, and the desalted hollow fiber membrane brine is converted into fresh water; S4, introducing fresh water in the electrodialysis system into the outer side of the membrane fibers of the hollow fiber membrane system, and cyclically performing steps S1 to S4; S5, concentration stage, pressurizing the hollow fiber membrane system, maintaining a low membrane surface flow rate, and concentrating until the concentration of the silk fibroin solution reaches 2-5%.

2. The process for desalination of a silk fibroin high-salt solution by hollow fiber membrane coupling electrodialysis according to claim 1, characterized in that: The low membrane surface velocity in steps S2 and S5 is 0.05 m / s to 0.5 m / s.

3. The process for desalination of silk fibroin high-salt solution by hollow fiber membrane coupled electrodialysis according to claim 2, characterized in that: The low membrane surface flow rate in step S5 is 5-10% smaller than the low membrane surface flow rate in step S2.

4. A silk fibroin high-salt solution hollow fiber membrane coupled electrodialysis desalination process according to claim 3, characterized in that: The transmembrane pressure difference in step S2 is less than 0.1 MPa, and the transmembrane pressure difference in step S5 is 0.1 MPa.

5. A silk fibroin high-salt solution hollow fiber membrane coupled electrodialysis desalination process according to claim 1 or 4, characterized in that: The membrane fibers in the hollow fiber membrane system are hydrophilic membrane materials.

6. A silk fibroin high-salt solution hollow fiber membrane coupled electrodialysis desalination process according to claim 5, characterized in that: The membrane fibers in the hollow fiber membrane system are ultrafiltration membranes with a molecular weight cutoff of 2KD to 50KD.

7. A process for desalination of a silk fibroin high-salt solution by hollow fiber membrane coupling electrodialysis according to claim 1 or 6, characterized in that: The electrodialysis uses a direct current power supply to form a direct current electric field, and adopts a constant current and constant voltage automatic switching mode.

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