Silk fibroin solution desalination and concentration system based on multi-stage membrane separation coordinated regulation

Abstract

The invention discloses a silk fibroin solution desalination and concentration system based on multi-stage membrane separation coordinated regulation, which breaks through the limitation of the traditional single membrane separation technology through integrated optimization of a microfiltration-washing filtration desalination-concentration three-stage membrane separation process, and realizes step-by-step precise treatment of a silk fibroin solution. In the microfiltration stage, macromolecular impurities are removed through synergism of dilution and pre-filtration, and a stable raw material is provided for subsequent precise separation; dynamic filter washing and membrane screening effects are combined in the filter washing and desalting stage, so that the desalting efficiency is remarkably improved; in the concentration stage, through membrane interception and volume regulation and control, the target concentration is realized while the salinity is reduced, protein aggregation is avoided, and stable product quality is ensured. Through multi-dimensional linkage of the conductivity sensor, the liquid level sensor and the pH sensor, automatic closed-loop control over the desalination degree, the concentration end point and wastewater discharge is achieved. The dynamic filter washing and secondary purification trigger mechanism ensures the consistency between batches, and the purity of the final product and the process stability are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of silk fibroin production technology, specifically to a silk fibroin solution desalting and concentration system based on multi-stage membrane separation synergistic regulation. Background Technology

[0002] In the field of biomaterials, silk fibroin has attracted much attention due to its excellent biocompatibility, biodegradability, and mechanical properties. To prepare high-quality silk fibroin solutions, degummed raw silk is typically dissolved in a high-concentration lithium bromide solution to form an inorganic salt solution of silk fibroin. However, this process often results in incompletely dissolved degummed raw silk residue. If these residues are not properly treated, they can impair subsequent filtration and membrane treatment steps, affecting the purity and quality of the silk fibroin solution.

[0003] Traditional filtration and desalination methods face numerous challenges when processing inorganic salt solutions of silk fibroin. On one hand, the high viscosity of the solution makes filtration difficult and prone to clogging the filter membrane. On the other hand, the removal of inorganic salt ions requires an efficient and continuous desalination process, but traditional desalination methods are often inefficient and cannot meet the needs of large-scale production. Furthermore, maintaining the integrity of silk fibroin molecules during desalination and preventing their damage is also a pressing issue that needs to be addressed in current technology. Summary of the Invention

[0004] To address the above technical problems, this invention provides a silk fibroin solution desalting and concentration system based on multi-stage membrane separation synergistic regulation, which utilizes the hollow fiber membrane tangential flow filtration principle to sequentially filter, wash, desalt, and concentrate the silk fibroin salt solution.

[0005] This invention is achieved through the following technical solution:

[0006] The first aspect of this invention provides a silk fibroin solution desalting and concentration system based on multi-stage membrane separation synergistic regulation, comprising the following steps:

[0007] (1) Degumming treatment of silkworm cocoons, dissolving the degummed raw silk in lithium bromide solution to obtain silk fibroin salt solution;

[0008] (2) Pass the silk fibroin salt solution obtained in step (1) into the first storage tank of the filtration unit, dilute it with water by 5-10 times, and filter it with a microfiltration membrane with a pore size of 0.45μm to obtain silk fibroin filtrate.

[0009] (3) Pass the silk fibroin filtrate obtained in step (2) into the second storage tank of the washing and desalting unit, and perform dialysis filtration using an ultrafiltration membrane with a molecular weight cutoff of 5 kDa. At the same time, inject water into the second storage tank at a flow rate equal to that of the permeate until the conductivity is ≤100 μS / cm to obtain the silk fibroin dialysis solution.

[0010] (4) Pass the silk fibroin dialysis solution obtained in step (3) into the third storage tank of the concentration unit, and use an ultrafiltration membrane with a molecular weight cutoff of 5 kDa for dialysis filtration and concentration. The volume of the concentrated solution is 150%-250% of the volume of the silk fibroin salt solution passed into the filtration unit in step (2), and the conductivity of the concentrated solution is ≤200 μS / cm, to obtain the desalted concentrated solution of silk fibroin.

[0011] This invention constructs a gradient desalting and concentration technology system for silk fibroin solutions based on multi-stage membrane separation and synergistic regulation. The method achieves efficient desalting and precise concentration of silk fibroin solutions through gradient coupling of three stages: microfiltration (i.e., filtration), dynamic elution (i.e., elution desalting), and tangential flow concentration. Specifically, the microfiltration stage uses a microfiltration membrane with a specific pore size to remove undissolved protein aggregates and impurities; the dynamic elution stage utilizes the molecular sieving effect of the ultrafiltration membrane and a simultaneous water replacement mechanism to synergistically desalinate, achieving a preset desalination standard; and the concentration stage combines transmembrane pressure drive and conductivity feedback control to achieve simultaneous regulation of the final volume and salinity.

[0012] Further, in step (1), the concentration of lithium bromide in the lithium bromide solution is 9-10 M.

[0013] Further, in step (1), the concentration of silk fibroin in the silk fibroin salt solution is 15-18 wt%.

[0014] Furthermore, in step (2), the microfiltration membrane is a hollow fiber membrane.

[0015] Further, in step (2), the inner diameter of the microfiltration membrane is 2.0-4.0 mm, and the ratio of the inner diameter to the average thickness of the microfiltration membrane is (8-12):1.

[0016] Furthermore, in step (2), the operating loading of the microfiltration membrane is 0.3-0.5 mL / cm³. 2 (Calculated based on the volume of silk fibroin salt solution passed into the filtration unit).

[0017] Furthermore, in step (2), the material of the microfiltration membrane is polyethersulfone.

[0018] Furthermore, in step (2), the operating parameters of the microfiltration membrane include: a shear force of 4000-5000 s. -1 The inlet pressure is 2.0-3.0 bar, the reflux pressure is 1.5-2.5 bar, the transmembrane pressure (TMP) is 1.8-2.8 bar, and the filtration rate is 15-20 LMH.

[0019] In step (2), through the synergistic effect of dilution and microfiltration membrane, a physicochemically stable filtrate is provided for the subsequent ultrafiltration membrane separation process. Controllable dilution significantly reduces the viscosity of the silk fibroin salt solution (≤15 mPa·s, 25℃), reducing fluid resistance and avoiding membrane pore blockage and decreased mass transfer efficiency caused by high viscosity. Utilizing the sieving effect of the microfiltration membrane, incompletely dissolved silk fibroin aggregates and large molecular impurities remaining after degumming (such as sericin fragments) are selectively retained, preventing these mechanical particles from scratching or deeply contaminating the downstream ultrafiltration membrane surface.

[0020] Specifically, in step (2), the filtration unit includes: a first storage tank and a first filter element. The inlet of the first storage tank is connected to a first water inlet pipe and a silk fibroin salt solution inlet channel. The outlet of the first storage tank is connected to the inlet of the first filter element. The return outlet of the first filter element is connected to the inlet of the first storage tank. The first filter element includes a microfiltration membrane.

[0021] Specifically, in step (2), the first water inlet pipe of the first storage tank is connected to a water peristaltic pump, the sample inlet pipe of the first filter element is connected to the output port of the first storage tank and the input port of the first filter element, the sample inlet pipe is connected to a first pump, the return liquid pipe of the first filter element is connected to the return liquid port of the first filter element and the input port of the first storage tank, and the permeate liquid pipe of the first filter element is connected to the output port of the first filter element and the input port of the second storage tank.

[0022] Specifically, the first pump is a peristaltic pump.

[0023] Specifically, in step (2), turbine flow meters and pressure sensors are installed on the inlet pipe, return pipe, and permeate pipe of the first filter element. The pressure sensor monitors the pressure of the solution in the channel in real time. If the pressure value is too high, it is determined that the first filter element is blocked, resulting in increased flow resistance of the solution. The first pump needs to be stopped in time, and the first filter element needs to be inspected and cleaned to avoid damage to the equipment. If the pressure value is too low, it is determined that the first pump is faulty or there is a leak in the pipeline. The corresponding components need to be inspected and repaired.

[0024] Specifically, in step (2), the silk fibroin salt solution obtained in step (1) is passed into the first storage tank of the filtration mechanism, and the water peristaltic pump of the first water inlet pipe is turned on to dilute the silk fibroin salt solution. After dilution, the peristaltic pump of the sample inlet tube of the first filter element is turned on, and the diluted silk fibroin salt solution is filtered by a microfiltration membrane until only 5% circulating liquid remains in the first storage tank (to avoid completely emptying the storage tank and causing the membrane surface to dry out). All the filtrate obtained enters the second storage tank.

[0025] Furthermore, in step (3), the ultrafiltration membrane is a hollow fiber membrane.

[0026] Further, in step (3), the inner diameter of the ultrafiltration membrane is 1.5-2.0 mm, the ratio of the inner diameter to the average thickness of the ultrafiltration membrane is (18-22):1, and the porosity of the ultrafiltration membrane is 35%-45%.

[0027] Furthermore, in step (3), the material of the ultrafiltration membrane is polyethersulfone.

[0028] Further, in step (3), the operating loading of the ultrafiltration membrane is 0.05-0.1 mL / cm³. 2 .

[0029] Furthermore, in step (3), the operating parameters of the ultrafiltration membrane include: a shear force of 2000-3000 s. -1 The inlet pressure is 1.0-1.7 bar, the reflux pressure is 0.8-1.5 bar, the transmembrane pressure is 0.9-1.6 bar, and the filtration rate is 9-16 LMH.

[0030] In step (3), based on the synergistic mechanism of tangential flow filtration and dynamic washing, efficient desalination is achieved through the sieving effect and diffusion mass transfer of the ultrafiltration membrane. A hollow fiber membrane with a molecular weight cutoff of 5 kDa is used to selectively retain large molecules of silk fibroin, while allowing small molecule salt ions such as lithium bromide (molecular weight < 0.1 kDa) to freely pass through the membrane pores into the permeate. Water is injected synchronously at a flow rate equal to that of the permeate (9-16 LMH), and the solute concentration of the liquid phase in the membrane system is changed by continuous displacement, establishing a transmembrane diffusion driving force and accelerating the migration of salt ions to the permeate side.

[0031] Specifically, in step (3), the washing and desalination unit includes: a second storage tank and a second filter element. The inlet of the second storage tank is connected to the outlet of the first filter element and is connected to a second water inlet pipe. The outlet of the second storage tank is connected to the inlet of the second filter element. The reflux outlet of the second filter element is connected to the inlet of the second storage tank and the inlet of the third storage tank, respectively. The second filter element includes an ultrafiltration membrane.

[0032] Specifically, in step (3), the second water inlet pipe of the second storage tank is connected to a water peristaltic pump, the sample inlet pipe of the second filter element is connected to the output port of the second storage tank and the input port of the second filter element, the sample inlet pipe is connected to a second pump, a part of the return liquid pipe of the second filter element is connected to the return liquid port of the second filter element and the input port of the second storage tank, the other part of the return liquid pipe of the second filter element is connected to the return liquid port of the second filter element and the input port of the second storage tank, and the permeate liquid pipe of the second filter element discharges wastewater.

[0033] Specifically, the second pump is a peristaltic pump.

[0034] Specifically, in step (3), the sample inlet tube, the return liquid tube and the permeate liquid tube are equipped with turbine flow meters and pressure sensors, and the blockage of the hollow fiber membrane can be observed by monitoring the turbine flow meters and pressure sensors.

[0035] Specifically, in step (3), the liquid pipe is connected to a pH detection sensor to detect the pH of the wastewater before it is discharged to the sewage treatment room for treatment.

[0036] Specifically, in step (3), water is continuously injected into the second storage tank through the second water inlet pipe, and the water injection flow rate is adjusted by the water peristaltic pump of the second water inlet pipe. The diluted silk fibroin filtrate is pumped into the second filter element through the peristaltic pump of the sample inlet pipe of the second filter element. The water injection flow rate is kept the same as the wastewater flow rate in the permeate pipe. When the volume of injected water and filtrate reaches 1:(0.8-1.2), one washing and filtration is completed. The washing and filtration is repeated 6-7 times until the conductivity of the silk fibroin dialysate drops below 100 μS / cm.

[0037] Furthermore, in step (4), the ultrafiltration membrane is a hollow fiber membrane.

[0038] In step (4), the silk fibroin solution is precisely concentrated through the efficient retention of the hollow fiber membrane. The sieving effect of the hollow fiber membrane (with a molecular weight cutoff of 5 kDa) is utilized to drive the volume compression of the solution through transmembrane pressure.

[0039] Further, in step (4), the inner diameter of the ultrafiltration membrane is 1.5-2.0 mm, the ratio of the inner diameter to the average thickness of the ultrafiltration membrane is (18-22):1, and the porosity of the ultrafiltration membrane is 35%-45%.

[0040] Furthermore, in step (4), the material of the ultrafiltration membrane is polyethersulfone.

[0041] Furthermore, in step (4), the operating loading of the ultrafiltration membrane is 0.1-0.2 mL / cm³. 2 .

[0042] Furthermore, in step (4), the operating parameters of the ultrafiltration membrane include: a shear force of 2000-3000 s. -1 The inlet pressure is 1.0-1.7 bar, the reflux pressure is 0.8-1.5 bar, the transmembrane pressure is 0.9-1.6 bar, and the filtration rate is 9-16 LMH.

[0043] Further, in step (4), when the conductivity of the concentrate is ≤200μS / cm, the silk fibroin desalted concentrate is discharged from the sample outlet; when the conductivity of the concentrate is >200μS / cm, a secondary purification procedure is triggered: the top water valve of the third storage tank is opened, and water is injected at a flow rate equal to that of the real-time permeate in step (4) until the conductivity reaches the standard and the volume of the concentrate is 150%-250% of the volume of the silk fibroin salt solution passed into the filter unit in step (2).

[0044] Specifically, in step (4), the concentration unit includes: a third storage tank and a third filter element. The inlet of the third storage tank is connected to the reflux pipe of the second filter element and is connected to a third water inlet pipe. The first outlet of the third storage tank is connected to the inlet of the third filter element. The second outlet of the third storage tank is the outlet of the desalted concentrated silk fibroin solution. The reflux port of the third filter element is connected to the inlet of the third storage tank. The third filter element includes an ultrafiltration membrane.

[0045] Specifically, in step (4), the third water inlet pipe of the third storage tank is connected to a water peristaltic pump, the sample inlet pipe of the third filter element is connected to the output port of the third storage tank and the input port of the third filter element, the sample inlet pipe is connected to a third pump, the return liquid pipe of the third filter element is connected to the output port of the third filter element and the input port of the third storage tank, and the permeate liquid pipe of the third filter element discharges wastewater.

[0046] Specifically, the third pump is a peristaltic pump.

[0047] Specifically, in step (4), the sample inlet tube, the return liquid tube and the permeate liquid tube are equipped with turbine flow meters and pressure sensors, and the blockage of the hollow fiber membrane can be observed by monitoring the turbine flow meters and pressure sensors.

[0048] Specifically, in step (4), when the conductivity of the silk fibroin dialysate in the second filter element drops below 100 μS / cm, the valve connecting the inlet of the third storage tank on the reflux pipe of the second filter element is opened, so that the dialysate after washing and desalting is passed into the third storage tank of the concentration unit. The dialysate is pumped into the third filter element by the peristaltic pump of the sample inlet tube of the third filter element, and the dialysate is concentrated by using a hollow fiber membrane.

[0049] Specifically, in step (4), the liquid pipe is connected to a pH detection sensor to detect the pH of the wastewater before it is discharged to the sewage treatment room for treatment.

[0050] Specifically, in step (4), the volume of the concentrated solution is determined by a liquid level sensor installed in the third storage tank according to the actual usage, thereby obtaining the desalted concentrate of the silk fibroin solution.

[0051] Furthermore, the first, second, and third storage tanks are all equipped with conductivity detectors.

[0052] The silk fibroin solution desalting and concentration system provided by this invention consists of a multi-stage membrane separation unit, a storage tank, and an automated detection module. Closed-loop linkage of level, conductivity, and pH sensors ensures process stability. This invention significantly reduces the risk of membrane fouling and improves desalting and concentration efficiency through membrane module flow channel optimization and parameterized synergy of shear force and transmembrane pressure. Furthermore, the use of dynamic displacement and threshold triggering mechanisms further reduces system dead volume, ensuring uniformity of final product concentration and recovery rate, providing a green and controllable solution for large-scale silk fibroin production.

[0053] The beneficial effects of this invention are:

[0054] 1. This invention overcomes the limitations of traditional single-membrane separation technologies by integrating and optimizing a three-stage membrane separation process of microfiltration, washing and desalting, and concentration, achieving precise step-by-step processing of silk fibroin solutions. The microfiltration stage removes large molecular impurities through dilution and pre-filtration, providing a stable raw material for subsequent precision separation; the washing and desalting stage combines dynamic washing and membrane sieving to significantly improve desalting efficiency; and the concentration stage, through membrane retention and volume control, achieves the target concentration while reducing salt content, preventing protein aggregation and ensuring stable product quality.

[0055] 2. This invention employs optimized membrane structure design and operating parameters (such as shear force control and transmembrane pressure regulation), combined with a real-time pressure and flow monitoring mechanism, to effectively reduce the risk of membrane fouling and extend service life. The unique membrane material (polyethersulfone) and tangential flow filtration mode further reduce protein adsorption, ensuring long-term continuous operation of the system.

[0056] 3. This invention achieves automated closed-loop control of desalination degree, concentration endpoint, and wastewater discharge through multi-dimensional linkage of conductivity, liquid level, and pH sensors. Dynamic washing and secondary purification triggering mechanisms ensure batch-to-batch consistency, significantly improving the purity of the final product and process stability. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the structure of the silk fibroin solution desalting and concentration system provided by the present invention.

[0058] Figure 2 This is a schematic diagram illustrating the working principle of the hollow fiber membrane provided by the present invention.

[0059] Figure 3 The image shows the outer wall of the hollow fiber membrane with a molecular weight cutoff of 5 kDa provided by this invention.

[0060] Figure 4This is a graph showing the changes in inlet pressure and reflux pressure of the washing and desalination unit in Example 1 over time.

[0061] Figure 5 This is a graph showing the change in filtration rate over time in the washing, filtration and desalination unit of Example 1.

[0062] Figure 6 This is a graph showing the change in conductivity of the silk fibroin dialysis solution in the washing, filtration and desalting unit of Example 1 over time.

[0063] Figure 7 This is a graph showing the change in conductivity over time of the desalted concentrate of the silk fibroin solution in the concentration unit of Example 1. Detailed Implementation

[0064] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0065] This invention provides a silk fibroin solution desalting and concentration system, comprising the following steps:

[0066] (1) Degumming treatment of silkworm cocoons, dissolving the degummed raw silk in lithium bromide solution to obtain silk fibroin salt solution;

[0067] (2) Pass the silk fibroin salt solution obtained in step (1) into the first storage tank of the filtration unit, dilute it with water by 5-10 times, and filter it with a microfiltration membrane with a pore size of 0.45μm to obtain silk fibroin filtrate.

[0068] (3) Pass the silk fibroin filtrate obtained in step (2) into the second storage tank of the washing and desalting unit, and use a hollow fiber membrane with a molecular weight cutoff of 5kDa for dialysis filtration. At the same time, inject water into the second storage tank at a flow rate equal to that of the permeate until the conductivity is ≤100μS / cm to obtain silk fibroin dialysis solution.

[0069] (4) The silk fibroin dialysis solution obtained in step (3) is fed into the third storage tank of the concentration unit and concentrated by dialysis filtration using a hollow fiber membrane with a molecular weight cutoff of 5 kDa. The final volume of the concentration is 200% of the initial volume, and the conductivity of the concentrate is ≤200 μS / cm, thus obtaining the desalted concentrate of the silk fibroin solution.

[0070] In one embodiment of the present invention, in step (2), the filtration unit includes: a first storage tank and a first filter element, the inlet of the first storage tank is externally connected to a first water inlet pipe and a silk fibroin salt solution inlet channel, the outlet of the first storage tank is connected to the inlet of the first filter element, and the return outlet of the first filter element is connected to the inlet of the first storage tank; the first filter element includes a microfiltration membrane.

[0071] In one embodiment of the present invention, in step (2), the first water inlet pipe of the first storage tank is connected to a water peristaltic pump, the sample inlet pipe of the first filter element is connected to the output port of the first storage tank and the input port of the first filter element, the sample inlet pipe is connected to a first pump, the return liquid pipe of the first filter element is connected to the return liquid port of the first filter element and the input port of the first storage tank, and the permeate liquid pipe of the first filter element is connected to the output port of the first filter element and the input port of the second storage tank.

[0072] In one embodiment of the present invention, in step (2), a turbine flow meter and a pressure sensor are installed on the sample inlet tube, the return liquid tube and the permeate liquid tube of the first filter element.

[0073] In one embodiment of the present invention, in step (3), the washing and desalination unit includes: a second storage tank and a second filter element, the inlet of the second storage tank is connected to the outlet of the first filter element and is externally connected to a second water inlet pipe, the outlet of the second storage tank is connected to the inlet of the second filter element, and the reflux outlet of the second filter element is connected to the inlet of the second storage tank and the inlet of the third storage tank; the second filter element includes an ultrafiltration membrane.

[0074] In one embodiment of the present invention, in step (3), the ultrafiltration membrane is a hollow fiber membrane.

[0075] In one embodiment of the present invention, in step (3), the second water inlet pipe of the second storage tank is connected to a water peristaltic pump, the sample inlet pipe of the second filter element is connected to the output port of the second storage tank and the input port of the second filter element, the sample inlet pipe is connected to a second pump, a part of the return liquid pipe of the second filter element is connected to the return liquid port of the second filter element and the input port of the second storage tank, the other part of the return liquid pipe of the second filter element is connected to the return liquid port of the second filter element and the input port of the second storage tank, and the permeate liquid pipe of the second filter element discharges wastewater.

[0076] In one embodiment of the present invention, in step (3), the sample inlet tube, the return liquid tube and the permeate liquid tube are equipped with a turbine flow meter and a pressure sensor.

[0077] In one embodiment of the present invention, in step (3), the permeable liquid tube is connected to a pH detection sensor.

[0078] In one embodiment of the present invention, in step (4), the concentration unit includes: a third storage tank and a third filter element. The inlet of the third storage tank is connected to the reflux pipe of the second filter element and is externally connected to a third water inlet pipe. The first outlet of the third storage tank is connected to the inlet of the third filter element. The second outlet of the third storage tank is the outlet of the desalted concentrate of the silk fibroin solution. The reflux port of the third filter element is connected to the inlet of the third storage tank. The third filter element includes an ultrafiltration membrane.

[0079] In one embodiment of the present invention, in step (4), the ultrafiltration membrane is a hollow fiber membrane.

[0080] In one embodiment of the present invention, in step (4), the third water inlet pipe of the third storage tank is connected to a water peristaltic pump, the sample inlet pipe of the third filter element is connected to the output port of the third storage tank and the input port of the third filter element, the sample inlet pipe is connected to a third pump, the return liquid pipe of the third filter element is connected to the output port of the third filter element and the input port of the third storage tank, and the permeate liquid pipe of the third filter element discharges wastewater.

[0081] In one embodiment of the present invention, in step (4), the sample inlet tube, the return liquid tube and the permeate liquid tube are equipped with a turbine flow meter and a pressure sensor.

[0082] In one embodiment of the present invention, in step (4), the permeable liquid tube is connected to a pH detection sensor.

[0083] In one embodiment of the present invention, the first storage tank, the second storage tank and the third storage tank are also equipped with a conductivity detector.

[0084] In one embodiment of the present invention, the first, second, and third pumps are all peristaltic pumps, capable of accurate metering and providing precise flow control. By adjusting the pump speed and frequency, precise metering and control can be achieved to meet the flow accuracy requirements of different processes. The fluid only comes into contact with the pipes or fittings, and no contamination occurs inside the pump.

[0085] A schematic diagram of the silk fibroin solution desalting and concentration system provided by this invention is shown below. Figure 1 As shown in the diagram, the working principle of the hollow fiber membrane provided by this invention is as follows: Figure 2 As shown, the outer wall scanning electron microscope (SEM) image of the hollow fiber membrane with a molecular weight cutoff of 5 kDa provided by the present invention is as follows. Figure 3 As shown.

[0086] In one embodiment of the present invention, the silk fibroin solution desalination and concentration system contains a silk fibroin salt solution to be concentrated in a first storage tank. Water is injected into the first storage tank through a first water inlet pipe to dilute the silk fibroin salt solution. The diluted silk fibroin inorganic salt solution is filtered through a microfiltration membrane and then enters a second storage tank. Water is continuously injected into the second storage tank through a second water inlet pipe, and the silk fibroin inorganic salt solution in the second storage tank is continuously washed and filtered with a second filter element to further reduce the inorganic salt content in the second storage tank. After the inorganic salt content in the second storage tank is not higher than a preset value, the silk fibroin solution in the second storage tank is allowed to pass through the second filter element and enter a third storage tank. The silk fibroin solution is concentrated in the third storage tank to increase the concentration of silk fibroin. The concentrated silk fibroin inorganic salt solution in the third storage tank is further washed, filtered, and desalted through a third water inlet pipe to ensure that the silk fibroin concentration meets the standard while avoiding excessively high inorganic salt concentration.

[0087] In one embodiment of the present invention, a first check valve is connected to the channel between the output port of the second filter element and the input port of the second storage tank; a second check valve is connected to the channel between the output port of the third filter element and the input port of the third storage tank. Both the first check valve and the second check valve are solenoid valves.

[0088] In one embodiment of the present invention, the first filter element employs a microfiltration membrane constructed from polyethersulfone (PES) material with a pore size of 0.45 micrometers. This pore size design selectively traps fiber fragments, undissolved protein aggregates, and large molecular impurities in the degummed raw silk solution, while allowing solvents and small molecules to pass through efficiently. This microfiltration membrane combines chemical stability with mechanical strength advantages. Under the synergistic regulation of shear force and transmembrane pressure, it can effectively achieve primary clarification of the solution, significantly reduce fluid viscosity resistance, and minimize the risk of membrane fouling, providing a physicochemically homogeneous feed solution basis for subsequent precision desalination and concentration processes.

[0089] In one embodiment of the present invention, the hollow fiber membranes used in the second and third filter elements are constructed based on PES material, and their specific molecular weight cutoff (5kDa) design enables molecular sieving effects. This hollow fiber membrane, through optimized internal diameter-to-thickness ratio and porosity, combined with a tangential flow filtration mode, simultaneously achieves efficient desalination and concentration during dynamic rinsing. The hydrophilic modification of the membrane surface significantly reduces non-specific protein adsorption, its chemical stability supports a wide pH adaptation range, and the high packing density of the hollow fiber structure improves mass transfer efficiency. During the rinsing and desalination stage, large silk fibroin molecules are retained by the membrane, while inorganic salt ions enter the permeate side through sieving and diffusion. The shear force generated by the tangential flow suppresses concentration polarization on the membrane surface, and the dynamic displacement mechanism of simultaneous water injection establishes a transmembrane diffusion driving force, accelerating salt ion migration. In the concentration stage, volume compression is driven by transmembrane pressure, combined with a secondary purification procedure triggered by a conductivity threshold, ensuring precise and controllable concentration endpoints. This process achieves stable operation of the entire desalination and concentration process by synergistically controlling membrane separation and fluid dynamics, thereby reducing the risk of membrane fouling.

[0090] In one embodiment of the present invention, the volumes of the first and second storage tanks are both larger than the volume of the third storage tank. The first storage tank is mainly used to receive the silk fibroin inorganic salt solution to be filtered and to dilute it. Since the initial silk fibroin inorganic salt solution has a high viscosity at high concentrations, which is not conducive to subsequent filtration operations, it needs to be diluted by injecting deionized water. The larger volume can hold a sufficient amount of solution and deionized water to meet the requirements of different dilution ratios.

[0091] In one embodiment of the invention, the second storage tank is used for washing and desalting operations. During the washing process, deionized water needs to be continuously injected into the second storage tank to cooperate with the second filter element in desalting the silk fibroin filtrate. The larger volume can hold more solution and deionized water, meeting the needs of multiple washing operations. The larger volume provides ample space for this multiple washing operation, ensuring that the desalting process can proceed fully and achieve a better desalting effect.

[0092] In one embodiment of the present invention, the third storage tank is mainly used for concentrating the silk fibroin dialysis solution after washing, filtration, and desalting. The hollow fiber membrane module flow channel is optimized and combined with the fluid dynamics distribution in tangential flow filtration mode, which can effectively reduce the dead volume of the system and improve the mass transfer efficiency. During the concentration process, the liquid level sensor monitors the volume change of the storage tank in real time. When the concentrate reaches 200% of the initial volume, the conductivity detector (threshold ≤ 200 μS / cm) triggers the discharge program; if the conductivity exceeds the standard, the secondary purification program is automatically started, and the salt concentration is synchronously controlled through the synergistic effect of dynamic water injection and transmembrane diffusion. This design, through the deep coupling of membrane separation parameters and automated control, ensures the consistency of the final product concentration and the stability of its quality while avoiding protein adsorption loss.

[0093] The present invention will be further described below with reference to specific drawings and embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0094] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0095] Example 1

[0096] A silk fibroin solution desalting and concentration system based on multi-stage membrane separation synergistic regulation includes the following steps:

[0097] (1) Degumming treatment was performed on the silkworm cocoons, and the degummed raw silk was dissolved in lithium bromide solution (lithium bromide concentration was 10M) to obtain 500mL of silk fibroin salt solution with a concentration of 15wt%.

[0098] (2) Pass the 500 mL silk fibroin salt solution obtained in step (1) into the first storage tank of the filter unit, inject water into the first storage tank through the first water inlet pipe, dilute it 10 times with water until the volume of the diluted silk fibroin salt solution is 5 L; turn on the first pump so that the diluted silk fibroin salt solution passes through the first filter element, the reflux liquid (the large molecular impurities that are retained) goes to the first storage tank through the reflux liquid pipe, and the permeate (silk fibroin filtrate) goes to the second storage tank through the permeate liquid pipe.

[0099] The first filter element uses a microfiltration membrane with a pore size of 0.45 μm (material: polyethersulfone, inner diameter: 4.0 mm, inner diameter to average thickness ratio: 10:1, operating capacity: 0.3 mL / cm). 2 The shear force during operation is 4000s. -1The inlet pressure is 2.0-3.0 bar, the reflux pressure is 1.5-2.5 bar, the TMP is 1.8-2.8 bar, the filtration rate is 15-20 LMH, the pumping speed of the first pump is 1.3 L / min, and the conductivity of the silk fibroin filtrate is 39.9 mS / cm.

[0100] (3) Pass the silk fibroin filtrate obtained in step (2) into the second storage tank of the washing and desalting unit, turn on the second pump, so that the silk fibroin filtrate passes through the second filter element, the return liquid (silk fibroin filtrate after circulating desalting) goes to the second storage tank through the return liquid pipe, and the permeate (containing lithium bromide salt solution) is discharged into the wastewater treatment room through the permeate pipe; while the second filter element is running, turn on the water peristaltic pump connected to the second water inlet pipe to slowly replenish the second storage tank with deionized water (the flow rate of deionized water is consistent with the flow rate of permeate outlet, so that the total volume of solution in the second storage tank is constant at 5L) for washing and desalting.

[0101] The second filter element uses an ultrafiltration membrane with a molecular weight cutoff of 5 kDa (material: polyethersulfone, inner diameter: 1.5 mm, inner diameter to average thickness ratio: 20:1), and an operating flow rate of 0.1 mL / cm². 2 The shear force during operation is 3000s. -1 The inlet pressure is 1.0-1.7 bar, the reflux pressure is 0.8-1.5 bar, the TMP is 0.9-1.6 bar, the filtration rate is 9-16 LMH, the pumped deionized water is about 28 L (equivalent to a 5.6-fold dilution), the running time is 5 h, and the conductivity of the silk fibroin dialysate after washing and filtration is 87 μS / cm.

[0102] After the conductivity of the silk fibroin dialysate meets the standard, close the valve connecting the return port of the second filter to the second storage tank, and open the valve connecting the return port of the second filter to the third storage tank, so that the silk fibroin dialysate can flow into the third storage tank.

[0103] (4) The silk fibroin dialysate obtained in step (3) is fed into the third storage tank of the concentration unit, and the third pump is turned on so that the silk fibroin dialysate passes through the third filter element. The reflux liquid goes to the third storage tank through the reflux liquid pipe, and the permeate (containing lithium bromide salt solution) is discharged into the wastewater treatment room through the permeate liquid pipe for concentration.

[0104] The third filter element uses an ultrafiltration membrane with a molecular weight cutoff of 5 kDa (material: polyethersulfone, inner diameter: 1.5 mm, inner diameter to average thickness ratio: 20:1), and an operating flow rate of 0.1 mL / cm². 2 The shear force during operation is 2000s. -1The inlet pressure is 1.0-1.7 bar, the reflux pressure is 0.8-1.5 bar, the TMP is 0.9-1.6 bar, the filtration rate is 9-16 LMH, the running time is 1 hour, the volume of the concentrate is confirmed to be 1 L by the liquid level transmitter, and the conductivity of the desalted concentrate of the silk fibroin solution is 150 μS / cm, which meets the standard. The desalted concentrate of the silk fibroin solution flows out through the outlet of the third storage tank.

[0105] The data graph showing the changes in inlet pressure and reflux pressure of the washing and desalination unit over time in Example 1 is shown below. Figure 4 As shown in the figure, the data graph of the filtration rate of the washing and desalination unit in Example 1 changing with time is as follows. Figure 5 As shown in the figure, the conductivity of the silk fibroin dialysis solution in the washing, filtration and desalting unit of Example 1 changes over time. Figure 6 As shown in the figure, the conductivity of the desalted concentrate of the silk fibroin solution in the concentration unit of Example 1 changes over time. Figure 7 As shown.

[0106] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art should understand that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A silk fibroin solution desalting and concentration system based on multi-stage membrane separation synergistic regulation, characterized in that, Includes the following steps: (1) Degumming treatment of silkworm cocoons, dissolving the degummed raw silk in lithium bromide solution to obtain silk fibroin salt solution; (2) Pass the silk fibroin salt solution obtained in step (1) into the first storage tank of the filtration unit, dilute it with water by 5-10 times, and filter it with a microfiltration membrane with a pore size of 0.45μm to obtain silk fibroin filtrate. (3) Pass the silk fibroin filtrate obtained in step (2) into the second storage tank of the washing and desalting unit, and perform dialysis filtration using a microfiltration membrane with a molecular weight cutoff of 5 kDa. At the same time, inject water into the second storage tank at a flow rate equal to that of the permeate until the conductivity is ≤100 μS / cm to obtain the silk fibroin dialysis solution. (4) The silk fibroin dialysis solution obtained in step (3) is passed into the third storage tank of the concentration unit, and a microfiltration membrane with a molecular weight cutoff of 5 kDa is used for dialysis filtration and concentration. The volume of the concentrated solution is 200% of the volume of the silk fibroin salt solution passed into the filtration unit in step (2), and the conductivity of the concentrated solution is ≤200 μS / cm, so as to obtain the desalted concentrated solution of silk fibroin solution.

2. The silk fibroin solution desalting and concentration system based on multi-stage membrane separation synergistic regulation according to claim 1, characterized in that, In step (1), the concentration of lithium bromide in the lithium bromide solution is 9-10 M.

3. The silk fibroin solution desalting and concentration system based on multi-stage membrane separation synergistic regulation according to claim 1, characterized in that, In step (1), the concentration of silk fibroin in the silk fibroin salt solution is 15-18 wt%.

4. The silk fibroin solution desalting and concentration system based on multi-stage membrane separation synergistic regulation according to claim 1, characterized in that, In step (2), the inner diameter of the microfiltration membrane is 2.0-4.0 mm, and the ratio of the inner diameter to the average thickness of the microfiltration membrane is (8-12):1; the operating capacity of the microfiltration membrane is 0.3-0.5 mL / cm². 2 .

5. The silk fibroin solution desalting and concentration system based on multi-stage membrane separation synergistic regulation according to claim 1, characterized in that, In step (2), the operating parameters of the microfiltration membrane include: shear force of 4000-5000s. -1 The inlet pressure is 2.0-3.0 bar, the reflux pressure is 1.5-2.5 bar, the transmembrane pressure is 1.8-2.8 bar, and the filtration rate is 15-20 LMH.

6. The silk fibroin solution desalting and concentration system based on multi-stage membrane separation synergistic regulation according to claim 1, characterized in that, In step (3), the inner diameter of the ultrafiltration membrane is 1.5-2.0 mm, the ratio of the inner diameter to the average thickness of the ultrafiltration membrane is (18-22):1, the porosity of the ultrafiltration membrane is 35%-45%, and the operating loading of the ultrafiltration membrane is 0.05-0.1 mL / cm³. 2 .

7. The silk fibroin solution desalting and concentration system based on multi-stage membrane separation synergistic regulation according to claim 1, characterized in that, In step (3), the operating parameters of the ultrafiltration membrane include: shear force of 2000-3000 s. -1 The inlet pressure is 1.0-1.7 bar, the reflux pressure is 0.8-1.5 bar, the transmembrane pressure is 0.9-1.6 bar, and the filtration rate is 9-16 LMH.

8. The silk fibroin solution desalting and concentration system based on multi-stage membrane separation synergistic regulation according to claim 1, characterized in that, In step (4), the inner diameter of the ultrafiltration membrane is 1.5-2.0 mm, the ratio of the inner diameter to the average thickness of the ultrafiltration membrane is (18-22):1, the porosity of the ultrafiltration membrane is 35%-45%, and the operating loading of the ultrafiltration membrane is 0.05-0.1 mL / cm². 2 .

9. The silk fibroin solution desalting and concentration system based on multi-stage membrane separation synergistic regulation according to claim 1, characterized in that, In step (4), the operating parameters of the ultrafiltration membrane include: shear force of 2000-3000 s. -1 The inlet pressure is 1.0-1.7 bar, the reflux pressure is 0.8-1.5 bar, the transmembrane pressure is 0.9-1.6 bar, and the filtration rate is 9-16 LMH.

10. The silk fibroin solution desalting and concentration system based on multi-stage membrane separation synergistic regulation according to claim 1, characterized in that, The first, second, and third storage tanks are all equipped with conductivity detectors.

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