Method for continuously and industrially producing monovalent ion selective cation exchange membrane and application of membrane

Abstract

The invention discloses a method for continuously and industrially producing a monovalent ion selective cation exchange membrane and application of the membrane, and the method comprises the following steps: unreeling a dry membrane roll of the cation exchange membrane, soaking the dry membrane roll in a water tank, putting the dry membrane roll into an electro-deposition tank, and electro-depositing polyethyleneimine in an electrolyte on one surface of the cation exchange membrane to obtain the monovalent ion selective cation exchange membrane. After the cation exchange membrane is taken out of the electrodeposition tank, spraying a glutaraldehyde aqueous solution on the surface of an electrodeposition layer of the cation exchange membrane, covering a layer of polyester film on the surface of the spraying layer, then entering the drying oven for cross-linking reaction, separating the polyester film from the cation exchange membrane after the cation exchange membrane is taken out of the drying oven, and rolling the polyester film to obtain the cation exchange membrane. And washing and rolling the cation exchange membrane to obtain the monovalent ion selective cation exchange membrane. The invention provides application of the prepared monovalent ion selective cation exchange membrane in extraction of lithium from old brine of a salt lake. According to the invention, continuous industrial production is realized, and the prepared membrane is low in resistance and high in monovalent cation selective permeability.

Description

Technical Field

[0001] The present invention belongs to the technical fields of functional polymer materials and electro-driven membrane separation technology, and particularly relates to a method for continuously and industrially producing a monovalent ion-selective cation exchange membrane and the application of the membrane in the electrodialysis lithium extraction from old brine in salt lakes. Background Art

[0002] With the development of society, higher and more specific requirements are put forward for the current ion membrane technology. Selective ion membranes meet the application requirements of many current industrial fields. For example, lithium extraction from brine, seawater desalination, hard water softening, and purification of miscellaneous salts all require ion membranes to have target ion selectivity.

[0003] Generally, ordinary ion exchange membranes have poor selectivity for ions of different valences with the same charge and cannot achieve the separation of monovalent ions and polyvalent ions during the electrodialysis process. For example, conventional cation exchange membranes can only simultaneously permeate monovalent cations (such as Na + , K + ), divalent cations (such as Ca 2+ , Mg 2+ ), and trivalent cations (such as Al 3+ ) and other cations of different valences without distinction under the drive of a direct current electric field, while the monovalent ion-selective cation exchange membrane will preferentially permeate monovalent cations and prevent the permeation of most divalent or higher-valent cations. However, at present, the continuous industrial production of monovalent ion-selective cation exchange membranes in China has not been achieved and only remains at the experimental stage.

[0004] Chinese Patent Invention 202111611168.2 discloses a monovalent cation exchange membrane, its preparation method and application. The preparation method is as follows: (1) Electrodeposit a cation exchange base membrane to obtain a modified cation exchange base membrane; (2) Mix polymer monomers, an oxidant, and the modified cation exchange base membrane obtained in step (1), and carry out a polymerization reaction to obtain the monovalent cation exchange membrane. The methods for preparing the monovalent cation exchange membrane using this invention cannot carry out continuous industrial production and can only adopt an intermittent production method. At the same time, the production process is complex, the production time is long, and the production cost is high. Summary of the Invention

[0005] The primary object of the present invention is to provide a method for continuously and industrially producing a monovalent ion-selective cation exchange membrane to solve the technical problem that the current monovalent ion-selective cation exchange membrane cannot achieve industrial continuous production.

[0006] The second object of the present invention is to provide the application of the monovalent ion-selective cation exchange membrane in the electrodialysis lithium extraction from old brine in salt lakes to reduce energy consumption.

[0007] The above object of the present invention is mainly achieved by the following technical solutions:

[0008] In a first aspect, the present invention provides a method for continuously and industrially producing a monovalent ion-selective cation exchange membrane, the method comprising the following steps:

[0009] After unrolling the dry film roll of the cation exchange membrane, it enters a water tank filled with an aqueous sodium chloride solution for soaking, and after leaving the water tank, it enters a first electro-deposition tank for electro-deposition. The electro-deposition solution in the first electro-deposition tank is composed of sodium chloride, water, and polyethyleneimine (PEI). During the electro-deposition process, the total organic carbon content in the electro-deposition solution is monitored in real time by a total organic carbon on-line detection analyzer, and the monitoring results are fed back to the PLC control system (programmable logic controller control system). The addition of the replenishing solution is controlled by the PLC control system. The replenishing solution is composed of sodium chloride, water, and polyethyleneimine (PEI). The concentration of sodium chloride in the replenishing solution is the same as that in the electro-deposition solution, but the concentration of polyethyleneimine is higher than that in the electro-deposition solution. That is, when the total organic carbon content in the electro-deposition solution is as low as 0.9 times the initial value, the replenishing solution is added to the first electro-deposition tank to supplement the consumed polyethyleneimine (PEI). When the total organic carbon content in the electro-deposition solution is as high as 1.1 times the initial value, the addition of the replenishing solution is stopped, so as to maintain the basic constancy of the total organic carbon content in the electro-deposition solution in the first electro-deposition tank (representing the basic constancy of the polyethyleneimine content), thereby realizing the uniform electro-deposition of polyethyleneimine (PEI) on one surface of the cation exchange membrane. After the cation exchange membrane leaves the first electro-deposition tank, it enters a spraying device to spray an aqueous glutaraldehyde solution onto the electro-deposited layer surface of the cation exchange membrane, and then the electro-deposited layer surface sprayed with the aqueous glutaraldehyde solution is compounded with a polyester film, and then enters a drying device for cross-linking reaction. After leaving the drying device, the polyester film and the cation exchange membrane are separated, and the cation exchange membrane is washed with water and then wound up, that is, a monovalent ion-selective cation exchange membrane is obtained.

[0010] In the present invention, the liquid in the water tank is an aqueous sodium chloride solution, preferably with the same weight ratio of sodium chloride to water as in the electro-deposition solution. This step can avoid the decrease in the sodium chloride concentration in the electro-deposition tank due to film soaking.

[0011] In the electrodeposition step of the present invention, since the PEI in the electrodeposition solution in the first electrodeposition tank is continuously consumed during the electrodeposition process, the concentration of PEI in the electrodeposition solution continuously decreases, which will affect the thickness uniformity of the PEI deposition layer, thereby leading to a decrease in the selectivity of mono- and polyvalent cations. Therefore, the present invention provides a total organic carbon on-line detection analyzer to real-time monitor the total organic carbon content in the electrodeposition solution of the first electrodeposition tank, and feedback the real-time monitoring results to the PLC control system. The PLC control system controls the addition of the replenishing solution to timely supplement the consumed polyethyleneimine (PEI) and maintain the basic constancy of the total organic carbon (i.e., polyethyleneimine) content in the electrodeposition solution in the first electrodeposition tank, so as to realize the uniform electrodeposition of polyethyleneimine (PEI) on the surface of the cation exchange membrane.

[0012] In the electrodeposition step of the present invention, the thickness of the PEI electrodeposition layer affects the performance of the monovalent ion selective cation exchange membrane. If the thickness of the PEI electrodeposition layer is too thin, the selectivity of mono- and polyvalent cations decreases; if the thickness of the PEI electrodeposition layer is too thick, it will affect the flux of monovalent ions. Preferably, the thickness of the PEI electrodeposition layer is controlled by controlling the electrodeposition conditions: the feeding weight ratio of sodium chloride, water, and polyethyleneimine (PEI) in the electrodeposition solution in the first electrodeposition tank is 18-30:1000:0.1-0.5, and the current density of electrodeposition is 1-5 mA / cm 2 , the temperature of electrodeposition is 25-35 °C, and the electrodeposition time is 30-60 minutes, wherein the electrodeposition time is controlled by the unwinding speed of the dry film roll of the cation exchange membrane and the length of the first electrodeposition tank. As a further preference, in the replenishing solution, the feeding weight ratio of sodium chloride, water, and polyethyleneimine (PEI) is 18-30:1000:1-5.

[0013] In the present invention, selecting high molecular weight PEI is beneficial to extending the service life of the monovalent ion selective cation exchange membrane compared with low molecular weight PEI. Preferably, the molecular weight of the polyethyleneimine (PEI) is 500,000-750,000.

[0014] In the present invention, the crosslinking agent glutaraldehyde is introduced by spraying. After spraying glutaraldehyde, a polyester film is covered on the spraying surface and then enters the oven, which can avoid the volatilization of glutaraldehyde and ensure that PEI and glutaraldehyde can be fully crosslinked. Otherwise, the crosslinking is insufficient, which on the one hand affects the selectivity of mono- and polyvalent cations, and on the other hand, it is easy to fall off during actual use, shortening the service life of the monovalent ion selective cation exchange membrane. Preferably, the mass concentration of the glutaraldehyde aqueous solution used for spraying is 0.1-0.5%, and the spraying amount is 10-20 g / m calculated by the mass of the glutaraldehyde aqueous solution sprayed on each square meter of the cation exchange membrane. 2The cross-linking reaction is carried out in a drying device, and the degree of cross-linking is controlled by controlling the cross-linking conditions: the temperature in the drying device is controlled at 35-45 °C, and the cross-linking reaction time is controlled at 30-60 min, wherein the cross-linking reaction time is controlled by the unwinding speed of the cation exchange membrane dry film and the length of the drying device.

[0015] In the present invention, it is preferred that the unwinding speed of the cation exchange membrane dry film roll is 0.2-0.3 m / min.

[0016] In the present invention, the liquid used for washing is water.

[0017] In the present invention, a circulation pipeline is arranged outside the first electro-deposition tank to circulate the electro-deposition liquid in the first electro-deposition tank, and the probe or sampling needle of the total organic carbon on-line detection analyzer is arranged in the circulation pipeline to monitor the total organic carbon content in the electro-deposition liquid in real time.

[0018] In a second aspect, the present invention provides an application of a univalent ion-selective cation exchange membrane prepared by the method according to the first aspect in the extraction of lithium from salt lake old brine by electrodialysis.

[0019] The extraction of lithium from salt lake old brine by electrodialysis refers to the use of a two-compartment electrodialysis device assembled by arranging univalent ion-selective cation exchange membranes and univalent ion-selective anion exchange membranes in an alternating arrangement of anode / cathode / anode / cathode / anode to extract lithium from salt lake old brine. The two compartments are a desalination compartment and a concentration compartment, wherein the feed liquid in the desalination compartment is salt lake old brine, and the feed liquid in the concentration compartment is pure water.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] First, the continuous industrial production of the univalent ion-selective cation exchange membrane is realized, the labor intensity is reduced, the product quality is improved, and the production cost is also reduced.

[0022] Second, by performing single-sided electro-deposition of the PEI layer and single-sided chemical cross-linking on the cation exchange membrane, a univalent ion-selective cation exchange membrane with a lower membrane resistance can be prepared and the univalent cation selective permeability of the membrane can be improved on the basis of ensuring that the univalent ion flux of the membrane is not reduced.

[0023] Third, the univalent ion-selective cation exchange membrane prepared by the present invention is used for the extraction of lithium from salt lake old brine, and can operate at a lower voltage and consume less energy compared with the existing univalent ion-selective cation exchange membrane. Description of the Drawings

[0024] Figure 1 It is a process flow chart of the continuous production process of the univalent ion-selective cation exchange membrane of the present invention.

[0025] 1 - First unwinding device, 2 - Water tank, 3 - First electro-deposition tank, 4 - First anode membrane tube, 5 - First cathode membrane tube, 6 - First metering pump, 7 - First supply tank, 8 - First overflow port, 9 - Spraying device, 10 - Drying device, 11 - Water washing tank, 12 - Second winding device, 13 - First circulation pipeline, 14 - First pump, 15 - Second unwinding device, 16 - First winding device, 17 - First heat exchange device, 18 - First heating device, 19 - Manual tension regulating valve, 20 - Second supply tank, 21 - Second metering pump, 22 - Total organic carbon on-line detection and analysis instrument. Detailed implementation mode

[0026] The present invention will be further described below in conjunction with specific embodiments.

[0027] In the embodiments of the present invention, those not specified under specific conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained by conventional technical means or purchased commercially.

[0028] As Figure 1 shown, the special device used in the embodiment includes a total organic carbon on-line detection and analysis instrument 22 and a first unwinding device 1, a water tank 2, a first electro-deposition tank 3, a spraying device 9, a second unwinding device 15, a drying device 10, a first winding device 16, a water washing tank 11 and a second winding device 12 arranged in sequence; between the first unwinding device 1 and the water tank 2, inside the water tank 2, between the water tank 2 and the first electro-deposition tank 3, inside the first electro-deposition tank 3, between the first electro-deposition tank 3 and the spraying device 9, between the spraying device 9 and the drying device 10, between the second unwinding device 15 and the drying device 10, between the drying device 10 and the first winding device 16, inside the water washing tank 11, and between the water washing tank 11 and the second winding device 12, over rollers are arranged for the transportation of the cation exchange membrane and / or polyester film; a first supply tank 7 is installed above the first electro-deposition tank 3, the bottom of the first supply tank 7 is communicated with the first electro-deposition tank 3 through a first connecting pipe, and a first metering pump 6 is arranged on the first connecting pipe;

[0029] The first electro-deposition tank 3 includes a first liquid storage tank, a first cathode membrane tube 5, a first anode membrane tube 4, a first heat exchange device 17, a first heating device 18, a first circulation pipeline 13 and a first pump 14. The upper and lower parts of the over-roller in the first liquid storage tank are respectively provided with the first anode membrane tube 4 and the first cathode membrane tube 5. The lower side of the first liquid storage tank is communicated with the inlet of the first liquid storage tank through the first circulation pipeline 13, and the first circulation pipeline 13 is provided with a first pump 14, a first heat exchange device 17 and a first heating device 18. The first cathode membrane tube 5 and the first anode membrane tube 4 are respectively connected to the negative electrode and the positive electrode. The first cathode membrane tube 5 and the first anode membrane tube 4 are respectively provided with inlets and outlets for the electrode solution, and are connected to the same electrode solution tank to form a circulation of the electrode solution. The upper side of the first liquid storage tank is provided with a first overflow port 8. Through the above structural design, the circulation and temperature control of the electro-deposition solution in the first electro-deposition tank 3 are realized.

[0030] The probe or sampling needle of the total organic carbon on-line detection analyzer 22 is arranged in the first circulation pipeline 13 to monitor the total organic carbon content in the electro-deposition solution in real time.

[0031] The spraying device 9 includes a spray head, a second metering pump 21 and a second supply tank 20 connected in sequence. The spray head is arranged below the second metering pump 21 and the spraying direction of the spray head is aligned with the surface of the cation exchange membrane electro-deposition layer. The second metering pump controls the spraying amount.

[0032] The drying device 10 includes an oven, a heating pack, an exhaust and a valve, an internal circulation and a valve, a fresh air and a valve, a lower air inlet and a valve, an upper air inlet and a valve, and a circulation fan.

[0033] The special device further includes a manual tension regulating valve 19, which is arranged between the spraying device 9 and the drying device 10 to ensure uniform fitting of the cation exchange membrane and the polyester film.

[0034] The membranes in the first cathode membrane tube 5 and the first anode membrane tube 4 are cation exchange membranes. This cation exchange membrane can use the cation exchange membrane used in the above electro-deposition, or a commercially available cation exchange membrane. The present invention has no special requirements for this.

[0035] The first winding device 16 is used for winding the polyester film, and the second winding device 12 is used for winding the monovalent ion selective cation exchange membrane. And the first winding device 16 and the second winding device 12 are respectively provided with deviation rectifiers.

[0036] The total organic carbon on-line detection analyzer used in the embodiments of the present invention is the HACH BIOTECTOR B7000 on-line total organic carbon (TOC) analyzer. In the embodiments, the membranes in the first cathode membrane tube 5 and the first anode membrane tube 4 are the polyethylene heterogeneous cation exchange membranes of Shanghai Shanghua Water Treatment Materials Co., Ltd.

[0037] Examples 1-9: Preparation method of a monovalent ion-selective cation exchange membrane for continuous industrial production, the steps are as follows:

[0038] After the cation exchange membrane dry film roll is unrolled by the first unrolling device 1 at a certain unrolling speed, it enters the water tank 2 for soaking, and after leaving the water tank 2, it enters the first electro-deposition tank 3 for electro-deposition. Polyethyleneimine (PEI) in the electro-deposition solution in the first electro-deposition tank 3 is electro-deposited on one surface of the cation exchange membrane. At the same time, after the electro-deposition solution in the first electro-deposition tank 3 is pumped out by the first pump 14, the electrode solution exchanges heat with the hot water heated by the first heating device 18 through the first heat exchange device 17 to control the temperature of the electro-deposition solution in the first electro-deposition tank 3. During the electro-deposition process, the total organic carbon content in the electro-deposition solution is monitored in real time by the total organic carbon on-line detection analyzer 22 and the monitoring results are fed back to the PLC control system. The opening and closing of the first metering pump 6 are controlled by the PLC control system, that is, when the total organic carbon content in the electro-deposition solution is lower than 0.9 times the initial value, the first metering pump 6 is opened to supplement the consumed polyethyleneimine (PEI) into the first electro-deposition tank 3. When the total organic carbon content in the electro-deposition solution exceeds 1.1 times the initial value, the first metering pump 6 is closed, so as to maintain the basic constancy of the total organic carbon content (this total organic carbon content is used to characterize the PEI content) in the electro-deposition solution in the first electro-deposition tank 3, thereby realizing the uniform electro-deposition of polyethyleneimine (PEI) on the surface of the cation exchange membrane. If the liquid level height of the solution in the first electro-deposition tank 3 reaches the first overflow port 8, the electro-deposition solution will flow out through the first overflow port 8. After the cation exchange membrane leaves the first electro-deposition tank 3, it enters the spraying device 9 to spray an aqueous glutaraldehyde solution on the electro-deposited layer surface of the cation exchange membrane, and after being compounded with the polyester film unrolled by the second unrolling device 15, it enters the drying device 10 for cross-linking reaction. After leaving the drying device 10, the polyester film and the cation exchange membrane are separated. The polyester film is wound by the first winding device 16, and the cation exchange membrane enters the water washing tank 11 for water washing. After leaving the water washing tank 11, it reaches the second winding device 12, and the wet film is wound to obtain the monovalent ion-selective cation exchange membrane. The specific process parameters and performances are shown in Table 1 below. Examples 1-7 and Comparative Example 1 all use the homogeneous cation exchange membranes of Zhejiang Baichen Low-Carbon Technology Co., Ltd. Among them, Examples 1-7 are surface-modified according to the process parameters in Table 1 below. Comparative Example 1 uses the cation exchange membrane dry film without surface modification, and Comparative Example 2 uses a Japanese imported monovalent cation-selective exchange membrane (model CIMS).

[0039] Comparative Example 3: Glutaraldehyde cross-linking without polyester film protection

[0040] After the cation exchange membrane dry film roll is unrolled at a certain unrolling speed by the first unrolling device 1, it enters the water tank 2 for soaking. After leaving the water tank 2, it enters the first electro-deposition tank 3 for electro-deposition. Polyethyleneimine (PEI) in the electro-deposition solution in the first electro-deposition tank 3 is electro-deposited on one surface of the cation exchange membrane. At the same time, after the electro-deposition solution in the first electro-deposition tank 3 is pumped out by the first pump 14, the electrode solution exchanges heat with the hot water heated by the first heating device 18 through the first heat exchange device 17 to control the temperature of the electro-deposition solution in the first electro-deposition tank 3. During the electro-deposition process, the total organic carbon content in the electro-deposition solution is monitored in real time by the total organic carbon on-line detection analyzer 22, and the monitoring results are fed back to the PLC control system. The opening and closing of the first metering pump 6 are controlled by the PLC control system, that is, when the total organic carbon content in the electro-deposition solution is lower than 0.9 times the initial value, the first metering pump 6 is opened to supplement the consumed polyethyleneimine (PEI) into the first electro-deposition tank 3. When the total organic carbon content in the electro-deposition solution exceeds 1.1 times the initial value, the first metering pump 6 is closed, so as to maintain the basic constancy of the total organic carbon content (this total organic carbon content is used to characterize the PEI content) in the electro-deposition solution in the first electro-deposition tank 3, thereby realizing the uniform electro-deposition of polyethyleneimine (PEI) on the surface of the cation exchange membrane. If the liquid level height of the solution in the first electro-deposition tank 3 reaches the first overflow port 8, the electro-deposition solution will flow out through the first overflow port 8. After the cation exchange membrane leaves the first electro-deposition tank 3, it enters the spraying device 9 to spray an aqueous glutaraldehyde solution onto the electro-deposited layer surface of the cation exchange membrane, and directly enters the drying device 10 for cross-linking reaction. After leaving the drying device 10, it enters the water washing tank 11 for water washing. After leaving the water washing tank 11, it reaches the second winding device 12, and the wet film is wound up, that is, a monovalent ion-selective cation exchange membrane is obtained.

[0041] The performance test method of the obtained monovalent cation-selective exchange membrane is as follows:

[0042] Test method: A small electro-dialysis device is used for testing. The electro-dialysis membrane stack specification is 110mm×270mm, 20 pairs of membranes, and the effective area of a single membrane is 0.0187m 2 , and the membranes are arranged in the pattern of anion / cation / anion / cation. The anion membrane uses a monovalent anion-selective exchange membrane (model BCSAMT) produced by Zhejiang Baichen Low-Carbon Technology Co., Ltd. The test conditions are as follows: a constant current mode with a current of 3.7A is adopted. The solution in the desalination chamber is a mixed aqueous solution of 0.5mol / L lithium chloride and 0.5mol / L magnesium chloride. The amount of water in the desalination chamber is 1.5L, the concentration chamber is pure water, and the amount of water is 0.4L. The solution in the electrode chamber is a 0.1mol / L sodium sulfate aqueous solution. The flow rate of the feed liquid in each compartment is 1L / min, and the electro-dialysis operation temperature is controlled at 30 - 32°C.

[0043] The definition of ion flux is: J = (C t - C0) / (S·N·t), where J is the ion flux, C0 is the ion concentration in the concentration chamber at the initial moment (mol / L), C t is the ion concentration in the concentration chamber at time t (mol / L), S is the effective area of the membrane, N is the number of membrane pairs in the membrane stack, t is the test time, and the test time in the specific implementation manner of the present invention is 2.5 h.

[0044] The definition of the selection separation coefficient is: where P is the selection separation coefficient, is the flux of monovalent cations calculated according to the above method, is the flux of divalent cations calculated according to the above method, is the concentration of monovalent cations in the diluate chamber at the initial time (mol / L), is the concentration of divalent cations in the diluate chamber at the initial time (mol / L). The cation concentration is detected by an inductively coupled plasma emission spectrometer, and the test standard is HJ776 - 2015.

[0045] The test results are shown in Table 1.

[0046] Table 1

[0047]

[0048]

[0049] Example 8: Application of old brine from salt lake

[0050] A small - scale electrodialysis device is used for testing. The specifications of the electrodialysis membrane stack are 110 mm × 270 mm, with 20 pairs of membranes. The effective area of a single membrane is 0.0187 m 2 , and the membranes are arranged in the order of anion / cation / anion / cation. The anion - exchange membrane is a monovalent anion - selective exchange membrane (model BCSAMT) produced by Zhejiang Baichen Low - Carbon Technology Co., Ltd., and the cation - exchange membrane is the monovalent cation - selective exchange membrane prepared in Example 5. The test conditions are as follows: a constant - current mode with a current of 3.7 A is adopted. The solution in the diluate chamber is old brine from a salt lake, with a volume of 20 L of old brine from the salt lake. The concentration chamber is pure water with a volume of 1.5 L. The solution in the electrode chamber is a 0.1 mol / L sodium sulfate solution. The flow rate of the feed liquid in each compartment is 1 L / min, and the electrodialysis operation temperature is controlled at 30 - 32 °C. The test time is 480 minutes. The ion concentration is detected by an inductively coupled plasma emission spectrometer, and the test standard is HJ776 - 2015.

[0051] Lithium recovery rate = (Initial lithium ion mass in the fresh water chamber - Final lithium ion mass in the fresh water chamber) / Initial lithium ion mass in the fresh water chamber × 100%;

[0052] Magnesium rejection rate = (Initial magnesium ion mass in the fresh water chamber - Final magnesium ion mass in the fresh water chamber) / Initial magnesium ion mass in the fresh water chamber × 100%;

[0053] Boron rejection rate % = (Initial boron mass in the fresh water chamber - Final boron mass in the fresh water chamber) / Initial boron mass in the fresh water chamber × 100%;

[0054] SO4 2- Rejection rate = (Initial sulfate ion mass in the fresh water chamber - Final sulfate ion mass in the fresh water chamber) / Initial sulfate ion mass in the fresh water chamber × 100%.

[0055] The data comparison of the monovalent cation selective exchange membranes obtained in Example 5 and Comparative Example 2 is shown in Table 2 below:

[0056] Table 2

[0057]

Claims

1. A method for continuously and industrially producing a monovalent ion-selective cation exchange membrane, characterized in that: The method includes the following steps: After unrolling the dry film roll of the cation exchange membrane, it enters a water tank filled with an aqueous sodium chloride solution for soaking. After leaving the water tank, it enters the first electro-deposition tank for electro-deposition. The electro-deposition solution in the first electro-deposition tank is composed of sodium chloride, water, and polyethyleneimine. During the electro-deposition process, the total organic carbon content in the electro-deposition solution is monitored in real time by a total organic carbon on-line detection analyzer, and the monitoring results are fed back to the PLC control system. The addition of the replenishment solution is controlled by the PLC control system. The replenishment solution is composed of sodium chloride, water, and polyethyleneimine. The sodium chloride concentration in the replenishment solution is the same as that in the electro-deposition solution, but the polyethyleneimine concentration is higher than that in the electro-deposition solution. That is, when the total organic carbon content in the electro-deposition solution is reduced to 0.9 times the initial value, the replenishment solution is added to the first electro-deposition tank to supplement the consumed polyethyleneimine. When the total organic carbon content in the electro-deposition solution is as high as 1.1 times the initial value, the addition of the replenishment solution is stopped, so as to maintain the basic constancy of the total organic carbon content in the electro-deposition solution in the first electro-deposition tank, thereby realizing the uniform electro-deposition of polyethyleneimine on one surface of the cation exchange membrane; after the cation exchange membrane leaves the first electro-deposition tank, it enters a spraying device to spray an aqueous glutaraldehyde solution onto the electro-deposited layer surface of the cation exchange membrane, and then the electro-deposited layer surface sprayed with the aqueous glutaraldehyde solution is laminated with a polyester film, and then enters a drying device for cross-linking reaction. After leaving the drying device, the polyester film and the cation exchange membrane are separated. The cation exchange membrane is washed with water and then wound up, that is, a monovalent ion-selective cation exchange membrane is obtained.

2. The method according to claim 1, wherein: In the electroplating solution in the first electroplating tank, the weight ratio of sodium chloride, water, and polyethyleneimine for feeding is 18-30:1000:0.1-0.5, and the current density of electroplating is 1-5 mA / cm 2 , the temperature of electroplating is 25-35 °C, and the electroplating time is 30-60 minutes; in the replenishing solution, the weight ratio of sodium chloride, water, and polyethyleneimine for feeding is 18-30:1000:1-5.

3. The method according to claim 1, characterized in that: The molecular weight of the polyethyleneimine is 500,000 - 750,000.

4. The method according to claim 1, characterized in that: The mass concentration of the glutaraldehyde aqueous solution used for spraying is 0.1 to 0.5%, and the spraying amount is 10 to 20 g / m calculated by the mass of the glutaraldehyde aqueous solution sprayed on each square meter of the cation exchange membrane 2 .

5. The method according to claim 1, characterized in that: The cross-linking reaction is carried out in the drying device, and the temperature in the drying device is controlled at 35 - 45 °C, and the cross-linking reaction time is controlled at 30 - 60 min.

6. The method according to claim 1, wherein: The unrolling speed of the dry film roll of the cation exchange membrane is 0.2 - 0.3 m / min.

7. The method according to claim 1, characterized in that: The weight ratio of sodium chloride to water in the aqueous sodium chloride solution in the water tank is the same as that in the electro-deposition solution.

8. The method according to claim 1, characterized in that: A circulation pipeline is arranged outside the first electro-deposition tank to circulate the electro-deposition solution in the first electro-deposition tank, and the probe or sampling needle of the total organic carbon on-line detection analyzer is arranged in the circulation pipeline to monitor the total organic carbon content in the electro-deposition solution in real time.

9. Application of a monovalent ion-selective cation exchange membrane prepared by the method according to any one of claims 1 - 8 in the electro-dialysis lithium extraction from old brine in salt lakes.

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