Ceramic membrane continuous brine refining device and refining method

Abstract

The invention discloses a ceramic membrane continuous brine refining device and a refining method, and belongs to the technical field of chlor-alkali industry brine treatment. The device comprises a salt dissolving tank, a precipitation reaction tank, a feed liquid tank and a multi-stage series filter membrane group as a core, and is also matched with a water production tank, a backflushing tank, an acid liquid tank and a blow-down tank, wherein the multi-stage series-connection filtering membrane group is composed of at least two stages of filtering membrane groups which are sequentially connected in series, each stage of filtering membrane group comprises at least two parallel-connection membrane assemblies, and each membrane assembly is provided with an independent control valve group so as to realize independent switching of filtering, backwashing and acid pickling. During maintenance, at least one membrane component is reserved in each stage of membrane group for filtering so as to guarantee the operation continuity; preferably, the device is filled with a silicon carbide ceramic membrane, and the surface of the silicon carbide ceramic membrane can be modified by zwitterions, so that the continuous brine refining performance at low membrane surface flow velocity is further improved. The invention breaks through the defect of maintenance shutdown of the traditional system, realizes continuous refining of saline water, ensures that the purity meets the requirement of ion membrane electrolysis, is suitable for chlor-alkali enterprises of various scales, and has remarkable technical and economic values.

Description

Technical Field

[0001] This invention belongs to the field of brine treatment technology in the chlor-alkali industry, specifically relating to a ceramic membrane continuous brine purification device and purification method. Background Technology

[0002] In chlor-alkali industrial production, brine purification is a crucial pre-processing step to ensure the efficient and stable operation of ion-exchange membrane electrolyzers. The purity of the purified brine directly determines the purity of the caustic soda product and has a critical impact on the antifouling ability and service life of the ion-exchange membrane. Currently, ceramic membrane brine purification technology, due to its advantages of short process, small footprint, and high filtration accuracy, has gradually replaced traditional sedimentation filtration technology as the mainstream technology in the industry. However, existing ceramic membrane purification systems still have significant shortcomings and cannot meet the needs of continuous industrial production. Specifically: Firstly, the filtration precision is mismatched with the system design. Traditional single-stage ceramic membrane filtration processes are limited by the retention capacity of a single-stage membrane module, making it difficult to deeply remove trace impurities (such as calcium and magnesium ion precipitates and colloids) from brine. The purity of the purified brine cannot meet the requirements of high-purity ion membrane electrolysis. Although some multi-stage series filtration systems improve precision by increasing the number of filtration stages, each membrane module adopts an overall linkage control mode without designing an independent control unit for each individual membrane module, resulting in insufficient system operational flexibility. Secondly, the conflict between regeneration maintenance and production continuity is prominent. In existing multi-stage series ceramic membrane systems, membrane modules are mostly controlled in parallel or series. When some membrane modules require backwashing or acid washing regeneration due to fouling, the operation of the entire series path must be suspended, resulting in a complete shutdown. The drawbacks of shutdown maintenance not only interrupt the production process and reduce equipment utilization, but also cause damage to membrane modules due to frequent start-ups and shutdowns, shortening the overall service life of the membranes. Even the series inorganic ceramic membrane filtration system disclosed in existing patented technologies (such as CN112870978B) has not yet overcome the inherent design limitation of requiring shutdown for maintenance, making continuous production impossible. Third, the performance of the membrane material is not compatible with the operating energy consumption. Traditional ceramic membrane systems mostly use alumina ceramic membranes as filter elements, which require 3-5 m·s -1 High membrane surface velocity is required to maintain basic filtration flux. This not only significantly increases the power consumption of the pump body during fluid transport, but also makes it difficult to adapt to the fluctuations in operating conditions caused by frequent valve switching during system maintenance due to the severe fluid disturbance at high flow rates. This can easily lead to problems such as membrane module sealing failure and sudden drop in flux, further exacerbating the instability of system operation.

[0003] In summary, existing ceramic membrane brine purification technology has significant shortcomings in continuous operation capability, energy consumption control, and maintenance flexibility, making it a key point and breakthrough for improving quality and reducing costs in the chlor-alkali industry. The industry urgently needs to develop a new type of ceramic membrane brine purification device that combines multi-stage series high-precision filtration, independent control and maintenance of single membrane modules, and low-energy membrane material compatibility to solve the core problems of traditional systems, such as downtime maintenance, high energy consumption, and unstable operation, thus meeting the continuous and efficient production needs of the chlor-alkali industry. Summary of the Invention

[0004] To address the aforementioned problems, this invention aims to provide a continuous brine purification device and method using ceramic membranes. Through innovative structures combining multi-stage series filtration membrane modules with independent control of individual membrane components, optimized surface properties of silicon carbide ceramic membrane materials, and a parallel operation design for backwashing / acid washing and production, it overcomes the technical bottleneck of mandatory maintenance shutdowns, ensuring continuous operation throughout the brine purification process. It also reduces membrane flow rate requirements and material loss, significantly decreasing energy consumption and costs for industrial operation. Furthermore, it improves filtration accuracy and system adaptability, meeting the high-purity brine requirements of ion-exchange membrane electrolyzers and allowing flexible adjustment of filtration parameters according to actual operating conditions. Ultimately, it provides the chlor-alkali industry with an efficient, stable, and economical brine purification solution.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a ceramic membrane continuous brine purification device, comprising: Salt dissolving pond, used for dissolving crude salt; Precipitation reaction vessel, used for the precipitation of impurities; Liquid tank is used for temporary storage of pretreatment liquid; Product water tank, used to store refined brine; Backwash tank, used to provide backwash fluid; Acid tank, used to supply pickling solution; Wastewater tank, used to collect backwash waste liquid; The salt treatment tank, sedimentation reaction tank, and feed tank are connected in sequence by pipelines, and the pipelines between adjacent components are equipped with power pumps for driving the feed liquid transportation. Multi-stage series filtration membrane modules are used for the step-by-step filtration and purification of crude brine. The multi-stage series filtration membrane group consists of at least two stages of filtration membrane groups connected in series. Each stage of the filtration membrane group contains at least two membrane modules, and the membrane modules in the same stage of the filtration membrane group are connected in parallel. Each membrane module is equipped with an independent control valve group to realize the switching of three working conditions: filtration, backwashing, and acid washing. The initial feed end of the multi-stage series filtration membrane module is connected to the feed tank. The concentrate discharged from the previous stage filtration membrane module is directly used as the feed for the next stage filtration membrane module. The concentrate discharged from the last stage filtration membrane module is returned to the feed tank. The water production end of each membrane module is connected to the water production tank. The backwash tank and acid tank are connected to the backwash liquid input end and acid input end of the multi-stage series filtration membrane group via pipelines with valves, respectively, and the sewage tank is connected to the backwash waste liquid output end of the multi-stage series filtration membrane group via pipelines with valves.

[0006] Furthermore, the independent control valve assembly includes: The feed valve is located on the feed line of the membrane module and is used to control the introduction of crude brine or concentrate into the membrane module. A reflux valve, located on the reflux line of the membrane module, is used to control the flow direction of concentrate that has not permeated through the membrane. The permeate valve is located on the permeate line of the membrane module and is used to control the output of refined brine. All permeate lines of the membrane modules are connected to the permeate tank. The backwash inlet valve is located on the backwash inlet pipeline of the membrane module. The feed end of the backwash inlet pipeline is connected to the backwash tank. Under the action of the air compressor, the backwash liquid is controlled to enter the membrane module. The backwash outlet valve is located on the backwash outlet pipeline of the membrane module, and the discharge end of the backwash outlet pipeline is connected to the sludge tank. The pickling inlet valve is located on the acid inlet pipeline of the membrane module. The feed end of the acid inlet pipeline is connected to the acid tank. The acid in the acid tank flows into the membrane module through the pickling inlet valve under the action of the power pump. The acid wash outlet valve is located on the acid waste liquid outlet pipeline of the membrane module, through which the acid waste liquid can flow back to the acid tank.

[0007] Furthermore, a permeate pipeline is provided between the backflushing tank and the product water tank. This pipeline is used to transport the permeate to the backflushing tank as backwashing fluid, and a backflushing tank permeate supply valve is provided on the permeate pipeline.

[0008] Furthermore, the membrane module is filled with a silicon carbide ceramic membrane with an average pore size of 20~600 nm.

[0009] Preferably, the surface of the silicon carbide ceramic film is provided with a zwitterionic modification layer, which is constructed by a two-step modification method: The first step involves immersing the silicon carbide ceramic membrane in a Tris buffer solution containing dopamine hydrochloride (PDA) and polyethyleneimine (PEI) and reacting it at a constant temperature of 25-30°C for 2-6 hours to introduce tertiary amine groups. The second step involves immersing the silicon carbide ceramic membrane treated in the first step into an aqueous solution of sodium 2-bromoethylsulfonate (SBES) and reacting it at 40-60°C for 8-16 hours to construct an amphoteric modified layer on the membrane surface.

[0010] Furthermore, the concentrations of dopamine hydrochloride and polyethyleneimine in the Tris buffer were 0.2–1.0 g·L⁻¹. -1 and 0.4~1.2 g·L-1 The concentration of the sodium 2-bromoethylsulfonate aqueous solution is 0.05~0.3 mol·L⁻¹. -1 .

[0011] The purification method based on the above-mentioned ceramic membrane continuous brine purification device is as follows: (1) Pretreatment: The crude salt is dissolved in the salt dissolving tank and allowed to stand and separate into layers. The supernatant is pumped to the precipitation reaction tank by a power pump for precipitation reaction. After the reaction, the supernatant is pumped to the material tank for temporary storage by a power pump. (2) Multi-stage filtration: The liquid in the feed tank is pumped to a multi-stage series filter membrane group by a power pump. It flows through each stage of the filter membrane group for filtration in sequence. The refined brine enters the product water tank, and the concentrate of the last stage filter membrane group flows back to the feed tank. (3) Maintenance operation: When the membrane module needs to be backwashed, close the feed valve, reflux valve, product water valve, backwash tank permeate supply valve, acid water inlet valve and acid wash outlet valve corresponding to the membrane module, open the backwash inlet valve and backwash outlet valve corresponding to the membrane module, turn on the air compressor, and use the backwash liquid in the backwash tank to flush. When the backwashing effect is not good, close the feed valve, reflux valve, product water valve, backwash inlet water valve and backwash outlet water valve corresponding to the membrane module, and open the acid washing inlet water valve and acid washing outlet water valve corresponding to the membrane module. Use the acid washing solution in the acid tank for acid washing. After acid washing, it is necessary to wash with water until the pH of the effluent is neutral. During the maintenance operation, at least one membrane module of each filtration membrane group must be kept in filtration state to ensure continuous operation of the device.

[0012] Furthermore, the operating conditions for multi-stage filtration are: transmembrane pressure difference 0.10~0.20 MPa, membrane surface flow velocity 1-2 m·s. -1 The equipment operates at a temperature of 50~60℃.

[0013] The beneficial effects of this invention are as follows: 1. The ceramic membrane continuous brine purification device disclosed in this application innovatively adopts a design of multi-stage series filtration membrane groups combined with independent control valve groups for each membrane module. Each membrane module connected in parallel in each filtration membrane group is equipped with an independent control valve group, which can independently realize the switching of filtration, backwashing and acid washing modes. When some membrane modules need to be regenerated and maintained, only the relevant valves of the membrane module to be maintained need to be closed, while other membrane modules in the same group can continue to filter normally. This ensures that the multi-stage series path is always effective, avoids the shutdown of the entire line, significantly improves the equipment utilization rate, and reduces the damage to membrane modules caused by frequent start-up and shutdown, which helps to extend the membrane life. 2. The device preferably uses a silicon carbide ceramic membrane as the filter element, which requires only 1~2 m·s. -1 A stable high flux can be maintained at a membrane surface flow rate of only 3~5 m·s, compared to traditional alumina ceramic membranes (which require 3~5 m·s). -1(High flow rate) The pump body power consumption during fluid transportation is significantly reduced, and it can effectively withstand the fluctuations in operating conditions caused by frequent valve switching during continuous system operation; 3. The device adopts a multi-stage series filtration design and utilizes the step-by-step interception effect of multi-stage filtration membrane modules to deeply remove calcium and magnesium ion precipitates and colloidal impurities from brine. The purity of the purified brine meets the high purity requirements of the ion membrane electrolyzer. Moreover, the number of parallel membrane modules at each stage can be flexibly adjusted according to the impurity content of the crude brine to adapt to the purification needs under different working conditions. 4. The structural stability of the silicon carbide ceramic membrane and the antifouling ability of the zwitterionic modified layer can further reduce membrane fouling and blockage, reduce flux decay rate, control system operating pressure difference fluctuations within a very small range, significantly improve filtration stability and reliability, and thus improve the continuous brine purification effect under low membrane flow rate. 5. The brine refining device disclosed in this application integrates functions such as salt dissolution, precipitation, filtration, maintenance, and storage into one unit, with a compact overall structure and controlled floor space. At the same time, the permeate circulation pipeline design of the backflushing tank and product water tank, and the acid recycling design of the acid tank further simplify the process and reduce the complexity of operation. In addition, the number of multi-stage series stages and the number of single-stage membrane modules in parallel can be flexibly adjusted according to the actual processing capacity and refining precision. It is suitable for intermittent production in small and medium-sized chlor-alkali enterprises, as well as large-scale continuous production in large enterprises, and has a wide range of applications. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a ceramic membrane continuous brine purification device; Among them, 1-salt tank, 2-sedimentation reaction tank, 3-feed tank, 4-multi-stage series filter membrane group, 5-product water tank, 6-backwash tank, 7-acid tank, 8-sewage tank, 9-suction pump one, 10-suction pump two, 11-suction pump three, 12-air compressor, 13-suction pump four. 41 - Primary filtration membrane module, 42 - Secondary filtration membrane module, 43 - Tertiary filtration membrane module; 411 - Membrane module; 4-1-Feed valve, 4-2-Return valve, 4-3-Product water valve, 4-4-Backwash water inlet valve, 4-5-Backwash water outlet valve, 4-6-Pickling water inlet valve, 4-7-Pickling water outlet valve; 6-1- Backflushing tank permeate supply valve. Detailed Implementation

[0015] To better understand the technical solution of the present invention, the technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments. Example 1

[0016] This embodiment discloses a ceramic membrane continuous brine purification device, which consists of core components such as a salt dissolving tank 1, a sedimentation reaction tank 2, a feed tank 3, a multi-stage series filtration membrane group 4, a product water tank 5, a backwash tank 6, an acid tank 7, and a sludge discharge tank 8.

[0017] The salt dissolving tank 1, sedimentation reaction tank 2, and feed tank 3 are connected sequentially by pipelines. A suction pump 9 is installed on the connecting pipeline between the salt dissolving tank 1 and the sedimentation reaction tank 2. After the coarse salt is fully dissolved and allowed to settle and separate into layers in the salt dissolving tank 1, the supernatant can enter the sedimentation reaction tank 2 under the action of suction pump 9 to complete the impurity sedimentation reaction. A suction pump 10 is installed on the connecting pipeline between the sedimentation reaction tank 2 and the feed tank 3. After the sedimentation reaction is completed, the supernatant enters the feed tank 3 under the drive of suction pump 10 for temporary storage, preparing material for subsequent filtration processes.

[0018] The multi-stage series filtration membrane module 4 serves as the core of the purification process, performing the function of filtering crude brine step by step. It consists of a primary filtration membrane module 41, a secondary filtration membrane module 42, and a tertiary filtration membrane module 43 connected in series. Each filtration membrane module adopts a differentiated parallel membrane component design. Specifically, the primary filtration membrane module 41 consists of five membrane components 411 connected in parallel, the secondary filtration membrane module 42 consists of three membrane components 411 connected in parallel, and the tertiary filtration membrane module 43 consists of two membrane components 411 connected in parallel. The feed end of the primary filtration membrane module 41 is connected to the feed tank 3 through a feed pipeline equipped with a suction pump 311. The pretreated feed solution in the feed tank 3 is pumped into the primary filtration membrane module 41 by the suction pump 311 to start the filtration process. The concentrate (liquid that has not permeated through the membrane) discharged from the primary filtration membrane module 41 is directly used as the feed for the secondary filtration membrane module 42, and is introduced through the feed pipe of the membrane module 411 of the secondary filtration membrane module 42 for secondary filtration. Similarly, the concentrate discharged from the secondary filtration membrane module 42 is used as the feed for the tertiary filtration membrane module 43, and is introduced through the feed pipe of the membrane module 411 of the tertiary filtration membrane module 43 to complete the third filtration. Finally, the concentrate discharged from the tertiary filtration membrane module 43 is returned to the feed tank 3 to achieve feed recycling.

[0019] Each membrane module 411 is equipped with an independent control valve group, which precisely controls the switching between filtration, backwashing, and acid washing modes through seven dedicated valves. The functions and connections of each valve are clearly defined (because the seven dedicated valves configured in the membrane module 411 within the same filtration membrane group use the same connection method, therefore...). Figure 1 In the diagram, only one membrane module 411 from each of the first, second, and third stage filtration membrane groups is selected, and the different types of valve structures equipped with it are labeled to avoid repetitive illustrations and ensure that the diagram is concise and clear. Feed valve 4-1 is installed on the feed line of membrane module 411 and is responsible for controlling the introduction of crude brine or concentrate into the membrane module to ensure stable feed. The reflux valve 4-2 is installed on the reflux pipeline of the membrane module 411 of each stage of the filter membrane group. By opening and closing the valve and adjusting the opening degree, the flow direction of the concentrate that has not passed through the membrane can be precisely controlled: it can either transport the feed liquid to be refined to the next stage of the filter membrane group, or return the final concentrate to the feed tank 3 to form a closed loop and improve the utilization rate of raw materials. Specifically, the concentrate flowing out of the primary filtration membrane module 41, under the control of the reflux valve 4-2, is directly fed into the secondary filtration membrane module 42 through a pipeline. It is introduced into the feed pipe of the membrane module 411 of the secondary filtration membrane module 42 and enters the secondary purification process. The concentrate filtered by the membrane module 411 of the secondary filtration membrane module 42 is also regulated by the reflux valve 4-2 and fed into the tertiary filtration membrane module 43 through the feed pipe of the membrane module 411 of the tertiary filtration membrane module 43 to complete the third purification. As the final stage of filtration, the concentrate produced by the membrane module 411 of the tertiary filtration membrane module 43 has completed multiple rounds of purification. Under the control of the reflux valve 4-2, it is no longer transported to the next stage, but is returned to the feed tank 3 through a dedicated pipeline, mixed with the pretreated new feed liquid, and re-enters the primary filtration membrane module to participate in the purification, thus realizing the recycling of the concentrate.

[0020] The permeate valve 4-3 is installed on the permeate pipeline of the membrane module 411 to control the output of refined brine. All permeate pipelines of the membrane module 411 are connected to the permeate tank 5, which centrally receives and stores the refined brine.

[0021] The backwash inlet valve 4-4 is installed on the backwash inlet pipeline of the membrane module 411. The feed end of the backwash inlet pipeline is connected to the backwash tank 6. Under the action of the air compressor 12, the backwash liquid is controlled to enter the membrane module 411 to complete the backwashing.

[0022] The backwash outlet valve 4-5 is installed on the backwash outlet pipeline of the membrane module 411. The discharge end of the backwash outlet pipeline is connected to the sewage tank 8 to control the discharge of backwash waste liquid and realize centralized collection of waste liquid.

[0023] The pickling inlet valve 4-6 is installed on the acid inlet pipeline of the membrane module 411. The feed end of the acid inlet pipeline is connected to the acid tank 7. The acid in the acid tank 7 flows into the membrane module 411 through the pickling inlet valve 4-6 under the action of the suction pump 413 for pickling.

[0024] The acid wash outlet valve 4-7 is installed on the acid waste liquid outlet pipeline of the membrane module 411 to control the discharge of acid waste liquid. The acid waste liquid can also be returned to the acid tank 7 through this pipeline to realize the recycling of acid liquid.

[0025] Backwash tank 6 is used to provide clean and sufficient backwash fluid for backwashing membrane module 411. To achieve efficient replenishment and recycling of backwash fluid, a dedicated permeate pipeline is provided between backwash tank 6 and product water tank 5 (which stores clean permeate produced by membrane module filtration). This pipeline is used to transport permeate to backwash tank 6 as backwash fluid. At the same time, a backwash tank permeate replenishment valve 6-1 is installed on this permeate pipeline to precisely control the timing and flow rate of permeate entering backwash tank 6, ensuring a stable reserve of backwash fluid in backwash tank 6 and the orderly connection of the backwashing process.

[0026] The permeate tank 5 is used to receive the refined brine output from the permeate pipelines of all membrane modules 411, enabling centralized storage of the finished product.

[0027] Wastewater tank 8 is used to collect backwash waste liquid discharged from the backwash outlet pipes of all membrane modules 411, so as to facilitate unified treatment of waste liquid.

[0028] Acid tank 7 has a dual function: on the one hand, it provides acid washing solution for the pickling of membrane module 411, and on the other hand, it receives acid waste liquid returned from the acid waste liquid outlet pipeline of membrane module 411, realizing acid recycling.

[0029] In this embodiment, each membrane assembly 411 is filled with three 19-channel silicon carbide ceramic membranes with an average pore size of 500 nm.

[0030] A 19-channel silicon carbide ceramic membrane was placed in conical flasks containing sodium hydroxide solution (pH=11.5) and 1 wt% hydrochloric acid solution, respectively. The flasks were then placed in a constant temperature water bath, and the system temperature was maintained at 50℃. After 8 days of corrosion testing, the ceramic membrane samples were removed and placed on a petri dish. They were first rinsed thoroughly with running tap water for 2 hours to remove residual acid and alkali solutions, and then dried in a 70℃ oven.

[0031] Characterization results of the corroded samples showed that the mass loss rate of the silicon carbide ceramic membrane was less than 0.5%, and the porosity did not fluctuate significantly. Further analysis indicated that its microstructure integrity and crystal phase composition remained stable. These results confirm that the silicon carbide ceramic membrane possesses excellent acid and alkali corrosion resistance, meeting the requirements for long-life operation of filter elements in brine purification processes.

[0032] The operation method for brine purification using the above-mentioned apparatus is as follows: 1) Conventional filtration: After the crude salt is fully dissolved in the salting tank 1 and allowed to settle and separate into layers, the supernatant is pumped to the sedimentation tank 2 using a suction pump 9. An excess of 200 mg·L⁻¹ salt is added to the sedimentation tank 2. -1Na₂CO₃ and NaOH were subjected to a precipitation reaction at 50℃ and a stirring speed of 100 rpm. The resulting solution was then pumped by a suction pump (210) into a multi-stage series filtration membrane module (4) for filtration at an operating pressure of 0.10 MPa and a membrane surface flow rate of 1 m / s. -1 The refined brine is transported to the product water tank 5, and the concentrate flowing out of the three-stage filtration membrane group 43 is returned to the feed tank 3.

[0033] 2) Backwashing steps: Taking membrane module 411 (marked as M1 in the figure) in the primary filtration membrane group 41 as an example, when backwashing M1, the feed valve 4-1, reflux valve 4-2, product water valve 4-3, acid wash water inlet valve 4-6, and acid wash water outlet valve 4-7 of membrane module M1 should be closed, and the permeate supply valve 6-1 of the backwash tank should be closed at the same time (to avoid permeate interfering with the backwashing process); only the backwash water inlet valve 4-4 (for backwashing liquid introduction) and the backwash water outlet valve 4-5 (for backwashing waste liquid discharge) of membrane module M1 should be opened.

[0034] After the valve switching is completed, the backwashing process is started: turn on the air compressor 12 and set the backwash pressure to 0.20 MPa. The air compressor 12 pumps air into the pipeline and uses the air pressure to drive the backwash liquid in the backwash tank 6 to flow through the membrane module M1 along the backwash water inlet pipeline to rinse the membrane surface and remove attached impurities. The waste liquid generated during the backwashing process is discharged into the drain tank 8 through the backwash water outlet pipeline.

[0035] After the backwashing operation is completed, the membrane module M1 needs to be switched back to normal filtration status: reopen the feed valve 4-1, reflux valve 4-2, and permeate valve 4-3 of the membrane module M1, and at the same time open the permeate supply valve 6-1 of the backwash tank; close the backwash inlet valve 4-4 and backwash outlet valve 4-5 of the membrane module M1. At this point, M1 will resume normal filtration function.

[0036] 3) Acid washing step: When the backwashing effect is not significant, acid is used to regenerate the ceramic membrane. Taking membrane module M1 as an example, when acid washing M1, the feed valve 4-1, reflux valve 4-2, permeate valve 4-3, backwash inlet valve 4-4, and backwash outlet valve 4-5 of membrane module M1 are closed (cutting off non-acid washing related passages), and the permeate supply valve 6-1 of the backwash tank is closed at the same time; only the acid washing inlet valve 4-6 (for acid introduction) and the acid washing outlet valve 4-7 (for acid circulation backflow) of membrane module M1 are opened.

[0037] After completing the valve switching, start the acid washing process: start suction pump 413 to pump hydrochloric acid from acid tank 7 into membrane module M1 through the acid washing inlet pipeline; maintain stable core parameters during acid washing: temperature set to 50℃, transmembrane pressure differential controlled at 0.10 MPa, and cross-flow velocity maintained at 2 m·s. -1 .

[0038] To avoid damage to the membrane module from residual acid, a water rinse is required after acid pickling: maintain the valve status (acid pickling inlet valves 4-6 and acid pickling outlet valves 4-7 open, other valves closed) and operating parameters (temperature 50℃, transmembrane pressure differential 0.10MPa, cross-flow velocity 2 m·s) from the acid pickling process. -1 The following steps remain unchanged: switch acid tank 7 to clean water supply (clean water tank not shown in the diagram), pump clean water into M1 through suction pump 413 for circulating water washing; continuously monitor the pH value of the liquid flowing out after water washing until the pH reaches neutral, at which point the water washing operation ends.

[0039] After the acid washing operation is completed, the membrane module M1 needs to be switched back to normal filtration status: reopen the feed valve 4-1, reflux valve 4-2, and permeate valve 4-3 of the membrane module M1, and at the same time open the permeate supply valve 6-1 of the backwash tank; close the acid washing inlet valve 4-6 and acid washing outlet valve 4-7 of the membrane module M1. At this point, M1 will resume normal filtration function.

[0040] It is worth noting that, in order to ensure the uninterrupted operation of the ceramic membrane continuous brine purification unit and achieve continuous production of crude brine to refined brine, when performing backwashing or acid washing operations on some membrane modules, the core principle of "multi-stage series path always being effective" must be strictly followed. That is, the series purification path composed of primary, secondary, and tertiary filtration membrane groups must not be interrupted. The crude brine must be able to flow through the primary, secondary, and tertiary filtration membrane groups in sequence to finally complete purification and generate qualified products.

[0041] In other words, in any stage of filtration membrane group (first, second, or third stage), multiple parallel membrane modules 411 must not be backwashed or acid-washed simultaneously. For example, if a first-stage filtration membrane group 41 contains 5 parallel membrane modules 411, backwashing / acid washing can only be performed on a maximum of 4 membrane modules 411, and at least one membrane module 411 must remain in normal filtration mode. Similarly, a second-stage filtration membrane group 42 (3 parallel membrane modules 411) must retain at least one membrane module 411 for online filtration, and a third-stage filtration membrane group 43 (2 parallel membrane modules 411) must also retain at least one membrane module 411 for online filtration. By retaining some membrane modules 411 for online filtration, it is ensured that each stage of filtration membrane group can maintain effective filtration function. Crude brine can normally enter the membrane group of that stage, and after filtration by the online membrane module, the concentrate can be smoothly transported to the next stage of membrane group, ultimately achieving an uninterrupted complete process of "first-stage filtration → second-stage filtration → third-stage filtration" and ensuring the continuous production of purified brine.

[0042] Furthermore, the multi-stage filtration membrane group provided in this embodiment is based on a series structure of "first-stage + second-stage + third-stage", wherein the number of membrane modules 411 connected in parallel for each stage is specified as follows: the first-stage filtration membrane group 41 contains 5 parallel membrane modules 411, the second-stage filtration membrane group 42 contains 3 parallel membrane modules 411, and the third-stage filtration membrane group 43 contains 2 parallel membrane modules 411. This configuration is a typical preferred solution selected to clearly illustrate the working principle and operating logic of the device, and is not the only limitation on the technical solution.

[0043] In practical applications, the core parameters of the multi-stage filtration membrane module can be adaptively adjusted according to specific operating conditions such as the impurity content of the crude brine, the required processing volume, and the purification precision standards. The adjustment range includes, but is not limited to: Series stage adjustment: The number of series stages of the filter membrane module can be increased or decreased (e.g., adjusted to two-stage series, four-stage series, etc.). Adjustment of the number of parallel membrane modules in a single stage: The number of membrane modules 411 connected in parallel in a single stage filtration membrane group can be changed (e.g., the first stage filtration membrane group 41 can be adjusted to 4 or 6 membrane modules 411 connected in parallel, the second stage filtration membrane group 42 can be adjusted to 2 or 4 membrane modules 411 connected in parallel, etc.).

[0044] The aforementioned adjustments to the "number of series membrane modules" and "number of single-stage parallel membrane modules" are all reasonable derivations based on the core logic of this technical solution (multi-stage series refining + single-stage parallel connection to ensure continuous operation). They do not change the core working principle and technical essence of the device. Therefore, all parameter adjustments that conform to this core logic should be included within the scope of protection of this application and should not be regarded as a limitation on this technical solution.

[0045] Comparative Example 1 The core difference between this comparative example and Example 1 is that the type of ceramic membrane used in the membrane module was changed. This comparative example used a 19-channel alumina ceramic membrane with an average pore size of 500 nm for brine purification experiments. During the brine purification process, all membrane modules were in a filtration preparation state. The experimental conditions were set as follows: transmembrane pressure difference of 0.10 MPa and operating temperature of 50°C; the membrane surface flow rate was controlled at 3 m / s. -1 After 1 hour of operation, the membrane's stable flux reached 150 L·m⁻¹. -2 ·h -1 .

[0046] In comparison, brine purification experiments were conducted using a 19-channel silicon carbide ceramic membrane with an average pore size of 500 nm under the same transmembrane pressure difference (0.10 MPa) and operating temperature (50℃): only the membrane surface flow rate needed to be reduced to 2 m·s. -1 After the equipment has been running for 1 hour, the stable flux of the membrane can be increased to 201 L·m. -2 ·h -1The key parameters and results of the two sets of experiments are detailed in Table 1.

[0047] Table 1. Comparison of filtration parameters and membrane flux of different types of ceramic membranes

[0048] As shown in Table 1, the filtration performance of silicon carbide ceramic membranes is significantly better than that of alumina ceramic membranes: First, under the same core experimental conditions, the stable flux of silicon carbide ceramic membranes is much higher than that of alumina ceramic membranes, meaning that silicon carbide ceramic membranes can process more brine per unit time, resulting in a significant improvement in filtration efficiency; second, while achieving a higher flux, silicon carbide ceramic membranes only require 2 m·s -1 The surface flow rate of the membrane is 3 m / s, while that of the alumina ceramic membrane is 3 m / s. -1 Lower membrane surface velocity. Lower membrane surface velocity can reduce energy consumption during fluid transport (such as pump power consumption), reduce equipment operation and maintenance costs, and has both economic advantages and energy-saving and carbon-reducing effects.

[0049] Considering the aforementioned characteristics of silicon carbide ceramics, such as resistance to acid and alkali corrosion, structural and crystalline stability, and a mass loss rate of <0.5%, it can be concluded that silicon carbide ceramic membranes not only have the dual advantages of high efficiency and low cost in brine purification, but also meet the requirements of long-term operation, making them a more suitable ceramic membrane choice for brine purification processes. Example 2

[0050] The core difference between this embodiment and Embodiment 1 is that a zwitterionic modification layer is constructed on the surface of the silicon carbide ceramic membrane used in Embodiment 1 using a two-step modification method, aiming to further improve its brine purification performance. The specific modification process and experimental results are as follows: Step 1: PDA / PEI co-deposition to modify silicon carbide ceramic film (introducing reactive sites) Tris(hydroxymethyl)aminomethane (Tris) was dissolved in pure water at room temperature and then reacted with 1 mol·L⁻¹ water. -1 Adjust the pH to 8.5 with hydrochloric acid and bring the volume to 1 L to prepare Tris buffer. Then add 0.5 g dopamine hydrochloride (PDA) and 0.5 g polyethyleneimine (PEI) to the buffer and stir thoroughly with a magnetic stirrer until the solutes are completely dissolved to obtain the first step of the modification solution.

[0051] The silicon carbide ceramic membrane to be modified was immersed in the above-mentioned modification solution and reacted at a constant temperature of 25°C for 4 hours. During this process, PDA and PEI co-deposited on the membrane surface, simultaneously introducing reactive tertiary amine groups onto the surface of the silicon carbide ceramic membrane. After the reaction was completed, the membrane tube was removed, and the membrane surface was first thoroughly rinsed with pure water to remove unreacted residual solutes. Then, it was dried in an oven at 25°C to obtain the PDA / PEI modified silicon carbide ceramic membrane.

[0052] Step 2: Zwitterionic functionalization of silicon carbide ceramic membrane (construction of zwitterionic modified layer) Dissolve 11.0719 g of sodium 2-bromoethylsulfonate (SBES) in 300 mL of pure water, stir magnetically for 3 h until the solute is completely dissolved, then transfer to a 500 mL volumetric flask and dilute to volume to prepare a 0.1 mol·L⁻¹ solution. -1 SBES solution.

[0053] The modified silicon carbide ceramic membrane from the first step was immersed in an SBES solution, and the system was placed in a 50°C constant temperature water bath for 12 h. During this time, the SBES in the solution underwent a quaternization reaction through the tertiary amine groups on the PEI chains on the membrane surface, generating sulfonamide zwitterions, thereby constructing a zwitterion-modified layer on the membrane surface. After the reaction was completed, the membrane tube was removed and thoroughly rinsed with pure water to remove impurities and unreacted reagents adsorbed on the membrane surface. It was then dried in a 25°C oven to finally obtain the zwitterion-functionalized silicon carbide ceramic membrane. Example 3

[0054] Using silicon carbide ceramic membranes before and after zwitterionic modification, under the same experimental conditions (transmembrane pressure difference 0.10 MPa, membrane surface flow velocity 2 m·s), -1 A brine purification experiment was conducted at a temperature of 50℃, with all membrane modules in filtration preparation mode. Results showed that after 1 hour of filtration operation, the flux of both membrane groups stabilized; the stable flux of the zwitterionic modified silicon carbide ceramic membrane reached 276 L·m⁻¹. -2 ·h -1 The stable flux was significantly higher than that of the unmodified silicon carbide ceramic membrane (201 L·m). -2 ·h -1 This study confirms that the two-step modification method can effectively improve the brine purification performance of silicon carbide ceramic membranes.

[0055] The content mainly describes the basic principles, main features and advantages of the present invention, but it is only a specific embodiment of the present invention. The technical features of the present invention are not limited thereto. Any other implementation methods derived by those skilled in the art without departing from the technical solution of the present invention should be covered within the scope of the present invention.

Claims

1. A ceramic membrane continuous brine purification device, characterized in that, include: Multi-stage series filtration membrane modules are used for the step-by-step filtration and purification of crude brine. The multi-stage series filtration membrane group consists of at least two stages of filtration membrane groups connected in series. Each stage of the filtration membrane group contains at least two membrane modules, and the membrane modules in the same stage of the filtration membrane group are connected in parallel. Each membrane module is equipped with an independent control valve group, which can realize the switching of three working conditions: filtration, backwashing, and acid washing. In the multi-stage cascaded filtration membrane group, the concentrate discharged from the previous stage filtration membrane group is directly used as the feed for the next stage filtration membrane group.

2. The ceramic membrane continuous brine purification apparatus as described in claim 1, characterized in that, Also includes: Salt dissolving pond, used for dissolving crude salt; Precipitation reaction vessel, used for the precipitation of impurities; Liquid tank is used for temporary storage of pretreatment liquid; The salt treatment tank, sedimentation reaction tank, and feed tank are connected in sequence by pipelines, and the pipelines between adjacent components are equipped with power pumps for driving the feed liquid transportation.

3. The ceramic membrane continuous brine purification apparatus as described in claim 1, characterized in that, Also includes: Backwash tank, used to provide backwash fluid; Acid tank, used to supply pickling solution; The backwash tank and acid tank are connected to the backwash liquid input end and acid input end of the multi-stage series filtration membrane group via pipelines with valves, respectively, and the sewage tank is connected to the backwash waste liquid output end of the multi-stage series filtration membrane group via pipelines with valves.

4. The ceramic membrane continuous brine purification apparatus as described in claim 1, characterized in that, The independent control valve group includes one or more of the following: The feed valve is located on the feed line of the membrane module and is used to control the introduction of crude brine or concentrate into the membrane module. A reflux valve, located on the reflux line of the membrane module, is used to control the flow direction of concentrate that has not permeated through the membrane. The permeate valve is located on the permeate line of the membrane module and is used to control the output of refined brine. All permeate lines of the membrane modules are connected to the permeate tank. The backwash inlet valve is located on the backwash inlet pipeline of the membrane module. The feed end of the backwash inlet pipeline is connected to the backwash tank. Under the action of the air compressor, the backwash liquid is controlled to enter the membrane module. The backwash outlet valve is located on the backwash outlet pipeline of the membrane module, and the discharge end of the backwash outlet pipeline is connected to the sludge tank. The pickling inlet valve is located on the acid inlet pipeline of the membrane module. The feed end of the acid inlet pipeline is connected to the acid tank. The acid in the acid tank flows into the membrane module through the pickling inlet valve under the action of the power pump. The acid wash outlet valve is located on the acid waste liquid outlet pipeline of the membrane module, through which the acid waste liquid can flow back to the acid tank.

5. The ceramic membrane continuous brine purification apparatus as described in claim 1, characterized in that, A permeate pipeline is provided between the backwash tank and the product water tank. This pipeline is used to transport the permeate to the backwash tank as backwashing fluid. A permeate supply valve for the backwash tank is provided on the permeate pipeline.

6. The ceramic membrane continuous brine purification apparatus as described in claim 1, characterized in that, The membrane module is filled with a silicon carbide ceramic membrane with an average pore size of 20~600 nm.

7. The ceramic membrane continuous brine purification apparatus as described in claim 4, characterized in that, A zwitterionic modification layer is provided on the surface of the silicon carbide ceramic film, which is constructed by a two-step modification method: The first step involves immersing a silicon carbide ceramic membrane in a Tris buffer solution containing dopamine hydrochloride and polyethyleneimine, and reacting it at a constant temperature of 0–50 °C for 0.1–20 h to introduce tertiary amine groups. The second step involves immersing the silicon carbide ceramic membrane treated in the first step into an aqueous solution of sodium 2-bromoethylsulfonate and reacting it at 10-70°C for 1-50 h to construct a zwitterionic modified layer on the membrane surface.

8. The ceramic membrane continuous brine purification apparatus as described in claim 5, characterized in that, The concentrations of dopamine hydrochloride and polyethyleneimine in the Tris buffer were 0.1–5.0 g·L⁻¹. -1 and 0.1~5 g·L -1 The concentration of the sodium 2-bromoethylsulfonate aqueous solution is 0.05~2 mol·L⁻¹. -1 .

9. A method for continuous brine purification using a ceramic membrane based on any one of claims 1-8, characterized in that, Includes the following steps: (1) Pretreatment: The crude salt is dissolved in the salt dissolving tank and allowed to stand and separate into layers. The supernatant is pumped to the precipitation reaction tank by a power pump for precipitation reaction. After the reaction, the supernatant is pumped to the material tank for temporary storage by a power pump. (2) Multi-stage filtration: The liquid in the feed tank is pumped to a multi-stage series filter membrane group by a power pump. It flows through each stage of the filter membrane group for filtration in sequence. The refined brine enters the product water tank, and the concentrate of the last stage filter membrane group flows back to the feed tank. (3) Maintenance operation: When the membrane module needs to be backwashed, close the feed valve, reflux valve, product water valve, backwash tank permeate supply valve, acid wash water inlet valve and acid wash water outlet valve corresponding to the membrane module, open the backwash water inlet valve and backwash water outlet valve corresponding to the membrane module, turn on the air compressor, and use the backwash liquid in the backwash tank to flush. When the backwashing effect is not good, close the feed valve, reflux valve, product water valve, backwash inlet valve and backwash outlet valve corresponding to the membrane module, and open the acid washing inlet valve and acid washing outlet valve corresponding to the membrane module. Use the acid washing solution in the acid tank for acid washing. After acid washing, it is necessary to wash with water until the pH of the effluent is neutral. During the maintenance operation, at least one membrane module of each filtration membrane group must be kept in filtration state to ensure continuous operation of the device.

10. The continuous brine purification method using a ceramic membrane as described in claim 9, characterized in that, The operating conditions for multi-stage filtration are: transmembrane pressure difference 0.10~0.20 MPa, membrane surface flow velocity 1-2 m·s. -1 The equipment operates at a temperature of 50~60℃.

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