A modified cation exchange membrane and its preparation method and application

Abstract

The present invention relates to a modified cation exchange membrane and a preparation method and application thereof. The modified cation exchange membrane comprises three functional groups: sulfonic acid group, carboxylic acid group and phosphonic acid group. Compared with industrial phosphoric acid, phosphoric acid prepared by the modified cation exchange membrane of the present invention has a lower SO4 2‑ Except for a slightly higher content, there is no significant difference in other aspects. 2‑ The problem of high content can be solved by increasing the amount of rinsing water, but the modified cation exchange membrane of the present invention has relatively lower power consumption and lower preparation cost, and the obtained ammonium sulfate can be sold as a by-product, which has good economic benefits. The various indicators of iron phosphate obtained by phosphoric acid prepared by the modified cation exchange membrane are basically the same as those of iron phosphate prepared by industrial phosphoric acid.

Description

Technical Field

[0001] The invention relates to the technical field of separation and purification, and in particular to a modified cation exchange membrane and a preparation method and application thereof. Background Art

[0002] Lithium iron phosphate has low cost, little environmental pollution, and good thermal stability, making it the most promising positive electrode material for power batteries. The raw materials phosphoric acid and iron phosphate are also crucial.

[0003] CN107565132A discloses a method for preparing an iron phosphate precursor suitable for preparing lithium iron phosphate, the iron phosphate prepared therefrom, and a method for preparing lithium iron phosphate and the lithium iron phosphate prepared therefrom; the method for preparing iron phosphate comprises the following steps: adding reduced iron powder to an aqueous solution containing sulfuric acid and an organic acid, reacting at 60-90°C for 5-10 hours, and filtering with high magnetic force after the reaction is completed to obtain an aqueous solution of ferrous sulfate; dripping a mixed solution consisting of ammonium persulfate, ammonium phosphate, and a nanoparticle control agent into the aqueous solution of ferrous sulfate, precipitating at 60-80°C and a pH value below 3, stirring and mixing to react for 5-8 hours, demagnetizing and filtering after the reaction is completed, pressing into a filter cake, rinsing, spray drying, and powdering to obtain an iron phosphate product.

[0004] In the prior art, the price of raw materials for the synthesis of ferric phosphate has risen sharply, among which the price of 85% wet-process phosphoric acid has reached more than 9,000 yuan / ton, which is relatively costly.

[0005] CN201670727U discloses a phosphoric acid purification device that utilizes an ion exchange membrane to purify phosphoric acid, and the device can obtain high-purity phosphoric acid. The phosphoric acid purification device includes an electrodialysis device, in which an anode and a cathode are arranged, a cation exchange membrane and an anion exchange membrane are arranged between the anode and the cathode, an intermediate chamber is formed between the cation exchange membrane and the anion exchange membrane, the cation exchange membrane is close to the cathode, a cathode chamber is formed between the cation exchange membrane and the cathode, and an anion exchange membrane is close to the anode, and an anode chamber is formed between the anion exchange membrane and the anode. That is, the anode, the anion exchange membrane, the cation exchange membrane and the cathode are sequentially arranged in the electrodialysis device, so that the device can effectively remove anion and cation impurities while permeating anions and cations, thereby improving the purification effect of phosphoric acid.

[0006] In the prior art, during the preparation of phosphoric acid using commercial cation exchange membranes, divalent and multivalent ions such as calcium and magnesium will pass through the cation exchange membrane, causing membrane scaling, which in turn leads to a shortened membrane life and increased power consumption. At the same time, phosphorus sources (monohydrogen phosphate ions and / or dihydrogen phosphate ions) will pass through the cation exchange membrane, causing phosphorus loss.

[0007] Therefore, it is urgent to develop a cation exchange membrane that can inhibit the scaling of calcium and magnesium ions and has a low reverse migration of the same ions, so as to prepare low-cost phosphoric acid and iron phosphate. Summary of the invention

[0008] In view of the shortcomings of the prior art, the present invention aims to provide a modified cation exchange membrane and a preparation method and application thereof. The phosphoric acid prepared by the modified cation exchange membrane has a higher SO4 removal rate than industrial phosphoric acid. 2- Except for a slightly higher content, there is no significant difference in other aspects. 2- The problem of high content can be solved by increasing the amount of rinsing water, but the modified cation exchange membrane of the present invention has relatively lower power consumption and lower preparation cost, and the obtained ammonium sulfate can be sold as a by-product, which has good economic benefits. The various indicators of iron phosphate obtained by phosphoric acid prepared by the modified cation exchange membrane are basically the same as those of iron phosphate prepared by industrial phosphoric acid.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a modified cation exchange membrane, wherein the modified cation exchange membrane comprises three functional groups: sulfonic acid group, carboxylic acid group and phosphonic acid group.

[0011] The modified cation exchange membrane of the present invention includes not only the sulfonic acid group in the commercial cation exchange membrane, but also the carboxylic acid group and the phosphonic acid group. The coordinated use of the three functional groups can inhibit the scaling of calcium and magnesium ions when used for the preparation of phosphoric acid, and the reverse migration amount of the same-name ions is low. The prepared phosphoric acid has low cost and good performance.

[0012] Preferably, the raw materials for preparing the modified cation exchange membrane include sulfonic acid type cation exchange membrane, monomers containing alkenyl and carboxylic acid groups, and monomers containing alkenyl and phosphonic acid groups.

[0013] Preferably, the base membrane of the sulfonic acid type cation exchange membrane includes any one of polyvinylidene fluoride (PVDF), polyethylene or polyvinyl chloride.

[0014] Preferably, the monomer containing an alkenyl group and a carboxylic acid group includes any one of butenoic acid, pentenoic acid or itaconic acid, or a combination of at least two of them, wherein typical but non-limiting combinations include: a combination of butenoic acid and pentenoic acid, a combination of pentenoic acid and itaconic acid, a combination of butenoic acid, pentenoic acid and itaconic acid, etc.

[0015] Preferably, the monomer containing an alkenyl group and a phosphonic acid group comprises any one of vinylphosphonic acid, cis-propylenephosphonic acid or iso-propylenephosphonic acid, or a combination of at least two thereof, wherein typical but non-limiting combinations include: a combination of vinylphosphonic acid and cis-propylenephosphonic acid, a combination of cis-propylenephosphonic acid and iso-propylenephosphonic acid, a combination of vinylphosphonic acid, cis-propylenephosphonic acid and iso-propylenephosphonic acid, and the like.

[0016] Preferably, the mass ratio of the monomer containing alkenyl and carboxylic acid groups to the monomer containing alkenyl and phosphonic acid groups is 1:(0.2-1), wherein 0.2-1 can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, etc., and 1:(0.4-0.8) is further preferred.

[0017] In the present invention, the mass ratio of the monomer containing alkenyl and carboxylic acid groups to the monomer containing alkenyl and phosphonic acid groups is preferably in the range of 1:(0.2-1), because: within this ratio range, the carboxylic acid group can improve the hydrophilicity of the membrane and effectively reduce the reverse migration rate of the hydroxide group, and the phosphonic acid group can reduce the reverse migration rate of the phosphate group, increase the charge density of the membrane, and reduce the membrane resistance; if the mass ratio of the two is too high, the reverse migration rate of the phosphate group will increase and the membrane resistance will increase; if the mass ratio of the two is too low, the reverse migration rate of the hydroxide group will increase.

[0018] In a second aspect, the present invention provides a method for preparing the modified cation exchange membrane according to the first aspect, the preparation method comprising the following steps:

[0019] The monomer containing alkenyl and carboxylic acid group and the monomer containing alkenyl and phosphonic acid group are polymerized on the sulfonic acid type cation exchange membrane to obtain the modified cation exchange membrane.

[0020] Preferably, the preparation method comprises: first swelling the sulfonic acid type cation exchange membrane in a solvent, then immersing it in a mixture of a monomer containing an olefinic group and a carboxylic acid group and a monomer containing an olefinic group and a phosphonic acid group, and finally performing a polymerization reaction under the action of an initiator to obtain the modified cation exchange membrane.

[0021] Preferably, the solvent comprises any one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO) or N-methylpyrrolidone (NMP) or a combination of at least two thereof, wherein typical but non-limiting combinations include: a combination of N,N-dimethylformamide and N,N-dimethylacetamide, a combination of dimethyl sulfoxide and N-methylpyrrolidone, a combination of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and N-methylpyrrolidone, and the like.

[0022] Preferably, the swelling time is 10-60 min, for example, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, etc.

[0023] Preferably, after the soaking, the sulfonic acid type cation exchange membrane is taken out from the mixture, placed in a solution of an initiator, and subjected to polymerization reaction under a protective atmosphere.

[0024] Preferably, the initiator comprises benzoyl peroxide.

[0025] Preferably, the solvent used in the initiator solution includes tetrahydrofuran.

[0026] Preferably, the polymerization reaction temperature is 60-80°C, such as 65°C, 70°C, 75°C, etc.

[0027] Preferably, the polymerization reaction time is 2-4 h, such as 2.5 h, 3 h, 3.5 h, etc.

[0028] Preferably, after the polymerization reaction, the product is further cleaned.

[0029] Preferably, the cleaning method includes soaking in water.

[0030] Preferably, the soaking temperature is 20-60°C, such as 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, etc.

[0031] Preferably, the soaking time is 1-3 hours, such as 1.5 hours, 2 hours, 2.5 hours, etc.

[0032] Preferably, the cleaning is performed at least twice, for example, three times, four times, five times, etc.

[0033] In a third aspect, the present invention provides a method for preparing phosphoric acid, the preparation method comprising: using monoammonium phosphate and / or diammonium phosphate as raw materials, preparing phosphoric acid by bipolar membrane electrodialysis, wherein the cation membrane used in the bipolar membrane electrodialysis comprises the modified cation exchange membrane described in the first aspect.

[0034] In the present invention, phosphoric acid is prepared by bipolar membrane electrodialysis using monoammonium phosphate and / or diammonium phosphate. The price of industrial monoammonium phosphate and diammonium phosphate is about 6,000 yuan / ton. The preparation process has low power consumption, the preparation cost of the phosphoric acid is low, the obtained phosphoric acid has low calcium ion content, and the loss of phosphorus element is small.

[0035] Preferably, the preparation method comprises the following steps:

[0036] (1) A three-compartment bipolar membrane is formed by using a modified cation exchange membrane, an anion membrane and a bipolar membrane to form an acid chamber, a salt chamber, a base chamber and an electrode chamber;

[0037] (2) adding monoammonium phosphate solution and / or diammonium phosphate solution into the salt chamber;

[0038] Add dilute phosphoric acid to the acid chamber;

[0039] Add dilute sulfuric acid to the alkali chamber;

[0040] Adding any one or a combination of at least two of sodium hydroxide solution, ammonium sulfate solution, monoammonium phosphate solution or diammonium phosphate solution into the electrode chamber;

[0041] (3) Performing electrodialysis to obtain the phosphoric acid.

[0042] In the present invention, an electrodialysis device commonly used in the prior art is used to prepare phosphoric acid, and a modified cation exchange membrane, an anion membrane and a bipolar membrane form a three-compartment bipolar membrane system to form an acid chamber, a salt chamber, an alkali chamber and an electrode chamber. Specifically, the bipolar membrane, the modified cation exchange membrane, the anion membrane and the bipolar membrane are arranged in sequence, an alkali chamber is formed between the bipolar membrane and the modified cation exchange membrane, an acid chamber is formed between the bipolar membrane and the anion membrane, and a salt chamber is formed between the modified cation exchange membrane and the anion membrane. The compartments between the bipolar membranes on both sides and the electrodes are filled with electrolytes to conduct electricity and form electrode chambers.

[0043] In the present invention, dilute phosphoric acid is added to the acid chamber as a starting liquid to reduce the initial resistance; dilute sulfuric acid is added to the alkali chamber as an ammonia absorption liquid to form ammonium sulfate, which is further recycled and utilized to improve economic benefits.

[0044] Preferably, in step (2), in the salt chamber, the mass concentrations of the monoammonium phosphate solution and the diammonium phosphate solution are independently 10%-20%, such as 12%, 14%, 16%, 18%, etc.

[0045] Preferably, the monoammonium phosphate solution and the diammonium phosphate solution are each independently subjected to impurity removal before being added to the salt chamber.

[0046] Preferably, the concentration of the dilute phosphoric acid is 0.1-0.15 mol / L, such as 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L, etc.

[0047] Preferably, the concentration of the dilute sulfuric acid is 0.5-1.2 mol / L, such as 0.6 mol / L, 0.8 mol / L, 1 mol / L, etc.

[0048] Preferably, the mass concentration of the solution in the electrode chamber is 2%-5%, for example, 2.5%, 3%, 3.5%, 4%, 4.5%, etc.

[0049] Preferably, in step (3), the current density of the electrodialysis is 500-1000 A / m 2 , for example 600A / m 2 , 700A / m 2 、800A / m 2 , 900A / m 2 wait.

[0050] Preferably, during the electrodialysis, the temperature of the system is 30-40°C, such as 32°C, 34°C, 36°C, 38°C, etc.

[0051] Preferably, the electrodialysis stops running when the conductivity of the salt chamber no longer decreases.

[0052] In a fourth aspect, the present invention provides a method for preparing ferric phosphate, the preparation method comprising the following steps:

[0053] (1') co-precipitating an iron source and a phosphorus source to obtain an iron phosphate slurry;

[0054] (2') filtering, washing and dispersing the iron phosphate slurry to obtain a secondary slurry;

[0055] (3') Using the phosphoric acid obtained by the preparation method described in the third aspect to adjust the pH of the secondary slurry, to obtain the iron phosphate.

[0056] Preferably, in step (1'), the iron source comprises ferrous sulfate solution.

[0057] Preferably, the phosphorus source comprises a monoammonium phosphate solution and / or a diammonium phosphate solution.

[0058] Preferably, the coprecipitation reaction is carried out under the action of an oxidant.

[0059] Preferably, the oxidant comprises any one of hydrogen peroxide, ozone, oxygen or air, or a combination of at least two of them, wherein typical but non-limiting combinations include: a combination of hydrogen peroxide, ozone and oxygen, a combination of ozone, oxygen and air, a combination of hydrogen peroxide, ozone, oxygen and air, etc.

[0060] Preferably, the molar concentration of the iron source is 0.5-1.5 mol / L, for example, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, etc.

[0061] Preferably, the molar concentration of the phosphorus source is 0.5-1.5 mol / L, for example, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, etc.

[0062] Preferably, the molar ratio of iron element to phosphorus element in the iron source and the phosphorus source is (0.95-1.05):1, wherein 0.95-1.05 can be 0.96, 0.98, 1, 1.02, 1.04, etc.

[0063] Preferably, in the coprecipitation reaction, the pH regulator used includes phosphoric acid and / or ammonia water.

[0064] Preferably, in the coprecipitation reaction, the pH of the system is 1.5-3, such as 1.6, 1.8, 2, 2.2, 2.4, 2.6, etc.

[0065] Preferably, the coprecipitation reaction temperature is 20-50°C, such as 25°C, 30°C, 35°C, 40°C, 45°C, etc.

[0066] Preferably, the coprecipitation reaction time is 30-60 min, for example, 35 min, 40 min, 45 min, 50 min, 55 min, etc.

[0067] Preferably, in step (3'), the pH of the secondary slurry is adjusted to 2-5, such as 2.5, 3, 3.5, 4, 4.5, etc.

[0068] Preferably, the pH adjustment further includes aging.

[0069] Preferably, the aging temperature is 85-95°C, such as 86°C, 88°C, 90°C, 92°C, 94°C, etc.

[0070] Preferably, the aging time is 1-3 h, for example, 1.2 h, 1.4 h, 1.6 h, 1.8 h, 2 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h, etc.

[0071] Preferably, the aging further includes filter pressing, washing, drying and crushing.

[0072] Compared with the prior art, the present invention has the following beneficial effects:

[0073] (1) Compared with industrial phosphoric acid, the phosphoric acid prepared by the modified cation exchange membrane of the present invention has a higher SO4 2- Except for a slightly higher content, there is no significant difference in other aspects. 2- The problem of high content can be solved by increasing the amount of rinsing water. However, the modified cation exchange membrane of the present invention has low power consumption, and the cost of the produced phosphoric acid is 2000-3000 yuan lower than that of commercially available industrial phosphoric acid. The obtained ammonium sulfate can be sold as a by-product, which has good economic benefits.

[0074] In the present invention, the phosphoric acid prepared by the modified cation exchange membrane has a mass concentration of 8.2%-12.2%, which can be further concentrated as needed; SO4 in phosphoric acid 2- The ratio is between 640-1180ppm, and the Ca content in ammonium sulfate is 2+ The ratio is between 2-8ppm, PO4 in ammonium sulfate 3- The ratio is between 1400-2100ppm, and the power consumption is between 980-1230kW·h / t phosphoric acid.

[0075] (2) In the present invention, the various indicators of the iron phosphate further obtained from the phosphoric acid prepared by the modified cation exchange membrane are basically the same as those of the iron phosphate prepared by industrial phosphoric acid.

[0076] In the present invention, the phosphoric acid prepared by the modified cation exchange membrane further obtains iron phosphate, SO4 2- The content is between 66-73ppm, the particle size range is between 2-5μm, and the moisture content is between 20.1wt%-20.3wt%. DETAILED DESCRIPTION

[0077] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0078] In the present invention, the purchase information of some raw materials involved in each embodiment is as follows:

[0079] Cation exchange membrane, sulfonic acid type PVDF cation exchange membrane, purchased from Suzhou Shengernuo Technology Co., Ltd.;

[0080] Butenoic acid, valenoic acid, and itaconic acid were purchased from Sinopharm Group;

[0081] Ethylene phosphonic acid, n-propylene phosphonic acid, and isopropyl phosphonic acid were purchased from Aldrich;

[0082] Industrial grade monoammonium phosphate was purchased from Guizhou Phosphate Co., Ltd.;

[0083] Industrial grade diammonium phosphate was purchased from Guizhou Phosphate Co., Ltd.;

[0084] 98% sulfuric acid, produced by Wanhua Chemical Co., Ltd.

[0085] 85% phosphoric acid, purchased from Guizhou Phosphate Co., Ltd.;

[0086] 32% sodium hydroxide, produced by Wanhua Chemical Co., Ltd.

[0087] Ferrous sulfate was purchased from Sichuan Development Longmang Co., Ltd.;

[0088] 27.5% hydrogen peroxide was purchased from Yantai Jinwo Chemical Co., Ltd.

[0089] The main equipment and instrument information used in this invention is as follows:

[0090] Bipolar membrane electrodialysis instrument, EX-3BT, Hangzhou Lanran Environmental Technology Co., Ltd.;

[0091] Inductively coupled plasma, 725ICP OES, Agilent Technologies;

[0092] Laser particle size analyzer, SALD-7500nano, Shimadzu Corporation;

[0093] Potentiometric titrator, 905-Titrando, Metrohm Co., Ltd.;

[0094] Ion chromatograph, Metrohm-881IC, Metrohm Co., Ltd.;

[0095] pH meter, OHS-3C, Shanghai Leici Instrument Co., Ltd.

[0096] Preparation Example 1

[0097] This preparation example provides a modified cation exchange membrane, which includes three functional groups: sulfonic acid group, carboxylic acid group and phosphonic acid group.

[0098] The modified cation exchange membrane is obtained by the following preparation method, which comprises the following steps:

[0099] (1) The sulfonic acid PVDF cation exchange membrane was swollen with DMF at room temperature for 30 min;

[0100] (2) immersing the swollen cation exchange membrane in a modified solution for 1 hour, wherein the modified solution is a mixture of crotonic acid and vinylphosphonic acid in a mass ratio of 5:4, so that the monomers enter the molecular gap of the PVDF main chain;

[0101] (3) taking the saturated cation exchange membrane out of the solution, removing excess liquid from the surface, and then immersing it in a tetrahydrofuran solution of benzoyl peroxide protected by nitrogen, wherein the mass concentration of benzoyl peroxide is 0.2 wt%, and continuing the reaction at 80° C. for 2 h to allow the carboxylic acid and phosphonic acid monomers to undergo free radical polymerization and form an interpenetrating network structure with the main chain of the base membrane PVDF;

[0102] (4) After the reaction is completed, the modified cation exchange membrane is immersed in pure water at 40° C. for 2 hours, and then replaced three times to remove monomers that have not participated in the reaction, oligomers on the membrane surface, benzoyl peroxide and tetrahydrofuran, thereby obtaining the modified cation exchange membrane.

[0103] Preparation Example 2-4

[0104] Preparation Examples 2-4 were prepared using a modified cation exchange membrane in substantially the same manner as Preparation Example 1, with the only difference being that the raw material composition and process parameters in Table 1 were different.

[0105] Table 1

[0106]

[0107] In Table 1, monomer A refers to a monomer containing an alkenyl group and a carboxylic acid group; and monomer B refers to a monomer containing an alkenyl group and a phosphonic acid group.

[0108] Example 1

[0109] This embodiment provides a method for preparing phosphoric acid, using the modified cation exchange membrane described in Preparation Example 1 to prepare phosphoric acid, the preparation method comprising the following steps:

[0110] (1) dissolving monoammonium phosphate in pure water and removing solid impurities using an ultrafiltration membrane;

[0111] (2) introducing a purified monoammonium phosphate aqueous solution having a mass concentration of 15 wt % into the salt chamber of the bipolar membrane electrodialysis stack;

[0112] (3) 0.12 mol / L of dilute phosphoric acid was introduced into the acid chamber of the bipolar membrane electrodialysis stack as a starting solution to reduce the initial resistance. The total mass of the dilute phosphoric acid added was adjusted according to the amount of solution in the salt chamber to ensure that the phosphoric acid concentration in the acid chamber was 1-1.5 mol / L after the experiment.

[0113] (4) adding 0.9 mol / L dilute sulfuric acid into the alkaline chamber of the bipolar membrane electrodialysis stack as an ammonia absorption liquid, and maintaining the pH of the alkaline chamber solution ≤ 2 during the entire operation;

[0114] (5) introducing a 3.5 wt % monoammonium phosphate aqueous solution into the electrode chamber of the bipolar membrane electrodialysis membrane stack;

[0115] (6) Apply direct current at both ends of the bipolar membrane electrodialysis stack with a current density of 800 A / m 2 , the average temperature of the control system during operation is 35°C;

[0116] (7) When the conductivity of the salt chamber no longer decreases, it indicates that the ammonium ions have basically migrated and the operation is stopped; after the dilute phosphoric acid obtained from the salt chamber and the acid chamber is mixed, the phosphoric acid concentration is 10.2%, of which the sulfate and ammonium ions are 790 ppm and 1270 ppm respectively. This phosphoric acid is used for the next step of iron phosphate synthesis.

[0117] Embodiment 2-4

[0118] Examples 2-4 respectively use the modified cation exchange membranes described in Preparation Examples 2-4 to prepare phosphoric acid, and the only difference from Example 1 is that the raw material composition and process parameters in Table 2 are different.

[0119] Comparative Example 1

[0120] The difference between this comparative example and Example 1 is that the modified cation exchange membrane is replaced by an unmodified cation exchange membrane, and the rest is the same as Example 1.

[0121] Table 2

[0122]

[0123] Application Example 1

[0124] This application example provides a method for preparing iron phosphate, which comprises the following steps:

[0125] (1) dissolving ferrous sulfate and removing impurities to prepare a 1 mol / L reaction solution A;

[0126] (2) dissolving monoammonium phosphate and removing impurities to prepare a 1 mol / L reaction solution B;

[0127] (3) Solution A, solution B and 27.5% H2O2 were mixed in a certain proportion, wherein the molar ratio of ferrous sulfate to monoammonium phosphate was 1:1, the excess rate of hydrogen peroxide was 20%, the pH of the mixed solution was adjusted to 2 with phosphoric acid prepared in Example 1, and the mixture was reacted at 30° C. for 40 min to prepare an amorphous iron phosphate slurry;

[0128] (4) filtering and washing the iron phosphate slurry to obtain a primary rinse filter cake;

[0129] (5) adding pure water to disperse the primary filter cake to obtain a secondary slurry; adding dilute phosphoric acid to the secondary slurry to adjust the pH to 3, and aging the slurry at 90° C. for 2 h;

[0130] (6) performing secondary filter pressing and washing treatment on the aged slurry to obtain a secondary rinsed filter cake;

[0131] (7) Drying and crushing the secondary rinse filter cake to obtain the ferric phosphate.

[0132] Application Example 2-4

[0133] Application Examples 2-4 respectively use the phosphoric acid described in Examples 2-4 to prepare iron phosphate, and the only difference from Application Example 1 is that the raw material composition and process parameters in Table 3 are different.

[0134] Application Comparative Example 1

[0135] This application example uses the phosphoric acid described in Example 1 to prepare iron phosphate, and the only difference from Application Example 1 is that the raw material composition and process parameters in Table 3 are different.

[0136] Application Comparative Example 2

[0137] The difference between this comparative example and application example 1 is that the phosphoric acid described in example 1 is replaced with industrial grade 85% phosphoric acid, and the rest is the same as example 1.

[0138] Table 3

[0139]

[0140]

[0141] Performance Testing

[0142] 1. The phosphoric acid prepared in Examples 1-4 and Comparative Example 1 and 85% industrial phosphoric acid were subjected to the following tests: phosphoric acid concentration, SO4 2- Content, Ca in ammonium sulfate 2+ Content, PO4 in ammonium sulfate 3- The test results are summarized in Table 4.

[0143] Table 4

[0144]

[0145]

[0146] According to the data in Table 4, in the present invention, the phosphoric acid prepared by the modified cation exchange membrane has a mass concentration of 8.2%-12.2%, which can be further concentrated as needed; SO4 in phosphoric acid 2- The ratio is between 640-1180ppm, and the Ca content in ammonium sulfate is 2+ The ratio is between 2-8ppm, PO4 in ammonium sulfate 3- The ratio is between 1400-2100ppm, and the power consumption is between 980-1230kW·h / t phosphoric acid; the phosphoric acid prepared by the modified cation exchange membrane of the present invention is more efficient in removing SO4 than industrial phosphoric acid. 2- Except for a slightly higher content, there is no significant difference in other aspects. 2- The problem of high content can be solved by increasing the amount of rinsing water, but the modified cation exchange membrane of the present invention has relatively lower power consumption, and the cost of the produced phosphoric acid is 2000-3000 yuan lower than that of commercially available industrial phosphoric acid. The obtained ammonium sulfate can be sold as a by-product, with good economic benefits.

[0147] Analysis of Comparative Example 1 and Example 1 shows that Comparative Example 1 uses conventional sulfonic acid cation exchange membrane to prepare phosphoric acid, and its power consumption is significantly higher. 2+ The content is also high.

[0148] 2. The iron phosphate prepared in Application Examples 1-4 and Comparative Example 2 was subjected to SO4 2- Testing for content, particle size range and moisture.

[0149] The test results are summarized in Table 5.

[0150] Table 5

[0151]

[0152]

[0153] According to the data in Table 5, in the present invention, the phosphoric acid prepared by the modified cation exchange membrane further obtains iron phosphate, SO4 2- The content is between 66-73ppm, the particle size range is between 2-5μm, and the moisture content is between 20.1wt%-20.3wt%; the various indicators of iron phosphate further obtained from phosphoric acid prepared by the modified cation exchange membrane of the present invention are basically the same as those of iron phosphate prepared by industrial phosphoric acid.

[0154] The present invention illustrates the detailed method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A modified cation exchange membrane, characterized in that: The modified cation exchange membrane includes three functional groups: sulfonic acid group, carboxylic acid group and phosphonic acid group; The raw materials for preparing the modified cation exchange membrane include sulfonic acid cation exchange membrane, monomers containing alkenyl and carboxylic acid groups, and monomers containing alkenyl and phosphonic acid groups; The mass ratio of the monomer containing alkenyl and carboxylic acid groups to the monomer containing alkenyl and phosphonic acid groups is 1:(0.2-1).

2. The modified cation exchange membrane according to claim 1, characterized in that The base membrane of the sulfonic acid type cation exchange membrane includes any one of polyvinylidene fluoride, polyethylene or polyvinyl chloride.

3. The modified cation exchange membrane according to claim 1, characterized in that The monomer containing an alkenyl group and a carboxylic acid group includes any one of butenoic acid, pentenoic acid or itaconic acid or a combination of at least two thereof.

4. The modified cation exchange membrane according to claim 1, characterized in that: The monomer containing an alkenyl group and a phosphonic acid group includes any one of vinylphosphonic acid, cis-propylenephosphonic acid or iso-propylenephosphonic acid, or a combination of at least two thereof.

5. A method for preparing a modified cation exchange membrane according to any one of claims 1 to 4, characterized in that: The preparation method comprises the following steps: The monomer containing alkenyl and carboxylic acid group and the monomer containing alkenyl and phosphonic acid group are polymerized on the sulfonic acid type cation exchange membrane to obtain the modified cation exchange membrane.

6. The preparation method according to claim 5, characterized in that: The preparation method comprises: firstly swelling the sulfonic acid type cation exchange membrane in a solvent, then soaking it in a mixture of a monomer containing alkenyl and carboxylic acid groups and a monomer containing alkenyl and phosphonic acid groups, and finally performing a polymerization reaction under the action of an initiator to obtain the modified cation exchange membrane.

7. The preparation method according to claim 6, characterized in that: The solvent includes any one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or N-methylpyrrolidone, or a combination of at least two thereof.

8. The preparation method according to claim 6, characterized in that: The swelling time is 10-60 min.

9. The preparation method according to claim 6, characterized in that: After the soaking, the sulfonic acid type cation exchange membrane is taken out from the mixture, placed in an initiator solution, and subjected to polymerization reaction under a protective atmosphere.

10. The preparation method according to claim 6, characterized in that: The initiator includes benzoyl peroxide.

11. The preparation method according to claim 9, characterized in that: In the initiator solution, the solvent used includes tetrahydrofuran.

12. The preparation method according to claim 6, characterized in that: The polymerization temperature is 60-80°C.

13. The preparation method according to claim 6, characterized in that: The polymerization reaction time is 2-4 hours.

14. The preparation method according to claim 6, characterized in that: After the polymerization reaction, the product is washed.

15. The preparation method according to claim 14, characterized in that: The cleaning method includes soaking in water.

16. The preparation method according to claim 15, characterized in that: The soaking temperature is 20-60°C.

17. The preparation method according to claim 15, characterized in that: The soaking time is 1-3 hours.

18. The preparation method according to claim 14, characterized in that: The cleaning is performed at least twice.

19. A method for preparing phosphoric acid, characterized in that: The preparation method comprises: using monoammonium phosphate and / or diammonium phosphate as raw materials to prepare phosphoric acid by bipolar membrane electrodialysis, wherein the cation membrane used in the bipolar membrane electrodialysis comprises the modified cation exchange membrane described in any one of claims 1 to 4.

20. The preparation method according to claim 19, characterized in that: The preparation method comprises the following steps: (1) A three-compartment bipolar membrane is formed by using a modified cation exchange membrane, an anion membrane and a bipolar membrane to form an acid chamber, a salt chamber, a base chamber and an electrode chamber; (2) adding monoammonium phosphate solution and / or diammonium phosphate solution into the salt chamber; Add dilute phosphoric acid to the acid chamber; Add dilute sulfuric acid to the alkali chamber; Adding any one or a combination of at least two of sodium hydroxide solution, ammonium sulfate solution, monoammonium phosphate solution or diammonium phosphate solution into the electrode chamber; (3) Performing electrodialysis to obtain the phosphoric acid.

21. The preparation method according to claim 20, characterized in that: In step (2), in the salt chamber, the mass concentrations of the monoammonium phosphate solution and the diammonium phosphate solution are independently 10%-20%.

22. The preparation method according to claim 20, characterized in that: The monoammonium phosphate solution and the diammonium phosphate solution are each independently purified before being added to the salt chamber.

23. The preparation method according to claim 20, characterized in that: The concentration of the dilute phosphoric acid is 0.1-0.15 mol / L.

24. The preparation method according to claim 20, characterized in that: The concentration of the dilute sulfuric acid is 0.5-1.2 mol / L.

25. The preparation method according to claim 20, characterized in that: The mass concentration of the solution in the electrode chamber is 2%-5%.

26. The preparation method according to claim 20, characterized in that: In step (3), the current density of the electrodialysis is 500-1000A / m 2 .

27. The preparation method according to claim 20, characterized in that: During the electrodialysis, the temperature of the system is 30-40°C.

28. The preparation method according to claim 20, characterized in that: The electrodialysis stops running until the conductivity of the salt chamber no longer decreases.

29. A method for preparing iron phosphate, characterized in that: The preparation method comprises the following steps: (1') co-precipitating an iron source and a phosphorus source to obtain an iron phosphate slurry; (2') filtering, washing and dispersing the iron phosphate slurry to obtain a secondary slurry; (3') Using phosphoric acid obtained by the preparation method according to any one of claims 19 to 28 to adjust the pH of the secondary slurry to obtain the iron phosphate.

30. The preparation method according to claim 29, characterized in that: In step (1'), the iron source includes ferrous sulfate solution.

31. The preparation method according to claim 29, characterized in that: The phosphorus source includes a monoammonium phosphate solution and / or a diammonium phosphate solution.

32. The preparation method according to claim 29, characterized in that: The coprecipitation reaction is carried out under the action of an oxidant.

33. The preparation method according to claim 32, characterized in that: The oxidant includes any one of hydrogen peroxide, ozone, oxygen or air, or a combination of at least two of them.

34. The preparation method according to claim 29, characterized in that: The molar concentration of the iron source is 0.5-1.5 mol / L.

35. The preparation method according to claim 29, characterized in that: The molar concentration of the phosphorus source is 0.5-1.5 mol / L.

36. The preparation method according to claim 29, characterized in that: The molar ratio of iron element to phosphorus element in the iron source and phosphorus source is (0.95-1.05):

1.

37. The preparation method according to claim 29, characterized in that: In the coprecipitation reaction, the pH regulator used includes phosphoric acid and / or ammonia water.

38. The preparation method according to claim 29, characterized in that: In the coprecipitation reaction, the pH of the system is 1.5-3.

39. The preparation method according to claim 29, characterized in that: The temperature of the coprecipitation reaction is 20-50°C.

40. The preparation method according to claim 29, characterized in that: The coprecipitation reaction time is 30-60 min.

41. The preparation method according to claim 29, characterized in that In step (3'), the pH of the secondary slurry is adjusted to 2-5.

42. The preparation method according to claim 29, characterized in that: The pH adjustment further includes aging.

43. The preparation method according to claim 42, characterized in that: The aging temperature is 85-95°C.

44. The preparation method according to claim 42, characterized in that: The aging time is 1-3h.

45. The preparation method according to claim 42, characterized in that: The aging process also includes filter pressing, washing, drying and crushing.

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