Acid-resistant nanofiltration membrane modification liquid, modified acid-resistant nanofiltration membrane and application of modified acid-resistant nanofiltration membrane

Abstract

The invention relates to the technical field of wet-process phosphoric acid purification, in particular to acid-resistant nanofiltration membrane modification liquid, a modified acid-resistant nanofiltration membrane and application of the modified acid-resistant nanofiltration membrane. The acid-resistant nanofiltration membrane modification liquid is prepared from the following components in percentage by mass: 26 to 32 percent of phosphoric acid, 2.0 to 3.0 percent of PEI1800 and 2.5 to 3.5 percent of N, N, N-trimethyloctadecane-1-ammonium iodide. The acid-resistant nanofiltration membrane is modified by using the modification liquid, so that a relatively high Zeta potential is attached to the surface of the acid-resistant nanofiltration membrane, the flux of the membrane is greatly improved under the condition that the interception performance of the membrane is not reduced, and the interception rate of the nanofiltration membrane on cation impurities in phosphoric acid is enhanced when the acid-resistant nanofiltration membrane is applied to purification of wet-process phosphoric acid or preparation of electronic-grade phosphoric acid; meanwhile, the rejection rate of the nanofiltration membrane on phosphoric acid is reduced, and efficient separation and purification of phosphoric acid and impurity ions are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of wet-process phosphoric acid purification, in particular to an acid-resistant nanofiltration membrane modifying liquid, a modified acid-resistant nanofiltration membrane and applications thereof. Background Art

[0002] According to the differences in production process and product purity, phosphoric acid can be divided into fertilizer grade, industrial grade, food grade, pharmaceutical grade, electronic grade, etc. Among them, electronic grade phosphoric acid is a high-purity phosphoric acid, which is used as a cleaning agent and etching agent in microelectronics industries such as large-scale integrated circuits, thin-film liquid crystal displays, and semiconductors. Its purity has a very important impact on the product rate, electrical properties, and reliability of electronic components. In addition, electronic grade phosphoric acid is also a key raw material for the preparation of high-purity phosphates and organophosphorus products, and is a key dopant in photovoltaic cells. With the continuous implementation of emerging network and electronic application fields such as artificial intelligence, cloud computing, the Internet of Things, intelligent driving, big data, and drones, the consumption of electronic grade phosphoric acid in my country will continue to grow rapidly. According to statistics and forecasts, my country's consumption of electronic grade phosphoric acid will reach 20,000 tons in 2020, and will maintain a growth rate of about 8% in the next few years.

[0003] At present, the preparation methods of electronic-grade phosphoric acid mainly include phosphorus compound conversion method and direct purification method of industrial phosphoric acid. The phosphorus compound conversion method can be further divided into phosphorus pentoxide hydration method, phosphine decomposition method, phosphorus trichloride reduction method, phosphorus oxychloride hydrolysis method, etc.; the deep purification method of industrial phosphoric acid is mainly divided into filtration purification method, melt crystallization method and cooling crystallization method, etc. However, these methods all have the problems of complex process, high process energy consumption, high phosphorus loss and high cost. And because there are many types of impurities in wet-process phosphoric acid and high impurity content, there is little technology to directly purify and produce high-purity electronic-grade phosphoric acid using it as a raw material. The currently disclosed purification methods for wet-process phosphoric acid can only achieve food grade at best.

[0004] Membrane separation technology is considered to be one of the most promising separation technologies, with the characteristics of low energy consumption, good separation effect, simple equipment, and environmental friendliness. In the prior art, membrane purification of phosphoric acid is also used to achieve the preparation of electronic grade phosphoric acid, but the existing membrane purification of phosphoric acid still has the following disadvantages: the reverse osmosis membrane cannot play a good role in purifying and separating phosphoric acid due to its high interception rate for phosphoric acid and impurity ions; the nanofiltration membrane has a low removal rate for impurity ions, especially for monovalent ions. The presence of impurities in wet phosphoric acid makes the nanofiltration membrane run at a low flux and poor purification effect during the purification process. At the same time, while intercepting impurity ions, it also intercepts more phosphoric acid, resulting in a low phosphoric acid yield. Summary of the invention

[0005] In order to solve the defects in the prior art, the present invention provides an acid-resistant nanofiltration membrane modifying liquid, a modified acid-resistant nanofiltration membrane and its application. The present invention uses the modifying liquid to modify the acid-resistant nanofiltration membrane so that the surface of the acid-resistant nanofiltration membrane has a higher Zeta potential, which greatly improves the flux of the membrane without reducing the interception performance of the membrane. In the process of purifying wet-process phosphoric acid or preparing electronic-grade phosphoric acid, the interception rate of the nanofiltration membrane for cationic impurities in phosphoric acid is enhanced, and the interception rate of the nanofiltration membrane for phosphoric acid is reduced, thereby realizing efficient separation and purification of phosphoric acid and impurity ions.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides an acid-resistant nanofiltration membrane modification liquid, which comprises, by mass concentration, 26-32% phosphoric acid, 2.0-3.0% PEI1800, and 2.5-3.5% N,N,N-trimethyloctadecane-1-ammonium iodide.

[0008] In a second aspect, the present invention provides a modified acid-resistant nanofiltration membrane obtained by modifying the acid-resistant nanofiltration membrane modifying liquid.

[0009] Preferably, the Zeta potential of the modified acid-resistant nanofiltration membrane is ≥75 mV.

[0010] In a third aspect, the present invention provides a method for preparing a modified acid-resistant nanofiltration membrane, comprising the following steps:

[0011] (1) statically immersing the nanofiltration membrane element in the modified liquid to obtain a statically immersed nanofiltration membrane element;

[0012] (2) loading the modified liquid into a membrane machine, and treating the statically soaked nanofiltration membrane element in the membrane machine;

[0013] (3) The nanofiltration membrane element treated in step (2) is statically immersed again.

[0014] Preferably, in step (1), the static soaking time is 12 to 15 hours and the temperature is 50 to 60°C.

[0015] Preferably, the operating conditions of the membrane machine in step (2) are: pressure 3-4 MPa, temperature 25-30° C., and cycle operation for 5-6 hours.

[0016] Preferably, the static immersion time in step (3) is more than 24 hours, and the temperature is 25-30°C.

[0017] In a fourth aspect, the present invention provides the use of the modified acid-resistant nanofiltration membrane in purifying wet-process phosphoric acid or preparing electronic-grade phosphoric acid.

[0018] Preferably, the application of preparing electronic grade phosphoric acid is specifically:

[0019] The wet-process phosphoric acid is filtered and then enters into an inorganic ultrafiltration membrane to obtain a concentrated phase 1 and a clear phase 1;

[0020] The clear phase 1 is diluted and enters into an acid-resistant ultrafiltration membrane to obtain a dense phase 2 and a clear phase 2;

[0021] The clear phase 2 enters the modified acid-resistant nanofiltration membrane to obtain a dense phase 3 and a clear phase 3;

[0022] The clear phase 3 is subjected to cation resin exchange and then concentrated to obtain electronic grade phosphoric acid.

[0023] Preferably, the filtration is plate and frame filtration.

[0024] Preferably, the operating pressure of the inorganic ultrafiltration membrane is 0.2-0.4 MPa and the temperature is 60-70°C.

[0025] Preferably, the inorganic ultrafiltration membrane is a silicon carbide ultrafiltration membrane or an aluminum oxide ceramic membrane.

[0026] Preferably, the operating pressure of the acid-resistant ultrafiltration membrane is 2-3 MPa and the temperature is 25-40°C.

[0027] Preferably, the modified acid-resistant nanofiltration membrane has an operating pressure of 4-6 MPa and a temperature of 25-45°C.

[0028] Preferably, the cation exchange resin is a cation exchange resin having a sulfonic acid group (—SO3H) on a macroporous styrene-divinylbenzene copolymer.

[0029] The beneficial effects of the present invention are:

[0030] The modified acid-resistant nanofiltration membrane of the present invention has a high Zeta potential on its surface, which greatly enhances the rejection rate of the nanofiltration membrane for various cations in phosphoric acid and greatly improves the selectivity of the nanofiltration membrane in the phosphoric acid system. At the same time, during the surface modification process of the membrane, phosphoric acid activates the functional layer of the nanofiltration membrane, greatly improving the flux of the membrane without reducing the interception performance of the membrane.

[0031] The acid-resistant nanofiltration membrane of the invention has simple preparation process, is easy to operate and is suitable for industrial production.

[0032] In the application process of the present invention in purifying wet-process phosphoric acid or preparing electronic-grade phosphoric acid, inorganic ultrafiltration membrane filtration, acid-resistant UF membrane separation and acid-resistant NF membrane separation are adopted for layer-by-layer interception. The membrane method removes multivalent cations in the phosphoric acid. The ion exchange method further deeply removes the monovalent cations remaining in the phosphoric acid. The membrane method and the ion exchange method are coupled and synergistically acted to improve the purification efficiency and quality of the phosphoric acid, and effectively remove organic matter in the wet-process phosphoric acid. The purified phosphoric acid substantially contains no organic matter, and after concentration, the electronic-grade phosphoric acid can be obtained without any post-treatment.

[0033] This application has the advantages of low operating cost, large product added value and high economic benefit. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The process flow chart for preparing modified acid-resistant nanofiltration membrane;

[0035] Figure 2 The figure is a simplified process flow diagram for preparing electronic grade phosphoric acid using wet-process phosphoric acid purification. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solution of the invention, the present invention is further described in detail below in conjunction with specific implementation methods.

[0037] Acid-resistant nanofiltration membrane is also called acid-resistant NF membrane. Aiming at the shortcomings of existing acid-resistant nanofiltration membrane in the wet phosphoric acid purification process, the present invention first provides an acid-resistant nanofiltration membrane modification liquid in order to obtain an acid-resistant NF membrane with a higher Zeta potential on the surface and excellent interception performance and flux. The acid-resistant nanofiltration membrane modification liquid comprises 26-32% phosphoric acid, 2.0-3.0% PEI1800 (polyethyleneimine), and 2.5-3.5% N,N,N-trimethyloctadecane-1-ammonium iodide in terms of mass concentration.

[0038] In some embodiments of the present invention, the mass concentration of phosphoric acid in the acid-resistant nanofiltration membrane modification liquid is any one of 26%, 30%, 32% or a value between the two; the mass concentration of PEI1800 in the acid-resistant nanofiltration membrane modification liquid is any one of 2.0%, 2.5%, 3.0% or a value between the two; the mass concentration of N,N,N-trimethyloctadecane-1-ammonium iodide in the acid-resistant nanofiltration membrane modification liquid is any one of 2.5%, 3.0%, 3.5% or a value between the two.

[0039] The present invention does not limit the remaining components in the modified liquid, which may be solvents, auxiliary materials or other various anionic and cationic components conventionally used in the art. As long as the main components are the above three components and the mass concentration is controlled within the range specified in the present invention, the modification effect described in the present invention can be achieved.

[0040] In a second aspect, the present invention provides a modified acid-resistant nanofiltration membrane, which is obtained by modifying the acid-resistant nanofiltration membrane modifying liquid. The surface of the modified acid-resistant nanofiltration membrane has a very high Zeta potential, which greatly enhances the rejection rate of the NF membrane to various cations in phosphoric acid, and greatly improves the selectivity of the nanofiltration membrane in the phosphoric acid system. At the same time, during the surface modification process of the membrane, phosphoric acid activates the functional layer of the nanofiltration membrane, and greatly improves the flux of the membrane without reducing the interception performance of the membrane.

[0041] Preferably, the Zeta potential of the modified acid-resistant nanofiltration membrane is ≥75 mV.

[0042] Preferably, the Zeta potential of the modified acid-resistant nanofiltration membrane is 75.5-78.3 mV. In some embodiments of the present invention, the Zeta potential of the modified acid-resistant nanofiltration membrane is any one of 75.5 mV, 76.2 mV, 77.2 mV, 78.1 mV, 78.3 mV or a value between the two.

[0043] In a third aspect, the present invention provides a method for preparing a modified acid-resistant nanofiltration membrane, comprising the following steps:

[0044] (1) statically immersing the nanofiltration membrane element in the modified liquid to obtain a statically immersed nanofiltration membrane element;

[0045] (2) loading the modified liquid into a membrane machine, and treating the statically soaked nanofiltration membrane element in the membrane machine;

[0046] (3) The nanofiltration membrane element treated in step (2) is statically immersed again.

[0047] Preferably, the static soaking time in step (1) is 12 to 15 hours, and the temperature is 50 to 60°C. In some embodiments of the present invention, the static soaking time in step (1) is any one of 12 hours, 13 hours, 15 hours, or a value between the two. In some embodiments of the present invention, the static soaking temperature in step (1) is any one of 50°C, 55°C, 60°C, or a value between the two.

[0048] Preferably, the operating conditions of the film machine in step (2) are: pressure 3-4MPa, temperature 25-30°C, and cyclic operation for 5-6h. In some embodiments of the present invention, the operating pressure of the film machine in step (2) is any one of 3MPa, 3.5MPa, 4MPa, or a value between the two. In some embodiments of the present invention, the operating temperature of the film machine in step (2) is any one of 25°C, 28°C, 30°C, or a value between the two. In some embodiments of the present invention, the operating time of the film machine in step (2) is any one of 5h, 5.5h, 6h, or a value between the two.

[0049] Preferably, the static immersion time in step (3) is more than 24 hours, and the temperature is 25-30°C.

[0050] In a fourth aspect, the present invention provides the use of the modified acid-resistant nanofiltration membrane in purifying wet-process phosphoric acid or preparing electronic-grade phosphoric acid.

[0051] Preferably, the application of preparing electronic grade phosphoric acid is specifically:

[0052] The wet-process phosphoric acid is filtered and then enters into an inorganic ultrafiltration membrane to obtain a concentrated phase 1 and a clear phase 1;

[0053] The clear phase 1 is diluted and enters into an acid-resistant ultrafiltration membrane to obtain a dense phase 2 and a clear phase 2;

[0054] The clear phase 2 enters the modified acid-resistant nanofiltration membrane to obtain a dense phase 3 and a clear phase 3;

[0055] The clear phase 3 is subjected to cation resin exchange and then concentrated to obtain electronic grade phosphoric acid.

[0056] In the present invention, the concentrated phase 1 can be returned to the filtration unit for re-filtration for recycling, the concentrated phase 2 can be transported to the phosphate fertilizer workshop to produce phosphate fertilizer to achieve resource utilization, the concentrated phase 3 can be returned to the acid-resistant ultrafiltration membrane for recycling, and the phosphoric acid solution obtained after the cationic resin exchange can be used as a raw material for acid-resistant nanofiltration membrane modification liquid to achieve resource utilization.

[0057] Preferably, the filtration is plate and frame filtration.

[0058] Preferably, the operating pressure of the inorganic ultrafiltration membrane is 0.2-0.4MPa, the temperature is 60-70°C, the clear phase flux is 1000-1200LMH, and the clear phase turbidity is less than 1NTU, so as to meet the feed requirements of subsequent acid-resistant ultrafiltration membrane and modified acid-resistant nanofiltration membrane, and the clear phase yield can reach more than 95%.

[0059] Preferably, the inorganic ultrafiltration membrane is a silicon carbide ultrafiltration membrane or an aluminum oxide ceramic membrane. More preferably, it is a silicon carbide ultrafiltration membrane, which has a relatively dense pore size (10-20nm), a higher flux and a stronger resistance to fouling and clogging, and can effectively intercept suspended fine particles and some macromolecular organic matter in phosphoric acid (TOC removal rate 30%).

[0060] Acid-resistant ultrafiltration membrane is also called acid-resistant UF membrane. In the present invention, the acid-resistant UF membrane is an acid-resistant organic ultrafiltration membrane with a filtration accuracy of 2000-2500Da, excellent acid resistance, a high retention rate for organic matter in phosphoric acid (TOC removal rate 60%) and a certain retention rate for multivalent ions in phosphoric acid (multivalent cation retention rate greater than 65%). Preferably, the operating pressure of the acid-resistant ultrafiltration membrane is 2-3MPa, the temperature is 25-40°C, and the clear phase flux is 200-400LMH.

[0061] In the present invention, the surface of the modified acid-resistant nanofiltration membrane has a very high Zeta potential, which greatly enhances the rejection rate of the NF membrane for each cation in phosphoric acid. At the same time, during the surface modification process of the membrane, phosphoric acid activates the functional layer of the nanofiltration membrane, greatly improving the flux of the membrane without reducing the retention performance of the membrane. Preferably, the operating pressure of the modified acid-resistant nanofiltration membrane is 4-6MPa, the temperature is 25-45°C, the clear phase flux is greater than 45LMH, and the yield of the entire NF membrane system reaches more than 85%. In some embodiments of the present invention, the operating pressure of the modified acid-resistant nanofiltration membrane is any one of 4MPa, 5MPa, and 6MPa or a value between the two; the operating temperature of the modified acid-resistant nanofiltration membrane is any one of 25°C, 30°C, and 45°C or a value between the two; the clear phase flux of the modified acid-resistant nanofiltration membrane is any one of 45.5LMH, 47.3LMH, and 49.8LMH or a value between the two. Since the acid-resistant NF membrane has a high retention rate for cations, especially multivalent cations, after passing through the NF membrane system, multivalent cations are basically undetectable in the system, but there are still a small amount of monovalent cations.

[0062] The clear phase after the modified acid-resistant nanofiltration membrane enters the cationic resin unit, and further adsorbs monovalent cations such as Na, K, and Li in the phosphoric acid through ion exchange reaction. Since the modified acid-resistant nanofiltration membrane contains almost no multivalent cations, the adsorption rate of the cationic resin to the residual monovalent cations is very high. Preferably, the cationic exchange resin is a cationic exchange resin with a sulfonic acid group (-SO3H) on a macroporous structure of styrene-divinylbenzene copolymer, and its removal rate for monovalent cations in phosphoric acid is greater than 95% on the basis of nanofiltration to remove multivalent cations.

[0063] The invention uses inorganic ultrafiltration, acid-resistant UF, acid-resistant NF and cationic resin exchange to make the purified wet-process phosphoric acid reach the electronic-grade phosphoric acid standard. The acid-resistant nanofiltration membrane uses a surface-modified acid-resistant nanofiltration membrane, and phosphoric acid from a workshop that has been pretreated is used as a raw material, so that after the phosphoric acid passes through the nanofiltration membrane, most of the cationic ions are intercepted, which greatly improves the selectivity of the nanofiltration membrane in the phosphoric acid system, and then the phosphoric acid is further deeply purified by the cationic exchange resin to obtain the electronic-grade phosphoric acid after purification.

[0064] The above is a detailed description of the present invention, and the following is an embodiment of the present invention.

[0065] Example 1 Preparation of modified acid-resistant nanofiltration membrane

[0066] Preparation of the modified liquid: Phosphoric acid comes from the phosphoric acid obtained after cationic resin exchange in the process of purifying wet-process phosphoric acid to prepare electronic-grade phosphoric acid in Example 6 of the present invention. PEI1800 and N,N,N-trimethyloctadecane-1-ammonium iodide are added thereto to obtain a modified liquid. The mass concentration of phosphoric acid in the modified liquid is adjusted to 30%, the mass concentration of PEI1800 is 2.5%, and the mass concentration of N,N,N-trimethyloctadecane-1-ammonium iodide is 3.0%.

[0067] Preparation of modified acid-resistant nanofiltration membrane (process flow as Figure 1 shown):

[0068] The nanofiltration membrane element was statically immersed in the modifying liquid for 13 hours at a temperature of 55°C; after the static treatment, the nanofiltration membrane element was loaded into the membrane machine, and the same modifying liquid was configured in the stock liquid barrel, and circulated for 5.5 hours at a pressure of 3.5MPa and a temperature of 28°C; after the operation, the nanofiltration membrane element was taken out and continued to be statically immersed in the modifying liquid at a temperature of 28°C for more than 24 hours; after the immersion, the nanofiltration membrane element was cleaned with pure water to obtain a modified acid-resistant nanofiltration membrane.

[0069] Example 2 Preparation of modified acid-resistant nanofiltration membrane

[0070] The same as Example 1, except that: the mass concentration of phosphoric acid in the modified solution is 32%, the mass concentration of PEI1800 is 3.0%, and the mass concentration of N,N,N-trimethyloctadecane-1-ammonium iodide is 3.5%.

[0071] Example 3 Preparation of modified acid-resistant nanofiltration membrane

[0072] The same as Example 1, except that the mass concentration of phosphoric acid in the modified solution is 26%, the mass concentration of PEI1800 is 2.0%, and the mass concentration of N,N,N-trimethyloctadecane-1-ammonium iodide is 2.5%.

[0073] Example 4 Preparation of modified acid-resistant nanofiltration membrane

[0074] The same as Example 1, except that: the nanofiltration membrane element is statically immersed in the modifying liquid for 15 hours at a temperature of 60°C; after the static treatment, the nanofiltration membrane element is loaded into the membrane machine, and the same modifying liquid is configured in the stock liquid barrel, and circulated for 6 hours under the conditions of pressure 4MPa and temperature 30°C; after the operation, the nanofiltration membrane element is taken out and continues to be statically immersed in the modifying liquid at a temperature of 30°C for more than 24 hours.

[0075] Example 5 Preparation of modified acid-resistant nanofiltration membrane

[0076] The same as Example 1, except that: the nanofiltration membrane element is statically immersed in the modifying liquid for 12 hours at a temperature of 50°C; after the static treatment, the nanofiltration membrane element is loaded into the membrane machine, and the same modifying liquid is configured in the stock liquid barrel, and circulated for 5 hours under the conditions of pressure 3MPa and temperature 25°C; after the operation, the nanofiltration membrane element is taken out and continues to be statically immersed in the modifying liquid at a temperature of 25°C for more than 24 hours.

[0077] Comparative Example 1

[0078] Same as Example 1, except that: N,N,N-trimethyloctadecane-1-ammonium iodide is not added to the modified solution.

[0079] Effect Example 1: Performance test of modified acid-resistant nanofiltration membrane

[0080] The flux, zeta potential and retention rate of the modified acid-resistant nanofiltration membranes prepared in Examples 1 to 5 and Comparative Example 1 were tested, and the results are shown in the following table:

[0081] Table 1 Flux of acid-resistant NF membrane

[0082]

[0083] Table 2 Zeta potential of acid-resistant NF membrane

[0084] Test subjects Before modification(mV) After modification (mV) Example 1 24.1 77.2 Example 2 22.3 78.3 Example 3 21.8 75.5 Example 4 22.6 78.1 Example 5 23.4 76.2 Comparative Example 1 23.2 45.8

[0085] Table 3 Retention rate of acid-resistant NF membrane

[0086]

[0087]

[0088]

[0089] Note: The test object of the retention rate in Table 3 is the clear phase after passing through the acid-resistant UF membrane in Example 6.

[0090] It can be seen from the performance test results of Tables 1 to 3 that the flux of the acid-resistant nanofiltration membrane treated with the modifying liquid of the present invention is improved, the Zeta potential of the surface is improved, and in the purification process of wet-process phosphoric acid, the content of impurity anions in the pretreated phosphoric acid is very low. Due to the Donan effect, the modified acid-resistant nanofiltration membrane obtained by the present invention can greatly improve the retention rate of the nanofiltration membrane for cations and the permeability of phosphoric acid, and greatly improve the phosphorus yield, laying a foundation for the preparation of electronic-grade phosphoric acid. If the acid-resistant nanofiltration membrane is treated with the modifying liquid of Comparative Example 1, the improvement of its flux, Zeta potential and retention rate is limited, and it is difficult to prepare electronic-grade phosphoric acid.

[0091] Example 6 Process for Purifying Wet-Process Phosphoric Acid to Prepare Electronic-Grade Phosphoric Acid

[0092] The indicators of semi-aqueous wet-process phosphoric acid after pretreatment from the phosphoric acid workshop are shown in Table 4.

[0093] Table 4 Composition of pretreated semi-aqueous wet-process phosphoric acid

[0094] <![CDATA[P2O5]]> ％ 41 TOC ppm 40 Fe ppm 1340 Al ppm 984 Ca ppm 2153 Mg ppm 9899 Na ppm 345 K ppm 584 <![CDATA[SO4 2- ]]> ppm 80 Cl ppm 0.1

[0095] Process flow: See the schematic diagram of the process flow for preparing electronic grade phosphoric acid using wet phosphoric acid purification. Figure 2 , the specific process is as follows:

[0096] The semi-aqueous wet-process phosphoric acid from the phosphoric acid workshop after pretreatment is first filtered (plate and frame filter press), and the filtrate is collected in the filtrate collection tank and enters the inorganic ultrafiltration membrane (silicon carbide ultrafiltration membrane) for membrane filtration to obtain concentrated phase 1 and clear phase 1. Concentrated phase 1 is returned for filtration, and clear phase 1 is diluted with pure water to a P2O5 concentration of about 24% and then enters the acid-resistant UF membrane system. The operating pressure of the inorganic ultrafiltration membrane is 0.3MPa and the temperature is 65°C. The silicon carbide ultrafiltration membrane has a high flux and strong resistance to fouling and clogging, and can effectively intercept suspended fine particles and some macromolecular organic matter in phosphoric acid. The clear phase flux of this process is 1150LMH, the clear phase turbidity is less than 1NTU, and the clear phase yield can reach more than 95%. The acid composition after treatment with the inorganic ultrafiltration membrane is shown in Table 5.

[0097] Table 5 Acid composition after inorganic ultrafiltration membrane treatment

[0098] <![CDATA[P2O5]]> ％ 41.02 TOC ppm 28 Fe ppm 1340 Al ppm 984 Ca ppm 2153 Mg ppm 9899 Na ppm 345 K ppm 584 <![CDATA[SO4 2- ]]> ppm 80 Cl ppm 0.1

[0099] After dilution, the clear phase 1 is separated by the acid-resistant UF membrane to obtain the concentrated phase 2 and the clear phase 2. The concentrated phase 2 is transported to the phosphate fertilizer workshop to produce phosphate fertilizer, and the clear phase 2 enters the modified acid-resistant NF membrane for membrane separation. The operating pressure of the acid-resistant UF membrane is 2.5MPa, the temperature is 30℃, and the clear phase flux is 300LMH. The acid-resistant UF membrane has excellent acid resistance, has a high retention rate for organic matter in phosphoric acid, and has a certain retention rate for multivalent ions in phosphoric acid. The composition of the acid after treatment with the acid-resistant UF membrane is shown in Table 6.

[0100] Table 6 Acid composition after acid-resistant UF membrane treatment

[0101]

[0102]

[0103] The clear phase 2 enters the modified acid-resistant NF membrane obtained in Example 1 for membrane separation to obtain a dense phase 3 and a clear phase 3. The dense phase 3 returns to the acid-resistant UF membrane, and the clear phase 3 enters the cationic resin for exchange treatment. The modified acid-resistant NF membrane has an operating pressure of 5MPa, a temperature of 30°C, a clear phase flux of 47.3LMH, and a yield of more than 85% for the entire NF membrane system. Since the modified acid-resistant NF membrane has a high retention rate for cations, especially multivalent cations, after passing through the NF membrane system, multivalent cations are basically undetectable in the system, but a small amount of monovalent cations are still contained. The composition of the acid after treatment with the modified acid-resistant NF membrane is shown in Table 7.

[0104] Table 7 Acid composition after acid-resistant NF membrane treatment

[0105] <![CDATA[P2O5]]> ％ 22 TOC ppm Not Detected Fe ppm Not Detected Al ppm Not Detected Ca ppm Not Detected Mg ppm 1 Na ppm 22 K ppm 44 <![CDATA[SO4 2- ]]> ppm 0.79

[0106] After the cationic resin exchange, the purified phosphoric acid is heated and concentrated to prepare electronic grade phosphoric acid. The phosphoric acid after the cationic resin exchange can be used for the preparation of the modified solution in Examples 1 to 5. Through the ion exchange reaction, the monovalent cations such as Na, K, and Li in the phosphoric acid can be further adsorbed. Since the modified acid-resistant NF membrane contains almost no multivalent cations, the cationic resin has a high adsorption rate for the residual monovalent cations. The acid components after the cationic resin treatment are shown in Table 8, and the product indicators of the electronic grade phosphoric acid are shown in Table 9.

[0107] Table 8 Acid composition after ion exchange

[0108]

[0109]

[0110] Table 9 Electronic grade phosphoric acid product indicators

[0111] <![CDATA[P2O5]]> ％ 62 <![CDATA[H3PO4]]> ％ 85.5 <![CDATA[NO 3- ]]> ppm 2 TOC ppm Not Detected <![CDATA[SO4 2- ]]> ppm 2.2 <![CDATA[Cl - ]]> ppm Not Detected Fe ppm Not Detected Al ppm Not Detected Ca ppm Not Detected Mg ppm Not Detected Na ppm Not Detected K ppm Not Detected Li ppm Not Detected As ppm Not Detected

[0112] It can be seen from the above that the present invention uses inorganic ultrafiltration membrane filtration, acid-resistant UF membrane separation, modified acid-resistant NF membrane separation and cation exchange processes to sequentially treat wet-process phosphoric acid to achieve layer-by-layer interception. The membrane method can sequentially remove multivalent cations in phosphoric acid, and the ion exchange method further deeply removes the monovalent cations remaining in the phosphoric acid. The membrane method and the ion exchange method are coupled and used synergistically to improve the purification efficiency and quality of phosphoric acid, and effectively remove organic matter in wet-process phosphoric acid. The purified phosphoric acid is basically free of organic matter, and after concentration, no post-treatment is required to obtain an electronic-grade phosphoric acid product with excellent quality.

[0113] Example 7: Purification of wet-process phosphoric acid to prepare electronic grade phosphoric acid

[0114] Same as Example 6, except that the modified acid-resistant NF membrane has an operating pressure of 6 MPa, a temperature of 45° C., and a clear phase flux of 49.8 LMH.

[0115] The composition of the acid after treatment of the modified acid-resistant NF membrane of this example is shown in Table 10.

[0116] Table 10 Acid composition after acid-resistant NF membrane treatment

[0117] <![CDATA[P2O5]]> ％ 21.5 TOC ppm Not Detected Fe ppm Not Detected Al ppm Not Detected Ca ppm Not Detected Mg ppm Not Detected Na ppm 15 K ppm 20 <![CDATA[SO4 2- ]]> ppm 0.11

[0118] Example 8: Purification of wet-process phosphoric acid to prepare electronic-grade phosphoric acid

[0119] Same as Example 6, except that the modified acid-resistant NF membrane has an operating pressure of 4 MPa, a temperature of 25° C., and a clear phase flux of 45.5 LMH.

[0120] The composition of the acid after treatment of the modified acid-resistant NF membrane of this example is shown in Table 11.

[0121] Table 11 Acid composition after acid-resistant NF membrane treatment

[0122] <![CDATA[P2O5]]> ％ 22.5 TOC ppm Not Detected Fe ppm Not Detected Al ppm Not Detected Ca ppm Not Detected Mg ppm 2 Na ppm 28 K ppm 47 <![CDATA[SO4 2- ]]> ppm 0.82

[0123] Comparative Example 2

[0124] Same as Example 6, except that the modified acid-resistant NF membrane has an operating pressure of 3 MPa, a temperature of 20° C., and a clear phase flux of 40.2 LMH.

[0125] The composition of the acid after treatment of the modified acid-resistant NF membrane of this comparative example is shown in Table 12.

[0126] Table 12 Acid composition after acid-resistant NF membrane treatment

[0127] <![CDATA[P2O5]]> ％ 23 TOC ppm Not Detected Fe ppm 5 Al ppm 7 Ca ppm 11 Mg ppm 13 Na ppm 67 K ppm 81 <![CDATA[SO4 2- ]]> ppm 1.5

[0128] From the comparison of Table 7, Table 10 and Table 11, it can be seen that in the process of purifying wet-process phosphoric acid, after the acid-resistant UF membrane is treated with the modified acid-resistant NF membrane of the present invention under the corresponding operating conditions, the system can basically detect no multivalent cations. Although it still contains monovalent cations, the content is less, which is conducive to the subsequent treatment to obtain electronic-grade phosphoric acid. If the operating conditions of the modified acid-resistant NF membrane exceed the limited range of the present invention (such as Comparative Example 2), it will significantly affect the use effect of the modified acid-resistant NF membrane, so that the content of impurity cations increases, which is not conducive to the subsequent acquisition of electronic-grade phosphoric acid.

[0129] The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. An acid-resistant nanofiltration membrane modifying liquid, characterized in that: Calculated by mass concentration, the composition includes 26-32% of phosphoric acid, 2.0-3.0% of PEI1800, and 2.5-3.5% of N,N,N-trimethyloctadecane-1-ammonium iodide.

2. A modified acid-resistant nanofiltration membrane, characterized in that: It is obtained by modifying the acid-resistant nanofiltration membrane modifying liquid described in claim 1.

3. The modified acid-resistant nanofiltration membrane according to claim 2, characterized in that: The Zeta potential of the modified acid-resistant nanofiltration membrane is ≥75mV.

4. A method for preparing a modified acid-resistant nanofiltration membrane, characterized in that: The following steps are involved: (1) statically immersing the nanofiltration membrane element in the modified liquid to obtain a statically immersed nanofiltration membrane element; (2) loading the modified liquid according to claim 1 into a membrane machine, and treating the statically soaked nanofiltration membrane element in the membrane machine; (3) The nanofiltration membrane element treated in step (2) is statically immersed again.

5. The preparation method according to claim 4, characterized in that: The static soaking time in step (1) is 12 to 15 hours, and the temperature is 50 to 60°C.

6. The preparation method according to claim 4, characterized in that: The operating conditions of the membrane machine in step (2) are: pressure 3-4 MPa, temperature 25-30° C., and cycle operation for 5-6 hours.

7. The preparation method according to claim 4, characterized in that: The static soaking time in step (3) is more than 24 hours, and the temperature is 25-30°C.

8. Use of the modified acid-resistant nanofiltration membrane according to claim 2 or 3 or the modified acid-resistant nanofiltration membrane prepared by any one of the preparation methods of claims 4 to 7 in purifying wet-process phosphoric acid or preparing electronic-grade phosphoric acid.

9. The use according to claim 8, characterized in that: The application of preparing electronic grade phosphoric acid is specifically: The wet-process phosphoric acid is filtered and then enters into an inorganic ultrafiltration membrane to obtain a concentrated phase 1 and a clear phase 1; The clear phase 1 is diluted and enters into an acid-resistant ultrafiltration membrane to obtain a dense phase 2 and a clear phase 2; The clear phase 2 enters the modified acid-resistant nanofiltration membrane to obtain a dense phase 3 and a clear phase 3; The clear phase 3 is subjected to cation resin exchange and then concentrated to obtain electronic grade phosphoric acid.

10. The use according to claim 9, characterized in that: The modified acid-resistant nanofiltration membrane has an operating pressure of 4-6 MPa and a temperature of 25-45°C.

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