CN115532081A - Acid-resistant positive charge nanofiltration composite membrane and preparation method thereof - Google Patents
Acid-resistant positive charge nanofiltration composite membrane and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of water treatment high-molecular separation membranes, and particularly relates to an acid-resistant positive charge nanofiltration composite membrane and a preparation method thereof. Immersing the surface of a polysulfone ultrafiltration basal membrane into an aqueous phase solution containing polyamine and urea compounds, and removing redundant aqueous phase after standing; then dip-coating an oil phase solution containing polyacyl chloride, standing and drying; immersing the obtained membrane into a coating solution, standing, washing and drying to obtain the nanofiltration membrane; the total mass concentration of the polyamine and the urea compound is 1-4%, the polyamine is one or more of diethylenetriamine, triethylene tetramine, tetraethylene pentamine and polyethyleneimine, and the mass concentration is 0.9-3.9%; the urea compound is one or more of methylsulfonyl bicyclic urea, 4-chlorophenyl urea, 1, 3-bis (4-chlorophenyl) thiourea and benzylthiourea, and the mass concentration is 0.1-1%. The nanofiltration membrane has excellent acid resistance and salt separation effect, is suitable for industrial application of acid salt solution, particularly lithium extraction, and has high practical value.
Description
Technical Field
The invention belongs to the technical field of water treatment high-molecular separation membranes, and particularly relates to an acid-resistant positive charge nanofiltration composite membrane and a preparation method thereof.
Background
With the continuous development of new energy technology, the demand of lithium ion batteries is increasing as an indispensable part; lithium element as the anode material of the lithium ion battery can not be directly obtained in nature, and generally exists in mineral lithium ores and salt lake brine lithium ores. The common technological process for extracting lithium carbonate from mineral lithium ore is sulfuric acid process, which includes roasting sulfuric acid and spodumene, adding water, leaching to obtain acid solution containing lithium, neutralizing and filtering to eliminate calcium, magnesium and other impurities from the leached solution.
The nanofiltration membrane is a novel separation membrane with the pore diameter between a reverse osmosis membrane and an ultrafiltration membrane, has the nanoscale membrane pore diameter, is provided with multiple charges on the membrane, allows low molecular salt to pass through and intercepts organic matters and multivalent ions with higher molecular weight, and has unique separation performance and higher separation precision. Currently, most of nanofiltration composite membranes in commercial production and industrial application are negatively charged membranes, which are composed of a porous supporting layer and a surface functional layer, and are prepared by interfacial polymerization between polyamine and polyacyl chloride, so that the selectivity is greatly reduced; in addition, the desalting function layer of the nanofiltration composite membrane is a polyamide material, and the amide bond can be hydrolyzed under the condition of low pH to cause the serious reduction of the membrane performance, thereby restricting the application of the nanofiltration composite membrane under some acidic conditions.
The separation mechanism of the nanofiltration membrane mainly comprises size sieving and electrostatic repulsion effects, the separation of ions depends on the size of the ions and the aperture of the nanofiltration membrane, and the other separation path utilizes the south-of-the-road effect to realize the separation of multivalent and monovalent ions. The divalent charge intensity is higher than monovalent, so that the repulsion action of the positively charged nanofiltration membrane on divalent cations is obviously higher than that of monovalent cations, and the separation of magnesium and lithium is facilitated. The literature reports that polyethyleneimine serving as a water-phase monomer is subjected to interfacial polymerization reaction with trimesoyl chloride on the surface of a polyether sulfone ultrafiltration membrane, and a positively charged nanofiltration membrane rich in amino is designed, so that the magnesium-lithium separation effect is improved. Patent 106621841A improves the divalent/monovalent salt separation by coating a base film with a positively charged coating solution of a mixed copolymer obtained by pre-crosslinking polyvinyl alcohol with a cationic polyelectrolyte. Therefore, designing a separation material to realize positive charge of the separation layer is the mainstream research direction of magnesium-lithium ion separation at present.
At present, the acid-resistant nanofiltration membrane material mainly comprises polysulfonamides, triazine rings, sulfonated polymers and polyelectrolytes. The polysulfonamide nanofiltration membrane can effectively resist acid, but under the condition of not adding other monomers, the sulfonyl chloride monomer has the defects of large molecular radius or less active groups, so that the polymer membrane is thicker, the pore diameter is larger, the density is not compact, and the retention rate and the flux of the membrane are poorer than those of a polyamide membrane. The triazine ring is a polymer with the triazine ring as a main chain, and a monomer (usually cyanuric chloride, CC) containing the triazine ring is used for replacing a traditional acyl chloride monomer to prepare a membrane, so that the membrane is endowed with good acid stability, but the CC reaction activity is low, so that the membrane rejection rate is low, and other organic phase monomers are still required to be added or an amine monomer containing the triazine ring structure is required to prepare the membrane. Polyelectrolytes are formed by assembling a separation layer on a support membrane by a polycation and polyanion alternating layer-by-layer self-assembly method, the stability of the membrane is improved by electrostatic interaction, and the polyelectrolyte is not suitable for large-scale industrial application due to complex and time-consuming operation. Therefore, the technical scheme formed in the prior art is difficult to combine good acid resistance and salt separation effect, and needs further improvement.
Due to the structural requirement specificity of the acid-resistant nanofiltration membrane material in the lithium extraction industrial application and the requirement of good long-time operation stability, a new nanofiltration composite membrane needs to be developed, so that the acid-resistant stability of the membrane can be improved, a good salt separation and lithium extraction effect can be achieved, and the method has important practical significance in expanding the industrial application of the nanofiltration membrane technology in lithium element extraction.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides an acid-resistant positive charge nanofiltration composite membrane and a preparation method thereof.
The invention mainly aims to provide a preparation method of an acid-resistant positive charge nanofiltration composite membrane.
The invention realizes the aim through the following technical scheme:
a preparation method of an acid-resistant positive charge nanofiltration composite membrane comprises the following steps:
s1, immersing the surface of a polysulfone ultrafiltration basement membrane into an aqueous solution containing polyamine and urea compounds, standing for a certain time, and removing the redundant aqueous solution on the surface of the basement membrane;
s2, dip-coating the membrane surface of the polysulfone ultrafiltration base membrane prepared in the step S1 with an oil phase solution containing polyacyl chloride, standing for a certain time, and drying the base membrane to obtain a nascent nanofiltration membrane;
s3, immersing the nanofiltration membrane obtained in the step S2 into a coating solution containing cationic polyelectrolyte, standing for a certain time, washing the membrane clean, and drying the membrane again to obtain the acid-resistant nanofiltration membrane with positive charges on the surface;
wherein the total mass concentration of the polyamine and the urea compound in the step S1 is 1-4%; the polyamine is one or a mixture of more of diethylenetriamine, triethylene tetramine, tetraethylene pentamine and polyethyleneimine, and the mass concentration of the polyamine is 0.9-3.9%; the urea compound is one or a mixture of more of methylsulfonyl bicyclic urea, 4-chlorophenyl urea, 1, 3-bis (4-chlorphenyl) thiourea and benzylthiourea, and the mass concentration is 0.1-1%.
At present, the conventional amines used in the water phase of the product are piperazine, and under the condition of low pH, polyamide is decomposed by an acid catalytic pathway as follows: during the protonation step, water molecules approach the carbon and form peptide bonds. When a water molecule is split, a proton is liberated. Then, a hydroxyl group is close to the carbon atom of the amide, and the base intermediate adsorbs a proton, and the C-N bond is broken. Therefore, most commercial nanofiltration membranes are not suitable for long term use due to their sensitivity to strong acids.
The water phase component used in the invention is a compound, one is aliphatic polyamine, has strong molecular chain movement and large free volume, and in addition, has higher diffusion rate and lower reactivity than PIP (piperazine), and the active layer tends to form a thick film, which is beneficial to preparing a membrane with stronger acid resistance; one is urea compound, which has strong hydrogen bonds and aliphatic amines also have strong hydrogen bonds, so that nucleophilic attack can be effectively improved, the acid resistance of the membrane is ensured, and the molecular structure of the separation layer is more compact due to the existence of the hydrogen bonds, and the salt rejection rate is improved.
Preferably, the standing time of the step S1 is 0.5-5 minutes, the removing is air knife blowing, and the air knife pressure is 15-50Psi.
Preferably, the polybasic acyl chloride monomer in the step S2 is one of isophthaloyl dichloride, biphenyl tetracarboxyl dichloride, trimesoyl dichloride or phthaloyl dichloride.
Preferably, the oil phase solvent in step S2 is one or more of cyclohexane, n-hexane, ISOPAR E or ISOPAR G.
Preferably, the standing time in step S2 is 5 to 60 seconds.
Preferably, the drying temperature in the step S2 is 40-80 ℃, and the drying time is 1-5 minutes.
The coating of cationic polyelectrolyte solution, the attack of hydrogen ion can be effectively weakened when the diaphragm is positive charge, promote the diaphragm acid resistance, make the nanofiltration membrane surface carry positive charge simultaneously, in the in-process of separating different valence state ionic salts, the rejection effect of membrane to bivalent cation is obviously higher than univalent cation, therefore univalent cation more easily permeates the membrane and gets into the penetrant, and bivalent cation is then held back, and then bivalent cation entrapment rate is higher than univalent cation, be favorable to magnesium-lithium separation, reach better salt separation and carry lithium effect.
Preferably, the coating solution in step S3 contains sodium chloride and polydiene dimethyl ammonium chloride, the mass concentration of the sodium chloride is 2% -10%, the mass concentration of the polydiene dimethyl ammonium chloride is 0.5% -5%, and the solvent is deionized water.
Preferably, the standing time in the step S3 is 2-10 minutes, the drying temperature is 70-90 ℃, and the drying time is 1-5 minutes.
The second purpose of the invention is to provide the acid-resistant positive charge nanofiltration composite membrane prepared by the method.
The invention also provides application of the nanofiltration composite membrane in industrial salt separation and lithium extraction, and the nanofiltration composite membrane is particularly suitable for acidic conditions.
Compared with the prior art, the invention has the beneficial effects that:
according to the invention, the aliphatic polyamines and the urea compounds are combined to be used as the water phase, the aliphatic polyamines have strong molecular chain movement and large free volume, have higher diffusion rate and lower reactivity than PIP, and the active layer tends to form a thick film, which is beneficial to preparing a membrane with stronger acid resistance. Meanwhile, single-layer coating of the polycation electrolyte solution is adopted, so that the attack of hydrogen ions can be effectively weakened when the membrane is positively charged, the acid resistance of the membrane is improved, the surface of the nanofiltration membrane is positively charged, and the salt separation effect of the membrane is further improved. The preparation process of the membrane can correspond to the existing production line, so that the membrane can be rapidly put into production through simple debugging, and the prepared acid-resistant positive charge nanofiltration composite membrane has important significance in the industrial application of lithium element extraction.
Detailed Description
The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments and comparative examples of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The test methods used in the following examples are all conventional methods unless otherwise specified; the materials, reagents and the like used are, unless otherwise specified, commercially available reagents and materials.
The polysulfone ultrafiltration-based membrane used in the present invention can be obtained by a conventional preparation method: adding polysulfone (16 wt%) into N, N-Dimethylformamide (DMF) solution, stirring at 75 deg.C for dissolving, vacuumizing for defoaming, pouring the dissolved polysulfone onto non-woven fabric, scraping the membrane with a scraper with a gap of 100 μm, immersing the membrane into deionized water to solidify the membrane, taking out the solidified membrane, and storing in deionized water for later use.
Example 1
A preparation method of an acid-resistant positive charge nanofiltration composite membrane comprises the following steps:
s1, immersing 1.9wt% of diethylenetriamine and 0.1wt% of a sulfobicyclo urea aqueous solution on the surface of a polysulfone ultrafiltration basement membrane, standing for 1 minute, and blowing off the redundant aqueous solution on the surface of the polysulfone ultrafiltration basement membrane by using an air knife with the air knife pressure of 30Psi;
s2, dip-coating a normal hexane solution containing 0.2wt% of trimesoyl chloride on the membrane surface of the polysulfone ultrafiltration basal membrane, standing for 15 seconds, putting the polysulfone ultrafiltration basal membrane into a 60 ℃ drying oven to be dried for 1.5 minutes to obtain a nascent nanofiltration membrane, and putting the nascent nanofiltration membrane into deionized water to be stored;
and S3, immersing the nanofiltration membrane into a coating aqueous solution containing 5wt% of sodium chloride and 1wt% of polydiene dimethyl ammonium chloride, standing for 5min, taking out the membrane, washing the membrane clean by using deionized water, and drying the membrane in an oven at 80 ℃ for 2min again to obtain the acid-resistant nanofiltration membrane with the positive charge on the surface.
Example 2
A preparation method of an acid-resistant positive charge nanofiltration composite membrane comprises the following steps:
s1, immersing 1.9wt% of diethylenetriamine and 0.1wt% of a sulfodicyclo urea aqueous solution on the surface of a polysulfone ultrafiltration basal membrane, standing for 1 minute, and blowing off the redundant aqueous solution on the surface of the polysulfone ultrafiltration basal membrane by using an air knife with the air knife pressure of 30Psi;
s2, dip-coating a normal hexane solution containing 0.2wt% of trimesoyl chloride on the membrane surface of the polysulfone ultrafiltration basal membrane, standing for 15 seconds, putting the polysulfone ultrafiltration basal membrane into a 60 ℃ oven to be dried for 1.5 minutes to obtain a nascent nanofiltration membrane, and putting the nascent nanofiltration membrane into deionized water to be stored;
and S3, immersing the nanofiltration membrane into an aqueous solution containing 5wt% of sodium chloride and 1.5wt% of polydiene dimethyl ammonium chloride coating, standing for 5min, taking out the membrane, washing the membrane clean by using deionized water, and drying the membrane in an oven at 80 ℃ for 2min again to obtain the acid-resistant nanofiltration membrane with the positive charge on the surface.
Example 3
A preparation method of an acid-resistant positive charge nanofiltration composite membrane comprises the following steps:
s1, immersing 2.5wt% of diethylenetriamine and 0.1wt% of a sulfodicyclo urea aqueous solution on the surface of a polysulfone ultrafiltration basal membrane, standing for 1 minute, and blowing off the redundant aqueous solution on the surface of the polysulfone ultrafiltration basal membrane by using an air knife with the air knife pressure of 30Psi;
s2, dip-coating a normal hexane solution containing 0.2wt% of trimesoyl chloride on the membrane surface of the polysulfone ultrafiltration basal membrane, standing for 15 seconds, putting the polysulfone ultrafiltration basal membrane into a 60 ℃ oven to be dried for 1.5 minutes to obtain a nascent nanofiltration membrane, and putting the nascent nanofiltration membrane into deionized water to be stored;
and S3, immersing the nanofiltration membrane into a coating aqueous solution containing 5wt% of sodium chloride and 1wt% of polydiene dimethyl ammonium chloride, standing for 5min, taking out the membrane, washing the membrane clean by using deionized water, and drying the membrane in an oven at 80 ℃ for 2min. Thus obtaining the acid-resistant nanofiltration membrane with positive charges on the surface.
Example 4
A preparation method of an acid-resistant positive charge nanofiltration composite membrane comprises the following steps:
s1, immersing 1.9wt% of diethylenetriamine and 0.1wt% of 4-chlorophenylurea aqueous solution into the surface of a polysulfone ultrafiltration basal membrane, standing for 1 minute, and blowing off the redundant aqueous solution on the surface of the polysulfone ultrafiltration basal membrane by using an air knife with the air knife pressure of 30Psi;
s2, dip-coating a normal hexane solution containing 0.2wt% of trimesoyl chloride on the membrane surface of the polysulfone ultrafiltration basal membrane, standing for 15 seconds, putting the polysulfone ultrafiltration basal membrane into a 60 ℃ drying oven for drying for 1.5 minutes to obtain a nascent nanofiltration membrane, and putting the nascent nanofiltration membrane into deionized water for storage;
and S3, immersing the nanofiltration membrane into a coating aqueous solution containing 5wt% of sodium chloride and 1wt% of polydiene dimethyl ammonium chloride, standing for 5min, taking out the membrane, washing the membrane clean by using deionized water, and drying the membrane in an oven at 80 ℃ for 2min again to obtain the acid-resistant nanofiltration membrane with the positive charge on the surface.
Example 5
A preparation method of an acid-resistant positive charge nanofiltration composite membrane comprises the following steps:
s1, immersing 1.9wt% of diethylenetriamine and 0.1wt% of 1, 3-bis (4-chlorophenyl) thiourea aqueous solution into the surface of the polysulfone ultrafiltration membrane, standing for 1 minute, and blowing off the excess aqueous solution from the surface of the polysulfone ultrafiltration membrane by using a wind knife with a wind knife pressure of 30Psi;
s2, dip-coating a normal hexane solution containing 0.2wt% of trimesoyl chloride on the membrane surface of the polysulfone ultrafiltration basal membrane, standing for 15 seconds, putting the polysulfone ultrafiltration basal membrane into a 60 ℃ oven to be dried for 1.5 minutes to obtain a nascent nanofiltration membrane, and putting the nascent nanofiltration membrane into deionized water to be stored;
and S3, immersing the nanofiltration membrane into an aqueous solution containing 5wt% of sodium chloride and 1wt% of polydiene dimethyl ammonium chloride coating, standing for 5min, taking out the membrane, washing the membrane clean by using deionized water, and drying the membrane in an oven at 80 ℃ for 2min again to obtain the acid-resistant nanofiltration membrane with the positive charge on the surface.
Example 6
A preparation method of an acid-resistant positive charge nanofiltration composite membrane comprises the following steps:
s1, immersing 1.9wt% of diethylenetriamine and 0.1wt% of a sulfobicyclo urea aqueous solution on the surface of a polysulfone ultrafiltration basement membrane, standing for 1 minute, and blowing off the redundant aqueous solution on the surface of the polysulfone ultrafiltration basement membrane by using an air knife with the air knife pressure of 30Psi;
s2, dip-coating a normal hexane solution containing 0.2wt% of isophthaloyl dichloride on the membrane surface of the polysulfone ultrafiltration basal membrane, standing for 15 seconds, putting the polysulfone ultrafiltration basal membrane into a 60 ℃ drying oven to be dried for 1.5 minutes to obtain a nascent nanofiltration membrane, and putting the nascent nanofiltration membrane into deionized water to be stored;
and S3, immersing the nanofiltration membrane into a coating aqueous solution containing 5wt% of sodium chloride and 1wt% of polydiene dimethyl ammonium chloride, standing for 5min, taking out the membrane, washing the membrane clean by using deionized water, and drying the membrane in an oven at 80 ℃ for 2min again to obtain the acid-resistant nanofiltration membrane with the positive charge on the surface.
Comparative example 1
S1, immersing 2wt% of piperazine aqueous phase solution on the surface of a polysulfone ultrafiltration basal membrane, standing for 1 minute, and blowing off the redundant aqueous phase solution on the surface of the polysulfone ultrafiltration basal membrane by using an air knife, wherein the air knife pressure is 30Psi;
s2, dip-coating a normal hexane solution containing 0.2wt% of trimesoyl chloride on the membrane surface of the polysulfone ultrafiltration basal membrane, standing for 15 seconds, putting the polysulfone ultrafiltration basal membrane into a 60 ℃ drying oven to dry for 1.5 minutes to obtain a nascent nanofiltration membrane, and storing in deionized water.
Comparative example 2
S1, immersing 1.9wt% of diethylenetriamine and 0.1wt% of a sulfobicyclo urea aqueous solution on the surface of a polysulfone ultrafiltration basement membrane, standing for 1 minute, and blowing off the redundant aqueous solution on the surface of the polysulfone ultrafiltration basement membrane by using an air knife with the air knife pressure of 30Psi;
s2, dip-coating a normal hexane solution containing 0.2wt% of trimesoyl chloride on the membrane surface of the polysulfone ultrafiltration basal membrane, standing for 15 seconds, putting the polysulfone ultrafiltration basal membrane into a 60 ℃ oven to be dried for 1.5 minutes to obtain a nascent nanofiltration membrane, and putting the nascent nanofiltration membrane into deionized water to be stored.
Comparative example 3
S1, immersing 1.5% of 3-aminobenzene sulfonamide aqueous phase solution on the surface of a polysulfone ultrafiltration basement membrane, standing for 1 minute, and blowing off redundant aqueous phase solution on the surface of the polysulfone ultrafiltration basement membrane by using an air knife, wherein the pressure of the air knife is 30Psi;
s2, dip-coating a normal hexane solution containing 0.2wt% of trimesoyl chloride on the membrane surface of the polysulfone ultrafiltration basal membrane, standing for 15 seconds, putting the polysulfone ultrafiltration basal membrane into a 60 ℃ oven to be dried for 1.5 minutes to obtain a nascent nanofiltration membrane, and putting the nascent nanofiltration membrane into deionized water to be stored.
Comparative example 4
S1, immersing 1% of 2, 2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane aqueous phase solution on the surface of a polysulfone ultrafiltration basement membrane, standing for 1 minute, and blowing off the redundant aqueous phase solution on the surface of the polysulfone ultrafiltration basement membrane by using an air knife, wherein the air knife pressure is 30Psi;
s2, dip-coating a normal hexane solution containing 0.2wt% of trimesoyl chloride on the membrane surface of the polysulfone ultrafiltration basal membrane, standing for 15 seconds, putting the polysulfone ultrafiltration basal membrane into a 60 ℃ oven to be dried for 1.5 minutes to obtain a nascent nanofiltration membrane, and putting the nascent nanofiltration membrane into deionized water to be stored.
Comparative example 5
S1, immersing 1.5% triethylene tetramine aqueous phase solution on the surface of a polysulfone ultrafiltration basal membrane, standing for 1 minute, and blowing off the redundant aqueous phase solution on the surface of the polysulfone ultrafiltration basal membrane by using an air knife, wherein the air knife pressure is 30Psi;
s2, dip-coating a normal hexane solution containing 0.2wt% of toluene-2, 6-diisocyanate on the membrane surface of the polysulfone ultrafiltration basal membrane, standing for 15 seconds, putting the polysulfone ultrafiltration basal membrane into a 60 ℃ oven to be dried for 1.5 minutes to obtain a nascent nanofiltration membrane, and storing in deionized water.
Comparative example 6
S1, immersing 1.5% triethylene tetramine aqueous phase solution on the surface of a polysulfone ultrafiltration basal membrane, standing for 1 minute, and blowing off the redundant aqueous phase solution on the surface of the polysulfone ultrafiltration basal membrane by using an air knife, wherein the air knife pressure is 30Psi;
s2, dip-coating a normal hexane solution containing 0.2wt% of toluene-2, 6-diisocyanate on the membrane surface of the polysulfone ultrafiltration basal membrane, standing for 15 seconds, putting the polysulfone ultrafiltration basal membrane into a 60 ℃ oven to be dried for 1.5 minutes to obtain a nascent nanofiltration membrane, and storing in deionized water.
And S3, immersing the nanofiltration membrane into a coating aqueous solution containing 5wt% of sodium chloride and 1wt% of polydiene dimethyl ammonium chloride, standing for 5min, taking out the membrane, washing the membrane clean by using deionized water, drying the membrane in an oven at 80 ℃ for 2min again to obtain a nascent nanofiltration membrane, and storing in the deionized water.
Comparative example 7
A preparation method of an acid-resistant positive charge nanofiltration composite membrane comprises the following steps:
s1, immersing 2.0wt% of diethylenetriamine aqueous phase solution on the surface of a polysulfone ultrafiltration basal membrane, standing for 1 minute, and blowing off the redundant aqueous phase solution on the surface of the polysulfone ultrafiltration basal membrane by using an air knife, wherein the air knife pressure is 30Psi;
s2, dip-coating the polysulfone ultrafiltration basal membrane in a normal hexane solution containing 0.2wt% of trimesoyl chloride on the membrane surface, standing for 15 seconds, putting the polysulfone ultrafiltration basal membrane into a 60 ℃ drying oven to be dried for 1.5 minutes to obtain a nascent nanofiltration membrane, and putting the nascent nanofiltration membrane into deionized water for storage.
Performance detection and analysis
And (3) evaluating the acid resistance of the nanofiltration membrane: the membranes prepared in the examples and comparative examples of the present invention were immersed in a 10% sulfuric acid solution at room temperature, and then rinsed with pure water to be tested.
Evaluation of salt separation performance of the nanofiltration membrane: the membrane is evaluated in a cross-flow filtration mode, 2000ppm magnesium sulfate solution and 2000ppm sodium chloride solution are respectively used as test solutions, the pH value is 7-8, and the water flux and the salt rejection rate of the membrane are tested under the pressure of 100 Psi.
Salt rejection R: salt concentration (C) in influent water under certain test conditions f ) With the salt concentration (C) in the produced water p ) The difference is divided by the salt concentration of the feed water:
R＝(1-C p /C f )*100％
water flux: water production per membrane area per unit time (GFD) under certain test conditions.
The test results of the films prepared in the examples of the present invention and the comparative example are shown in table 1.
The detection result of the acid resistance stability of the nanofiltration membrane prepared by the embodiment of the invention is shown in table 2.
TABLE 1
As can be seen from the data in Table 1, in the comparative example 1, piperazine is used as a water phase, and after the prepared nanofiltration membrane is soaked under an acidic condition, the membrane structure is seriously damaged, and the rejection rate is obviously reduced. In the comparative example 2, diethylenetriamine and sulfometyl bicyclic urea are used as water phases, and the acid resistance and the salt separation effect of the membrane are obviously superior to those of the comparative example 1 after the membrane is soaked in acid resistance. However, comparative example 2 is not coated with polycation electrolyte, compared with comparative example 2, the rejection rate of the membrane coated with polycation electrolyte in example 1 for magnesium sulfate is improved to a certain extent, and the rejection rate for sodium chloride is obviously reduced, which shows that the separation effect of monovalent and divalent cations of the membrane is further improved along with the coating of the polyoxyionic electrolyte layer. Comparative examples 3, 4 and 5 respectively use different types of monomers to prepare membranes, the acid resistance is good, but the rejection rate of monovalent divalent salt is generally increased, and the salt separation effect is not good. Comparative example 6 compared with comparative example 5, although the salt separation effect was improved to some extent after the polycationic electrolyte was coated, the salt separation effect was far from the actual use requirement and was poor. Compared with the water phase in the comparative example 7, no urea compound is added, the prepared nanofiltration membrane has poor separation effect on monovalent/divalent salt, and the introduction of urea has an important effect on the salt splitting effect. In the embodiment of the invention, the water phase component and the oil phase component are reasonably matched, and the prepared positively-charged nanofiltration membrane has better acid resistance and simultaneously achieves better salt separation effect. As can be seen from the data in Table 2, through a one-month acid resistance continuous test, the performance change of the positively charged nanofiltration membrane prepared by the method is not obvious, and the positively charged nanofiltration membrane has good long-time running stability.
TABLE 2
It should be understood that the above-mentioned embodiments of the present invention are only examples for clearly illustrating the technical solutions of the present invention, and are not intended to limit the specific embodiments of the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the claims of the present invention should be included in the protection scope of the claims of the present invention.
Claims (10)
1. A preparation method of an acid-resistant positive charge nanofiltration composite membrane is characterized by comprising the following steps:
s1, immersing the surface of a polysulfone ultrafiltration basement membrane into an aqueous solution containing polyamine and urea compounds, standing, and removing the redundant aqueous solution on the surface of the basement membrane;
s2, dip-coating the membrane surface of the polysulfone ultrafiltration base membrane prepared in the step S1 with an oil phase solution containing polyacyl chloride, standing, and drying the base membrane to obtain a nascent nanofiltration membrane;
s3, soaking the nanofiltration membrane obtained in the step S2 into a coating solution containing cationic polyelectrolyte, standing, washing a membrane, and drying again to obtain the acid-resistant positive charge nanofiltration composite membrane;
wherein the total mass concentration of the polyamine and the urea compound in the step S1 is 1-4%; the polyamine is one or a mixture of more of diethylenetriamine, triethylene tetramine, tetraethylene pentamine and polyethyleneimine, and the mass concentration of the polyamine is 0.9-3.9%; the urea compound is one or a mixture of more of methylsulfonyl bicyclic urea, 4-chlorophenyl urea, 1, 3-bis (4-chlorphenyl) thiourea and benzylthiourea, and the mass concentration is 0.1-1%.
2. The method for preparing an acid-resistant positive charge nanofiltration composite membrane according to claim 1, wherein the standing time of step S1 is 0.5 to 5 minutes, and the removal is performed by blowing with an air knife, and the air knife pressure is 15 to 50Psi.
3. The method of claim 1, wherein the monomer of the poly-acyl chloride in step S2 is one of isophthaloyl dichloride, biphenyltetracarboxylic acid dichloride, trimesoyl chloride, or phthaloyl chloride.
4. The method of claim 1, wherein the oil phase solvent in step S2 is one or more selected from cyclohexane, n-hexane, ISOPAR E and ISOPAR G.
5. The method of claim 1, wherein the standing time in step S2 is 5 to 60 seconds.
6. The method of claim 1, wherein the drying temperature in step S2 is 40-80 ℃ and the drying time is 1-5 minutes.
7. The method as claimed in claim 1, wherein the coating solution in step S3 comprises sodium chloride and polydiene dimethyl ammonium chloride, the mass concentration of sodium chloride is 2% -10%, the mass concentration of polydiene dimethyl ammonium chloride is 0.5% -5%, and the solvent is deionized water.
8. The method of claim 1, wherein the standing time in step S3 is 2-10 minutes, the drying temperature is 70-90 ℃, and the drying time is 1-5 minutes.
9. An acid-resistant positive charge nanofiltration composite membrane, characterized by being prepared by the method of any one of claims 1 to 8.
10. The use of an acid-resistant positive charge nanofiltration composite membrane according to claim 9 for salt-separated extraction of lithium under acidic conditions.
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