CN114797490B - A kind of preparation method of high-selectivity separation membrane for separating anion salts - Google Patents

Abstract

The invention discloses a preparation method of a high-selectivity separation membrane for separating anionic salts, comprising the following steps: (1) dissolving a surfactant and a porous organic molecular cage in water to prepare a host-guest solution, and stirring at a temperature of 30 ℃ Stir for 2~10h under the condition of ~50℃, centrifuge and wash to obtain the supramolecular complex of surfactant and porous organic molecular cage; (2) mix the above supramolecular complex, acid absorbent and the balance of water Mix and prepare an aqueous solution; (3) contact the supported membrane with the aqueous solution to obtain a supported membrane adsorbed with supramolecular complexes; (4) combine the supported membrane with adsorbed supramolecular complexes with a binary When contacted with the organic phase solution of the above acid chloride molecules, an interfacial polymerization reaction occurs. The present invention adopts the preparation method of a high-selectivity separation membrane for separating anionic salts with the above-mentioned structure, so as to solve the problem that the selectivity of monovalent/divalent anion salts of traditional nanofiltration membrane materials is low and it is difficult to meet the purity requirements of industrial salts.

Description

A kind of preparation method of high-selectivity separation membrane for separating anion salts

technical field

The invention relates to the technical field of nanofiltration membrane separation, in particular to a preparation method of a high-selectivity separation membrane for separating anionic salts.

Background technique

The separation of NaCl/Na ₂ SO ₄ inorganic salt mixture solution has huge application demands in the fields of concentrated brine reuse, chlor-alkali brine denitrification, water softening and harmful ion removal. The main components of the concentrated water of desalination plants, the export water of sewage treatment plants, and the salty wastewater from the mining and processing industries are NaCl, NaCl/Na ₂ SO ₄ and other salts, which have low industrial application value and need to be treated with monovalent/divalent salts. Separation to improve product salt purity. The wastewater in the chlor-alkali production industry contains high concentrations of Na ⁺ , Cl ^- and SO ₄ ^2- ions, and the recovery of Na ₂ SO ₄ and water with reasonable treatment technology will realize resource recycling.

Nanofiltration membrane separation technology is an emerging method for the separation of monovalent/divalent inorganic salt solutions, which has broad application potential in terms of economy and operability. The preparation of high-performance nanofiltration membranes is the key to improve the separation efficiency of monovalent/divalent inorganic salts. The preparation process of nanofiltration membrane mainly includes interfacial polymerization method, layer-by-layer self-assembly method and phase inversion method. Commercial nanofiltration membranes are generally polyamide membranes prepared by interfacial polymerization of piperazine and trimesoyl chloride. The rejection rate of divalent salts is high, but the selectivity of monovalent/divalent inorganic salts is difficult to meet the separation of industrial salts. demand. Therefore, to enable efficient and precise separation of NaCl/ _Na2SO4 , the development of highly selective nanofiltration membranes with monovalent salt channels is required _.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for preparing a high-selectivity separation membrane for separating anion salts, so as to solve the problems that the monovalent/divalent anion salt selectivity of the above-mentioned traditional nanofiltration membrane materials is low and it is difficult to meet the purity requirements of industrial salts .

In order to achieve the above object, the present invention provides a preparation method of a high-selectivity separation membrane for separating anionic salts, comprising the following steps:

(1) Dissolve the surfactant and the porous organic molecular cage in water to prepare a host-guest solution, stir at a stirring temperature of 30-50 °C for 2-10 h, centrifuge and wash to obtain the surfactant and porous organic molecules A caged supramolecular complex; the mass fraction of the porous organic molecular cages in the host-guest solution is 0.1-2%, and the molar ratio of the porous organic molecular cages to the surfactant is 1:1-1:10;

(2) Mix 0.1~2% of the above supramolecular complex, 0.1~2% acid absorbent and the balance of water according to the mass fraction to prepare an aqueous solution;

(3) contacting the supported membrane with an aqueous solution to obtain a supported membrane adsorbed with supramolecular complexes;

(4) Contacting the supported membrane with the adsorbed supramolecular complexes with an organic phase solution containing two or more acyl chloride molecules, an interfacial polymerization reaction occurs; the organic phase solution includes 0.1 to 2% of organic phase monolayers according to the mass fraction. body and the balance of organic solvent;

(5) The membrane obtained in the above step is placed in a drying box for heat treatment to obtain a monovalent/divalent inorganic salt separation membrane.

Preferably, the surfactant is selected from sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, Tween 20, dodecyltrimethylammonium bromide, cetyltrimethyl bromide One or more of ammonium.

More preferably, the surfactant is one or more of sodium dodecyl sulfate and dodecyl trimethyl ammonium bromide.

Preferably, the porous organic molecular cage is prepared from 1,3,5-benzenetricarbaldehyde and 1,2-cyclohexanediamine through dehydration condensation and unsaturated bond addition reaction, and is RCC1, RCC2, One or more of RCC3 and RCC4 with a window pore size of 2~10 Å.

Preferably, the support membrane is selected from polymer porous membranes with a molecular weight cut-off of 10 kDa to 50 kDa.

Preferably, the material of the polymer porous membrane is one of polyethylene, polypropylene, polyvinylidene fluoride, polyamide, polyacrylonitrile, polysulfone, polyethersulfone, polyimide, and polytetrafluoroethylene or more.

Preferably, the acid absorbent is selected from one or more of sodium hydroxide, sodium carbonate and sodium bicarbonate.

More preferably, the acid absorbent is one or more of sodium carbonate and sodium bicarbonate.

Preferably, the divalent and above acid chloride molecules are selected from 1,3,5-benzenetricarbonyl chloride, suberoyl chloride malonyl chloride, glutaryl chloride, terephthaloyl chloride, 1,7-pimelyl chloride, decyl Diacid dichloride, adipoyl dichloride, sebacate dichloride, azelaic dichloride, 1,3-benzenedisulfonyl chloride, 4,4'-biphenyldisulfonyl chloride, 4,4'-oxybis(benzoyl chloride)m- One or more of phthaloyl chlorides.

More preferably, the divalent and above acid chloride molecules are selected from one or more of 1,3-benzenedisulfonyl chloride and terephthaloyl chloride.

Preferably, the organic solvent is selected from one or more of n-hexane, n-heptane, isohexane, cyclohexane, cycloheptane, and isoheptane.

More preferably, the organic solvent is selected from one or more of n-hexane and n-heptane.

Preferably, in step (3), the contact operation of the support membrane and the aqueous phase solution is infiltration or dipping, the contact time is 1-10 min, and the temperature of the aqueous phase solution is 15-40°C.

Preferably, in step (4), the contact operation is soaking or dipping, the contact time is 1-10 min, and the temperature of the organic phase mixed solution is 15-40°C.

The mechanism of the present invention: the surfactant in the host-guest solution of the present invention can replace the high-energy water molecules in the cavity of the porous organic molecular cage through hydrophobic interaction to form a supramolecular complex with host-guest interaction, so as to improve the RCC3 water solubility and dispersibility, while promoting the diffusion of aqueous monomer RCC3@DTAB to the phase interface. Furthermore, the amino group of the porous organic molecular cage and the acid chloride group of the dibasic or higher acid chloride molecule in the supramolecular complex undergo interfacial polymerization to form a supramolecular separation membrane with an ordered, porous and topological structure. Among them, the window diameter of the porous organic molecular cage can play the role of the transport channel of monovalent ions and water molecules, and play the function of selective separation of NaCl/Na ₂ SO ₄ . The surface of supramolecular separation membrane can repel hydrated ions with larger radius and higher hydration energy through the separation layer membrane pore size. Compared with monovalent hydrated ions such as Na ⁺ and Cl ^- , divalent hydrated ions such as SO ₄ ^2- and Mg ²⁺ The ions have a larger hydration ion radius and a more stable hydration layer structure, the hydration layer is not easy to fall off when transporting across the membrane, the steric hindrance is relatively large, and the membrane channel only allows water molecules and monovalent ions (Na ⁺ and Cl ^- ) through. Therefore, the supramolecular separation membrane of the present invention has supramolecular channels for efficient separation of monovalent/divalent salts, thereby having high permeation flux and monovalent/divalent salt selectivity.

The types and concentrations of porous organic molecular cages, the types and concentrations of surfactants, and the types and concentrations of binary and above acid chloride molecules are related to the structure of the formed supramolecular membrane. The pH value of the aqueous solution can be adjusted by adding an acid acceptor, and the polymerization reaction of porous organic molecular cages and binary and above acid chloride molecules can be promoted. The surface of the prepared separation membrane is negatively charged, which has a strong repulsion effect on anions (Cl ^- , SO ₄ ^2- ), and can promote the separation of monovalent/dianionic salts (NaCl/Na ₂ SO ₄ , etc.). The strength of electrostatic repulsion mainly depends on the total amount of charge carried by the ions. Compared with monovalent hydrated ions such as Cl ^- , divalent ions such as SO ₄ ^2- carry more charges, so they have greater electrostatic repulsion. Therefore, the Na ₂ SO ₄ rejection of the separation membrane is higher than that of NaCl.

Therefore, the present invention adopts the preparation method of a NaCl/Na ₂ SO ₄ high-selectivity separation membrane of the above-mentioned structure, which has at least one or a part of the following beneficial effects:

(1) The separation layer of the NaCl/Na ₂ SO ₄ high-selectivity separation membrane is stable and firm, with large permeation flux and good long-term operation stability;

(2) The selectivity of NaCl/Na ₂ SO ₄ is high, which can be applied to the reuse of concentrated brine, denitrification of chlor-alkali brine, water softening and removal of harmful ions;

(3) The preparation method with high selectivity of NaCl/Na ₂ SO ₄ has the advantages of simple process, mild preparation conditions, wide application range, easy to enlarge and popularize, and easy to realize industrial production.

The technical solutions of the present invention will be further described in detail below through the accompanying drawings and embodiments.

Description of drawings

Fig. 1 is the surface scanning electron microscope picture of support film in the embodiment of the present invention 1;

Fig. 2 is the surface scanning electron microscope image of NaCl/Na ₂ SO ₄ high-selectivity separation membrane in Example 1 of the present invention;

3 is a cross-sectional SEM image of the NaCl/Na ₂ SO ₄ high-selectivity separation membrane in Example 1 of the present invention.

Detailed ways

The present invention will be further described below. It should be noted that this embodiment is based on the technical solution, and provides a detailed implementation manner and a specific operation process, but the present invention is not limited to this embodiment.

Materials used in the present invention: In the present invention and the following examples, the sources of all raw materials are not particularly limited, and they are commercially available.

The separation and selectivity parameters of the membrane are mainly composed of permeate flux ( P ), rejection ( R ) and selectivity ( α ). Permeate flux ( P ) refers to the volume of solution permeated per unit time, unit pressure and unit membrane area, and the calculation formula is as follows:

Among them, P (unit: L·m ^-2 ·h ^-1 ·bar ^-1 ) is the solution permeate flux, V' (unit: L) is the volume of permeate collected in a certain period of time, A (unit: m ² ) is the effective filtration area of the membrane, Δt (unit: h) is the permeation time, and ΔP (unit: bar) is the transmembrane pressure.

The retention rate ( R ) refers to the degree of retention of inorganic salts in the solution by the separation membrane, which is obtained from the salt concentration of the feed liquid and permeate liquid, and the calculation formula is as follows:

Here, C _p (unit: g·L ^-1 ) is the concentration of the permeated liquid, and C _f (unit: g·L ^-1 ) is the concentration of the raw material liquid.

Selectivity ( α ) refers to the ability of the separation membrane to select mixed monovalent and divalent salts, which is obtained from the retention rates of monovalent and divalent ions. The calculation formula is as follows:

Wherein, R _m (unit: %) is the rejection rate of monovalent salt; R _d (unit: %) is the rejection rate of divalent salt.

The salt concentration in the rejection test was 1000 mg·L ^-1 NaCl or 1000 mg·L ^-1 Na ₂ SO ₄ . The concentration of NaCl/Na ₂ SO ₄ mixed salt in the selectivity test was 2000 mg·L ^-1 , and the ratio of monovalent/divalent ion concentration was 1:1. Monovalent or divalent ion concentrations were detected using inductively coupled plasma emission spectroscopy (ICP-OES, VISTA-MPX, Varian).

Preparation of porous organic molecular cage RCC3:

(1) Weigh 0.5 g of 1,3,5-benzenetricarboxaldehyde and dissolve it in 10 mL of dichloromethane, marked as solution A. Weigh 0.5g of 1,2-cyclohexanediamine and dissolve it in 10 mL of dichloromethane, marked as solution B. The B solution was added to the A solution, and 10 μL of trifluoroacetic acid was added to promote the formation of imine bonds. After stirring the reaction for 7 days, the white precipitate was collected, washed and dried to obtain a white powder.

(2) Dissolve the white powder in 25 mL of dichloromethane and methanol solution (V:V=1:1), add 0.5 g of sodium borohydride, stir at room temperature for 15 h, add 1 mL of deionized water, and stir for 9 h. The samples were collected, rotary evaporated, washed and dried to obtain porous organic molecular cage powder.

(3) Weigh 100 g of molecular cage powder and dissolve it in 10 mL of acetone. After standing for 24 hours, collect the sample by centrifugation, put it into 10 mL of a mixed solution of dichloromethane and ethanol (vol: vol=1:1), and add 0.1 mL of deionized water, stirred for 48 h, and removed the solvent to obtain purified RCC3 particles, which were used for later use.

Example 1

An aqueous solution of sodium dodecyltrimethylbenzene sulfonate containing 0.1% porous organic molecular cage RCC3 and 0.1% RCC3 in a molar ratio of 1:1 (mol:mol) was prepared, stirred at 30 °C for 2 h; Sodium carbonate is used as the aqueous phase mixture. A n-heptane solution containing 0.5% terephthaloyl chloride was prepared as an organic phase mixed solution. First, the aqueous phase mixture was placed on the surface of the polysulfone supported membrane, adsorbed at 30 °C for 10 min, and the excess solution was removed. Then, the organic phase mixture was placed on the membrane surface, reacted for 1 min, the excess solution was removed, and the unreacted solution was rinsed with n-hexane. Then, the membrane was dried in a blast drying oven at 80 °C for 10 min, and the prepared separation membrane was stored in deionized water for further testing of its separation performance.

After testing, the separation membrane has a rejection rate of ~20% for NaCl, ~98% for Na ₂ SO ₄ , a selectivity of NaCl/Na ₂ SO ₄ of ~ 42, and a water permeation flux of ~ 14 L· m ^-2 ·h ^-1 ·bar ^-1 .

Example 2

Prepare an aqueous solution containing 1% porous organic molecular cage RCC4, sodium dodecyl sulfate and 0.4% sodium bicarbonate at a molar ratio of 1:4 (mol:mol) to 1% RCC4, and stir at 50 °C for 8 h; Add to the aqueous phase mixture. The n-hexane solution containing 1.2% 1,3-benzenedisulfonyl chloride was prepared as an organic phase mixed solution. First, the aqueous phase mixture was placed on the surface of the polyamide support membrane, adsorbed at 50 °C for 5 min, and the excess solution was removed. Then, the organic phase mixture was placed on the membrane surface, reacted for 9 min, the excess solution was removed, and the unreacted solution was rinsed with n-hexane. Then, the membrane was dried in a blast drying oven at 80 °C for 10 min, and the prepared separation membrane was stored in deionized water for further testing of its separation performance.

After testing, the separation membrane has a rejection rate of ~15% for NaCl, ~95% for Na ₂ SO ₄ , a selectivity of NaCl/Na ₂ SO ₄ of ~ 20, and a water permeation flux of ~ 25 L· m ^-2 ·h ^-1 ·bar ^-1 .

Example 3

Prepare sodium dodecyl sulfate containing 1.4% porous organic molecular cage RCC2 and 1.4% RCC2 in a molar ratio of 1:6 (mol:mol), stir at 40 °C for 4 h; then add 0.4% aqueous solution of sodium hydroxide as Aqueous mixture. A n-heptane solution containing 0.5% 1,3-benzenedisulfonyl chloride was prepared as an organic phase mixed solution. First, the aqueous phase mixture was placed on the surface of the polyimide support membrane, adsorbed at 40 °C for 3 min, and the excess solution was removed. Then, the organic phase mixture was placed on the membrane surface, reacted for 7 min, the excess solution was removed, and washed with n-hexane. The unreacted monomer was then dried in a forced air drying oven at 80 °C for 10 min, and the prepared separation membrane was stored in deionized water for further testing of its separation performance.

After testing, the separation membrane has a rejection rate of ~30% for NaCl, ~99% for Na ₂ SO ₄ , a selectivity of NaCl/Na ₂ SO ₄ of ~ 47, and a water permeation flux of ~ 15 L· m ^-2 ·h ^-1 ·bar ^-1 .

Comparative ratio

The aqueous phase mixture of this comparative example does not contain porous molecular cages, and the others are the same as in Example 1.

After testing, the separation membrane has a rejection rate of ~10% for NaCl, ~65% for _Na2SO4 , ~17 for _NaCl / _Na2SO4 selectivity, and a water permeation flux of ~ ₄ L· m ^-2 ·h ^-1 ·bar ^-1 .

Comparing the test results of Example 1 and Comparative Example, it can be seen that the retention rates of Example 1 to NaCl and Na ₂ SO ₄ are quite different, the selectivity of NaCl/Na ₂ SO ₄ is higher, and the water permeation flux of Example 1 The water permeation flux is far greater than that of the comparative example, indicating that the organic porous molecular cage is not added in the reaction process of the organic monomer and the water-phase monomer in the comparative example, and the organic monomer and the water-phase monomer directly undergo a polymerization reaction, which cannot form the present invention. Ordered, porous, topologically structured water molecules and monovalent ion channels make it difficult to obtain separation membranes with high water permeation flux and high NaCl/Na ₂ SO ₄ selectivity.

The separation membrane obtained in Example 1 was tested for long-term stability. After 72 hours of continuous separation testing, the water permeation flux and NaCl/Na ₂ SO ₄ selectivity of the membrane were basically unchanged, indicating that the prepared NaCl/Na ₂ The _SO4 separation membrane has good long-term stability. The high-selectivity NaCl/Na ₂ SO ₄ separation membrane obtained in Example 1 was characterized by scanning electron microscopy. Figure 1 shows the surface morphology of the support membrane, and Figure 2 and Figure 3 show the surface morphology of the obtained membrane. and cross-sectional morphology, it can be seen from the analysis that the surface of the separation membrane is relatively smooth, and the attached particles are also smaller, indicating that the RCC3 supramolecules complexed by the surfactant show better dispersibility in the aqueous solution. It can be seen from the cross-sectional diagram. , the separation membrane exhibits a selective layer thickness around 100 nm. The morphological changes of the surface and cross-section are mainly due to the introduction of DTAB to improve the dispersibility of RCC3 molecules in aqueous solution and promote the interfacial polymerization reaction between the water/organic phase monomers.

Therefore, the present invention adopts a preparation method of a high-selectivity NaCl/Na ₂ SO ₄ separation membrane with the above-mentioned structure. The separation layer of the Na ₂ SO ₄ separation membrane has strong firmness, large permeation flux, and good long-term operation stability.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: it is still The technical solutions of the present invention may be modified or equivalently replaced, and these modifications or equivalent replacements cannot make the modified technical solutions depart from the spirit and scope of the technical solutions of the present invention.

Claims (10)

1. a preparation method of the high-selectivity separation membrane separating monovalent/dianion salt, is characterized in that, comprises the following steps: (1) Dissolve the surfactant and the porous organic molecular cage in water to prepare a host-guest solution, stir at a stirring temperature of 30-50 °C for 2-10 h, centrifuge and wash to obtain the surfactant and porous organic molecules The supramolecular complex of the cage; the mass fraction of the porous organic molecular cage in the host-guest solution is 0.1-2%, and the molar ratio of the porous organic molecular cage to the surfactant is 1:1-1:10; the porous organic molecular cage is The organic molecular cage is one or more of RCC1, RCC2, RCC3 and RCC4, and the window pore size is 2~10 Å; (2) Mix 0.1~2% of the above supramolecular complex, 0.1~2% acid absorbent and the balance of water according to the mass fraction to prepare an aqueous solution; (3) contacting the supported membrane with an aqueous solution to obtain a supported membrane adsorbed with supramolecular complexes; (4) Contacting the supported membrane with the adsorbed supramolecular complexes with an organic phase solution containing two or more acyl chloride molecules, an interfacial polymerization reaction occurs; the organic phase solution includes 0.1 to 2% of organic phase monolayers according to the mass fraction. body and the balance of organic solvent; (5) The membrane obtained in the above steps is placed in a drying box for heat treatment to obtain a high-selectivity separation membrane of monovalent/dianionic salts. 2. the preparation method of the highly selective separation membrane of a kind of separation monovalent/dianion salt according to claim 1, is characterized in that: described surfactant is selected from sodium dodecylbenzenesulfonate, dodecyl One or more of sodium alkyl sulfate, Tween 20, dodecyl trimethyl ammonium bromide and hexadecyl trimethyl ammonium bromide. 3. the preparation method of the highly selective separation membrane of a kind of separation monovalent/dianion salt according to claim 1, is characterized in that: described porous organic molecular cage RCC3 is made of 1,3,5-benzenetricarboxaldehyde and 1,2-cyclohexanediamine are prepared by dehydration condensation and unsaturated bond addition reaction. 4. The method for preparing a high-selectivity separation membrane for separating monovalent/dianionic salts according to claim 1, wherein the supporting membrane is selected from the group consisting of porous polymers with a molecular weight cut-off of 10 kDa to 50 kDa membrane. 5. The preparation method of a highly selective separation membrane for separating monovalent/dianionic salts according to claim 4, wherein the material of the polymer porous membrane is polyethylene, polypropylene, polyvinylidene fluoride One of ethylene, polyamide, polyacrylonitrile, polysulfone, polyethersulfone, polyimide, and polytetrafluoroethylene. 6. the preparation method of the high-selectivity separation membrane of a kind of separation monovalent/dianion salt according to claim 1, is characterized in that: described acid absorbent is selected from among sodium hydroxide, sodium carbonate, sodium bicarbonate one or more of. 7. The preparation method of a highly selective separation membrane for separating monovalent/dianionic salts according to claim 1, wherein the binary and above acid chloride molecules are selected from 1,3,5-benzenetrimethyl Acid chloride, suberoyl chloride, malonyl chloride, glutaryl chloride, terephthaloyl chloride, 1,7-pimelyl chloride, decyl dichloride, adipic acid chloride, sebacyl chloride, azelaic acid chloride, 1,3 - One or more of benzenedisulfonyl chloride, 4,4'-biphenyldisulfonyl chloride, 4,4'-oxybis(benzoyl chloride)isophthaloyl chloride. 8. the preparation method of the highly selective separation membrane of a kind of separation monovalent/dianion salt according to claim 1, is characterized in that: described organic solvent is selected from n-hexane, n-heptane, isohexane, cyclohexane One or more of alkane, cycloheptane, and isoheptane. 9 . The method for preparing a highly selective separation membrane for separating monovalent/dianionic salts according to claim 1 , wherein in step (3), the contact operation of the supporting membrane with the aqueous solution is infiltration or dipping. 10 . , the contact time is 1-10 min, and the temperature of the aqueous solution is 15-40 °C. 10 . The method for preparing a highly selective separation membrane for separating monovalent/dianionic salts according to claim 1 , wherein: in step (4), the contact operation is soaking or dipping, and the contact time is 1 ~ 10 . For 10 min, the temperature of the organic phase mixture was 15-40 °C.

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