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CN-120204962-B - Preparation method and application of transmembrane back-diffusion in-situ growth ZIF modified polyvinyl polyamide positively-charged nanofiltration membrane

CN120204962BCN 120204962 BCN120204962 BCN 120204962BCN-120204962-B

Abstract

The invention discloses a preparation method and application of a trans-membrane back-diffusion in-situ growth ZIF modified polyvinyl polyamide positively charged nanofiltration membrane, firstly, an organic phase solution containing trimesoyl chloride monomer is used for coating a support membrane, and then, pouring a mixed aqueous solution of polyethylenimine and zinc nitrate hexahydrate above the membrane for interfacial polymerization, turning over a support base membrane after polymerization, pouring a 2-methylimidazole aqueous solution on the surface, performing in-situ growth of ZIF (zinc fluoride) through a base membrane, and performing heat treatment and alcohol activation on the membrane after growth. The method can lead ZIF particles to be more uniformly grown in the membrane, avoid interfacial gaps caused by MOF agglomeration, prepare a high positive layer by combining a reverse phase interfacial polymerization method which uses polyethyleneimine as a water phase monomer, greatly improve water permeation flux while keeping high interception of magnesium ions, solve the problem of mutual restriction of permeability-selectivity, and have simple process and mild preparation conditions.

Inventors

  • XUE LIXIN
  • CHEN MENGYAO
  • LU YEQIANG
  • Huang Yangxiang

Assignees

  • 浙江工业大学

Dates

Publication Date
20260508
Application Date
20250515

Claims (8)

  1. 1. The preparation method of the trans-membrane back-diffusion in-situ growth ZIF modified polyvinyl polyamide positively-charged nanofiltration membrane is characterized by comprising the following steps of: Step 1, preparing a mixed aqueous solution of polyethylenimine and zinc ions as an aqueous phase solution, preparing an alkane solution of aromatic acyl chloride as an organic phase solution, and preparing an aqueous or alcoholic solution containing imidazole monomers as an anti-diffusion imidazole solution; the molecular weight of the polyethyleneimine monomer is 700 to 7 ten thousand channels; the aromatic acyl chloride is trimesoyl chloride, and the solvent in the alkane solution of the aromatic acyl chloride is one or more of n-hexane, cyclohexane, ethyl acetate and dodecane; The imidazole monomer is one or more of dimethyl imidazole and benzimidazole, the water is deionized water, the alcohol is one or more of methanol and ethanol, and the step 2 is to coat the organic phase solution prepared in the step 1 on one side surface of the porous polyolefin support base film, and remove redundant solution after infiltration; step 3, the supporting base film infiltrated with the organic phase monomer obtained in the step 2 is cast by using the aqueous phase solution prepared in the step 1, and after reversed phase interfacial polymerization, redundant solution is removed to obtain a porous polyolefin supporting material; Step 4, pouring the back-diffusion imidazole solution prepared in the step 1 on the surface of one side of the porous polyolefin support material which is not subjected to interfacial polymerization, and removing redundant solution after back-diffusion in-situ growth to obtain a nanofiltration membrane; And 5, performing heat treatment and alcohol activation on the nanofiltration membrane obtained in the step 4 to obtain the trans-base membrane back-diffusion in-situ growth ZIF modified polyvinyl polyamide positively charged nanofiltration membrane.
  2. 2. The preparation method of the aqueous solution according to claim 1, wherein in the step 1, the dosage ratio of the polyethyleneimine to the water in the aqueous solution is 0.1-2.0 g/100 mL, and the concentration of zinc ions in the aqueous solution is 0.0002-0.002 mol/L; The dosage ratio of the aromatic acyl chloride to the alkane in the organic phase solution is 0.01-0.1 g:100 mL; The concentration of imidazole ligand in the back-diffused imidazole solution is 0.003-0.03 mol/L.
  3. 3. The preparation method according to claim 1, wherein in the step 2, the organic phase solution is poured for 1-10 minutes.
  4. 4. The preparation method of claim 1, wherein in the step 3, the casting time of the aqueous phase solution is 1-10 minutes.
  5. 5. The method according to claim 1, wherein in the step 4, the time for pouring the back-diffused imidazole solution is 1 to 60 minutes.
  6. 6. The preparation method according to claim 1, wherein in the step 5, the heat treatment is performed under the conditions that the drying temperature is 50-80 ℃ and the drying time is 10-20 minutes.
  7. 7. The process according to claim 1, wherein in step 5, the alcohol type used for the alcohol activation is isopropyl alcohol, and the alcohol activation time is 1 to 3 minutes.
  8. 8. The application of a trans-membrane back-diffusion in-situ growth ZIF modified polyvinyl polyamide positively charged nanofiltration membrane prepared by the preparation method according to any one of claims 1-7 in water treatment magnesium-lithium separation.

Description

Preparation method and application of transmembrane back-diffusion in-situ growth ZIF modified polyvinyl polyamide positively-charged nanofiltration membrane Technical field: The invention relates to the field of nanofiltration membranes, in particular to a preparation method and application of a trans-membrane back-diffusion in-situ growth ZIF modified polyvinyl polyamide positively charged nanofiltration membrane. The background technology is as follows: In the field of extracting lithium from salt lake brine, the nanofiltration membrane technology has the advantages of low energy consumption and ion selectivity, and is regarded as a core scheme for realizing efficient separation of magnesium and lithium. Traditional nanofiltration membranes can preferentially intercept high-valence ions (such as Mg 2-) and allow monovalent ions (such as Li-) to permeate based on a synergistic mechanism of the Tang-Nannan effect and the size sieving effect. However, the difference of the hydration radius of magnesium and lithium ions in an actual salt lake brine system is small, so that the separation selectivity of the conventional polyamide nanofiltration membrane on magnesium and lithium is drastically reduced. At present, commercial nanofiltration membranes can enhance the interception of magnesium ions by reducing the pore diameter, but the permeation flux of the membranes can be drastically reduced due to the mutual restriction problem of permeability-selectivity, and in addition, the surfaces of more commercial nanofiltration membranes are negatively charged, so that the interception of magnesium ions is more unfavorable. In addition, the traditional polysulfone substrate membrane has high cost and complex preparation process, so that the use of a low-cost and good-mechanical-property polyethylene ion battery diaphragm (PE) to replace the polysulfone membrane becomes a research hot spot. However, the inertia of the PE surface causes the porous polyamide layer formed by conventional interfacial polymerization, the retention rate of magnesium ions is low, researchers try to build a compact positive layer on the Polyethylene (PE) by adopting conventional diamine monomers such as piperazine (PIP) and trimellitic chloride (TMC) through reverse interfacial polymerization, the obtained multi-layer composite polyamide (TFC-PE/PA) nanofiltration membrane still has electronegativity, the permeation flux is only 4.8L.m -2·h-1·bar-1, the researchers increase the water flux by a method of directly doping nano particles, but the conventional nano materials are mixed into an aqueous phase or an oil phase for interfacial polymerization, the agglomeration of nano particles is unavoidable, and non-selective defects are formed, so that the separation performance of the membrane is reduced. Therefore, how to improve the permeation flux of water under the condition of guaranteeing the separation performance of magnesium and lithium is one of the difficulties of the current magnesium and lithium separation technology. The invention comprises the following steps: Aiming at the defects, the invention provides a preparation method and application of a trans-base membrane back-diffusion in-situ growth ZIF modified polyvinyl polyamide positively charged nanofiltration membrane, and on the premise of guaranteeing the magnesium-lithium separation performance, the water permeation flux is greatly improved. A preparation method of a trans-membrane back-diffusion in-situ growth ZIF modified polyvinyl polyamide positively-charged nanofiltration membrane comprises the following steps: Firstly, an organic phase solution containing trimesoyl chloride monomer is used for coating one surface of a support base film, then a mixed aqueous phase solution containing polyethylenimine monomer and zinc nitrate hexahydrate is coated, reverse phase interfacial polymerization is carried out, after the reaction is finished, back diffusion of imidazole solution is carried out on the surface of one side of the support base film which is not subjected to the interfacial polymerization, and in-situ growth is carried out to form a uniformly grown ZIF composite nanofiltration membrane, namely the trans-base film back diffusion in-situ growth ZIF modified polyvinyl polyamide positively charged nanofiltration membrane. The method comprises the following specific steps: step 1, preparing a mixed aqueous solution of polyethylenimine and zinc ions as an aqueous phase solution, preparing an alkane solution of aromatic acyl chloride as an organic phase solution, and preparing an aqueous or alcoholic solution containing imidazole monomers as a ligand solution for back diffusion; Step 2, the organic phase solution prepared in the step 1 is poured on any side surface of the porous polyolefin support base film, soaked for a period of time and redundant solution is removed; step 3, the aqueous phase solution prepared in the step 1 is used for carrying out pouring coating on the sup