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CN-116036877-B - High-interception positively charged composite nanofiltration membrane and preparation method thereof

CN116036877BCN 116036877 BCN116036877 BCN 116036877BCN-116036877-B

Abstract

The invention relates to the technical field of separation membrane composite materials, and discloses a high-interception positively charged composite nanofiltration membrane and a preparation method thereof. The preparation method comprises the following steps of firstly bonding polyvinyl alcohol on the surface of a base film through a crosslinking reaction, then epoxypropyl dodecyl dimethyl ammonium chloride on the surface of the base film to obtain a pretreated base film, and then sequentially immersing the pretreated base film into a quaternized polyethyleneimine aqueous phase solution and an acyl chloride monomer organic phase solution, and performing aftertreatment and thermal curing crosslinking to obtain the high-interception positively charged composite nanofiltration membrane. The composite nanofiltration membrane separation layer prepared by the method has higher aperture uniformity and higher interception effect on high-valence cations.

Inventors

  • WEI JIANG
  • Duan Guobo
  • CHEN CHULONG
  • FENG WEI
  • YOU XIAOWEI

Assignees

  • 浙江美易膜科技有限公司

Dates

Publication Date
20260512
Application Date
20221205

Claims (9)

  1. 1. The preparation method of the high-interception positively charged composite nanofiltration membrane is characterized by comprising the following steps of: 1) Preparing a base film, immersing the base film into a polyvinyl alcohol solution, and performing a crosslinking reaction under the action of a crosslinking agent to bond the crosslinked polyvinyl alcohol on the surface of the base film; 2) Enabling hydroxyl groups on cross-linked polyvinyl alcohol molecules bonded on the surface of the base film to carry out ring-opening reaction with epoxy groups on epoxypropyl dodecyl dimethyl ammonium chloride, and grafting the epoxypropyl dodecyl dimethyl ammonium chloride on the surface of the base film to obtain a pretreated base film; 3) Dissolving an acyl chloride monomer with at least two acyl chloride groups in a solvent to obtain an organic phase solution; 4) Dissolving quaternized polyethyleneimine in water, adding a surfactant and an acid neutralizer, and uniformly dispersing to obtain a water phase solution; 5) The pretreatment base film is contacted with the aqueous phase solution firstly, then placed in air for standing, and then contacted with the organic phase solution for interfacial polymerization reaction to obtain the nascent compound nanofiltration membrane; 6) And (5) post-treatment, namely performing heat treatment on the nascent composite nanofiltration membrane.
  2. 2. The method for preparing the high-interception positively charged composite nanofiltration membrane according to claim 1, wherein the crosslinking reaction time in the step 1) is 12-18min.
  3. 3. The method for preparing the high-interception positively charged composite nanofiltration membrane according to claim 1, wherein the ring-opening reaction in the step 2) is carried out by heating to 170-200 ℃ under the condition of sodium hydroxide catalyst, and reacting at constant temperature for 1-5h.
  4. 4. The method for preparing the high-interception positively charged composite nanofiltration membrane according to claim 1, wherein the acyl chloride monomer in the step 3) is at least one of trimesic chloride and pyromellitic chloride.
  5. 5. The method for preparing the high-interception positively charged composite nanofiltration membrane according to claim 1, wherein the mass concentration of the acid chloride monomer in the organic phase solution in the step 3) is 0.01-1%.
  6. 6. The method for preparing the high-interception positively-charged composite nanofiltration membrane according to claim 1, wherein the mass concentration of the quaternized polyethyleneimine in the aqueous phase solution in the step 4) is 0.5-1.5%.
  7. 7. The method for preparing the high-retention positively charged composite nanofiltration membrane according to claim 1, wherein the standing time in the air in the step 5) is controlled to be 10-30min.
  8. 8. A high-retention positively charged composite nanofiltration membrane, characterized in that the membrane is prepared by the method of any one of claims 1-7.
  9. 9. The high-retention positively charged composite nanofiltration membrane according to claim 8, wherein the nanofiltration membrane is applied to the field of hard water softening or salt lake lithium extraction.

Description

High-interception positively charged composite nanofiltration membrane and preparation method thereof Technical Field The invention relates to the technical field of separation membrane composite materials, in particular to a high-interception positively charged composite nanofiltration membrane and a preparation method thereof. Background The membrane separation technology is an efficient, energy-saving and environment-friendly water treatment technology, and becomes an important means for solving the problems of water resource shortage and water pollution. Nanofiltration is a membrane separation technique between ultrafiltration and reverse osmosis, typically with a nanofiltration cut-off of 200-1000Da and an effective membrane pore size of 0.5-2nm. The nanofiltration membrane has better separation performance for high-valence, bivalent salt and micromolecular organic matters, has the advantages of low operation pressure, high pure water flux, lower cost and the like, and has wide application prospect in the fields of water softening, desalination, wastewater treatment and the like. Currently commercial nanofiltration membranes are mostly negative nanofiltration membranes. The trapping effect of the negative nanofiltration membrane on the divalent metal ions mainly depends on the sieving action of the pore diameter, so in order to obtain the nanofiltration membrane with higher removal rate of the divalent and higher valence metal ions, the pore diameter of the membrane needs to be smaller, thereby trapping the divalent and higher valence cations, but the operation pressure of the membrane is increased, and the cost of the membrane separation process is increased. The positively charged nanofiltration membrane can prevent high-valence and divalent cations from penetrating the nanofiltration membrane by virtue of the charge repulsion action of the membrane surface, so that metal ions are removed, the aperture of the nanofiltration membrane is not required to be reduced, and the operation pressure of the nanofiltration membrane is reduced. However, in the process of preparing the positively charged nanofiltration membrane by interfacial polymerization, the prepared nanofiltration membrane has nonuniform pore diameter of a separation layer, so that the rejection rate of the nanofiltration membrane on metal ions is reduced. Chinese patent publication No. CN112755817 discloses a composite nanofiltration membrane with high performance, a preparation method and application thereof, wherein the composite nanofiltration membrane comprises a porous ultrafiltration base membrane and a polyamide selective separation layer arranged on the base membrane, the polyamide selective separation layer is mainly formed by interfacial polymerization reaction of a polyamine monomer and a polybasic acyl chloride monomer under the regulation and control action of a surfactant, one of the adopted implementation modes is that polyethyleneimine and trimesoyl chloride are subjected to interfacial polymerization on a polyethersulfone ultrafiltration base membrane, and the obtained polyamide separation layer has poor pore size uniformity and influences the rejection rate of the composite nanofiltration membrane to cations. Disclosure of Invention The invention provides a high-interception positively charged composite nanofiltration membrane and a preparation method thereof, aiming at solving the problem of ion interception rate reduction caused by poor pore diameter uniformity of a nanofiltration membrane separation layer. The composite nanofiltration membrane separation layer prepared by the method has higher aperture uniformity and higher interception effect on high-valence cations. In order to achieve the above object, the present invention adopts the following technical scheme: The preparation method of the high-interception positively charged composite nanofiltration membrane comprises the following steps: 1) Preparing a base film, immersing the base film into a polyvinyl alcohol solution, and performing a crosslinking reaction under the action of a crosslinking agent to bond the crosslinked polyvinyl alcohol on the surface of the base film; 2) Enabling hydroxyl groups on cross-linked polyvinyl alcohol molecules bonded on the surface of the base film to carry out ring-opening reaction with epoxy groups on epoxypropyl dodecyl dimethyl ammonium chloride, and grafting the epoxypropyl dodecyl dimethyl ammonium chloride on the surface of the base film to obtain a pretreated base film; 3) Dissolving an acyl chloride monomer with at least two acyl chloride groups in a solvent to obtain an organic phase solution; 4) Dissolving quaternized polyethyleneimine in water, adding a surfactant and an acid neutralizer, and uniformly dispersing to obtain a water phase solution; 5) The pretreatment base film is contacted with the aqueous phase solution firstly, then placed in air for standing, and then contacted with the organic phase solution for int