Preparation of nanofiltration membranes based on alicyclic chloride monomers for magnesium-lithium separation

Abstract

Nanofiltration (NF) membranes have great potential for lithium extraction from salt lakes, however, issues like low permeability and low selectivity have impeded further development. This study introduces 1,3,5-cyclohexane tricarbonyl chloride (HTC), an alicyclic chloride monomer with a certain spatial conformation, as the oil-phase monomer for preparing NF membranes via interfacial polymerization (IP) reaction with polyethyleneimine (PEI) as the aqueous-phase monomer. The overall performance of NF membranes is improved by adjusting the internal structure of the separation layer and optimizing the chemical properties of the membrane surface. The research results show that the NF membranes fabricated using HTC as the organic phase monomer exhibit larger pore size and thickness, and superior wettability than traditional NF membranes synthesized with trimethyl chloride (TMC). Moreover, the permeability and magnesium-lithium separation factors are superior to traditional NF membranes. The permeability of the PEI-HTC NF membrane prepared under optimal conditions is 47.30 L/(m2·h·MPa), doubling that of traditional NF membranes. The separation factor of the PEI-HTC NF membrane is 12.37, being 1.61 times that of traditional NF membranes. Under long-term operation, the PEI-HTC NF membrane maintains good selectivity and excellent structural stability, demonstrating great potential for application in lithium extraction from salt lakes.