The Optimization Of Supports Of Composite Membranes By Interfacial Polymerization For CO₂ Separation

Efficient CO₂ separation membrane technology is an effective means to relieve the energy and environment crisis.It shows promising applications in greenhouse gases reduction and energy gases purification.However,it is still a challenge for extant CO₂ separation membranes to meet the requirements of most practical application by now.As one of the most common membrane configurations,composite membranes consist of a selective layer and a support.CO₂ separation performances of composite membranes can be improved by optimizing both two layers,respectively.This work primarily focused on the optimization of the supports.According to the resistance model,we explored the methods to improve the permeance of supports by decreasing the thickness of intermediate layer,reducing the intrusion depth of intermediate layer material and increasing the permeability of intermediate layer material.Firstly,the supports were prepared by casting poly（dimethylsiloxane）（PDMS）solutions with different concentrations on the polysulfone（PSf）ultrafiltration membrane.The optimum PDMS concentration of coating solution was explored considering both permeance and selectivity.Then the composite membranes with an ultrathin polyamide selective layer were developed on the PDMS/PSf supports by interfacial polymerization（IP）with trimesoyl chloride（TMC）and 3,3’-diamino-N-methyldipropylamine（DNMDAm）as monomers in the organic phase and aqueous phase,respectively.The decrease of PDMS layer thickness induced the reduction of the resistance of PDMS/PSf support,thus increased the gas separation performance of the composite membrane.Furthermore,the PSf membrane was immersed into the deionized water to fill the membrane pores before coating the PDMS solution.Therefore,the intrusion depth of PDMS was reduced and the permeance of support was improved.Consequently,the composite membrane fabricated by IP on PDMS/PSf support showed an excellent CO₂ separation performance.After that,mixed matrix supports were developed via incorporating ZIF-8 nanoporous particles into PDMS matrix.Subsequently,the DNMDAm-TMC/PDMS-ZIF-8/PSf composite membranes were made by IP on PDMS-ZIF-8/PSf supports.The existence of abundant organic ligands in hydrophobic ZIF-8 particles favored the formation of the compatible interface morphology with hydrophobic polymer PDMS.In addition,the appropriate pore aperture and abundant CO₂ adsorption sites of ZIF-8 were beneficial for the transport of CO₂ molecules and blocked the N2 molecules.Moreover,the CO₂ separation permeance of support was optimized by altering the ZIF-8 loading in PDMS matrix.Consequently,the composite membrane displayed a notably enhanced CO₂ separation performance owing to the increase of CO₂ permeance of the support.