Preparation And CO₂ Separation Properties Of Phloroglucinol-Melamine-Formaldehyde Polymeric Nanofibers–PDMS Mixed-Matrix Membranes

Evidences continue confirming that the increasing emissions of carbon dioxide?CO₂?are the major contributor to the aggrevation of greenhouse effect,which has a great negative impact on our living environment.From the perspective of energy and environment,capturing or separating CO₂ from flue gas and natural gas is of great significance to the steady and long-term development of human society.Compared to the conventional separation technology,gas membrane separation technology exhibits good potential prospect in the field of CO₂ capture and separation,due to the merits of high efficiency,energy saving and low carbon emission,etc.Membrane separation is regarded as a new low-carbon technology for the efficient separation of CO₂.The mixed-matrix membrane?MMMs?,prepared by the matrix of uniform interpenetrating polymer and the filler of inorganic particles,combine the benefits of both polymeric and inorganic materials,becoming a focus of the next-generation gas separation membranes.Amine-based porous materials have aboundant adsorption sites for CO₂,performing good CO₂ adsorption selectivities.On the other hand,polydimethylsiloxane?PDMS?is a semi-organic and semi-inorganic polymeric material with many merits,such as heat resistance,large free volume,and weak inter-molecular interaction,etc.,which is one of the best polymeric membrane materials in terms of permeability.In this thesis,a microporous organic material,i.e.phloroglucinol-melamine-formaldehyde polymeric nanofibers?PMF?,was incorperated into the matrix of PDMS to prepare a series of PMF-PDMS self-standing MMMs and PMF-PDMS/Al₂O₃ supported MMMs.The CO₂ gas separation performance was invesigated.The content of this thesis consists of two parts as follow:1.PMF-PDMS self-standing MMMs composed of PMF fibers as the filler and PDMS as the matrix were prepared by a simple solvent evaporation method.The effect of different PMF loadings on the physicochemical properties as well as the CO₂separation performance of membranes was systematically studied.Compared to the pure PDMS membrane,the incorperation of PMF greatly increased the CO₂permeability and the ideal selectivity.When the content of PMF was 2.0 wt.%,the PMF-PDMS self-standing MMMs exhibited the best CO₂ separation performance with a CO₂ permeatbility of 4931 Barrer and ideal selectivities of 14.8 and 5.1 for CO₂/N₂ and CO₂/CH₄,respectively.The improvements of permeablity and selectivity were related to the microporosity of the filler,confirmed by the characterizations of N₂ adsoption-desorption,SEM,FTIR,TG,etc.After a 144 h continuous test,the permeation and the ideal selectivity showed no obvious decay,indicating the membrane has the potential for the separation of CO₂.2.PMF-PDMS/Al₂O₃ supported MMMs were prepared by spin-coating the mixed matrix casting solution on?-alumina?Al2O3?supports.Characterizations of SEM,indicated that dense and flat PMF-PDMS self-standing MMMs with thickness of about 10?m on the Al₂O₃ support could be fabricated.The effect of different PMF loadings on the CO₂ separation performance of membranes was systematically studied.Single gas permeation tests of CO₂,N₂ and CH₄ on PMF-PDMS/Al₂O₃ supported MMMs prepared with different PMF loadings indicated that both the ideal selectivity and the gas permeance increased with the increase of PMF filling content.When the PMF loading was 2.0 wt.%,the permeance of CO₂ was 3.21×10^-88 mol?m^-2?s^-1?Pa^-1with ideal selectivitis of 14.3 and 4.4 for CO₂/N₂ and CO₂/CH₄,respectively.Compared to the PMF-PDMS self-standing MMMs,which showed a permeance of CO₂ of 2.87×10^-99 mol?m^-2?s^-1?Pa^-1,the PMF-PDMS/Al₂O₃ supported MMMs with thinner thickness and high ideal selectivity displayed higher CO₂ permeation rate.