The Experimental And Maxwell-stefan Study Of Binary Gas Permeation Through Polymeric And Inorganic Membranes

Membrane technology as an economical and green technology for gas separation has attracted many researchers.In the current market there are two types of membrane which are popular for gas separation:polymeric and inorganic membranes with different transport mechanisms(solution-diffusion vs adsorption-diffusion).The primary objective of this thesis is to study the binary gas permeation behaviors on both polymeric and inorganic membranes,and simulate the permeating process in the inorganic membraneA novel time-lag rig with the cold trap will be introduced to effectively measure the permeation behaviors of each species in binary mixtures.The transient state behaviors regarding binary permeation are found to be significantly different between polymeric and inorganic membranes,while the steady state exhibit similar performances.This work pays more attention to the binary permeation study on inorganic carbon membranes.Three binary mixtures,CO2-He,CO2-N2 and CO2-CH4,will be investigated through carbon membranes.CO2-He permeation follows the competitive adsorption-dominate scenario that the effect of competitive adsorption dominates the overall permeation behaviors.The permeabilities(flux)of both species are less than their corresponding unary permeabilities due to the loss of concentration(driving forces),in the meanwhile,the permeability of He receives more deterioration due to its weak adsorption affinity.CO2-N2 and CO2-CH4 follow the competitive diffusion-dominate scenario that the effect of competitive diffusion(intermolecular friction)controls the whole process and over-compensates the negative effect of competitive adsorption.The fast CO2 molecules will pass part of mobility to the tardier N2 or CH4 molecules after collision.Therefore,The CO2 permeability is slowed-down to be lower than its corresponding unary permeability while the N2/CH4 permeability is speeded-up to be higher than its corresponding unary permeability.This speeding-up phenomenon will be reinforced with the increase of CO2%in feed mixture.Next,this work aims to accurately predict the binary permeation only using the unary dataThe famous Maxwell-Stefan equation combining the Modified HIO model is applied for fitting the binary data.Three attempts regarding the expression of exchange coefficients will be complied into Maxwell-Stefan model:(1)Neglecting the species-species friction leads to a significant deviation from binary data;(2)Vignes model underestimates the strength of species-species interaction;(3)The proposed constant exchange coefficients can well-fit the binary data that the gas diffusion coefficients are around 10～100 times than exchange coefficients.The novel steady state concentration profile of each species in the mixture can be revealed.