Water/salt Transport Performance Study Based On Cellulose Triacetate Mixed Matrix Membrane

Polymer membrane-based desalination(e.g.reverse osmosis(RO)and nano filtration(NF))has been extensively developed since the 1960s and is well-established process.The separation performance of desalination membranes is usually described in terms of water flux(or permance)and salt rejection.Based on the survey of available data,water permeance and NaCl rejection are often inversely correlated,and there may be an upper bound,similar to that observed in gas separation membranes,beyond which there are very few data points.At present,commercial reverse osmosis membranes are mostly polyamide(PA)reverse osmosis membranes.PA RO membrane are susceptible to all kinds of foulants and free chloride which limited its wide application and long-term performance.Cellulose acetate(CA)RO membrane have better antifouling and chlorine resistance.However,CA RO membrane technology is subjected to many technical limitations.The attempts to improve the properties of CA RO membrane are only based on some empirical rules.The mechanism of water molecular and salt ions transport properties is unknown.Based on this,according to the solution-diffusion theory,the vwater/salt transport mechanism of cellulose triacetate(CTA)membrane was studied,which can provided theoretical guidance for the improvement of CTA RO membrane.In the article,inorganic particles,such as reduced graphene oxide(RGO),ZSM-5 zeolite,MCM-41 zeolite,ZIF-8,SiO2 and graphene oxide(GO),were added to the CTA casting solution to prepare the CTA mixed matrix dense membrane.The surface morphology of the mixed matrix membranes were investigated by thermal field emission scanning electron microscopy(TESEM)and energy-dispersive X-ray spectroscopy(EDX).On the basis of solution-diffusion model,the equilibrium water uptake(or water volume fraction)decrease slightly with the increase of hydrophobic inorganic particles content.Addition the hydrophilic inorganic particle to the CTA membrane,the equilibrium water uptake(or water volume fraction)increase.The salt sorption coefficient of mixed matrix membrane is not particularly significant.The of contents of the inorganic particle is less than lwt%,water permeability and diffusion coefficient maintain the same order of magnitude.Salt permeability and diffusion coefficient of mixed matrix membranes decreased,which illustrates that in organic particles can impede the transport of Na+ and Cl-.The data for the water/salt solution.diffusion and permeability coefficients of the mixed matrix membranes are all above the CTA membrane,indicating that the water/salt selectivity has increased.GO/CTA mixed matrix membrane have higher water and salt transport properties than others.In all,a certain amount of in organic particle(such as ZSM-5,ZIF-8 or GO)prepared the mixed matrix RO membrane is expected to increase water flux and salt rejection simultaneously.