Study On The Structures And Desalination Properties Of Composite Pervaporation Desalination Mambranes

The application of seawater reverse osmosis has alleviated the worldwide water shortage problem greatly,but has also produced a large amount of concentrated brine solutions.Pervaporation(PV)desalination has the ability to further extract fresh water from these concentrated brines so that reduces the discharged amount.However,the water fluxes of current PV desalination membranes are still low.In this study,we developed high flux PV desalination membranes via smart adjustments of the structures of the selective layer,and the porous support.Decreasing the thickness of the dense selective layer and enlarge the pore size and porosity of the support layer can reduce the transport resistance of the composite PV membranes.But it often leads to the formation of defects on the skin layer.To solve this issue,we utilized a macromolecular crosslinker,poly(acrylic acid-co-2-acrylamido-2-methyl propane sulfonic acid)(P(AA-AMPS))to crosslink PVA to improve the toughness of the selective layer.Consequently,we deposited the crosslinked PVA layer on to a microporous PTFE support using spray coating.The resulting defect-free PVA/PTFE membrane with a dense layer thickness of 1.1μm was obtained.When desalinating a 3.5 wt.%Na Cl solution at 75oC,a water flux of 256.6±31.3 kg/(m~2·h)with a salt rejection of 99.9%was realized.To further increase the desalination property,we designed the separation layer structure with hydrophilic surface layer and hydrophobic sublayer.The hydrophobically modified molecular sieve H-MCM-41 was deposited in the PVA/PTFE composite membrane.The idea is to take advantage of the low friction of the hydrophobic channel,formed by hydrophobic modified molecular sieve H-MCM-41,to water molecules.As a result,the PVA/H-MCM-41/PTFE composite membrane has a water flux of 276.2kg/(m~2·h),salt rejection of 99.9%as treating a 3.5 wt.%Na Cl solution at 75oC.The high-water flux exceeds all reported water fluxes of PV desalination membranes to our best knowledge.This demonstrates great industrial values of these PV desalination membranes.