Preparation And Characterization Of PVC Blended Substrate Based High-performance TFC-FO Membrane

Without requiring a high hydraulic pressure,forward osmosis?FO?utilizes osmotic pressure diferences to drive the water across the FO membrane from a low-osmotic-pressure feed solution to a high-osmotic-pressure draw solution,hence it becomes a focal technology in membrane separation field.Lack of high-performance FO membranes is a major obstacle for the commercialization application of FO technology.Thin flim comparison?TFC?FO membranes became the most concerned FO membranes because of its high water flux and wide pH range.However,the inevitable internal concentration polarization?ICP?would reduce the osmotic pressure differences across the membranes to degrade the performance of the FO membranes.The properties and structures of the substrates of the TFC FO membranes contribute important effects for ICP,thus fabrication of novel substrates to reduce ICP is a research hotspot in FO membranes field.Polyvinyl chloride?PVC?was chosen as a backbone material and blended with five hydrophilic materials to prepare the substrates for thin-film composite?TFC?FO membrane,respectively.Then,the TFC membranes were prepared by interfacial polymerization process using m-Phenylenediamine?MPD?and trimesoyl chloride?TMC?as monomers on the prepared substrates.Thses five hydrophilic materials are three commercial materials?polyvinyl butyral?PVB?,sulfonated polysulfone?SPSU?,and cellulose acetate butyrate?CAB??and two lab-made materials?cellulose carbamate?CC?,and quaternized polyphenylene oxide?QPPO??.The impacts of the blend ratios of these five hydrophilic materials to the properties and performances for the TFC membranes were investigated.The results showed that the performances for the TFC membranes were improved significantly after these five materials were introduced in.And,the optimal blend ratios for PVB,SPSU,CAB,CC and QPPO were30%?2.5%?20%?10%and 40%?denoted as TFC-B-30,TFC-U-2.5,TFC-A-20,TFC-C-10and TFC-Q-40?,respectively.When 1 mol/L NaCl was used as draw solution and DI water as feed solution to operate FO performance tests under FO/PRO mode:the water flux was improved from 4.02/6.50 L?m^-2?h^-1 to 9.37/49.85 L?m^-2?h^-1,25.53/48.37 L?m^-2?h^-1,23.58/44.52L?m^-2?h^-1,21.63/40.40 L?m^-2?h^-1 and 36.39/68.84 L?m^-2?h^-1,respectively;the specific salt flux was reduced from 0.558/0.614 g?L^-1 to 0.109/0.098 g?L^-1,0.101/0.093 g?L^-1,0.193/0.172 g?L^-1,0.110/0.099 g?L^-1 and 0.081/0.079 g?L^-1,respectively.The reasons for these improvements are the two following items.Firstly,the porosity,mean pore size and hydrophilicity were improved after the hydrophilic materials were blended in,which would lead to higher efficiency of mass-transfer between the solutions inside and outside the substrates and slighter ICP during the FO process.Secondly,the substrate changes of the substrates affected the interfacial polymerization process and led in the changes of the morphologies and crosslinked degrees of the active layer.The water permeabilities of the active layers were significantly improved and the salts rejection rates were controlled in reasonable ranges.The FO performance of these five TFC membranes were compared by water flux and specific salt flux,the comparison confirmed that these five materials improved performance of the TFC membranes significantly.The sorting for the performance of these five optimal TFC membranes were:TFC-Q-40>TFC-B-30>TFC-U-2.5>TFC-C-10>TFC-A-20.Moreover,all these five TFC FO membranes exhibited better performance than the commercial TFC FO membrane from HTI corporation.