ABSTRACT
Casting, characterization and performance of blend polymeric membranes were carried out in detail in this study. Three different types of polymers polysulfone (PSF), polyacrylonitrile (PAN) and thermoplastic polyurethane (TPU) were used as base polymers.
Effects of molecular weight and concentration of polyethylene glycol (PEG) as additive in PSF based membranes were investigated including the variation of solvent. It was observed that more porous membranes were formed using N-methyl-2- pyrrolidone (NMP) as solvent compared to N, N- dimethylformamide (DMF). A wide range of molecular weight cut-off (MWCO) membranes, from 10 to 70 kDa was obtained. Performance of cast membranes to clarify the turbid water was successfully tested. Simultaneous use of organic (PEG 200), and inorganic (ZnCl2) additives to polysulfone resulted in a novel nanofiltration (NF) membrane. The membranes were tested with monovalent and divalent electrolytes, sucrose, glucose and three dyes having the molecular weight in the range of 263 to 697 Da. Electrostatic interaction was found to play a significant role in rejection of salts, whereas, size exclusion was prevailing mechanism for rejection of dyes. Two stage nanofiltration was successfully implemented for treatment of real textile effluent, so that the final treated water confirmed the quality parameters for reuse or safe disposal to surface water. In this work technical feasibility of two stage nanofiltration for laboratory developed membranes is shown. For actual plant scenario, the economical feasibility will be investigated in subsequent studies.
Polyacrylonitrile (PAN) is a low cost, easily available widely accepted base polymer to cast porous membranes in the range of ultrafiltration and microfiltration.
A detailed study on the effect of molecular weight of PAN homopolymer and its concentration on the cast membrane was undertaken including the effects of additive (PEG) molecular weight and concentration. Anti-fouling property of various membranes was evaluated using filtration of bovine serum albumin (BSA) solution.
Efficacy of these membranes was also studied for treatment of used engine oil.
Membrane with 8 wt% PEG 400 showed the best antifouling performance. Flux
decline ratio for this membrane was the lowest in between 10% to 20% and flux recovery ratio was above 90% for oil concentration between 100 to 1000 mg/l at 276 kPa transmembrane pressure (TMP). The experimental observation showed that oil concentration in permeate was found to be well within the permissible limit.
Casting of flat sheet polyacrylonitrile (PAN)/polyurethane (PU) blend membranes was reported for the first time in this work. PU made the membrane more porous. Ternary phase diagram indicated that addition of PU increases thermodynamic instability of the blend. PAN/PU blend membrane (70:30) exhibited the maximum antifouling characteristic with 99% flux recovery ratio associated with complete removal of turbidity and organic matters.
Flat sheet mixed-matrix membranes (MMM) were cast by blending PAN with iron oxide nanoparticles (Fe3O4) followed by chitosan coating. Removal of humic acids and microorganisms from wastewater was tested using these membranes. The long term stability of MMM was demonstrated by conducting the experiment for 50 hours under continuous cross flow mode. Effects of various operating conditions like transmembrane pressure, cross flow rate and feed concentration on membrane performance were also investigated.
Keywords: Ultrafiltration, nanofiltration; molecular weight cut-off; flux recovery ratio; flux decline ratio; polymer blend; ternary phase diagram; mixed matrix membrane; iron oxide nanoparticles.
