Separation of dimethylformamide-water mixtures using sodium alginate, sodium alginate/poly(vinyl pyrrolidone) and N-vinyl-2-pyrrolidone-g-sodium alginate membranes

In this study, separation of dimethylformamide-water mixtures was investigatedusing pervaporation (PV), evapomeation (EV) and temperature differenceevapomeation (TDEV) methods. Sodium alginate (NaAlg) based membraneswere used in the separation. NaAlg was modified usingpoly(vinyl pyrrolidone) (PVP) or grafting N-vinyl-2-pyrrolidone (NVP) ontoit. Membranes prepared were characterized using Fourier transforminfrared spectrometer (FTIR), differential scanning calorimeter (DSC)and scanning electron microscope (SEM).Experimental studies were focused on the effect of membrane thickness,operating temperature, membrane surrounding temperature and the feedcomposition on the permeation rate (flux) and the separation factor (selectivity).Experimental study was carried out in three parts. In the first part; DMFmixtures were separated using NaAlg membranes by pervaporation. Theoptimum operating temperature and membrane thickness were determined as40 0C and 70 µm.In the second part; NaAlg/PVP blend membranes were prepared. OptimumNaAlg/PVP ratio was determined as 75/25 (w/w) for 20 wt% DMF mixtures at40 0C. It was observed that blending PVP with NaAlg increased the permeationrate whereas decreased the separating factor.In the third part of the study; NVP was grafted onto NaAlg under N2atmosphere with benzophenone. The graft copolymerization was carried out byirridiating with UV light. The copolymer synthesized with the grafting efficiencyof 33% was used in the separation of DMF-water mixtures with the threemethods. It was determined that grafting of NVP onto alginate increased thepermeation rate whereas decreased the separation factor.It was observed that the permeation rates and the separation factors changesdepending on the method used. Highest separation factors were obtained in theTDEV method whereas permeation rates obtained in PV were higher than EVand TDEV methods.Key Words : Pervaporation, evapomeation, temperature differenceevapomeation, dimethylformamide-water mixtures.