In some dyeing processes almost 50% of the color of reactive dyes is discharged into the effluent due to the poor fixation characteristics of the dyes, and disposal of these streams in public waterways is not acceptable. Nanofiltration (NF) may provide an economical method for both recovering the salt from dye solutions and decreasing the volume of contaminated water. Our recent work examined the potential of a polyelectrolyte NF membrane for isolation of dyes from NaCl solutions. Membranes for such processes should show essentially 100% rejection of dyes while allowing passage of NaCl to both recover the salt and decrease osmotic pressure. Poly(styene sulfonate)/protonated poly(allylamine) films on alumina supports exhibit >99.9% rejection of all the dyes shown below, which is considerably higher than rejections reported for any commercial NF membranes. Moreover, the polyelectrolyte films simultaneously allow ~80% salt passage. Thus, they are potentially very attractive for these separations. This work is described in a recent article in Industrial and Engineering Chemistry Research.
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