Salt removal from synthetic process solutions in liquid dye production by low-pressure nanofiltration

The use of low-pressure nanofiltration (NF) for the removal of salt (NaCl) and concentrated dye (reactive dye 5, RB5) from synthetic process solutions employed in liquid dye production was examined. Effects of the feed dye concentration (1-30 kg-m^-3), salt concentration (1-50 kg-m^-3), solution pH (5.0, 10.5), pressure (0.25-0.4 MPa) applied on the flux, and the rejection of dye and salt were investigated. It was found that salt concentration had a significant effect on the flux. The rejection of dye increased when the applied pressure and feed dye concentration. However, the rejection of salt increased with increasing the applied pressure, the amount of feed dye, or the salt concentration increased. Moreover, the rejection of dye and salt from the solution at a pH of 10.5 was greater than that at a pH of 5. Under the conditions studied, the rejection of dye and the removal of salt were exceeded 96% and 87%, respectively. The transport parameters of salt in this low-pressure NF process were also evaluated and are discussed, here.