Effective dye purification using tight ceramic ultrafiltration membrane

Nanofiltration (NF) has attracted increasing interest for dye and NaCl fractionation in textile industry. However, it typically shows high rejections to divalent salts (i.e., Na₂SO₄), compromising to effectively purify dye from dye/Na₂SO₄ mixtures, which is crucial in digital ink-jet printing. This study used a tight ceramic ultrafiltration (UF) membrane (MWCO of 2410 Da) to desalinate diverse reactive dye species with molecular weights from 626.6 to 1205.4 Da. The UF membrane showed considerably high rejections to all the reactive dyes (> 98.12%) and nearly complete salt transmission (rejections < 0.1% and < 1.5% with 60 g L⁻¹ NaCl and Na₂SO₄, respectively). Operational conditions, i.e., dye concentration, applied pressure and salt addition, have insignificant impacts on the dye rejection, due to dye aggregation. An integrated UF-diafiltration process, including pre-concentration, diafiltration and post-concentration, was designed to fractionate reactive dyes and Na₂SO₄. The model dye, reactive blue 19, can be concentrated to 142.60 g L⁻¹ with a purity of 99.83% in the process, since low salt rejection and high dye retention of the membrane allows for 99.88% salt removal and 2.3% dye loss after ca. 9 diavolumes. These results indicate that tight ceramic UF membranes have high potential as a state-of-the-art technology in reactive dyes and Na₂SO₄ fractionation for digital ink-jet printing applications.