Experimental study on the rejection of salt and dye with cellulose acetate nanofiltration membrane

In this study, the rejections of dye, salt, and dye intermediate by a cellulose acetate (CA) nanofiltration membrane were investigated. The rejections of sodium chloride and sodium sulfate were moderate and declined with the increase of concentration. The rejection of five reactive dyes by a CA nanofiltration membrane was higher than 99.0% at low concentration, and high rejection of five reactive dyes was still achievable at higher dye concentration. However, the rejections of five dye intermediates varied from low to moderate when the molecular weight increased. In the C.I. Reactive Black 5 diafiltration and concentration process, the concentration and constant volume diafiltration mode had a better desalting degree than the constant volume diafiltration and concentration mode. However, the constant volume diafiltration and concentration mode is necessary for C.I. Reactive Blue 13 solution due to its low solubility. This study illustrates that nanofiltration is a promising process for dye desalting and concentrating.