Investigation Of Dye Desalting By Nanofiltration Membranes Separation

Nanofiltration membranes are widely used for two features: first, they have intermediate molecular weight cut-offs (MWCO) between those of reverse-osmosis and ultrafiltration membranes; the MWCOs range from 200 to 2000; second, most of the nanofiltration membranes are charged due to their materials, thus they have some rejection to electrolytes because of the Donnan effect.The dyestuff always contains much salt in the produce process .Because the molecular weights of dye are usually larger than 500 D, while salt always is the inorganic salt such as NaCl, it is possible to chose a nanofiltration membrane which MWCO is between 300 and 500 D. If the membrane can reject dye effectively and has little rejection to inorganic salt, dye and salt can be separate effectively.At first, the preliminary experiments of rejection to dye and salt with the NF45, G5, NTR7450, NF200, NF270, DL, DK, SU200 membranes were done.The DK membrane was chosen for the follow experiment .In the diaflltration desalting experiment, the concentration variations of dye and salts in the feed and the rejection to salt with the total diaflltration solvent volume were studied. The concentrations of the dye and the salts in the solution were both found to the expectant concentrations . The comparisons between the discontinuous batch diaflltration and the continuous batch diaflltration were studied in this paper. We also discussed the calculation of the variable salt rejection in the continuous batch diaflltration.Based on the results of the experiments, a simulation for the dye desalting diaflltration was presented to predict the separation time and dissolvent needed. We found that if the same desalting and concentration were demanded, the continuous batch diaflltration at the best diaflltration concentration was more economical than the process not at the best diaflltration concentration, also than the direct diaflltration .