Desalination And Concentration Of Reactive Dye Solution By Nanofiltration Membranes And The Process Simulation

Batch diafiltration experiments of industrial reactive purple dye solution werecarried out by using the three kinds of NF membranes which were DK (DesalinationCorporation), DL(Desalination Corporation) and NF270 (DOW Chemical Corporation)membranes, in order to choose the nanofiltration membrane having high permeationflux, low rejection of NaCl component and high rejection of dye. Thus, the DKmembrane in the operation mode of batch diafiltration was used for the concentrationand desalination of reactive purple dye solution. Under the temperature 25℃ andapplied pressure of 1.0MPa, observed rejection of dye component reached 100%.After nine-stage batch diafiltration operation, concentration of dye increased (去除to)3 times, and the purity of reactive dye increased from 84% to 99%. Theexperimental results showed that nanofiltration membrane DK in batch diafiltrationoperation mode was applicable to desalination and concentration of reactive dyesolution. Next, for the purpose of desalination and concentration of the reactive dyesolution, batch constant volume diafiltration process, combined process ofpreconcentration phase- continuous constant volume diafiltration phase- postconcentration phase and continuous variable volume diafiltration process werestudied. These separation and purification processes were simulated and used topredict the changes of process parameters. The work will provide useful theoreticalguide for the engineering application and embody its value. (1) The simulation ofbatch constant volume diafiltration process was used to determine the effects of thevolume concentration factor (1.5, 2, 3) on desalting and purifying of dye solution. Thesimulative results suggested that to obtain the same concentration of NaCl and purityof dye in the retentate, the higher concentration factor is, the less process time andwater quantity are required for the processed volume . With the times increased of therepeated operations of concentration-dilution , the salt concentration in the retenatewas descreased. (2) The simulation of three-phrase combined process was used todetermine the effects of the volume concentration factor in pre-concentration phase(1.5, 2, 3) on the process parameters, and the process time was optimized. For theminimum consumption of process time, the optimum value of dye concentration at idiafiltration was 0.264mol/L. Thus, to obtain the same concentration of NaCl and dyecomponent in the retentate, the optimum appears to be a combined process where thefeed was first pre-concentrated about 3 times by nanofiltration, followed bycontinuous constant volume diafiltration and post-concentration. The required volumeof added water depended on volume concentration factor in pre-concentration phase,salt rejection and desired salt concentration in the retentate. (3) The simulation ofcontinuous variable volume diafiltration process was to discuss the effect of finalconcentration of dye and salt in the retentate. The simulative results showed that if thesame salt concentration are obtained in the retentate, the higher the dye concentration,the longer the process time and the less volume required of added water; and if thesame dye concentration are obtained in the retentate, the lower the salt concentration,the longer the process time and the more volume required of water added. When the same dye and salt concentration (Cdye/Cdye,0 = 3, Csalt,0/Csalt = 16) areachieved, those three processes were compared. The total process time and requiredvolume of added water in the combined process were least, compared with the othertwo processes.