Desalination And Concentration Of Aqueous Dye Solutions By Nanofiltration Membranes And The Process Simulation

Permeation experiments of aqueous industrial fluorescent dye solution were carried out by using the two kinds of NF membranes, which were NF270 (DOW Chemical Corporation, USA) and NTR7450 (Nitto Denko, Japan) membranes, in order to chose the nanofiltration membrane having high permeation flux, low rejection of NaCl component and high rejection of dye. Thus, the NF270 membrane in the operation mode of batch diafiltration was used for the concentration and desalination of aqueous dye solution. Under temperature 25℃ and applied pressure of 1.0MPa, observed rejection of dye component reached 100%. After six-stage batch diafiltration operation, concentration of dye increased 2.6 times, and concentration of NaCl decreased from 0.214mol/L to 0.0025mol/L. The experimental results showed that nanofiltration membrane NF270 in batch diafiltration operation mode was applicable in desalination and concentration of aqueous dye solution. In present dissertation, for the purpose of desalination and concentration of this aqueous dye solution, batch constant volume diafiltration process, combined process of preconcentration phase- continuous constant volume diafiltration phase- post concentration phase and continuous variable volume diafiltration process were studied. These separation and purification processes were simulated and derived to predict the changes of process parameters. The work will provide useful theoretical guide for the engineering application and embody its value. (1) The simulation of batch constant volume diafiltration process was used to determine the effects of the volume concentration factor (1.25, 2, 3) or volumes of adding water (0.2V0 , 0.5V0 , 2/3V0)and rejection of NaCl component on desalting and purifying of dye solution. The simulative results suggested that to obtain the same concentration of NaCl and purity of dye in the retentate, the less volume concentration factor and the higher rejection of salt, the more volume of required adding water. With the increasing of repeated concentration-dilution operation times, the efficiency of removal of salt was descreased. (2) The simulation of combined process of three phases was used todetermine the effects of the volume concentration factor in preconcentration phase (1.25, 2, 3) and rejection of NaCl component on the process parameters, and the process time was optimized. For the minimum process time, the optimum value of dye concentration at diafiltration was 11.8%. Thus, to obtain the same concentration of NaCl and dye component in the retentate, the optimum appears to be a combined process where the feed was first preconcentrated about 2 times by nanofiltration, followed by continuous constant volume diafiltration and postconcentration. The required volume of adding water depended on volume concentration factor in preconcentration phase, salt rejection and desired salt concentration in the retentate. (3) The simulation of continuous variable volume diafiltration process was to discuss the effect of final concentration of dye and salt in the retentate and salt rejection on the process performance. The simulative results showed that if the same salt concentration are obtained in the retentate, the higher the dye concentration, the longer the process time and the less volume of required adding water; and if the same dye concentration are obtained in the retentate, the lower the salt concentration, the longer the process time and the more required volume of adding water.When the same dye and salt concentration (Cdye/Cdye,0 = 3, Csalt,0/Csalt = 81) are achieved, these three process were compared. The total process time and required volume of adding water in the batch constant volume diafiltration process were identical with the continuous variable volume diafiltration process, which show that their average permeation fluxes are also same. However, compared with these two processes, the combined process of three phases required the minimum process time when the feed was preconcentrated about 2 times. In the combined process, the required volu...