Sulfate removal from chlor-alkali brine using nanofiltration: Parameters investigation and optimization via Taguchi design method

摘要

This work was aimed to optimize and investigate the effects of pH, temperature, pressure, feed flow rate, and concentrations of NaCl and Na2SO4 on retention of sulfate (SO42-) and chloride (Cl-) as well as permeate flow rate in almost saturated chlor-alkali brine nanofiltration (NF). For this purposes, a NF commercial membrane named NF-3 (Sepro) was used. The main goals of the current separation process were maximum and minimum retention of SO42- and Cl-, respectively, along with higher possible permeate flow rate. Based on Taguchi design method, a number of 16 trials with different levels of variations were considered as follows: temperature (27, 45 degrees C), pressure (5, 9 bar), feed flow rate (180, 360 mL/min), NaCl concentration (25, 50, 100, 225 g/L), and Na2SO4 concentration (1, 7, 15, 25 g/L). Using mean of means and S/N ratio diagrams, the impact of each factor on NF process were studied. Analysis of variance (ANOVA) was also performed to determine the significance of each factor. The obtained results showed that SO42- and Cl-retentions were ranging 86.3%-93.4% and 26.7%-45.6%, respectively. Moreover, the permeate flow rate was obtained in the range from 0.24 to 2.44 mL/min for the flat sheet membrane with specific area of 112 cm(2). Finally, the effect of pH on separation performance and also chlorate (ClO3-) removal were investigated separately.