The measured Ej and Ep values using the above plots for the pervaporation Cy5.5 NHS ester of seawater desalination over the membranes are given in Table 3. The Ej and Ep values were found to be in the range of 23.07 to 25.80 kJ/mol and − 21.01 to − 23.24 kJ/mol, respectively. The calculated Ep values were − 17.42 to − 20.15 kJ/mol, which were different from the experimental values by about 10–20%. The Ej values were found to be slightly lower for the separation using the aqueous feed of higher NaCl concentration. The decrease of the Ej value with an increase in salt concentration had been observed in many other pervaporation separation systems ,  and . The Ej value for the separation was expected to decrease over the thicker membrane because of lower flux which was in agreement with a ~ 9% decrease in the Ej value when the membrane thickness was increased. The pervaporation experiments were also conducted on the membrane with variation in cross-linking density. Fig. 13 shows the flux vs. temperature plots of these membranes from the separation experiments for the aqueous feed of 30,000–50,000 ppm NaCl concentration. The decrease in flux was observed for the membrane prepared with an increase in the amount of the cross-linker (maleic acid). The flux for the membranes was varied from about 1.8 L/m2/h to 7.4 L/m2/h for the experiments at 298 K–344 K, respectively for the aqueous feed of 30,000 ppm NaCl concentration. At higher NaCl concentration of 40,000–50,000 ppm of the feed, the membranes exhibited a slightly lower flux which can be explained according to the phenomenon of vapor pressure reduction for saline water as discussed above.