Ionically cross-linked sodium alginate and polyamidoamine dendrimers for ethanol/water separation through pervaporation

The pervaporation process is an energy-conservative and environmentally friendly method to separate organic solvent from water. It efficiently separates close boiling point and azeotrope mixtures unlike the distillation process. Herein, primary amine-terminated polyamidoamine (PAMAM) dendrimers are proposed to interact with the highly hydrophilic and negatively charged sodium alginate (SA) polymer chains for the preparation of pervaporation composite membranes. Different generations of PAMAM dendrimer (G0, G1, and G2) have different number of terminal primary groups (P4, P8, and P16). That is, a higher generation number means there are more terminal amine groups available for interaction. The addition of PAMAM contributed to the stronger hydrogen bonding of SA and inhibited the swelling of pristine SA/PVDF composite membranes. Interestingly, the free volume characteristics of the SA/PVDF membranes with PAMAM altered the number and size of the free volume spaces as confirmed by positron annihilation spectroscopy (PAS). The more terminal primary amine groups of PAMAM resulted to a higher ionic interaction with the sodium alginate polymer chains producing a denser structure. The denser structure of SA-P8/PVDF and SA-P16/PVDF resulted to a lower flux than with SA-P4/ PVDF. The SA-P4/PVSDF at 40 ppm loading achieved the highest separation performance for the dehydration of 90/10 wt% ethanol/water mixture at 25 degrees C with a permeation flux of 1,039 g m-2h- 1 and a water concentration in permeate of 99.41 wt%. Furthermore, the SA-P4/PVDF membrane can withstand high water content in feed up to 50 wt% and high operating temperature of 70 degrees C showing enhanced stability of the selective layer due to the interactions between SA and PAMAM dendrimer.

Automated summary

The modification with PAMAM can improve the performance of SA/PVDF composite membranes, enhance the interaction with SA, reduce membrane swelling, and increase separation efficiency.