Villanueva López, Liliana R

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    Brackish water desalination with a novel polymer nanocomposite membrane
    (2019-04-05) Villanueva López, Liliana R; Suleiman Rosado, David; College of Engineering; Saliceti Piazza, Lorenzo; Tarafa Vélez, Pedro; Department of Chemical Engineering; Negrón Ríos, Gloriselle
    The rapid growth of the global population, the industrialization and environmental problems caused by global warming have made it necessary to implement advanced water purification techniques capable of fulfilling the increasing demand for drinking water. Salty water is the most abundant on earth which represents approximately 97% of the water available. However, it is the less recovered source of water, because of the high costs of power consumption required by the thermal desalination processes. The ion exchange technologies by membranes have acquired special attention as an economical alternative, and it is still the most commonly used method for desalination, due to their high efficiency and environmentally benign nature. In this research, sulfonated poly(styrene-isobutylene-styrene) (SIBS) was used to validate its performance as a desalination media for brackish water by ion exchange mechanism. The effect of counter-ion substitution in the ionic domains (e.g., Ba+2 and Mg+2) was used to change the nanostructure and the resulting transport properties of water and salt, as it was reflected in the percentages removal of sodium obtained. Materials characterization techniques were employed to evaluate the chemical structure and physical properties of the polymer membranes such as infrared spectroscopy, elemental analysis, water absorption, and ion exchange capacity depending on the levels of sulfonation and substitution with Ba+2 and Mg+2 counter-ions. Sulfonation levels calculated by elemental analysis results were 50.3%, 68.7%, and 88%. Infrared spectroscopy technique confirmed the presence of sulfonic groups and interactions with Ba+2 and Mg+2 counter-ions in the SIBS polymer structure. Overall, the results show that high values of ion exchange capacity and percentages of water absorption were directly related to the high degree of sulfonation in the SIBS polymer. Maximum values obtained from ion exchange capacity and water absorption were 1.75 mequiv/g and 581.3%. The incorporation of metallic counter-ions such as Ba+2 and Mg+2 significantly reduced these two properties thanks to the ionic cross-linking formed by them in the structure of the sulfonated SIBS polymer.A factorial experimental design and analysis of variance were performed to evaluate the effect of fixed factors such as sulfonation levels, counter-ion substitution and sodium chloride concentration on the percentage of sodium removal. Results of ANOVA showed that the significant factors evaluated individually on the percentage of sodium removal were the sulfonation level and the counter-ion substitution, both with P values of 0.000 indicating high significance. Significant interactions were obtained between factors such as sulfonation level/counter-ion substitution and sodium chloride concentration/counter-ion substitution with P values of 0.022 and 0.001, respectively. Finally, the performance in desalination of sulfonated SIBS membranes and subsequently substituted with Ba+2 and Mg+2 counter-ions was evaluated considering the percentages of sodium removal obtained by exposing the membranes for 24 hours to sodium chloride solutions with concentrations between 5 and 30 g/L. The sodium removal percentages of sulfonated membranes substituted with both counter-ions were over 99%, regardless of the concentration of sodium chloride. Percentages of sodium removal obtained with sulfonated membranes exposed to 5 g/L of sodium chloride concentration decreased when the sulfonation level increased, However, increasing the concentration of sodium chloride to 30 g/L improved the percentage of sodium removal for sulfonation levels of 68.7% and 88.0%.