(337z) Advanced Separation Processes; From Development of Membranes of Vanadium Redox Flow Batteries to Elucidate the Properties of Oil-Water Emulsions

Part 1:

Sulfonated Lignin-based Ionomer Bio-composites with Improved Proton Selectivity for Redox Flow Batteries

The current benchmark membrane for vanadium redox flow batteries (VRFBs), Nafion, accounts for up to 40 % of the cost of the battery. As such, the development of better performing, more cost-effective ionomer membranes have been an ongoing area of interest. One such alternative, sulfonated poly(ether ether ketone) (SPEEK), has garnered attention in recent years due to its lower cost and similar performance properties to that of Nafion. However, like Nafion, SPEEK suffers from poor ion selectivity, leading to diminished battery performance. In this study, we address the issue of poor ion selectivity by developing SPEEK composite membranes containing fractionated and renewably processed lignin. Prior to membrane fabrication, the lignin was functionalized with sulfonic acid groups to both help improve dispersion of the lignin in the SPEEK matrix, as well as provide sites for ion-hopping. The lignin was first phenolated before sulfonating to help improve the reactivity of the lignin, resulting in a higher degree of sulfonation (DS). Specifically, the impact of the sulfonated lignin on the ion and water transport properties of these ionomer bio-composites was investigated. In the case of SPEEK, two values of DS were selected (70% and 80%), while the lignin loading was varied from 0 mass % to 25 mass %. The DS of both the SPEEK and lignin were measured by titration and 1H nuclear magnetic resonance (NMR) spectroscopy. The hydroxyl content of phenolated lignin and clean lignin were measured using 31P NMR. The phenolic hydroxyl content of the phenolated lignin was found to increase by approximately 40% when compared to the unreacted lignin. After fabrication, the permeability of vanadium ions – specifically the vanadyl ion (VO2+) through the membranes were measured using ultraviolet- visible spectroscopy, where both the DS and lignin concentration were seen to have a direct impact on VO2+ permeability. In addition to ion permeability, the proton conductivity of the ionomer bio-composites were measured, where lignin-containing samples were seen to exhibit improved proton selectivity when compared to their unmodified counterparts. Finally, the dispersion state of the sulfonated lignin in the ionomer was directly imaged via transmission electron microscopy. In general, enhanced proton selectivity was observed in sulfonated lignin-containing ionomers when compared to neat SPEEK and Nafion. In addition, the cost of these membranes is significantly lower, by over an order of magnitude, than the current benchmark material for redox flow batteries. The results obtained help elucidate the relationship between ionomer processing and final performance properties, providing a pathway for the development of the next generation of ionomer membranes for redox flow batteries.

Part 2:

Effect of processing conditions and composition on interfacial tension, density and viscosity of oil distributed in O/W emulsion

The reason for studying the properties of oil droplets which are distributed in O/W emulsion is to predict the behavior of these droplets as a function of composition and processing conditions like shear, temperature, and pressure to name a few. Effect of shear stress on the breakage of the droplet is an important phenomena to understand. For example, under a given shear stress, there exists an equilibrium between the rate of droplet-droplet coalescence and droplet breakage, if the droplet breaks into tiny droplets, then it might become stable inside the system and the separation of oil from the water will become difficult. Hence, the study of the effect of physical properties on reaction rate is important. In this study, experimental analyses of physical properties of soybean oil (SBO) dispersed in O/W emulsion are found by varying the temperatures and adding different concentrations of various impurities (phospholipids, free fatty acids, diacylglycerols, and monoacylglycerols to name a few). The physical properties of the pure SBO was found out as a baseline. Pure SBO was produced by passing the refined bleached and deodorized (RBD) SBO through a packed bed column packed with Florisil, a mixture of synthetic magnesium silicate which is a highly selective adsorbent. The interfacial tension (IFT) of the pure SBO in water was found using a "pendant droplet method" of tensiometer which is mounted on a goniometer with varying the temperature. The major factor while conducting this experiment was to make sure that everything is clean because even a small amount of impurity would affect the IFT. The IFT at ambient temperature was found to be around 33 dyne/cm whereas increasing the temperature led to a decrease in the IFT to around 26 dyne/cm. In the ambient temperature, the IFT was found to be a constant value with time whereas, for higher temperatures, the IFT had a decreasing trend with time. Similar experiments were done after the addition of various impurities of different concentrations. Adding impurities made the IFT to decrease and as the concentration of the impurities were increased, the IFT decreased further. The density was also experimentally determined by using a pycnometer which was also used in an error correction for the IFT as change in density will also affect the IFT. Finally the viscosity of SBO was determined using a viscometer in different temperatures and different concentrations of the impurities. These data obtained are essential for understanding the behavior of oil droplets in water under the shear stress in a reactor. The results obtained will eventually help in the innovation of technology in the separation of SBO from water.