Maximizing the Degree of Sulfonation of Polysulfone Supports in TFC Membranes for Osmotically Driven Processes

Abstract

In this work, thin‐film composite (TFC) polyamide membranes are prepared by introducing the highest amount of sulfonated polysulfone into the polysulfone‐based support layer with the goal to improve membrane performance in osmotically driven processes. Sulfonated polymers are synthesized via a one‐step reaction and used in suitable blends with pristine polysulfone to cast porous layers by phase inversion process. The sulfonated support substrates exhibit enhanced wettability over the traditional polysulfone layers as confirmed by a two‐fold decrease in water contact angle. Using a 0.35 mm NaCl draw solution, the best sulfonated TFC membranes achieve up to 16 and 21 L m−2 h−1 under forward osmosis (FO) and pressure‐retarded osmosis (PRO) configurations, respectively. However, no significant alterations in the support layer morphology can be detected. It is speculated, therefore, that wettability is the key factor for the observed improved osmotic flux, with a trade‐off between water and reverse salt fluxes.

Polysulfone with Different Degrees of Sulfonation: Simple Method with Acetyl Sulfate

“…The PSU polymer is well known for its thermal stability, presented only in one step of mass loss around 500°C that corresponds to the decomposition of the main chain, confirmed by literature values [29.32]. Different of PSU, its sulfonated derivates, PSU-SA and PSU-SB, show TGA/DSC thermograms presenting three separate steps, the first stage corresponding to the loss of hydration water and solvents; the second stage corresponding to the thermal desulfonation and the third indicates the degradation of the main chain [29,31,32]. In Table 1, it's possible to verify the data of weight loss on the three highlighted bands of the samples represented in Figure 7; and the values of DSTGA and IECTGA.…”

“…Over time, lots of reactants have been employed in PSU sulfonation, being able to highlight the sulfur trioxide-triethyl phosphate complex (SO3/TEP) [21][22][23], fuming and concentrated sulfuric acid [24], trimethylsilyl chlorosulfonate (TMSClS) [25][26][27][28][29][30][31][32] and chlorosulfonic acid (HSO3Cl) [14,19,20,[29][30][31][33][34][35][36]. These reaction conditions need more careful handling compared to the method proposed in this work.…”