University of Twente Student Theses


In-situ characterization of thin layer polysulfone in water-toluene mixtures

Timmerhuis, N. (2015) In-situ characterization of thin layer polysulfone in water-toluene mixtures.

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Abstract:Thin layer membranes are a kind of Solvent resistant nanofiltration (SRNF) membranes, which can be used to separate waste from waters on amolecular level. Thin filmcompositemembranes consist of a polymeric top-layer on top of a porous support. Although SRNF membranes seem a promising technique, many challenges need to be overcome before the technique can be implemented on the large scale. One of the main challenges is the loss in stability. In many commercial membranes polysulfone (PSf) is used as support layer. However, this polymer dissolves in a liquid water/toluene mixture. The reason behind this is unclear. This report researches the behavior of PSf in water/toluene mixtures at different temperatures and toluene activities. The results show that PSf dissolves at a temperature range of 18-30°C in a liquid water/toluene mixture. The PSf dissolves faster with increasing temperature. PSf reached a 250% swelling before dissolution in these measurements. The thin layer consists of 50% solvent and 50% polymer when a 100% swelling is reached. The normal dissolution mechanism is the most likely to occur during these measurements. Thismechanism consists of two steps: solvent diffusion into the polymer and polymer chain disentangle into the solvent. Secondly, the swelling behavior of the polysulfone is studied in toluene vapor. The swelling behavior is different in vapors compared to liquids. In toluene vapor the swelling degree is lower and other steps can be distinguished in the dynamics over time. According to Flory and Huggins, the activity decreases when the volume fraction of solvent in the polymer decreases. The activity of the toluene in the system most likely to be below 1 in the toluene vapor systems. At last, toluene vapor is bubbled through water in the cell. Here, the activity seems lower with a lower toluene vapor flow at 18 °C. The toluene vapor refluxes in the top of the saturaters, which means that the toluene in the vapor flow is lower at 30 °C compared to 18 °C. This system has the opportunity to provide the information which is needed to distinguish the relation between the activity and toluene volume fractions, but improvements are needed to achieve this goal.
Item Type:Essay (Bachelor)
Faculty:TNW: Science and Technology
Subject:35 chemistry, 58 process technology
Programme:Chemical Engineering BSc (56960)
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