碩士 / 國立臺灣大學 / 化學工程學研究所 / 106 / As an alternative for high energy-intensive reverse osmosis (RO) in seawater desalination, the novel approach known as forward osmosis (FO) has recently attracted much attention. Unlike RO which uses the high pressure difference as the driving force, FO utilizes the chemical potential gradient, or osmotic pressure, to drive the mass transfer. However, some studies showed that FO is actually not an energy-efficient approach, which may require more thermal energy and lead to higher cost in total. A new desalination scheme using lower critical solution temperature (LCST) ionic liquids as the draw solutes is presented. Despite higher energy consumption, the approach could replace the high cost electricity with low cost waste heat in plants or solar heat in the overall process. The osmotic pressure, required work, LCST and the miscibility gap are the most significant factors for the evaluation of the feasibility of ionic liquid draw solutes. In this work, we use COSMO-SAC 2010 + Pitzer-Debye–Hückel (PDH) model to perform a priori and efficient prediction of phase behavior. In the model the molecular structures are the only input in the model. We show that COSMO-SAC is able to differentiate the LCST and upper critical solution temperature (UCST) mixtures. Though our model provides poor quantitative prediction of LCSTs and the miscibility gaps (ARD%-LCST = 40.00%; ARD%-LLE 35.22%), the model appears to have great performance in qualitative agreement with experimental data. The thermodynamic properties including osmotic pressure, enthalpy of mixing, and the theoretical minimum work for the process are also evaluated. We analyze the temperature effect near the spinodal boundaries in order to have a molecular insight into LCST-positive phase behavior. Our results show that it is the preference of high entropy at high temperature that dominate in LCST-negative phase separations, while competition between molecular interactions, especially the hydrogen bonding interactions, play a more important role in the temperature dependence in the LCST-type phase separation. It is also demonstrated by our model that though with much higher required thermal energy, hybrid FO + RO process consume less electrical duty theoretically, allowing an energy-efficient use of waste heat. We propose a quick and feasible procedure for the screening ionic liquid draw solutes for FO processes.
| Identifer | oai:union.ndltd.org:TW/106NTU05063039 |
| Date | January 2018 |
| Creators | Ya-Ruei Tsai, 蔡亞叡 |
| Contributors | Shiang-Tai Lin, 林祥泰 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 142 |
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