Effect of the structural changes in thermo-responsive ionic liquids-based draw solutes for forward osmosis

다국어 초록 (Multilingual Abstract)

The applicability of the ionic liquids (ILs) as the draw solutes in a forward osmosis (FO) system was investigated through a study on the effect of the structural change of the ion on the FO performance. First, we synthesized the ILs, tributylalkylphosphonium styrenesulfonate ([P444#][SS], # = 4, 6, and 8) and tetrabutylammonium styrenesulfonate ([N4444][SS]), where # is the number of carbons of the alkyl groups in tributylalkylphosphonium. ILs in an aqueous solution exhibited a lower critical solution temperature (LCST)-type phase transition, which enables the recovery of the draw solute or water from the diluted draw solution. LCSTs of 50 wt% aqueous [P4444][SS] and [N4444][SS] solutions were approximately 33 and 66 ºC, respectively. The water and reverse solute fluxes of the [P4444][SS] aqueous solution, which is more efficient in terms of solute recovery, were approximately 8.51 LMH and 1.66 gMH at 50 wt%, respectively, in the active layer facing the draw solution (AL-DS) mode. Second, we synthesized the ILs composed of tetrabutylphosphonium cation ([P4444] +) and benzenesulfonate anion ([BS]−), para-position alkyl-substituted benzenesulfonate anions (p-methylbenzenesulfonate ([MBS]−) and p- ethylbenzenesulfonate ([EBS−])), and methanesulfonate anion ([MS]−). The analysis of the thermo-responsive properties suggested that the [P4444][MBS] and [P4444][EBS] ILs have LCSTs. At 20 wt% of an aqueous solution, the LCSTs of [P4444][MBS] and [P4444][EBS] were approximately 36 and 25 °C, respectively. The water flux and reverse solute flux of the [P4444][MBS] aqueous solution with higher osmolality than [P4444][EBS] were 7.36 LMH and 5.98 gMH in the AL-DS mode and active layer facing the feed solution (AL-FS) mode at osmotic pressure of 25 atm, respectively. Third, we synthesized the ILs, tributylalkylphosphonium 3-sulfopropyl methacrylate ([P444#][C3S], # = 4, 6, and 8), where # is the number of carbons of the alkyl groups in tributylalkylphosphonium. The LCSTs of 33, 26, 23, and 18 °C were obtained from 2.5, 5.0, 7.5, and 10.0 wt% aqueous solutions of [P4446][C3S]. When deionized water, 2000 ppm NaCl solution, and 10.0 wt% orange juice aqueous solution were used as feed solution, the water fluxes of the aqueous [P4446][C3S] solutions were approximately 4.49, 3.87, and 1.55 LMH, respectively, in the AL-DS mode at 7.5 wt% of draw solution. Finally, we synthesized the tributyl-4-vinylbenzylphosphonium alkanesulfonate ([TVBP][CnS], n = 4, 5, 6), where n is the number of carbons of the alkane in alkanesulfonate. [TVBP][C5S] and [TVBP][C6S] exhibited LCSTs from 6 to 34 °C at different concentrations, enabling their recovery. When using distilled water, 2000 ppm NaCl, and 20 wt% orange juice aqueous solutions as the feed solution, the water flux of the 8 wt% [TVBP][C5S] solution was approximately 11.26, 8.01, and 6.76 LMH, respectively, in the mode of the AL-DS. The effect of changing the hydrophobic moiety of ILs on their osmolality and LCST behavior was systematically observed. These investigations provide a guide for the development of draw solutes in improving the efficiency of the FO system.

목차 (Table of Contents)

• Ⅰ. Introduction 1
• References 6
• Ⅱ. Part 1 – Evaluation of styrenesulfonate-based ionic liquids as draw solute for forward osmosis 12
• 1. Experimental 12
• 1.1 Materials 12
• 1.2 Synthesis of styrenesulfonate-based ionic liquids with tetrabutylammonium and tributylalkylphosphonium 12
• 1.3 Forward osmosis performance 14
• 1.4 Instruments 16
• 2. Results and discussion 16
• 2.1 Synthesis and structure analysis of styrenesulfonate-based ionic liquids with tributylalkylphosphonium and tetrabutylammonium 16
• 2.2 Conductivity 21
• 2.3 Osmotic pressure 24
• 2.4 Thermo-responsive property 26
• 2.5 Forward osmosis performance 29
• 3. Conclusions 32
• References 33
• Ⅲ. Part 2 - Evaluation of benzenesulfonate derivatives-based ionic liquids as draw solute for forward osmosis 36
• 1. Experimental 36
• 1.1 Materials 36
• 1.2 Synthesis of benzenesulfonate derivatives-based ionic liquids with tetrabutylphosphonium 36
• 1.3 Forward osmosis performance 37
• 1.4 Instruments 38
• 2. Results and discussion 39
• 2.1 Synthesis and structure analysis of benzenesulfonate derivatives-based ionic liquids with tetrabutylphosphonium 39
• 2.2 Conductivity 44
• 2.3 Osmotic pressure 46
• 2.4 Thermo-responsive property 49
• 2.5 Contact angle 52
• 2.6 Forward osmosis performance 54
• 2.7 Recyclability test 56
• 3. Conclusions 58
• References 59
• Ⅳ. Part 3 - Evaluation of 3-sulfopropylmethacrylate derivatives-based ionic liquids as draw solute for forward osmosis 63
• 1. Experimental 63
• 1.1 Materials 63
• 1.2 Synthesis of 3-sulfopropylmethacrylate-based ionic liquids with tributylalkylphosphonium 63
• 1.3 Forward osmosis performance 64
• 1.4 Instruments 65
• 2. Results and discussion 66
• 2.1 Synthesis and structure analysis of 3-sulfopropylmethacrylate-based ionic liquids with tributylalkylphosphonium 66
• 2.2 Viscosity 71
• 2.3 Conductivity 73
• 2.4 Osmotic pressure 75
• 2.5 Thermo-responsive property 77
• 2.6 Forward osmosis performance 80
• 3. Conclusions 83
• References 84
• Ⅳ. Part 4 - Evaluation of tributyl-4-vinylbenzylphosphonium-based ionic liquids as draw solute for forward osmosis 88
• 1. Experimental 88
• 1.1 Materials 88
• 1.2 Synthesis of tributyl-4-vinylbenzylphosphonium-based ionic liquids with alkanesulfonate 88
• 1.2.1 Synthesis of tributyl-4-vinylbenzylphosphonium chloride 88
• 1.2.2 Synthesis of tributyl-4-vinylbenzylphosphonium alkanesulfonate 89
• 1.3 Forward osmosis performance 90
• 1.4 Instruments 91
• 2. Results and discussion 92
• 2.1 Synthesis and structure analysis of tributyl-4-vinylbenzylphosphonium-based ionic liquids with alkanesulfonate 92
• 2.2 Thermo-responsive property 98
• 2.3 Conductivity 104
• 2.4 Viscosity 106
• 2.5 Osmotic pressure 107
• 2.6 Forward osmosis performance 109
• 2.7 Recyclability test 112
• 3. Conclusions 114
• References 115
• 국문초록 119
• 감사의 글 121