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Permeability and Selectivity Limits of Polymeric and Biomimetic Desalination Membranes.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Permeability and Selectivity Limits of Polymeric and Biomimetic Desalination Membranes.
Author:	Werber, Jay R.
Published:	Ann Arbor : ProQuest Dissertations & Theses, 2018
Description:	242 p.
Notes:	Source: Dissertations Abstracts International, Volume: 80-09, Section: B.
Notes:	Publisher info.: Dissertation/Thesis.
Notes:	Advisor: Elimelech, Menachem.
Contained By:	Dissertations Abstracts International80-09B.
Subject:	Chemical engineering.
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=13850218
ISBN:	9780438973503

Permeability and Selectivity Limits of Polymeric and Biomimetic Desalination Membranes.
Werber, Jay R.

Permeability and Selectivity Limits of Polymeric and Biomimetic Desalination Membranes. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 242 p.

Source: Dissertations Abstracts International, Volume: 80-09, Section: B.

Thesis (Ph.D.)--Yale University, 2018.

This item must not be added to any third party search indexes.

Water scarcity is one of the foremost challenges that we will face this century. While optimized water management will be important, technologies that enable the expansion of potable water supplies from non-potable sources are equally essential. One such technology is reverse osmosis (RO), which is already the premier desalination technology for the purification of seawater and brackish water. RO is also the central step in treatment processes that enable the potable reuse of municipal wastewater. Due to population growth and climate change, desalination and wastewater reuse will be increasingly important sources of potable water supplies in regions around the world. The critical component in RO is the membrane itself. This dissertation focuses on the main task of RO membranes, namely their ability to separate water from other molecular species. The fundamental membrane properties that define this ability are the water permeability and the water/solute selectivity, which is the ratio between the water and solute penneabilities. The polyamide thin-film composite (TFC) membranes that are the industry standard for RO follow a permeability—selectivity trade-off, meaning that increases in water permeability are typically paired with decreases in selectivity. To help guide membrane research, this dissertation considers whether improved water permeability or improved selectivity would be more practically important. Increased selectivity is found to yield great benefits for water quality and process efficiency, through the elimination of redundant treatment processes, whereas increased water permeability has relatively little impact. Increased selectivity should thus be the goal for novel RO membranes. Several possible materials that could achieve this goal are highlighted. Through optimized fabrication methods, the performance of TFC membranes has improved incrementally over the last two decades. In this dissertation, a novel modification method is proposed wherein newly synthesized membranes are immersed into solutions of alcohols, amines, or ammonia to quench unreacted acyl chloride groups in the nascent polyamide film. Separation performance follows a previously established permeability—selectivity trade-off relationship, illustrating the difficulty in breaking the trade-off with conventional materials. The quenching method additionally decreases the density of carboxyl groups, which confer a negative charge to the membrane surface that affects salt rejection. organic fouling, and inorganic scaling. In order to quantify these carboxyl groups, a new method is developed in which silver (Ag+) ions are bound to ionized carboxyl groups, eluted in nitric acid. and measured using inductively coupled plasma mass spectrometry. The method is rigorously verified and used to measure carboxyl densities and ionization behavior of six commercial RO membranes. The ease-of-use, accuracy, and reliability of the new method should enable widespread usage in research on TFC membranes. The trade-off behavior incentivizes novel RO materials, of which biomimetic desalination membranes are some of the most promising. Such membranes incorporate aquaporin — a perfectly-selective biological water channel — or synthetic water channels like carbon nanotubes. In this dissertation, the performance of biomimetic membranes is projected through systematic permeability measurements of lipid and block copolymer bilayers, which form the matrix around the water channels in a biomimetic membrane. Water/salt selectivity of a defect-free biomimetic membrane is projected to be 7-8 orders of magnitude greater than TFC membranes, providing near-perfect salt rejection. Additionally, boron rejection is projected to reach up to 99.9%, depending on the bilayer type used. The superlative rejections projected for salt and boron would be highly beneficial in seawater RO. However, permeability of neutral solutes through amphiphilic bilayers is found to correlate strongly with solute hydrophobicity. As a result, many hydrophobic organic pollutants present in wastewater would rapidly permeate a defect-free biomimetic selective layer, limiting its potential for wastewater reuse. As a possible mitigation strategy, performance is modeled wherein size-selective TFC membranes are used as support layers for aquaporin-based biomimetic selective layers. This strategy is projected to not only largely eliminate permeation of hydrophobic pollutants, but also decrease the impact of defects in the biomimetic selective layer. Even with reasonable levels of defects, salt rejections well above the highest rejections achieved by TFC membranes should be attainable. Overall, this dissertation assesses real-world processes to determine that increased selectivity is important for RO membranes, demonstrates through fundamental permeability measurements and performance modeling that biomimetic membranes have tremendous potential to reach this target compared with conventional TFC membranes, and provides a reasonable fabrication strategy to achieve this potential. The findings in this dissertation could help lead to next-generation, ultra-selective membranes for use in desalination and water treatment.

ISBN: 9780438973503Subjects--Topical Terms:

206267
Chemical engineering.

Permeability and Selectivity Limits of Polymeric and Biomimetic Desalination Membranes.
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520 $a Water scarcity is one of the foremost challenges that we will face this century. While optimized water management will be important, technologies that enable the expansion of potable water supplies from non-potable sources are equally essential. One such technology is reverse osmosis (RO), which is already the premier desalination technology for the purification of seawater and brackish water. RO is also the central step in treatment processes that enable the potable reuse of municipal wastewater. Due to population growth and climate change, desalination and wastewater reuse will be increasingly important sources of potable water supplies in regions around the world. The critical component in RO is the membrane itself. This dissertation focuses on the main task of RO membranes, namely their ability to separate water from other molecular species. The fundamental membrane properties that define this ability are the water permeability and the water/solute selectivity, which is the ratio between the water and solute penneabilities. The polyamide thin-film composite (TFC) membranes that are the industry standard for RO follow a permeability—selectivity trade-off, meaning that increases in water permeability are typically paired with decreases in selectivity. To help guide membrane research, this dissertation considers whether improved water permeability or improved selectivity would be more practically important. Increased selectivity is found to yield great benefits for water quality and process efficiency, through the elimination of redundant treatment processes, whereas increased water permeability has relatively little impact. Increased selectivity should thus be the goal for novel RO membranes. Several possible materials that could achieve this goal are highlighted. Through optimized fabrication methods, the performance of TFC membranes has improved incrementally over the last two decades. In this dissertation, a novel modification method is proposed wherein newly synthesized membranes are immersed into solutions of alcohols, amines, or ammonia to quench unreacted acyl chloride groups in the nascent polyamide film. Separation performance follows a previously established permeability—selectivity trade-off relationship, illustrating the difficulty in breaking the trade-off with conventional materials. The quenching method additionally decreases the density of carboxyl groups, which confer a negative charge to the membrane surface that affects salt rejection. organic fouling, and inorganic scaling. In order to quantify these carboxyl groups, a new method is developed in which silver (Ag+) ions are bound to ionized carboxyl groups, eluted in nitric acid. and measured using inductively coupled plasma mass spectrometry. The method is rigorously verified and used to measure carboxyl densities and ionization behavior of six commercial RO membranes. The ease-of-use, accuracy, and reliability of the new method should enable widespread usage in research on TFC membranes. The trade-off behavior incentivizes novel RO materials, of which biomimetic desalination membranes are some of the most promising. Such membranes incorporate aquaporin — a perfectly-selective biological water channel — or synthetic water channels like carbon nanotubes. In this dissertation, the performance of biomimetic membranes is projected through systematic permeability measurements of lipid and block copolymer bilayers, which form the matrix around the water channels in a biomimetic membrane. Water/salt selectivity of a defect-free biomimetic membrane is projected to be 7-8 orders of magnitude greater than TFC membranes, providing near-perfect salt rejection. Additionally, boron rejection is projected to reach up to 99.9%, depending on the bilayer type used. The superlative rejections projected for salt and boron would be highly beneficial in seawater RO. However, permeability of neutral solutes through amphiphilic bilayers is found to correlate strongly with solute hydrophobicity. As a result, many hydrophobic organic pollutants present in wastewater would rapidly permeate a defect-free biomimetic selective layer, limiting its potential for wastewater reuse. As a possible mitigation strategy, performance is modeled wherein size-selective TFC membranes are used as support layers for aquaporin-based biomimetic selective layers. This strategy is projected to not only largely eliminate permeation of hydrophobic pollutants, but also decrease the impact of defects in the biomimetic selective layer. Even with reasonable levels of defects, salt rejections well above the highest rejections achieved by TFC membranes should be attainable. Overall, this dissertation assesses real-world processes to determine that increased selectivity is important for RO membranes, demonstrates through fundamental permeability measurements and performance modeling that biomimetic membranes have tremendous potential to reach this target compared with conventional TFC membranes, and provides a reasonable fabrication strategy to achieve this potential. The findings in this dissertation could help lead to next-generation, ultra-selective membranes for use in desalination and water treatment.
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