Water purification by membranes: The role of polymer science

Abstract

Two of the greatest challenges facing the 21st century involve providing sustainable supplies of clean water and energy, two highly interrelated resources, at affordable costs. Membrane technology is expected to continue to dominate the water purification technologies owing to its energy efficiency. However, there is a need for improved membranes that have higher flux, are more selective, are less prone to various types of fouling, and are more resistant to the chemical environment, especially chlorine, of these processes. This article summarizes the nature of the global water problem and reviews the state of the art of membrane technology. Existing deficiencies of current membranes and the opportunities to resolve them with innovative polymer chemistry and physics are identified. Extensive background is provided to help the reader understand the fundamental issues involved. Ph.D. students and two postdoctoral fellows performing fundamental research in gas and liquid separations using polymer membranes and barrier packaging. His research group focuses on include structure/property correlation development for desalination and vapor separation membrane materials, new materials for hydrogen separation and natural gas purification, nanocomposite membranes, reactive barrier packaging materials, and new materials for improving fouling resistance and permeation performance in liquid separation membranes. His research is described in more than 250 publications, and he has coedited four books on these topics. He has won a number of national awards for his research contributions, including the ACS

Ionic Resistance and Permselectivity Tradeoffs in Anion Exchange Membranes

“…20−27 Water uptake, or more precisely water volume fraction, is a key property that affects ion transport in water-swollen polymers. 5,7,28,29 In addition to polymer backbone structure, molecular weight, and cross-link density, water volume fraction can be modulated by adjusting the degree of fixed charge functionalization, i.e., the gravimetric ion exchange capacity (IEC) of the polymer in units of mequiv/g (dry polymer), and increasing the IEC generally increases the water uptake of a polymer. 7,28 While IEC is a useful metric for characterizing polymer structure, it does not reflect the ion concentration of the water-swollen polymer.…”

“…29 Fixed charge concentration, C A , is more useful in this regard because C A is determined by both the IEC and water uptake of the polymer. 5,29,30 One of the challenges in comparing structure−property studies of membranes in the literature is inconsistency in the parameters (particularly those relating to the fixed charge group content of the polymer) used to characterize the polymers. We adopt the definition of fixed charge concentration, in units of mequiv cm −3 (swollen polymer), recommended by Helfferich for treatment of transport data, which is equivalent to molar concentrations in mol L −1 (swollen polymer).…”

Effect of pore penetration on transport through supported membranes studied by electron microscopy and pervaporation

“…Supported membranes are an increasingly important part of chemical separations [1][2][3][4]. They comprise a microporous support underneath a thin, selective, dense membrane.…”

“…This supported membrane configuration is inevitable in practical applications because flux through the membrane is inversely proportional to thickness; very thin membranes do not have the necessary mechanical properties and thus must be supported. Supported membranes are currently used in numerous applications including gas separation [5,6], water purification [3,7], and pervaporation [8].…”

Sorption dynamics of Direct Orange 26 dye onto a corncob plant sorbent

“…Technology options in water treatment include oxidising, ion exchange, adsorption, extraction, coagulation, sedimentation, ultrafiltration, neutralisation etc. [1].…”