Chapter 1
Introduction
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Isabel C. Escobar*,1 and Bart Van der Bruggen2 1Chemical
and Environmental Engineering Dept., The University of Toledo, Toledo, OH, U.S.A. 2Department of Chemical Engineering, K.U.Leuven *E-mail:
[email protected] Energy, water, affordable healthcare and global warming are four major concerns globally resulting from resource depletion, record high oil prices, clean water shortages, high costs of pharmaceuticals, and changing climate conditions. Among many potential solutions, advance in membrane technology is one of the most direct, effective and feasible approaches to solve these sophisticated issues.
Membrane separation technologies are used in diverse applications ranging from production of potable water and wastewater treatment, to tissue repair, power generation, processing of food and beverages, therapeutic procedures and production of pharmaceuticals. The growth in demand can be attributed to the wide adoption by key end-use markets such as wastewater and water treatment and food and beverages industry; replacement of traditional filtration equipment; augmented focus on purity levels of process fluids; and stringent regulations with respect to wastewater and water quality (1). The combined U.S. market for membranes used in liquid and gas separations applications is estimated at approximately $1.7 billion in 2010, and is forecast to grow by 2015 to reach $2.3 billion (2). The exponential growth in ‘classical’ applications of membrane technology also catalyzes research on new applications, representing separations that were not yet possible, or that were difficult or costly to achieve. Membranologists are particularly active in finding new ways to separate what seems to be inseparable, and to push reaction and separation systems beyond their limits. Scale-up inevitably takes time, and it might take a decade or even several decades for
© 2011 American Chemical Society In Modern Applications in Membrane Science and Technology; Escobar, I., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.
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some challenges to be solved on industrial scale with membranes. Nevertheless, the creativity in imagining membrane-assisted solutions is evident today, and this creativity will translate into tomorrow’s practices, in every aspect of human life. Technology and industrial production are at the forefront, but membranes have already found their way in many less obvious areas as well. Perhaps the most important of these is human development. Drinking water production and wastewater treatment have always been core business for membranes; technological progress allows us today to speculate about low-cost membrane filtration systems applied on a massive scale. Alternatively, solutions may be found in high-tech solutions for desalination with efficiencies approaching thermodynamic limits – of course, using membranes. We clearly understand today that this in turn links to the energy challenge: energy is used for separation, but the reverse is possible as well. Few people understood this ten, twenty years ago, while it is plausible today. This is no more than a modest beginning; in ten, twenty years from now we will smile at the state-of-the-art of today and wonder how we could live without using membranes. New applications of membranes in environmental protection include CO2 separation, which was not of any particular interest in the 1990’s, but has now become a critical challenge. Interestingly, the negative motivation for CO2 capture – avoiding or at least decelerate global warming – has now turned into an opportunity. If we can develop systems with sufficient performance, waste CO2 may be used as a source of energy and of chemicals. Again, we push the limits beyond what we could once imagine. Membranes are among the most prominent toys we use to make this happen. This membrane book is aimed at presenting cutting-edge membrane research and development for water reuse and desalination, energy development including biofuels, CO2 capture, among others. The proposed two Parts are: membranes for energy, gas separation and CO2 capture; and membranes for liquid separations.
Part I: Membranes for Energy, Gas Separation, and CO2 Capture The book starts with an overview of membranes for energy, gas separations and CO2 capture (Chapter 2). While several membrane-based gas separations are now mature, during the last decade, membrane gas separations have received a new impulse mainly due to emerging environmental application, and the integration of energy production/consumption with environmental concerns. This resulted in a second wave of innovations on all levels, from membrane development to process engineering. From this overview, the first Part of the book then proceeds to describe some of the latest advancements in membranes for gas separations. One such is the use of CuPd alloys as a promising materials for future hydrogen separation membranes and membrane reactor applications because of their high hydrogen selectivity and permeability, improved sulfur poisoning resistance and mechanical properties (Chapter 3). In another study, functional nanocomposite network membranes (FNNM) consisting of polymer matrix, nanofiber network and fixed 2 In Modern Applications in Membrane Science and Technology; Escobar, I., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.
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carrier molecules, were developed as a platform mixed matrix membrane material and investigated for selective recovery of CO2 from gas streams (Chapter 6). The development of a potential new generation of polymer nanopore membranes containing 5 nm long and narrow through-pores with controlled surface chemistry is then described (Chapter 4). Another study shown here focused on tuning of free volume element distributions and sizes in polymer design (using an iptycene-based monomer, i.e., triptycene) to improve fast, selective mass transport (Chapter 8). On the field of pervaporation, hydrophilic zeolite filled membranes were used to compare fermentation broth pervaporation to ethanol/water pervaporation (Chapter 5). In another study, The performance of a series of soluble aromatic polyimides for the separation of benzene/n-heptane and toluene/n-heptane mixtures by pervaporation is reported (Chapter 7). Part I of the book ends with an overview and study on membrane fiber spinning, which is used to manufacture hollow fibers for the membrane industry. Simulations of solid fiber and hollow fiber spinning are summarized including both one-dimensional and two-dimensional approaches (Chapter 9).
Part II: Membranes for Liquid Separations Part II focuses on liquid separations and it starts with two overview chapters. The first one outlines membranes for water treatment applications (Chapter 10). Water purification is a rigorous process, which requires removal of a large number of impurities of varying size, shape and solubility depending on the nature of the water source. Membranes of varying pore size distributions and molecular weight cutoffs (MWCO) are used for this purpose. The second chapter provides a review of all membrane separations used in the dairy industry with suggestions for future processing (Chapter 11). Chapters then proceed to discuss membrane biofouling and its prevention. Biofouling of membranes is often called membrane cancer, and it has been and will continue to be a problem that must be addressed. Biofouling has been associated to feed spacers, so the effects of using anti-microbial copper charged feed spacers are investigated (Chapter 12). The role of membrane chemical heterogeneities and morphology in biofouling and their effect on solute chemistry using chemical force microscopy as a characterization tool is discussed (Chapter 14). A chapter focuses on a novel hybrid membrane process that uses reversible ion exchange-membranes (RIX-M) for desalination to eliminate scale formation potentials by changing the chemistry of the feed water through the introduction of a reversible cation exchange step before the membrane based desalination step. The cation exchange step has the potential to reduce the osmotic pressure of the resultant feed solution to the membrane. Thus, the membrane process can operate with high permeate water recovery and enhanced energy efficiency (Chapter 17). Membrane materials are also the focus of studies shown in Part II. Sulfonated polymers are investigated due to their chlorine tolerance and hydrophilicity, as well as due to their ion exchange ability during desalination to increase sodium chloride rejection (Chapter 13). In a different study, composite 3 In Modern Applications in Membrane Science and Technology; Escobar, I., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.
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membranes were prepared using polyethersulfone (PES) and multi-walled carbon nanotube (MWCNT) to investigate the influence of addition of MWCNT on the morphologies, permeation properties and antifouling (Chapter 15). The next chapter discussed the effects of polysulfone (PSf) dope concentration, membrane thickness and presence/absence of an inorganic additive (i.e. lithium chloride (LiCl)) on the filtration of different salt concentrations (Chapter 16). Lastly, polybenzimidizole nanofiltration membranes were cast and functionalized to investigate their ability to reject monovalent ions for future forward osmosis applications (Chapter 18). The main goal of this book is to deliver some of the latest breakthroughs and findings in membrane technology and research. These latest research discoveries will hopefully spark new ideas to continue advancements in the field of membrane science.
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4 In Modern Applications in Membrane Science and Technology; Escobar, I., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.
