Über die Autorin bzw. den Autor

Benny D.Freeman - Kenneth A. Kobe and Paul D. and Betty Robertson Meek & American Petrofina Foundation Centennial Professor of Chemical Engineering University of Texas at Austin, Center for Energy and Environmental Resources. He researches in polymer science and engineering and, more specifically, in mass transport in polymers. His work in this field started in North Carolina State University, where he worked as assistant, associate professor and full professor during the period 1989-2002. In 2002 he moved to Department of Chemical Engineering of the University of Texas at Austin and currently directs 18 Ph.D. students and one postdoctoral fellow performing fundamental research in mass transport in polymers. I have taught a variety of short courses in the membranes area for societies such the ACS, the North American Membrane Society, and the International Congress on Membranes. I have also taught a course on this topic at the graduate level at the university. I have co-edited 4 books. Professor Freeman will be the 2009 ACS Awardee in Polymer Science in 2009.

Yuri Yampolskii, Professor, Head of Laboratory of membrane gas separation, A.V.Topchiev Institute of Petrochemical Synthesis, Moscow, Russia. Since the middle of 70s has been engaged in the studies of membrane separation, polymer physical chemistry and related subjects. At present he is Head of the laboratory dealing with the problems of membrane separation and pervaporation, gas permeation properties of various polymeric materials, vapor separation processes, sorption thermodynamics, free volume in polymers. He has published about 200 papers in peer reviewed journals and authored or co-authored several books.

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Gas separation membranes offer a number of benefits over other separation technologies, and they play an increasingly important role in reducing the environmental impacts and costs of many industrial processes.

This book describes recent and emerging results in membrane gas separation, including highlights of nanoscience and technology, novel polymeric and inorganic membrane materials, new membrane approaches to solve environmental problems e.g. greenhouse gases, aspects of membrane engineering, and recent achievements in industrial gas separation. It includes:

• Hyperbranched polyimides, amorphous glassy polymers and perfluorinated copolymers
• Nanocomposite (mixed matrix) membranes
• Polymeric magnetic membranes
• Sequestration of CO2 to reduce global warming
• Industrial applications of gas separation

Developed from sessions of the most recent International Congress on Membranes and Membrane Processes, Membrane Gas Separation gives a snapshot of the current situation, and presents both fundamental results and applied achievements.

Aus dem Klappentext

Gas separation membranes offer a number of benefits over other separation technologies, and they play an increasingly important role in reducing the environmental impacts and costs of many industrial processes.

This book describes recent and emerging results in membrane gas separation, including highlights of nanoscience and technology, novel polymeric and inorganic membrane materials, new membrane approaches to solve environmental problems e.g. greenhouse gases, aspects of membrane engineering, and recent achievements in industrial gas separation. It includes:

• Hyperbranched polyimides, amorphous glassy polymers and perfluorinated copolymers
• Nanocomposite (mixed matrix) membranes
• Polymeric magnetic membranes
• Sequestration of CO2 to reduce global warming
• Industrial applications of gas separation

Developed from sessions of the most recent International Congress on Membranes and Membrane Processes, Membrane Gas Separation gives a snapshot of the current situation, and presents both fundamental results and applied achievements.

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Membrane Gas Separation

John Wiley & Sons

Chapter One

Shinji Kanehashi, Shuichi Sato and Kazukiyo Nagai Department of Applied Chemistry, Meiji University, Tama-ku, Kawasaki, Japan

1.1 Introduction

Recently, the polymer science field has focused on the role of polymers as membrane materials with precise, well-ordered structures through the development of defined synthesis and analysis of polymers. Among these well-ordered polymers are the hyperbranched polymers (e.g. hyperbranched polyimides). Part of the interest in such polymers is due to the expectation that they could have different properties as compared to common linear polymers. Also, cross-linked polyimides have attracted much attention from researchers, as can be judged by a high number of publications.

In general, hyperbranched polymers have many orderly branching units whose structures are different compared to linear and randomly cross-linked polymers. According to the Commission on Macromolecular Nomenclature of the International Union of Pure and Applied Chemistry (IUPAC), a crosslink polymer is defined as a polymer having a small region in a macromolecule from which at least four chains emanate. It is formed by reactions involving sites or groups on existing macromolecules or by interactions between existing macromolecules. The word 'network' is also defined as a highly ramified macromolecule in which essentially each constitutional unit is connected to each other constitutional unit and to the macroscopic phase boundary by many permanent paths through the macromolecule, the number of such paths increasing with the average number of intervening bonds; the paths must on the average be coextensive with the macromolecule. In this chapter, we use the term crosslink polymer to describe a random cross-linked network between polymer segments.

Precisely branched polymers include hyperbranched polymers, dendrimers and dendrons. Dendrimers and dendrons are characterized by perfectly controlled structures in three dimensions such as tree branch architecture, and they have attractive features such as a well-ordered chemical structure, molecular mass, size and configuration of polymers. Although the precise order of shape of hyperbranched polymers is less than that of dendrimers and dendrons, hyperbranched polymers have unique properties such as low viscosity attributed to the lack of entanglement of polymer segments, and the possibility of chemical modification in terminal functional groups such as in dendrimers.

Synthesis of hyperbranched polymers is typically performed through the selfpoly-condensation reaction of AB₂-type monomers (Scheme 1.1). The theoretical study of the random AB_x polycondensation has already been reported by Flory in 1952. He pointed out that the synthesis of hyperbranched polymers from AB_x monomers should resemble linear polymers in their elusion of infinite network (i.e. gelation) formation, which cannot occur except through the intervention of other interlinking reactions. Since then, there have only been a few experimental data made available on hyperbranched polymers; some have even been overlooked due to the fact that the use of the term hyperbranched polymers began only in the late 1980s. However, in early 1990s, hyperbranched polyphenylene was synthesized from AB₂-type monomers. This marked the beginning of the reawakened hyperbranched polymer concept. A variety of hyperbranched polymers such as polyphenylene, polyimide, polyamide, polyester, polyetherketone and polycarbonate have been reported in recent years. It is important that hyperbranched polymers with feathers of closed dendrons can be synthesized through the self-polycondensation one-step reaction because dendrimers and dendrons are synthesized by multistep procedures (e.g. protection, coupling and deprotection cycles). Producing dendrimers and dendrons is also costly and requires complicated manufacturing processes for industrial applications.

On the one hand, linear aromatic polyimides have been generally used as electronic and aerospace materials because of their excellent mechanical strength, thermal, chemical and electronic/optic properties compared with other common amorphous polymers. Polyimides are also excellent membrane materials for gas separation due to their rigid chemical structures, allowing the production of larger functional free volume. Over the past decades, numerous polyimides have been synthesized and their gas transport properties have been investigated. Scheme 1.2 shows the chemical structures of acid anhydrides and diamines mentioned in this chapter.

On the other hand, hyperbranched polyimides not only have the features of other hyperbranched polymers (e.g. low viscosity, good solubility) but also possess high thermal and physical stability, which is attributed to their rigid imide ring. It is commonly known that the kinds of terminal functional groups affect their physical properties, such as glass transition temperature and solubility. Hyperbranched polyimides have weak polymer chain interactions (lack of entanglement) and this affects their density, dielectric constant, refractive index and other properties. It is expected that they could provide an alternative to conventional polymer materials as novel functional and high-value added materials. Furthermore, hyperbranched polyimides could have a well-ordered structure compared with linear polyimides, which have a random distribution of polymer segments. Therefore, hyperbranched polyimides are expected to have favourable gas separation performance since their controlled branched structure could be advantageous in separating small molecules. Since the early 2000s, research on hyperbranched polyimides as gas separation materials has been reported, and these studies are still in progress.

Plasticization behaviour induced by condensable gases and vapours (e.g. carbon dioxide, hydrocarbons and other organic vapours) in polymer membranes is still a painful problem in polymeric membrane-based gas separation applications. Recently, novel hyperbranched polyimides were prepared from telechelic polyimides and an attempt was made to improve its gas separation performance and physical stability by obtaining plasticization-resistant materials (see e.g. Chapters 4, 6 and 7 of this book).

This chapter presents a review of numerous publications devoted to the concept and synthesis of hyperbranched and cross-linked polyimides. Also, gas permeation properties of these polymers are considered in detail.

1.2 Molecular Designs for Membranes

There exist different architectures of polymer macromolecules, as is shown in Figure 1.1.

Type I represents common linear polymers such as polysulfone, polycarbonate or polystyrene, for example. In glassy polymers, the movement of segments is frozen, though small-scale mobility of side groups is possible. In general they have good solubility in various organic solvents; however, their gas permeation properties in the presence of organic vapours are affected by plasticization phenomena.

Type II. In randomly cross-linked polymers the solubility in organic solvents gradually decreases with the increasing degree of crosslink density. Too frequent crosslinks result in the gelation of the polymer and a decline in gas permeability while simultaneously...