ABSTRACT
Membrane separation processes have numerous industrial applications and provide the following advantages: They offer appreciable energy savings; they are environmentally benign; the technology is clean and easy to operate; they replace conventional processes like ltration, distillation, and ion exchange; they produce high-quality products; and they offer greater exibility in system design. Although it is difcult to introduce new technologies in industry, there is nevertheless a large demand for new improved processes, especially in the eld of separation technology. Stringent demands are made of these new separation technologies in order to compete with existing proven technologies and to meet stricter product-quality requirements, environmental legislation, energyefciency demands, and, last but not least, needs for cost reduction [1]. In order to meet these ever-increasing needs, there is a tendency to combine different processes into single
hybrid processes. The applications of membrane contactors are of interest to the chemical, petrochemical, pharmaceutical, and galvanic industries, both as end-of-pipe technology and for product recovery in water and gas treatment and as an integrated process solution [2,3]. In many applications, the contactor is not even called a contactor but rather is referred to by other names, depending on the specic application in which it is deployed. Examples include blood oxygenator (the earliest use of a membrane contactor), gas transfer membrane, membrane degasier, membrane deaerator, membrane distillation (MD) device, osmotic distillation (OD) device, membrane gas absorber, membrane extractor, and membrane humidier [4-7]. It has been found to be a cost-effective technology and is therefore used to supplant or replace other technologies that may or may not be membrane based. In some situations, membrane contacting has emerged as an enabling technology that is lling certain previously unmet
4.1 Introduction ....................................................................................................................................................................... 53 4.2 Description of Technology ................................................................................................................................................. 54
4.2.1 Description of Membrane Contactors and Principle of Operation ........................................................................ 54 4.2.2 Mass-Transfer Process in Membrane Contactors .................................................................................................. 55
4.3 Material and Equipments ................................................................................................................................................... 56 4.4 Potential of Membrane Contactors in Different Industries ............................................................................................... 57
4.4.1 Membrane Absorbers and Strippers ...................................................................................................................... 57 4.4.2 Membrane Crystallization ..................................................................................................................................... 59 4.4.3 Membrane Emulsication ...................................................................................................................................... 61 4.4.4 Membrane Contactors in Phase-Transfer Catalysis ............................................................................................... 62 4.4.5 Membrane Distillation and Osmotic Distillation .................................................................................................. 63
4.5 Pilot-Plant and Full-Scale Membrane Contactor Installations in Industry ....................................................................... 65 4.5.1 Installation for the Recovery of Aromatic Compounds from Wastewater ............................................................ 66 4.5.2 Membrane Contactors for Degassing .................................................................................................................... 66 4.5.3 Installation to Extend the Lifetime of Passivating Bath Liquids ........................................................................... 66 4.5.4 Membrane Gas Absorption Installation for Ammonia Recovery ......................................................................... 67 4.5.5 Pilot-Plant Experiments at a Potato Starch Production Plant ................................................................................ 68 4.5.6 Installation for CO2 Removal................................................................................................................................. 68 4.5.7 CO2 Production for Greenhouses........................................................................................................................... 68 4.5.8 Membrane-Based Solvent Extraction Using HFM ................................................................................................ 69 4.5.9 Application of Membrane Contactors in Pharmaceutical Industry ....................................................................... 70 4.5.10 Application of Membrane Contactors in Petroleum Industry and in Environmental Protection .......................... 70
4.6 Concluding Remarks and Future Directions ..................................................................................................................... 71 Acknowledgments ....................................................................................................................................................................... 72 Nomenclature and List of Symbols ............................................................................................................................................. 72 References ................................................................................................................................................................................... 72
commercial needs. The recent proposals to use hollow-ber contactors in space missions to recycle wastewater [8,9] or as an articial lung for patients aficted with different lung diseases [10] have opened a new horizon for this technology. As regards continuous improvements, hollow-ber renewal liquid membrane (HFRLM) [11], a new liquid membrane (LM) technique that draws on surface renewal theory, has been used to simultaneously remove and recover metal ions from aqueous media. The authors claim that this technique integrates the advantages of the hollow-ber membrane (HFM) extraction process [12], the liquid lm permeation process [13], and other LM systems. The intent of this chapter is to explain the technology and principles of operation of this technology with some remarks on the mass-transfer process in membrane contactors. This general introduction will be followed by some examples of successfully developed, full-scale industrial membrane contactor installations and a discussion of ongoing developments in the eld. This chapter aims to provide a comprehensive summary of current knowledge on membrane-based extraction techniques for various metallic and nonmetallic applications. Membrane stability, transport mechanisms, other important parameters, and their future directions in current research area are also described.
