ABSTRACT
Membrane 100 4.5.6 Other Applications ............................................................................................................................................. 101
4.5.6.1 Water Vapor Removal from Air .......................................................................................................... 101 4.5.6.2 Dehydration of Natural Gas................................................................................................................. 101 4.5.6.3 Helium Recovery ................................................................................................................................. 101 4.5.6.4 Recovery of Aggressive Gases: Cl2 and HCl...................................................................................... 101
4.6 Summary ........................................................................................................................................................................ 101 Acknowledgments.................................................................................................................................................................... 101 References ................................................................................................................................................................................ 102
The application of membranes for gas separation is a fairly young technology compared to the use of membranes for liquid separation. Although the basic theoretical principles were partly understood and date back to the early nineteenth and twentieth century with Fick’s law (1855), osmotic pressure (Van t’Hoff, 1887 and Einstein 1905), and membrane equilibrium (Donnan 1911), it was not until around 1950 that theories for gas transport through a membrane were presented and later further developed (pore model by Schmid in 1950 and Meares in 1956, solution-diffusion model by Lonsdale in 1965) [1]. The breakthrough for industrial membrane applications came with the development of the asymmetric membranes achieved by Loeb and Sourirajan around 1960 [2]. These membranes were developed for reverse osmosis and consisted of a very thin dense top layer (thickness <0.5 mm) supported by a thicker porous sublayer; hence the flux which is inversely proportional to the selective membrane thickness could be dramatically increased. The work of Loeb and Sourirajan resulted in commercialization of the reverse osmosis process for desalting of water, and had also a major impact on the further development of ultrafiltration and microfiltration processes. The development of gas separation membranes is based on their achievement and about 20 years later (~1980) the work of Henis and Tripodi made industrial gas separation economically feasible. They developed further the technique of putting a very thin homogenous layer of a highly gas permeable polymer on top of an asymmetric membrane, ensuring that pores were filled so that a leak-free composite membrane for gas separation was obtained. The first major development was the Monsanto Prism membrane for hydrogen recovery from a gas stream at a petrochemical plant [3]. Within a few years Dow Chemical Company was producing systems to separate nitrogen from air, and Cynara NATCO Group and Separex UOP LLC systems for separation of carbon dioxide from natural gas. These first membranes were all composite membranes where a very thin nonporous layer with high gas permeation rate (usually polysulfone or cellulose acetate (CA)) was placed on a support structure for mechanical strength-later other techniques for membrane formation were developed (i.e., interfacial polymerization, multilayer casting, and coating).
