Chapter 3 - Structure and gas transport of nanocomposite membranes

Abstract

Like conventionally used polymeric membranes, nanocomposite membranes can be fabricated into two major configurations, i.e. flat sheet and hollow fiber. Flat sheet membranes can be obtained by casting the polymer dope as a thin film onto a substrate. For large-scale application, flat sheet membranes are moduled into spiral wound. The spiral wound module is pressurized with the feed gas where the more permeable gas transport across the membrane and leave the central perforated tube. Nanocomposite membrane can be fabricated with thickness varies from a few nanometers to few hundred micrometers. The structural characteristics of the membrane in terms of thickness and porosity profiles such as pore size, pore volume and tortuosity are the strong factors of the membrane performance. In terms of the structures, two types of nanocomposite gas membranes have been developed, namely mixed matrix membrane and multilayer nanocomposite membranes. Mixed matrix membrane generally refers to nanocomposite membranes consisting of a dispersed phase of inorganic nanofillers within a polymeric host matrix. Mixed matrix membrane can be prepared in symmetrical or asymmetrical structures. The introduction of multilayer membranes is a major breakthrough in gas separation membrane. Multilayer composite membrane consists of a thin selective layer that responsible for the separation capability and a non-selective substrate that provides the mechanical strength. In multilayer composite membrane, a thin layer consisting of two principal zones is deposited on a highly porous support. The interactions between nanofiller and polymer matrix is a complex phenomenon as the introduction of nanofiller causes several profound changes in polymer matrix. The properties of the interface has been understood better by considering the findings obtained from gas permeation experiments that coupled with appropriate modeling.