1.1Introduction to Ceramic Membranes
We start this book with a brief idea about the basics and fundamental concepts of ceramic membranes and their recent trends in different drives along with examples. An overview of the fabrication, characterization, and use of low-cost ceramic membranes in the development of hybrid membranes is then discussed in the following chapters; then we move to the most challenging and advanced sector of membrane technology (i.e., catalytic membrane and membrane reactors and their applications).
In general, a ceramic membrane can be defined as a permselective barrier placed between two phases that permits one or more components to selectively pass from one phase to the other in the presence of an appropriate driving force.
In the fourteenth century, ceramic was mainly known as an art and used widely for interior home decorations (pottery, tableware, and cookware) and still is [1]. Any details of ceramic processing and manufacturing were difficult to understand as researchers showed no interest. But, from the nineteenth century on, the scenario has completely changed. Researchers have started showing interest in ceramic material in the field of novel separations due to its high thermal resistivity, excellent mechanical and chemical stability, and, most importantly, high permeability and selectivity as performance parameters. Ceramics now include domestic, industrial, and building products, as well as a wide range of ceramic art and are in a strong position to compete with polymeric membranes. From the twentieth century, new ceramic materials have been developed for use in advanced ceramic engineering, such as structural ceramics, electrical and electronic ceramics, ceramic coating and chemical processing, and environmental ceramics [2].
Ceramic membranes are usually porous and dense in nature. Factors like permeation and separation for porous ceramic membranes are based on thickness, pore size, and porosity of the membrane, whereas, for dense ceramic membranes, the concept of permeation and separation is more difficult to predict. Applications and separations in porous and dense ceramic membranes are mainly based on their pore size as shown in Table 1.1.
Table 1.1Classification of Porous Ceramic Membranes | Category | Pore Size (nm) | Separation Mechanism | Applications |
| Microporous | <2 | Micropore diffusion | Gas separation |
| Mesoporous | 2–50 | Knudsen diffusion | UF, NF, gas separation |
| Macroporous | >50 | Sieving | UF, MF |
| Dense | – | Diffusion | Gas separation |
Ceramic membranes are typically a combination of a number of layers of one or more different materials by conventional means, called a composite. These layers are categorized in three different segments as macroporous support (bottom layer), mesoporous intermediate layers (one or more), and a microporous top surface layer, as shown in Figure 1.1. The bottom layer (macroporous support) provides mechanical support, whereas the intermediate layers connect the pore size differences between the support layer and the top layer; the actual separation takes place at the top layer [3].
Figure 1.1Schematic diagram of ceramic membrane (composite).
Manufacturing of ceramic membranes is usually based on many different compositions combined with pore-formers and binders in a wide variety of proportions. Based on a literature survey, the use of raw materials, including pore-formers and binders in terms of manufacturing cost and its effect on properties, is an influential and effective approach. This attention to the raw materials along with pore-formers and binders and its influence on membrane morphology (pore size, porosity, and surface texture) and thermal, mechanical, and chemical stability is the principal concept of research on ceramic membranes.
To be completely successful, the pore-forming mechanism of pore-formers must be understood in a broad sense. On the other hand, we are concerned about the influence of pore-formers on the morphology and mecha...
