Inorganic Membranes for Gas Separation
Inorganic membranes such as carbon, zeolite, and silica membranes have defined micropores; this structure differs from that of polymeric membranes, where pores may be generated from the movement of polymer chains. To obtain superior gas separation performances, tailoring of the pore size and structure is important. Through intensive research in this field, facile routes for material synthesis and film processing to control the pore structure and size of inorganic membranes have been developed. Recent focus has gradually shifted to thinning the membranes. Thin membranes are beneficial for the enhancement of the gas permeance by reducing the diffusion passage. However, the possibility of forming defects on the membranes increases, which is a critical issue to overcome. In this chapter, we focus on preparations of inorganic membranes in order to improve the separation performance toward gas and vapor mixtures. This chapter is divided in four sections based on the inorganic material used: silica, carbon, zeolite, and metal-organic framework (MOF) membranes. MOF membranes are not considered inorganic membranes because of the organic chains contained in their frameworks; however, considering the promising properties of MOF membranes for use in gas separation, we include a discussion of these materials in the final section.