(234c) Nanoporous Layered Silicate AMH-3/Cellulose Acetate Composite Membranes for Gas Separations

The layered silicate AMH-3 contains nanometer-thick silicate sheets of crystalline porous structure and a pore size of ~3.4 Å. Such materials offer potential for obtaining higher gas separation performance over conventional polymeric and zeolite/polymer composite membranes, by dispersing their thin and high-aspect-ratio nanolayers in a polymeric membrane matrix. In such membranes, the layered material would ideally be exfoliated into individual layers (or stacks of a few layers) and dispersed uniformly thoughout a polymeric matrix. In previous work, we reported detailed studies of swelling and functionalization of AMH-3 layers, which are important prerequisites for the fabrication of polymer/AMH-3 membranes. A modified swelling method using diamine swelling agents allowed better  control of layer structure during the swelling process. Also, surface functionalization using silane condensation reactions improved the surface hydrophobicity, a putatively beneficial feature for improving surface compatibility with hydrophobic polymer matrices.

In this talk, we will discuss the fabrication and characterization of AMH-3/cellulose acetate membranes. Cellulose acetate (CA) membrane is the commercially established polymer material for the fabrication of hollow fiber membranes used in natural gas separation applications. It possesses high chemical and thermal resistance of CA ; however, increases in its throughput and selectivity would be advantageous. Further, it is expected that the addition of nanoporous layered materials to CA would be compatible with the hollow fiber spinning process used for CA membrane manufacturing.  Composite membranes of CA/Swollen AMH-3 and CA/Functionalized AMH-3 were fabricated, and characterized by a range of techniques.  The effects of using high-shear nanolayer dispersion/exfoliation methods such as homogenization via a high speed (~8000 rpm) agitator are discussed. The microstructure of the composite membranes was analyzed in detail using SAXS (small angle X-ray scattering) techniques. The permeation properties of the composite membranes for gas separations (e.g., CO₂/CH₄) will be discussed.