Immobilized liquid membranes for facilitated transport and gas separation

Separation and purification of gas mixtures is a major area of activity in chemical engineering. Gas separation using facilitated transport membranes has been the subject of considerable research for many years. Immobilized liquid membranes (ILMs) are an important class of facilitated transport membranes. Despite their potential to provide superior performance, they could not achieve commercial success so far due to their instability. Recent research addressed the issue of stability of ILMs by replacing water as the solvent successfully with glycerol. In the present thesis, the relevance of glycerol as an ideal solvent for developing stable ILMs is demonstrated using the separation of olefin-paraffin gas mixtures with silver nitrate-glycerol ILMs. It would be ideal if the use of solvent in forming the ILM can be completely eliminated. Such a radically different concept of forming ILMs was demonstrated with Polyamidoamine (PAMAM) dendrimer as the liquid membrane in its pure form. The pure dendrimer ILMs studied in the present thesis functioned as C02-selective molecular-gate membranes. It was also demonstrated that a judicious use of glycerol as a solvent in dendrimer solutions results in improving the performance of dendrimer membranes. There is always a need for physical solvents with enhanced solubility for the gas species of interest, particularly for CO2. The present thesis identified one such solvent, glycerol carbonate, and demonstrated its unique features for CO2 separation. Enhancement of CO2 fluxes with the addition of carriers such as dendrimers was also briefly explored to identify future directions for this new area of research. For any membrane process to be commercially successful, the process should have higher fluxes for the gas species of interest (e.g. CO2) without compromising on the selectivity of the membrane. The present thesis proposed and explored two novel concepts in preparing thinner liquid membranes. One approach uses the asymmetric nature of pores in the substrates to position the liquid membrane in a small section of the substrate. The other approach utilizes a traditional interfacial polymerization technique to form a thin support layer for immobilizing the liquid membrane on it. Both approaches have the potential to define the success of immobilized liquid membranes for solving the gas separation problems with efficiency and economy