Concentrated Emulsion Pathway to Novel Composite Polymeric Membranes and Their Use in Pervaporation

Abstract

Novel composite polymeric membranes have been prepared, using concentrated emulsions as precursors, and employed in the pervaporation of various liquid mixtures. In a concentrated emulsion, which has the appearance of a gel, the volume fraction of the dispersed phase is larger than 0.74 (which represents the most compact arrangement of spheres of equal radii) and can be as large as 0.99. The concentrated emulsions were prepared at room temperature by dispersing a hydrophobic (hydrophilic) monomer(s) into a small amount of a hydrophilic (hydrophobic) monomer(s) containing a suitable dispersant. In order to improve the stability of the concentrated emulsion, the hydrophilicity and/or the hydrophobicity of the phases involved must be increased by replacing them with their solutions in water and/or in a hydrocarbon, respectively. Another possibility of improving the stability is to increase the viscosity of the phases, by partial polymerization of one or both phases before preparing the concentrated emulsion. The emulsion gel was subsequently transformed into a polymer composite by polymerizing both phases. The dispersed phase should be selected to yield a hydrophobic (hydrophilic) polymer which is compatible with the components selected for separation and incompatible with the other components, while the continuous phase should be selected to yield a hydrophilic (hydrophobic) polymer which is incompatible with all of the components of the mixture, and thus it can ensure the integrity of the membrane. As examples, several composite polymeric membranes were designed, prepared, and employed in the separation by pervaporation of water-ethanol, aromatics-paraffinics (toluene-cyclohexane, benzene-cyclohexane), and aromatics-alcohol (benzene-ethanol) mixtures