(149d) Multifold CO2 Transport Property Enhancement of Interfacially Constrained Nanocomposite Membranes

Lakshmi S. Kocherlakota, Tiep Hoang Pham, René M. Overney^*

AIChE 2012-Abstract

Polymeric membranes are gaining wide attention in separation processes owing to their economic viability and operational flexibility. Poly(l-trimethylsilyl-1-propyne)(PTMSP), a high free volume glassy polymer, exhibits extraordinarily high gas permeability coefficients and high organic-vapor/permanent-gas selectivities. These unusual transport properties in PTMSP are attributed to its high fractional free volume. In this paper, we will address the impact on interfacial constraints on PTMSP’s free volume and transport properties. In particular, we found that within the submicrometer regime towards silicon-oxide surfaces, PTMSP membranes reveal CO₂/helium selectivities that exceed bulk PTMSP transport properties by up to three-fold.¹ This finding was attributed to a further increase in free volume, as verified by molecular energetic mobility analysis² (intrinsic friction analysis, IFA) that showed an enhancement of  the methyl side groups in ultrathin membranes compared to bulk membranes¹. For scale-up purposes,  “inverse” nanocomposites, made up of nanorods (100 to 200 nm diameter) of PTMSP within anodic alumina oxides sieve membranes were produced, yielding a two-fold increase of CO₂ permeability over virgin bulk membranes, and about a 20% improvement of the selectivity of CO₂extraction from helium and nitrogen. While PTMSP membrane are notorious for aging under ambient conditions, the embedded inverse nanocomposite systems show improved longevity.

¹           Kocherlakota LS, Daniel B. Knorr Jr. , Laura Foster, René M. Overney, Enhanced gas transport properties and molecular mobilities in nano-constrained poly[1-(trimethylsilyl)-1-propyne] membranes, Polymer 2012; doi:10.1016/j.polymer.2012.03.067

²            Knorr DB, Kocherlakota LS, and Overney RM. Journal of Membrane Science 2010;346(2):302-309.