Roy's presentation at the North American Membrane Society's (NAMS) 2006 Annual Meeting in Chicago, Illinois, entitled, "A Fundamental Study of Mixture Permeability, Solubility, and Diffusivity in Vapor Selective Polymers". Co-authors Roy Raharjo, Benny D. Freeman, and Ed Sanders from Air Liquide, Newport Delaware.
Abstract
Membrane separation technology has recently emerged as a potential alternative technique to remove higher hydrocarbons (C3+) from natural gas1. The material that could be suitable, and, in fact, is currently being considered, for such separation is silicone rubber or poly(dimethylsiloxane) (PDMS). Aside from its high gas permeabilities (i.e., highest among rubbery polymers), this polymer is more permeable to the larger, more condensable higher hydrocarbon than to smaller, less condensable permanent gases, such as methane. As a result, methane, the major constituent in natural gas, can be kept at high pressure, which eliminates the cost of recompression that would be incurred if a methane-selective membrane were used for this separation.
The gas sorption and transport properties in PDMS have been studied in the past. Most of the references in the literature, however, report only its pure gas properties; only a few actually investigate its mixture properties. To accurately estimate the membrane separation performance, the use of mixtures in the study is required. This paper presents the n C4H10/CH4 mixed gas permeability, solubility, and diffusivity in PDMS at various temperatures from -20oC to 50oC. The dilation isotherms of the mixture are also reported to complement the mixture sorption data.
The CH4 permeability, solubility, and diffusivity increase as the n C4H10 fugacity in the mixture increases. The n C4H10 sorption and transport properties in mixtures are unaffected by the presence of CH4 and are similar to those in pure gas conditions. The overall n C4H10/CH4 selectivity increases as n C4H10 activity in the mixture increases and temperature decreases. This report represents the first combined presentation of gas mixture permeability, solubility, and diffusivity in PDMS, which is the most widely used vapor separation polymer.
Another polymer whose properties will be discussed is poly(1-trimethylsilyl-1-propyne) (PTMSP), an ultra-high free volume, solubility selective, glassy polymer. These studies will help illustrate the fundamental mechanism of the competitive permeation, sorption, and diffusion in glassy polymers.