"Development of Polymeric Membranes for Organic Vapor Separation Applications"
Ingo Pinnau, Membrane Technologies & Research, Inc.
The separation of organic vapors from permanent gases has become an increasingly important unit operation in the chemical process industry. This presentation will focus on the development of high-performance polymeric membranes for vapor separation applications. Design rules for advanced membrane materials that offer high permeabilities and selectivities will be discussed.
The permeability of rubbery and glassy polymers is typically described by the solution/diffusion model, P=DxS, where D is the diffusion coefficient and S is the solubility coefficient of the vapor or gas in the membrane. A measure of the ability of a membrane to separate a vapor from a gas is the selectivity of the vapor to the gas: (Dvapor/Dgas)x(Svapor/Sgas). The ratio of the diffusion coefficients depends on the chain mobility and the size of the penetrants relative to the inter- and intra- molecular chain gaps in the polymer, and is always less than unity, reflecting the large size of an organic vapor molecule relative to a small permanent gas (e.g., H2 or N2). The ratio (Svapor/Sgas) is the solubility selectivity and reflects the relative sorption of the gases. In the separation of organic vapors from permanent gases, the solubility selectivity is always much greater than unity. The balance between solubility and diffusivity determines whether a membrane material is selective for organic vapors or for permanent gases. In rubbery polymers the solubility selectivity dominates and they are usually organic-vapor-selective. In glassy polymers the diffusivity selectivity usually dominates and they are permanent-gas-selective. All commercial membranes are made from rubbery polymers that exhibit high organic vapor permeability coupled with high organic vapor selectivity (e.g., polydimethylsiloxane, PDMS).
Recent studies at MTR show that glassy, high-free- volume polyacetylene-based polymers can exhibit unexpectedly superior properties for organic vapor separation, in contrast to conventional glassy polymers. Poly(1-trimethylsilyl-1- propyne (PTMSP), a glassy disubstituted polyacetylene, is the most permeable polymer known. The unusual gas and vapor transport properties of PTMSP and similar polymers result from both high levels of excess free volume and interconnectivity of the free volume. The gas transport properties of these novel glassy polymers indicate that these materials are nanoporous with interconnected chain gaps of 5 to 10 Angstroms.
Dr. Ingo Pinnau directs the Materials and Membrane Development Group at Membrane Technology and Research, Inc. (MTR) and is an Adjunct Professor in the Chemical Engineering Dept. at North Carolina State University. His research interests focus on membrane separation processes, vapor and gas transport in membranes, and the formation of ultrathin polymeric and metal membranes. He is an AIChE short course lecturer on "Membrane Separation Processes". He has 15 patents and more than 50 scientific publications.
Thursday, July 23, 1998
Michaels at Shoreline
Shoreline Park, Mountain View
Social - 6:00 P. M.
Dinner - 7:00 P. M.
Lecture - 8:00 P. M.
Cost: $30, includes Social & Dinner.
No charge to attend lecture only at 8:00 PM. (but please let us know for headcount purposes)
Dinner choices: Broiled Salmon, London Broil or Vegetarian Lasagna
Directions to Michaels at Shoreline:
From 101 north or south, take the Shoreline Boulevard Exit, turning left going towards the bay. Drive past the amphitheater into Shoreline Park. After a mile or so, a sign will direct you to turn left into the parking lot. Address: 2960 N Shoreline Blvd. Phone: 962-1014
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