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Production of Ion Transport Membrane Structures with Low Pressure Drop

IP.com Disclosure Number: IPCOM000019414D
Publication Date: 2003-Sep-12
Document File: 3 page(s) / 73K

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Abstract

Oxygen can be recovered from air at high temperatures by passing a hot compressed oxygen-containing gas, preferably air, over non-porous, mixed-conducting ceramic membranes. These membranes, known in the art generically as ion transport membranes (ITM), utilize a pressure differential across the membrane to cause oxygen ions to migrate through the membrane. In addition to conducting the oxygen ions, these mixed-conductors allow electrons to move in the opposite direction for the formation of the oxygen ions on the feed side and oxygen molecules on the permeate side of the membrane. They have high oxygen permeation rates at theoretically infinite selectivity at elevated temperatures. Membranes can be fabricated as tubes or flat plates that are arranged in modules for efficient contacting with hot compressed air. High-purity oxygen permeate and nitrogen-enriched non-permeate products are withdrawn from the modules. A class of ITM membranes that are not mixed-conducting materials can also be used in this application. In these cases, the oxygen ions are driven through the membrane by applying an external voltage potential to the membrane. A comprehensive review of ion transport membranes is given by J. D. Wright and R. J. Copeland in Report No. TDA-GRI-90/0303 prepared for the Gas Research Institute, September 1990.

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Production of Ion Transport Membrane Structures with Low Pressure Drop

         Oxygen can be recovered from air at high temperatures by passing a hot compressed oxygen-containing gas, preferably air, over non-porous, mixed-conducting ceramic membranes. These membranes, known in the art generically as ion transport membranes (ITM), utilize a pressure differential across the membrane to cause oxygen ions to migrate through the membrane. In addition to conducting the oxygen ions, these mixed-conductors allow electrons to move in the opposite direction for the formation of the oxygen ions on the feed side and oxygen molecules on the permeate side of the membrane. They have high oxygen permeation rates at theoretically infinite selectivity at elevated temperatures. Membranes can be fabricated as tubes or flat plates that are arranged in modules for efficient contacting with hot compressed air. High-purity oxygen permeate and nitrogen-enriched non-permeate products are withdrawn from the modules. A class of ITM membranes that are not mixed-conducting materials can also be used in this application. In these cases, the oxygen ions are driven through the membrane by applying an external voltage potential to the membrane. A comprehensive review of ion transport membranes is given by J. D. Wright and R. J. Copeland in Report No. TDA-GRI-90/0303 prepared for the Gas Research Institute, September 1990.

Most of the extant design concepts envision using thin (5-100 μm) ion transport membrane films supported on a porous ceramic substrate to maximize the flux through these membranes. In most of the available ceramic substrates, the oxygen throughput is limited by the support pore size. Generally, fabrication constraints limit the pore size to diameters of 1-5 μm. This introduces a significant substrate pressure drop that can effectively limit the oxygen flux through a supported thin film ITM membrane.

An alternative to the use of traditional sintered powder bodies as substrates is the use of open cell ceramic foams as the porous substrate for the ITM thin films. These films are fabricated by infiltrating an open cell polyurethane foam with ceramic powder slurry, which, upon polymer burn-out and sintering of the ceramic, yields a ceramic replica of the foam structure. These foams are typically ~85% porous by volume with pore (cell) sizes ranging from ~200 μm to ~1700 μm in diameter. Due to the very low gas flow resistance of these open cell foam structures, the structures themselves can form the oxygen permeate passage. This would improve permeate side gas flow characteristics. Thus, in the case of tubular membrane geometries, the substrates can take the form of porous rods as well as thin walled tubes. In a planar geometry, the substrates will form thin sheets having membranes on both surfaces rather than individual supported membrane layers with an oxygen channel between them. In fact, due to the inherently low pressure drop of these foams, the foam could form b...