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Composite ITM Materials for the Direct Conversion of Methane to Syngas

IP.com Disclosure Number: IPCOM000019433D
Publication Date: 2003-Sep-12
Document File: 3 page(s) / 64K

Publishing Venue

The IP.com Prior Art Database

Abstract

Synthesis gas, a mixture of hydrogen and carbon monoxide, can be produced by oxidatively-reforming a hydrocarbon-containing stream which passes on one side of a non-porous, mixed conducting ceramic membrane, with oxygen from a hot, oxygen-containing gas, preferably air, which passes on the other side of the ceramic membrane. These membranes, known in the art generically as ion transport membranes (ITMs), utilize an oxygen chemical potential gradient across the membrane to cause oxygen ions to migrate through the membrane.

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Composite ITM Materials for the Direct Conversion of Methane to Syngas

Synthesis gas, a mixture of hydrogen and carbon monoxide, can be produced by oxidatively-reforming a hydrocarbon-containing stream which passes on one side of a non-porous, mixed conducting ceramic membrane, with oxygen from a hot, oxygen-containing gas, preferably air, which passes on the other side of the ceramic membrane. These membranes, known in the art generically as ion transport membranes (ITMs), utilize an oxygen chemical potential gradient across the membrane to cause oxygen ions to migrate through the membrane.

Membranes can be fabricated as tubes or flat plates that are arranged in modules for efficient contact with the hot air and hydrocarbon-containing streams. Synthesis gas and nitrogen-enriched non-permeate products are withdrawn from the modules. A comprehensive review of ion transport membranes is given by M. Stoukides in Catalysis Reviews - Science and Engineering, 42(1&2), 2000.

The direct partial oxidation of methane to syngas using an ITM reactor with air feed places the ITM membrane under a very large oxygen partial pressure gradient.

 

Air/ ITM

 

2CH4 + O2

 

2CO + 4H2

 

700-900°C

 

Syngas pressures of 300-1000 psig are required for the direct POX process, depending on the methane supply pressure and the downstream process requirements for the syngas. On the syngas side of the membrane, the effective oxygen partial pressure is extremely low, PO2 ~10-6 to 10-19 atmospheres. The air may be fed at atmospheric pressure or at elevated pressure. Consequently, the oxygen partial pressure range on the air side of the membrane can be approximately 0.2 -10 atmospheres.

It is difficult to find a mixed conducting oxide material that is stable at the operating temperatures under these oxygen partial pressure extremes. Decomposition of the surface of the membrane under the reducing or oxidizing atmosphere that exists on opposite surfaces causes deactivation and stresses that lead to mechanical failure.

A solution lies in the use of layered or graded materials to form composite membrane structures in which the composition of each surface is optimized for the local conditions. Layere...