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Ion Transport Membrane and Pressure Swing Adsorption System to Produce Hydrogen Disclosure Number: IPCOM000021491D
Publication Date: 2004-Jan-21
Document File: 3 page(s) / 74K

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Ion Transport Membrane and Pressure Swing Adsorption System to Produce Hydrogen

Synthesis gas, a mixture of hydrogen and carbon monoxide, can be produced by oxidatively-reforming a hydrocarbon-containing stream that 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 Synthesis gas and nitrogen-enriched non-permeate products are withdrawn from the modules.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.

This article describes a process concept that integrates a hydrogen pressure swing adsorption (PSA) system with an ITM synthesis gas production system to produce hydrogen. Specifically, the blowdown gas from the PSA is collected separately from the purge effluent from the PSA. This arrangement preserves the blowdown gas at sufficient pressure to fuel the direct-fired air preheater supplying hot oxidant to the ITM reactor. The PSA purge effluent, at essentially ambient pressure, would not be useful to direct-fire the air preheater; but can be used as a low-pressure fuel elsewhere in the ITM synthesis gas process or the overall plant. A process flow diagram that illustrates the concepts is shown in Figure 1.

In Figure 1, a hydrocarbon feed gas containing methane, and possibly some heavier hydrocarbons, is adjusted in pressure to about 200-400 psig and preheated to about 700°F. It is optionally mixed with some hydrogen in a molar ratio of about 0.1%-10%, and fed into a vessel filled with hydrogenation catalyst, followed by a bed of sulfur sorbent. The desulfurized feed gas contacts an excess of warm water in a suitable contacting vessel, wherein some water evaporates into the feed to generate a humid feed at a steam-to-carbon ratio of about 2 to 5. In an alternative configuration (not shown), the water-gas saturator system could be replaced with a steam generation system, well known in the art, with steam mixed directly with the desulfurized feed.

The humid feed is then further preheated to between about 700°F and 1100°F before being fed to an adiabatic prereformer, which is a vessel filled with a catalyst that is active for steam reforming of hydrocarbons at these relatively low temperatures.

Ambient air is compressed to about 10-25 psig in a low-pressure blower. The compressed air is preheated in a direct-fired air preheater to a temperature up to about 200°F warmer than the hydrocarbon feed to the ITM reactor.

The direct-fired air preheater exhaust (oxidant) and the ...