Hydrogen processing, pressure-swing

The impurities usually found in raw hydrogen are CO2, CO, N2, H2O, CH, and higher hydrocarbons. Removal of these impurities by shift catalysis, H2S and CO2 removal, and the pressure-swing adsorption (PSA) process have been described (vide supra). Traces of oxygen in electrolytic hydrogen are usually removed on a palladium or platinum catalyst at room temperature. 

Figure 4.1. A process for producing hydrogen by steam reforming of hydrocarbons (1) reforming furnace (2,3) purification section, (4) shift converter, (5) pressure swing adsorption.

Pressure swing adsorption cycle sequence for a four-bed system. (Adapted from Miller, G.Q. and Stocker,., Selection of a Hydrogen Separation Process, UOP Report, January 1999, available at http //www.uop.com/ objects/SelOfHydroSepProc.pdf Cassidy, R.T., Adsorption and ion exchange with synthetic zeolites, in ACS Symposium Series, ed. W.H. Flank, American Chemical Society, Washington, Vol. 135, p. 275,1980.)... 

In hydrogen fuel supply schemes using coal as feedstock, the same gasification processes as for the production of CTL fuels are applied. The synthesis gas from the gasifier is then converted to hydrogen by CO shift and pressure-swing adsorption (see Table 7.20). 

Within such a plant, depending on the pressure of the syngas, the separation can be performed by chemical absorption (usually with amine solvents) under lower pressure conditions or by physical absorption (e.g., with methanol) under higher pressure conditions (see also Chapter 6). Likewise, pressure-swing absorption can be employed. With the special properties of hydrogen, membrane separation processes could also be a very promising solution for the separation task. 

Because of the modular nature of fuel cells, they are attractive for use in small portable units, ranging in size from 5 W or smaller to 100 W power levels. Examples of uses include the Ballard fuel cell, demonstrating 20 hour operation of a portable power unit (32), and an IFC military backpack. There has also been technology transfer from fuel cell system components. The best example is a joint IFC and Praxair, Inc., venture to develop a unit that converts natural gas to 99.999% pure hydrogen based on using fuel cell reformer technology and pressure swing adsorption process. 

Polybed7 Pressure-Swing Adsorption Hydrogen Processing... 

Cyclic adsorption processes such as parametric pumping, cycling zone adsorption and heatless adsorption have received much attention both theoretically and experimentally in the past several years (3j. Skarstrom (4J has reviewed applications of heatless adsorption (synonymous with pressure swing adsorption) to air drying, hydrogen purification and air fractionation. 

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