H2S Adsorption Thermodynamics

How low a sorbent is able to reduce the H2S level in the reformate depends theoretically on the thermodynamic property of the sorbent, composition of the reformate, and the adsorption conditions. As well known, the reformate contains not only H2 and H2S, but also H20, CO, and C02. These coexisting compounds might influence the desulfurization over the metal oxide sorbents via the following reactions  

It indicates that H20 strongly inhibits the degree of the desulfurization, and at 600 °C in the presence of 20 vol % H20(g), ZnO is unable thermodynamically to remove H2S from H2 gas to less than 7.4ppbv. 

The coexisting CO and C02 in the reformate might also influence the desulfurization performance of metal oxide-based materials. Novochinskii et al. found that the coexisting C02 reduces the kinetic capacity of ZnO.177,178 They contributed it to competitive adsorption between H2S and C02 in the presence of steam. Another 

The thermodynamic calculations on the basis of Equations 5.6-5.8 indicate that ZnO might be unable to reduce the sulfur in the reformate to the level for PEMFC applications when the fuel gas contains a large amount of H20, CO, and C02 due to the thermodynamic factor. ZnO is not efficient for removing COS. It needs to catch more close attention to the effects of the coexisting H20, CO, and C02 on the H2S removal from the reformate in the design of a post-desulfurization process in a hydrocarbon fuel processor, especially at high temperature. 

Among fossil fuels, coal is the most abundant fossil fuel and could meet the human need for more than 200 years from now. In the U.S., coal is also our nation s most abundant domestic fossil fuel resource, about 5800 quadrillion BTUs.184 Consequently, coal is the most prospective resource for mass hydrogen production in the 21st century. For near- to midterm applications, hydrogen production from coal is expected to be the most economical pathway until other resources, such as renewable sources, become available to produce hydrogen in large scale at lower costs.184 

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