Using Ag to remove H2S from gas flow 1

[bonzoboy]

Does anyone know if there has ever been a commercial process to remove low concentrations of H2S from a gas flow? Since H2S reacts with Ag to make the sulfide, I was curious if silver could be used (under reducing conditions) to act as a final filtration to scrub the gases free of sulfur (or reduce it to ppb levels).

Any data on temperature dependence of H2S + Ag?

 

[pipehead]

there are already to many other process that remove H2S, I can't imagine why you would use such a high cost mineral.

 

[ash9144]

An aqueous ammonia solution would be effective to remove H2S.

 

[bonzoboy]

My thought about Ag, or any other metal that forms the sulfide, is that it might be a better sulfur scrubber at the very lowest concentrations (I'm not sure about that, but that's just my guesswork). Also, since it is a solid, it should have less risk of carryover.

I keep running into these processes where amines are used for H2S capture, but only reach 1-10 ppm (by volume) of concentration. And if I want < 50 ppb, it seems that the only solvent people recommend is methanol (at <-40 F, which is a lot of energy to throw into the process).

Any thoughts?

 

[mbeychok]

bonzoboy:

Hundreds of ammonia synthesis plants worldwide use zinc oxide beds to remove trace amounts of H2S from their methane feedstock. That should be much, much cheaper than using silver ... and it is a tried and true process.

It is a semi-batch process using two or more zinc oxide beds so that at least one bed is on-stream while another bed is being dumped and re-filled with zinc oxide.

If you are interested in more information, contact some of the major engineering and construction companies that design and build ammonia plants. For example, Haldor Topsoe of Denmark, Lurgi AG of Germany, Uhde of Germany, and Kellogg, Brown and Root of the USA.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[dcasto]

You can use molesieves, the latest versions of Zinc Oxide also has a catalyst promoter to help it work at low temperatures.

 

[kenvlach]

"Any data on temperature dependence of H2S + Ag?"

Yes, there are thermochemical data for the equilibrium

2 Ag + H₂S = Ag₂S + H₂

E.g., [&Delta;]G_Rxn = [&Delta;]G_{f, Ag2S} - [&Delta;]G_{f, H2S} is known as f(T).

for both Ag(s), Ag(liquid) and even Ag at reduced activity, as when alloyed with gold (electrum). For the Ag-Ag₂S equilibrium,

[&Delta;]G_Rxn = - RT ln [P_H2/P_H2S]

so from [&Delta;]G_Rxn can solve for either gas pressure if know inital conditions, e.g., P_H2 = 1 atm at t_o and a given T.

 

[bonzoboy]

Thanks everybody. I don't know why I didn't think of the ZnO process first. Got to be a lot cheaper, eh....