H2S--Can it be dissociated via Microwaves

[bonzoboy]

Another H2S question---Has anybody ever tried microwaves to breakdown the H2S? I haven't looked at the thermo, but I figure that the structue might be labile to microwave degradation. Any thoughts?

 

[dcasto]

If you want to break it down, just burn it. If its with methane, that you don't want to burn, I'd guess that the energy and frequency that breaks the HS bond would break the CH bond too.

 

[kenvlach]

1) I doubt that microwaving would be efficient at breaking down H₂S. Note that a microwave oven excites H₂O molecules of the same structure but doesn't come close to breaking them.

2) If one did break apart an H₂S molecule (maybe using a laser), you'd have 2 H^. and one S^.. radical in close proximity. Maybe reform H₂S!

3) Maybe useful to consider the thermal stability of H₂S on the above. Above the melting point of sulfur, have

[Δ]G_fH2S = -86920.2 + 7.26474*T*log(T) + 23.95049*T J/mol [T = 800-1200 K]
derived from JANAF data.

 

[Flareman]

Bonzoboy

Kenvlach's response reminds me that one of the problems with handling H2S in the first place (in pipelines) is its propensity to dissociate and drop out solid sulfur. At the same time it gives off H+ which can migrate through the lattice of the containment vessel material giving rise to the need for highZ plate and HIC testing.

If you are trying to separate sulfur from hydrogen in large amounts, be prepared for metallurgical issues.

Otherwise, I'd go with Kenvlach's heat of formation solution. In a given containment volume you can calculate the input energy requirements to raise the H2S to instability which will give you the cooking time. H2S is an unsymmetrical molecule so it should be excitable.

You would need some fancy design for the containment vessel. Where would you put the magnetron?
Laser might be a more easily controlled tool.

Stand very clear the first time you try it.


Wild scheme.. fill a ballon with H2S, Cook it to dissociate the gas and finish up with hydrogen on the outside and sulfur on the inside ... WOW!! I'm a genius.
Or did someone already invent the molecular seive?

 

[bonzoboy]

It sounds that if H2S breaks down in a pipeline, it breaks down at fairly low temperatures, or conditions that are no too severe....

 

[Flareman]

Bonzoboy

Full thermal dissociation is around 650 degC I think.
I suspct that the low pressure dissociation is promoted by low partial pressure. I never looked at the energy structure in any detail but there has to be someone out there who did.
There has been research doing this with electrical potentials.

If you are rally serious about this I suggest going to your local technical library and do some searches on

http://www.ScienceDirect.com

David

 

[kenvlach]

Hydrogen sulfide breakdown is aided by a catalyst surface & the presence of oxygen to form water and sometimes SO₂. The standard enthalpy of combustion of H₂S is -518 kJ/mole. Forget about a purely thermal decompsition unless you have a metal to act as a sulfur 'sink' by forming sulfide; H₂S-H₂ gas mixtures are used to study metal-metal sulfide equilibria over a wide range of temperatures.

Some very interesting papers:
'Electrochemical Membrane Separation (EMS) of Hydrogen Sulfide from Coal Gasification Streams.'

http://www.osti.gov/bridge/servlets/purl/837310-f3CDuK/native/837310.pdf

'Hydrogen Production from Hydrocarbons, H2O and H2S,. Stimulated by Non-Thermal Atmospheric Pressure Plasma

http://mechse.uiuc.edu/research/glumac/NSFW/Fridman.pdf

'High-Temperature Pyrolysis by Laser Gas Breakdown' Ind. Eng. Chem. Prod. Res. Dev., vol. 20, 396-399 (1981)

http://pubs.acs.org/cgi-bin/abstract.cgi/iepra6/1981/20/i02/f-pdf/f_i300002a032.pdf?sessid=6006l3

[abstract only]

'Production of Hydrogen and Sulfur from Hydrogen Sulfide in a Nonthermal-Plasma Pulsed Corona Discharge Reactor'
-- abstract only, from a 2005 conference:

http://aiche.confex.com/aiche/2005/preliminaryprogram/abstract_26564.htm

 

[sulphuric]

In the publication "Sulphur" March 1993 there is an article that talks about the use of microwaves for recovery of sulphur from waste gas containing H2S. This research used a microwave discharge to generate "cold" non-equilibrium plasma that dissociates hydrogen sulphide into hydrogen and sulphur. The research was being done in the US and Russia.

http://www.accessmylibrary.com/coms2/summary_0286-5494907_ITM