Elemental sulfur dew point

[Andrea10]

Hi to everybody!
Can anyone suggest me a method or a software available on the net in order to evaluate elemental sulfur dew point in a syngas mixture (S approx 1.5% mol)?
Thanks in advance!
Bye.

 

[kenvlach]

It's a bit difficult to define sulfur vapor pressure, since elemental sulfur vapor consists of S, S₂, S₃...S₈ species. Equations below are for total sulfur vapor pressure above liquid sulfur.

Recent data from T.E. Daubert et al. (1997) are shown in a graph, Figure 13, at

http://www.osti.gov/bridge/servlets/purl/859449-QJVVfc/859449.PDF

A curve fit to data at 400, 450 & 500 ^oF gives

log P(atm) = 5.515 - 3820/T(K) [note units]

At P = 0.015 atm, this gives T = 520.5 K = 247.4 ^oC = 477 ^oF.

Another source, Lange's Handbook of Chemistry, 14th Edn., page 5.37 (1992), gives
log P(Torr) = 6.84359 - 2500.12/(t^oC + 186.30) [note units]

Solving this equation at P = (0.015 x 760) = 11.4 Torr gives t = 245.75 ^oC = 474 ^oF in good agreement.

If your total pressure is higher than 1 atm, just solve for the higher P(sulfur).

 

[Andrea10]

Dear kenvlach,
thank you so much for your quick and detailed answer.
Hence, if I have a syngas with 1.5% mol of elemental sulfur at 5 atm absolute, dew point will be 300°C approx. But in this case liquid sulfur will be characterised by high viscosity...how do I manage that? Do I have to cool in any case my syngas down to 150-130°C (low viscosity region) hoping that sulfur will not plug my heat exchanger when it reaches dew point temperature?
Thank you in advance for your appreciated reply.
Bye!

 

[25362]

Andrea10, the vapor pressures of liquid sulfur are tabulated in the CRC manual. Your estimated dew point for S is about right.

Indeed liquid sulfur is unusual, not to say anomalous, in its viscosity-temperature behaviour due to ring cleavage and catenation. For this reason, have you considered converting it, for example, into H₂S by hydrogenation ?

 

[Andrea10]

Hi 25362!
Thanks for your answer!
Yes...I've read about the anomalous behaviour of liquid sulfur viscosity.
My problem is that I have to produce sulfur...I mean I start from H2S and I want to evaluate its oxidation, so I can't transform sulfur back to H2S.
But as the estimated sulfur dew point is about 300°C (high viscosity region), what can I do in order not to plug my cooling system? Do I have to cool rapidly in any case my syngas down to 150-130°C (low viscosity region) hoping that sulfur will not plug my heat exchanger when it reaches dew point temperature?
Thanks in advance for your reply.
Bye

 

[25362]

Off-hand I'd say you look for "sulfur condensers" in the net. One link might be:

http://www.goarallison.com/Improving SRU Reliability through Engineering Design.pdf

especially pages 12+.

 

[kenvlach]

Please read the report at the link in my first post. It describes the successful field test of catalytic oxidation of H₂S at 180^oC & 2.7 atm (absolute) pressure into S + H₂O from a gas stream approximately 8000 ppm of H₂S, 60% CO₂, 20% CH₄, and 20% ethane, propane, butane and traces of higher hydrocarbons. Process flow & equipment diagrams & photos, properties of sulfur, and details of a sulfur trap & condenser & heat traced liquid sulfur handling piping are given. Also, for commercial application, a heated coalescing filter would be used.

 

[Andrea10]

Dear 25362 and kenvlach,
thanks one more time for your kind and useful help.
Regards.