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Elemental sulfur

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soumya1478

soumya1478

Chemical
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In hydrotreating reactor with 20 bar inlet pr and 6 bar outlet pr at temps 0f 240 C will elemental sulfur decompose to H2S in excess hydrogen atmosphere or end in product as elemental sulfur in product?
Thanks in advance
 
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soumya1478:

Your question confuses me. Are you under the impression that the feed to an oil refinery hydrotreater contains elemental sulfur? If so, that is not correct. The feed does not contain elemental sulfur. Instead, it contains organic sulfur compounds. And it is those organic sulfur compounds that are converted into gaseous H2S in the reactor.

As for elemental sulfur appearing in the end product from a hydrotreater, I have never heard of that having occurred and I doubt that it has ever occurred.

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

 
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Typical naphtha hydrotreating reactors (prior to catalytic reformers) reduce sulfur content from 400 ppm to 1 ppm.
 
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Elemental sulfur will react very strongly with hot CoMo catalyst in the presence of hydrogen; it reduces to H2S just like other sulfur compounds. The expected equilibrium concentration of elemental sulfur at the outlet of a tail gas reactor is almost non detectable, but I've never heard of elemental sulfur being present in a HDS.
 
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soumya1478
I do think 100% will convert. Some Presulfided catalyst like the ones used to be from CRI, had more or less pure sulfur coated catalyst (think they called it polysuflides but in reality it were elementary sulfur) and during the heat up this sulfur were converted to H2S and sulfided the catalyst. I guess the exact mechanism can be debated i.e. if the sulfur reacted to H2S or more or less directly with the catalyst.
The term presulfided is somewhat misleading since the catalyst were still in oxidic state. A german company later came with true sulfidic catalyst that were coated with some waxy material that melted off during heat up and one could avoid the time and the exotherm during sulfidation. How efficient this is, I dont know since I havent done this operation myself.
I hope this clear the confusion for existence of elementary sulfur in a hydrotreating reactor
 
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Thanks to all for your reply
Let me clarify the question a bit more.The feed to HDS reactor is from a condensate refinery which contain dissolved elemental sulfur.Now the question is will it decompose?
I have heard of elemental sulfur being used for sulfiding but not now a days as you have got polysulfiding agents.


once again thanks for the replies
 
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Do you mean catalyst sulfiding ?
 
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I'd expect the equilibrium concentration of elemental sulfur downstream of a reactor with hot, sulfided catalyst to be essentially zero. Think about it, effectively no stearic hindrance.
 
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soumya1478
Interesting
You mention 240°C which i quite low for a hydrotreater. I have seen some elementary sulphur exiting a hydrotreater when loosing the hydrogen partial pressure and we detected this in the LPG. This was on a Kero-minus hydrotreater treating everything from LPG to Kerosene.
Small amounts but enough to get the LPG off spec on residue. So I guess it is a combination of pH2 and temperature, that can let some of the sulphur to pass. In this case the sulphur was believed to be formed in the reactor, when restoring the pH2 the problem vent away. However the concentration should be very low so most of the sulphur will be converted, however if you are unlucky (depends on the products) you might be able to get above the specification/limits for your products. Some increase in temperature and higher pH2 will most likely convert all sulphur if htis is the case.
 
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The purpose of a HDS is to remove sulfur compounds, for example R-S-R or R-S-H. These compounds in the prescence of the catalyst and hydrogen will break those bonds to form H2S. I have never heard of elemental sulfur being fed to a HDS reactor - with the exception for pre-sulfiding. I would suggest you contact your catalyst vendor and ask them the question.
 
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As far as I know presulfiding is done with polysulfides, R-S-S-S-(....)-R, not with elemental sulphur. (I assume presulfided catalyst would otherwise be yellowish, not black). During activation with H2 the polysulfides are converted to H2S as you wrote, with which the metal sites are then sulfided.

To get back to the original question: is the purpose to approve a new feed stream or to find the origin of elemental sulphur found somewhere downstream the HDS reactor?
 
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To epoisses, you are most surely right. However there is a patent by ESSO from 1979 dealing with the subject of sulfiding with elemental sulfur: USP 4177136.
 
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