Converting ppm to mole% 1

[azwanshah]

All,

Can someone help me on converting ppm of H2S (in stabilized crude oil) into mole%?

 

[Montemayor]

azwanshah:

I'm assuming that you are a degreed chemical engineer and know what moles are. Therefore, I expect a chem eng to readily know the complexity of what is a simple chemistry problem: You don't know the composition of the crude oil - it's a complex mixture. Also - and just as important - what do you - as a chem eng, again - mean by "ppm"? Parts per million can mean "per mass", "per volume", etc., etc. I'll assume you mean ppm(m) - per mass.

In order to find the mole % of the H2S content you have to know the total number of moles in the crude oil. For that, you have to have a complete and accurate molecular or weight composition of the crude oil - something that is rare, if not unobtainable. If you do have a detailed composition of your crude oil, then convert the individual weights of each component to the respective moles, add up the result and divide the total moles into the moles of H2S. It's all done very efficiently on a spreadsheet; however, the trick is getting the detailed crude oil composition!

 

[25362]

Here are some tangential remarks. It is a fact that S is the third most abundant atomic constituent of crude oils, following C and H.

It has been postulated that since S is not a major constituent of biogenic molecules, where it is by far well preceded by N and O, it must have been incorporated into organic structures en route from biological sources to petroleum or while the crude stood in its reservoirs.

Some comments on the sulfur compounds present in crude oil which are frequently responsible -among others- for its odor and color.

Hydrogen sulfide is present in some sour crudes, but is mostly formed by thermal and catalytic decomposition of sulfur compounds during distillation, cracking, reforming, etc.

Mercaptans aka thiols, are present in most crudes, and may also be formed during processes for the decomposition of organic sulfur compounds.

Neutral sulfur compounds which undergo changes in the course of processing that alters their type, distribution, molecular weight, etc. Those known to occur are CS₂, monosulfides, disulfides, thiophens.

Elemental sulfur and COS are very rarely present. Air absorption during intermediate storage may oxidize hydrogen sulfide to elemental sulfur. Carbonyl sulfide is probably formed during thermal and catalytic cracking.

Petroleum porphirins which are complex organometallic compounds containing porphin skeletons related to chlorophyll or h[æ]min, with polar C- S- and N- compounds.
It is apparent that the color of crudes stems mainly from the "NSO" compounds which tend to concentrate in the lube oil and residual (asphaltic bitumen) fractions.

 

[Mutt]

Excuse my question but why do you have to have the total sulphur in the crude, expressed as mol% H2S? Generally just want to know how much sulphur to remove and mass is just as good a basis. As Montemayor says, mole weights of crude are hard to come by as not used generally in designs.

 

[liberoSimulation]

Conversion factor of 10000 might be used to convert mol% (or wt%) to ppmv (or ppmw)by dividing mol% by 10000 to get ppmv!
I am not sure if this conversion can be used all the time or for some cases.


Regards