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Converting an H2S analysis result in ppm (w/w) to ppm (v/v

nichs2 (Chemical) (OP)
14 Jan 09 7:29
Hi,

I've got a sulphur survey in which results are presented in ppm (w/w) (i.e. mg/kg).  I need, in order to do some classifcation of our plant based on H2S concentrations, the results in ppm (v/v).  I thought I knew how to convert this using molecular weights and assuming ideal gases etc. but I don't believe some of my answers.  I have results for both gas-phase samples(e.g. H2S in propane product) and liquid phase samples (e.g. H2S in crude and produced water).

If anyone feels like doing an answer for me, H2S in produced water is 7.3mg/kg, H2S in propane is 1.5mg/kg!
MortenA (Petroleum)
15 Jan 09 1:20
gas:

Use mol weight of gas and mol weight of H2S to convert
ppm(v/v)=ppm(w/w)*Mw(gas)/Mw(H2S)

Liquids: Hell i dont know. Imo it dosnt make the the same sence. Its like molality (molar koncentration in water). Here its costume to write number of moles pr liter of water - not number of moles pr. moles of water+moles og your compond - and whats the molality of water in water (when theres other compounds)? When its a coumpound that eventually becomes a solid e.g. like salts then your could use that refernce for ppm 8v/v) but H2S is a gas and when its free it take a lot of space - but the density of the water dosnt drop correspondingly. My feeling is that ppm (w/w) is more accurate here.

Best regards

Morten

 
Unotec (Chemical)
16 Jan 09 11:18
I am not completely sure, but for liquids I think you can correlate the gas equation MortenA posted but by densities:
ppm(v/v)liq=ppm(w/w)lliq*(density solution)/(density solid)
I might be wrong though, I have not done this in a while

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying " Damn that was fun!" - Unknown>>

MortenA (Petroleum)
19 Jan 09 6:43
I think you are wrong smile

H2S is not a solid at the given P and T!

Best regards

Morten
Unotec (Chemical)
19 Jan 09 10:40
.... yes, you're right... should read (density H2S)... it was a Friday, though.  

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying " Damn that was fun!" - Unknown>>

MortenA (Petroleum)
21 Jan 09 4:01
well you know what the Briths say:

Always check on mondays what was made on fridays after (pub) lunch smile

Anyway i still think its wrong: The density of H2S as a gas in the state AS A GAS is something you can calculate - but as a dissolev gas?

Best regards

Morten
Chacuncha (Petroleum)
11 Feb 09 14:27
you have to use the equation the Gram molecular weight of a gas occupies 22.4 Litres at STP. you need P and T to carry out the calculation, thus use P1 V1/T1 =p2 v2/t2, you get the volume of gas at the STP temperature, from this volume you can get the weight of H2S.
mxmaciek (Chemical)
12 Feb 09 8:21
Chacuncha,
H2S is dissolving with water. As it is forming the solution, not gas bubbles in the liquid.
Chacuncha (Petroleum)
15 Feb 09 11:31
I found the density of H2S is about 1.39 g/L, wouldnt this work for converting ppm w/w to ppm v/v?

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