Several questions about sulfur compound detection in NG

[lotusf33t]

I have a project that requires me to have excellent capacity to detect sulfur on the input side and the exit side of a sulfur cleanup process. For starters I will be sending in fairly high concentration of -

• * H2S
  * tert-butyl mercaptan
  * tetrahydrothiophene
  * carbony sulfide

When I say high, I mean up to 10 ppm, much higher levels than normally occur in at least US pipeline natural gas.

On the output of my cleanup process I would like to be able to detect down to 50ppb or lower with repeatability if not accuracy (minimum threshold).

questions:

1. 1. if you had no equipment (GC, detector, CDS) and no budget limit how would you solve this problem?
   2. if you were going to use a MicroGC 490 with a MS5A (permanent gases), PPQ (hydrocarbons to C3-ish), and a third column for sulfur compounds, what would you use for the third column and detector?
   3. if you were going to buy a new or used Perkin Elmer Clarus 580 GC, what kind of detector and column configuration would you look for?
   4. do you have any other advice for a sulfur in gas newbie?

That is all for now, thanks for your attention and hopefully replies.

Regards,

JF

[GasMan]

Low levels of sulfur compounds are a challenge with GC. For the low levels you are looking for, a TCD detector will not be sensitive enough, so this rules out a 490 microGC. For the very low levels a SCD (Sulfur Chemiluminescence Detector) would be recommended, but these are expensive. The GC it self would need to have ALL lines in contact with the sample inert treated otherwise you will get the sulfur compounds absorbed on the non treated surfaces resulting in varying results.

I would think that the chances of picking up a second hand GC ready to go would be slim, and I suggest you contact GC manufacturers for suggestions. However, whoever you go with will NOT be cheap...........

Gasman

[lotusf33t]

Low levels of sulfur compounds are a challenge with GC. For the low levels you are looking for, a TCD detector will not be sensitive enough, so this rules out a 490 microGC. For the very low levels a SCD (Sulfur Chemiluminescence Detector) would be recommended, but these are expensive. The GC it self would need to have ALL lines in contact with the sample inert treated otherwise you will get the sulfur compounds absorbed on the non treated surfaces resulting in varying results.

I would think that the chances of picking up a second hand GC ready to go would be slim, and I suggest you contact GC manufacturers for suggestions. However, whoever you go with will NOT be cheap...........

Gasman

Thanks for your reply, GM

I am not sure I fully understand your comment on inert-treating the sample lines, but I will look into it. I was planning on using PVDF or stainless steel sample lines. If I understand you correctly, this may not be adequate to prevent interference with the results.

Regards,

JF

[GasMan]

Inert tubing is stainless steel tubing with a special coating on the inside. Two suppliers that I know of are Restek and Agilent. Agilent markets their tubing as 'Ultimetal' and Restek markets their tubing under the names Siltek, Sulfinert and Silcosteel. Any tubing that is in contact with the sample should be made of this type of treated tubing.

Gasman