micro& packed columns
Applications
note
Restek Corporation • (800) 356-1688 • (814) 353-1300 •
#59573A
Sulfur compounds in petroleum streams can have detrimental
effects on the performance and longevity of the catalysts used
in hydrocarbon processing. Furthermore, the toxicity and odor
associatedwith sulfurs is of significant environmental impor-
tance. In short, to protect both processing equipment and the
environment, ability to quantify sulfur compounds to ppb levels
is imperative.
Gas chromatography is themethod of choice for the analysis of
sulfur compounds. Both packed and capillaryGC columns have
been successfully used for this application.Although gas chro-
matographic analysis of the sulfur compounds in petroleum
streams is important, this often is a difficult application.With
packed columns, the choice of column tubing is critical for
accurate determination of sulfur compounds, particularly at low
concentrations.Analyses on glass, Teflon
®
, or stainless steel
columns all present distinct problems. Glass columns exhibit
poor inertness and lack ruggedness for field or process control
use, and results are subject to variability because of column-to-
column variation in ID. Teflon
®
tubing, althoughmore robust
than glass, is plagued by three significant problems: 1) shrink-
age as the column cools causes back diffusion of oxygen and
water into the packingmaterial which, if not addressed, can
cause retention times to vary by asmuch as 15%; 2) oxygen and
water diffuse through the tubingwall, significantly decreasing
column longevity and creating reproducibility problems; 3) a
maximum column temperature limit of only 210ºCmakes it
impossible to quickly elute highmolecular weight sulfur com-
pounds.Without specialized surface passivation, stainless steel
columns simply do not offer the inertness needed tomonitor
active sulfur compounds at ppb levels.
One of the proven approaches for analyzing sulfur compounds
byGC is to use a thick film, 100% polydimethylsiloxaneRtx
®
-1
capillary column. Figure 1 illustrates the analysis of sulfur com-
pounds on a 60-meter x 0.53mm ID x 7µmRtx
®
-1 column. The
thick film is needed to resolve the volatile sulfur compounds,
but makes for long retention times for highermolecular weight
AnalyzeSulfur Compounds at ppb Levels, Using anRt-XLSulfur
MicropackedGCColumn or anRtx
fi
-1 Thick FilmCapillaryGCColumn
60m, 0.53mm ID, 7.0µmRtx
®
-1 (cat.# 10193)
100µL direct injection of sulfur compounds, approximately 10ppm each.
Oven temp.:
50°C to 200°C@15°C/min.;
Inj. / det. temp.:
50°C / 230°C;
Carrier gas:
helium;
Linear velocity:
30cm/sec. set@50°C;
Det.:
FPD
min. 0
4
8
12
1
2
3
4
5 6
7
8 9
10
11
12
13
14
15
GC_PC00200
1. hydrogen sulfide
2. sulfur dioxide& carbonyl sulfide
3. methyl mercaptan
4. ethyl mercaptan
5. carbon disulfide
6. dimethyl sulfide
7. 2-propyl mercaptan
8. allyl mercaptan
9. 1-propyl mercaptan
10. ethyl sulfide
11. butyl mercaptan
12. dimethyl disulfide
13. allyl sulfide
14. propyl sulfide
15. butyl sulfide&
allyl disulfide
Figure 1
Sulfur compounds on a thick filmRtx
®
-1 capillary column.
