012345 time [minutes] h 2 s mesh 50% propane matrix column:silica plot 30m*0.32mm oven: 100 °...

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H2S

MeSH

50% propane matrix

Column: Silica PLOT30m*0.32mm

Oven: 100 ° CisothermFlow: 2.0 ml/min HeInj: 100µl, split 1:40

Det: PFPD

< 60% recovery of H2S

COS

Accurate trace level quantification of sulfurUnlike GC columns with silica stationary phases, the Agilent J&W Select Low Sulfur GC column is highly inert in the presence of sulfur components, drastically lowering detection limits.

ConditionsColumn: Agilent J&W Select Low Sulfur

60 m × 0.32 mm (Agilent part #CP8575)Oven: 65 °C IsothermCarrier gas: Helium, constant flow, 2.0 mL/minInjection volume: 1 mLInjection: Gas sampling valve

Figure 2. 7890 GC-SCD

Application of sulfur compounds in propyleneThe stationary phase shows good selectivity between H2S,COS, and low mercaptans in various C3 hydrocarbon matrices. Co-elution of the sulfur components and the matrix, which causes “quenching”, is avoided.

7890 GC-SCDThe system was equipped with a gas sampling valve. The detector settings are shown in Table 1.

Introduction

Table 1. Detector SCD SettingsHydrogen sulfide (H2S), carbonyl sulfide (COS), and methyl mercaptan (MeSH) are common components in light hydrocarbon streams. They have corrosive and toxic properties, causing damage to pipes and equipment. The emission of undesired odors caused by volatile sulfur compounds in intermediates and final products have serious economic and environmental impact. In addition, the presence of sulfur can affect the performance of industrial processes, causing undesired chemical reactions, loss of catalyst activity (catalyst poisoning), and ultimately lower yield.

These sulfur components must be quantified at low parts per billion (ppb) levels. They can be measured with sulfur specific detection devices such as the Sulfur Chemiluminescence Detector (SCD) and Pulsed Flame Photometric Detector (PFPD) but large sample volumes are needed to reach the desired low ppb detection limits. This creates matrix overload and quenching effects (decreased signal/sensitivity due to background interferences) on most sulfur specific detectors, limiting the detector’s sensitivity and linearity and raising quantification limits. The capillary PLOT column, Agilent J&W Select Low Sulfur column, with a novel stationary phase was developed for the analysis of sulfur species such as H2S, COS and MeSH in light hydrocarbon C3 matrices, with high loadability properties and unique selectivity giving baseline resolution for sulfur components and matrix components.

GC Columns for ppb analysis of H2S and COSCapillary GC columns for the ppb analysis of H2S and COS in C3 matrices should ideally fulfill the following criteria:

1.Highly inert, providing good H2S response levels at < 100 ppb.2.Good separation between H2S/COS and ethylene or propylene matrix avoiding detector quenching.3.High sample capacity, catering for the larger injection volumes needed for low ppb level detection.

Some advantages and limitations of commercially available columns used for H2S and COS detection:

Non-Polar Liquid Phase, Thick film PDMS 3 - 5μm Highly inert phase with high H2S responses

Not selective, H2S/ethylene, COS/propylene co-elutionPorous polymer, DVB porous polymer

Absorption of H2S already at low ppm levelsH2S/COS and propylene well separated

Porous Silica, COS/ethylene, propylene well separatedH2S/ethylene, propylene well separatedAbsorption of H2S a low ppb levels

Results and Discussion

The Agilent J&W Select Low Sulfur column used in a GC with a sulfur specific detector, such as an SCD or PFPD, can detect H2S, COS, and MeSH at trace levels in a propylene matrix as a result of excellent separation of the sulfur compounds and the matrix.

Separating the matrix from the sulfur components eliminates the “quenching” effects caused by the matrix. This provides a better response for the sulfur compounds. The column provides a good response for reactive sulfur compounds, such as H2S, making detections of 20 ppb possible.

Although this is a PLOT column, no spikes will be observed because the column does not shed particles. It can therefore be used safely in combination with switching valves.

H2S elutes together with ethylene this makes the column unsuitable for the ppb H2S detection in ethylene feeds.

Results of the Agilent J&W Select Low Sulfur GC Column on a 7890-SCD systemThe Agilent J&W Select Low Sulfur column addresses the specific needs of petrochemical chemists who need lower detection limits for sulfur components in propylene. The unique selectivity and inertness offered by this new column provides significantly lower detection limits due to highest inertness towards volatile reactive sulfur components. The unique selectivity and no-particle shedding results in more reliable, higher-quality data. In Figure 5 the linearity of the sulfur compounds are shown using the column in combination with an SCD detector. A 24-hour sequence of programmed runs shows a nice reproducible signal for H2S, COS, and MeSH. Results are shown in Figure 6 and Table 3.

Elution of Hydrocarbons on Select Low Sulfur GC Column

Pittcon 2011Poster # 940-

12 P

Results and DiscussionResults and Discussion

Conclusions

Results and Discussion

PLOT Column Choices for ppb Level Detection of Sulfur CompoundsPLOT Column Choices for ppb Level Detection of Sulfur CompoundsJohan Kuipers, Helena Jacobse, Max B Erwine, Frans Biermans Agilent Technologies, Inc.

R² = 0.9992

R² = 0.9986

R² = 0.998

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Concentration [ppb]

Linearity of active sulfurs on the Agilent J&W Select Low Sulfur using a GC-SCD

H2SCOSMethyl mercaptan

These columns tend to exhibit adsorption of H2S and COS, limiting recoveries as shown on a porous silica PLOT.

PFPD settings

Air (1) 17 mL/min

Tube voltage

550 V

H2 13 mL/min

Sampling delay

6 ms

Air (2) 10 mL/min

Sampling width

20 ms

Trigger level

250 mV

SCD settings

Burner temperature 800°C

Vacuum of burner 370 torr

Reactor hydrogen flow

40 mL/min

Reactor air flow 65 ml/min

Ozone air pressure 5 psig

Experimental and Results

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H2S, COS and MeSH on select Low sulfur using SCD

H2SCOSMeSH

2 3 4 5 6 7 8Time [min]

H2S, COS and MeSH in Propylene matrix

H2S

COS

MeSH

7890 GC-SCD Injector: 200°C, split 1:10 Detector: SCD, 200°C Sample: Propylene matrix with

~300 ppb H2S and MeSH,

~500 ppb COS

3 4 5 6 7 8Time [min]

H2S, COS and MeSH in Propylene matrix

H2S

COS

Propylene MeSH

GC-PFPD Injector: 200°C, split 1:20 Detector: PFPD, 200°C Sample: Propylene matrix

~500 ppb H2S, COS and MeSH

Conc [ppb]pg S

on column

Average area

% RSD

H2S 475 61.6 3426 1.9%

COS 471 61.1 3631 1.8%MM 483 62.7 3146 1.6%

Mercaptans

Natural gas

Meth

yl

merc

ap

tan

Eth

yl m

erc

ap

tan

Pro

pyl

merc

ap

tan

Bu

tyl m

erc

ap

tan

C2C1 C3 Iso-C4 C4 Iso-C5 C5

Figure 1. H2S and COS response on a silica PLOT

Figure 4. Chromatogram of H2S, COS and MeSH in Propylene using the Agilent Select Low Sulfur with GC-PFPD.

GC-PFPDThe system was equipped with a gas sampling valve. The detector settings are shown in Table 2.Table 2. Detector PFPD Settings

Figure 3. Chromatogram of H2S, COS and MeSH in Propylene using the Agilent Select Low Sulfur with 7890 GC-SCD.

Table 3. Reproducibility during 24-hour sequence

Figure 6. Reproducibility of programmed runs on a 7890-SCD

Figure 5. Linearity of active sulfurs, 20 ppbv - 290 ppbv, SCD

The figure below shows an mirror of natural gas and the elution of mercaptans.

Figure 7. Analysis of H2S, COS and MeSH in N2 approx. 20 bbpv.

Figure 10. Mirror plot of natural gas and mercaptans, FIDChromatogram courtesy of R. Gras and J. Luong, Dow Chemical Canada, Analytical Technology Centre

min4.46 4.48 4.5 4.52 4.54 4.56 4.58 4.6 4.62

Norm.

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FID1 B, (GCFIDSCD011.D)

Figure 8. Natural gas, elution profile of methaneChromatogram courtesy of R. Gras and J. Luong, Dow Chemical Canada, Analytical Technology Centre

The PLOT behavior of the Select Low Sulfur stationary phase is evident from the characteristic overload elution profile of adsorption gas chromatography.

Conditions: Column: Select Low Sulfur, 60m*0.32mm Oven: 65°C (6.5) --> 185°C Flow: 2.0 ml/min, Helium Detector: PFPD Inj. volume: 1mL, split ratio 25:1 Sample: 75%propylene, 23%propane

Figure 9. H2S and COS in propylene/propane on the Agilent J&W Select for Low Sulfur. Data courtesy of L. Chambers, OI Analytical, College Station, TX

The column appears to be well suited for the accurate detection of ppb level H2S and COS in propylene/propane streams of variable concentrations without noticeable absorption of H2S .

H2S, COS, and MeSH in 50% propane on a silica PLOT