Figure 2: ASTM D5504 GC Confi guration Trace Sulphur response of 50 ppb
FIGURE 4: Linearity plot H2
S - Response factors from 5ppb - 10ppm
Figure 3: ~ 50 ppb dilution (MFC) from a calibration standard contain H2
S. COS, MeSH, EtSH and DMS.
Component Concentration (ppm)
(ppm) H2 S COS
MeSH EtSH DMS
0.49 0.48 0.48 0.50 0.50
0.00143 0.00136 0.00137 0.00143 0.00137
RF
Deviation RF to H2
S 0.0%
-4.9% -4.1% -0.3% -4.3%
Repeatability Measured
0.002 0.003 0.002 0.003 0.003
Repeatability
St.dev
ASTM D5504 0.1
0.06 0.1
Table1: Equimolarity and precision data (results in ppm). LINEARITY
The linearity of response for the analyzer is verifi ed by creating dynamic dilutions of a certifi ed calibration gas. Concentrations from 10 ppm down to 5 ppb have been created for Hydrogen Sulfi de (H2
S), as outlined in Figure 4. The calibration line has a linearity correlation > 0.9999.
Concentration repeatability according ASTM D5504-12 is measured for 8 consecutive runs for a calibration standard blend diluted to ~ 500 ppb single peak. Repeatability is compared with the precision statement of the method. Table 1 also represents precision data. The obtained precision (r) is well within the limits of ASTM D5504.
NATURAL GAS SAMPLE:
A natural gas sample (taken from the local distribution network) is analysed with an ASTM D5504 confi guration using SeNse. The main peak is THT (Tetra Hydro Thiophene) which is added to the natural gas network as an odor component by the supplier at ~18 mg/m3. The measured concentration is 4.55 ppm mol THT, which complies with 16.99 mg/m3.
Zoomed in on the baseline, various sulfur compounds (i.a. DMS) are determined at single digit ppb levels.
Figure 5: Oder component Tetra Hydro Thiophene in Natural gas. CONCLUSION
Item Target Sensitivity
Stability Linearity
Equimolarity Selectivity
< 0.3 pgS/s
< 2% RSD per 2 hrs < 3% RSD per 24 hrs > 10 4 < 10 % > 10 7
The redesign of the new Sulfur Chemiluminescence Detector has resulted in a unit with unsurpassed stability, increased sensitivity, and provides an excellent equimolar response in addition to a large dynamic range and selectivity. Its performance not only meets but exceeds ASTM D5504 requirements, ensuring the best quality data that can be used to estimate effects of Sulfur compounds in Natural Gas and Gaseous Fuels.
Author Contact Details Marijn van Harmelen, MSc. PAC Chemical Analysis • Innsbruckweg 35, 3047 AG Rotterdam, The Netherlands, • Tel. +31 10 462 4811 Email:
pacsales@paclp.com •
www.paclp.com
All of our articles are online! To view and download them, visit:
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