The Application Notebook
Natural gas and other gaseous fuels contain varying amounts and types of sulfur compounds which can be corrosive to equipment and can inhibit or destroy gas processing catalysts. Small amounts of sulfur odorants are added to natural gas and liquefied petroleum gases (LPGs) for safety purposes. Accurate measurement of sulfur species ensures proper process operation and odorant levels for public safety.
This application note describes the use of a pulsed flame photometric detector (PFPD) for determination of sulfur species in natural gas and LPGs by ASTM Method D 6228-11: Standard Test Method for Determination of Sulfur Compounds in Natural Gas and Gaseous Fuels by Gas Chromatography and Flame Photometric Detection.
Instrumentation used for this study was an OI Analytical SPRO-Select GC system equipped with a 5380 Pulsed Flame Photometric Detector. Two capillary PLOT columns were evaluated: the Agilent J&W Select Low Sulfur column and Agilent GS-GasPro column.
Two natural gas samples were blended for this project. Both contained five sulfur compounds at concentrations ranging from 3 to 6 ppmv, and one or more representative hydrocarbons found in different grades of natural gas. The composition of Sample #1 and its repeatability results on two different columns are shown in Table I.
Table I: Blended natural gas sample #1 and repeatability results on two GC columns
Any capillary column that can provide adequate separation of the target sulfur compounds can be used with the PFPD for ASTM Method D 6228-11. The columns evaluated in this study were chosen because of their superior peak shape, excellent sensitivity for sulfur compounds, and retention time repeatability. Figure 1 illustrates the simultaneous sulfur and hydrocarbon chromatograms obtained from Sample #2 using an OI Analytical SPRO-Select GC system and Agilent Select Low Sulfur column. For complete results of this study, refer to OI Analytical Application Note #3671 (1).
Figure 1: Simultaneous sulfur and hydrocarbon chromatograms obtained from a blended natural gas sample using the SPRO-Select GC system and Agilent J&W Select Low Sulfur column.
The SPRO-Select GC system equipped with a PFPD detects and measures sulfur species in natural gas by ASTM Method D 6228-11 with a high level of precision and accuracy, meeting all method requirements. Both capillary PLOT columns evaluated in this study yielded reproducible chromatograms with symmetric peak shape and chromatographic resolution of the sulfur and hydrocarbon peaks of interest.
(1) OI Analytical Application Note #3671, "Determination of Sulfur in Natural Gas by ASTM Method D 6228-11 Using a Pulsed Flame Photometric Detector (PFPD)."
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