ASTM D5303 Standard Test Method for Trace Carbonyl Sulfide in Propylene by Gas Chromatography
3. Summary of Test Method
3.1 A procedure is given for removing a sample from the sample cylinder, separating COS from propylene, detecting COS, calibrating the detector, quantitating COS content in the sample, and assaying the gas standard. General comments and recommended techniques are given.
3.2 Arelatively large volume ofsample is injected into a gas chromatograph having a single packed column, operated isothermally at 10 to 50°C, that separates COS from propylene. COS is detected with a flame photometric detector.
3.3 Calibration data, based on peak areas, are obtained using a known gas standard blend of COS in the range expected for the sample. The COS peak area in the sample is measured and the concentration of COS calculated.
3.4 The COS gas standard blend is assayed prior to use for calibration.
4. Significance and Use
4.1 In processes producing propylene, COS usually remains with the C3 hydrocarbons and must be removed, since it affects product quality. COS acts as a poison to commercial polymerization catalysts, resulting in deactivation and costly process downtime.
4.2 Accurate gas chromatographic determination of trace COS in propylene involves unique analytical problems because ofthe chemical nature of COS and idiosyncracies of trace level analyses. These problems result from the reactive and absorptive nature of COS, the low concentration levels being measured, the type of detector needed, and the interferences from the propylene sample matrix. This test method addresses these analytical problems and ways to properly handle them to assure accurate and precise analyses.
4.3 This test method provides a basis for agreement between two laboratories when the determination of trace COS in propylene is important. The test method permits several calibration techniques. For best agreement between two labs, it is recommended that they use the same calibration technique.
5. Interferences
5.1 Hydrogen sulfide (H2S) or sulfur dioxide (SO2) can be present in the propylene and must be separated from COS. (See Note 2.)
NOTE 2 - H2S and SO2 are separated from COS with the Carbopack BHT 100 columns or with the Chromosil 300 column.
