CARBONYL SULFIDE IN PROPYLENE BY GAS CHROMATOGRAPHY: D5303
EXPLANATION
In processes producing propylene, COS usually remains with the C3 hydrocarbons, and must be removed since it affects the product quality. COS acts as a poison to commercial polymerization catalysts, resulting in deactivation and costly process downtime. This test method overcomes a unique physical problem involved in COS measurement due to its reactive and absorptive nature and trace levels present. The test method permits several calibration techniques. For best agreement between two labs it is recommended that they use the same calibration technique. The method is applicable to COS concentrations from 0.5 - 4.0 mg/ kg; however, the lower limit of detection of this method is believed to be below 0.1 mg/ kg.
TEST SUMMARY
The test method gives a procedure 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. A relatively large amount of sample is injected into a gas chromatograph having a single packed column, operated isothermally at 10 - 50° C, that separates COS from propylene. COS is detected with a flame photometric detector. 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.
Hydrogen sulfide and sulfur dioxide can be present in the propylene and must be separated from COS. This can be done with the Carbopack BHT 100 columns or with the Chromosil 300 columns.
TEST PRECISION
Repeatability: 0.15 X
Reproducibility: 1.0 X
Where X is the average of two results in mg/kg.
The bias of this method has not been determined since there is no acceptable reference material suitable for this analysis.
