Liquefied petroleum gas sampling

Simple evaporation tests in conjunction with vapor pressure measurement give a further guide to composition. In these tests a liquefied petroleum gas sample is allowed to evaporate naturally from an open graduated vessel. Results are recorded on the basis of volume and temperature changes, such as the temperature recorded when 95% has evaporated or the volume left at a particular temperature (ASTM D1837). 

Because dew point can be calculated from composition, direct determination of dew point for a particular liquefied petroleum gas sample is a measure of composition. It is, of course, of more direct practical value and if there are small quantities of higher-molecular-weight material present, it is preferable to use a direct measurement. 

Total sulfur in gas can be determined by combustion (ASTM D-1072), by the lamp method (ASTM D-1266), or by hydrogenation (ASTM D-3031, ASTM D-4468). Trace total organic and bound nitrogen is determined (ASTM D-4629). The current test method for heavy residues in liquefied petroleum gas (ASTM D-2158) involves evaporation of a liquefied petroleum gas sample, measuring the volume of residue and observing the residue for oil stain on a piece of filter paper. 

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