Fuel for Thought

New Application Notes Highlight Case Studies for Latest ASTM Revisions for GC Residue Analysis of LPG

Apr 27 2017 Comments 0

ASTM recently updated the LPG specification standard D1835-16 to include the gas chromatographic (GC) method for residue analysis: D7756-13. This GC method is based on the Liquefied Gas Injector technique developed by Da Vinci Laboratory Solutions, which eliminates the need to evaporate the liquefied gas.

When performing analysis of automotive LPG by the oil stain method, control over residue content is essential in end-use applications. Residues can lead to an accumulation of tiresome deposits that may corrode or plug the fuel filter, the regulators, the fuel mixer or the control solenoids. The revised specification standard for oily residue in LPG lists ASTM Method D2158- the oil stain method- and D7756 -the GC method.

D2158 requires the evaporation of 100 milliliters of LPG. After evaporation, the remaining volume of the residue is read from the glass evaporation tube. Next step is to dissolve the residue in a solvent, drip the resulting solution slowly onto the adsorption paper. The size and persistence of the stain, which remains on the paper after the solvent evaporates, is the second quantification of the oily residue. Both quantifications are not very accurate and offer a safety risk due to the evaporation of the flammable LPG samples.

For GC residue analysis in LPG, Da Vinci Laboratory Solutions have developed a safe, fast and accurate technique to determine oily residue in C3 and C4 streams: the Liquefied Gas Injector. The technique has been standardised as ASTM D7756 & EN 16423 and uses a direct injection technique.

The direct injection approach of the Liquefied Gas Injector includes the proven fuel direct injection technique used by the automotive industry to inject fuel into the automotive engine combustion chamber. The LGI is connected to a standard GC injector needle, which is inserted into a GC large volume on-column injection system. Solenoid activation transfers the pressurised sample through the needle directly on-column. A sliding device moves the needle downwards for the injection and upwards for purging.

The sample is injected under a constant pressure. The chromatographic analysis after the sample introduction is based on boiling point separation of the oily residues and contaminants.
The total residue is quantified using area summation of the components in the range of C10 to C40. The result is reported in parts per million (w/w) of residue in LPG.

Several case studies demonstrate an excellent and fast performance of the LGI. The case studies are described in the various application notes available from Da Vinci, these are: ‘Oily residues and light contaminants in LPG (ASTM D7756, EN 16423)’, ‘Hydrocarbon composition of LPG (ASTM D 2163, ISO 7941)’, ‘Sulphur compounds in liquefied petroleum gases’, ‘Desulphurisation additives in LPG: DIPA, MEA and DEA’, ‘Inhibitors, additives and Dimers in Butadiene: ACN, ρTBC, Butadiene Dimer’ and ‘Nitrogen, carbon dioxide, hydrogen sulfide and C1-C36+ hydrocarbons in unstabilised gas condensate.’.

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