A Safe and Fast Solution for Accurate Quantification of Heavy Residues in LPG by Gas Chromatography: Representative Liquefied Gas Sample Introduction via High Pressure On-Column Injection into a Gas Chromatographic System - Lenny Kouwenhoven & Ani

One of the specifications of commercial LPG is the amount of oily residue. Oily residue leads to troublesome deposits that will accumulate and corrode or plug the LPG fuel filter, the pressure regulators, the fuel mixer or

the control solenoids. Currently ASTM D2158 or ISO 13757 are used. These methods main disadvantage is that large amounts of LPG need to be evaporated which is a safety risk. The preferred alternative technique is gas

chromatography. However, the quantitative analysis of high boiling components in low boiling matrices is an analytical challenge. The limitation is the sample introduction. Residue adsorption on transfer lines, vaporisers

and valves lead to cross sample contamination or quantitative bias due to the fractionation of the heavy material. A new liquefied gas injector is developed by Da Vinci Europe to inject under pressure directly onto the

column. The sample remains in liquid phase, at room temperature and without contact with transfer lines, vaporisers or valves and therefore overcomes all limitations of the conventional sample introduction techniques.

The chromatography after this representative sample introduction is based on boiling point separation and the total amount is reported in parts per million.

Control over the residue content is essential in end-use applications of automotive LPG. These residues can lead to troublesome deposits that will accumulate and corrode or plug the LPG fuel filter, the low pressure

regulators, the fuel mixer or the control solenoids.

LPG can become contaminated by oily residues during its production or transport. Transport contamination can come from shared pipelines, valves and trucks used for the distribution of other products. Production sources such as the desulfurisation process may contribute sulfur absorbent oil to the LPG stream.

Commercial LPG, especially automotive applications, should comply with current fuel specifications for oily residue as described in ASTM Method D2158[1] or ISO 13757[2]. ASTM Method D2158 is commonly called oil stain method. After evaporating 100 milliliters of the LPG stream, the residue is dissolved in a solvent and the resulting solution is slowly dripped on the adsorption paper. The size and persistence of the stain which

remains on the paper after the solvent evaporates is an empirical measure of the oily residue in the LPG sample.

The ISO 13757 method quantifies the oily residue by weighing what remains after evaporation of two kilograms of the LPG. Both of these procedures offer an undue safety risk due to the required evaporation step

into the immediate environment.