ISO 6978-2 specifies a method for the determination of total mercury content of pipeline quality natural gas using a sampling method by amalgamation on gold/platinum (Au/Pt) alloy thread. This method is applicable to the sampling of raw natural gas when no condensation is present. At atmospheric pressure, this method is suitable for the determination of mercury content within the range of 0,01 μg/m3 to 100 μg/m3 in natural gas samples.
At higher pressures (up to 8 MPa), this sampling method is suitable for the determination of mercury contents within the range of 0,001μg/m3 to 1 μg/m3. The collected mercury is determined by measuring the absorbance or fluorescence of mercury vapour at 253,7 nm.
Note: ISO6978-1 gives a sampling method suitable for the determination of mercury contents in natural gas by chemisorption on iodine-impregnated silica gel for the working range of 0,1 μg/m3 to 5 000 μg/m3 for sampling at pressures up to 40 MPa.
ISO 6978-2 on determination of total mercury content of pipeline quality natural gas is useful for:
Natural gases may contain considerable amounts of mercury, which are generally present in the elemental form. Gases with high mercury content have to be purified to avoid the condensation of mercury during processing and transport as well as to be compliant with the demands of gas sales contracts. Low mercury concentrations are specified when natural gas is to be liquefied. This is to avoid severe corrosion problems, for instance in aluminium heat exchangers of liquefaction plants.
Since the presence of hydrocarbons, in particular aromatic hydrocarbons present in low concentrations in almost every natural gas, interferes in the determination of mercury by atomic absorption spectrometry (AAS)or atomic fluorescence spectrometry (AFS), mercury cannot be determined directly in natural gas. Therefore, prior to the analytical determination, mercury has to be collected and separated from aromatic hydrocarbons.
The purpose of ISO 6978-2 for the determination of the mercury content is:
Several methods for the collection or enrichment of mercury from natural gas have been developed. The collection of mercury from dry natural gas normally poses no particular problem. However, care should be taken when sampling mercury from natural gases under nearly condensing conditions (see ISO 6570). The two parts of ISO 6978 describe the principles of sampling and specify the general requirements for methods for sampling mercury and for determining total mercury in pipeline quality natural gas.
ISO 6978-2 specifies a method of sampling mercury by amalgamation on gold/platinum alloy thread whereas Part 1 specifies a method of sampling mercury by chemisorption on iodine-impregnated silica gel.
EN ISO 6978-2:2005/AC:2016
ISO 6978-2:2003/COR 1:2004
ISO 6978-2:2003/Cor 2:2006