Analytical Sciences

Determination of Water Content of Nitrogen Containing Hydrogen Sulfide by Karl Fischer Coulometric Titration

Xuting ZHI,* Haifeng WANG,** Baijun LIU,* Xiaoping SONG,** Zhanyuan LI,** and Jia LI**

*China University of Petroleum-Beijing, Beijing 102249, China
**National Institute of Metrology of China, Beijing 100029, China

Measuring the water content in natural gas is important for safety; however, complex matrixes make the results inaccurate. Natural gas contains hydrogen sulfide (H₂S), which react with iodine (I₂), causing Karl Fischer coulometric titration (KFCT) to give higher results. The KFCT method for the determination of water content of nitrogen containing H₂S was investigated. A chilled mirror hygrometer offered a reference water content to calibrate the KFCT. The interfering of H₂S was reduced by subtracting I₂ consumed by H₂S according to the reaction mechanism of ISO 10101; however, the modified results remained higher. A possible reaction mechanism with a stoichiometry of H₂S to I₂ of 1:2.5 was proposed. The improved KFCT method had an error of water content no more than (3 + 2%·x) mg/kg (x, water content in mg/kg) and had the potential of online monitoring of natural gas.

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