Odor fading in natural gas distribution systems

•Odor fading happens due to mercaptan adsorption on iron oxide layer inside pipelines.•Odor fading is affected by pressure, temperature, rust amount, and gas flow rate.•Mercaptan is adsorbed more in more rust, and at higher pressure and temperature.•Lower gas flow rate and lower odorant concentration, increase mercaptan adsorption. Since natural gas is odorless, to assure the customer safety, odorants are added to it to alarm the consumer in the case of a gas leak. Although the odorization is a common practice in natural gas distribution systems, odor fading has been reported in pipelines, which is a great safety risk. This paper summarizes results of experiments conducted to investigate possible chemical and physical mechanisms responsible for odor fading. In these experiments, X-ray photoelectron spectroscopy (XPS) and gas chromatography were used to check the possible interactions of tertiary butyl mercaptan (TBM) as odorant with the pipe material. Evidences of chemisorption, adsorption and desorption of TBM on the iron oxide inside the pipe were observed. It was found that by increasing pressure, rusted surface of the pipe, and temperature or by decreasing the gas flow rate and odorant concentration the mercaptan removal was increased.