Abstract
The ISO 14687-2 standard sets requirements for the purity of the hydrogen that is delivered at refuelling stations. These specifications cover a wide range of impurities and include challenging measurements, mainly due to the very low levels of the required detection limits and the need for “total” measurements (total hydrocarbons, total sulphur compounds, halogenated compounds). Most of the compounds belonging to the species are organic. Thermal desorption often coupled with gas chromatography is a common speciation method used to determine the content of organic impurities. However, no existing sorbent tubes are sufficiently universal to trap all possible impurities; depending on the sorbents and the sampling volume, some compounds may irreversibly adsorb or may break through. It is therefore necessary to evaluate sorbents for the compounds targeted at the level required. In this study, the suitability of sorbent tubes for trapping organic impurities in hydrogen was investigated. Suitable sorbents were selected based on a literature review of suitable sorbent materials. Short-term stability studies for compounds among hydrocarbons, halogenated compounds and sulphur compounds on the selected sorbents have then been performed for storage periods of two weeks since this is the period typically required to complete the collection, transport and analysis of hydrogen samples. The study clearly shows that the method is promising for total species, even through the results show that not all of the compounds belonging to the three total species to be analysed when performing hydrogen purity analysis can be quantified on one unique sorbent. A multibed sorbent consisting of Tenax TA (weak), Carboxen 1003 (medium), Carbograph 1 (strong) is shown to be a versatile sorbent suitable for the three “total species”; only a few compounds from each family would need to be analysed using other analytical methods. This method proposed here for total species will not only provide a sum of concentrations, but also an identification of which compound(s) is/are actually present in the hydrogen.
Highlights
Hydrogen vehicles are currently commercially available from, or in development by, many manufacturers [1]
Due to the large number of impurities to analyse at stringent detection limits, performing the whole set of analyses required for hydrogen purity testing (ISO 14687) is both technically challenging and time-consuming for any laboratory and will require a combination of several analytical techniques or instruments
Vessels used to sample hydrogen from a refuelling station have not fully been tested to demonstrate that the concentration of gaseous impurities listed in ISO 14687 remain stable during sampling and transport, which is a requirement to ensure that the sample analysed is representative of the fuel delivered at the station
Summary
Hydrogen vehicles are currently commercially available from, or in development by, many manufacturers [1]. With regards to performance, fuelling time and range, these vehicles are nowadays comparable to conventional engines and have one major advantage: they only produce water in the exhaust. The implementation of these vehicles into the consumer market is necessary to help Europe meet the challenging targets for lowering carbon dioxide levels. The implementation of these vehicles requires the development of a sizable hydrogen fuelling infrastructure.
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