The raw gas composition from primary aluminium production depends mostly on the process technology applied and the composition of the raw materials. At steady state, a stationary condition is established among the material sources, gas production and sinks: the gas treatment centre and escaping gases. Only a few papers discuss the off-gas composition itself; most papers deal with the gas composition from laboratory-scale experiments performed under inert conditions. In this article, an overview of the literature describing gas production from aluminium electrolysis is given. Effects of temperature and chemical equilibrium on the stationary condition are also discussed. The typical chemical composition of the raw materials is presented to evaluate their input into the gas composition, especially with respect to their impurity levels.

Maritime transport is investigating several options to reduce its greenhouse gases and air pollutant emissions. An experimental ship, Energy Observer, is using excess renewable energy to generate onboard hydrogen by electrolysis of purified seawater. As a promising option for storing energy, it can provide on-demand energy to the ship through a hydrogen fuel cell (FC). As hydrogen FCs lifetime and performance are correlated to hydrogen quality, the hydrogen produced onboard needs to be monitored. This study assesses the probability of contaminants presence for this electrolyser, using purified seawater and supports the results with a hydrogen fuel quality analysis from the Energy Observer ship. It demonstrates that an electrolyser using onboard purified seawater can generate hydrogen of a quality compliant with ISO 14687:2019. Additional contaminants (i.e., ions, heavy metal) were also measured. The study highlights the potential contaminants to be monitored and future research on new contaminants from seawater to further develop hydrogen fuel for maritime applications.

As part of FCH-JU funded HyCoRA project running from 2014 to 2017, 28 gaseous and 13 particulate samples were collected from hydrogen refueling stations in Europe. Samples were collected with commercial sampling instruments and analysis performed in compliance with prevailing fuel quality standards. Sampling was conducted with focus on diversity in feedstock as well as commissioning date of the HRS. Results indicate that the strategy for sampling was good. No evidence of impurity cross-over was observed. Parallel samples collected indicate some variation in analytical results. It was however found that fuel quality was generally good. Fourteen analytical results were in violation with the fuel tolerance limits. Therefore, eight or 29% of the samples were in violation with the fuel quality requirements. Nitrogen, oxygen and organics were the predominant impurities quantified. Particulate impurities were found to be within fuel quality specifications. No correlation between fuel quality and hydrogen feedstock or HRS commissioning date was found. Nitrogen to oxygen ratios gave no indication of samples being contaminated by air. A comparison of analytical results between two different laboratories were conducted. Some difference in analytical results were observed.