Chemical diversity and residual levels of trace compounds in grid-injected biomethane: Multi-analytical eight-year study.

This eight-year study characterized trace compounds in grid-injected biomethane from methanization using a multi-analytical strategy combining broad thermal desorption gas chromatography-mass spectrometry (TD-GC/MS) screening with targeted quantitative methods. Between 2016 and 2023, 75 sampling campaigns were conducted at 40 French biomethane injection plants, covering diverse feedstocks and upgrading technologies. 530 organic compounds across nine chemical families were identified by TD-GC/MS. Of these, 65 calibrated compounds were quantified and 465 non-target compounds were semi-quantitatively estimated as order-of-magnitude concentrations. Most compounds occurred sporadically and at low levels: only 100 were detected in more than ten samples, whereas 207 appeared only once, with an average of 48 trace compounds per sample. Average concentrations were generally low, with only 13 % exceeding 100 µg/Nm3. Hydrocarbons were dominant, followed by oxygenated compounds, while terpenes, organic sulfur compounds, siloxanes, halocarbons and amines occurred less frequently. Chemometric analysis of 45 selected TD-GC/MS compounds showed broadly similar biomethane trace profiles, with no robust clustering by feedstock or upgrading technology. Targeted analyses quantified compounds of regulatory or operational relevance, including monoaromatic hydrocarbons, terpenes, sulfur species, ammonia, mercury and trace elements. Regulated sulfur species, ammonia, mercury and siloxanes remained below current injection requirements, and compounds shared with conventional natural gas were generally comparable to or lower than natural-gas reference levels. This information-rich dataset demonstrates the complementarity of analytical strategies and shows that grid-injected biomethane contains a chemically diverse but low-abundance trace-compound fraction, supporting secure grid integration and future monitoring, standardization and specification evolution.