Thermal Desorption Hyphenated to Comprehensive Two-Dimensional Gas Chromatography-Time-of-Flight Mass Spectrometry for Trace Analysis in Raw Renewable Gases–Application to Hydrothermal Gasification

In the context of the energy transition, European countries pursue the common goal of increasing the share of renewable gases (from anaerobic digestion, pyrogasification, and hydrothermal gasification for instance) in the gas mix. Although produced gases are mainly composed of methane after upgrading, impurities of various natures and quantities may also be present in the produced raw gases and still after upgrading, including volatile organic compounds (VOCs) at trace levels that may have an impact on different stages of the gas chain even at low concentrations. These new renewable and/or low-carbon gases imply the need to develop new analytical tools to deeply characterize them, and thus fully manage their integration into the gas value chain. In this study focused on VOC analysis, a sampling approach using pre-concentration on an adsorbent phase was developed for gas sampling to ensure rapid collection, requiring only a small volume (≈ 100 mL). Traces were then analyzed by thermal desorption hyphenated to a comprehensive two-dimensional gas chromatography time-of-flight mass spectrometer. After identifying the compounds, a semi-quantification method was developed to provide an estimation of the concentration of VOCs for each chemical family. The method was first developed on a biomethane sample before being successfully applied to a raw gas produced by hydrothermal gasification, in which around 250 compounds were detected at a trace level (total concentration equivalent at 200 µg/L).