Evaluation of sampling techniques for gas-phase siloxanes in biogas

Biogas from landfills and wastewater treatment facilities typically contain siloxane contaminants that can cause severe operational problems in engines and boilers when biogas is used as fuel. Likely due to their relatively low volatility, reliable siloxane sampling and analysis has proven challenging, and no standard sampling technique for gas-phase siloxanes exists, leading to high variability in analytical results. This study evaluates four techniques commonly used for sampling gas-phase siloxanes. Samples of a reference gas containing decamethylcyclopentasiloxane (D5) were taken using these techniques and measured D5 concentrations were compared to the reference gas D5 concentration. Methanol impingers and thermal desorption tubes proved to be most accurate and reliable, whereas Tedlar (R) bags and SUMMA canisters yielded lower D5 recovery rates due to adsorption to container surfaces. Based on these results, the methanol impinger and thermal desorption tube sampling methods appear to be more suitable for the quantitative analysis of gas-phase siloxanes in biogas.