Biogas Diagnostics: Sampling and Analysis for Simplified Quantification of Siloxanes in Biogas

Siloxanes have long been a nuisance for the energy use of biogas – right from physical damage caused by silica particles formed during combustion to deactivation of active sites in fuel cell applications. Irrespective of whether improved gas cleaning systems need to be developed or more resilient energy infrastructure should be designed, accurate and traceable quantification is needed to deal with this trace pollutant. This study demonstrates the efficacy of a liquid quench sampling system (LQ) in capturing and pre-concentrating siloxanes present in biogas, which can be stored for at least 4 weeks, within 10% stability accuracy. LQ allows on-site biogas sampling with a relatively simpler workflow of sample handling, storage and quantification compared to existing gas sampling methods. The calibration can be done using liquid standards, thereby, eliminating the complications of working with gaseous standards. The quantification is done using a gas chromatograph hyphenated with an inductively coupled plasma mass spectrometer (GC-ICP-MS). The LQ can operate over a broad concentration range and capture the siloxanes with >94% efficiency. This opens up the possibility of measuring siloxanes concentrations across different biogas systems and determining the gas cleaning efficiency. The application of the here presented LQ-GC-ICP-MS method for siloxane analysis has the potential for a significant techno-economic impact, enabling the optimization of biogas systems across various applications. By being able to quantify siloxanes at lower concentrations, this method ensures that the biogas operation remains within safe and efficient operating parameters, even when the biogas comes from heterogeneous waste or biowaste feedstocks.