Determination of Siloxanes and other Volatile Silicon Compounds in Biogas Samples Using Sample Preconcentration with GC-MS and GC-ICP-MS.

Organic silicone compounds, used in a wide range of household and commercial products, ultimately make their way into landfills and wastewater treatment facilities. Many of these compounds are volatilized into the methane-rich biogas produced by landfills and anaerobic digesters of wastewater treatment plants. The biogas, a valuable source of renewable energy, can be collected and used as a fuel for combustion engines. During combustion, volatile silicon compounds (VSiCs), including siloxanes, are converted into silica particles that can coat surfaces, mask catalyst pores, cause abrasion damage and increase maintenance costs. Scrubbers used to control VSiC levels in the biogas must be evaluated regularly, so a variety of sample collection and quantification methods have been investigated. There is also interest in quantifying siloxanes in air and gas streams that are regulated for photochemical smog precursors. Fully methylated siloxanes are exempt from the photochemically reactive volatile organic compound (VOC) compound list but are measured using standard methods for the analysis of non-methane non-ethane organic compounds (NMNEOCs). Accurately quantifying NMNEOCs without including the VOC-exempt fully methylated siloxanes requires an accurate and sensitive method for VSiC analysis. This paper describes a method of analysis for VSiCs that allows the use of a sample preconcentration system with gas chromatography/mass spectrometry (GC-MS). This method can detect low concentrations of VSiCs, including eight relevant fully methylated siloxanes, in biogas. We are also developing a method for the use of a gas chromatograph/inductively coupled plasma/mass spectrometer (GC-ICP-MS) to speciate VSiCs and quantify the silicon levels of each compound, as well as total silicon concentration in the sample.