Influence of Sampling Methods and Storage Condition on Volatile Methyl Siloxanes Quantification in Biogas

Siloxanes are widely distributed in biogas and have a negative impact on energy applications of biogas. So far, there is no standard method for the sampling and analysis of siloxanes in biogas. The appropriate sampling method must ensure that the composition of samples collected in siloxanes does not change during sampling and analysis. To this end, three sampling methods (two-tandem (section A and B) impingers with acetone as adsorbent (TTIA), coconut activated carbon adsorbent tubes (CACT), and silica gel adsorbent tubes (SGT)) were evaluated in this paper. Hexamethyldisiloxane (L2), hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), and decamethylcyclopentasiloxane (D5) detected in section B were less than 7% of those in section A of three methods. The gas chromatography coupled with mass spectrometry (GC-MS) was used for quantitative analysis of the siloxane in samples. The results demonstrated that target compounds were completely adsorbed by three methods. For D3, D4, and D5, there was no significant difference between recovery rates of CACT and SGT, whereas they were higher than those of TTIA. The siloxane contents in dry synthesis gas collected by three methods were generally higher than those in wet synthesis gas. The effect of storage time and temperature on the short-term stability of siloxanes in SGT was further investigated. The contents of D3, D4, and D5 did not change significantly with storage temperatures except L2. However, the content of D3 stored at 25 ℃ was not stable over time, which reduced by 16.2% on average at 12 h.