Influence of sampling methods and storage condition on volatile methyl siloxanes quantification in biogas

Abstract

There has been no standard method for sampling and analysis of siloxane 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 absorbent (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 the three methods. The gas chromatography coupled with mass spectrometry (GC-MS) was used for quantitative analysis of the siloxane in the samples. The results demonstrated that target compounds were completely adsorbed by the three methods. For D3, D4, and D5, recovery rates of CACT were 103%, 126%, and 120%, recovery rates of SGT were 114%, 112%, and 114%, and recovery rates of TTIA were 45%, 86%, and 92%, respectively. According to the one-way analysis of variance test, 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 contents of D3, D4, and D5 did not change significantly with storage temperatures except L2. However, the content of D3 stored at 25 °C was unstable over time, which reduced by 16% on average at 12 h.