Siloxanes Update.pdf

Siloxanes are man-made organic compounds containing silicon, oxygen, and methyl groups, used in personal hygiene, healthcare, and industrial products. They volatilize into digester gas and landfill gas, which can cause silicon dioxide deposits when combusted, leading to equipment damage. The Los Angeles County Sanitation Districts collected siloxane data and conducted pilot testing on removal methods.

Key findings include:
- Siloxanes are present in landfill gas, with D4 and D5 being the most common.
- Siloxane concentrations are higher in digester gas than in landfill gas.
- Common analysis methods include methanol impinger-GC/MS and metal canister-GC/MS.
- The methanol impinger method has reporting limits of 16-49 ppbv, while the metal canister method can detect all eight targeted siloxanes.
- Siloxane removal systems are available, but their cost-effectiveness is still being evaluated.

Selected properties of cyclic and linear organosiloxanes are listed in Table 1, including molecular weight, vapor pressure, boiling point, and water solubility. The most common siloxanes found in biogas are D4 and D5, with concentrations varying depending on the source.

Removal of siloxanes can help reduce maintenance costs, but its cost-effectiveness is still uncertain. Manufacturers of combustion turbines and reciprocating engines are increasingly interested in siloxane control, despite successful operation without controls in the past. Further research is needed to fully understand the impact of siloxanes on biogas utilization and to develop effective removal methods.