Siloxane Testing

Analytical testing dots Siloxane Testing

Siloxanes are organic and inorganic chemical compounds comprised of silicon, oxygen, and usually carbon and hydrogen. They are based on the structural unit R2SiO, where R is a hydrogen atom or a hydrocarbon group, and belong to the wider class of organosilicon compounds.

Siloxanes can be found in products such as cosmetics, deodorants, defoamers, water-repelling windshield coating, food additives and some soaps. They are being evaluated as alternatives to perchloroethylene (PCE) for dry cleaning.

When combusted, silicon-containing compounds such as siloxanes react to form silicon dioxide. When these compounds are present in applications where combustion engines are utilized, such as landfill-gas-to-energy or biogas-to-energy operations, the combustion can result in the formation of deposits on the internal components of the engines. These deposits can greatly impede the performance efficiency of the power-generating turbines; therefore siloxanes should be removed from the gas by either chemical or mechanical means.

While siloxanes are not currently considered to pose risks to human health, they can have very real mechanical impacts on power-generating equipment.

The following is a list of common siloxanes, also referred to as volatile organic silicon compounds (VOSCs):

Name Formula Abbreviations
Hexamethylcyclotrisiloxane C12H18O3Si3 D3
Octamethylcyclotetrasiloxane C8H24O4Si4 D4
Decamethylcyclopentasiloxane   C10H30O5Si5 D5
Dodecamethylcyclohexasiloxane C12H36O6Si6 D6
Hexamethyldisiloxane C6H18Si2O   L2, MM
Octamethyltrisiloxane C8H24Si3O2 L3, MDM  
Decamethyltetrasiloxane C10H30Si4O3 L4, MD2M  
Dodecamethylpentasiloxane C12H36Si5O4 L5, MD3M  
Trimethysilanol C3H10OSi TMS

D3, D4, D5, L2, L3 and TMS are the siloxanes most commonly detected in landfill gas.

ALS Environmental has developed a novel sampling and analytical approach for siloxanes. It involves collecting landfill gas with a sorbent tube, followed by extraction at the laboratory and analysis by gas chromatography/mass spectrometry.

Benefits of this new approach:

  • Sampling is relatively simple. It does not require ice baths or complicated setups. Depending on the configuration of the sampling location, it can be as simple as connecting a length of tubing to a sampling port, connecting a rotameter to moderate the flow rate, and attaching the sample tube. After approximately 30 minutes, the sampling is completed, and the tubes may be disconnected and submitted to the lab for analysis.
  • Since the samples are collected on tubes, rather than with impingers of methanol solutions or in bags with flammable landfill gas, they do not represent a Dangerous Good or Hazardous Material. Therefore, they can be shipped more cost-effectively by normal shipping procedures. They do not require special boxes, containers, labels, documentation or procedures.
  • The data is reported in several units: µg/Tube, µg/m³, and as µg/m³ as Silicon, to accommodate a variety of uses or calculations by the end user.

Our Sampling Kit comes with all the equipment necessary to collect a sample of landfill gas or biogas:

  • A rotameter
  • A pre-set slip stream: Stainless steel T-fitting equipped with ¼’’ silicone tubing fitted with a plug. The slip stream is used to provide an outlet for excess pressure. When the rotameter constricts the flow of the gas to reach the correct sample flow rate, the slip stream provides an outlet to avoid a buildup of back pressure in the sampling train.
  • Extra nuts and ferrules
  • Labeled calibration tube
  • Sample sorbent tube: Specially prepared from the laboratory. Tubes may be stored at ambient temperature.
  • Silicone tubing for connections

For a full sampling guide, download our PDF.

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ALS Environmental offers the following methods often used to characterize biogas:

  • Methane by EPA Method 3C modified or EPA Method 25C modified
  • Carbon Dioxide by EPA 3C modified
  • Hydrogen, Oxygen, Nitrogen, Carbon Monoxide by EPA 3C modified
  • TNMOC by EPA 25C modified
  • BTU analysis by ASTM D3588
  • Hydrogen Sulfide and reduced sulfur compounds by ASTM D5504
  • VOCs by EPA TO-15
  • Siloxanes by CAS in-house method

Analytical testing dotsLearn more about Landfill Gas Monitoring...

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