Siloxanes in biogas and landfill gas

ALS offers reliable siloxane testing using ASTM D8230, along with expert sampling guidance and easy-to-understand reporting. This guide is designed to help operators make informed operational and compliance decisions.

What are siloxanes?

Siloxanes are silicon-oxygen compounds commonly used in everyday consumer and industrial products such as personal care products, cosmetics, cleaning products, lubricants, sealants and coatings. As these products break down in landfills or wastewater treatment systems, volatile methyl siloxanes (VMS) are released into the gas stream.

Why does siloxane removal matter?

Although siloxanes are typically present in biogas at relatively low concentrations, they can become a significant concern when the gas is used as a fuel source. During combustion, siloxanes are converted into silicon dioxide (silica), a hard, abrasive material that accumulates on engines, turbines, catalytic converters, heat exchangers, combustion chambers and other critical equipment surfaces.

Over time, these silica deposits can reduce equipment efficiency, increase maintenance requirements, shorten equipment life and lead to costly unplanned downtime.

Will high humidity affect the sample results?

Because some of the siloxane compounds are soluble in water (most notably Trimethylsilanol and D3), high humidity (>90%) may hinder overall siloxane recovery. Appreciable water buildup inside sampling tubes may also reduce the performance of the sorbent.

Laboratory analysis of siloxanes

Siloxane testing is valuable for organizations involved in biogas production, renewable energy and gas utilization. Understanding siloxane concentrations before combustion allows operators to determine when gas treatment is necessary and evaluate the effectiveness of existing siloxane removal systems.

ALS analyzes siloxanes using ASTM D8230, an industry-recognized method for determining volatile siloxanes in gas samples.

Our testing helps customers:

• Meet renewable natural gas (RNG) and pipeline quality requirements
• Select appropriate siloxane removal technologies
• Monitor treatment system performance
• Track changes in gas quality over time
• Generate defensible analytical data for regulatory and contractual requirements.

What are the sampling options?

Proper sample collection is essential for obtaining accurate siloxane results. ALS supports two common sampling methods:

• Sorbent tube sampling (recommended)
• Tedlar® bag sampling

Sorbent tube sampling is the preferred method due to its safety and performance advantages. Siloxane sorbent tubes are non-flammable and non-toxic, allowing them to be shipped via standard carriers such as UPS or FedEx.

This method enables the collection of larger sample volumes, resulting in lower reporting limits. Samples collected using sorbent tubes have a holding time of up to 14 days.

In contrast, Tedlar bag sampling has additional considerations. If the collected sample contains flammable concentrations of methane, the bag may be classified as dangerous or hazardous goods. In these cases, it is the shipper’s responsibility to properly characterize the sample and ensure compliance with applicable DOT regulations.

Due to the limit on sample volume, this method typically results in higher reporting limits. Samples collected in Tedlar bags must be transferred to a sorbent within 72 hours to extend the holding time.

See the siloxane sampling instructions

ALS laboratory reports

ALS offers the reliable analytical data you need to make confident decisions, protect critical equipment and maintain compliance. Every laboratory report provides clear, actionable data including:

• Individual siloxane compound concentrations
• Reporting limits and analytical units
• Quality control results, including blanks.
• Contact ALS today to request a quote or learn more about our siloxane testing services.