How everyday products are supercharging landfill gas, and what that means

November 13, 2019

ANN ARBOR--Synthetic compounds increasingly used in everyday products like shampoo and motor oil are finding their way into landfills and supercharging the biogas those landfills produce, researchers at the University of Michigan have found.

While it's a problem today, the researchers say it could be an opportunity to get more energy out of landfill gas.

The compounds, called "siloxanes," are efficient at conducting heat and interacting with water, and as such their popularity has increased in a variety of consumer products. That means more and more siloxanes are headed to your local landfill.

Biogas refers to fuel gases that are synthesized from different biological or organic feedstocks like landfill gas and wastewater treatment plants. In recent years, it has become clear that siloxanes have been damaging the power-generating equipment that's fueled with landfill gas. But the researchers say the siloxanes could actually be harnessed to produce more energy.

The U-M team conducted the first chemical analysis of how siloxanes affect biogas. The researchers found that siloxanes increase the reactivity of biogas, leading to faster ignition in engines and the release of more energy. But those engines--typically power-generating gas turbines and reciprocating piston engines--can be damaged by the siloxanes in the biogas.

"Siloxanes are highly ignitable," said Margaret Wooldridge, the Arthur F. Thurnau Professor of Mechanical Engineering and director of the Dow Sustainability Fellows Program at U-M. "They change the chemistry of biogas like crazy. The stuff is like rocket fuel, literally--crazy-reactive."

The siloxanes essentially change the biogas's "flame speed," which is a measure of how quickly a fuel combusts and drives a turbine or piston.

Biogas is composed mainly of methane. Methane gas is found in nature but it is also produced when organic material decomposes in landfills, along with hydrogen, carbon monoxide, and other hydrocarbons. Methane is the main component of natural gas and biogas, making both valuable sources of fuel and energy that are cleaner than coal.

In the atmosphere, however, methane is particularly good at trapping heat, adding to our global warming problem. In particular, methane is 30 times more effective a greenhouse gas than CO2. And according to the EPA, municipal solid waste landfills account for 14% of all human-related methane emissions in the U.S. each year--the third-largest source behind the gas and petroleum industry and agriculture.

That property has spurred efforts to capture methane from landfills and use it as a fuel, instead of allowing it to escape unchecked.

Measuring 'ignitability'

In this study, U-M researchers separately tested hydrogen and carbon monoxide mixtures containing two siloxanes--trimethylsilanol (TMSO) and hexamethyldisiloxane (HMDSO)--against hydrogen and carbon monoxide mixtures with no siloxanes.

Specifically, the researchers clocked how long it took for each mixture to ignite. Fuels that have a shorter ignition delay are considered more ignitable or reactive--and hydrogen is one of the most reactive fuels we use.

Hydrogen and carbon monoxide with TMSO produced ignition delay times that were 37% faster than the reference case. And HMDSO-infused methane produced delay times 50% faster.

The results of U-M's research are published in the latest edition of Combustion and Flame. Researchers hope their work sheds light on how siloxanes alter engine performance when used as a fuel.

"Trace concentrations of siloxanes have been a known problem in biogas applications--leading to the formation of abrasive silica deposits on engine components," said Rachel Schwind, a doctoral student and study co-author. "For this reason, most prior research in this area has focused on how to remove them from the captured gas."

Harnessing siloxanes, rather than removing them

Along with the problem siloxanes pose, there is also potential. Wooldridge said siloxanes could be key to deriving bolstered energy production from biogas.

"We would love to be able to harness them as an energy source," she said.

Analyzing the combustion chemistry is a step in that direction.

"That would potentially negate the need for scrubbing or removal during biogas processing and reduce costs," Schwind said. "If we can reduce those costs, it moves biogas closer to being a truly carbon neutral fuel. And if we can make landfill gas a more economically attractive option, landfill operators will have more incentive to capture and utilize this harmful greenhouse gas."
The research was supported by the U.S. Department of Energy's Basic Energy Sciences program.

Study: Effects of Organic Silicon Compounds on Syngas Auto-ignition Behavior

Wooldridge Combustion Laboratory

University of Michigan

Related Methane Articles from Brightsurf:

When methane-eating microbes eat ammonia instead
As a side effect of their metabolism, microorganisms living on methane can also convert ammonia.

Making more of methane
Looking closely at the chemical process that transforms methane into useful products could help unveil more efficient ways to use natural gas.

Methane: emissions increase and it's not a good news
It is the second greenhouse gas with even a global warming potential larger than CO2.

Measuring methane from space
A group of researchers from Alaska and Germany is reporting for the first time on remote sensing methods that can observe thousands of lakes and thus allow more precise estimates of methane emissions.

New 3D view of methane tracks sources
NASA's new 3-dimensional portrait of methane concentrations shows the world's second largest contributor to greenhouse warming.

Show me the methane
Though not as prevalent in the atmosphere as carbon dioxide, methane is a far more potent greenhouse gas.

Containing methane and its contribution to global warming
Methane is a gas that deserves more attention in the climate debate as it contributes to almost half of human-made global warming in the short-term.

Microorganisms reduce methane release from the ocean
Bacteria in the Pacific Ocean remove large amounts of the greenhouse gas methane.

Origin of massive methane reservoir identified
New research provides evidence of the formation and abundance of abiotic methane -- methane formed by chemical reactions that don't involve organic matter -- on Earth and shows how the gases could have a similar origin on other planets and moons, even those no longer home to liquid water.

Unexpected culprit -- wetlands as source of methane
Knowing how emissions are created can help reduce them.

Read More: Methane News and Methane Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to