Graphene Membranes Could Turn Methane From Pollutant To Source Of Power

Graphene's suitability as a filter has led to many exciting possible uses, but the capture of methane from biogas could be the biggest yet, removing a major source of warming gasses and providing a carbon-neutral fuel. Hinkle Group CC By-NC-SA 2.0

The world is concerned about reports of methane erupting from the floor of the Arctic Ocean, but so far the quantities are considerably smaller than what is released from our own landfills and waste. Some of this is captured and burned for clean electricity, but now the wonder material graphene may be about to make that much more widespread.

Methane is produced by anaerobic bacteria, which break down organic material in the absence of oxygen. The wastewater treatment plants of our major cities provide a perfect environment, producing around 25 million tonnes each year.

Capturing and burning this methane prevents it from reaching the atmosphere, where it is a far more powerful greenhouse gas than carbon dioxide. If the energy generated is used, it displaces fossil fuels. However, so-called biogas collected from waste facilities usually contains impurities, notably carbon dioxide, that hinder its use. Dr Rakesh Joshi of the University of New South Wales has demonstrated that graphene membranes can separate methane from other gasses more effectively than existing systems, potentially making the collection and burning of waste methane viable where it currently isn't.

Ironically, Joshi didn't start out working on methane. Instead, he was attempting to use graphene (single layers of carbon in a hexagonal lattice) to help Sydney Water improve their water purification process to remove organic material from its wastewater and make it drinkable. Joshi has demonstrated the capacity of graphene to take out 99 percent of the impurities other water processing techniques left behind.

In the process, Joshi realized Sydney Water was also filtering its biogas to power its own operations and wondered if graphene could do a better job by tuning the size of the holes in graphene's honeycomb structure. Not only did he confirm this, but he told IFLScience that graphene membranes are cheaper to make than existing options.

Although it produces carbon dioxide when burned, methane from wastewater ultimately comes from breaking down plants that draw equal amounts of carbon from the atmosphere, making it a greenhouse neutral energy source that can balance out renewable electricity grids during periods of low sun and wind.

So far, the effectiveness of the technique has only been demonstrated at laboratory scale, but Sydney Water's Dr Heri Bustamante is hopeful: “The use of graphene will enable increased capture of methane to expand potential uses beyond the requirements of Sydney Water. Production of methane to fuel buses could be a potential future use, for example,” he said in a statement

The inventors are thinking even bigger. Joshi told IFLScience the idea of capturing gas produced by natural wetlands and separating out the methane “is also a goal for the future.”

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