Filter may be a match for fracking water

A new superhydrophilic filter has proven able to remove greater than 90 per cent of hydrocarbons, as well as all bacteria and particulates from contaminated water produced by hydraulic fracturing (fracking) operations at shale oil and gas wells, according to researchers at the Energy Safety Research Institute at Swansea University in collaboration with researchers at Rice University.

The work by Prof Andrew R Barron and his colleagues turns a ceramic membrane with microscale pores into a superhydrophilic filter that “essentially eliminates” the common problem of fouling.

The researchers determined one pass through the membrane should clean contaminated water enough for reuse at a well, significantly cutting the amount that has to be stored or transported.

The work is reported in Nature's open-access Scientific Reports.

The filters keep emulsified hydrocarbons from passing through the material's ionically charged pores, which are about one-fifth of a micron wide, small enough that other contaminants cannot pass through. The charge attracts a thin layer of water that adheres to the entire surface of the filter to repel globules of oil and other hydrocarbons and keep it from clogging.

A hydraulically fractured well uses more than 5 million gallons of water on average, of which only 10 to 15 per cent is recovered during the flow back stage, Barron said.

“This makes it very important to be able to re-use this water”

Not every type of filter reliably removes every type of contaminant, he said.

Solubilized hydrocarbon molecules slip right through micro filters designed to remove bacteria. Natural organic matter, like sugars from guar gum used to make fracking fluids more viscous, require ultra- or nanofiltration, but those foul easily, especially from hydrocarbons that emulsify into globules. A multistage filter that could remove all the contaminants isn't practical due to cost and the energy it would consume.

Frac water and produced waters represent a significant challenge on a technical level. If you use a membrane with pores small enough to separate they foul, and this renders the membrane useless. In our case, the superhydrophilic treatment results in an increased flux (flow) of water through the membrane as well as inhibiting any hydrophobic material – such as oil – from passing through. The difference in solubility of the contaminants thus works to allow for separation of molecules that should in theory pass through the membrane.

Barron and his colleagues used cysteic acid to modify the surface of an alumina-based ceramic membrane, making it superhydrophilic, or extremely attracted to water. The superhydrophilic surface has a contact angle of 5 degrees.

The acid covered not only the surface but also the inside of the pores, and that kept particulates from sticking to them and fouling the filter.

In tests with fracking flow back or produced water that contained guar gum, the alumna membrane showed a slow initial decrease in flux — a measure of the flow of mass through a material — but it stabilized for the duration of lab tests. Untreated membranes showed a dramatic decrease within 18 hours.

The researchers theorized the initial decrease in flow through the ceramics was due to purging of air from the pores, after which the superhydrophilic pores trapped the thin layer of water that prevented fouling.

“This membrane doesn't foul, so it lasts,” Barron said. “It requires lower operating pressures, so you need a smaller pump that consumes less electricity. And that's all better for the environment.”

“Fracking has proved highly controversial in the UK in part as a result of the pollution generated from produced waters”, co-author Darren Oatley-Radcliffe, an associate professor, at Swansea University, said, “However, with this new super-hydrophilic membrane we can clean up this waste produced water to a very high standard and recycle all of the materials, significantly improving the environmental performance of the fracking process.”

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Rice alumnus Samuel Maguire-Boyle is lead author of the paper. Co-authors are Rice alumnus Joseph Huseman; graduate student Thomas Ainscough at Swansea University, Wales; and Abdullah Alabdulkarem, of the Mechanical Engineering Department, and Sattam Fahad Al-Mojil, an assistant professor and environmental adviser, at King Saud University, Riyadh, Saudi Arabia. Barron is the Sêr Cymru Chair of Low Carbon Energy and Environment at Swansea and the Charles W. Duncan Jr.-Welch Professor of Chemistry and a professor of materials science and nanoengineering at Rice.

The research was supported by the Welsh Government Sêr Cymru Program, FLEXIS, which is partially funded by the European Regional Development Fund, and the Robert A. Welch Foundation.

Notes

• Read the abstract at http://www.nature.com/articles/s41598-017-12499-w
• For more information about ESRI go to http://www.esri-swansea.org/en/. Follow ESRI via Twitter @ESRI_Swansea
• Swansea University is a world-class, research-led, dual campus university. The University was established in 1920 and was the first campus university in the UK. It currently offers around 350 undergraduate courses and 350 postgraduate courses to circa 20,000 undergraduate and postgraduate students.

   

The University's 46-acre Singleton Park Campus is located in beautiful parkland with views across Swansea Bay. The University's 65-acre science and innovation Bay Campus, which opened in September 2015, is located a few miles away on the eastern approach to the city. It has the distinction of having direct access to a beach and its own seafront promenade. Both campuses are close to the Gower Peninsula, the UK's first Area of Outstanding Natural Beauty.

Swansea is ranked the top university in Wales and is currently The Times and The Sunday Times 'Welsh University of the Year' for 2017. It is also ranked within the top 300 best universities in the world in the Times Higher Education World University rankings.

The results of the Research Excellence Framework (REF) 2014 showed the University has achieved its ambition to be a top 30 research University, soaring up the league table to 26th in the UK, with the 'biggest leap among research-intensive institutions' (Times Higher Education, December 2014) in the UK.

The University has ambitious expansion plans as it moves towards its centenary in 2020, as it continues to extend its global reach and realising its domestic and international ambitions.