Rice University Scientists Produce Filter to Reclaim Fracturing Water

(October 24, 2017) — A new filter produced by Rice University scientists has proven able to remove more than 90% of hydrocarbons, bacteria, and particulates from contaminated water produced by hydraulic fracturing operations at shale oil and gas wells. The work, by Rice chemist Andrew Barron and colleagues, turns a ceramic membrane with microscale pores into a super-hydrophilic filter that “essentially eliminates” the common problem of fouling.

Researchers determined that one pass through the membrane should clean contaminated water enough for reuse, significantly cutting the amount that has to be stored or transported. The filters keep emulsied 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 five million gallons of water on average, of which only 10% to 15% is recovered during the flow-back stage. “This makes it very important to be able to reuse this water,” Barron said, adding that not every type of filter reliably removes every type of contaminant. Hydro-carbon molecules in solution slip through micro- filters designed to remove bacteria. Natural organic matters, like sugars from guar gum used to make hydraulic fracturing fluid more viscous, require ultra- or nano-filtration, but those can foul, especially from hydrocarbons that emulsify into globules. A multistate filter that could remove all the contaminants isn’t practical due to cost and the energy consumed.

“Frac water and produced waters represent a significant challenge on a technical level,” said Barron. “If you use a membrane with pores small enough to separate, they foul, and this renders the membrane useless. In our case, the super-hydrophilic treatment results in an increased flux—flow—of water through the membrane and inhibits 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 super-hydrophilic, or extremely attracted to water. The acid covered not only the surface but also the insides of the pores, and kept particles from sticking 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. Researchers theorized the initial decrease in flow through the ceramics was due to purging of air from the pores, after which the super- hydrophilic 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.” The work is reported in the journal Nature’s open-access Scientific Reports.

(SOURCE: The Weekly Propane Newsletter, October 23, 2017)