Clearing the way for faster and more cost-effective separations

Trial-and-error separations could be replaced by quantitative and predictive molecular methods, researchers find

The process of separating useful molecules from mixtures of other substances accounts for 15% of the entire energy in the United States, while emitting 100 million tons of carbon dioxide and costing $4 billion annually.

Commercial manufacturers produce columns of porous materials to separate potential new drugs developed by the pharmaceutical industry, as well as the energy and chemical production sectors, environmental science and making foods and beverages.

However, a research team at Case Western Reserve University, (CWRU) Cleveland, US, has found that these manufactured separation materials often don’t function as intended because the pores are so packed with polymer that they become blocked. This means the separations are inefficient and can prove to be unnecessarily expensive.

Lydia Kisley, Ambrose Swasey Assistant Professor of physics and chemistry at CWRU, used what is known as single-molecule microscopy to find that solutions containing molecules of interest mainly diffused and adsorbed around the outer edge of the porous materials, and left the centre of the column almost entirely unused.

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“While these materials are described as ‘fully porous,’ [according to our research] they aren’t,” said Kisley, who led the work.

“We were really surprised by this. And why isn’t this material working in the way it was designed?”

Kisley, along with colleagues Professor Burcu Gurkan and Associate Professor Christine Duval, from the Case School of Engineering’s Department of Chemical and Biomolecular Engineering, set out to discover the reasons why.

Single-molecule fluorescence microscopy, allows for the visualisation and analysis of the behaviour of individual molecules, and allowed Kisley and her team to measure the molecular dynamics at the nanoscale.

“We used light to be able to observe individual molecules,” she said, “shining a bluer laser to get the molecules to fluoresce in red.”

Gurkan and Muhammad Zeeshan, a postdoctoral researcher in her lab, first tested the materials as specified by industry (but not under the solution conditions in which they are actually used). Tested in this way they found them to work as described by their manufacturers.

However, by imaging the same materials under conditions used in actual separations, Kisley found that the manufacturers had added so much cellulose material in order to capture molecules that it actually blocked the pores. Using a solvent to remove extra material improved the potential separations.

Kisley hopes their findings will help manufacturers design more efficient separations.

 “Half the cost of bringing a new drug to market is trying to separate molecules, a process which may be done between 10 and 20 times for one substance,” she said.

The single-molecule microscopy technique can demonstrate exactly how separators are actually working and predict their performance. If adopted by industry, this could eliminate much of the trial-and-error waste from separation science, she said.

“Maybe you could get more efficient separations and eliminate entire steps,” she said. “And converge faster on the successful drug to help treat disease.”

Kisley cited Ricardo Monge Neria, a CWRU graduate student in physics, for leading the experimental research and writing the published paper.

Rachel Saylor, an associate professor of chemistry and biochemistry at Oberlin College, also collaborated on the study, along with researchers at the Case School of Engineering Swagelok Center for the Surface Analysis of Materials.

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