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Dias lab publishes cover article detailing alternative to costly industrial separation process

Devaborniny Parasar, UTA postdoctoral fellow in chemistry and biochemistry

Chemistry researchers at The University of Texas at Arlington have published a new study that shows promise in finding a sustainable method for a vital but costly industrial separation process.

The paper is an international collaboration led by Rasika Dias, professor of chemistry and biochemistry, and students in his laboratory. The study, titled “Overcoming Fundamental Limitations in Adsorbent Design: Alkene Adsorption by Non-porous Copper(I) Complexes,” was published in the November 16 edition of Angewandte Chemie, a journal of the German Chemical Society, and is featured on the issue’s cover. The journal also gave it the special distinction of “Hot Paper”.

Devaborniny Parasar, who received her Ph.D. this summer under Dias’ supervision, and is now a postdoctoral fellow in Dias’ lab, is lead author. Other UTA co-authors are Naleen Jayaratna, a Ph.D. graduate from Dias’ lab, and Brian Edwards, research engineering scientist. The team also includes Ahmed Elashkar and Matthew Cowan of the University of Canterbury in Christchurch, New Zealand; Andrey Yakovenko of the Argonne National Laboratory in Argonne, IL; and Shane Telfer of Massey University in Palmerston North, New Zealand.

“I am extremely grateful to Dr. Dias for giving me the opportunity to work on this project,” Parasar said. “It was exciting to not only contribute in a scientific way but also realizing that this work has a potential positive economic and environmental impact. It is a great honor to get our work recognized and to be featured on the cover of such a highly reputed journal as Angewandte Chemie.”

Alkenes like ethylene and propylene, also called olefins, are compounds made up of hydrogen and carbon that contain a double bond between a pair of carbon atoms. They are examples of unsaturated hydrocarbons. Alkanes, also called paraffins, are hydrogen and carbon compounds where the carbon chain has only single bonds. They are examples of saturated hydrocarbons.

Olefins are used for the production of raw chemicals and polymers. Separating olefin from paraffin is an important process which consumes enormous amounts of energy. Nearly every commercial industry uses these inputs to make products from olefins, including plastic bottles, pipes, detergents, packaging, and clothing, among many others.

Scientists have been searching for more energy-efficient alternatives to current cryogenic high-pressure distillation methods for years. The cryogenic high-pressure distillation process requires large distillation columns to separate the mixture into its component parts, due to the similar sizes and boiling points of olefins and paraffin. This process necessitates the use of massive amounts of energy.

Some of the alternative methods which have been studied in recent years include preferential adsorption, membrane separation, molecular sieving, and hybrid distillation–membrane processes. Adsorption is the adhesion of ions or molecules from a gas, liquid or dissolved solid to a surface.

Trade-offs between kinetics, selectivity, capacity, and heat of adsorption have prevented production of an optimal adsorbent, the team explained in their project’s abstract. In their new study, they utilized non-porous copper complexes for this task and discovered that they work surprisingly well.

“We found that copper containing materials we developed in our lab selectively absorb small olefins like ethylene (ethene) from a mixture of ethylene and ethane (olefin-paraffin mixture) at slightly above atmospheric pressure and at room temperature leaving behind the ethane (paraffin component),” Dias said. “Then, it is possible to release and recover the pure ethene from these materials by just releasing the pressure. This allows a way to separate and purify olefins by a simple pressure-swing (pressure variation) method.”

These non-porous copper complexes adsorb ethene using a fundamentally different mechanism to porous materials, and feature moderate capacity, high selectivity, fast rates of adsorption and desorption, and low heat of adsorption for the gaseous alkenes ethene and propene compared to other alkene adsorbents, the team wrote in their study.

“The olefin uptake and release by this non-porous solid material is also fast, which is remarkable and unexpected, as these are solids with no pores or holes for gas permeation,” Dias said. “We have also uncovered the mechanism of this olefin uptake and release using an X-ray diffraction method that uses the high-powered X-ray source at Argonne National Lab. Our olefin-paraffin separation method is also a low-energy process, meaning it does not need much cooling or heating.”

The team concluded in their paper that the non-porous copper complexes they utilized may find application in alkene/alkane separation processes and provide environmental and economic benefits on a global scale.

“Overall, our discovery features several unique and attractive features that could be utilized to create a new sustainable process to separate olefins from an olefin-paraffin mixture,” Dias said.

Fred MacDonnell, professor and chair of the UTA Department of Chemistry and Biochemistry, hailed the group’s work and said it could have significant positive economic and environmental impact.

“This research by Dr. Dias and his students, along with a team of international collaborators, shows promising progress in the search for a more energy efficient alternative to cryogenic high-pressure distillation,” MacDonnell said. “This new method they describe in their study is fast and uses far less energy than the method now in use. The fact that a prestigious journal chose to feature their work on the cover testifies to their study’s importance and is further evidence of the high quality of work being done in the UTA Department of Chemistry.”