A Fascination With Filtration
Friday, December 18, 2020
Shah’s work with ionic liquids could lead to improvements in space travel and exploration
Humans need water — especially in space. And a spring shower of fresh water isn’t falling out there.
So one team of researchers at Oklahoma State University is working on a project that could improve water filtration in space, allowing for longer stays and longer explorations.
Dr. Jindal Shah, an associate professor of chemical engineering at OSU, is working with ionic liquids, which could be the future of space wastewater filtration systems. Ionic liquids are chemical compounds composed of cations (positively charged) and anions (negatively charged) particles — much like table salt, but with a weaker bond so that they are liquid below 100 degrees Celsius, he said.
“My fascination with ionic liquids started while pursuing my Ph.D. at the University of Notre Dame almost two decades ago,” Shah said. “I was excited to work on ionic liquids as the research in the chemical engineering discipline was just beginning, so it presented an enormous opportunity to contribute to the field.”
Many of these solvents do not evaporate, reducing air pollution, he added.
“From a chemical engineering perspective, ionic liquids afford numerous possibilities to be applied in many areas of the chemical and petrochemical industry,” he said. “One can tailor the properties of ionic liquids by selecting an appropriate cation and anion from a large pool of candidates, (so the options are) practically limitless.”
While working on a NASA Early CAREER proposal, Shah contacted Dr. Eric Fox at Marshall Space Flight Center to learn about research on ionic liquids there. Fox told Shah about a notice that listed topics of interests to NASA. One topic was related to exploring novel ways for removing dimethylsilanediol (DMSD) — and the idea of using ionic liquids for this purpose was born, Shah said.
Since 2010, the high levels of total organic carbon measured in water produced from the water processor assembly (WPA) in the International Space Station have been attributed to the presence of DMSD, which can be harmful to the process, Shah said. The WPA produces drinkable water from humidity condensate, carbon dioxide reduction water, water obtained from fuel cells, reclaimed urine distillate, shower, handwashing and oral hygiene wastewaters, according to NASA.
Current approaches for removing DMSD rely on finding appropriate adsorbents and conversions of DMSD via catalytic reduction, he added.
“Our project with NASA adopts an entirely novel approach using ionic liquids in an extractive distillation process to remove DMSD from wastewater … to produce contaminant free water for reuse aboard space shuttles for deep space exploration and the ISS,” Shah said. The research group conducts molecular simulation to predict how various ionic liquids will modify how DMSD attaches to water, Shah said.
To be able to correctly predict the trends with variations in ionic liquid structures, the team needs molecularlevel information on how ionic liquids interact with water and DMSD. Shah’s team is also collaborating with Dr. Joan Brennecke, a renowned expert in ionic liquids from the University of Texas at Austin.
“Dr. Brennecke’s group conducts experiments to determine a thermodynamic quantity known as the activity coefficient — an indirect measure of interaction between two molecules,” Shah said. “We use this information to tune the parameters needed in our calculations to reproduce the experimental data as closely as possible.”
These parameters help Shah and his team determine how much ionic liquid might be needed per kilogram of water to remove the contaminant. “The primary goal of the research activities in this project is to generate fundamental knowledge on the feasibility of ionic liquids for the removal of DMSD,” Shah said.
Shah also anticipates the concept could be used in difficult separation processes in chemical and petrochemical industries.
This could benefit oil and gas companies in Oklahoma, and Shah has a long-term plan to work with them.
“We leverage the design flexibility of ionic liquids to identify ionic liquids that can weaken the interaction between water and DMSD,” Shah said. “Ionic liquids are particularly suited for the application as they can be designed to be non-volatile, which is quite an advantage aboard the ISS.”
This non-volatility means the liquid does not evaporate, which is also beneficial for separating ionic liquids from water once DMSD is removed, Shah said.
Reducing the pressure on the mixture would let the water vaporize while the ionic liquid remains in the liquid state. This research could lead to a more efficient water filtration system, allowing longer trips into space.
“Ionic liquids are transitioning from academic curiosity to industrial applications,” Shah said