News

Four billion people face severe potable water distress due to water pollution and a limited supply of freshwater reserves, according to the World Resources Institute.

“One potential solution is seawater desalination,” said MIT Chemical Engineering and Chemistry Professor Heather Kulik, who recently illustrated how to accomplish this by using U.S. National Science Foundation (NSF) ACCESS allocations on the Expanse system at the San Diego Supercomputer Center (SDSC) — part of the School of Computing, Information and Data Sciences at University of California San Diego.

The most common way to clean seawater is reverse osmosis, but it is an expensive and time-consuming undertaking. Think of it like pushing water through an extremely fine filter that captures salt and impurities while allowing clean water to pass through. In Tunisia, cleaning one cubic meter of seawater costs three times more than getting the same amount of water from lakes and rivers; that water is already expensive and hard to find.

“While oil-rich countries can afford this energy-intensive process, others struggle to bear the economic burden,” said Akash K. Ball, an MIT graduate student who was the first author of the study. “Therefore, it is imperative that we advance the efficiency of reverse osmosis desalination.”

With help from NSF ACCESS allocations on SDSC’s Expanse, Kulik and her team spearheaded an effort to identify metal-organic frameworks (MOFs) that could be used as permeable membranes in seawater desalination from a set of experimentally synthesized MOFs that were identified as water-stable with Kulik’s previously developed data-driven models.

“By using SDSC’s Expanse to run computationally demanding simulations, we were able to identify over 70 promising MOFs that would offer both high water-stability and high water uptake,” Kulik said.

“MOFs are an exceptional class of porous materials with great promise for desalination — thanks to their distinctive porous structures and tunable properties,” Kulik continued. “However, a key challenge limiting the adoption of MOFs for water-related applications is their inadequate stability when exposed to water — many of them tend to break down over time. This means we need to screen a large number of MOFs to find ones with ‘Goldilocks’ traits of stability and permeability.”

While this might seem like a critical drawback for MOFs, they do offer a distinct advantage over their traditional counterparts: permeability. Using highly permeable MOF membranes could lead to energy savings and reduce reverse osmosis costs in a few ways. Since a more permeable membrane requires less applied pressure to achieve the same flow rate as a less permeable membrane, the pumps that push seawater through a desalination system using a MOF membrane would use less power to produce the same amount of freshwater.

Another cost-saving avenue is scaling — with the improved permeability offered by MOFs, smaller membranes and smaller pumps could be used to create smaller, less expensive desalination plants that would produce the same amount of freshwater as larger plants that use traditional membranes.

“In the future, we hope to collaborate with experimentalists to verify the characteristics of these materials in the real world so that they may be used to improve the efficacy of reverse osmosis desalination across the globe,” Kulik said.

Details of the research have been published in ACS Applied Materials and Interfaces.

The study was supported by the Center for Enhanced Nanofluidic Transport, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award DE-SC0019112. The simulations made use of Expanse at SDSC through the U.S. NSF ACCESS program (allocation no. CHE140073).