In many industrial processes, a common way to separate gases, liquids, or ions is to use heat to purify the mixture, taking advantage of slight differences in boiling points. These thermal processes account for about 10 percent of U.S. energy use.
MIT chemical engineer Zachary Smith hopes to reduce costs and carbon emissions by replacing these energy-intensive processes with sophisticated filters that can separate gases, liquids, and ions at room temperature.
In his MIT lab, Smith is designing membranes with tiny pores that can filter out small molecules based on their size. These membranes could be useful for purifying biogas, capturing carbon dioxide from power plant exhaust fumes, and producing hydrogen fuel.
“We’re taking a material that has the unique ability to separate molecules and ions very precisely and applying it to applications where current processes are inefficient and have very large carbon emissions,” said Smith, an associate professor of chemical engineering.
Smith and several former students have started a company called Osmoses that is working to develop these materials for large-scale use in gas purification. Eliminating the need for high temperatures in these common industrial processes could have a major impact on energy consumption, reducing it by up to 90 percent.
“I want to see a world where there are no temperature differences and where temperature is not an issue in building what we need and producing the energy we need,” Smith said.
Passionate about research
As a high school student, Smith was interested in engineering but didn’t have many role models in the field: His parents, both doctors, always encouraged him to study hard.
“I didn’t grow up knowing much about engineers, I didn’t know anything about chemical engineers, but I do know that I really enjoy seeing how the world works. “I was always interested in chemistry and how math helps explain this branch of science,” recalls Smith, who grew up near Harrisburg, Pennsylvania. “Chemical engineering seemed to incorporate all of that, but I didn’t really know what it was.”
At Penn State, Smith worked with Professor Henry “Hank” Foley on a research project to design carbon-based materials to create “molecular sieves” for separating gases. Through a time-consuming, repetitive layering process, he created a sieve that could remove oxygen and nitrogen from the air.
“I kept adding more and more coatings of special materials that could be carbonized, and eventually we started to get selectivity. “Eventually, I created a membrane that could screen molecules that differed in size by just 0.18 angstroms,” he says. “At that point I was drawn to the research, and it inspired me to do more in the membrane field.”
After graduating in 2008, Smith went on to do graduate work in chemical engineering at the University of Texas at Austin, where he continued developing membranes for gas separation, this time using a different material: polymers. By controlling the polymer structure, it is possible to create membranes with pores that filter out specific molecules, such as carbon dioxide and other gases.
“Polymers are the type of material that can actually be molded into large devices that can be integrated into world-class chemical plants ,” Smith said. “It’s exciting to have a scalable material that can really have an impact on solving problems related to CO2 and other energy-efficient separation methods .”
After earning his PhD, he wanted to learn more about chemistry and ended up doing a postdoctoral research position at the University of California, Berkeley.
“I want to learn how to create my own molecules and materials,” he said. “I wanted to do my own reactions more systematically.”
At Berkeley, he learned how to make compounds called metal-organic frameworks (MOFs), cage-like molecules that hold promise for applications in gas separation and many other fields, and he also realized that, although he loved chemistry, he was definitely a chemical engineer at heart.
“I learned a lot there, but also a lot about myself,” he said. “I love chemistry, and I work with and mentor chemists on my team, but I’m definitely a chemical engineer, with a focus on process and applications.”
Solving global problems
While interviewing for teaching positions, Smith was attracted to the mindset of the people he met and decided to attend MIT.
“I began to realize not only the caliber of faculty and students, but also that the way they thought was completely different from other places I’d been,” he said. “They’re not just doing things to advance their field a little bit. They’re actually creating new fields. There’s something inspiring about people who want to solve global problems, like those who come to MIT.”
In his MIT lab, Smith currently works on a number of global problems, including water purification, vital element recovery, renewable energy, battery development, and carbon sequestration.
Working closely with Stanford University professor Yang Xia, Smith recently developed a gas separation membrane that incorporates a new type of polymer called a “stepped polymer,” which he is currently scaling up for deployment at his startup. Traditionally, the use of polymers in gas separation has been limited by a trade-off between permeability and selectivity: membranes that allow gas to pass through them faster are less selective, meaning impurities tend to pass through.
Using ladder polymers, which consist of double chains connected by ladder-like links, the researchers were able to create a gas separation membrane that is both highly permeable and highly selective. Smith said that because of the increased permeability (a 100- to 1,000-fold improvement over traditional materials), the membrane could potentially replace some of the high-energy techniques currently used to separate gases.
“This allows us to imagine large-scale industrial problems being solved with small devices,” he said. “If we can really miniaturize the systems, the solutions we are developing in the lab could easily be applied to large-scale industries, like the chemical industry.”
These and many other developments are some of the many advances achieved by collaborators, students, postdocs and researchers in Smith’s group.
“I was surrounded by an incredible research group of talented and hard-working students and postdocs who taught me topics that will be important to my professional life,” said Smith. “MIT is a playground for exploring and learning new things. I’m excited about what my team will explore next and grateful for the opportunity to contribute to solving so many important global problems.”
