Is it possible to build safe and sustainable small-scale chemical factories? The kind of plants that could — among other things — convert biomass into biofuel, on the very farms that produce those crops?
Perhaps. But that requires determining, in part, a more benign hydrogenation process, the chemical reaction between molecular hydrogen and other compounds and elements that is used to create new molecules.
Srinivas Rangarajan, Assistant Professor of Chemical and Biomolecular Engineering at PC Rossin College of Engineering and Applied Science at Lehigh University, recently received support from the National Science Foundation’s Faculty of Early Career Development (CAREER) program for his proposal develop new tools to better understand a promising chemistry called catalytic transfer hydrogenation (CTH).
The prestigious NSF CAREER Award is presented annually to young faculty in the United States who exemplify the role of teacher-researchers through outstanding research, excellent education, and the integration of education and research. Each scholarship provides stable support of approximately $ 500,000 for a period of five years.
When hydrogenation is used to make ultra-low sulfur diesel, for example, it requires a huge catalytic reactor, temperatures up to 500 degrees Celsius, and hundreds of pounds of pressure.
Similar chemistry could be used on a much smaller scale to do things like process biomass, recycle plastic waste, or make specialty chemicals. But such distributed processing would require reactors much smaller and operating at much lower temperatures and pressures.
And that means using a different source of hydrogen.
“The problem with molecular hydrogen is that it’s very light,” Rangarajan explains. “To transport it you have to compress it using very high pressures. And to use it you need very high pressures. But if you can use a different molecule that can chemically transport hydrogen, that molecule could be used as a hydrogen donor. It will break down or convert and, in the process, lose hydrogen, which then becomes available for something like biomass conversion. ”
The process of transferring hydrogen atoms from a hydrogen donor to a hydrogen acceptor is called catalytic transfer hydrogenation. “So instead of using molecular hydrogen, you are using a liquid molecule that can be shipped very easily from where it’s produced to where it’s needed,” he explains. “It can then be used at temperatures close to room temperature and at atmospheric pressure. In that sense, CTH could therefore lead to a more compact, safe and modular process.”
While this is a big picture, Rangarajan focuses on the molecular level. He will develop a new computational framework to answer two fundamental questions: how exactly does this hydrogen transfer work on a molecular scale, and which is the right donor and the right catalyst for a given acceptor?
“I use a model compound called acrolein as a hydrogen acceptor,” he says. “It has features representative of many biomass compounds and many unsaturated chemicals that appear in the chemical industry, for example, oleochemicals, solvents, and pharmaceuticals. To hydrogenate acrolein, I have to find out which is the right molecule to deliver hydrogen, and what is the right catalyst that can do this chemistry selectively, that is, without creating unwanted byproducts. ”
To address the possible combinations of donors and catalysts that number in the tens of thousands, Rangarajan will build on his previous work, as well as his recent work at Lehigh, to create a technique called high throughput kinetic modeling. It integrates quantum chemistry, optimization, and machine learning to create models that will provide data on how different parameters affect performance.
“This technique allows us to determine how the parameters affect the rate of the reaction and whether the desired product will actually be formed,” he says. “It hasn’t been done before.”
The ultimate goal is to develop more energy efficient processes. The potential impact could be huge, he says, given that 45 million tonnes of hydrogen are used worldwide each year to make chemicals and energy carriers like fuels. Alternatives to molecular hydrogen could reduce plant operating expenses by reducing infrastructure, storage and transportation costs.
But more immediately, where economies of scale don’t work, “like a farm looking to transform their biomass or a specialty chemical company that doesn’t have significant production needs, the main idea is that you look for an intensification of the processes, “he says. “Smaller, more cost-effective and secure solutions that are energy and carbon efficient.”
CAREER funding will also support educational awareness around what Rangarajan calls “computational thinking” among undergraduates and graduate students. It is developing a range of activities including software development research projects, a new data science course for chemical engineers, and experiential learning opportunities through the Creative Investigation Bureau. by Lehigh focused on interactive construction data visualization models. It will also assist secondary school teachers in the region interested in programming or modeling.
“Calculations and data science are becoming increasingly common in chemical engineering,” he says. “We are increasingly using mathematics, mathematical modeling and data to solve problems in industry and academia. I am really looking forward to promoting algorithmic thinking to the next generation of scientists and engineers. ”
About Srinivas Rangarajan
Srinivas Rangarajan is Assistant Professor of Chemical and Biomolecular Engineering at Lehigh University. He joined the faculty of PC Rossin College of Engineering and Applied Science in January 2017, after his stint as a postdoctoral researcher at the University of Wisconsin, Madison. He obtained his B.Tech. (2007) from the Indian Institute of Technology, Madras, and PhD (2013) from the University of Minnesota, both in chemical engineering. His industrial experience includes previous employment (2007-2008) at Shell Global Solutions in the Netherlands and India as Senior Associate Hydrotreatment Technologist.
Search in the Rangarajan group is at the intersection of heterogeneous catalysis, materials science and process systems engineering. The group develops and applies a variety of computer tools to model and design catalytic systems and materials relevant to energy and the environment and governed by complex chemistries. The suite of tools includes electronic structure calculations using Density Functional Theory (DFT), microcinetic modeling, optimization, pathformatics, automated mechanism generation, and machine learning.
Rangarajan has published more than 35 peer-reviewed articles, including a dozen since joining Lehigh, in reputable journals such as ACS catalysis, Applied catalysis B, Chemical research accounts, and Nature Communication. His recent awards and honors include the David Smith Graduate Publication Award from the American Institute of Chemical Engineers (CAST division), the PC Rossin Assistant Professorship and the John Ochs Faculty Achievement Award from the Baker Institute of Creative Inquiry. His group has been supported by grants from the NSF, the Doctoral New Investigator Award (ACS-PRF) and the Commonwealth of Pennsylvania (PITA).