The future of recycling? New catalyst turns waste into valuable and environmentally friendly products
Photograph of a plastic bag underwater.
A team of scientists led by Aaron Sadow, an Ames National Laboratory researcher, professor of chemistry at Iowa State University and director of the Institute for Cooperative Plastic Recycling (iCOUP), has developed a new catalyst that converts hydrocarbons into higher hydrocarbons. value chemicals and materials that are more recyclable and environmentally friendly. This catalyst can convert materials such as motor oil, single-use plastic bags, water or milk bottles, caps, and even natural gas into more stable substances.
The new catalyst is designed to add functional groups to aliphatic hydrocarbons, which are organic compounds consisting exclusively of hydrogen and carbon. These hydrocarbons are usually immiscible with water and form separate layers due to their lack of functional groups. By incorporating functional groups into these hydrocarbon chains, the properties of materials can be significantly altered and made more recyclable.
“The methane in natural gas is the simplest of the hydrocarbons, having nothing but carbon-hydrogen (CH) bonds. Oils and polymers have chains of carbon atoms linked by carbon-carbon (CC) bonds,” Sadow explained.
Aliphatic hydrocarbons are found in many petroleum and refined products such as plastics and motor oils. These materials “have no other functional groups, which means they are not easily biodegradable,” Sadow said. “So the goal in catalysis has long been to be able to take these materials and add other atoms like oxygen or create new structures from these simple chemicals.”
Unfortunately, the traditional way of adding atoms to hydrocarbon chains requires a significant amount of energy. Oil is first “broken down” by heat and pressure into small building blocks. These building blocks are then used to grow chains. Finally, the desired atoms are added at the end of the chains. In this new approach, existing aliphatic hydrocarbons are converted directly without cracking and at low temperatures.
Sadow’s team had previously used a catalyst to break the CC bonds in these hydrocarbon chains and simultaneously attach aluminum to the ends of the smaller chains. They then inserted oxygen or other atoms to introduce functional groups. To develop an additional process, the team found a way to avoid the CC disconnect step. “Depending on the chain length of the starting material and the desired product properties, we may want to shorten the chains or simply add an oxygen functional group,” Sadow said. “If we could avoid CC splitting, we could, in principle, just transfer the chains from the catalyst to aluminum and then add air to establish the functional group.”
Sadow explained that the catalyst is synthesized by adding a commercially available zirconium compound to a commercially available aluminosilicate. All substances are widely available and inexpensive, which is advantageous for potential commercial applications in the future.
In addition, the catalyst and reactant are advantageous in terms of stability and cost. Aluminum is the most abundant metal on earth and the aluminum reagent used is synthesized without the formation of by-products. The zirconium alkoxide-based catalyst precursor is stable in air, readily available, and activated in the reactor. “Thus, unlike many early organometallic chemistries, which are extremely sensitive to air, this catalyst precursor is easy to handle,” Sadow said.
This chemistry is a step towards being able to influence the physical properties of various plastics, such as making them stronger and more easily paintable. “As catalysis continues to evolve, we expect to be able to incorporate more and more functional groups to influence the physical properties of polymers,” Sadow said.
Sadow attributed the success of this project to the collaborative nature of iCOUP. Perras’ group at Ames National Laboratory studied the structures of catalysts using nuclear magnetic resonance (NMR) spectroscopy. Coates, LaPointe, and Delferro’s teams at Cornell University and Argonne National Laboratory investigated the structure and physical properties of the polymer. And Peters’ group at the University of Illinois statistically modeled the functionalization of a polymer. “The success of the project at the center is based on the contributions of the experience of many groups,” Sadow said. “This work highlights the benefits of team science.”
Reference: “Zirconium-Catalyzed CH Aluminization of Polyolefins, Paraffins and Methane” by Uddhav Kanbur, Alexander L. Paterson, Jessica Rodriguez, Andrew L. Kotzen, Ryan Yappert, Ryan A. Hackler, Yi-Yu Wang, Baron Peters. , Massimiliano Delferro, Ann M. LaPoint, Jeffrey W. Coates, Frederick A. Perras, and Aaron D. Sadow, January 25, 2023, Journal of the American Chemical Society.
DOI: 10.1021/jacs.2c11056
The work was also featured in JACS Spotlight, “A New Versatile Tool for the Production of Commercial Chemicals”.
The study was conducted by the Institute for Collaborative Processing of Plastics (iCOUP), led by Ames National Laboratory. iCOUP is an Energy Frontier research center comprised of scientists from Ames National Laboratory, Argonne National Laboratory, UC Santa Barbara, University of South Carolina, Cornell University, Northwestern University, and the University of Illinois at Urbana-Champaign.
