Activating Rings in Electrochemical Systems

Project Overview

Cyclic compounds are often precursors to create valuable aliphatic products via ring-opening thermocatalytic activation that uses high temperatures and releases potent greenhouse gases (GHGs) as byproducts. One such aliphatic compound is adipic acid (AA)- a precursor to billion-dollar polymer industries such as nylon, plasticizers, and polyurethane. The current state-of-the- art process for producing adipic acid is energy-intense and releases N2O, a GHG that is 265 times more potent than CO2. To address these challenges, the aim of this project was to explore the feasibility of using electrochemistry to activate the ring opening of a simple biomass-derived ringed compound - 5-Hydroxymethylfurfural (HMF) to synthesize AA. This alternative route was explored to enhance our fundamental understanding of ring-opening electrochemistry and to decarbonize an energy and emission-intense process.

Our scientific approach encompassed several key steps, including the fabrication of custom electrochemical reactors through 3D printing, the synthesis of Cu, Ag, Zn, and Pt catalysts using physical vapor deposition (PVD), an extensive investigation of their electrochemical activity under varying environmental conditions (acidic, neutral, and alkaline), and precise quantification of reaction products via high-pressure liquid chromatography (HPLC). Our findings revealed a two-step process in the conversion of HMF to AA: the initial oxidation of HMF to furandicarboxylic acid (FDCA) successfully demonstrated over Cu and Ag catalysts, followed by the subsequent reduction of FDCA to AA, demonstrated under neutral to acidic conditions employing Zn and Pt catalysts. Notably, this conversion was achieved without the emission of greenhouse gases (GHGs), holding promise for decarbonizing ring-opening chemistry and advancing the field of electrochemistry. 

Mission Impact

By exploring electrochemical methods to convert HMF into AA, it directly addresses LLNL's Mission Focus Area on Climate Impacts & Resilience by offering a sustainable alternative to the energy-intensive and greenhouse gas-emitting processes currently employed in AA production. Demonstration of this type of electrochemistry has meaningfully impacted our fundamental understanding of ring-opening chemistry via electrochemical routes and can garner interest in pursuing this study on a larger scale with developing reactor and catalyst configurations for electrochemical plastic upcycling With the vast application of ringed compounds in the production of plastics, this study is also in line with the DOE's roadmap to renewable plastics.