Catalytic Adipic Acid Production on Zeolites from Biomass-Derived Tetrahydrofuran-2,5-dicarboxylic Acid

Adipic acid (AA) is an important precursor for the production of Nylon-66, and renewable routes for AA are being explored. Previously we have shown the use of HI and molecular H2 to be an effective combination for the selective ring-opening of tetrahydrofuran-2,5-dicarboxylic acid (THFDCA) in organic acids without the need for a metal catalyst. However, the use of HI could deter this system from large scale use for renewable AA. In this work, we employ zeolites as an effective proton source in combination with iodide salts (NaI), which obtains high AA rates in a similar metal-free pathway. Kinetic measurements coupled with zeolite characterization suggest that a dominant mechanism for THFDCA activation is bulk-phase protonation promoted by in situ ion-exchange via the metal cation from the iodide salt. Zeolites can be regenerated multiple times with minimal loss in reactivity, which enhances the commercial applicability of the system.