Bio-adipic acid production by catalysed hydrogenation of muconic acid in mild operating conditions

- Muconic to adipic acid hydrogenation on 5% Pt/C.
- Mild conditions: 4 bar, 50-70 °C, 60-90 min.
- Catalyst is stable and reusable, 100% selective.
- Catalyst characterization pre-post reaction.
- Insight on industrial bioprocess downstream.

In this work trans,trans-muconic acid was hydrogenated to adipic acid, a strategic intermediate for the industry of polyamides and high performance polymers. This study: (1) develops a new and robust analytical method for the evaluation of muconic acid conversion and adipic acid selectivity, (2) defines a standard procedure for the confirmation of the kinetic regime using experimental data and some practical criteria to exclude mass transfer limitations, (3) tests Pt/C 5% commercial catalyst for the study of muconic acid hydrogenation at different operating conditions, (4) hypothesizes a reaction pathway in aqueous media, and (5) demonstrates the possibility to recycle the catalyst without loss in activity and selectivity. The developed analytical method evaluates muconic acid conversion by UV-vis analyses, while the selectivity towards adipic acid and mono-unsatured intermediates was determined by GC/TCD analysis after derivatization of the reaction mixture. Under optimized conditions the hydrogenation reaction (70 °C, 4 bar of hydrogen and 10 substrate/catalyst ratio (wt/wt)) reached full conversion with full selectivity toward adipic acid in 2 h. Finally, recycling tests revealed the possibility to reuse catalyst up to 10 times without loss in conversion and selectivity opening the way to a scaling up of the process.

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