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

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.