Bio adipic acid production from sodium muconate and muconic acid

The limited fossil resources availability and the climate change are raising wide interest between the scientific researchers and the civil community. Among the several subjects, the production of bulk chemicals from renewable sources is one of the great challenges that researchers are facing. Concerning this theme, adipic acid (AdA) production from wood biomass is one of the most important topics due to the large amount of AdA consumed and the market growth, in particular for the production of polyamides (Nylon 6,6). Bio-AdA can be produced from t,t-muconic acid (t,t-MA), a metabolic intermediate of the catechol ortho-cleavage pathway.[1] In nature, microorganisms displaying this pathway are quite common and they can accumulate at least 13.5 g/l of MA as sodium muconate.[2] The so produced sodium muconate is then converted to AdA with a heterogeneous hydrogenation chemical reaction. MA coming from the fermenter needs a purification step due to the high purity grade required for the market. The purification process consists in an acidification and crystallization steps, that transform sodium muconate into muconic acid, separating this chemical from all the compounds used in the fermenter. Considering water as hydrogenation reaction media, unfortunately MA is less soluble than sodium muconate. On the basis of these considerations different hydrogenation reactions were performed varying the operating conditions both on muconic acid and sodium muconate hydrogenation. The reaction was performed using mild operating conditions (T= 50 °C, P(H2)=1 bar and metal to substrate ratio=1/200 mol/mol) and home-made catalysts (Pd/AC 1%) prepared by sol-immobilization method [3] in which the stabilizer (polyvinyl alcohol, PVA) to metal ratio was varied from 0 to 1.2 (wt/wt). Initial activity was evaluated considering the conversion per unit of time divided by the moles of active metal. t,t-MA was fully hydrogenated to AdA in 90 min while for Na-Muc hydrogenation only 1.2PVA catalyst gave 100% yield of sodium adipate. All the home-made catalysts showed an initial activity higher than the commercial Pd/AC 5% (Sigma Aldrich), in particular during Na-Muc hydrogenation (Figure 1). Catalyst characterization revealed the presence of higher amount of Pd in 0.65PVA and 1.2PVA samples, sign of a possible higher activity.