Integrated electrocatalytic processing of levulinic acid and formic acid to produce biofuel intermediate valeric acid†
Herein, we report integrated electrocatalytic processing of simulated acid-catalyzed cellulose hydrolysis downstream (levulinic acid + formic acid) to the biofuel intermediate valeric acid (VA). This green electro-biorefining process does not require complex steps to separate levulinic acid and formic acid (FA) from H2SO4; instead it couples electrocatalytic hydrogenation (ECH) of levulinic acid (LA) in a single electrocatalytic flow cell reactor and electrocatalytic oxidation of formic acid in a proton exchange membrane-direct formic acid fuel cell (DFAFC). The presence of FA has shown no negative effect on the ECH of LA and a high VA selectivity of >90% can be achieved on a non-precious Pb electrode while the Faradaic efficiency remains >47% during 8 hours of reaction in the single electrocatalytic flow cell reactor. This stream is fed directly to the DFAFC with a Pd/C anode catalyst to self-sustainably remove FA where 47% conversion of FA can be reached in 6 hours. However, electro-oxidation of FA over Pd/C appears to be reversibly inhibited by the product VA produced during ECH of LA. The electro-oxidation of FA + C2–C5 alkyl carboxylic acid in the half cell study shows that such an inhibition effect could have originated from the –COOH adsorption on the Pd surface. Higher carboxylic acid concentration and longer carbon chain lead to more serious loss of the electrocatalytic surface area (ECSA) of Pd/C.