Benzyl alcohol oxidation to benzaldehyde in multiphase membrane reactor

Alcohol oxidations are typically performed with stoichiometric reagents that generate hazardous waste and are usually run in halogenated solvents. A biphasic water-alcohol system with a hydrophobic PVDF membrane at the interface, operating in a flat membrane reactor, is a new solution for the selective oxidation of benzyl alcohol (BzOH) to benzaldehyde (BzH). BzOH can be oxided selectively to benzaldehyde with hydrogen peroxide as oxidizing agent and ammomium molybdate as catalyst. The obtained results showed that, by operating in counter-current mode with an organic-phase flow rate of 1.7 x 10(3) mL/h and an aqueous-phase flow rate of 10 x 10(3) mL/h using composite membrane M1, a conversion of BzOH to BzH of 5.13% with a selectivity of 97.6% has been obtained. The conversion increased up to 47.9% with a selectivity of 98.4% by keeping the two phases in contact using symmetric membrane M4. Compared with conventional reactors, the obtained results affirmed that the use of a membrane contactor plays a crucial role, similar to that of phase-transfer catalyst without the need for organic solvents. The use of hydrogen peroxide oxidant and the absence of promoters and other additives make the reaction interesting from both an economic and environmental point of view.