Continuous Synthesis of Methacrolein over Sulfonic Acid Resin Catalysts: Unraveling the Effect of Acid Strength and Solvent Permittivity

Herein, a novel continuous fixed-bed process for methacrolein (MAL) production via aldol condensation of formaldehyde with propionaldehyde over a sulfonic acid resin was developed, which exhibited high efficiency and remarkable catalytic stability. The influence of Brønsted acid strength and solvent permittivity on aldol reaction was revealed, and the optimal sulfonic acid resin (NKC-9) with suitable acid strength (H0 = 0.46) was identified. Meanwhile, the occupancy of water molecules on acid sites, which would lead to side reactions and catalyst deactivation, could be effectively inhibited through the construction of a liquid–solid catalytic system in non-polar media. The propionaldehyde conversion and MAL yield could reach up to 97.3 and 90.1% after optimization using the response surface method, respectively. Kinetic studies revealed that the surface reaction was the rate-limiting step with an activation energy of 57.1 kJ/mol. No deactivation behavior was observed for this kind of catalyst after 300 h on stream.