Side Reactions in Heterogeneous Catalysed Reactive Distillation using the Example of the Production of Butyl Acetate

Reactive distillation can outperform conventional processes for equilibrium-limited or consecutive reactions by continuously removing products, but in heterogeneously catalyzed systems it may also promote side reactions that can determine process feasibility. This work investigates heterogeneously catalyzed reactive distillation for producing n-butyl acetate, with emphasis on key side reactions: n-butanol self-condensation to di-n-butyl ether, n-butanol dehydration to butene isomers, and n-butyl acetate cleavage to butenes and acetic acid. A combined experimental and modeling program is presented, including kinetic studies in an isothermal fixed-bed tubular reactor and a trickle-bed reactor, plus laboratory reactive-distillation experiments (50 mm diameter column) using Katapak-SP11 catalytic packing. Three ion-exchange resin catalysts are compared: fully sulfonated Purolite CT269 and Amberlyst 48 versus surface-sulfonated Amberlyst 46. Thermodynamics are modeled consistently with UNIQUAC; the activity-based equilibrium constant for esterification is derived from literature data, while side reactions are treated as irreversible. Fixed-bed experiments show the main esterification occurs largely on the external catalyst surface, whereas side reactions occur mainly within the polymer matrix of fully sulfonated resins, making surface-sulfonated Amberlyst 46 favorable for high main-reaction rates with reduced byproduct formation. Water is found to inhibit side-product formation, and di-n-butyl ether formation is largely independent of n-butanol concentration in liquid-phase reactor tests; these effects are incorporated into a pseudohomogeneous kinetic model that matches reactor data well. Transferability to reactive-distillation hydrodynamics is assessed in a dedicated trickle-bed setup packed with Katapak-SP11, where reaction rates are lower than in the fixed bed and are captured via a lumped transfer factor mainly dependent on liquid load (≈0.8–0.9). Reactive-distillation experiments detect butenes mainly in the decanter organic phase and cooling trap, while di-n-butyl ether appears throughout the column; oversized reaction zones cause strong selectivity losses. Experiments indicate that combining a conventional reactor with a reactive distillation column having a small reaction zone can maintain high conversion while limiting ether formation, and that Amberlyst 46 further suppresses side reactions. An equilibrium-stage model using fixed-bed esterification kinetics predicts column performance well, and butene formation is reproduced satisfactorily. However, ether formation under boiling reactive-distillation conditions shows n-butanol dependence not observed in liquid-phase kinetics, requiring an adjusted (≈1.3 order) butanol dependence to match column data, suggesting that standard liquid-phase kinetic measurements may be insufficient for boiling reactive-distillation environments and motivating future kinetics studies under boiling conditions and models that account for bulk–polymer phase partitioning.