Reaction kinetics of the aldol condensation of mixed C 7 aldehydes

Abstract

A novel process couples hydroformylation with aldol condensation to form detergent alcohols from low-cost branched hexenes. Kinetic studies for the aldol condensation of the hydroformylation products, mixed heptanals, were performed to find ways of increasing the very slow reaction rates. The effects of co-solvent concentration, base concentration, batch residence times, temperature and aldehyde concentration were evaluated in batch experimental runs. Results showed that increasing the concentration of a methanol co-solvent and of the NaOH gave faster reaction rates. When methanol or other hydrophilic organic compound was not used as a co-solvent for the aldol condensation reaction, the reaction was first order in aldehyde concentration. However, methanol made the reaction second order in aldehyde concentration. Separate kinetic models were developed for the α-branched aldehydes and for the aldehydes unbranched at the α-position. The α-branched aldehydes must cross-aldol with aldehydes unbranched at the α-position for condensation to occur, and a different kinetic model results. Complete kinetic equations were derived and rate constants at 110 °C were determined for each aldehyde.