Application of semibatch technology on the investigation of homogeneously catalyzed consecutive and parallel-consecutive liquid-phase reactions: Kinetic measurements and modelling

Experimental measurements of the reaction kinetics of complex consecutive and parallel-consecutive reactions is a challenge, because the reaction rates of the sequence are often very different, the primary reactions being much more rapid while the secondary and tertiary reactions might be much slower requiring very long kinetic experiments. An approach to surmount this dilemma is proposed for homogeneously catalyzed liquid-phase reactions by adding the catalyst gradually into the reaction mixture: in this way the primary reactions are slowed down but the secondary and tertiary reactions are accelerated. A mathematical model for this approach was developed and complex reaction systems were simulated numerically in the Damköhler space. The applicability of the approach was illustrated with experimental data obtained for the formation of mono- and diesters from carboxylic acids and dialcohols in the presence of homogeneous strong acid catalysts. Acetic acid and ethylene glycol were used as reagents in the experimental work and aqueous hydrogen chloride was the homogeneous catalyst. Rate equations for this reaction systems were derived based on molecular mechanisms and the kinetic parameters in the rate equations were estimated with regression analysis. Simulation of the esterification model illustrated the benefits of the proposed experimental semibatch approach for complex reaction systems.