Juha Lehtonen

Development of a kinetic model for the esterification of acetic acid with methanol in the presence of a homogeneous acid catalyst

Abstract The esterification kinetics of acetic acid with methanol in the presence of hydrogen iodide as a homogeneous acid catalyst was studied with isothermal batch experiments at 30–60°C. The catalyst concentration was varied between 0.05 and 10.0 wt%. The experiments revealed that besides the main reaction, the esterification of acetic acid, a side reaction appeared: the catalyst, hydrogen iodide, was esterified by methanol to methyl iodide. Plausible reaction mechanisms for methyl acetate and methyl iodide formation were proposed. The rate-determining step in the acetic acid esterification was assumed to be the nucleophilic attack of methanol to the carbenium ion formed through proton donation to acetic acid, whereas the rate-determining step in the hydrogen iodide esterification was presumed to be the substitution of the iodide to protonated methanol. Hydrogen iodide and acetic acid act as proton donors; thus the protolysis equilibria of acetic acid and hydrogen iodide were included in the mechanism. Rate equations, concentration-based as well as activity-based with UNIFAC activity coefficient estimations, were derived, and the kinetic and equilibrium parameters included in the rate equations were estimated from experimental data with regression analysis. Simulation of the models with the estimated parameters revealed that the rate equations predict correctly the experimental trends in the acid catalyzed esterification.

Comparison of polyvinylbenzene and polyolefin supported sulphonic acid catalysts in the esterification of acetic acid

Abstract New polyolefin supported sulphonic acid catalysts were used in the esterification of acetic acid with methanol. The new catalysts turned out to be stable and active in esterification. The esterification kinetics was modelled with a mechanistic rate equation, the parameters of which were determined by non-linear regression. The esterification rate constant of the most active modification of the new catalyst was 9.6×10 −10 xa0dm 9 /(mol 2 xa0gxa0min) at 55°C, which clearly exceeds the corresponding value obtained with a traditional polyvinylbenzene supported catalyst, 1.5×10 −10 xa0dm 9 /(mol 2 xa0gxa0min).

Polyesterification kinetics of complex mixtures in semibatch reactors

Abstract A systematic stoichiometric and kinetic model was developed for the acid-catalysed polyesterification of unsaturated dicarboxylic acids and mixtures of dicarboxylic acids. The model was based on a rigorous treatment of the functional groups and their reactions: esterification, cis–trans isomerization and double-bond saturation through Ordelt reaction. The model was applied on the polyesterification of maleic and phthalic acids with ethylene glycol, propylene glycol, diethylene glycol and dipropylene glycol in a semi-batch reactor at 160–195°C. Kinetic and thermodynamic parameters included in the model were estimated with non-linear regression. It was found that important simplifications can be introduced: the rate constants of the different esterification and isomerization reactions can be set equal, whereas it was necessary to treat the different double-bond saturation reactions with individual rate constants. A comparison of model predictions with experimental data revealed that the proposed kinetic treatment is relevant for polyesterification of complex mixtures.

ASYMPTOTIC ANALYSIS OF CHEMICAL REACTIONS

Abstract Chemical reaction schemes are typically simplified by considering the controlling steps of the process, the ‘fast’ reactions being taken into account by quasi-equilibrium assumptions. Traditionally, intuitive reasoning is employed to arrive at the simplified system. This may, however, be cumbersome and sometimes misleading. In this paper a systematic approach is presented that guarantees that the simplified model coincides with the asymptotics of the original one.

Modelling and scale-up of a loop reactor for hydrogenation processes

A dynamic model for the scale-up of semibatch loop reactors was developed. The mathematical model comprises the essential parts of the loop reactor: the reaction vessel, the ejector and the circulation loop. Tanks-in-series and axial dispersion concepts were applied on the description of the non-ideal flow pattern of the reactor. The dynamic axial dispersion model was discretized with finite differences with respect to the spatial coordinate, and the created ordinary differential equations were solved with the backward difference method suitable for stiff differential equations. The loop reactor model was tested with a case study, a homogeneously-heterogeneously catalyzed reaction system, reductive alkylation of aromatic amines. Simulations showed that rate equations obtained from laboratory-scale experiments can be successfully combined to the flow model of the loop reactor: the behaviour of a large-scale loop reactor was predicted with satisfactory accuracy.

Modelling of speciality chemicals production in liquid–liquid reactors—A case study: synthesis of diols

Abstract Generalized mass balance models were derived for semibatch liquid–liquid reactors, which are frequently used in the production of fine and speciality chemicals. The model comprises the reaction kinetics, liquid–liquid equilibria as well as interfacial mass transfer effects. The reactor model was applied on a case study, homogeneously catalyzed synthesis of diols through aldol condensation and Cannizzaro reaction. Rate equations for the process were obtained by applying steady-state approximations on ionic reaction intermediates. The rate equation were incorporated into the mass balances and tested with experimental kinetic data. The model was able to imitate the experimental behaviour of the two-phase system.

Dynamic modelling of simultaneous reaction and distillation in a semibatch reactor system

A dynamic model for a system containing a semi-batchwise operating reaction vessel connected to a distillation unit was developed. The approach consisted of kinetic equations for the reactions as well as a dynamic model for the distillation unit. As an example reaction, the catalyzed polyesterification of maleic acid with propylene glycol was used. The kinetic and the mass transfer parameters at 170°C were estimated from experimental data. The fit of the model to the data indicated that the approach is suitable for the description of semibatch liquid phase reaction-separation systems.

Kinetic analysis of the reaction network in the catalyzed polyesterification of unsaturated carboxylic acids

Abstract A generally applicable model was developed for the kinetic analysis of the reaction network in the polyesterification of unsaturated dicarboxylic acids with diols in the presence of homogeneous acid catalysts. The network consists of the esterification reactions as well as the side reactions, i.e. the cis-trans isomerization and the double bond saturation reactions. Rate equations based on plausible reaction mechanisms were derived and the parameters of the rate equations were determined, with non-linear regression analysis using the polyesterification of maleic acid with propylene glycol at 140–190 °C as a demonstration system. Comparisons of the model predictions with the experimental data showed that the approach provides a reasonable description of the polyesterification network.

Modelling of complex liquid–solid reaction systems in semibatch reactors: Claisen condensation in industrial scale

Several organic liquid-phase reactions are carried out in the presence of a sparingly soluble reactive solid phase which is gradually dissolved during the course of the reaction. The presence of the reactive solid phase complicates the treatment of kinetic data, since the overall reaction rate is influenced by the solubility equilibrium and mass transfer rate of the solid compound. A mathematical model has been derived for an organic reaction system with one reactive solid compound. The modelling concept was applied on a linear multistep reaction system, Claisen condensation. The solubility of the solid compound was measured under non-reactive conditions and the kinetic parameters for the reaction system were determined from the data obtained with semibatch experiments. Model simulations elucidated the behaviour of the sparingly soluble reactive compound in the process and they indicated that the rate equations describe the experimental kinetic data well.