Modeling of batch reactions with in situ spectroscopic measurements and calorimetry

This paper describes kinetic fitting of UV‐visible spectra and energy flow measured as a function of time from a reaction calorimeter, giving a single global model that achieves fusion of spectroscopic and calorimetry data. We demonstrate that a temperature controlled model of a reaction mechanism fitted to in situ spectroscopic measurements can be coupled to an energy balance model, since the amount of energy released by the reaction is proportional to the change in concentration of reactants and products with time. This allows simultaneous determination of the reaction mechanism parameters and the reaction enthalpy by fitting the coupled model to the spectroscopic and temperature data. The resulting model fully characterizes the kinetics and thermochemical properties of reactions that take place during a batch titration reaction of salicylic acid (SA) with acetic anhydride (AA) to form acetylsalicylic acid (ASA). The model comprises a system of ordinary differential equations fit directly to the spectroscopic and calorimetry data. It permits accurate estimates of model parameters producing estimates of concentration and reaction temperature profiles as a function of time, provided a sufficiently accurate description of the reaction mechanism is specified. No standards or pure component spectra were required, giving calibration‐free estimates of concentration and temperature profiles. The parameters estimated in the model include kinetic rate constants and heat of reaction of the reactions observed during the experiment. In addition, heat capacities of reagents flowing into the reactor and thermal transfer coefficients were estimated. Copyright © 2006 John Wiley & Sons, Ltd.