Combined Online Spectroscopic, Calorimetric, and Chemometric Analysis: Reaction Enthalpy Determinations in Single and Parallel Reactions

Abstract

Calorimetry and signal processing: Vibrational spectroscopies, heat-flow microcalorimetry, and multivariate analysis are combined to decouple the reaction enthalpies of parallel reactions [picture: see text]. This methodology allows the evaluation of reaction enthalpy from complex systems without recourse to conventional kinetic modeling. Simultaneous in situ/online spectroscopy and heat-flow measurements as well as multivariate analyses are performed, apparently for the first time, to determine heats of reaction for single and parallel reactions. Two different vibrational spectroscopy techniques, namely Raman and FTIR spectroscopy, are used in conjunction with flow-through TAM III microcalorimetry. With respect to the spectroscopic analysis, the reaction spectra are first analyzed to determine the pure-component spectra and the corresponding concentrations without recourse to external calibration. With respect to the calorimetric analysis, a soft modeling approach is employed to determine the heats of reaction without recourse to any conventional kinetic models. This combined approach is implemented to determine the extents of reaction as well as the corresponding heats of reaction at 298.15 K and 0.1 MPa for a) the hydrolysis of acetic anhydride (single reaction) and b) the hydrolysis of methyl paraben and ethyl paraben in alkaline solution (both single and parallel reactions). In the latter case, the heat-flow contributions from the two simultaneous reactions are successfully decoupled. Taken together, these results demonstrate proof of concept for the present approach. The newly developed methodology appears to be quite general and particularly useful for investigating complex reaction systems. This is particularly true for multiple simultaneous reactions and reactions where the detailed kinetic expressions are not available, or cannot be easily determined. The use of extents of reaction is also very helpful where there is high variability in reaction rates, that is, due to the presence of impurities, changes in catalyst activity, or concentrations, temperature, and pH.

Online Reaction Monitoring and Evaluation of Kinetic Parameters for Dilute Reactions Using Refractive Index Measurements

“…These values are also compared to those previously and independently determined using FTIR spectroscopy as well as calorimetric measurements. 8,10 The results show that the rate constants determined from the present refractive index method are in good agreement with those determined from other techniques. It is also noted, however, that the standard deviations of the rate constants determined from the present refractive index measurements are typically greater than those determined from both spectroscopic and calorimetric measurements.…”

“… a Standard deviations are reported as 2σ. b Evaluated directly from concentration data (obtained using FTIR spectroscopy) as reported in ref . c Evaluated directly from heat flow data (obtained using flow-through Thermal Activity Monitor (TAM) III microcalorimeter) as reported in ref . d Reference . e Independently measured using TAM III microcalorimeter with ampoule measurements. Detailed procedure can be found in ref . …”

“… b Evaluated directly from concentration data (obtained using FTIR spectroscopy) as reported in ref . …”

“…In addition to spectroscopic measurements, several physico-chemical property measurements such as refractive index, , volume, , surface tension, , conductivity, viscosity, heat-flow, − etc. can also be used to monitor a reaction.…”

Estudio de la transferencia de calor en la etapa de cocido en la elaboración de aceitunas verdes al estilo sevillano

“…Estos iones provocan la rotura de los enlaces és-ter, tanto de la oleuropeína (que es el objetivo del tratamiento) como de los polisacáridos estructurales (pectina, hemicelulosa y celulosa) (Marsilio et al, 1996). La hidrólisis alcalina de un éster libera calor, es exotérmica (Schneider y Stoessel, 2005;Tjahjono et al, 2009;Taylor y Kluger, 1992;Wadsö, 1958), de modo que las reacciones que se producen dentro de la aceituna generan calor y pueden ser responsables, junto con la transferencia de calor de las aceitunas a la solución y con la dilución de la concentración de sosa, del aumento de temperatura progresivo durante la etapa de cocido.…”