Sequential Identification
of Model Parameters by Derivative
Double Two-Dimensional Correlation Spectroscopy and Calibration-Free
Approach for Chemical Reaction Systems
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Abstract
A sequential identification approach by two-dimensional
(2D) correlation
analysis for the identification of a chemical reaction model, activation,
and thermodynamic parameters is presented in this paper. The identification
task is decomposed into a sequence of subproblems. The first step
is the construction of a reaction model with the suggested information
by model-free 2D correlation analysis using a novel technique called
derivative double 2D correlation spectroscopy (DD2DCOS), which enables
one to analyze intensities with nonlinear behavior and overlapped
bands. The second step is a model-based 2D correlation analysis where
the activation and thermodynamic parameters are estimated by an indirect
implicit calibration or a calibration-free approach. In this way,
a minimization process for the spectral information by sample–sample
2D correlation spectroscopy and kinetic hard modeling (using ordinary
differential equations) of the chemical reaction model is carried
out. The sequential identification by 2D correlation analysis is illustrated
with reference to the isomeric structure of diphenylurethane synthesized
from phenylisocyanate and phenol. The reaction was investigated by
FT-IR spectroscopy. The activation and thermodynamic parameters of
the isomeric structures of diphenylurethane linked through a hydrogen
bonding equilibrium were studied by means of an integration of model-free
and model-based 2D correlation analysis called a sequential identification
approach. The study determined the enthalpy (Δ<i>H</i> = 15.25 kJ/mol) and entropy (<i>T</i>Δ<i>S</i> = 13.20 kJ/mol) of CO···H hydrogen bonding
of diphenylurethane through direct calculation from the differences
in the kinetic parameters (δΔ<sup>⧧</sup><i>H</i>, −<i>T</i>δΔ<sup>⧧</sup><i>S</i>) at equilibrium in the chemical reaction system