(481e) Integrated Thermodynamic and Mechanistic Model of Homogeneous Catalytic N-Oxidation Processes

Integrated thermodynamic and
mechanistic model of homogeneous catalytic N-oxidation processes

Jingyao Wang^a,b, M. Sam Mannan^a,b, Benjamin
A. Wilhite^a,b

a Artie
McFerrin Department of Chemical Engineering, Texas A&M University,
3122 TAMU, College Station, Texas 77843, United
States

b Mary Kay O¡¯Connor Process Safety Center, Texas A&M
University, 3122 TAMU, College Station, Texas 77843, United States

The homogeneous phosphotungstic
acid catalyzed N-oxidation of alkylpyridines by hydrogen peroxide has
important applications in pharmaceutical and fine chemical industries. Current
industry practice is to employ a semi-batch reactor with gradually dosing of
hydrogen peroxide into an alkylpyridine/catalyst solution under isothermal conditions.
However, due to lack of understanding of reaction mechanism and thermodynamic
behavior, this system is subject to significant risk of reactor overpressure
due to hydrogen peroxide decomposition. In this study, semibatch N-oxidation
process was executed in an isothermal reaction calorimeter (RC1) over a wide
range of temperature, catalyst amount and oxidizer dosing rates. Reactor
pressure, reaction heat generation rate and in-situ FTIR spectra of
liquid phase species were recorded in real-time during experiments, and final
product was quantified using HPLC and GC-MS analytical tools. An integrated
thermodynamic and mechanistic model of homogeneous N-oxidation reaction
was proposed based on experimental results. More specifically, Wilson excess
Gibbs model was employed to estimate activity coefficients of highly non-ideal
liquid mixture. Ideal gas law was found satisfactory in calculating
incondensable oxygen pressure. First principle reaction mechanism and kinetics
parameters of (i) catalytic N-oxidation reaction; (ii) catalytic
hydrogen peroxide decomposition reaction; (iii) non-catalytic N-oxidation
reaction; (iv) non-catalytic hydrogen peroxide decomposition reaction was
derived based on experimental findings of this study and past literature. The
proposed integrated thermodynamic model and mechanistic model successfully
predicted highly nonlinear reactor pressure, species mole and reaction duty
profile of homogenous catalytic N-oxidation reaction. The optimal
reactions conditions with maximum N-oxide product yield and minimum
reactor pressure and catalyst usage was theoretically identified and further
verified by experiments. The obtained model can be used for inherently safer
reactor design and application to other homogeneous tungstic acid catalytic
hydrogen peroxide oxidation processes.