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The nonlinear frequency response (NFR) method, which is an analytical, fast, and easy method for evaluating the performance of forced periodically operated chemical reactors, was used to investigate possible improvements to a nonisothermal continuous stirred tank reactor (CSTR) when inlet concentration and/or flow rate is periodically modulated. The product yield corresponding to periodic operation is defined, expressions for its estimation, based on the NFR method, are derived, and it is used to evaluate the performance improvements due to periodic operation. Part I considers the general nonisothermal case. In Part II, these results are applied to an adiabatic CSTR and used to evaluate possible improvements for the case of the hydrolysis reaction of acetic anhydride.

In this theoretical contribution, nonlinear frequency response analysis was applied for the investigation of electrochemical methanol oxidation. This technique expresses the input-output behavior of any weakly nonlinear system with the help of the Volterra series expansion and generalized Fourier transform into so-called higher order frequency response functions. These functions contain the system's nonlinear fingerprint. They can be derived analytically from a nonlinear model. These functions can be obtained experimentally from the measurement of higher harmonics induced by a high amplitude sinusoidal perturbation of the system of interest. Frequency response functions up to the second order have been derived analytically for four different model varieties describing the kinetics of the electrochemical methanol oxidation. The first-order frequency response function corresponds to the reciprocal value of the well-known electrochemical impedance, which represents the linear part of the frequency response. This function does not contain sufficient information for discrimination between the different kinetic models. In contrast, the symmetrical second-order frequency response functions H 2 ͑,͒ show differences in shape, which substantiate the availability of the theoretical prerequisites for model discrimination. A detailed parametric study for all four model variants has been performed. The results show that the basic features of the shapes of the H 2 ͑,͒ amplitude spectra corresponding to the four models remain unique. The ubiquitousness of the qualitative differences between the competing models, for the whole set of parameters chosen for our analysis, suggests that the aforementioned amplitude spectra contain sufficient information for an unequivocal model discrimination.In direct methanol fuel cells ͑DMFCs͒, the fuel methanol is electrochemically oxidized without being converted into hydrogen in a reformer unit. This has many advantages compared to using hydrogen gas as the fuel, but due to the more complex structure of the methanol molecule, the kinetics of its oxidation is more complicated and imposes severe kinetic limitations to DMFC operation. For this reason, the kinetics of methanol oxidation has been the subject of intensive research activities. 1-5 The major motivation was to identify a rate expression for methanol oxidation in DMFC by applying a combined experimental and model-based approach. Thus, the kinetics of methanol oxidation was experimentally investigated by using different electrochemical methods under technically relevant conditions ͑membrane electrode assembly, defined mass-transfer conditions͒. For half-cell studies, a specially designed electrochemical cell was prepared. 6 The measurements were followed by the formulation of suitable kinetic models for methanol oxidation. Based on literature findings and on our own experimental data, a lumped mechanism for methanol oxidation was selected and, based on this mechanism, four different kinetic models were formulated by introducing two types ...

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Nonlinear Frequency Response (NFR) method is a relatively new method which can be used for fast evaluation of possible process improvements through periodic operations. The method is analytical and approximate. Its main task is to give an answer whether periodic modulation of one or more process inputs can result in improved process performance. The method is explained in brief and an overview of the existing applications is given. The review covers simple reactions performed in isothermal and non‐isothermal stirred tank reactors exposed to different modulated inputs (inlet concentration, flow‐rate, inlet temperature, temperature of the heating/cooling medium). Processes with two simultaneously modulated inputs and different shapes of the periodic input are also considered. The results of the NFR method are compared with the results of numerical simulation and a critical evaluation of the method is given.