Evaluation of nonlinear frequency response method for the hydrolysis of acetic anhydride

Abstract

The method of nonlinear frequency response (NFR) attempts to predict the outcome of perturbation for the instructive input variables using nonlinear functions within the model equations. The aim of the derived models is the estimation of optimal frequencies and amplitudes for sinusoidal changes of the total inlet flow, concentration, temperature and the cooling temperature, as well as combinations of several of these inputs. As a model reaction the hydrolysis of acetic anhydride in a continuously stirred tank reactor (CSTR) has been chosen. This exothermal reaction is investigated for the cases of separately and simultaneously modulated inlet concentrations and feed flow rates. For the experimental validation of predicted model-based results at first a verification and adjustment of the kinetic parameters is performed. Based on these results an optimal steady-state is calculated, which is used as an initial state of periodic operations. To estimate the performance of the reaction system mean values of the conversion of acetic anhydride and the yield of acetic acid are compared to the corresponding steady-state values of the reactor. Different forcing frequencies, input amplitudes and, for multiple input parameter, phase shift between them are investigated. The theoretical foundation as well as systematic exploration of the experimental possibilities will be presented.