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The phenomenon of conservatively perturbed-equilibrium (CPE) in multi-route catalytic reactions was studied in the plug-flow reactor (PFR). The following multi-route mechanisms were chosen for studying, i.e., the two-route mechanism with the single common intermediate, the three-route mechanism with some common steps, and the two-route mechanism with the single common step and two common intermediates. All mentioned mechanisms exhibit the CPE-phenomenon. At given rate coefficients, the mechanism with the single common intermediate showed the greater CPE-effect than the mechanism with the common steps. A special computer experiment was performed in which the kinetic characteristics of non-catalytic and catalytic reactions have been compared. In this experiment, both non-catalytic and catalytic reactions have the same overall-reactions with the given equilibrium constant. It was shown that the absolute values of extreme concentrations at the CPE-point are almost the same. In this case, it is possible to estimate the concentrations at the CPE-values for complex reactions based on similar characteristics of the corresponding simple ones. [ABSTRACT FROM AUTHOR]

In the recently introduced concept of Conservatively Perturbed Equilibrium (CPE), a chemical system is instantaneously perturbed from equilibrium while keeping the temperature and the total amount of every element constant. The concentrations of the system's species are then monitored until equilibrium is recovered. If the concentration of a given species was not initially modified by the perturbation, it will change from the initial equilibrium value over a transient evolution back to that equilibrium value. Such an unperturbed species must therefore reach at least one unavoidable extreme concentration value, a maximum or a minimum. For reversible first-order reactions, theoretical and computational procedures are presented in this paper for optimizing the maximal concentration during the transition. The main result is that this reduces the n - dimensional optimization problem of choosing the optimal initial condition and optimal stopping time to n - 1 one-dimensional problems. The developed approach is illustrated by a 4-step cyclic reaction. [ABSTRACT FROM AUTHOR]

The "conservatively perturbed equilibrium" (CPE) technique for a complex chemical system is computationally analyzed in a batch reactor considering different linear mechanisms with three and four species. Contrary to traditional chemical relaxation procedures, in CPE experiments only some initial concentrations are modified; other conditions, including the total amount of chemical elements and temperature are kept unchanged. Generally, for "unperturbed" species with initial concentrations equal to their corresponding equilibrium concentrations, unavoidable extreme values are observed during relaxation to the equilibrium. If the unperturbed species is involved in one step only, this extremum is a momentary equilibrium of the step; if the unperturbed species is involved in more reactions, the extremum is not a momentary equilibrium. The acyclic mechanism with four species may exhibit two extrema and an inflection point, which corresponds to an extremum of the rate of the species change. These facts provide essential information about the detailed mechanism of the complex reaction. [ABSTRACT FROM AUTHOR]

• The phenomenon of CPE is experimentally verified for a non-linear chemical reaction. • The transient extremum can be an approximate momentary partial equilibrium. • Kinetic parameters can be determined based on the "reactant-product" intersection. The phenomenon of "conservatively perturbed equilibrium" (CPE) for a complex non-linear chemical system was experimentally verified in a batch reactor in which ethanol and benzyl alcohol react with acetic acid producing two different esters and water. Three possible CPE cases, i.e., acetic acid and water unperturbed, ethanol and ethyl acetate unperturbed, benzyl alcohol and benzyl acetate unperturbed, were systematically investigated. For unperturbed substances with initial concentrations of their corresponding equilibrium concentrations, unavoidable extreme values were observed in relaxation to the equilibrium. If the unperturbed substances were involved in two reactions, a proper momentary partial equilibrium was not observed at the transient extremum. However, the transient extremum could be an approximate momentary partial equilibrium for the reaction of the unperturbed substance if the rate of some step is insignificant. This fact provides essential information about the detailed mechanism of the complex reaction. [ABSTRACT FROM AUTHOR]

Highlights • Initial concentrations are replaced by equilibrium concentrations for some substances. • Unavoidable extreme values are observed in relaxation to the equilibrium. • At extreme value some reactions can be at momentary partial equilibrium. • In particular cases, the extremum time does not depend on initial conditions. • The necessary conditions for CPE observation were determined. Abstract The phenomenon of "Conservatively Perturbed Equilibrium" (CPE) in chemical kinetics is distinguished using a sequence of first-order reactions (linear mechanism) and non-linear mechanisms as well. In this phenomenon, some, not all initial concentrations of the closed chemical system are replaced by the corresponding equilibrium concentrations at the same total amount of each chemical element. Properties of CPE-phenomenon are described: 1. For the substance which initial concentration is taken as the equilibrium one, the concentration extremum in a way to the equilibrium is unavoidable. 2. This extremum can be a momentary partial equilibrium for some steps of the chemical mechanism. 3. Time of occurrence of this extremum is independent of the perturbation. Properties 1 and 2 are general properties. Property 3 is specific for the linear mechanism studied. [ABSTRACT FROM AUTHOR]