COMBINATION OF OVERALL REACTION-RATE WITH GIBBS ENERGY MINIMIZATION

A method to calculate multi-component chemical reaction mixtures as a sequence of time-dependent, intermediate thermochemical states is pres ented. The method combines the: overall reaction kinetics with thermod ynamic Gibbs energy minimization, The overall reaction is assumed to p roceed according to the Arrhenius rate law. During the time-course of the reaction, the temperature;md composition of the reaction mixture a re calculated by a thermodynamic subroutine, which minimizes the Gibbs energy of the system, The extent of the overall reaction is algorithm ically constrained in the Gibbs energy minimization procedure, During the sequential calculation, the kinetic condition is removed by finite differences, The temperature of each intermediate state is reached by an iterative procedure, which takes into acconnt the heat transfer be tween the system and its surroundings and the enthalpy changes due to the chemical reactions, Thus, the method allows for the effect of temp erature on the reaction kinetics as the reaction evolves. The chemical species present in each intermediate state are virtually independent and there is a chemical potential assigned to each of these species. T he gradual chemical change in the thermodynamic system proceeds from t he initial state of mixed reactants to the final state of product mixt ure, Both stationary and transient phenomena may be calculated, The me thod has been applied to some well-known industrial multi-component re action systems and a fair agreement between the calculated and measure d values has been obtained. The application of the thermochemical algo rithm in reaction calorimetry is discussed. (C) 1997 Elsevier Science B.V.