Modelling of reversible novolac type phenol-formaldehyde polymerization

Abstract

The reversible polymerization of acid-catalysed phenol and formaldehyde has been modelled through the use of five species A to E. There are two possible mechanisms for the reverse reaction of the polymer formation based upon which two possible kinetic models (1 and 2) have been proposed. These two models arise because during the reverse reaction between these species and water, two possible routes can occur. It has been shown analytically that both these kinetic models would yield identical concentrations of A to E in the reaction mass; only an uncertainity in predicting concentrations of formaldehyde and bound CH₂OH exists. Thus any of these models may be equivalently chosen if the purpose of the simulation is to analyse the product formed. Analysis of the batch reactor under the variation of the ratio of phenol and formaldehyde,[P]₀ /[F]₀, in the feed shows that the maximum branching in the polymer occurs at a ratio of 0.5 whereas a ratio 1.60 is found to maximize the formation of linear chains. The application of a vacuum to the reaction mass has been modelled to give a constant but lower water concentration. The effect of the vacuum has been examined and is found to give a longer but more branched polymer compared with that for batch reactors with no vacuum.