A new pair of reactions to characterize imperfect macro-mixing and partial segregation in a stirred semi-batch reactor

Abstract A new pair of reactions has been developed based on a first order decay (an internal clock) and a parallel second order diazotisation coupling reaction, represented by A → S and A+B → R. By adjustment of concentrations and pH, the pair of rate constants can be ‘tuned’ to various reaction speeds giving scope for assessing various rates of mixing and agitation. When B is added semi-batchwise to A, any region rich in A favours the decomposition reaction. Imperfect macro—mixing therefore leads to an increase in the less desirable by—product S. Experiments have been performed using different rates of stirring and different addition points (liquid surface or impeller). The pair of reaction show sensitive yield variations under these different mixing conditions. Quantitative interpretation of the experiments has been based on a networks—of—backmixed zones model, using networks of size (20×20)+(20×40) comprising some 1200 zones. Individual species concentrations in space are presented as sectional image reconstructions. The model helps the understanding of the experimental results and reasonable agreement is obtained.