AbstractA discrete six‐lump kinetic model for the thermal cracking of vacuum residue in the visbreaking process has been developed, and the time‐dependent behavior of each individual lump has been determined. A combination of the heuristic method and gradient‐based method (hybrid method) has been taken into account to optimize the parameters of the model. A new concept of objective functions has been presented and applied for optimization, so more acceptable results have been obtained. Such an approach has not been presented before. A number of 60 parameters was considered primarily, which has been reduced to 36 with the aim of flash calculation information, and optimized. The obtained results are in good agreement with experimental data. The analysis of the estimated rate constants showed that the cracking of vacuum residue to lighter products was the more dominant reaction pathway during the visbreaking process over the temperature range of 400–430 °C.