The liquid phase backmixing has been reduced significantly by introducing horizontal perforated sieve plates into a 6.2 cm diameter and 77 cm height and in a 20 cm diameter and 90 cm height bubble columns. For the visbreaking operation of the petroleum residue, where the bubble column is used as soaker such a sectionalization has been suggested. The effect of the introduction of different gas quantities at various axial locations has also been studied to check the effect of increasing gas quantity formed in the visbreaking operation. The nonideality in the liquid phase backmixing has been studied by measuring liquid phase RTD and analysed by using one parameter dispersion model. A new parameter FP (flow parameter) has been defined and a correlation to predict liquid phase dispersion coefficient has been developed which covers the entire range of variables used in the present work.