Two phase gas–liquid reaction studies in a circular capillary

The hydrogenation of 4-nitrobenzoic acid to 4-aminobenzoic acid was studied in a circular capillary, wash coated with a Pd on alumina catalyst, operated in vertical two phase down flow. The influence of multiphase flow pattern (slug (Taylor) flow, annular, bubble and churn) upon the observed reaction rate was investigated; in slug flow the reaction rate was a function of the liquid slug and gas bubble lengths. Mass transfer models for the different flow patterns are proposed based on previous mass transfer coefficient models.