The mass transfer in catalyst capsule is analysed.It is pointed out that the wetting incompletion of catalyst beads and the concentration gradient within the catalyst capsule reduce catalyst efficiency.The effectiveness factor of catalyst capsule equals to the product of η s and η c.The former

the effective wetting rate of catalyst beads

represents the influences of wetting incompletion of catalyst on catalyst efficiency

the latter represents that of concentration gradient.A two- dimensional model is established and an equation to calculate η c is given.It is indicated that η c is influenced not only by radial diffusion

but also by axial liquid flow.The influence of diffusion resistance on effectiveness factor is greatly weakened by axial liquid flow.