An experimental technique for determining the significance of intraparticle diffusion in an aging catalyst

The effects of simultaneous decay and diffusion on a first order reactiion have been investigated. Two limiting types of behaviour are observed. In the first, cumulative conversion on diffusion limited catalysts is shown to behave in a manner opposite to that expected if the catalyst were non‐aging, in that conversion decreases with decreasing particle size. The other extreme shows behaviour consistent with that observed on a non‐decaying catalyst; that is, conversion increases with decreasing catalyst size. Experimental evidence for such behaviour is observed with cumene cracking and gas oil cracking, both on zeolite catalysts. As a consequence of the above observations, it is proposed that a new test involving experimentation at constant cat/oil ratio and over a range of space velocities be used to determine the significance of intraparticle diffusion on a catalyst subject to decay.