APPLICATION OF A STOCHASTIC NETWORK PORE MODEL TO A CATALYST PELLET

Abstract

Abstract A previously developed stochastic two-dimensional network pore structure model has been applied directly to a nickel/alumina commercial catalyst pellet. A technique has been devised to determine the pore diameter distribution function of cylindrical pore segments for any prescribed network dimension which will exactly replicate the experimentally observed mercury penetration curve for the pellet in the method of mercury porosimetry. This stochastic network representation for the catalyst pellet pore structure is superior to the classical parallel bundle model since it incorporates the element of pore interconnectivity. The model has been extended to investigate the phenomena occurring during the accumulation of a foulant deposit (e.g. coke in hydrocarbon catalysis) for the pore structure determined for a 10 × 10 set of network elements for the pellet under study. The analysis shows how the build-up of a deposit causes physical blocking of the smaller pores at quite low accumulations of foulant which results in inaccessibility of parts of the interior pore structure. This necessarily results in only partial filling of the pore structure with deposit, with a tendency for greater accumulation towards the pellet exterior. This kind of behaviour is not possible with the parallel bundle model. A detailed comparison of the two pore models in respect of accessible interior volume at various foulant accumulations is presented. The derived network model based upon the penetration curve gives an independent prediction of the mercury porosimeter retraction curve which is in reasonably close agreement with the experimental result, thus confirming the probable utility of the model in predicting and correlating other macroscopic properties of the catalyst pellet.