Investigation of the problems with using gas adsorption to probe catalyst pore structure evolution during coking

Abstract

A common approach to try to understand the mechanism of coking in heterogeneous catalysts is to monitor the evolution of the pore structure using gas adsorption analysis of discharged pellets. However, the standard methods of analysis of gas adsorption data, to obtain pore-size distributions, make the key assumption of thermodynamically-independent pores. This assumption neglects the possibility of co-operative adsorption phenomena, which will shown to be a critical problem when looking at coking catalysts. In this work the serial adsorption technique has been used to detect and assess the extent of co-operative effects in adsorption within coking catalysts. The reaction of decane over a hydroprocessing catalyst was used as a case study. It has been shown that the conventional analysis method would lead to a flawed picture of the pore structure changes during the coking process. For the case-study considered in this work, it was found that co-operative adsorption effects meant that 26% of the measured adsorption was occurring in pores up to three times larger than the size conventional analysis would presume. The serial adsorption technique was thus shown to provide important additional information on pore structure evolution during coking. A study of the kinetics of adsorption has been used to infer information about the general spatial location of the coking process within a pellet.

Characterization of pore coking in catalyst for thermal down-hole upgrading of heavy oil

“…An additional technique, which is gaining popularity, is thermoporometry. However, these techniques have problems with pore-pore interaction phenomena affecting the accuracy of the pore size distributions for disordered solids that are particularly acute for coked catalysts (Gopinathan et al, 2013). However, these issues, which will be described in more detail below, can be overcome by the novel integrated method used in this paper (Shiko et al, 2012).…”