Optimal Conditions for Coke Extraction of Spent Catalyst by Accelerated Solvent Extraction Compared to Soxhlet

Abstract

Catalyst deactivation by coke deposition is a problem of great and continuing concern in residue hydroprocessing operations. To reach a better understanding of coke formation, it is desirable to obtain information on the amount and composition of soluble fractions of coke deposited. Since extraction of spent catalysts by a number of solvents with gradually increasing polarity is time-consuming, this study was undertaken to evaluate two extraction methodsSoxhlet extraction and accelerated solvent extraction (ASE)with regard to their efficiency and relevancy (recovery, experiment time, and volume of solvent used) for characterization of coke. In both methods, spent catalysts were successively extracted with n-heptane, toluene, tetrahydrofuran, and dichloromethane. 13C nuclear magnetic resonance (NMR) was used to study both the soluble coke and the insoluble coke on the catalysts. ASE was found to be the superior extraction method because ASE reached the same efficency as Soxhlet after 5 min of extraction compared with 6−12 h by Soxhlet using less solvent.