Evaluation of Spent Catalyst Structure Changes during Ethylbenzene Dehydrogenation in Different Technologies

Ethylbenzene (EB) dehydrogenation to styrene (SM) on an industrial scale is generally performed using classic and SMART (Styrene Monomer Advanced Reheat Technology) technologies. In the current study, spent catalysts structural changes through classic and SMART technologies were investigated and compared with the fresh catalyst. For this purpose, XRF, XRD, SEM-EDX, FT-IR, BET and crushing strength analysis were employed. It was found that styrene production via SMART technology with 40% potassium loss is led to more catalyst deactivation than the classic ones (26%). Due to pore mouth blocking by coke formation, the average pore radius in both classic and SMART spent catalysts is reduced about 33% and 53% compared to the fresh ones, respectively. SEM analysis showed that potassium migration mechanism is related to the temperature gradient in the classic spent catalysts and chemical vapour transportation in the SMART spent catalysts. Comparative evaluation of the catalysts performance indicated that the SMART spent catalyst with about 72% activity loss is more deactivated than the classic ones (61%).The large drop of styrene yield (72-74%) of SMART spent catalyst revealed that the activity is more depending on the pore mouth size, rather than the specific surface area. However, in situ steam injection redistributed migrated potassium and increased the selectivity of the classic spent catalyst, but it was led to more potassium migration and catalyst deactivation in the SMART spent ones. According to this study, styrene production and industrial unit design based on SMART technology not recommended strongly.