(138c) Impact of Silica on the Performance of Reforming Catalysts

Carbon rejection technologies such as delayed cokers are a popular means to improve the profitability of processing heavy crudes. Given the growing trend to process heavy sour crudes, more refiners are forced to process coker naphtha with high contents of sulfur, olefins, nitrogen and Si-compounds.

Reforming catalysts become contaminated with Si if the naphtha hydrotreating (NHT) catalyst is operated beyond its Si breakthrough. The cyclic trimer and tetramer Si-containing compounds originate from the decomposition of the polydimethylsiloxane de-foaming agent injected in the coke drums to control the foam-over to the coker fractionator. These Si compounds are transferred in the hydrotreated naphtha feeding the Reformer unit and will irreversibly poison the reforming catalyst.

Several refiners operating Platforming CCR units started to experience both production and catalyst performance issues that were linked to the heavily Si-contaminated reforming catalysts. We will show that Si-poisoned aged catalysts are less stable, active and selective than fresh reforming catalysts. Si contamination can also lead to alumina thermal damage and poor chloride retention. EDXRF and SEM analyses of the aged catalyst pills confirmed the extent of Si-contamination and ²⁹Si-MASNMR indicated that Si is present as silica, several layers thick anchored to the alumina surface, present as islands mainly on the edges of the catalyst pills.