Mechanism of Reboiler Fouling during Reforming

Abstract

Friedel−Crafts chemistry pathways catalyzed by iron chloride and/or aluminum chloride were determined to be responsible for fouling observed on the shell side of a reformer reboiler unit. Characterization of the foulant material and reformate led to elucidating the mechanism and proposed mitigation routes. The reboiler solid foulant material was found to contain primarily coke (86 wt %) and inorganics (14 wt %). The inorganics are mostly iron-based materials as iron sulfide, chloride, and oxide. These corrosion products can also increase the lay-down and subsequent coking of heavy-end materials. In addition to the iron compounds, the balance of metal types are mostly ppm levels of alumina and silica. Analyses of the reformate revealed the presence of multi-ring compounds in the product. Additional evidence that aluminum chloride is present in the reformate lead to the conclusion that the heavy ends are more than likely forming via Friedel−Crafts reactions. With the significant liquid hold-up in the reboiler and skin temperatures near 500 °C, these heavy-end materials have the opportunity to lay down on the shell-side surface of the heat bundle and degrade to coke over time. The addition of a chloride trap to this reformer should eliminate or reduce this fouling while possibly also reducing system corrosion and observed ammonium chloride fouling in the stabilizer.