PTQ Q4 2026 Issue

Mitigation of ammonium chloride salt formation in FCC main fractionator

Commercial case study on the reduction of saline deposits in continuous operation of the FCC unit

Adilson Cavalheiro Borges Gutierres FCCSA Carlos Alberto Rivera Corredor and Manuel Julian Ardila Pimiento Ecopetrol Eric Rutan and Cliff Avery Ketjen Corporation

T he deposition of ammonium chloride (NH₄Cl) salts in the main fractionator of fluid catalytic cracking (FCC) units is a significant operational issue, associated with increased pressure drop, loss of separation efficiency, and the risk of under-deposit corrosion. The authors present the analysis of an industrial case in an FCC unit where recurrent formation of salt deposits was observed in the overhead system of the fractionator, directly affecting operational performance. The phenomenon was evaluated based on the behaviour of differential pressure, chloride balance, and operating conditions of the system. Two operational periods with significantly different behaviours were compared. In the first case, the unit showed high chloride levels, persistent deposit formation, and reliance on mitigation strategies, such as water injec- tion and the use of dispersants. In the second case, after adjustments to the system’s chloride balance, a substan- tial reduction in salt formation was observed, along with the elimination of the need for chemical mitigation and an improvement in fractionation efficiency. The results indicate that controlling the chloride balance, including all potential sources within the unit, is a key factor in mitigating the formation of ammonium chloride (NH₄Cl) and improving overall distillation performance in the main fractionator. Salt deposits The formation of salt deposits in overhead systems is a widely documented phenomenon in refining units, particularly in those where chlorine species and nitrogen compounds coexist. In FCC units, the main fractionator represents one of the most sensitive areas to this type of problem due to the combination of thermal gradients, partial condensation of hydrocarbons, and the presence of reactive species in the vapour phase. Among the commonly observed deposits, NH₄Cl is one of the most critical. This compound can be formed in the vapour phase from the reaction between ammonia (NH₃) and hydro- chloric acid (HCl). It subsequently deposit in areas where the temperature falls below its thermodynamic stability point. The formation and deposition of NH₄Cl depend mainly on the partial pressure of its precursors and on the system’s

thermal profile, with the behaviour of the fractionator over- head being especially important. From an operational point of view, this phenomenon usu- ally manifests itself through: • Progressive increase of the differential pressure in the overhead system. In industrial practice, the control of these deposits is usu- ally addressed through mitigation strategies, such as water injection and the use of dispersant chemicals. However, these measures do not address the root cause of the problem; rather, they aim to limit its effects on the operation. In this context, the analysis of the chloride balance in the unit plays a central role. Chlorine sources may include the feedstock, internal streams, operational contaminants, and the catalyst. The interaction between these sources and the operational conditions defines the propensity for NH₄Cl formation. Further analysis of this article’s industrial case of an FCC unit shows where salt formation reduction was achieved through a change in catalyst technology, highlighting the impact of the chloride balance on the behaviour of differen - tial pressure and main fractionator performance. Main sources of FCC unit chlorides • Reduction of separation efficiency. • Operational restrictions in the unit. • Risk of corrosion under-deposit. Formation of NH₄Cl salts in FCC units is directly related to the availability of precursor species in the system, par- ticularly ammonia (NH₃) and chlorine compounds that can generate hydrochloric acid (HCl). Ammonia is primarily produced from the thermal decomposition of nitrogen-con- taining compounds present in the feed. On the other hand, chlorine sources can be multiple and, in many cases, simul- taneous, making it difficult to identify a single cause for the formation of salts. The main sources of FCC unit chlorides include: • Fresh feed : Presence of residual inorganic salts due to lim- itations in the desalting process. • Internal streams: Incorporation of slops or recycled mate- rials containing chlorides. • Operational contamination: Ingress of saline water or fail- ures in separation systems.

PTQ Q4 2026