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Modelling Electrolytic Hydrofluoric Acid In The Fractionation Phase Change Corrosion Zone Of HF Alkylation Units

Hydrofluoric acid (HF) is used as a catalyst in the alkylation process to react isobutane with olefin feeds to manufacture a high octane alkylate product used in gasoline blending. The HF catalyst is added in its anhydrous liquid form (< 400 ppmw H2O) but as it circulates in the reaction system, residual water in the Paper No. 17520 liquid hydrocarbon feed is absorbed by the acid such that the circulating reaction acid builds up a small percentage (0.5 to 2.0 mass%) of water. This water/HF mixture is also referred to as rich HF (RHF). In addition, the alkylation reactions also will generate fluorocarbons and acid soluble oils (ASOs).

Product Number: 51322-17520-SG
Author: Andy C. Gysbers, J. Tim Korstanje, Michael S. Cayard, Peiming Wang, Ezequiel Vincent
Publication Date: 2022
Industry: Coatings
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Electrolytic hydrofluoric acid (HF containing water) continues to be a significant carbon steel corrosion concern in the industry, particularly in the regime where water/HF undergoes phase changes as it is heated and cooled in the fractionation section of the HF alkylation process. This corrosion may be attributed to the formation of a water enriched  electrolyte phase. An industry sponsored Joint Industry Project (JIP) was undertaken to better understand this corrosion relationship by developing an electrolyte thermodynamic database and relationships of HF/Water/Hydrocarbon interactions that could be used in process models to evaluate the impact of operating changes on the corrosion potential in these systems. This paper will discuss the creation of the electrolyte thermodynamic model and its application in evaluating the phase transitions that occur in user plants as a function of operating conditions through process simulation. 

Electrolytic hydrofluoric acid (HF containing water) continues to be a significant carbon steel corrosion concern in the industry, particularly in the regime where water/HF undergoes phase changes as it is heated and cooled in the fractionation section of the HF alkylation process. This corrosion may be attributed to the formation of a water enriched  electrolyte phase. An industry sponsored Joint Industry Project (JIP) was undertaken to better understand this corrosion relationship by developing an electrolyte thermodynamic database and relationships of HF/Water/Hydrocarbon interactions that could be used in process models to evaluate the impact of operating changes on the corrosion potential in these systems. This paper will discuss the creation of the electrolyte thermodynamic model and its application in evaluating the phase transitions that occur in user plants as a function of operating conditions through process simulation. 

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