(5b) Process Simulation Predicts Corrosive Conditions in HF Alkylation Fractionators

Maximum corrosion rates in hydrofluoric acid (HF) alkylation units occur when free acid phases reach 30 wt% water (H₂O). Unfortunately, measuring the presence or composition of free acid phases on column stages is impractical. Bryan Research & Engineering’s (BR&E) process simulation software, ProMax, can simulate HF alkylation and free acid phase composition in the isostripper to help refiners avoid corrosive situations.

Using experimental data for HF/Hydrocarbon and HF/HO mixtures, BR&E tuned the relevant binary interaction parameters to match this system. The resulting Peng-Robinson Polar and SRK Polar thermodynamic packages accurately model the three-phase equilibrium and HF/H₂O azeotrope in an HF alkylation process.

Entrainment of HF within the hydrocarbons in the acid settler and internal acid regeneration provide routes for HF entry into the isostripper column. ProMax can show whether a free acid phase forms on an isostripper stage. Simulation analysis predicts HF/H₂O compositions in the acid phase for subsequent assessment of corrosivity.