Evaluating Effectiveness of Inherently Safer Risk Reduction Options for HF Alkylation

Alkylation is a process that combines low value refinery by-product olefins with isobutane to form alkylate — a clean burning, low volatility gasoline blendstock used to increase gasoline octane rating. With changing fuel regulations and the global phase-out of leaded gasoline, alkylate continues to play an ever increasing role in gasoline formulations. Both hydrofluoric (HF) and sulfuric acids, which are used as catalysts in the alkylation process, are highly corrosive and hazardous if an accidental release occurs. Due to the lower boiling point of HF and its higher propensity to aerosolize into small droplets, releases of HF acid from HF Alkylation units are expected to pose a safety hazard at distances much greater than would be expected for comparable sulfuric acid units. As a result of industry and government sponsored research illustrating the impact potential from an HF release, there is a general perception that HF Alkylation units are high risk and sulfuric acid units are low risk. The author has conducted numerous Quantitative Risk Assessment studies of HF alkylation units along with potential risk reduction options that include passive systems, active systems, and inherently safer options. These studies have demonstrated that HF alkylation is not necessarily “high risk.” Furthermore, HF Alkylation units with effective risk mitigation strategies are compared with a comparably sized sulfuric alkylation unit for illustrative purposes. The lessons learned not only help address risks associated with HF alkylation units, but also can be applied to other highly hazardous processes.