Quantitative Risk Assessment of Refinery Alkylation Processes

        Refinery alkylation units are critical to the production of clean, reformulated fuels which meet the requirements of the Clean Air Act. The two major commercial, competing alkylation processes use large quantities of strong acids (hydrofluoric and sulfuric) as catalysts in the production of "alkylate," the key blending component for these clean, reformulated fuels.

        Over the past decade there has been significant debate over the relative safety and operability merits of these two alkylation processes, with hydrofluoric (HF) acid generally considered to provide improved operating efficiency, but with greater potential consequences for an accidental release.

        Recently, a proposed HF alkylation technology which incorporates the use of an additive to lower the catalyst mixture vapor pressure has undergone a detailed quantitative risk comparison with a commercial sulfuric acid alkylation process. The results of the quantitative risk comparison performed by Mobil identified that, for the Torrance Refinery, these processes were of comparable risk, with alkylation using a modified HF catalyst resulting in lower calculated best estimate risk values.

        An independent evaluation of this quantitative risk comparison was submitted to meet a December 31, 1994, court deadline, and is currently undergoing critique by the City of Torrance and Mobil Oil Corporation. The outcome of this comment phase, the implementation of this new technology, and the potential impact on refinery alkylation. technologies in the United States will be identified in an upcoming risk assessment news brief. 

Published in SCSRA Risk Resources, February 1995