Alkylation
Alkylation is a refining process that provides an economic outlet for very light olefins produced at the FCC and Coker. Alkylation is the opposite of cracking. The process takes small molecules and combines them into larger molecules with high octane and low vapor pressure characteristics.
In the Alkylation Unit, propylene, butylenes and sometimes pentylenes (also known as amylenes) are combined with iso-butane in the presence of a strong acid catalyst (either hydrofluoric (HF) or sulfuric acid) to form branched, saturated molecules. Alkylate has an octane around 95 (R+M)/2 and low vapor pressure making it a valuable gasoline blending component particularly for premium grade products. It contains no olefins, aromatics or sulfur.
Sulfuric Acid Alkylation runs at 35-60˚F (2-15˚C) to minimize polymerization reactions while HF Alkylation, which is less sensitive to polymerization reactions, runs at 70-100˚F (20-38˚C). Chilling or refrigeration is required to remove heat of reaction.
Alkylation products are distilled to remove propane, iso-butane and alkylate. Sulfuric acid sludge must be removed and regenerated. HF is neutralized with KOH, which may be regenerated and returned to the process.
