Octane compositions in sulfuric acid catalyzed isobutane/butene alkylation products: experimental and quantum chemistry studies

Octanes in alkylation products obtained from industrial alkylation were studied by batch experiments. More than eight octane isomers were identified and quantified by gas chromatography-mass spectrometry. Based on a classic carbenium ion mechanism, the carbocation transition states in concentrated sulfuric acid catalyzed alkylation were investigated using quantum-chemical simulations and predicted the concentration and octane isomerization products including trimethylpentane and dimethylhexane as well as the formation of heavier compounds that resulted from the oligomerization of octane and butene. The agreement between model calculations and experimental data was quite satisfactory. Calculation results indicated that composition and content of trimethylpentanes in the alkylation products were 2,2,4-trimethylpentane > 2,3,3-trimethylpentane > 2,3,4-trimethylpentane > 2,2,3-trimethylpentane whether the 2-butene or i-butene acts as olefin. Heavier compounds in the alkylate were primarily formed by the oligomerization of dimethylhexane with 1-butene. Hopefully, the carbocation transition state models developed in this work will be useful for understanding the product distributions of octane in alkylation products.