Abstract: Petroleum acids in Fengcheng heavy crude were separated by potassium hydroxide-ethanol aqueous solution extraction. The compositions and structures of petroleum acids were determined by elemental analysis, IR, NMR, ESI-MS, UV and Fluorescence Spectrum. The results show that the petroleum acid in Fengcheng heavy crude is mainly composed of dimers of mono-carboxylic acids with an average molecular weight of 665, the empirical formula is C43.51H78.47O3.78 with a hydrogen-carbon mole ratio of 1.80. The contents of naphthenic acids and aliphatic acids occupy 79.84% and 20.16%, respectively. The contents of naphthenic acids with different structures (including 1-3 ring naphthenic acids, 4-ring naphthenic acids/aromatic carboxylic acids, 5-ring naphthenic acids/benzonaphthenic carboxylic acids with one ring, 6-ring naphthenic acids/benzonaphthenic carboxylic acids with 2-ring) are close to each other, ranging from 11.00% to 18.88%. Trace amount of 3-4 ring aromatic in petroleum acids are also observed.

Key words: petroleum acid, naphthenic acid, IR, ESI-MS, NMR, viscous crude