关键词: 实沸点蒸馏, ESI, FT-ICR MS, 石油酸, 高酸原油

Abstract: The carboxylic acid molecular transformations of heavy acid SL crude before and after true boiling point distillation are examined by ultrahigh-resolution negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The acid class (heteroatom number), type (z numbers) and carbon number distributions were positively characterized. It was found the total acid number (TAN) of SL crude decreased after true boiling point distillation, and the abundance of O2 class in mass spectrum was also found to be reduced from 67.6% to 34.5% in SL TBP mixed crude in MS spectrum, suggesting the potential carboxylic acid decomposition. However, it was interesting that both oils’ carboxylic acid type distributions were almost the same although their relative abundance of SL TBP mixed crude turned to be much lower, indicative of that various petroleum carboxylic acid types have the similar thermal decomposition reaction behavior. Furthermore, for each O2 type in SL TBP mixed crude, the abundance of carboxylic acid with carbon number higher than 35 was reduced greatly, especially for those with carbon number higher than 60, which mass peaks were nearly totally removed, indicating the large carboxylic acid molecules in heavy fractions decomposed much more because of longer heating time in the true boiling point distillation process. As a result, the reducing of TAN may be due to the thermal decomposition of carboxylic acids especially those with high carbon number, suggesting quick distillation or much lower pressure is suggested to avoid the thermal decomposition.

Key words: true boiling point distillation, ESI, FT-ICR MS, carboxylic acid, acidic crude, Total Acid Number