| Carboxylic acids are not only an important factor of equipment corrosion in oil processing but also the important component influencing the petrochemical wastewater treatment.In recent years,Electrospray ionization combined with high resolution mass spectrometry technology can realize molecular composition analysis of carboxylic acids.However,the results analysized by mass spectrometry can not provide the information of molecular structure.The subject of this study was to establish a separation method of carboxylic acids and characterize their detailed molecular composition.Based on the extraction chromatography of alkali-treated silica gel,we improved and optimized the separation method of petroleum acids and realized the subject to concentrate carboxylic acids with high purity and high yield.The isolated carboxylic acids were transformed into corresponding methyl ester by CH2N2.The methyl ester was then separated into three subfractions,including naphthenic acid methyl ester,a mixture of naphthenic and aromatic carboxylic acid methyl ester,aromatic carboxylic acid methyl ester,by the silica gel column modified by silver ions.The subfractions were hydrolyzed respectively to acquire the corresponding naphthenic acids,naphthenic/aromatic carboxylic acids,aromatic carboxylic acids.Separation methods established by vacuum distillate were suitable for the crude oil.Using Gas Chromatogram and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry(FT-ICR MS)to analyse the molecular composition of carboxylic acids and their subfractions,we found that the main components of carboxylic acids in Bohai basin crude oil are the naphthenic acids with rings from 1 to 4,that the main components of aromatic carboxylic acids are aromatic rings from 2 to 4,and that the carbon atoms of carboxylic acids are mainly distributed between 20 and 40.Through the separation,aromatic carboxylic acids with high condensated degree were analysed effectively.The ionization efficiency of naphthenic and aromatic carboxylic acids in the electrospray ionization existed obvious difference that naphthenic acids showed stronger ion selectivity.The results of this study provide some references for the composition analysis of carboxylic acids and acquire the deeper molecular composition of carboxylic acids in Bohai basin crude oil.The prepared carboxylic acids and their subfractions can be used as mixed prototype,which provides sample conditions for further quantitative analysis by FT-ICR MS. |
