Understanding the molecular composition of petroleum and its distillation cuts

Abstract

Because petroleum is one of the most complex mixtures in the world, complete characterization becomes a difficult task due to its molecular diversity and its different physicochemical properties. One way to address this problem is through the comprehensive assessment of crude oil distillation cuts. The correlation of molecular data with the physicochemical properties of petroleum can be employed in prediction models and process simulators in the oil industry. Therefore, the purpose of this study was to detail the chemical compositions of the selected crude oils and their distillation cuts using powerful analytical techniques to obtain chemical information about these matrices. A set of 48 petroleum samples, that is, 10 whole crude oil samples and their distillation cuts in different ranges of distillation temperatures (8 naphtha samples: 15–150 °C; 10 kerosene samples: 150–250 °C; 10 diesel samples: 150–400 °C; 10 gas oil samples: 400–540 °C), were analyzed via comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC − TOFMS) and GC × GC coupled with flame detector ionization (GC × GC − FID), here with the aim of a group-type identification and quantification. A repeatability evaluation of the quantification method was carried out; the most abundant classes showed good precision, with a relative standard deviation (RSD) lower than 30%. Naphtha and kerosene fractions were analyzed directly without fractionation. The GC × GC data provided a large amount of information for assessing the quality of these matrices, offering an innovative proposal in the context of oil assessment, this can help reduce the number of analytical techniques that are traditionally employed in the complete characterization of crude oils and their derivatives. Quantitative data by GC × GC − FID enabled the construction of simulated distillation (SIMDIS) curves for each whole crude oil. This work achieved detailed characterization of different Brazilian petroleum types in a wide range of API gravities, distinct basins and wells, providing information for the oil industry to make predictions and facilitate the prevention and mitigation of upstream, midstream, and downstream activities. The present study offers an innovative and practical proposal in the context of oil assessment aiming to reduce the number of analytical techniques that are traditionally employed in crude oil and its derivatives assay. Therefore, with faster and more reliable data, GC × GC has become a relevant technique in understanding the molecular chemical composition of real samples of crude oils and their distillation cuts by acquiring a substantial amount of information in a single analysis, representing a potential analytical tool within petroleomics.